pulse width modulator pulses getting squashed

Thread Starter

PCL

Joined Jun 12, 2012
2
i am using a PWM circuit that uses a SG3525 PWM/Controller chip capable of sinking and sourcing 400ma; have tried using both a BUK9535-55 and IRF1404 hi-current MOSFETs (just 1, not 2 in parallel?) to control the intensity of no less than 325 LEDs (rated at 3.2vdc, 25-30ma each). A 12vdc, 6A switching power supply is in the drain ckt of the MOSFET.
When this setup is used to drive 5 LEDs in parallel it works ideally; when it is used to drive 325 LEDs in parallel, it squashes the output pulse train such that approx. 2vdc (and not 12vdc) is the max peak output voltage.
I am very confused as to what the solution is other than the need seemingly to somehow "buffer," perhaps the load from the ckt.
any suggestions would be GREATLY appreciated. MANY THANKS for your attention to this query.
 

#12

Joined Nov 30, 2010
18,210
Not without a drawing of what you have built.
use, Go advanced, manage attachments, post a drawing in .png format.
 

Thread Starter

PCL

Joined Jun 12, 2012
2
Hi #12
thank you. this is my first post and i think your recommendation is a very good one!
i will post a drawing asap.
 

#12

Joined Nov 30, 2010
18,210
Good. A drawing eliminates the possibility of dozens of errors that we would have never imagined with only a word description.
 
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