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Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
You don't have a DC blocking capacitor in series with your primary, which is absolutely needed. Check if your mosfets aren't dead already.
Second big pitfall, if the circuit fails to oscillate, one of those mosfets driving the GDT will short out the power supply and die.
You need to have a halfbridge gate driver and a reliable start up circuit.
Steve Ward used NE555 to excite the base of antenna, but I myself couldn't be satisfied with this for a CT and got into much more complex approach.
You should look at how his circuits are done, they seemed pretty reliable so far.
If you don't have gate drive IC's, you can use discrete gate drivers made from one mosfet level shifter stage and class B push pull of complementary bipolar transistors in emitter follower configuration, which is going to be more than enough for small mosfets like IRF530.Still I would prefer some mosfets that can be ran from mains voltage, IRF740 should do well.
2N2222 and 2N2907 are good complementary pair for that purpose. The mosfet preamplifier needs to be nothing more than a BS170 and 100ohm resistor to Ucc; it's purpose is to shift the voltage level, and if you use higher voltage logic you could even get away without it maybe.
And absolutely remember to use a DC blocking capacitor in series with the GDT too.
and today i said to myself ill stop putting money on that... i destroyed 30,- piece (90... that is a lot of money here... ) i was building from HV viki here, somebody could write more to H bridge, since there was no capacitor...
i hate world...
the better thing is i still have 2 IRF510, so i only buy another 2 510s and i hope i will be fine... or else i will kick that thing... -----------------------------------------
---------- but to that schematics : when i add that capacitors, will it be fine? i tried that in half bridge and it was working, but not so powerfully as i expected, i think i must add more voltage to GDT. AND how far can i go with primary woltage, when i have 100V mosfets? is it rule of 2/3 as i know? (so somewhere about 60/70? )
so, i bought new IRF530 (the last thing i am buing to end of summer...)
i connected, and it worked. But the performance... No sparks at all, i was only able to light a lightbulb "tlejivka" ... better performance i could have only with 74hc14, and a lot better with just one IRF530
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troubles with h bridge
only 1 mosfet is alive... 