Half Bridge with PWM- gate signal problem

by scouseydaniel   Last Updated July 24, 2019 12:25 PM - source

After making a half bridge inverter using a square wave (I asked a question on this website about it previously) I have now decided to use PWM signal in order to obtain a sine wave output and have come across some new issues.

Here is the circuit on LTSpice:

enter image description here

The load is an 100u inductor and the PWM is created and input into a gate drive before it is used to drive the MOSFETs.

When I run the simulation, the high side mosfet signal (HO)- linked to the behaviour of Vs- follows the shape of the current in the inductor L1 and does not reach 0V and turn off as it should for much of the time causing the circuit to not work. If I increase the inductor value and therefore decreased the current in the circuit the problem is fixed. However I am not sure I understand why a high current would cause the voltage to not reach zero.

Here are the waveforms from the simulation- the second set is the same but zoomed in to better show what is happening. enter image description here

enter image description here

Can anyone explain what is causing this or what I need to change in order to fix this circuit?

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