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My first LED driver - minimum PWM with 555?
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alcs2000au:
Hi guys

I am currently designing my first LED driver around the TPS61165 for the Bridgelux Gen 7 V10 LEDs. I would appreciate a quick check on the circuit and some guidance on how to calculate RT1, RT2 in the third image below, to get the minimum 25% duty cycle (so I get minimum 100ma supplied to the LED). I wanted to use a 555 for the PWM signal because that way the PWM generating part could also be replaced by a microcontroller if needed.

Thanks









madires:
Let's start with the LED driver. It won't work that way. ;) COMP should go to C4, FB to R1 and SW to L1. The PWM duty cycle is determined by the trimmer, i.e. the resistance ratio between charge and discharge. If you want a minimum duty cycle you would have to add an additional resistor to the charge path. For a minimum duty cycle of 25% that resistor should be 25% of the trimmer.
alcs2000au:
Thanks :-) I must have played around with the other use cases too much. How about like this?



Cheers
madires:
The next step is to test your circuit. ;)
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