MOSFET + Relay to Control a Motor

Posted on Feb 6, 2014

Basically, the circuit is using relay (2 set of Relay for each Motor) to switch the direction of the motor and MOSFET (1 set of MOSFET for each Motor) to control the speed of the motor. I will divide the MOSFET + Relay circuit into 3 part for the description, hope that you can completely understand the schematic. This part is basically about how m

MOSFET + Relay to Control a Motor
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icrocontroller output ports drive Relays. I hope you understand about how a Relay operate or you can read more about Relay here. To control a Relay from microcontroller, you need to convert the digital output signal (normally 0V for logic 0 and 5V for logic 1) from microcontroller to the coil voltage of the Relay, in this case 12V. For your information the INPUT1 and INPUT2 pin should be connected to microcontroller. When the INPUT1 is logic 1, which is 5V, the Q1 will be turned ON, which also means RELAY1 pin will be shorted to GND. What happen here is the K1 Relay will be turned ON. The K1 Relay coil, Port 1 is actually connected to 12V by default and now Port 2 is shorted to GND (due the Logic 1 output from INPUT1) which complete the circuit and turn ON the K1 Relay. However if the INPUT1 is logic 0, which will turn OFF the Q1 transistor, and RELAY1 pin will no longer shorted to GND. This will break the K1 Relay coil circuit and the K1 Relay will be turned OFF. Looking at the Relay and Motor, try to focus on how the NC (Normally Close), COM (Common), and NO (Normally Open) is connected to the Motor terminal (labeled M1 and M2). M1 and M2 is basically connected to the COM of both relay, NC of both Relay is connected to 12V and NO of both Relay is connected to MOSFET, where it will be shorted to GND when the MOSFET is turned ON (this will be discuss on the next part). Looking at the diagram above, when K1 is turned OFF and...

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