PWM With Rotation Inversion (MEC097E)

The circuit we present makes use of an H-bridge in an anti-phase control in order to obtain changes in the speed of a two-way motor.

With the transistors used the maximum recommended current is of the order of 1 A, but higher current capacity transistors can be used.

The base of the circuit is an oscillator with the active duty cycle drawn up around one of the doors of a 4093.

The other three ports are used to apply opposite phase signals to the H-bridge which controls the motor.

One drawback of this circuit is that at the 50% active duty cycle, which corresponds to the motor stopped, the motor remains consuming power and depending on the application it can oscillate.

In Figure 1 we have the complete diagram of the speed control PWM with rotation inversion.

Figure 1 - Complete control diagram

The printed circuit board for the assembly is shown in Figure 2.

Figure 2 - Printed circuit board for the assembly

Transistors must be fitted with heat sinks and their position, as well as the integrated circuit, must be observed.

The resistors are 1/8 W with any tolerance and the capacitor C1 must have its value chosen according to the motor, so that it does not vibrate too much.

For a better control, a double potentiometer can be used, so that when one section has increased resistance the other has decreased it, according to the connection shown in Figure 3.

Figure 3 - Using double potentiometer