Hi.
I am trying to realize a LED Controller for a Dive Torch. I use 7 CREE XP-E2 LED's in Series, and I want to drive them with up to 1 A.
I designed a Circuit based on an example I found, trying to realize a Buck/Boost-Converter. Supply Voltage will be around 22V, LED Voltage should be at abround 23V.
I do not use an external Mosfet, because the 3952A should drive my 1A easyly (according to the datasheet).
I simulated the circuit in LTSpice and it works very well, giving 1A at the output no matter what the supply voltage is (between 8 and 22 V).
But the final build up circuit does not work, it seems it goes immediately to Shutdown Mode.
The only thing that looks not so nice to me is the waveform of the INTVCC-Pin. I bypassed it as suggested with a 2.2uF capacitor against GND, but the Voltage drops down below 1.86V each time the Switching starts (well at least it seems so to me). There is a 20ns peek down to 1.86, then it returns to 3V (see the attached Picture).
Any suggestion what the problem could be?
Thanks a lot,
regards
Hans
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