Zener Diode Tester [250772]
Adjustable current source. Measure Zener diodes and other components. 54 V max. at 1, 2, 5, 10, 20 and 50 mA. 5 V limit switchable. Supply voltage ranges from 5 to 12 V (2 A). Internal 60 V DC-DC converter.
Based on https://www.elektormagazine.com/labs/zener-diode-tester by Philippe LE GUEN.
Specifications and properties
4 mm banana sockets to connect a multimeter
2 mm banana sockets to connect test clips
USB-C socket to connect a power supply
PCB designed for use with Hammond 1591XXSSBK ABS enclosure (specifically position of mounting holes)
This adjustable current source is initially designed to measure the voltage of Zener diodes up to 54 V. 6 fixed currents can be selected: 1, 2, 5, 10, 20 and 50 mA. LED’s or other diodes can be tested as well. The output voltage can be limited to approximately 5 V by switching a 5.1 V Zener diode parallel to the output internally with a toggle switch. This is a protection in case the wires are crossed or the connections of the DUT are unknown to reduce the maximum output voltage to a safe level, for almost all semiconductors. With a few extra external components and an additional power supply power transistors can also be tested by using this current source as the base current. The supply voltage of this tester ranges from 5 to 12 V by using a step-up converter. It produces 60 VDC for the current source circuit. If the load has a very high impedance the output voltage is close to this internal supply voltage when S1 is pushed, so almost 60 V! There’s a small drop across diode D4.
Fig. 1 Schematic of the Zener Diode Tester (250772-1 v1.1).
The principle of this tester is straightforward. A Zener diode or another DUT is biased by an adjustable current source. The voltage across the DUT can be measured with a multimeter. The voltage of most (small) Zener diodes are specified at a current of 5 mA. Depending on the application the voltage at other currents can also be of interest. That’s why 6 current settings are available: 1, 2, 5, 10, 20 and 50 mA. LED’s are often specified at a current of 20 mA, this value is added (compared to the original design).
60 VDC power supply
The tester is compatible with various power supplies. DC-DC converter controller MC34063 (IC1) converts any input voltage from 5 to 12 V to a stable 60 V. To make the controller operate from 5 V MOSFET T2 must have a very low Gate Threshold Voltage. A high efficiency of the DC-DC converter is possible by a very low Drain-Source On Resistance. The STP40NF10L has those specifications. The Gate Threshold Voltage is typically 1.7 V (2.5 V max.) and the Drain-Source On Resistance is typically 0.03 Ω (at an UGS of 5 V). The maximum Drain-Source voltage is 100 V.
The MC34063 is used in a standard application, a discontinuous step-up mode. The peak current of T2 is set by R2 to 2 A. This current level depends on the relation of ton and toff, which in turn depends largely on the desired output voltage and minimum input voltage. The minimum inductance of L1 depends on the frequency chosen. At a too high frequency the large input capacitance of T2 will reduce efficiency of the converter. The larger this capacitance, the slower the switching speed of T2. To speed up the discharging of the gate of T2 the circuit of T1 and D1 are added. The Switch Emitter output of IC1 (pin 2) can only source current. If this output is turned off T1 will discharge the gate of T2, since R4 will pull the base of T1 to ground.
At an input voltage of 5 V the frequency is about 17.8 kHz. A 100 µH inductor is used. By using the formulas in the datasheet, ton is 40.82 µs (L 100 µH, Vin min. 5 V, Vsat 0.1 V, VF 0.8 V). Calculating CT (C3), depends on ton and results in 1.84 nF. A standard 2.2 nF is chosen. ton should then be 48.9 µs and ton + toff 53.2 µs. The calculated switching frequency is 18.8 kHz then. At 5 V 17.8 kHz was measured. The difference can be explained by various tolerances and voltage drops. The prototype produces a stable 60 VDC, even when the input voltage is as low as 4.64 V (prototype) and 50 mA output current. Total load of the +60 VDC is approximately 62 mA (including voltage divider R5/R6).
The input voltage is decoupled with a low ESR electrolytic capacitor and a ceramic capacitor, C1 and C2 respectively, since the peak current is 2 A. The 60 V output voltage is decoupled with a 100 V 100 µF capacitor and a 1 µF ceramic capacitor. The output capacitors C4 and C5 are charged through Power Schottky Rectifier D2, a STPS3150RL. It’s forward voltage drop at 2 A is less than 0.8 V. Voltage divider R5/R6 sets the output voltage of the DC-DC converter: (R5/R6 +1) * 1.25 V = 60.0 V. Given tolerances of the reference voltage and resistors the exact voltage can vary. Theoretical maximum, with 1 % resistors and tolerance of the reference voltage, is (47.47 / 0.99 + 1) * 1.275 = 62.41 V. Theoretical minimum is (46.53 / 1.01 + 1) * 1.225 = 57.66 V. The maximum and minimum voltage of the current source is approximately 61,9 V and 57.16 V due to the voltage drop of protection diode D4 in the output. The voltage drop across D4 is less than 0.5 V at 50 mA, 0.3 V at 1 mA).
A USB-C connector is used for the supply voltage of the tester. There’s a catch trying to use a AC adapter complying to the Power Delivery standard. Often something like ‘PD/QC 3.0’ is mentioned on such devices. The adapter will probably not output any voltage if 2 certain 5 kΩ pull-down resistors are missing. The USB-C socket used here only has two wires for the supply voltage. Otherwise consider using a standard AC adapter and replace the USB-C socket with a matching DC power socket.
The current source
The Zener diode or DUT to be tested is measured with respect to ground. As the current source is to deliver a positive current its refence voltage (5 V, IC2, LM4040 Precision Micropower Shunt Voltage Reference) is referenced to the +60 V supply voltage. A P-channel MOSFET (T3) is used because the DC current of drain and source current are identical and the output current can be set with high accuracy. IC3 compares the voltage drop across the selected source resistor with the +5 V reference voltage and adjusts the gate voltage of T3 accordingly. IC3 is a low-offset JFET opamp. Its bias currents are in the order of pA and the voltage drop across feedback resistor R12 negligible, compared to the reference voltage. The same is true for the input offset voltage, typically less than a millivolt. C6 and R12 ensure stability.
The output current of T3 is changed by selecting a different source resistor with rotary switch S2. Since 6 different currents are chosen S2 is 2 pole 6 position rotary switch. To reduce the effect of contact resistances the two parts of S2 are connected in parallel. This also extends the lifespan of the tester. D4 in the output protects the tester from any possible reverse voltage, just to be sure.
To limit the gate voltage the supply voltage of IC3 is limited to approximately 17 V. The Gate-Source Threshold Voltage of T3 is maximal -4 V. The output voltage of the TL051 is minimal 2.7 V (VOM-) above its negative supply voltage, needing worst case at least Vref + VGS(th) + VOM– = 5 + 4 + 2.7 = 11.7 V supply voltage. At 50 mA drain current the gate-source voltage is only slightly higher than the threshold voltage. The minimum common mode input voltage ranges from 1 V below the positive supply voltage to 4 V above the negative supply voltage. So, 12 V would be enough. A 18 V Zener diode (D3) was chosen to create a stable enough supply voltage for IC3 and leave enough headroom. The operating current of voltage reference IC2 is set to 1.3 mA by R10. The total load of the +60 VDC supply by the current source circuit is 3.2 (IC3, max.) + 1.3 (IC2) + 1.6 (LED2) = 6.1 mA. The current of T3 is a separate load on the +60 V supply voltage. The current of Zener diode D3 is set by 1 W resistor R7 to a little over 10 mA, leaving about 4 mA to create the 18 V.
S1 is the test button, it connects the entire current source circuit with the 18 V supply voltage. R8 limits the peak current through the switch causing a voltage drop of 1 V. The Zener voltage can be higher or lower but this doesn’t influence the test current. Push button S1 also contains a red LED which is used as a Power On indicator. This LED is LED1 in the schematic and is connected separately via R1 to the input voltage. S1 has 4 connections, two for the switch and two for the LED (the solder lug for the cathode is indicated by a grey spot next to it).
To limit the maximum output voltage to a safe level, 5 V is the voltage most datasheets of diodes and transistor (base-emitter) list as a maximum reverse voltage, a Zener diode of 5.1 V (D5) can be connected to the output by S3. The contact rating of almost all small switches is 24 or 30 VDC. A higher rating means a lot more expensive, if you can find one. To use a standard toggle switch for the 5 V limitation a small MOSFET (T4) is used to connect D4 parallel to the output. S3 connects the gate of T4 with the input voltage of K1. R19 makes sure T4 is switched off if the contact of T3 is open. T4 is a 2N7000 and its maximum drain-source voltage is 60 V. D4 and D5 are connected in series with the drain of T4 and so the voltage here will be less than 60 V. Important, best practice is not change position of S2 and S3 when S1 is pushed, making sure T4 turns on or off and the contacts of S2 switch without any voltage present.
The value for the source resistors are easy to calculate: Vref/Iout. The following values are needed for 1, 2, 5, 10, 20 and 50 mA: 5 kΩ, 2.5 kΩ, 1 kΩ. 500 Ω, 250 Ω and 100 Ω. Of course the values of 5 2.5, 500 and 250 are not found in the standard E-series, although resistors exist with these values, but are expensive. Using additional resistors in series or parallel would make the circuit and PCB larger. The nearest E-96 values are used for R18, R17, R15 and R14: 4.99 kΩ, 2.49 kΩ, 499 Ω and 249 Ω. The error is an additional 0.2 and 0.4 %.
Mounting parts on the PCB
Fig. 2 PCB of the Zenerdiode tester (250772-1 v1.1).
Fig. 3 All parts (except the wires).
In a nutshell, start by soldering the lowest parts first and the highest last. Then fasten the two power transistors to their heat sinks and mount the assemblies onto the PCB. Next the rotary switch S2 and place IC1 and IC2 into the sockets (observe the correct orientation).
Recommended order:
D5
R1 ,R3-R6, R8-R19
D3
D1
R2, R7
IC sockets
D2, D4
C3
C2, C3
C4, C6, C7
Screw terminal blocks K1, K2, S1, S3
Fig. 4 Resistors, diodes and screw terminal blocks soldered (PCB 250772-1 v1.0).
Next
T1, T4 and IC2 (all have TO-92 packages)
2-way pin headers for LED1 and LED2
L1
C5
C1
Fig. 5 T1, T4, IC2, pin headers, L1, C5 and C1 soldered (PCB 250772-1 v1.0).
Next
Apply a thin layer thermal grease on the back of T2 and T3. No insulation is needed, the transistors can be fitted directly on the heat sinks. First a screw and a nut are used to fasten each transistor to the heat sink. Temporarily place the screw of the heat sinks in the mounting hole on the PCB to see where the leads of the transistors must be bend perpendicular. There is some room for error here. Bend the leads. Place the heat sinks on the PCB, the leads of the transistors should fit smoothly through the designated pads, and fasten each with a second nut on the bottom side. Do not place the heat sinks against the PCB, this can cause short circuits! The copper plane on top is connected to ground but has large clearances where the 2 screws from the heat sinks are, so the nut on the top side can’t make contact. The screws are connected to the drain of the MOSFETs. Only now solder the leads of T2 and T3.
Place rotary switch S2 and solder all its pins. Be sure it’s placed fully flat against the PCB!
Put IC1 and IC3 in the IC sockets.
Fig. 6 Heat sinks fixed to the PCB, T2, T3 and S2 soldered, IC1 and IC3 placed in their sockets.
Fig. 7 Mounting of the heat sinks, side view.
Fig. 8 Side view on the mounting of the heat sink of T3. Heat sink of T2 visible in the back.
The PCB is now ready for testing. Connect the mA inputs of a multimeter directly with the output (K2) and measure the 6 test currents. Also measure the +60 VDC supply voltage at 50 mA output current, on cathode of D2 with respect to ground. Be careful not to touch anything while testing!
Construction of the prototype
A PDF of a front design with dimensions is available (see Project Elements – Other).
Fig. 9 Dimensions of the front design with respect to the PCB and enclosure. All are referenced to the spindle of the rotary switch in the center of the front.
The size of the design is 106 x 78 mm, a rounded rectangle marks the borders (center of the lines). In figure 9 the sides of the enclosure are also shown as the outer rounded rectangle. Print it on normal paper and make sure the borders have the correct dimensions. Cut the inner rounded rectangle with scissors from the paper and cut the round 6 mm hole for the spindle of the rotary switch with a sharp hobby knife. The location of the spindle of the rotary switch is the only critical location, it is in the exact center of the enclosure. The PCB is designed this way. Helpful in the inside of the enclosure is a small circle, also in the center. This can also be used to drill a hole in the correct position for the 6 mm spindle of the rotary switch first. Use adhesive tape to temporarily fasten it to the top side of the enclosure. Place it in the exact center of the front, the holes for the spindle should align now. Create the other 3 holes on the top of the enclosure:
6.3 mm for the toggle switch S3
8 mm for pushbutton S1
3 mm for LED2, use a 2.5 mm drill first and use a small round file to make just big enough for the LED to stick. Using a 3 mm drill could just result in little too big hole for it to stay stuck. Use a small round file to make it bigger and test several time if the LED will fit through and is fixed properly.
For the other holes start by making smaller holes with for instance a 2 mm drill. Maybe by hand, the plastic enclosure is very easy to work on, or maybe too easy to work on. Be patient when making the holes, the ABS plastic is soft and a hole can be made too large without applying much force.
When the holes in the top of the enclosure are ready drill the holes for the 2 mm banana sockets with a 4.5 mm drill. The 6 mm thread (approx. 5.7 mm width) has two flat sides less than 5 mm wide. Use a small half rounded file to slowly make the connectors fit and are in line.
The two holes for the two 4 mm banana connectors are round and should be 7.4 mm in diameter.
Also make a slotted hole for the USB-C socket to fit through. Not too wide or it will get pulled out with a plugged-in USB-connector.
The center of the holes in the sides are 18 mm from the top of the enclosure.
Fig. 10 Front design with logo and corporate identity color and typography.
Print the front design on a self-adhesive (glossy) photo paper and make sure the size is correct, exactly the same as printed before on normal paper, 106 x 78 mm. I used a cheaper paper and it acted a little like blotting paper when printing in high quality. Printing in standard quality was fine. The matte version was worse than the glossy paper. Test with different printer settings. Stick the front design in the center onto the enclosure, exactly like the normal paper before, and make sure it is perfectly aligned with all the holes so the scale aligns with the rotary switch and the text with the two switches. Cut out the paper that covers the 4 holes carefully with a sharp hobby knife. Fit the two switches and the 3 mm LED. Tighten the nut of the toggle switch very carefully, not damaging the front when doing so. Shorten the leads of the LED but leave the short lead a little shorter to still indicate the cathode. Use a drop of superglue to make sure the LED will never fall back inside the enclosure. Maybe secure the USB-C connector also with a drop of super glue.
Wiring
Fig. 11 Front sticker (earlier design), connectors and switches fitted and PCB to the bottom of the enclosure.
In figure 11 a sticker with an earlier design is fixed to the front. All the connectors are mounted and the PCB is fixed to the bottom of the enclosure by four #4-1/4” self-tapping screws.
Fig. 12 Inside view on the enclosure with connectors and switches fitted.
Next place the top of the enclosure on it side. Place the bottom right next to it. Now everything can be wired with 0.25 mm2 (24 AWG) wire. Next is a list with a logical order and length of the pieces of wire needed. On pushbutton S1 the solder lug of the cathode of the LED is marked with a grey spot. Place it toward the side of the enclosure. The solder lug on the opposite side is the anode. The two other solder lugs, to the left and right, are of the switch. Place the two 2way pin sockets on the 2way pin headers of the LEDs. Twist the wires of each pair before soldering.
In total 63 mm red wire is needed and 60 mm black wire.
Fig. 13. Everything is connected.
Check all wiring. When placing the top of the enclosure on the bottom make sure the wires are not touching the heatsinks, just to be cautious. In normal use they don’t get hot. Next to do is shortening the spindle of the rotary switch S2. Remove about 11 mm, maybe a little more. The plastic is surprisingly tough. When placing the knob over the spindle it shouldn’t be able to touch the front, the printed front layout is vulnerable. Best is to do this before starting the wiring. Clamp the top of the spindle in a bench vise and use a saw to remove the 11 mm of the spindle. Place the top of the enclosure on the bottom and check if enough is removed. The knob of the prototype is secured with a headless Allen screw. A 1.5 mm Allen screwdriver is needed to fix this knob. When this is done the Zener Diode tester is ready for use.
Fig. 14 Three views of finished prototype.
The test clips can each be connected with 30 cm 0.25 mm2 (24 AWG) wire to the 2 mm banana plugs. This length should be long enough. To measure SMD components and similar devices, where the test clips can’t be attached to, standard measuring cables with test tips for 4 mm banana plugs can be connected to the 4 mm banana sockets on the enclosure. Most measuring cables can be connected in parallel as their plugs also has have a 4 mm socket. A multimeter can then be connected parallel to the measuring cables to the DUT.
Replacing the sticker
Since the sticker is a printed with an inkjet printer the front can get damaged easily, get covered with scratches over time. Remove the knob and open the enclosure by removing the 4 screws in the bottom. Remove the sockets of the LEDs from the 2way pin headers. Remove the wires from the pushbutton S1 from its screw terminal. Remove the nut from the toggle switch and from the inside pull it out of the front. The pushbutton can be pushed out of the front from the inside. The wires will fit through the hole. Remove the old sticker by pulling it very slowly of the front. Remove residual glue and paper with sticker remover and make sure the front is dry and clean. Place the top back on the bottom the spindle of the rotary switch is now protruding trough the front. After printing a new sticker cut it from the sheet of self-adhesive photopaper. Cut the round 6 mm hole for the rotary switch and hole for the led, latter hole a little smaller than 3 mm. Peel of and cut of a part of the protecting paper from the sticker with a pair of scissors at the side where the LED is, about 2.5 cm. Place the sticker over the spindle and make sure the hole for the LED is exactly placed over the led and push the sticker on to the front. Take top of the enclosure of the bottom and remove the rest of the protecting paper from the back of the sticker and push it carefully and evenly onto the front. Cut the holes for the two switches with a sharp hobby knife and place the switches back. Connect all the wires and close the enclosure. Place the knob on the spindle and the tester is as good as new.
Measurements
As an example a variety of Zener diodes was measured. With the test clips it is not necessary to cut them from the tape first.
Zener diodes tested:
4.7 V/0.5 W, BZX79-C4V7.113
5.1 V/0.5 W, 1N5231B
5,6 V/0.5 W, 1N752A
12 V/1.3 W, 1N4742A-TAP
18 V/1.3 W, BZX85C18-TAP
27 V/ 3 W, 1N5935BRLG
51 V/5 W, 1N5369BRLG
Values listed are taken after pushing S1 for 5 seconds. At higher currents the values keep changing after prolonged pressing of S1. Especially when measuring near the maximum rated power of the Zener diodes.
The test current for the values in red is no longer accurate. The selected test current will be less when the Zener voltage rises above 54 V, in this case due to the temperature of the diode rising.
Fig. 15 The tester in practice. Measurement 1 of 5, 12 V/1.3 W Zener diode 1N4742A at 1 mA.
Another application is the testing of the equality of brightness of LED’s. Quite a number can be placed in series, easily done by using a solderless breadboard. Next photo show a test of 30 LEDs at once. Total voltage is 54 V at a current of 5 mA
Fig. 16 Testing the brightness of 30 red LEDs in series at 5 mA.
Bill of materials (PCB 250772-1 v1.1)
Resistor
R1 = 3.3 kΩ, 600 mW, 1 %
R2 = 0.15 Ω, 1 W, 5 %, lead spacing 12.7 mm, diam. 3.5 mm
R3, R8 = 180R, 600 mW, 1 %
R4, R6, R16 = 1 kΩ, 600 mW, 1 %
R5, R19 = 47kΩ, 600 mW, 1 %
R7 = 3.9 kΩ, 1 W, 5 %, lead spacing 12.7 mm, diam. 3.5 mm
R9, R10, R12 = 10kΩ, 600 mW, 1 %
R11, R13 = 100 Ω, 600 mW 1 %
R14 = 249 Ω, 600 mW, 1 %
R15 = 499 Ω, 600 mW, 1 %
R17 = 2.49 kΩ, 250 mW, 1 %
R18 = 4.99 kΩ, 250 mW, 1 %
Inductor
L1 = 100 uH, Irms 2.4 A, Isat 3.5 A. 0.09 Ω, radial, pitch 2.5/5/10 mm, Diam. 14 mm max. (Kemet SBC8-101-242)
Capacitor
C1 = 470 uF, 35 V, 20 %, Ir 1.86 A, D 12.5 mm, LS 5 mm, ESR 0.038 Ω (Panasonic EEUTP1V471)
C2 = 1 uF, 100 V, 10 %, cer. X7R, LS 5 mm
C3 = 2.2 nF, 50 V, 10 %, cer. X7R, LS 5 mm
C4, C7 = 100 nF, 100 V, 10 %, cer. X7R, LS 5 mm
C5 = 100 uF, 100 V, 20%, D 14 mm max., LS 5 mm
C6 = 1 nF, 100 V, 10 %, cer. X7R, LS 5 mm
Semiconductor/
D1 = MUR120G, DO-41
D2, D4 = STPS3150RL, DO-201AD
D3 = Zener diode, 18 V, 1.3 W (BZX85C18)
D5 = Zener diode, 5.1 V, 0.5 W (1N5231B)
LED1 = LED in pushbutton S1
LED2 = LED, green, T-1 (3 mm)
IC1 = MC34063, DIP-8
IC2 = LM4040ABIZ-5.0/NOPB, TO-92 (TO-226AA-3)
IC3 = TL051CP, DIP-8
T1 = BC327.25, TO-92
T2 = STP40NF10L, TO-220
T3 = IRF9510PBF, TO-220
T4 = 2N7000, TO-92
Other
K1, K2, S1, S3 = 2way screw terminal block, LS 3.5 mm, max. 1.5 mm²
connected to K1 = USB-C socket, 30 V / 3 A, chassis mounted, wired, 9 x 16 mm
connected to K2 = Banana Connector, 2 mm, Socket, 60 VDC, Panel Mount, Red (Multicomp 24.102.1)
connected to K2 = Banana Connector, 2 mm, Socket, 60 VDC, Panel Mount, Black (Multicomp 24.102.2)
Test clip, red, 30 VAC/60 VDC (Hirschmann 931467101)
Test clip, black, 30 VAC/60 VDC (Hirschmann 931467100)
S1 (= LED1) = Pushbutton, panel mount, SPST-NO, 30 VDC, 100 mA, red illuminated
S2 = Rotary Switch, 6 Position, 2 Pole, 30 °, 150 mA, 250 V
S3 = Toggle switch, panel mount, SPDT, solder lugs, 28 VDC
T2, T3 = Heat sink FK 214 SA-CB, 15°C/W
Enclosure Hammond 1591XXSSBK, ABS, 110x82x44 mm
S2 = Knob, Round Shaft 6 mm, Diam. 21 mm, with indicator line (Multicomp CP-LB21-6-6D)
Self-tapping screw #4-1/4", carbon steel, pan head
Banana plug, red, 2 mm, 60 VDC (Multicomp 25.205.1)
Banana plug, black, 2 mm, 60 VDC (Multicomp 25.205.2)
4 mm banana socket, panel mount, black
4 mm banana socket, panel mount, red
LED1, LED2 = Pin header, 1x2, vertical, pitch 2.54 mm
LED1, LED2 = Pin socket, 1x2, vertical. pitch 2.54 mm
T2, T3 = M3 screw, 10 mm, steel, pan head
2 x M3 washer, plain, steel
4 x M3 nut
IC1, IC3 = DIP-8 socket
Black wire, 0.25 mm2 (24 AWG), stranded 14 x 0.15 mm, 1 m
Red wire, 0.25 mm2 (24 AWG), stranded 14 x 0.15 mm, 1 m
PCB 250772-1 v1.1
Fig. 17 Top overlay of the PCB of the Zenerdiode tester (250772-1 v1.1).
Fig. 18 Bottom overlay of PCB of the Zener diode tester (250772-1 v1.1).
Fig. 19 Copper on top of PCB of the Zener diode tester (250772-1 v1.1).
Fig. 20 Copper on bottom of PCB of the Zener diode tester (250772-1 v1.1).
Specifications and properties
| Supply voltage | 5…12 V/2 A (USB-C, see text) |
| Supply current (Itest = 50 mA) | 1,1 A (5V) |
| 412 mA (12V) | |
| Selectable output currents (fixed) | 1, 2, 5, 10, 20, 50 mA |
| Maximum test voltage | > 54 V (when Itest is correct) |
| Maximum no load output voltage | 60 V (Itest << value selected) |
| 5 V limit voltage | 4.5 V @ Itest = 1 mA |
| 5.18 V @ Itest = 50 mA | |
| Dimensions enclosure | 110 x 82 x 44 mm |
| Size PCB | 105.4 x 67.3 mm |
4 mm banana sockets to connect a multimeter
2 mm banana sockets to connect test clips
USB-C socket to connect a power supply
PCB designed for use with Hammond 1591XXSSBK ABS enclosure (specifically position of mounting holes)
This adjustable current source is initially designed to measure the voltage of Zener diodes up to 54 V. 6 fixed currents can be selected: 1, 2, 5, 10, 20 and 50 mA. LED’s or other diodes can be tested as well. The output voltage can be limited to approximately 5 V by switching a 5.1 V Zener diode parallel to the output internally with a toggle switch. This is a protection in case the wires are crossed or the connections of the DUT are unknown to reduce the maximum output voltage to a safe level, for almost all semiconductors. With a few extra external components and an additional power supply power transistors can also be tested by using this current source as the base current. The supply voltage of this tester ranges from 5 to 12 V by using a step-up converter. It produces 60 VDC for the current source circuit. If the load has a very high impedance the output voltage is close to this internal supply voltage when S1 is pushed, so almost 60 V! There’s a small drop across diode D4.
Fig. 1 Schematic of the Zener Diode Tester (250772-1 v1.1).
The principle of this tester is straightforward. A Zener diode or another DUT is biased by an adjustable current source. The voltage across the DUT can be measured with a multimeter. The voltage of most (small) Zener diodes are specified at a current of 5 mA. Depending on the application the voltage at other currents can also be of interest. That’s why 6 current settings are available: 1, 2, 5, 10, 20 and 50 mA. LED’s are often specified at a current of 20 mA, this value is added (compared to the original design).
60 VDC power supply
The tester is compatible with various power supplies. DC-DC converter controller MC34063 (IC1) converts any input voltage from 5 to 12 V to a stable 60 V. To make the controller operate from 5 V MOSFET T2 must have a very low Gate Threshold Voltage. A high efficiency of the DC-DC converter is possible by a very low Drain-Source On Resistance. The STP40NF10L has those specifications. The Gate Threshold Voltage is typically 1.7 V (2.5 V max.) and the Drain-Source On Resistance is typically 0.03 Ω (at an UGS of 5 V). The maximum Drain-Source voltage is 100 V.
The MC34063 is used in a standard application, a discontinuous step-up mode. The peak current of T2 is set by R2 to 2 A. This current level depends on the relation of ton and toff, which in turn depends largely on the desired output voltage and minimum input voltage. The minimum inductance of L1 depends on the frequency chosen. At a too high frequency the large input capacitance of T2 will reduce efficiency of the converter. The larger this capacitance, the slower the switching speed of T2. To speed up the discharging of the gate of T2 the circuit of T1 and D1 are added. The Switch Emitter output of IC1 (pin 2) can only source current. If this output is turned off T1 will discharge the gate of T2, since R4 will pull the base of T1 to ground.
At an input voltage of 5 V the frequency is about 17.8 kHz. A 100 µH inductor is used. By using the formulas in the datasheet, ton is 40.82 µs (L 100 µH, Vin min. 5 V, Vsat 0.1 V, VF 0.8 V). Calculating CT (C3), depends on ton and results in 1.84 nF. A standard 2.2 nF is chosen. ton should then be 48.9 µs and ton + toff 53.2 µs. The calculated switching frequency is 18.8 kHz then. At 5 V 17.8 kHz was measured. The difference can be explained by various tolerances and voltage drops. The prototype produces a stable 60 VDC, even when the input voltage is as low as 4.64 V (prototype) and 50 mA output current. Total load of the +60 VDC is approximately 62 mA (including voltage divider R5/R6).
The input voltage is decoupled with a low ESR electrolytic capacitor and a ceramic capacitor, C1 and C2 respectively, since the peak current is 2 A. The 60 V output voltage is decoupled with a 100 V 100 µF capacitor and a 1 µF ceramic capacitor. The output capacitors C4 and C5 are charged through Power Schottky Rectifier D2, a STPS3150RL. It’s forward voltage drop at 2 A is less than 0.8 V. Voltage divider R5/R6 sets the output voltage of the DC-DC converter: (R5/R6 +1) * 1.25 V = 60.0 V. Given tolerances of the reference voltage and resistors the exact voltage can vary. Theoretical maximum, with 1 % resistors and tolerance of the reference voltage, is (47.47 / 0.99 + 1) * 1.275 = 62.41 V. Theoretical minimum is (46.53 / 1.01 + 1) * 1.225 = 57.66 V. The maximum and minimum voltage of the current source is approximately 61,9 V and 57.16 V due to the voltage drop of protection diode D4 in the output. The voltage drop across D4 is less than 0.5 V at 50 mA, 0.3 V at 1 mA).
A USB-C connector is used for the supply voltage of the tester. There’s a catch trying to use a AC adapter complying to the Power Delivery standard. Often something like ‘PD/QC 3.0’ is mentioned on such devices. The adapter will probably not output any voltage if 2 certain 5 kΩ pull-down resistors are missing. The USB-C socket used here only has two wires for the supply voltage. Otherwise consider using a standard AC adapter and replace the USB-C socket with a matching DC power socket.
The current source
The Zener diode or DUT to be tested is measured with respect to ground. As the current source is to deliver a positive current its refence voltage (5 V, IC2, LM4040 Precision Micropower Shunt Voltage Reference) is referenced to the +60 V supply voltage. A P-channel MOSFET (T3) is used because the DC current of drain and source current are identical and the output current can be set with high accuracy. IC3 compares the voltage drop across the selected source resistor with the +5 V reference voltage and adjusts the gate voltage of T3 accordingly. IC3 is a low-offset JFET opamp. Its bias currents are in the order of pA and the voltage drop across feedback resistor R12 negligible, compared to the reference voltage. The same is true for the input offset voltage, typically less than a millivolt. C6 and R12 ensure stability.
The output current of T3 is changed by selecting a different source resistor with rotary switch S2. Since 6 different currents are chosen S2 is 2 pole 6 position rotary switch. To reduce the effect of contact resistances the two parts of S2 are connected in parallel. This also extends the lifespan of the tester. D4 in the output protects the tester from any possible reverse voltage, just to be sure.
To limit the gate voltage the supply voltage of IC3 is limited to approximately 17 V. The Gate-Source Threshold Voltage of T3 is maximal -4 V. The output voltage of the TL051 is minimal 2.7 V (VOM-) above its negative supply voltage, needing worst case at least Vref + VGS(th) + VOM– = 5 + 4 + 2.7 = 11.7 V supply voltage. At 50 mA drain current the gate-source voltage is only slightly higher than the threshold voltage. The minimum common mode input voltage ranges from 1 V below the positive supply voltage to 4 V above the negative supply voltage. So, 12 V would be enough. A 18 V Zener diode (D3) was chosen to create a stable enough supply voltage for IC3 and leave enough headroom. The operating current of voltage reference IC2 is set to 1.3 mA by R10. The total load of the +60 VDC supply by the current source circuit is 3.2 (IC3, max.) + 1.3 (IC2) + 1.6 (LED2) = 6.1 mA. The current of T3 is a separate load on the +60 V supply voltage. The current of Zener diode D3 is set by 1 W resistor R7 to a little over 10 mA, leaving about 4 mA to create the 18 V.
S1 is the test button, it connects the entire current source circuit with the 18 V supply voltage. R8 limits the peak current through the switch causing a voltage drop of 1 V. The Zener voltage can be higher or lower but this doesn’t influence the test current. Push button S1 also contains a red LED which is used as a Power On indicator. This LED is LED1 in the schematic and is connected separately via R1 to the input voltage. S1 has 4 connections, two for the switch and two for the LED (the solder lug for the cathode is indicated by a grey spot next to it).
To limit the maximum output voltage to a safe level, 5 V is the voltage most datasheets of diodes and transistor (base-emitter) list as a maximum reverse voltage, a Zener diode of 5.1 V (D5) can be connected to the output by S3. The contact rating of almost all small switches is 24 or 30 VDC. A higher rating means a lot more expensive, if you can find one. To use a standard toggle switch for the 5 V limitation a small MOSFET (T4) is used to connect D4 parallel to the output. S3 connects the gate of T4 with the input voltage of K1. R19 makes sure T4 is switched off if the contact of T3 is open. T4 is a 2N7000 and its maximum drain-source voltage is 60 V. D4 and D5 are connected in series with the drain of T4 and so the voltage here will be less than 60 V. Important, best practice is not change position of S2 and S3 when S1 is pushed, making sure T4 turns on or off and the contacts of S2 switch without any voltage present.
The value for the source resistors are easy to calculate: Vref/Iout. The following values are needed for 1, 2, 5, 10, 20 and 50 mA: 5 kΩ, 2.5 kΩ, 1 kΩ. 500 Ω, 250 Ω and 100 Ω. Of course the values of 5 2.5, 500 and 250 are not found in the standard E-series, although resistors exist with these values, but are expensive. Using additional resistors in series or parallel would make the circuit and PCB larger. The nearest E-96 values are used for R18, R17, R15 and R14: 4.99 kΩ, 2.49 kΩ, 499 Ω and 249 Ω. The error is an additional 0.2 and 0.4 %.
Mounting parts on the PCB
Fig. 2 PCB of the Zenerdiode tester (250772-1 v1.1).
Fig. 3 All parts (except the wires).
In a nutshell, start by soldering the lowest parts first and the highest last. Then fasten the two power transistors to their heat sinks and mount the assemblies onto the PCB. Next the rotary switch S2 and place IC1 and IC2 into the sockets (observe the correct orientation).
Recommended order:
D5
R1 ,R3-R6, R8-R19
D3
D1
R2, R7
IC sockets
D2, D4
C3
C2, C3
C4, C6, C7
Screw terminal blocks K1, K2, S1, S3
Fig. 4 Resistors, diodes and screw terminal blocks soldered (PCB 250772-1 v1.0).
Next
T1, T4 and IC2 (all have TO-92 packages)
2-way pin headers for LED1 and LED2
L1
C5
C1
Fig. 5 T1, T4, IC2, pin headers, L1, C5 and C1 soldered (PCB 250772-1 v1.0).
Next
Apply a thin layer thermal grease on the back of T2 and T3. No insulation is needed, the transistors can be fitted directly on the heat sinks. First a screw and a nut are used to fasten each transistor to the heat sink. Temporarily place the screw of the heat sinks in the mounting hole on the PCB to see where the leads of the transistors must be bend perpendicular. There is some room for error here. Bend the leads. Place the heat sinks on the PCB, the leads of the transistors should fit smoothly through the designated pads, and fasten each with a second nut on the bottom side. Do not place the heat sinks against the PCB, this can cause short circuits! The copper plane on top is connected to ground but has large clearances where the 2 screws from the heat sinks are, so the nut on the top side can’t make contact. The screws are connected to the drain of the MOSFETs. Only now solder the leads of T2 and T3.
Place rotary switch S2 and solder all its pins. Be sure it’s placed fully flat against the PCB!
Put IC1 and IC3 in the IC sockets.
Fig. 6 Heat sinks fixed to the PCB, T2, T3 and S2 soldered, IC1 and IC3 placed in their sockets.
Fig. 7 Mounting of the heat sinks, side view.
Fig. 8 Side view on the mounting of the heat sink of T3. Heat sink of T2 visible in the back.
The PCB is now ready for testing. Connect the mA inputs of a multimeter directly with the output (K2) and measure the 6 test currents. Also measure the +60 VDC supply voltage at 50 mA output current, on cathode of D2 with respect to ground. Be careful not to touch anything while testing!
Construction of the prototype
A PDF of a front design with dimensions is available (see Project Elements – Other).
Fig. 9 Dimensions of the front design with respect to the PCB and enclosure. All are referenced to the spindle of the rotary switch in the center of the front.
The size of the design is 106 x 78 mm, a rounded rectangle marks the borders (center of the lines). In figure 9 the sides of the enclosure are also shown as the outer rounded rectangle. Print it on normal paper and make sure the borders have the correct dimensions. Cut the inner rounded rectangle with scissors from the paper and cut the round 6 mm hole for the spindle of the rotary switch with a sharp hobby knife. The location of the spindle of the rotary switch is the only critical location, it is in the exact center of the enclosure. The PCB is designed this way. Helpful in the inside of the enclosure is a small circle, also in the center. This can also be used to drill a hole in the correct position for the 6 mm spindle of the rotary switch first. Use adhesive tape to temporarily fasten it to the top side of the enclosure. Place it in the exact center of the front, the holes for the spindle should align now. Create the other 3 holes on the top of the enclosure:
6.3 mm for the toggle switch S3
8 mm for pushbutton S1
3 mm for LED2, use a 2.5 mm drill first and use a small round file to make just big enough for the LED to stick. Using a 3 mm drill could just result in little too big hole for it to stay stuck. Use a small round file to make it bigger and test several time if the LED will fit through and is fixed properly.
For the other holes start by making smaller holes with for instance a 2 mm drill. Maybe by hand, the plastic enclosure is very easy to work on, or maybe too easy to work on. Be patient when making the holes, the ABS plastic is soft and a hole can be made too large without applying much force.
When the holes in the top of the enclosure are ready drill the holes for the 2 mm banana sockets with a 4.5 mm drill. The 6 mm thread (approx. 5.7 mm width) has two flat sides less than 5 mm wide. Use a small half rounded file to slowly make the connectors fit and are in line.
The two holes for the two 4 mm banana connectors are round and should be 7.4 mm in diameter.
Also make a slotted hole for the USB-C socket to fit through. Not too wide or it will get pulled out with a plugged-in USB-connector.
The center of the holes in the sides are 18 mm from the top of the enclosure.
Fig. 10 Front design with logo and corporate identity color and typography.
Print the front design on a self-adhesive (glossy) photo paper and make sure the size is correct, exactly the same as printed before on normal paper, 106 x 78 mm. I used a cheaper paper and it acted a little like blotting paper when printing in high quality. Printing in standard quality was fine. The matte version was worse than the glossy paper. Test with different printer settings. Stick the front design in the center onto the enclosure, exactly like the normal paper before, and make sure it is perfectly aligned with all the holes so the scale aligns with the rotary switch and the text with the two switches. Cut out the paper that covers the 4 holes carefully with a sharp hobby knife. Fit the two switches and the 3 mm LED. Tighten the nut of the toggle switch very carefully, not damaging the front when doing so. Shorten the leads of the LED but leave the short lead a little shorter to still indicate the cathode. Use a drop of superglue to make sure the LED will never fall back inside the enclosure. Maybe secure the USB-C connector also with a drop of super glue.
Wiring
Fig. 11 Front sticker (earlier design), connectors and switches fitted and PCB to the bottom of the enclosure.
In figure 11 a sticker with an earlier design is fixed to the front. All the connectors are mounted and the PCB is fixed to the bottom of the enclosure by four #4-1/4” self-tapping screws.
Fig. 12 Inside view on the enclosure with connectors and switches fitted.
Next place the top of the enclosure on it side. Place the bottom right next to it. Now everything can be wired with 0.25 mm2 (24 AWG) wire. Next is a list with a logical order and length of the pieces of wire needed. On pushbutton S1 the solder lug of the cathode of the LED is marked with a grey spot. Place it toward the side of the enclosure. The solder lug on the opposite side is the anode. The two other solder lugs, to the left and right, are of the switch. Place the two 2way pin sockets on the 2way pin headers of the LEDs. Twist the wires of each pair before soldering.
| Connect (from PCB) | Color | Length | Comment |
| [cm] | |||
| S3 to toggle switch | red | 10 | |
| black | 10 | ||
| LED1 to pushbutton | black | 12 | cathode only |
| S1 to pushbutton | red | 10 | |
| black | 10 | ||
| LED1 to pushbutton | red | 12 | anode |
| LED2 to green LED | red | 10 | anode |
| black | 10 | cathode | |
| 4 mm banana to | red | 9 | red to red connector |
| 2 mm banana | black | 6 | black to black connector |
| + of DUT (K2) | red | 12 | to red 2 mm banana connector |
| - of DUT (K2) | black | 12 | to black 2 mm banana connector |
In total 63 mm red wire is needed and 60 mm black wire.
Fig. 13. Everything is connected.
Check all wiring. When placing the top of the enclosure on the bottom make sure the wires are not touching the heatsinks, just to be cautious. In normal use they don’t get hot. Next to do is shortening the spindle of the rotary switch S2. Remove about 11 mm, maybe a little more. The plastic is surprisingly tough. When placing the knob over the spindle it shouldn’t be able to touch the front, the printed front layout is vulnerable. Best is to do this before starting the wiring. Clamp the top of the spindle in a bench vise and use a saw to remove the 11 mm of the spindle. Place the top of the enclosure on the bottom and check if enough is removed. The knob of the prototype is secured with a headless Allen screw. A 1.5 mm Allen screwdriver is needed to fix this knob. When this is done the Zener Diode tester is ready for use.
Fig. 14 Three views of finished prototype.
The test clips can each be connected with 30 cm 0.25 mm2 (24 AWG) wire to the 2 mm banana plugs. This length should be long enough. To measure SMD components and similar devices, where the test clips can’t be attached to, standard measuring cables with test tips for 4 mm banana plugs can be connected to the 4 mm banana sockets on the enclosure. Most measuring cables can be connected in parallel as their plugs also has have a 4 mm socket. A multimeter can then be connected parallel to the measuring cables to the DUT.
Replacing the sticker
Since the sticker is a printed with an inkjet printer the front can get damaged easily, get covered with scratches over time. Remove the knob and open the enclosure by removing the 4 screws in the bottom. Remove the sockets of the LEDs from the 2way pin headers. Remove the wires from the pushbutton S1 from its screw terminal. Remove the nut from the toggle switch and from the inside pull it out of the front. The pushbutton can be pushed out of the front from the inside. The wires will fit through the hole. Remove the old sticker by pulling it very slowly of the front. Remove residual glue and paper with sticker remover and make sure the front is dry and clean. Place the top back on the bottom the spindle of the rotary switch is now protruding trough the front. After printing a new sticker cut it from the sheet of self-adhesive photopaper. Cut the round 6 mm hole for the rotary switch and hole for the led, latter hole a little smaller than 3 mm. Peel of and cut of a part of the protecting paper from the sticker with a pair of scissors at the side where the LED is, about 2.5 cm. Place the sticker over the spindle and make sure the hole for the LED is exactly placed over the led and push the sticker on to the front. Take top of the enclosure of the bottom and remove the rest of the protecting paper from the back of the sticker and push it carefully and evenly onto the front. Cut the holes for the two switches with a sharp hobby knife and place the switches back. Connect all the wires and close the enclosure. Place the knob on the spindle and the tester is as good as new.
Measurements
As an example a variety of Zener diodes was measured. With the test clips it is not necessary to cut them from the tape first.
Zener diodes tested:
4.7 V/0.5 W, BZX79-C4V7.113
5.1 V/0.5 W, 1N5231B
5,6 V/0.5 W, 1N752A
12 V/1.3 W, 1N4742A-TAP
18 V/1.3 W, BZX85C18-TAP
27 V/ 3 W, 1N5935BRLG
51 V/5 W, 1N5369BRLG
Values listed are taken after pushing S1 for 5 seconds. At higher currents the values keep changing after prolonged pressing of S1. Especially when measuring near the maximum rated power of the Zener diodes.
| V | 1 mA | 2 mA | 5 mA | 10 mA | 20 mA | 50 mA |
| 4.7 | 4.236 | 4.461 | 4.708 | 4.855 | 4.968 | 5.094 |
| 5.1 | 4.466 | 4.654 | 4.821 | 4.902 | 4.963 | 5.052 |
| 5.1 | 4.661 | 4.815 | 4.943 | 5.003 | 5.053 | 5.145 |
| 5.6 | 5.629 | 5.632 | 5.642 | 5.661 | 5.691 | 5.798 |
| 5.6 | 5.433 | 5.439 | 5.452 | 5.478 | 5.513 | 5.635 |
| 12 | 11.683 | 11.691 | 11.743 | 11.820 | 11.963 | 11.973 |
| 12 | 11.701 | 11.712 | 11.751 | 11.831 | 11.980 | 12.430 |
| 18 | 18.361 | 18.406 | 18.540 | 18.768 | 19.296 | 20.891 |
| 18 | 18.164 | 18.196 | 18.313 | 18.548 | 18.962 | 20.287 |
| 27 | 26.687 | 26.772 | 26.971 | 27.205 | 27.754 | 29.103 |
| 27 | 26.458 | 26.493 | 26.634 | 26.883 | 27.344 | 28.704 |
| 51 | 49.725 | 49.858 | 50.11 | 50.50 | 51.63 | 54.46 |
| 51 | 50.98 | 51.10 | 51.40 | 51.89 | 52.87 | 55.69 |
The test current for the values in red is no longer accurate. The selected test current will be less when the Zener voltage rises above 54 V, in this case due to the temperature of the diode rising.
Fig. 15 The tester in practice. Measurement 1 of 5, 12 V/1.3 W Zener diode 1N4742A at 1 mA.
Another application is the testing of the equality of brightness of LED’s. Quite a number can be placed in series, easily done by using a solderless breadboard. Next photo show a test of 30 LEDs at once. Total voltage is 54 V at a current of 5 mA
Fig. 16 Testing the brightness of 30 red LEDs in series at 5 mA.
Bill of materials (PCB 250772-1 v1.1)
Resistor
R1 = 3.3 kΩ, 600 mW, 1 %
R2 = 0.15 Ω, 1 W, 5 %, lead spacing 12.7 mm, diam. 3.5 mm
R3, R8 = 180R, 600 mW, 1 %
R4, R6, R16 = 1 kΩ, 600 mW, 1 %
R5, R19 = 47kΩ, 600 mW, 1 %
R7 = 3.9 kΩ, 1 W, 5 %, lead spacing 12.7 mm, diam. 3.5 mm
R9, R10, R12 = 10kΩ, 600 mW, 1 %
R11, R13 = 100 Ω, 600 mW 1 %
R14 = 249 Ω, 600 mW, 1 %
R15 = 499 Ω, 600 mW, 1 %
R17 = 2.49 kΩ, 250 mW, 1 %
R18 = 4.99 kΩ, 250 mW, 1 %
Inductor
L1 = 100 uH, Irms 2.4 A, Isat 3.5 A. 0.09 Ω, radial, pitch 2.5/5/10 mm, Diam. 14 mm max. (Kemet SBC8-101-242)
Capacitor
C1 = 470 uF, 35 V, 20 %, Ir 1.86 A, D 12.5 mm, LS 5 mm, ESR 0.038 Ω (Panasonic EEUTP1V471)
C2 = 1 uF, 100 V, 10 %, cer. X7R, LS 5 mm
C3 = 2.2 nF, 50 V, 10 %, cer. X7R, LS 5 mm
C4, C7 = 100 nF, 100 V, 10 %, cer. X7R, LS 5 mm
C5 = 100 uF, 100 V, 20%, D 14 mm max., LS 5 mm
C6 = 1 nF, 100 V, 10 %, cer. X7R, LS 5 mm
Semiconductor/
D1 = MUR120G, DO-41
D2, D4 = STPS3150RL, DO-201AD
D3 = Zener diode, 18 V, 1.3 W (BZX85C18)
D5 = Zener diode, 5.1 V, 0.5 W (1N5231B)
LED1 = LED in pushbutton S1
LED2 = LED, green, T-1 (3 mm)
IC1 = MC34063, DIP-8
IC2 = LM4040ABIZ-5.0/NOPB, TO-92 (TO-226AA-3)
IC3 = TL051CP, DIP-8
T1 = BC327.25, TO-92
T2 = STP40NF10L, TO-220
T3 = IRF9510PBF, TO-220
T4 = 2N7000, TO-92
Other
K1, K2, S1, S3 = 2way screw terminal block, LS 3.5 mm, max. 1.5 mm²
connected to K1 = USB-C socket, 30 V / 3 A, chassis mounted, wired, 9 x 16 mm
connected to K2 = Banana Connector, 2 mm, Socket, 60 VDC, Panel Mount, Red (Multicomp 24.102.1)
connected to K2 = Banana Connector, 2 mm, Socket, 60 VDC, Panel Mount, Black (Multicomp 24.102.2)
Test clip, red, 30 VAC/60 VDC (Hirschmann 931467101)
Test clip, black, 30 VAC/60 VDC (Hirschmann 931467100)
S1 (= LED1) = Pushbutton, panel mount, SPST-NO, 30 VDC, 100 mA, red illuminated
S2 = Rotary Switch, 6 Position, 2 Pole, 30 °, 150 mA, 250 V
S3 = Toggle switch, panel mount, SPDT, solder lugs, 28 VDC
T2, T3 = Heat sink FK 214 SA-CB, 15°C/W
Enclosure Hammond 1591XXSSBK, ABS, 110x82x44 mm
S2 = Knob, Round Shaft 6 mm, Diam. 21 mm, with indicator line (Multicomp CP-LB21-6-6D)
Self-tapping screw #4-1/4", carbon steel, pan head
Banana plug, red, 2 mm, 60 VDC (Multicomp 25.205.1)
Banana plug, black, 2 mm, 60 VDC (Multicomp 25.205.2)
4 mm banana socket, panel mount, black
4 mm banana socket, panel mount, red
LED1, LED2 = Pin header, 1x2, vertical, pitch 2.54 mm
LED1, LED2 = Pin socket, 1x2, vertical. pitch 2.54 mm
T2, T3 = M3 screw, 10 mm, steel, pan head
2 x M3 washer, plain, steel
4 x M3 nut
IC1, IC3 = DIP-8 socket
Black wire, 0.25 mm2 (24 AWG), stranded 14 x 0.15 mm, 1 m
Red wire, 0.25 mm2 (24 AWG), stranded 14 x 0.15 mm, 1 m
PCB 250772-1 v1.1
Fig. 17 Top overlay of the PCB of the Zenerdiode tester (250772-1 v1.1).
Fig. 18 Bottom overlay of PCB of the Zener diode tester (250772-1 v1.1).
Fig. 19 Copper on top of PCB of the Zener diode tester (250772-1 v1.1).
Fig. 20 Copper on bottom of PCB of the Zener diode tester (250772-1 v1.1).
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