Confusion with "switching diodes"

Thread Starter

Max Kreeger

Joined Oct 1, 2013
95
I have the following circuit built from the 'choppy' pwm controller kit.
enter image description here
After testing it with an LED strip, I realized that the 1N4148 diodes were actually in reverse...after switching them around to the correct direction. Nothing changed visually with respect to circuit operation?

What is the purpose of these diodes and why did the incorrect polarity not affect the circuit?
 

k1ng 1337

Joined Sep 11, 2020
681
The diodes and VR1 allow duty cycle to be set. Reversing polarity of the diodes does not matter as both configurations are electrically equivalent if the pot is at the half way point. Set duty cycle to 75% then reverse the diodes. You should see a new duty cycle of 25%. That's a hint of what's happening.
 
Last edited:

MrChips

Joined Oct 2, 2009
27,113
Reversing D1 and D2 absolutely makes no difference, except for the position of VR1 (clockwise vs counter-clockwise rotation).
All you are doing is swapping D1 and D2.
 
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