Guru
Joined: 02/02/2017
Location: AustraliaPosts: 1470
| Posted: 01:21am 09 Feb 2026 |
time to look at Gate voltages.
first is the switch on/off for the totem pole board, using a 10R current limit resistor and a 1N4148 diode for faster gate control when pulling it to ground (or source pin)
The drive current is supplied by a pair of TIP41 and TIP42 transistors.
test conditions are identical for both boards.
54V DC in, 200W out.
Yellow is low side gate voltage
Dark Blue is high side gate voltage
and
this is not too bad, not a lot of high frequency ringing.
Now we see the new board, with no gate current limiting resistor, nor the diode.
I connect the gate direct to the FOD 3182 output pin.
and
certainly we can see much faster switch on and off but there is now a lot
of Mhz or more ringing. This is seen in the Dark Blue trace when it goes from low voltage to about 15V, pulling the inverter output up to 54V.
I know that there should be a gate resistor according to just about all
power electrics design practice but I wanted to see what it looks like
without it.
One aim of this design is to have the smallest amount of "stuff" that makes up
the high side gate drive. I wanted to minimise the capacitance and inductance of this
by having just the drive side of the FOD3182, it's supply cap and 2 inches of thin PCB trace that follows the high side output as it switches from 0V DC to 54V DC at 20 kHz. I have got what I wanted.
time to see if a 4R7 gate resistor helps things. And after that I will add the 1N4148
for faster switch off.