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Simple PWM Controller Based On IC 555

05/13/2009 Category: Control

If you need simple PWM controller? May be this IC 555 based PWM could be your choice. This controller is aimed at speed control of small motors or for dimming low-voltage lighting. It will control the output from about 5% up to at least 95% of full power. The Main project part is popular 555 chip, and common NPN bipolar or N-channel MOSFET as the switching transistor.


How it works
When the 555 output is high (+12v), capacitor C1 is charged by current flow through D2, the bottom section of VR1 and R1; at the same time, transistor Q1 is switched on, and with it, power to the load. When the voltage across C1 reaches 8v (2/3 of the supply voltage), the 555 switches and the output goes low, turning off the transistor and power to the load. C1 now discharges by way of R1, the top section of VR1 and D1. When C1 has discharged to a 4v level (1/3 the supply voltage), the 555 switches over again and the cycle repeats.


With VR1 turned right down, the resistance in the charging circuit is only R1 (1k); resistance in the discharge circuit is VR1 + R1 (101k). Charging time (load On) is at a minimum, discharge time (load Off) is around 100x longer, giving a very low duty cycle. As the potentiometer is turned up, the charge (On) time increases, discharge (Off) time decreases, so the PWM duty cycle increases until the On time is around 100x the Off time for the maximum duty cycle.

PWM Controller
Simple 555 Pulse Modulation Controller