This circuit is intended for motion control applications, a common occurrence in robotics! This affordable PWM DC Motor controller can control any PMDC motor specified at 12 V to 30 V and 3 Amps max. Motor direction is controlled with a slide switch and motor speed, with an ordinary potentiometer. The circuit diagram in Figure 1 shows ICs type LMD18200 and SG3525 at the heart of the circuit. The SG3525 is a pulsewidth modulator control circuit and the LMD18200, an H-Bridge to enable the motor to be run in both directions. The SG3525 affords frequency control and duty cycle control. The oscillator fre-quency is determined by the components attached to pins 5 and 6. Preset P2 serves to adjust the frequency between 1.16 kHz and 35 kHz. Although it is generally rec-ommended to stay above 20 kHz as oth-erwise the motor will produce audible sound, in some cases that’s just not pos-sible depending on the motor you’re using. Pot P1 determines the duty cycle, which can be adjusted from 10% to 100% to effectively control the motor speed.’ Inter-nal transistors are used in a such a way as to obtain 100% duty cycle. The internal driver transistors are grounded by pins 11 and 14 for alternate oscillator cycles. Pin 16 of the IC is the REF V terminal, which gives 5 V out.
Resistor R1 feeds the sup-ply voltage to an open collector-transistor for TEL-level PWM output. Moving on to the LMD18200, slide switch SI (on header SI) governs the Direction control input (pin 3) to change the direc-tion of the motor from cw to ccw or vice versa. R4 is connected to thermal flag pin T (pin 9), which is not used here. The func-tion may be used to flag a warning when the chip temperature is 145 degrees. The IC is automatically shut down when 170 degrees C is reached. Pin 8 of the LMD18200 is the current sense input. R6 connects this pin to ground. The Brake input (pin 4) is hard wired to ground. C2 and C4 at the motor output are ‘bootstrap’ capacitors. Pins 2 and 10 are the H-Bridge outputs powering the DC motor. In the power supply section, capacitors C5 through C9 serve to suppress noise on the two supply rails. The L7805ACV voltage regulator for the logic supply accepts any unstabilised DC voltage between 7.5 V to 18 V applied to K2. The other supply con-nector, K3, is for the motor power. The capacity of the motor supply of course depends on the motor used. If the motor is specified at 12 V then R7 should be 1 ka, and if it is 24 V then 11d15 should be fitted. If you want to use a heavy-duty motor consuming more than about 1 A, it may be worthwhile to strengthen the cop-per tracks to/from K2/K3 with lengths of 1.5 mm2 solid copper wire.
If you want to interface the driver with a source supplying 0-5 V, simply remove potentiometer P1 and apply the analog voltage to pin 2 of IC. Figure 2 shows the PCB designed for the driver, which should fit many applications at crucial locations in a robot. After all, most forms of motion of a robot will require a motor of some kind. The board has been designed for compactness whist using leaded components only, i.e., no SMDs in sight here. The copper track lay-out and component mounting plan are contained in free download no. 060339- 1.zip from our website.
