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Low dropout switching regulator

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Hero999

Banned
Here's an idea I had for a switching regulator when I was bored.

This one doesn't boast excellent efficiency (LTSPICE says about 80% @150mA, with 9V in and 85% with 6V in) but it has a drop out voltage of 0.7V.

This is idea for powering 5V circuits with reasonable power drain (about 150mA) from a 9V battery or 3.3V circuits from four AA cells.
 

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Sceadwian

Banned
If you're worried about voltage drop out have you ever thought of making a Sepic converter, they'll even step up once the voltage goes under the output setpoint.
 
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Hero999

Banned
Yes, I've heard of those but try building one without a specialised IC.

Another option is to use a transformer rather than an inductor.

Like lots of the circuits I think of, I'll probably never use it. I thought this one was more useful than half the crap my brain generates so I thought I'd post it in case someone else finds it useful.
 

Sceadwian

Banned
Wikipedia has a circuit for a basic sepic converter, doesn't look too bad.
 

mneary

New Member
A typical switching regulator has a separate oscillator from the control loop because that design is too sensitive to the characteristics of the output capacitor.

Put a microhenry of ESL into the 100uF capacitor and you'll see what I mean.
 

Hero999

Banned
Just tried that, it still works but there's much more ripple on the output, still I doubt you'll get that much ELS on a 100:mu:F capacitor, I would say 200nH is more reasonable.

It's a typical hysteric converter so yes it can be unstable
 

mneary

New Member
I was looking at the collector of the switching transistor and was concerned that the switching frequency went from 30 kHz to 50 MHz. Was wondering if this is real and how my ham neighbor on 6 meters would feel about it. I guess it would have to be really well shielded.
 
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