All right, I'm building a Royer oscillator, basic push/pull configuration, if I use BJTs as the drive transistors there are no problems, aside from BJTs being massively inefficent when used in 12V power electronics, so they tend to cook themselves when I try to add a load. 2 BJTs in parellel wasn't quite enough, so I would need to use at least 6 20A BJTs total to build the oscillator, and add more heat sink, obviously this is getting ridiculous, so I thought, why not use FETs instead?
Anyhow, so I found these FETs:
https://www.digikey.com/en/products/detail/vishay-siliconix/SUP70101EL-GE3/7622840
They refuse to run properly on their own when used in the same configuration as the BJTs (the BJTs always require a control winding that is a few turns larger than the primary, exactly how many extra can be kinda random), or in the configuration in this schematic:
they both turn ON at the same time whenever they are driven directly by the feedback winding when a 500 ohm bootstrap resistor is added between the gate and ground (PNP instead of NPN), the BJTs were perfectly fine with this configuration, 1Kohm has the same effect, basically they will not bootstrap properly, adding more winds to the feedback winding does not help. I stuck a BJT to the gate as an amp, the feedback winding can't shut off the gate because the BJT blocks it, so I added a 250ohm pull up resistor to the gate to shut the FETs off when not being driven by the BJTs, this finally got the FETs to behave themselves, sort of, they started heating up rapidly, even with no load attached, and the voltage is a lot lower than it should be, it should be ~24V across the primary, but it's only +-7V, less than half of what's expected, the frequency is a lot lower as well ~1.3KHz instead of the ~3.9KHz the BJTs were running at, like they are being driven in their linear region (which doesn't make any sense, the BJT is switching the gate directly to ground), or aren't shutting off all the way. The waves look square, if the gate wasn't being shut off fast enough by the pull up resistor I would expect to see it on the scope, same for a slow turn on. Reducing the input voltage to 8V only slightly reduces the voltage, and frequency, dropping to 3.7 is very odd, the frequency goes up instead of down, 2.6KHz, peak voltage is ~4V, waveform has the same spikes the circuit has when using BJTs only.
Obviously I'm missing something here.
Anyhow, so I found these FETs:
https://www.digikey.com/en/products/detail/vishay-siliconix/SUP70101EL-GE3/7622840
They refuse to run properly on their own when used in the same configuration as the BJTs (the BJTs always require a control winding that is a few turns larger than the primary, exactly how many extra can be kinda random), or in the configuration in this schematic:
they both turn ON at the same time whenever they are driven directly by the feedback winding when a 500 ohm bootstrap resistor is added between the gate and ground (PNP instead of NPN), the BJTs were perfectly fine with this configuration, 1Kohm has the same effect, basically they will not bootstrap properly, adding more winds to the feedback winding does not help. I stuck a BJT to the gate as an amp, the feedback winding can't shut off the gate because the BJT blocks it, so I added a 250ohm pull up resistor to the gate to shut the FETs off when not being driven by the BJTs, this finally got the FETs to behave themselves, sort of, they started heating up rapidly, even with no load attached, and the voltage is a lot lower than it should be, it should be ~24V across the primary, but it's only +-7V, less than half of what's expected, the frequency is a lot lower as well ~1.3KHz instead of the ~3.9KHz the BJTs were running at, like they are being driven in their linear region (which doesn't make any sense, the BJT is switching the gate directly to ground), or aren't shutting off all the way. The waves look square, if the gate wasn't being shut off fast enough by the pull up resistor I would expect to see it on the scope, same for a slow turn on. Reducing the input voltage to 8V only slightly reduces the voltage, and frequency, dropping to 3.7 is very odd, the frequency goes up instead of down, 2.6KHz, peak voltage is ~4V, waveform has the same spikes the circuit has when using BJTs only.
Obviously I'm missing something here.