Is there anyway this circuit could be improved?

[chesschaser]

Hi guys!
I'm learning electronics and have challenged myself to design a PWM dimmer circuit for a halogen bulb. I have build the circuit below and it works but I always want to learn from these so is there any way this could be improved?

 

[Bluejets]

What is lamp wattage??

 

[Harald Kapp]

Every circuit can be improved.
Always.
It mostly depends on your definition of "improved":

• less parts
• less cost
• less power dissipation
• less PCB real estate
• higher reliability
• better accuracy
• ...

What is it you want to improve?

 

[chesschaser]

What is lamp wattage??

20W

 

[chesschaser]

Every circuit can be improved.
Always.
It mostly depends on your definition of "improved":

• less parts
• less cost
• less power dissipation
• less PCB real estate
• higher reliability
• better accuracy
• ...

What is it you want to improve?

The bulb whines at lower duty cycles. Is there any way this can be prevented?

 

[Harald Kapp]

Increase the frequency of the PWM above the audible range to e.g. 30 kHz.

 

[chesschaser]

ok. what is the maximum switching frequency of the tip31c though?

 

[Harald Kapp]

The datasheet states a min. current gain bandwidth product of 3 @ 1 MHz. So 30 kHz should be a no brainer.

 

[chesschaser]

The datasheet states a min. current gain bandwidth product of 3 @ 1 MHz. So 30 kHz should be a no brainer.

i measured the output and when i adjust the r2 potentiometer the frequency changes alongside the duty cycle. how can i prevent this?

 

[Harald Kapp]

Look up "555 fixed frequency pwm" using the search engine of your choice.

 

[chesschaser]

Look up "555 fixed frequency pwm" using the search engine of your choice.

Thank you!

 

[bertus]

Hello,

You could also try the following circuit:

PWM generator using IC-555

A simple PWM (Pulse Width Modulation) Generator by using IC-555. The basic theury is f = .693*R1*C1. C1 capacitor Charging through D1 diode and Discharge through D2 diode. But both case in every fu…

sujjad.wordpress.com

Make C1 1 nF for higher pwm frequency.

Bertus

 

[Alec_t]

The configuration shown in post #1 only allows duty cycle adjustment between about 17% and 50%. Is that ok for your needs? If not, the post #12 configuration would be better as it allows almost 0% to 100% duty cycle variation.
Why does a change in frequency with duty cycle matter to you in this application?