PWM LED Circuit LTspice Problems


Joined Nov 29, 2011
so the inductor is possibly the problem? I was hoping that the inductor was going to be an efficiency boost.

is there a reason FETS are preferred over BJTs in the 555 circuits?
The inductor is probably your problem. See the ringing in dannyf's simulation? This is due to the indutor. A well functioning PWM circuit will approach 100% efficiency, so how could adding an inductor boost efficiency?

FETs are preferred over BJTs because of lower "on" resistance.


Joined Oct 15, 2009
Meanwell LDD drivers = cheap/done and 0% (actually off) to 100% dimming via 5V PWM
Just in case you get tired of rolling your own and just want it done.. Those LDD's are the "best"

Thread Starter


Joined Feb 29, 2016
I found the Meanwell drivers you mentioned, those seem to be in need of the PWM signal still.
Great little module. I had been looking at the LM2596 boards on ebay that had voltage and output current adjust.
I was playing with PWM to an NPN transistor that would interupt the connection of the on/off pin(5) on the main chip. I figured if I could unsolder it and bend it up I could make it work.

I was reading something about pull up resistors and that is when I was unsure of drawing the pull up from the input or output.