Motor Control Circuits

The purpose of this document is to explain the theory and application of Micro Linears ML4425 and ML4426 brushless DC motor controller ICs, with speed control. It shows typical applications, along with information about choosing the various components necessary for proper operation. It presents in depth control system information for those who wish to use it, but the user can pick component values without extensive analysis by using the formulas developed for each component...

An electronic speed control for an AC Motor can be designed with a Light Dimmer IC by limiting the minimum firing angle of the triac so that the motor wont stall. This can be done effectively for high volume applications by making a minor change to the IC. An alternative to modifying the IC is illustrated in Figure 2...

Figure 2 is a diagram of the control circuit built on a 1.45 X 1.8 inch PC board. IC1 is an LMC555 CMOS timer that generates a 200 microsecond wide clock pulses to step the motor and control its speed. The speed can be varied by changing the pulse repetition rate with R1...

This motor starter protects singlephase motors against voltage fluctuations and overloading. Its salient feature is a soft on/off electronic switch for easy operation...

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...

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...

M1 is a stepper taken from an old disk drive. There are five pins, i.e., common, coil 1, 2, 3 and 4. Resistance measured between common pin and each coil is about 75 Ohms. Driving current for each coil is then needed about 60mA at +5V supply. A darlington transistor array, ULN2003 is used to increase driving capacity of the 2051 chip...

The circuit controls fan speed by sensing the ambient temperature in the system enclosure and reducing the fan`s supply voltage when maximum cooling is unnecessary. Reducing the operating speed of the fan saves power, extends operating life, and reduces acoustic noise...

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...

You will find this identical circuit inside most 3 wire computer fans with speed monitoring output to the motherboard. Peel off the sticker from the fan hub in order to access a motor winding pin for connecting up the tacho circuit...

This DC Motor Controller circuit will control a 12V dc motor. The system will have three pushbuttons: a START button, a REVERSE button and a STOP button. Initially, the motor must not be running. When the START button is pressed, the motor will run in one direction. Pressing the REVERSE button (while the motor is running in START direction) must have no effect on the motor. Pressing the STOP button must stop the motor from running...

These two schematics are variations on another PWM circuit that I designed. The diagrams are for 12V operation only and there are high side (common ground) and low side (common +12V) versions. The low side version of the circuit uses an N Channel FET, the high side version of the circuit uses a P Channel FET. N Channel devices tend to handle more current than P Channel devices, they are also less expensive. The high side version of the circuit is useful when one side of the load has to be grounded...

A pulse width modulator (PWM) is a device that may be used as an efficient light dimmer or DC motor speed controller. The circuit described here is for a general purpose device that can control DC devices which draw up to a few amps of current. The circuit may be used in either 12 or 24 Volt systems with only a few minor wiring changes. This device has been used to control the brightness of an automotive tail lamp and as a motor speed control for small DC fans of the type used in computer power supplies...

This is a circuit for controlling the speed of small DC motors, it works nicely as a speed controller for an HO or N gauge model railroad...

Physical motion of some form helps differentiate a robot from a computer. It would be nice if a motor could be attached directly to a chip that controlled the movement. But, most chips can`t pass enough current or voltage to spin a motor. Also, motors tend to be electrically noisy (spikes) and can slam power back into the control lines when the motor direction or speed is changed. Specialized circuits (motor drivers) have been developed to supply motors with power and to isolate the other ICs from electrical problems. These circuits can be designed such that they can be completely separate boards, reusable from project to project...