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Registered Member #1348
Joined: Sun Feb 24 2008, 01:48AM
Location: Michigan's Upper Peninsula
Posts: 22
EDIT: i forgot to mention that the following refers to simple resistive charging (i.e. bridge, resistor and tank capacitor only).
if i drive a SGTC with DC do i need some sort of RF filter between the diode bridge and tank to protect the diodes from deteriorating, or can diodes withstand RF?
what would i use--RF bypass caps?
assuming the tank cap is connected across the two legs of the diode bridge (but of course after a resistor) would it double as a RF bypass?
Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
depending on how large your tesla coil is going to be determines how big your rf filter charging choke has to be and yes it is ABSOLUTELY necessary or things could go very wrong. As for designing the choke i would recommend you watching and that is the best and most efficent way to eliminate all the rf in the charging tank circut ad protect your diodes and high voltage transformers.
Registered Member #1348
Joined: Sun Feb 24 2008, 01:48AM
Location: Michigan's Upper Peninsula
Posts: 22
with DC resonant charging the charging choke is one of the main circuit components. and it doubles as an RF blocking device. but with simple resistive charging there is no choke. so how would i protect the diodes? perhaps i could still use a choke?...problem is, i'd want a choke with very low inductance so that i don't risk primary voltage doubling by inductive kick. (some might see the extra voltage as a benefit but i don't want excessively high primary voltages).
so, would a low inductance choke still be effective at blocking RF? i don't have any experience with filters...
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Well, with resistive charging, the resistor will protect the diodes fine I guess. Maybe split the resistance in half and put one in each wire of the DC charging supply. Also check out Terry Fritz's Terry Filter to get an idea of what effective RF protection for Tesla coils looks like.
You do NOT want to connect the tank capacitor across the diode bridge output: you want to charge across the spark gap, the same as recommended for AC Tesla coils. If you put it across the tank cap, the diodes will conduct on the negative half-cycles of the RF oscillation, and die pretty quickly.
The tank capacitor isn't a RF bypass, it's a huge source of RF. The spark gap on the other hand is just a short circuit during the oscillations.
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RF filter required in DC Tesla Coil?
