How evil is a P-Channel MOSFET in the real world?

[CrazyIvan]

From what I've read, P-Channel devices are slower, have higher "on" resistance and are more expensive than N-Channel devices.

But using a P & N channel combination would surely make a H-bridge much simpler (no high-side drivers, no bootstrapping limitations, no need for locked antiphase driving).

I had a look at a pair of devices IRF1010N & IRF4905 (both around $2.00).

Device, Drain-Source Voltage, Drain-Source Current, Drain-Source On-Resistance, Gate-Source Charge, Rise Time, Fall Time
[N-Channel IRF1010N] 55V 85A 11mΩ 32nC 76nS 48nS
[P-Channel IRF4905] -55V 74A 20mΩ 19nC 99nS 96nS

Would a H-bridge design with these two really be that bad?
A P-Channel device at lower voltages (55V) has reasonable On-Resistance (although this triples @100V, and it 7 times greater @150V).

[Zig]

Ah the evil P channel.. actually an interesting aspect of the specs You have published is that the stored charge ( remember you got to get rid of this charge to change the state of the FET ) is actually lower in case of P channel device.

I think it might be an idea go back to the manufacturers data sheets and check out the TEST CIRCUIT and practicability of the test circuit to ascertain just how relevant the rise time specs are.

[Larken]

If your really into cost savings then an Nchannel is better, but a Pchannel can make a simpler H bridge with just a pull down resistor drive circuit, no high side driver needed.

I made a stepper drive for 10 years (in 90's) with a p-channel top end and they were very reliable, but ran a bit hotter than if it was Nchannel. A Pchannel can make a simpler more reliable circuit, because mosfet drivers fail quite easily when stressed.
I drove the top pchannels with a ULN2003 and a simple resistor divider. I used IRF520 and IRF9520 mosfets.

btw ,When running high voltage, a slower turn-on can be better

Larry K

[guru_florida]

We use P-channel in openservo.com open source servo. I think IRF mosfets were used in one of the hardware iterations. You might want to take a gander over there and look at the schematics. The main cpu is Atmel Atmega168.

[themotorman]

Originally Posted by Larken If your really into cost savings then an Nchannel is better, but a Pchannel can make a simpler H bridge with just a pull down resistor drive circuit, no high side driver needed. I made a stepper drive for 10 years (in 90's) with a p-channel top end and they were very reliable, but ran a bit hotter than if it was Nchannel. A Pchannel can make a simpler more reliable circuit, because mosfet drivers fail quite easily when stressed. I drove the top pchannels with a ULN2003 and a simple resistor divider. I used IRF520 and IRF9520 mosfets. btw ,When running high voltage, a slower turn-on can be better Larry K

I would suggest you check out the IR IRS2110 it is a hi side and lo side combo that is only about $5 at digikey it will drive almost and system upto 500 volts.. P channel are t worth using except for a few low power cases

[Larken]

I would suggest you check out the IR IRS2110 it is a hi side and lo side combo that is only about $5 at digikey it will drive almost and system upto 500 volts.. P channel are t worth using except for a few low power cases

I already use thousands of IR2104's a year.

$5 each.. your kidding right ?? I pay 0.35 each

[guru_florida]

Originally Posted by Larken I already use thousands of IR2104's a year. $5 each.. your kidding right ?? I pay 0.35 each

Must be that great Canadian dollar, eh?!?

What do you use a thousand of them for?

(I can crack Canadian jokes...I am Canadian. hehe)

[themotorman]

Originally Posted by guru_florida Must be that great Canadian dollar, eh?!? What do you use a thousand of them for? (I can crack Canadian jokes...I am Canadian. hehe)

The 2110 can dish out nearly 2 amps the 2104 only 250 or so mA.. I need the high current for power MOSFETS , igh speed = high current due to gate capacitance. Either way it is easy to use only N channel by rearranging the circuit.
IR have some good app notes on using these chips.. check 'em out..

[guru_florida]

Originally Posted by themotorman The 2110 can dish out nearly 2 amps the 2104 only 250 or so mA.. I need the high current for power MOSFETS , igh speed = high current due to gate capacitance. Either way it is easy to use only N channel by rearranging the circuit. IR have some good app notes on using these chips.. check 'em out..

Actually, what I meant was what product do you make that requires that many? I assume you aren't going through that many yourself unless you are popping them in the microwave. Sounds like you might have an interesting product.

[Larken]

Originally Posted by Florida_guru Actually, what I meant was what product do you make that requires that many?

I make the Viper servos drives.
Its written right at the bottom of this message.

Originally Posted by themotorman The 2110 can dish out nearly 2 amps the 2104 only 250 or so mA.. I need the high current for power MOSFETS ,

IR made the 2104 to drive power mosfets as well, so why do you need 2 amps when it works fine with 250ma ??
I drive IRFP4232's (pretty big mosfets) with 2104's