REALLY NEED HELP DESIGNING AC/DC POWER SUPPLY CIRCUIT FOR PCB 1

[bob8907]

Here is the deal. We have a couple custom circuits that we are designing that use no more than 1A at 5V. Power supplies to run our circuits will vary so we want to make something that will accept say 10-100V AC or DC. Usually we might do a bridge and a reg but regs rarely deal with this much fluctuation.

I have seen this type of supply on several modern components and not sure how it is done. There is a small LCD monitor that accepts 10-400V !! With what we are doing now, ours will blow up at 32V. We really need to handle fairly dirty AC well and power a PIC without problems.

Looking for a diagram or maybe even a contact if someone wishes to chat.

Thanks

 

[IRstuff]

You need to talk to a power supply designer. This is not something that can be immediately comprehended from a random schematic.

TTFN

FAQ731-376

 

[bob8907]

I was hoping to find a PS designer here

 

[VEBill]

United States Patent 5126652 is close. At the very least it might give you some ideas.

 

[itsmoked]

There are so many ways to skin this cat.. But they each drop out of the running on small details. You will have lots of issues with the 100V though.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jimkirk]

Do you need something that can handle fast order of magnitude fluctuations in voltage, or something that can plug into a 10 volt supply one time and a 100 volt supply another time?

One way to do this would use the following blocks:

First, a rectifier/filter cap to convert everything to DC. Easily done over a 10 volt to 100 volt range.

Then using high voltage components, build a comparator circuit to switch the input DC voltage to a pre-regulator if it is above some voltage, say 25 volts. This doesn't have to be terribly accurate.

The pre-regulator would be a DC/DC converter that converts 25 to 100 volts input down to 20 volts, which would be applied to power your 5 volt/1 amp regulator. A custom design using high voltage components is probably what you'll need. Again, the accuracy & regulation doesn't have to be terribly accurate.

If the input DC voltage is less than 25 volts, the comparator/switch circuit would apply it directly to the 5 volt regulator.

You should build in some hysteresis to the comparator so it's not switching back and forth in the input voltage is neat the threshold.

Depending on how you realize this, this might be able to handle full range fluctuations, but that would require some modeling, breadboarding and testing.

 

[xfmrman]

Look for switching power supply designs they can easily handle this type of input variation.

 

[MacGyverS2000]

Aren't we all...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[xfmrman]

I haven't done this in a while but look at Top Switch integrated circuits they are basically a switching supply on a chip.

 

[DHambley]

Bob8907,
I've created circuits similar to what you need, "something that will accept say 10-100V AC or DC". One was a PFC converter (what's used often for AC) which, when given a DC signal, works as a boost-mode converter with no changes; same inputs, no AC/DC switch, no re-wiring for AC vs. DC. 1A at 5V = 5W; That means you'd have about 7W or so input. You'd still have to satisfy EISA and FCC and maybe E star if it's commercial.

 

[docellen]

This sounds similar to a supply I once designed for a portable scope that was to operate without a battery, using anything from 10V to 220V, AC or DC. Start with a bridge rectifier to convert the input to DC. Connect a 1:1 transformer, primary terminal 1 to the positive from the rectifier, terminal 2 to the collector of a 1000-volt NPN, emitter to rectifier negative (and ground). Now when you apply pulses to the base of the NPN, the current through the primary of the transformer will ramp up, then cut off abruptly. This will produce a kick at the secondary that can be rectified and stored on a capacitor. The pulse generator senses the voltage on the output capacitor, and turns off the pulses when the output is at the desired voltage.

Some extra tips, depending on how reliable this needs to be:
1) There will be positive spikes on the collector, due to leakage inductance of the primary. If the NPN can't handle these, bridge the collector to emitter with an energy-absorbing surge protector.
2) Watch out for saturation of the transformer core. You might want to sense the peak current with a small resistor from the NPN emmitter to ground. If the peak exceeds what the transformer can handle, cut off the pulse.
3) The output will have a lot of ripple and noise. You may want to follow that with a standard DC regulator.