05-14-2023, 02:08 PM
(05-14-2023, 08:10 AM)tihomir Wrote: I think the duty cycle is a very important feature. Let me share my experiment. I'm just cap dumping into a primary coil of a Tesla transformer.
My coil is 31 uH, the capacitor is a 400 V 22 uF. That gives me a resonant frequency of 1.9 kHz. My SCR cap dump is using a neon lamp (100 V) for the trigger.
I set my function generator to 50% and at a high frequency (11 KHz) and the capacitor did not charge, because the spikes were not very high voltage. I lowered the frequency and the capacitor quickly charged, but once the dump was initiated I was not able to get the SCR to turn off, because current was always flowing in. I had to short the capacitor out so the SCR gets closed. If I did not, current was alwaysing flowing in from my DC power supply (that was set to 6 V, 20 mA limit and at that moment it was drawing 20 mA at 1.5 V, almost like a short circuit case). I don't know if it's the SCR (some 800 V one) or the frequency or the capacitor, but at 50% duty cycle I was not able to get it working at any frequency (tried up to 1 MHz).
I changed the capacitor with a 200 nF non-eelctrolytic one and I was able to make it work at 23 KHz at 50% duty cycle, but the cap dump was very slow - 11 Hz and a lot of power has been drawn - 1.3 V at 20 mA (26 mW). I changed the duty cycle to 8%, the cap dumps' frequency was the same (11 times a second), but the power consumption was 6 V at 2 mA (12 mW). Mostly voltage, as it should. The power consumption is just from the DC power supply. I'm not including the frequency generator in the calculation.
With that I just wanted to note the importance of the duty cycle. I guess that a 50% duty cycle would work fine with smaller caps, but not smaller coils because they won't give you enough voltage spikes to charge a capacitor up to 100 V. This means you'll probably need to trigger it with a Zenner diode. I tried to connect it to the base of the SCR (just like the neon lamp) and it did not seem to work as expected though (I only have a 5 V one). I don't have much time to experiment right now in order to find out the reason.
Yes I believe the duty cycle means lots. In my opinion 50 percent duty cycle in a traditional sense will never be able to trigger more output energy unless you know of a farther down the line mechanism to make up for it. Because we need to remember that the trigger current is one thing but so is the current usage from our pulse/switching circuit. So it's very important keeping it as most basic as possible so all together we only operate in the low milliwatts range. At this consumption, We have much greater chances of taking advantage of increased back emf amplitudes, feed back etc....