P Channel Mosfet - Page 1
Forum section: electronics / beginners

author: j_car
author_rank: Contributor
timestamp: October 02, 2018, 10:23:40 am
content: Hi, I want to know how to get a P Channel Mosfet to operate with 0-48v supplied by a PWM speed controller and to be turned on/off with a unipolar Hall Effect Switch. Please reply in very simple terms as I have NO electronic knowledge. Thanks John.

author: madires
author_rank: Super Contributor
timestamp: October 02, 2018, 10:51:47 am
content: Could you please elaborate on what you are trying to accomplish? Which components do you have already?

author: j_car
author_rank: Contributor
timestamp: October 02, 2018, 02:34:50 pm
content: I am trying to make an H bridge. The N channel side works with the speed controller and Hall Switch but I Can't get the P channel to work, it gets hot and reduces the power going through it.

author: Prithul0218
author_rank: Contributor
timestamp: October 02, 2018, 03:28:01 pm
content: Quote from: j_car on October 02, 2018, 02:34:50 pmYou are probably not turning "on" the MOSFET properly. That's why it's resistance is high and so it's heating up. Check the datasheet of your MOSFET and check the required Vgs or gate to source voltage in order to turn on the MOSFET fully to achieve lowest resistance.Or if you're trying to control the speed of the motor using PWM, then you are probably not turning the MOSFET on and off fast enough.

author: j_car
author_rank: Contributor
timestamp: October 02, 2018, 03:56:13 pm
content: Yes, that was my conclusion. But I don't know how to get it to fully turn on with the variable power of the speed controller(0-48v) going through it. Without the speed controller with just 12v it works fine, doesn't hot. I would like to get the mosfet to work with the speed controller and then I will look at turning it on/off with the Hall Switch later. The mosfet is a IRF9Z34NPBF.

author: madires
author_rank: Super Contributor
timestamp: October 02, 2018, 06:58:21 pm
content: How do you drive the p-ch MOSFET?

author: rstofer
author_rank: Super Contributor
timestamp: October 02, 2018, 07:09:38 pm
content: Engineers, and there are plenty hiding out here, can't even talk without a pencil or pen in their hands. Always drawing things - like a schematic.

author: j_car
author_rank: Contributor
timestamp: October 03, 2018, 08:42:33 am
content: When connected to 12v supply, Gate is connected to negative with a 1k resistor to source, source connected to positive, drain to motor and motor to negative. This works OK. When I try with the speed controller it doesn't work(mosfet gets hot). I think, therefore, there is an issue with the negative to the gate when the speed controller is used(speed controller has to be connected to a 24v supply).

author: Alex Nikitin
author_rank: Super Contributor
timestamp: October 03, 2018, 09:43:00 am
content: Quote from: j_car on October 03, 2018, 08:42:33 amAs one of possible explanations - the speed controller is most likely not producing a DC voltage output but a modulated 0 to 24V output with a variable duty cycle (PWM) . That may create a problem for the P channel switch. However without further details on the speed controller and the circuit used it is difficult to give a better advice.CheersAlex

author: madires
author_rank: Super Contributor
timestamp: October 03, 2018, 10:22:43 am
content: The maximum V_GS of the p-ch MOSFET is 20V, i.e. the voltage between source (positive) and gate must not exceed 20V. When you pull down the gate to ground (negative) for switching on the MOSFET V_GS equals the voltage of the power supply. The PSU's 24V are too high. Therefore you would need a driver circuit, a MOSFET driver chip for example. Alex has explained another possible issue. And I agree that more details about the speed controller and a circuit diagram would be helpful.

author: j_car
author_rank: Contributor
timestamp: October 03, 2018, 12:31:50 pm
content: The only info I have on the speed controller is CC & CV PWM v1.3 sync 100v 200a brushed PWM speed controller. The diagram is the best I can do to show what I've tried to achieve. Sorry if it's not very good.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: October 03, 2018, 12:48:58 pm
content: It is not that the diagram is not good (it is OK, clear enough), it is the actual circuit which is wrong. The Hall switch will produce the output voltage between 0V and +12V (if it is a push-pull output) but the source of the MOSFET sits at 24V at least some of the time (as the controller is PWM the output is switched between 0 and +24V rapidly , possibly with some filtering applied). If the source voltage is above a certain level (around +15V) , FET won't close. If the Hall switch has an open collector/drain output, than it is the PWM transients which may screw things up. Could you clarify what Hall switch do you use?CheersAlex

author: j_car
author_rank: Contributor
timestamp: October 03, 2018, 01:01:40 pm
content: How can I get it to work?

author: Alex Nikitin
author_rank: Super Contributor
timestamp: October 03, 2018, 01:10:30 pm
content: Quote from: j_car on October 03, 2018, 01:01:40 pmSorry, not enough information to answer this question. And I'm afraid that with a PWM controller there are no easy answers. You need at least a scope to see what actually is happening in the circuit.CheersAlex

author: j_car
author_rank: Contributor
timestamp: October 03, 2018, 01:21:35 pm
content: OK. Thank you very much for your help.

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 03, 2018, 01:37:44 pm
content: Quote from: rstofer on October 02, 2018, 07:09:38 pmThis is a corollary of a schematic is worth 10,000 word description.

author: madires
author_rank: Super Contributor
timestamp: October 03, 2018, 02:18:39 pm
content: Does the speed controller have some control lines/signals which could be used with the Hall switch?