H-bridge doesnt supply any current.

[Dmeads]

Hi folks!

I followed the Lewis Loflin H bridge tutorial for an SPWM signal which is great

I have included my schematic, but I used a square wave to simulate in LTspice instead of the SPWM switching.

also I used IRFZ24N instead of IRFZ44N MOSFETs.

I get a nice sinusoidal output with a high resistance RC filter, but no matter what load i stick on the bridge, my power supply says the H bridge never draws more than 1mA, which from simulation I learned is for the 10kohm pullup resistors with a 10V supply voltage.

Does anyone know how my H bridge can output more current? I would eventually like to use it to drive an induction motor.

Thanks!

[james_s]

Your circuit is not the same. One has all N channel mosfets, the other has N and P channel mosfets, at least it looks that way from the picture.

[garethw]

You’re trying to turn on an N-channel mosfet by grounding it and that will not work. You can’t swap p and n channel devices without reconfiguring the circuit.


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[Mechatrommer]

if you do that in real life, you will burn all the mosfets.

[mc172]

if you do that in real life, you will burn all the mosfets.

Well that's a great help to the OP, nice one for helping him to understand why.

[Mechatrommer]

if you do that in real life, you will burn all the mosfets.

Well that's a great help to the OP, nice one for helping him to understand why.

i thought the OP can figure that out but since you asked, because the upper NMOSFETs will by default turned ON due to pull up resistors R4 and R5 (if their respective controller LO). say if V2 toggled HI, M3 will be turned ON, since M2 is ON (V3 LO), it will create a short M2 to M3 and poof, vice versa on V3 HI, M1 -> M4. the safe state is when V2 == V3 in which case motor will be clamped to either V1 or GND, and those states are useless to drive a motor spinning. ymmv.