Zener diode tester circuit

Zener diodes are widely used in electronic products, such as the voltage stabilizing circuits and protection circuits in color TVs. In recent years, due to the introduction of a large number of foreign electronic products and components, it is difficult to find the parameters of many Zener diodes, which brings certain troubles to maintenance. In addition, when making and repairing electronic products, sometimes the parameters of Zener diodes are more stringent (such as the Zener diodes in the protection circuits of color TVs), which requires the detection and selection of newly purchased or suspected Zener diodes. Therefore, it is necessary to make a simple Zener diode tester. Now I will introduce a Zener diode tester I made to everyone for reference and imitation. The circuit is shown in the figure.

　　The parameters shown in the figure can measure the stable voltage value of a low-power voltage-stabilizing diode within the range of 0 to 250V. If the voltage-stabilizing value of the voltage-stabilizing diode being measured is low, the voltage of the secondary of the transformer can be appropriately reduced.
　　The voltmeter in the figure can be replaced by the DC voltage block of a multimeter, and the transformer can also be replaced by the power transformer of a tube radio. I used a power transformer of a three-filament tube radio when making it. It should be noted that if the voltage-stabilizing value of the voltage-stabilizing diode being measured is high, R2 in the figure must not be omitted, otherwise you may get an electric shock. In addition, if you feel it is inconvenient to use a key switch, you can also use a torsion switch.
　　When using it, connect the diode to be tested in the direction shown in the figure, press the power switch, and you can read the stable voltage value of the voltage-stabilizing diode from the voltmeter. At this time, LED1 should emit green light, indicating that the test is in progress.
　　In addition, if the C and E poles of the transistor are connected, the withstand voltage value of the transistor can be measured. This device can measure tubes with a withstand voltage of about 300V or less. Please note that the leakage current of 3AD type tubes is large, and the measured value is obviously low. Of course, if you want to do a simple test on color TV line tubes, you can further increase the secondary voltage of the transformer, but the insulation during winding must be taken seriously.