N-Chan or P-Chan in H Bridge

[toyo22r]

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

Regards,

Paul

 

[Frank Bemelman]

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.

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.

 

[Tim Wescott]

-snip-

Oh, and do some research on buckets.

For holding the broken and burnt pieces?

 

[Roger Hamlett]

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

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

 

[Spehro Pefhany]

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

 

[Joerg]

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

 

[toyo22r]

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 b
170Vdc.

Paul