PWM and power control schematics

This handy circuit can be used as a speed controller for a 12V motor rated up to 5A (continuous) or as a dimmer for a 12V halogen or standard incandescent lamp rated up to 50W. It varies the power to the load (motor or lamp) using pulse width modulation (PWM) at a pulse frequency of around 220Hz.... [read more]

This circuit takes advantage of the voltage drop across bridge rectifier diodes to produce a 5-position variable voltage supply to a DC fan or other small DC motor. It is not as efficient as a switch-mode circuit but it has the virtues of simplicity and no switching hash. The four full-wave bridges are connected so that each has two pairs of series diodes in parallel, giving a voltage drop of about 1.4V, depending on the load current.... [read more]

PWM waveforms are commonly used to control the speed of DC motors. The mark/space ratio of the digital wave-form can be defined either by using an adjustable analogue voltage level (in the case of a NE555 based PWM generator) or digitally using binary values. Digitally derived PWM waveforms are most often produced by the timer/counter modules in microcontrollers but if you do not want to include a microcontroller in your circuit it’s also quite simple to generate the signals using discrete logic components.... [read more]

Stepper motors are available in several versions and sizes with a variety of operating voltages. The advantage of this general-purpose controller is that is can be used with a wide range of operating voltages, from approximately 5 V to 18 V. It can drive the motor with a peak voltage equal to half the supply voltage, so it can easily handle stepper motors designed for voltages between 2.5 V and 9 V.... [read more]

In this circuit, an SCR is used to slowly vary the intensity of a 120 volt light bulb by controlling the time that the AC line voltage is applied to the lamp during each half cycle.... [read more]

One reason why commercial soldering stations are expensive is that, in general, they require the use of soldering irons with inbuilt temperature sensors, such as thermocouples. This circuit eliminates the need for a special sensor because it senses the temperature of a soldering iron heating element directly from its resistance. Thus this circuit will, in principle, work with any iron with a resistance which varies predictably and in the right direction with temperature (ie, positive temperature coefficient).... [read more]

This is a very good integrated circuit. There is no need for any external glue logic to drive the circuit, there is only 2 pins to drive the motor, one for controlling the direction and the other to trigger the stepping pulses. It provides a very compact design that drives 5 or 6 or 8 wire stepper motors.... [read more]

Fancontrol... [read more]

DC Motor Control Circuit... [read more]

The ckt is built around two 555 timer ICs. U1 and U2. U1 is wired as a variable duty cycle oscillator with a constant time period of around 0.1 second. Duty cycle can be varied from 0 to 100 per cent by R4 potentiometer. The output of U1 (pin 3) is connected to the rest input (pin 4) of U2.... [read more]

The 555 Ic is wired as an astable and the frequency is constant and independent of the duty cycle, as the total resistance (R charge + R discharge, notice the diode) is constant and equal to 22Kohm (givin a frequency of about 1Khz, notice the hum). When the potentiomenter is all up, the Rcharge resistance is 1,0 Kohm (the diode prevents the capacitor to charge through the second potentiometer section and the other 1,0 Kohm resistor) , and Rdischarge is 21 Kohm, giving a 5% on duty cycle and a 1Khz frequency.... [read more]

Often, people attempt to control DC motors with a variable resistor or variable resistor connected to a transistor. While the latter approach works well, it generates heat and hence wastes power.... [read more]

his circuit is built from standard components and can easily be adapted to be controlled by a computer. If you use cheap surplus transistors and stepper motor, the price of the circuit can be kept to under $10.... [read more]