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
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.