inductance of the multimeter doesn’t affect the readout
When measuring an unknown zener diode and the
yellow LED lights up, check to see if the diode is open by
checking its forward voltage drop with a multimeter, or
just reverse it in the tester. If the yellow LED goes out with
the zener in the forward direction, then the diode is likely
good but has a breakdown voltage above 55V. If you wish
to measure the breakdown voltage in that case, insert an
external variable power supply across the yellow and black
terminals, with the minus terminal of the power supply
connected to the yellow terminal. Increase the value of
the supply slowly until the yellow LED is just extinguished,
then measure the voltage across the diode.
I’ve measured zener diodes with breakdown voltages
near 200V in this manner, as well as MOVs and other high
voltage protective devices without concern for excessive
power dissipation since the diode current when the yellow
LED turns off is quite low.
The circuit configuration back in Figure 1 is robust
and will operate with a variety of modifications. The three
variable elements you can experiment with are: the
secondary winding of T1; the resistor R6, which
determines peak current in Q1; and the breakdown
voltage of D2.
If you want the output voltage to have lower
maximum voltage, you can eliminate one winding in the
secondary or reduce the breakdown voltage of D2. If you
want a higher maximum voltage at the output, you can
put a third winding (there are two unused windings on T1)
in series with the two shown, or simply replace D2 with a
higher voltage zener diode. If you take this latter route,
then you’ll need to pick a higher breakdown voltage
transistor, like the MPSA06 (VCEO = 80V vs. 40V for the
Capacitors C4 and C5 are rated at 520V, and D3 has
a reverse breakdown voltage of 600 volts, so there’s room
to play ... but be careful if you go to higher voltages.
Although C4 is a small value (0.22 µF), energy storage
goes up as the square of voltage, so higher voltages can
deliver a very dangerous and potentially fatal jolt! Be
If you want to increase or decrease the power
delivered to the DUT, then decrease or increase the value
30 November 2014
to celebrate our anniversary!
ships from the U.S.
** as compared with
purchase of the
Reflow Kit V3
Toll free: 888-977-7443