Polarity protection question/idea

[cockaroacha]

Have a quick question for polarity protection. I haven't completely thought it out, but has anyone tried using a bridge rectifier -> 100uF Ecap to ground -> 78L09 regulator? With a 9v input from battery or wallwart, ou'd probably get somewhere around 11VDC out of the rectifier, which the 78L09 would bring down to a steady 9v, even when the battery ran down some. Plus, with a bridge, you can input DC with either polarity & you always get the same correct polarity at the output of the bridge. Lots of internal power supplies used in telecom equipment use bridge rectifiers on DC inputs so that one can input either +24VDC or -48VDC, without concern for polarity on the input.

Like I said, I haven't completely thought it out in the context of stompboxes (current draw & minimum voltage input for the 78L09 for example), but I haven't seen it mentioned before, & it seems that it would solve at least SOME of the problems of the other polarity protection schemes. Just not sure that it won't introduce different problems.

[MartyMart]

Depends on your approach and PSU I guess ... I ALWAY"S stick a 1N4001/2 reversed from 9v to ground
along with 100uf 16v cap and 0.1uf poly/ceramic.
Even on the smallest/simplest builds.
works for me ! and only introduces three parts ...

MM.

[cd]

With 9VDC input you'd get less than 9VDC from the bridge rectifier, depending on the voltage drop of the diodes in the bridge.

Read geofex.com for more than two easily implemented and completely reliable methods of polarity protection.

[mac]

I am trying a different way. I use a 220V to 12 - 18V DC unregulated to feed all my diy boxes. Into the pedal I put a 1N4xxx in series and before the 78L09, and the usual filter caps.
The only pedal that does not like much this is the FF, of course. That is because the regulation and the diode have different resistance than a carbon battery.

mac