This circuit is intended for inverter application and i wanted to simulate it using proteus but the problem is It behaves strangely when i use bc547 to drive the mosfets.

enter image description here (I didn't have a proper transformer model for proteus so i just put a resistor R8 for just a quick simulation)

When I removed BC547 and put the input signals(10 khz) directly to the gate resistors I got good waveforms:

enter image description here

Is BC547 really that bad, Or that is something wrong I did? And what other solutions do I have (Mosfet current will be 10A.)?


When you turn the BC547 ON, the low output impedance (emitter follower) quickly charges up the gate and pulls the output low quickly.

When you turn the the BC547 OFF, the gate has to discharge through the resistor network you have which takes some time; the simulator drive is probably set to a very low output impedance and that is why the simulation using direct drive seem to work well.

If you think you need extra gate drive, then either a push-pull arrangement (which actively drives the gate high and low) or a MOSFET driver would work.

You can find an interesting post about it at this location.

To drive a MOSFET you need a low impedance source that can provide the current necessary to charge and discharge the gate quickly; there are some op-amps that can handle it, but check the effective output impedance versus frequency (better amplifiers have it in the characteristics) because the charge current must be provided very quickly.

In an application driving a transformer, using an op-amp may not be practical due to drain-gate feedthrough.

I would note that LTSpice is supported by Wurth with a full set of transformer models that may let you see the effects more clearly.

  • \$\begingroup\$ So it won't be that bad if i used my circuit, right? I've check the circuits in the link especially the one with push-pull driver and I think it's not too much different from mine. \$\endgroup\$ – iMohaned Apr 8 '17 at 15:56
  • \$\begingroup\$ I do not know what load you want to drive (except it is a transformer) but the push-pull solution is quite common in that situation. \$\endgroup\$ – Peter Smith Apr 8 '17 at 15:57
  • \$\begingroup\$ Just for pure curiosity, i connected opamp as a buffer to provide low output impedance and it showed perfect square waveforms... Is that practical? \$\endgroup\$ – iMohaned Apr 8 '17 at 16:16
  • \$\begingroup\$ I updated the answer; extended comments that extend the answer are frowned upon :) \$\endgroup\$ – Peter Smith Apr 8 '17 at 16:23

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