Best Way to Drive FET in SMPS

driving fet

I'm designing a SMPS and have looked at various circuits. This is actually going to be a battery charger. See attachment; V1 is a 15 V dc supply and V2 is a 200 kHz 5v pp square wave. The load is connected across C2. In the final version, a PIC will replace V2 to drive the FET from one of its PWM outputs and that's the bit I'm having a problem with...

...the Source of the FET is referenced to +15v and +5v on the PIC will be referenced to ground (so I can use the onboard AD converter). I'm looking for ideas on what is the best / simplest / cheapest way for driving the FET from a ground-referenced 5v PWM signal.

I have shown a P-Channel FET in the cct as I have seen one used like this in many similar circuits but I could use an N Channel plus other circuitry. I gave some thought to using a bipolar transistor but I don't want to re-invent the wheel.

FYI, I'm aiming for 200 kHz PWM and the max current to the load current will be around 7 Amps

Thanks in advance

Hello,

You may try to use a bipolar pnp-npn driver circuit discussed here:



But please correct the schematics as I indicated in my comments. Read the whole text I wrote there to understand.

Your +5V drive pulses may come at/as the VG1 generator shown at lower left.

I know there may be even simpler driving solutions, others here may show you something else.

unkarc

i think your circuit will meet some problem, if your output voltage will not feedback to adjust the drive signal of the power mosfet

rfzheng

You are right, the circuit I created was only so I could look at the FET drive; as I said before, V2 is replaced by a PIC that will sense the output voltage and adjust the PWA accordingly.

Right now I'm looking at a SEPIC system that uses a coupled inductor and only needs a low-side N-Channel FET.

There are some chips which work for control and gate drive for battery charger. Those chips have build in level shifter and bootstrap circuit for high side floating drive.
Using SEPIC, you need low side drive only, however, SEPIC cannot give you continuous current output.