Hi,
I have to make a dimmer with 25% - 50% - 75% duty cycle but without potentiometer , only 3 resistor or something that connected to selection key .

It is possible?

 

hi arvin,
It is possible.
Please post your basic circuit so that we can suggest values.
E

 

https://cdn.sparkfun.com/assets/7/d/0/2/4/52433239757b7fb7798b4567.png

 

The circuit can't be 0 to 100%, it just closing, because the R2 will limits the values of charge time.

The R2 should be labels as R1 and the R1 should be labels as VR1.

 

The circuit can't be 0 to 100%, it just closing, because the R2 will limits the values of charge time.

The R2 should be labels as R1 and the R1 should be labels as VR1.

yes you right, it is 1% to 99%.

 

hi,
The frame rate period is 4mSec, is that what you are expecting.?
E

 

hi,
The frame rate period is 4mSec, is that what you are expecting.?
E

yes even bigger , it has to drive a mosfet which connected to a heater.

 

hi,
Look at this option.
Assumed a linear relationship with timing.
E
W is the switch Wiper

 

hi,
Look at this option.
Assumed a linear relationship with timing.
E
W is the switch Wiper

View attachment 167861

Wowwww! thanks it works!

 

Wowwww! thanks it works!

Thanks for the feedback.

The Invoice is in the post.

 

Thanks for the feedback.

The Invoice is in the post.

Hopefully just crediting your circuit when they turn in their assignment will be sufficient.

 

To eliminate the relatively high current through R1 and the discharge pin, disconnect the wire between R1/D1 and DIS, and connect a wire between R1/D1 and OUT.

ak

 

How can I modify this circuit to have 100% duty cycle, now i have 99.6%.

 

Use a relay to bypass the entire circuit... Did you read post #4? And your reply in post #5?

 

To eliminate the relatively high current through R1 and the discharge pin, disconnect the wire between R1/D1 and DIS, and connect a wire between R1/D1 and OUT.

ak

I checked it but not a good different still i have 99%

 

Use a relay to bypass the entire circuit... Did you read post #4? And your reply in post #5?

Yes, I have read it. but I don't get your idea.

 

For any periodic waveform, there is no such thing as a 100% duty cycle. A 100% duty cycle square wave is DC; the output is spending 100% of the time in one state and 0% of the time in the other state.

Why do you think you need a 100% duty cycle output? What is it you are trying to achieve?

ak

 

Below is an LM339 PWM circuit with LTspice simulation that can go from 0% (full off) to 100% (full on) duty cycle.

 

See 25% 75% 100%