N-Chan or P-Chan in H Bridge

I've been researching H-bridge designs, while seemingly simple I have a question. Why are some designed with all N-Channel MOSFETs and others have P-Channel and N-Channel FETs (eg. P-chan on top and N-chan on bottom of H-bridge)? Is there an advantage to one setup over the other? My intended use will be the output of a PWM power supply.

Regards,

Paul

I've been researching H-bridge designs, while seemingly simple I have a question. Why are some designed with all N-Channel MOSFETs and others have P-Channel and N-Channel FETs (eg. P-chan on top and N-chan on bottom of H-bridge)? Is there an advantage to one setup over the other? My intended use will be the output of a PWM power supply.

Regards,

Paul

Usually you'll find that designs that use complementary MOSFETs will be for use on relatively low voltage rails (roughly < 50V).

For a given cost/size etc. you'll find that N-channel MOSFETs generally deliver quite a bit lower Rds(on) for a given dollar than the equivalently rated P-channel part (if you can even find an equivalent).

OTOH, drive circuitry is often necessarily more complex if the design uses only one kind of MOSFET.

So, if your 'power supply' is intended to drive a 12V DC motor, you might use complementary MOSFETs. If it's for a 180VDC motor, you'll probably use all N-channel MOSFETs or IGBTs. If multiple supplies are available then additional choices may suggest themselves to the seasoned (coriander, freshly ground black pepper) designer.

Best regards, Spehro Pefhany

Using P, and N, makes driving simpler. The rails needed to drive the FETs are 'between' the two supplies. Using N for both rails, requires developing another supply rail 'above' the +ve rail. However N types, have got normally better (lower) on state resistances, for a given unit size. In the past it was generally easier to use mixed types. Now with drivers available, that generate their own 'boost' rail to operate the N type, this is probably the preferred method, since you then have equal resistances, and switching speeds.

Best Wishes

"toyo22r" schreef in bericht news:h8mdnbAadOePYy_eRVn snipped-for-privacy@giganews.com...

Check power mosfets and compare RDS-on for P-chan and N-chan. For a (relative) low power bridge (and low frequency) a p-chan can simplify the design.

It makes more sense when you start putting one together. First the 50W version, then 250W, and so on.

Oh, and do some research on buckets.

Hello Paul,

Just to add one more reason why there often are only N-channels: Cost. When it came down to the mat I even designed bridges in the 100V/20mA class with N-channel only. The N-channels cost a little less than P-channel and also this reduced the parts variety on the circuit board by one line item. This reduces SMT placement rigging costs and purchasing overhead.

Regards, Joerg

Thanks for all the responses. N-Channels it is then... My rail will be

Paul