555 as a Buck Converter

288

03:21:52

discharge pin abuse

published 8 years ago

WTFCircuit

8 years ago

Interesting concept

nikisalli

8 years ago

Nice

hurz

8 years ago

Im concerned about the high voltage at pin7. Its an open collector, but if there are ESD protecting diodes inside to Vcc and GND they will clamp any voltage outside 555 supply. Anyway 555 as BJT is probably only till 30V specified. Im afraid you have to spend an extra transistor with Uce > 50V

hurz

8 years ago

Meanwhile i checked a TI sample NE555 and measured for an ESD protecting diode at pin7 and its not there! Specification does says nothing at all. But still the risc of to high Uce, cause all inputs are max at Vcc specified. 18V

faceblast

8 years ago

yeah needs either a drive circuit or just a fat P MOS switch

hurz

8 years ago

Or optocoupler, or let 555 ride on the gate voltage, but with a similar problem to still have the high voltage diff from output to 555. But this might be more relaxed then having a overvoltage open collector unspecified.

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