0 Simple Zener Tester Schematic

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.

Construction:
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.

Using
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.

 Simple Zener Tester Circuit Schematic

parts List

     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)

Detail: Simple Zener Tester Schematic

0 Simple Circuit Board Checker

This little circuit indicates the basic integrity of a printed board, detecting 0V, positive supply voltage from less than 3V to 30V and floating parts. If the probe is floating, as it would be in a broken track, then both LEDs barely light up, since there is no current to drive the transistors, but if the probe touches 0V or a positive voltage one or other lights. A digital signal should light them in proportion to the mark-space ratio whereas the output of a circuit oscillating at a frequency rate below about 20Hz will cause the LEDs to flicker alternatively. The LEDs will illuminate always at a constant intensity, no matter the voltage supply used, because they are fed by a very simple FET constant-current generator (Q1).

Circuit diagram:

Circuit Board Checker Circuit Diagram

 
Parts:

R1 = 22K
R2 = 22K
D1 = Red LED
D2 = Green LED
Q1 = BF245
Q2 = BC547
Q3 = BC557

Notes:

• The Black clip must be connected to the negative ground of the board under test.
• The Red clip should be connected to a positive voltage source (not exceeding 30V) available on the same board.
• Metal probe is suitable for this circuit.
• Two Miniature Crocodile Clips (Red and Black) are also necessary.

Detail: Simple Circuit Board Checker