PWM is a simple way to vary the voltage applied to the motor. Our How Microcontrollers Work post illustrates how to use NMOS and PMOS transistors to build logic gates such as NOT, AND, OR, etc. Most logic gates are designed using NMOS and PMOS in a complementary way. ![]() In the logic world, this is known as CMOS circuitry. The H-bridge uses NMOS and PMOS resistors in a complementary fashion. The motor direction can be reversed by toggling PWMA and PWMB. ![]() The circuit works by setting PWMB to logic zero (Q2 on Q4 off) and then setting PWMA to logic high (Q1 off Q3 on). A typical H-bridge circuit with logic scaling circuitry is shown above.Įach side of the H-bridge has two transistors with the gates tied together resulting in complementary operation–Q3 is always off when Q1 is on and vice versa. To maximize efficiency, the transistors are driven at a higher voltage than the microcontroller. Several design challenges include preventing shoot-through, implementingĪ snubber circuit, as well as open and closed loop (such as PID) controlĪn H-bridge circuit consists of four transistors (usually two PMOS’s and two NMOS’s). With pulse-width modulation (PWM) from a microcontroller to vary ![]() Bi-directional motor control can be done using an H-bridge circuit
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