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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Don't you think a buffer - such as a simple NPN/PNP totem pole - between the 555 and the gate, would make switching a bit more snappy? The capacitance of both the gate and your TVS diode have to be charged up afresh on each cycle, so the gate waveform could start to look as mole hills do after a shower of rain, and where would your dv/dt be then?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Proud Mary wrote ...
Don't you think a buffer - such as a simple NPN/PNP totem pole - between the 555 and the gate, would make switching a bit more snappy? The capacitance of both the gate and your TVS diode have to be charged up afresh on each cycle, so the gate waveform could start to look as mole hills do after a shower of rain, and where would your dv/dt be then?
Alright I suppose I could tolerate more components in exchange for more V. I assume you say totem pole as that would be your first choice?
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
Pin 5 shall be connected to ground with a 0.1 uF capacitor. Pin 4 goes to Vcc. You can use pin 5 to implement a protection against excessive current. Something like this: Your second circuit is better. The capacitor shall be chosen so the voltage at the drain of the transistor doesn't get too high when it switches off.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Im going to switch over to a 556 timer, one 556-1/2 will be setting the on time (monostable), while the other 556-2/2 will be triggering the first 1/2 astable (frequency).
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Patrick wrote ...
Im going to switch over to a 556 timer, one 556-1/2 will be setting the on time (monostable), while the other 556-2/2 will be triggering the first 1/2 astable (frequency).
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Proud Mary wrote ...
Don't forget that CMOS varieties like the TLC556 series can motor along at up to 2 MHz.
This particular circuit will top out at 25kHz, but I guess near vertical sides will be helped out at 2Mhz. Then again the transistors will have more to do with rise/fall time then the timer driving them.
When I used the double diode trick for independent timing resistors, I forgot that changing one on/off time also changes the other off/on time. So 556 it is.
I beleive I will be able to adjust the on-time for best voltage/spark length, while the frequency can be increased or decreased as needed for average power.
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