Hi.

Is there anyway of regulating voltage, but without any headroom at all?
I.e. I want a regulator that gives out the same voltage as is going in to it, but regulates it... Or is that pointless? (I would know the voltage, I don't want it to change the voltage that it gives out, that would be very pointless).

Bassically, I want smoothing, and all the other benefits that regulators offer.

Thanks

Tim

 

No it is not very practical or possible.

Even LDR's (Low Dropout Regulators) require around 1 Volt Difference.

Alternately you could step up the voltage and than regulate it down again, but that would be more expensive.

Gary

 

Doesn't regulation imply that the output voltage is maintained at a fixed level even if the input voltage changes?

If the same voltage going in is coming out, then it would be pointless to put in any sophisticated regulation circuitry.

If you want to smooth out any spikes, would some capacitors and inductors be suitable for your needs?[/quote]

 

Look up buck-boost regulator. You will need a transformer to not invert the voltage, but it will give a constant output as the input goes higher or lower.

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You seem to have misunderstod slightly.

I don't want the output to change, depending on the input - that would be silly.

This is a hyperthetical question, which is why I was a bit ambiguous.

If I had a 24v supply (for example), but wanted to get rid of spikes etc, and to have regulated power, but wanted the output to be 24v also. Even if the input changed, I still want the output to be 24v.

Basically, I am looking for a regulating circuit that requires no headroom at all.

Yeah, caps and inductors would be suitable.

I will look up buck-boost, thanks Russlk

As I say, this is not a real situation, I just wondered if there was any common way of doing this.

 

As already suggested, you need some kind of switchmode PSU, in order to regulate you have to have more voltage available in order to drop it down.

A switchmode supply might not have a higher voltage anywhere in it, but it must have the 'capacity' to do so.

So, assume you have a 24V input, and your switchmode supply is outputing 24V using a 50% mark/space ratio. If the input voltage now falls to 20V, the mark/space ratio will have to increase in proportion to maintain the 24V output. As there is no regulator on the output, you don't have a higher voltage and drop it down, it's all down using feedback in the switchmode circuit.

A great deal depends what you are wanting to do, this sort of supply is likely to be far more complicated and expensive than a simple linear one. If you are designing from scratch, it's probably easier to design it to use a lower HT rail and use a linear regulator - but if that's not an option, a switchmode one would do the job, and be more efficient at it as well.

For any 'old TV engineers' out there, the old Ferguson 9000 TV set used a 'Cyclops' combined PSU/LOPT stage. This enabled the set to work on any mains input voltage from 90V to about 280V - which was an incredibly impressive range!.

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I never really understood switchmode power supplies, but I think I sort of get what they are all about now... Cheers Nigel.

It wasn't for a real situation, and the answer to my original question was basically no, so i'll drop the whole thing. It was a bit of a silly question anyway.

Thanks guys

Tim

 

Make it two stages...
First bust the voltage and then regulate it down to your needs but this
will be expencive and inefficient (probably less than 50%).
If all you need is 24VDC, just get industrial PSU, 24V is standard and
it's not too expencive.

 

How about a big electrolytic capacitor. After all it's job is to oppose any change in voltage. If the voltage tries to increase it will oppose it by charging, if the voltage tries to decrease it will oppose it by discharging.

Don't those folks with their high powered automobile amplifiers us big capacitors to stabilize the supply voltage to their amps on sound peaks?

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