Notes:
Using a single 555 Timer IC and a small transformer to
generate a high voltage, this circuit will test zener diodes
of voltage ratings up to 50VDC. The 555 timer is used in the
astable mode, the output at pin3 drives a small audio
transformer such as the LT700. This has a primary impedance
of 1K and a secondary impedance of 8 ohms. Used in reverse
the unloaded ac voltage is around 120volts ac. This is
rectified by the 1N4004 diode and smoothed by the 2.2u
capacitor which MUST be rated at 150 VDC. The zener under
test is measured with a multimeter set to DC volts as shown.
The load current switch enables the zener to be tested at 1
or 2mA DC. The rectified DC load, but a good zener should
maintain the reading on the volt meter. |
