I am designing (rather redesigning) an H-Bridge circuit to drive TEC modules, and I am having trouble coming up with a suitable gate drive circuit for the P-Channel MOSFETs on the high side. I've found some integrated gate drivers for the N-Channels from Diodes, Inc, p/n ZXGD300xE6 (x = 1, 2... 6) that seems like they will work fairly well, but there is no equivalent for driving P-Channels. The P-channels have a source voltage of 24V, so I can't just drive the gates to ground because Vgs max is 20V, so I need to somehow vary the gate voltage between 24V (Vs) and about 12V. Here are the specs of my circuit:
PWM_f = 15.625 kHz
PWM_res = 6-bit
smallest PWM "on" pulse length = 1.00us (1 / 15.625kHz) / (2^6)
Vsupply = 24V
Imax (TEC) = 12A
Pchannel gate capacitance = 1200pF
Pchannel max gate charge = 63nC
PWM controller = PIC @5V
PWM voltage = 5V
Since the smallest pulse length is 1us, I'd like to be able to fully turn on and turn off the MOSFET within 200ns, which means my driver needs to be able to sink and source about 300mA (63nC/200ns). The previous circuit had a small signal n-channel mosfet (2n7000) with two 10k resistor in series connected between the drain of the 2n7000 and the 24V rail. This was way too slow since the turn on time was around 10us and the turn off time was like 20us.
It seems like I need some sort of "totem-pole" output stage on the driver in order to properly charge and discharge the gate, but I haven't seen an circuits that don't discharge the gate directly to ground, which, in my circuit's case, would exceed the Vgs max rating. Is there a simple way to discharge the gate into 12V somehow? (indepenent 12V regulator?, zener between totem pole negative rail and ground, etc...?)
I'm sure some people want to tell me to use an N-Channel as a high side switch, but I am looking for information for using a P-channel.
The P-Channel part number is IRF5305PBF.
Thank you,
Owen
PWM_f = 15.625 kHz
PWM_res = 6-bit
smallest PWM "on" pulse length = 1.00us (1 / 15.625kHz) / (2^6)
Vsupply = 24V
Imax (TEC) = 12A
Pchannel gate capacitance = 1200pF
Pchannel max gate charge = 63nC
PWM controller = PIC @5V
PWM voltage = 5V
Since the smallest pulse length is 1us, I'd like to be able to fully turn on and turn off the MOSFET within 200ns, which means my driver needs to be able to sink and source about 300mA (63nC/200ns). The previous circuit had a small signal n-channel mosfet (2n7000) with two 10k resistor in series connected between the drain of the 2n7000 and the 24V rail. This was way too slow since the turn on time was around 10us and the turn off time was like 20us.
It seems like I need some sort of "totem-pole" output stage on the driver in order to properly charge and discharge the gate, but I haven't seen an circuits that don't discharge the gate directly to ground, which, in my circuit's case, would exceed the Vgs max rating. Is there a simple way to discharge the gate into 12V somehow? (indepenent 12V regulator?, zener between totem pole negative rail and ground, etc...?)
I'm sure some people want to tell me to use an N-Channel as a high side switch, but I am looking for information for using a P-channel.
The P-Channel part number is IRF5305PBF.
Thank you,
Owen
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