This post is about PWM Dimmer Circuit for 12V DC Lamp which controls lamp brightness and saves energy.
Main part of this circuit is IC 555 timer chip which make PWM signal.
PWM signal change power to lamp by duty cycle.
IC 555 timer works like astable multivibrator at 2.8KHz which is the is the key part.
PWM dimmer is better than old way because there is no waste power and lamp is fast ON and OFF
Transistor TIP122 uses as Darlington driver for 12V lamp brightness.
Circuit Working:
Parts List:
| Component | Value/Type | Quantity |
|---|---|---|
| Resistors | 1k 1/4 watts | 3 |
| Potentiometer 50k | 1 | |
| Capacitors | Ceramic 0.01µF | 2 |
| Semiconductors | IC 555 | 1 |
| Transistor TIP122 | 1 | |
| Diode 1N4007 | 1 | |
| Load 12V/5W Incandescent lamp | 1 |
Circuit uses 555 timer as astable multivibrator.
It make PWM signal.
Duty cycle time ON and OFF can change with pot VR1.
Change duty cycle to control lamp brightness.
Q1 TIP122 transistor is used and Darlington type can handle 12V/5W lamp current.
PWM signal from pin 3 of 555 goes to TIP122 base through resistor R3.
This turn transistor ON and OFF.
555 timer always make pulse signal at pin 3 in astable mode.
Diode D1 help bypass lower part of VR1 when charging.
This make ON and OFF time control separate.
Adjust VR1 to fine tune lamp brightness by changing PWM duty cycle.
Formulas with Calculations:
Frequency Calculation (Astable Mode of 555 Timer):
Frequency f = 1.44 / ((RA + 2RB) * C)
RA = 1kΩ, RB = VR1 pot (0 to 50kΩ), C = 0.01µF
At RB = 0kΩ (min):
f max = 1.44 / (1kΩ * 0.01µF) = 144kHz
At RB = 50kΩ (max):
f min = 1.44 / ((1kΩ + 100kΩ) * 0.01µF) = 1.4kHz
Frequency change from 1.4kHz to 144kHz by VR1 pot.
Duty cycle D = ((RA + RB) / (RA + 2RB)) * 100%
At RB = 0kΩ (min):
D max = (1kΩ / 1kΩ) * 100% = 100%
At RB = 50kΩ (max):
D min = (51kΩ / 101kΩ) * 100% = 50.5%
So duty cycle change from 50.5% to 100%.
How to Build:
To build a PWM Dimmer Circuit for 12V DC Lamp following the below mentioned steps:
- Pin 1 of IC1 goes to GND
- Pin 2 of IC1 connect to pin 6 of IC1
- Pin 3 of IC1 connect to base of Q1 via R3
- Pin 4 and pin 8 of IC1 go to +12V supply
- Pin 5 of IC1 goes to GND through C2
- C1 connect between pins 6 & 2 of IC1 and GND
- R2 and VR1 pot connect between pins 6 and 7 of IC1
- R1 from pin 7 of IC1go to +12V supply
- D1 diode from pin 7 of IC1 go between R2 and VR1 pot
- Collector of Q1go to one end of 12V lamp
- Other end of lamp go to +12V supply
- Emitter of Q1 go to GND
Conclusion:
This PWM Dimmer Circuit for 12V DC Lamp uses PWM to change lamp bright.
It save power with no wastage.
555 timer make PWM signal we can adjust.
TIP122 transistor help make circuit easy and good.
It is good for dim LED, control motor speed and battery lights.
References:
PWM Automotive 12V Dimmer for instrument cluster, clima leds