Message 26919 in TECH.WW
From: G8MNY
Date: Thu, 30 Jul 26 08:43:00 Z
Newsgroups: TECH.WW
Subject: Simple PIV Test Circuit
Message-ID: <644_GB7CIP>
Path: N2MH4|VE3KPG|GB7CIP
R:260730/0848Z 34626@N2MH4.#SENC.NC.USA.NOAM LinBPQ6.0.24
R:260730/0848Z 27571@VE3KPG.#ECON.ON.CAN.NOAM BPQ6.0.25
R:260730/0843Z @:GB7CIP.#32.GBR.EURO #:644 [Caterham Surrey GBR] $:644_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Nov 19)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I use this rather dangerous circuit to test high voltage diode Peak Inverse
Voltage & high voltage transistors breakdown voltage.
As shown this circuit may trip out house ELCB. If that is a problem take point
"a" to earth instead of live, for lower voltage isolated tester!
Small Valve Current Scope
Radio Mains Limiting Attenuator
Transformer Resistors
The use of a test button means that the high voltage is not applied until you
are ready and WELL CLEAR of the circuit!
The phase of the secondary connection (a & b) to the mains is important if
>700V RMS is wanted for testing. (also assuming you don't have a very sensitive
RCD mains trip.)
The 4x 22K 1W are not "rated" so tests are limited to a few seconds. The 4 Rs
limit the maximum test current to 15mA, which is not enough to damage power
devices. (but could just harm U!)
The DC scope needs a high voltage probe, that can just be several high value Rs
in series with the scopes standard 1M input to give approx 10:1 reduction.
N.B. Commercial scope probes (1:10 or 1:100) are not normally rated at such
high voltages!
The scope then shows the polarity & safe breakdown voltage....
_ _+1350V _
/' `\ /' `\ _____
| | | | +ve conducting | | ^1000v
| | -ve conducting | | -ve conducting &
-1350V_ \._./ Diode/Transistor \._./ zener breakdown
No Load PIV breakdown > 1400V action.
For exact PIV measurement you can easily calibrate your scope gain to the ratio
arm by measuring the known mains voltage and applying x 1.4 peak factor (or
times 2.8 pk-pk).
Sometimes you see proper avalanche where at the breakdown voltage the device
conducts heavily (SCR like), or oscillates at HF (negative Z). Components like
these used say on the mains or mains PSU can will be destroyed in a few uS of
the triggering PIV peak is ever reached!
SCR like breakdown Negative Z
The oscillating negative Z of a device in a power circuit can easily cause
horrendous amounts QRM, change the device & all is quiet!
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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