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G8MNY > TECH 05.07.06 21:22l 64 Lines 2772 Bytes #999 (0) @ WW
BID : 37103_GB7CIP
Read: DL1LCA DL8ZX GUEST
Subj: Simple PIV Test Circuit
Path: DB0FHN<DB0FOR<DB0SIF<DB0GV<DB0LJ<DB0RES<DK0WUE<7M3TJZ<ZL2BAU<GB7PZT<
GB7YFS<GB7CIP
Sent: 060705/0902Z @:GB7CIP.#32.GBR.EU #:37103 [Caterham] $:37103_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New Jul 06)
(8 Bit ASCII Graphics use code page 437 or 850)
I use this rather dangerous circuit to test high voltage diode Peak Inverse
Voltage & high voltage transistors breakdown voltage.
Small Valve Radio
Mains Transformer
ÚÄÄÄ¿a ÚÄÄ22kÄÄ22kÄÄÄÂÄÄÄÄÄ3M3ÄÄ3M3Ä¿
____ ³ º( 360V 22k all ³ ³ _____
Live >ÄÄo oÄÄÄ´ º(_ 0V ³ 1W o 1/10 3M3 ³ÚÄÄÄ¿³ Scope
240V TEST )º( 360V 22k Component Ratio ³ ³³ ³³
)º(_________³ 1350V under Arm ÀÄÄ´ÀÄÄÄÙ³
)º b peak test Y ³o 0 o³
Neutral>ÄÄÄÄÄÄÄÙ º __ 6v o Input ÀÄÂÄÄÄÙ
º(__Lamp ³ ³
Earth>ÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
The use of a test button means that the high voltage is not applied until you
are ready & 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. The 4 22k 1W (not rated!) 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 standard 1Mê I/P to give approx 10:1 reduction.
N.B. Commercial probes are not normally rated at a high enough voltage!
The scope then shows the polarity & safe breakdown voltage....
_ _+1350V _
/' `\ /' `\ _____
| | | | +ve conducting | | ^1000v
³ ³ ³ ³______³ ______ ³ ³_____ v PIV
³ ³ ³ ³ ³
| | -ve conducting | | -ve conducting &
-1350V_\._./ Diode/Transistor \._./ zener breakdown
No Load PIV breakdown > 1400V action.
For exact PIV measurement you can calibate the scope gain to the ratio arm by
measuring the known mains voltage & applying x1.4 peak factor (or X 2.8 p-p).
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 with say mains & a PSU cap will be destroyed in a few uS if the
triggering PIV peak is ever reached.
/| OR /°°°°
| ³ | °°°°
³ ³_____________ ³ °°°°_________
SCR like breakdown Negative Z
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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