Andris Lusis
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[SOLVED] Problem with H-bridge design
Dear forum members,
I have designed a H bridge driving circuit according to the IR application notes. At the moment i have put it together on a breadboard.
The LO and HI inputs of both drivers are driven with 20kHz square wave pwm sequentially ( 20kHz HI for 10msec, 20kHz LO for 10msec (the sequence rate is 100Hz)).
I am able to measure the correct pwm signal on the driver input and also on the driver output and directly between the gate and the source terminal of all 4 mosfets.
However measuring the output i get a distorted 100Hz wave +/-15V with some small 1v amplitude sawtooth on the top, resembling my pwm.
It looks like the mosfet is correctly turned on when it's driving pwm starts, however it is never turned off.... When the pwm stops the signal turns off slowly -- within 1 millisecond (!).
Therefore i conclude that both the high and low side mosfets indeed are turning on - otherwise there would be no ac signal output, however for some reason the switch off time is 1ms, not 50ns as per datasheet, and that is the reason that my pwm is not seen.
Could the reason be that i'm supplying the cap with only 15V and not the full design inteded voltage (325v) ? I am afraid to connect the full voltage before the circuit is acting as it should.
I have never before built a h bridge myself, could someone experienced please point the error in my driving circuit.
Dear forum members,
I have designed a H bridge driving circuit according to the IR application notes. At the moment i have put it together on a breadboard.
The LO and HI inputs of both drivers are driven with 20kHz square wave pwm sequentially ( 20kHz HI for 10msec, 20kHz LO for 10msec (the sequence rate is 100Hz)).
I am able to measure the correct pwm signal on the driver input and also on the driver output and directly between the gate and the source terminal of all 4 mosfets.
However measuring the output i get a distorted 100Hz wave +/-15V with some small 1v amplitude sawtooth on the top, resembling my pwm.
It looks like the mosfet is correctly turned on when it's driving pwm starts, however it is never turned off.... When the pwm stops the signal turns off slowly -- within 1 millisecond (!).
Therefore i conclude that both the high and low side mosfets indeed are turning on - otherwise there would be no ac signal output, however for some reason the switch off time is 1ms, not 50ns as per datasheet, and that is the reason that my pwm is not seen.
Could the reason be that i'm supplying the cap with only 15V and not the full design inteded voltage (325v) ? I am afraid to connect the full voltage before the circuit is acting as it should.
I have never before built a h bridge myself, could someone experienced please point the error in my driving circuit.
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