Gandalf_Sr
Member level 1
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
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