Will this work?

[EasyGoing1]

[eccerr0r]

Re: Will this work?

No, it will not measure the temperature of the room.

Nor will the motor turn.

[EasyGoing1]

Re: Will this work?

No, it will not measure the temperature of the room.

Nor will the motor turn.

OK, so for a simple small motor that will be switched on and off rapidly, do you think just a mosfet with a flyback diode would be best?

[budm]

Re: Will this work?

Nope, will not work.
How did you come up with the circuit?

[stj]

Re: Will this work?

why??
why are you trying to switch both poles????

[Dannyx]

Re: Will this work?

There's others who are far more skilled with stuff like this than I am, but I'll drop by just for curiosity's sake: the way I see it is that the top P-channel will be stuck off all the time due to R3 pulling it up. If all you're trying to do is run that motor, just the N-channel part+flyback diode should suffice IMO, provided the transistor is kept within its specs. Cheers.

[budm]

Re: Will this work?

1) Top MOSFET Q2 is N-CH, bottom MOSFET Q1 is P-CH.
2) 5V is not enough to turn on high side Q2 N-CH MOSFET.
3) Q1 P-ch MOFET's body diode D1 will be forward bias so when Q2 is turned on, so why have Q1 in the circuit?
I have no idea what the OP is trying to do.

[eccerr0r]

Re: Will this work?

Yeah only need one pull up or pull down transistor to turn the motor on/off. Probably easier to do N-channel pull down when doing the level shift from 5V control to 12V output. And yes, as budm indicated, the top transistor's schematic symbol is Enhancement-N and the bottom is Enhancement-P - and neither will work properly because both are deep in the cutoff region as gates will be negative relative to source (Q2-N) or positive relative to source (Q1-P).

This is not to mention Q1's body diode is anti-parallel to D4, and thus one will always be conducting with Vf of a diode drop no matter if the power is AC or whatever. D3 and Q2's body diode are parallel to each other and thus D3 is redundant if the body diode can take the load.

Yeah sorry about the tongue in cheek response of "trying to measure temperature in room" because the objective(s) were not stated. However it is true that if wired the way it's drawn the motor will not turn, mainly because Q2 will remain deep in cutoff and have no way of turning on as drawn.

(incidentally I was thinking about how to design a grid tie inverter h-bridge for my solar panel project, and came to the conclusion that power darlington transistor suck %#*&! and IGBTs should be paired with NPN if I had the right IGBTs in my parts bin. Too bad I have a boatload of useless NPN and PNP power darlingtons and most likely I have to do high side N-ch MOSFET because I don't have IGBTs or P-ch MOSFETs.)

[redwire]

Re: Will this work?

OP is trying to cheat by building an H-bridge with only two switches. Using extra diodes does not work. You need four switches (mosfets) to reverse polarity to a load, in a proper H-bridge.
Only one switch (mosfet) is needed to turn a motor on and off.

[stj]

Re: Will this work?

i think he wants a pwm speed controller.

[Dannyx]

Re: Will this work?

i think he wants a pwm speed controller.

Provided he only wants it to run in a single direction, a single N-channel FET can be used for that, can't it ? Provided it's rated accordingly.

[stj]

Re: Will this work?

any transistor will do - the current is pretty low.
and a 555 timer.

[EasyGoing1]

Re: Will this work?

Provided he only wants it to run in a single direction, a single N-channel FET can be used for that, can't it ? Provided it's rated accordingly.

That's exactly what I want. I was reading about H-bridges, which seem to be pretty popular in motor control circuits, but since I don't need the motor to switch direction, I thought maybe half an H-bridge would be a more suitable circuit for turning the motor on and off ... perhaps with more solid fly back protection than a single diode?

It was just a thought...

When I put the circuit into a schematic, I was looking at it trying to visualize current flow and I wasn't so sure it would actually work so I posted it here.

[Dannyx]

Re: Will this work?

H bridges are mostly used to switch direction on motors. They're redundant if you only plan to turn it on/off (and maybe do some speed control too) - a simple transistor will work for that, depending on your motor's power requirements of course.

[Curious.George]

Re: Will this work?

OP is trying to cheat by building an H-bridge with only two switches. Using extra diodes does not work. You need four switches (mosfets) to reverse polarity to a load, in a proper H-bridge.
Only one switch (mosfet) is needed to turn a motor on and off.

If you have split supplies, you can do this with just 2.

[eccerr0r]

Re: Will this work?

If you want to really build half an h-bridge or half bridge, you could use the other transistor to stop the motor faster

[EasyGoing1]

Re: Will this work?

H bridges are mostly used to switch direction on motors. They're redundant if you only plan to turn it on/off (and maybe do some speed control too) - a simple transistor will work for that, depending on your motor's power requirements of course.

It's a small motor ... similar to the kind that they put in game console controllers for vibration feedback.