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Okay really need help on constructing a MOSFET based H-bridge circuit with a switch. I've got two p type and two n type mosfets.

I understand you have to apply voltage to the gates to turn the transistors on but I'm not sure how you turn certain transistors ON while leaving others OFF.

Also wiring and connecting the circuit up on a breadboard, I get you should have a resistor before the gate to protect the transistors? And I believe the source pin of the MOSFET just connects to ground? Does the drain just connect to the motor? Having trouble understand how and where to connect the components. Also need to incorporate a switch that allows the direction of the motor to be selected. Please I need some help, backed into a corner here!

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  • \$\begingroup\$ What type of controller are you starting with? Do you have a MCU that you plan to use? \$\endgroup\$ – Dan Laks Oct 8 '14 at 17:10
  • \$\begingroup\$ Also, what voltage do you plan to drive the motor with? And how much current do you expect it to draw? If you don't know the answers, post a link to the motor's datasheet. \$\endgroup\$ – Dan Laks Oct 8 '14 at 17:48
  • \$\begingroup\$ I think you need to find some more online guides/tutorials/instructables about H bridges. You can also search the many H-bridge related questions on this site. The theory of operation and how things are connected (and how the input signals turn on/off each of the FETs) will become more apparant as you read more. \$\endgroup\$ – KyranF Oct 8 '14 at 18:09
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There are plenty of circuits for controlling a motor via a MOSFET H bridge - just google "mosfet h bridge". Here's the first one in the list: -

enter image description here

Here's the website I got this from - it'll give you loads of good ideas.

Basically, the motor spins one direction when inputs B and C are taken to the appropriate logic level. To reverse the motor take inputs A and D to the appropriate logic level and make sure you don't try and control it both ways because you might short out and damage your power supply or battery.

Obviously if you are running your logic signals at 3V3 you'll need to choose a MOSFET that reacts to this sort of gate voltage correctly. If using switches then having them controlled from the 12 V supply is fine but, in reality, performance and circuit is determined by your power supply voltage.

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  • \$\begingroup\$ I am trying to power the circuit with a 9v battery. An H‐bridge is a simple switching circuit that can be used to control the direction of a DC motor. If MOSFETs are used as the switching elements the direction can be electronically controlled. For this project you need to design a MOSFET based H‐bridge circuit capable of switching the direction of a small DC motor (max draw 500 mA, peak 1A). For the purposes of demonstration a switch should be incorporated that provides the input to the H‐ Bridge circuit and allows the direction of the motor to be selected. \$\endgroup\$ – user153458 Oct 10 '14 at 14:51
  • \$\begingroup\$ The problem with this topology is the slow turn-off of the two high-side P-types as 10k is used to draw the charge out of the gate. As long as the interlock is wide enough to mitigate shoot throughs \$\endgroup\$ – JonRB Nov 7 '14 at 21:37
  • \$\begingroup\$ @JonRB - I said that the circuit shown was first on the list that I googled and that the website linked will give more ideas. Also take note that I don't believe this is a PWM application. \$\endgroup\$ – Andy aka Nov 8 '14 at 12:21

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