The circuit can be simply Q1 is connected as a current source. By D1, there is a constant voltage on the base, and it is worth considering the selected resistor in the emitter approximately 5.6 V. With an emitter resistor of 5K6 R2 will then 1mA through the transistor.
With the chosen resistors in the circuit the current is approximately: 1mA, 2mA, 5mA, 10mA and 20mA. Great precision is not required.
If meter is chosen here for a small DVM module. However, every other meter is applicable, provided that the input resistance is high enough.
The circuit is simple to build on a piece of PCB holes. Note that the DVM module separate from the circuit galvanic isolated power supply needs.
Connect the test zener diode between the terminal A and K. Start with a current of 2mA. This is a safe value for most type zener diodes. Depending on the type of zener diode, may be chosen for a greater current. Than the Zener voltage will vary slightly.
Join the zener diode on backwards, the meter will indicate approximately 0.7V. The same picture shows an ordinary silicon diode. A germanium diode, a voltage of about 0.3 V to 0.4 V indicate when a Schottky approximately 0.2 V indicates.
Connect an LED to A and K, it will be highlighted and the Vforward (LED voltage) of the LED indicate.
The diode / LED failure, the meter displays zero if the voltage at the collector of Q1 is, this is> 25V.
Bridge rectifier BR1 = 40V 500mA
R1 = 3k3 ¼ W
R2 = 5K6 ¼ W
R3 = 2k7 ¼ W
R4 = 1k ¼ W
R5 = 560 ohm W ½
R6 = 270 ohm ½ W
C1 = 470µF 35V
D1 = 6V2 zener 400mW
Q1 = BC161-16
S1 = on / off switch
S2 = 5 modes 1 mom ignition switch
ENG = The diode under test (Device Under Test)
DVM DVM = module of BACO or Dick Best (input adapted to 200V)