Thursday, August 7, 2014

Easy PWM driver

A friend wanted to highlight the model, purchased specifically for this purpose LED strip and power supply.
It turned out that all the lights bright too much, and he need a system limiting the intensity of illumination. The natural course of things was to create a simple PWM controller.
The system was built on a piece of universal PCB without any schematic (the one below was developed after the completion of the work) in about 2 hours. The main part of the driver is immortal cube 555 Potentiometer R2 is responsible for adjusting the duty cycle of the output. 555 works in the astable mode, alternately charging and discharging the capacitor C1. Charging is done via resistor R1 diode D1 and potentiometer R2 between terminals 3 and 2. Capacitor discharges through the diode D2 and the resistance of the potentiometer R2 between terminals 1 and 2. This action results in a square-wave signal at the output of the system of filling depends on the setting of the potentiometer . In practice it turned out that adjustment is possible in the range of about 8-100%. I can change the way of charging capacitor C1, but it much easier to make an additional negation using the transistor Q1. Transistors Q2 and Q3 form a totem pole system . This allows to quickly reload the gate capacitance of the MOSFET Q4, and thus reduces the power losses in the transistor. Resistor R6 prevents excessive currents during switching. The capacitor C3 reduces the ripple in the keying system. In this case elements values ​​are not critical.

The effect is satisfactory, the potentiometer can be continuously adjusted intensity from zero to almost maximum.
The darkest:

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