Motor Control Circuits

This page features H-Bridge circuits used for controlling direct current motors. Several designs are shown using both CMOS and Bi-Polar power devices.

The heart of the Chloroplast is the Motorola MC34164-3 Micro power Undervoltage Sensing Circuit (U1 in the following diagram). In normal use, this component monitors the voltage at pin 2, and applies a ground at pin 1 ( out ) when the monitored voltage drops below 3V (34164-3 monitors 3 volts, 34164-5 monitors 5 volts). This low will then be used to assert a RESET on a microprocessor circuit. The output (an open collector) will be open when the output is above the threshold voltage.

This is a slightly revised version of the 6-transistor H-bridge designed by Mark Tilden and found on the BEAM Tek website (now only available via archive). I encourage anyone interested in H-bridges to read Mark's article, as it gives an excellent step-by-step explanation of how the bridge works. In particular, it discusses variations on the bridge, such as the positive-input and negative-input versions.

These circuits could be used as the basis for Model Railroad DCC Boosters or PWM motor controllers. The first schematic is for a basic 3 Amp - DCC Booster using the LMD 18200 CMOS, H-Bridge. Included in the design is a 5Volt regulator that supplies power to the DCC signal generation and display circuitry.

If you want to build a "freeform" version of the "Bolt light" circuit, here's a very compact layout (note that this diagram shows the transistors in "dead-bug" fashion, i.e., with the chips "down," and their legs pointing up towards you).

Using a CMOS version of the 555 timer, this circuit can be used to control the speed of a motor by adjusting the duty cycle of the pulses sent to the motor.

Mark Tilden's 6-transistor H-bridge Design, limitations, usage This is the six transistor "Tilden style" H-bridge; while not as old as the original "basic H-bridge," this goes "way back," and is the basis for many BEAM driver circuits * Up to 800 mA capacity (using PN2222 and PN2907 transistors) * 30 connections per bridge (so, 30 holes if you make a PCB) * Not "smoke-proof" (i.e., it can't handle drive voltage in both directions at once)

A simple, time-honored approach is to use one or more 74*245 chips (normally the 74AC245 is used for maximum current capability) to provide motor drive current. Here, each channel of drive power is provided by one or more buffer on the chip.

There are so many ways to drive a stepper motor, Here is another circuit that use 74LS194 4 bit bi-directional universal shift register as a phase generator and UDN2543B to drive the unipolar stepper motor. U1 74LS04 provide the necessary clock pulse for the circuit. S1 is the direction selection switch and S2 turns ON/OFF the motor.

A solar engine design using a 555 timer IC. Wilf Rigter simplified this circuit a bit, made it phototropic, and doubled it up to yield a photopopper design in a post later the same day. I've got this design written up elsewhere in the library.