I need to shift a PWM signal (switching freq - 300kHz) from (0 to 5V) to (-50 to -45V). Output is going into an IR2011 gate driver. Available supplies are +/- 50V, +5V and GND.
I'm told I should be looking at using a PNP level shifting circuit, can anyone comment and elaborate as to what that is?
Thanks,
David.
Something like this (it also inverts) with R around 1K.
+5V | .-. | | R | | '-' | |< 0V/5V -| |\ | | | | +-----------o -50V/-46V | | | .-. | | | | R '-' | | -50VBest regards, Spehro Pefhany
This works well for no load, but when going into the gate driver input the signal amplitude shrinks to almost nill. Is something then fishy about the gate driver's input impedance?
Dave.
The IR2011 inputs have pulldown resistors- poorly characterized and temperature sensitive. If you use the ~1K resistors that I suggested it should work fine. If you don't like the ~200mW "on" power dissipation in the transistor, you can add a series resistor (maybe
5.6K) on the collector to knock it down a bit.Best regards, Spehro Pefhany
ASCII art:
VCC ! / \ / \ ! !/ e Signal ------! PNP !\ ! +-------- Load ! / \ / \ ! -50V
AFAIK there are gate drivers with integrated level shifters. You should look for those. If you connect the GND from the 5V to -50V, you can use 2 high side drivers.
OR
You could, if you have the supply to do it, add a emitter follower pair at the MOSFET input.
View in a fixed-width font such as Courier.
NON-INVERTING 5V LEVEL SHIFT | | |\ 390 >----| >---/\/\---+ |/ | |buffer | |cmos e | |/ GND----+---------| 2N5401 |\ c | | / 3.9K 1W / \ | +-----> to IR2011 | / 390 / \ | -50V
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