Simple PWM Dimmer Circuit for 12V DC Lamp

A simple PWM dimmer circuit for a 12V DC lamp is a great way to control how bright the lamp is while saving energy.

The main part of this circuit is the IC 555 timer, which is a popular chip used to create a PWM signal.

This signal changes how much power goes to the lamp by adjusting the duty cycle.

The 555 timer is set up as an astable multivibrator working at a frequency of 2.8KHz and it is the key component in this design.

Unlike old fashioned dimming methods that waste power, PWM dimming makes things more efficient by quickly turning the lamp on and off.

Also, transistor TIP122 is used to build a Darlington driver stage that is perfect for the 12V lamp brightness.

Circuit Working:

Parts List:

The circuit here is cleverly built around a 555 timer chip set up to work as an astable multivibrator.

This means it creates a pulse width modulation PWM signal.

The duty cycle of this signal, which is how long it stays ON compared to how long it stays OFF can be adjusted using a potentiometer called VR1.

By changing this you can control how long the signal stays ON and OFF.

The circuit also includes a Q1 TIP122 transistor which is a type of Darlington power transistor that can handle the current needed to run a 12V/5W lamp.

The PWM signal comes out from pin 3 of the timer and goes to the base of the TIP122 through a resistor R3.

This setup helps the transistor switch on and off.

When you change the duty cycle of the PWM signal the brightness of the lamp changes too giving you control over how bright it is.

For generating the PWM the IC 555 timer is set up in astable mode which means it continuously produces a pulse waveform at pin 3.

The duty cycle of this waveform is adjusted by the potentiometer VR1.

The diode D1 that helps by bypassing the lower part of VR1 when the astable multivibrator is charging.

This setup ensures that the charging and discharging paths are separate allowing you to control the ON and OFF times independently.

In the end you can fine tune the lamps brightness by adjusting VR1 pot which changes the PWM duty cycle.

Formulas with Calculations:

Frequency Calculation (Astable Mode of 555 Timer):

The frequency (f) of the PWM signal generated by the 555 timer is determined using the formula:

f = 1.44 / ((RA + 2RB) * C)

where,

RA is R1 is 1kΩ

RB is VR1 pot 0kΩ to 50kΩ)

C is C1 is 0.01µF

For minimum RB (0kΩ):

f_max = 1.44 / ((1kΩ + 2(0kΩ)) * 0.01µF)

= 1.44 / (1kΩ * 0.01µF)

= 1.44 / 0.00001 = 144kHz

For maximum RB (50kΩ):

f_min = 1.44 / ((1kΩ + 2(50kΩ)) * 0.01µF)

= 1.44 / (1kΩ + 100kΩ) * 0.01µF

= 1.44 / (101kΩ * 0.01µF)

= 1.44 / 0.00101 = 1.4kHz

Thus, the frequency varies from 1.4kHz to 144kHz based on the setting of the potentiometer.

Duty Cycle Calculation:

The duty cycle (D) of the PWM waveform is given by:

D = ((RA + RB) / (RA + 2RB)) * 100%

For minimum RB (0kΩ):

D_max = ((1kΩ + 0kΩ) / (1kΩ + 2(0kΩ))) * 100%

= (1kΩ / 1kΩ) * 100% = 100%

For maximum RB (50kΩ):

D_min = ((1kΩ + 50kΩ) / (1kΩ + 2(50kΩ))) * 100%

= (51kΩ / 101kΩ) * 100% = 50.5%

Thus, the duty cycle varies from 50.5% to 100%

How to Build:

To build a Simple PWM Dimmer Circuit for 12V DC Lamp following the below mentioned steps:

• Gather all the components mentioned in the above circuit diagram
• Connect pin 1 of IC1 555 to GND of the circuit.
• Connect pin 2 of IC1 to pin 6 of IC1.
• Connect pin 3 of IC1 to base of transistor Q1 through resistor R3
• Connect pin 4 and pin 8 of IC1 to positive supply terminal of 12V DC
• Connect pin 5 of IC1 to GND through capacitor C2.
• Connect capacitor C1 from pin 6 and pin 2 of IC1 to GND.
• Connect resistor R2 and potentiometer VR1 between pin 6 and 7 of IC1.
• Connect resistor R1 from pin 7 of IC1 and positive supply
• Connect diode D1 from pin 7 of IC1 and between resistor R2 and VR1 pot.
• Connect the collector of transistor Q1 to one end of 12V incandescent lamp and other end of lamp connect to positive supply
• Connect the emitter of transistor Q1 to GND of the circuit.

Conclusion:

This Simple PWM Dimmer Circuit for 12V DC Lamp uses PWM technology to control how bright a 12V DC lamp shines and it does this without wasting too much power.

The 555 timer creates a PWM signal that you can adjust and by using TIP122 transistor the whole setup is easier and works better.

This makes it perfect for dimming LEDs, controlling motor speeds and for lights that run on batteries.

References:

PWM Automotive 12V Dimmer for instrument cluster, clima leds