26-06-2024, 08:48 PM
I've decided even 5 CMOS gates in parallel isn't enough to drive the IRF740. The issue is charging and discharging that gate capacitance of nearly 1700 pF.
The previous IRF1404Z is about 8 nF in the datasheet though statically measures at about 6700 pF on the component tester.
Typically I use 2N3904 and 2N3906 for most things, but they are Ic max =200mA. The BC3xx family parts I have loads of are only 100mA.
I seem to have loads of TO92 MPSA05 (NPN and 500 mA, 60V) and 2N5401 (PNP 600 mA, 150V), so while not at all a matched complementary pair the gain looks OK at typically over 100 (measured nearly 200) and fT both about 100 MHz. The PWM is 19 kHz.
I've soldered them up and mounted an ext/int huge toggle switch (10A or more?). The IRF740 drain is mounted to the H- panel socket and source goes to toggle switch, either main PCB 0V or external supply negative. The toggle switch connects the external supply positive to H+ panel socket. A 1uF 250V met poly goes from FET source (H- supply) to H+ (the laptop PSU +19.1 for the μTracer) on the rear off the panel.
Perhaps it will work. Maybe test tomorrow. I'll need to fit a connector for external supply.
Is this the highest voltage heater? 117Z3 and similar tubes with heater running direct off USA mains. https://www.radiomuseum.org/tubes/tube_117z3.html
The previous IRF1404Z is about 8 nF in the datasheet though statically measures at about 6700 pF on the component tester.
Typically I use 2N3904 and 2N3906 for most things, but they are Ic max =200mA. The BC3xx family parts I have loads of are only 100mA.
I seem to have loads of TO92 MPSA05 (NPN and 500 mA, 60V) and 2N5401 (PNP 600 mA, 150V), so while not at all a matched complementary pair the gain looks OK at typically over 100 (measured nearly 200) and fT both about 100 MHz. The PWM is 19 kHz.
I've soldered them up and mounted an ext/int huge toggle switch (10A or more?). The IRF740 drain is mounted to the H- panel socket and source goes to toggle switch, either main PCB 0V or external supply negative. The toggle switch connects the external supply positive to H+ panel socket. A 1uF 250V met poly goes from FET source (H- supply) to H+ (the laptop PSU +19.1 for the μTracer) on the rear off the panel.
Perhaps it will work. Maybe test tomorrow. I'll need to fit a connector for external supply.
Is this the highest voltage heater? 117Z3 and similar tubes with heater running direct off USA mains. https://www.radiomuseum.org/tubes/tube_117z3.html
