stunningly simple general purpose solid state tesla driver

Why are 555 timer and/or dedicated PWM IC based solid state tesla coils not any good?
Half-bridge section: 

Click for enlargement. Schematic for the off-line half-bridge. Transformers on the left depict
the single gate drive xfmr of the 555 schematic. The xfmr has two isolated secondary windings.

This is the actual half-bridge part of the circuit. The mains voltage is rectified by D9 which should be some standard >3A 600V diode, but not from the 1N400x series which are only 1A.

The capacitors smooth out the rectified mains and place one end of the primary coil, L1, in the middle of the supply voltage (0V). The other end is switched between up and down, to +160V and -160V. The 470nF caps should be FKP or MKP types and 250VAC.

The mosfets can be IRF740 or IRF780, for sake of lesser expenses. Two >8A >400V n-channel mosfets will work, too. The zener diodes on the gates are 18V 1/2W. Diodes D5 and D6 are soft recovery ultrafast diodes, >2A >400V, for example one of BYW34 - BYW36 or the faster SF26 - SF28. D7 and D8 can be any >3A >10V schottkys like 1n5822 - the voltage rating doesn't matter much as long as the schottky is cheap.

Both mosfets must be mounted on their own heatsinks. Although switching losses are minimal when the driver is in tune with the TC secondary, the mosfets still have a drain-source resistance in the order of 0.5 ohms, so 3A rms means about 3W dissipation per mosfet (5W total), which can be unhealthy in the long run...

See PCBs and Eagle schematic for the half-bridge:
>> half-bridge PCB


The new 555 driver circuit with the two output mosfets is capable of driving a mosfet gate drive pulse transformer directly, with 15A source 8.8A sink, so  a IR2110 (shown in above left pic, right side) is not needed.


(C) 2001 Jan Wagner