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Power supply design problem

Hi,

This is my first question in this groups. Because my mother tongue is not english, I'm afraid whether my question will be well expressed or not.

The question is as follows. My major interest is mechanics. But since I have so much interest in electronics, I've been studying electronics by myself.(It's really exciting for me, fortunately.) Recently, I've been making a power amplifier for ultrasound applications. Using power op-amp the main amp parts are almost finished. But I want to make my power amp as compact as possible. The problem is a power supply system. I'm using the commercial power supply system which can be used for very wide range of applications. I want to make this power system of my own. Is it sufficient to use a power supply circuit which is consist of transformer, bridge diode, and some filtering components as capacitor and inductor? Since the required output voltage is about 80V or more, semiconductor based chip such as 7805 or LM317 is impossible. The power amp will generate pulse signals of some hundred kHz and the required current will be 1~3A.

Can you recommend any source circuit or textbook or internet site? Please help me.

Reply to
Gundal21
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Do you need this supply to be regulated? How much ripple can you stand?

The basic transformer and rectifier power supply works quite well if you remember the following general rules:

(1) The transformer should have at least 1.5 times as many VA rating as the average load is in Watts.

(2) The filter capacitors should be just a little bigger than needed to make the ripple value you need. For your ripple calculation just assume that the capacitor is discharged by a constant load current. This leads you to use a bit too big of capacitor.

(3) Assume the worst case current that the power switch turned on at the peak of the input with the capacitors discharged. You need to limit this surge to what the rectifiers can stand.

(4) Small value lossy inductors or resistances should appear in nearly all paths to and from the rectifiers. Even just the wiring may count as many of these. As the rectifiers turn off they make an abrupt change in current. You want to keep this from getting out of the section. A small capacitor or two at the recifiers also helps.

Reply to
MooseFET

Your writing has a bit of an accent, but it is quite clear.

Depending on the amount of regulation you need you can just use a filter capacitor, or a filter capacitor and an inductor. You can also build a high-level linear regulation circuit based on an LM723 if you're careful about how you go about it. If you _really_ want to go overboard you could build an off-line switching regulator, but that would be much more involved than the rest of the project, combined.

If you can get surplus parts where you are, consider using a pair of 48V switching supplies. They're often isolated so you can connect their outputs in series for 96V (I'd verify isolation first, though).

Be careful -- you're definitely getting into voltages that'll hurt if you come into contact with them, and could be fatal on a bad day. You may want to google around for safety rules & see if you can find them.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
Reply to
Tim Wescott

Reply to
wingnutzac

Is that peak or average current. Average current would make it a 100-250 Watt supply, in which case you don't want to build. If it's peak, how about giving us a worst case average, anything under 25W is accessible to the hobbyist.

Reply to
Fred Bloggs

80V or more and 1 to 3 amps.. Top power ~240Watts...that's gonna be a beefy transformer. (Or a small one that gets very hot and doesn't last long. :P )

You missed out on a nice supply on E*bay Item 230223284480 A Kenwood PD110-5D 0 to 110VDC 0 to 5A. Digital display of current and voltage. Adjustable V and I Winning bid was $57.99! + shipping Say $100.00... Certainly not worth making a supply when you can get one for $100.00.

D from BC British Columbia Canada.

Reply to
D from BC

Regarding safety, go for ECMA 287 from ecma international. It is almost similar to IEC 950, but free. Regarding a non regulated rectified supply. Note that the no load rectified voltage can be about

30% above the full load voltage. Also, you cannot fully load the transformer. When you have, for example, a transformer that can deliver 10A ac, you can load it with about 6.6A DC when using a full wave rectifier with storage capacitors. also take into account mains supply variations. when you require at least about 80V (regulated) output voltage, your no load rectified voltage will be in the 120V range. This aren't SELV levels.

When you want to make a compact regulated power supply that is able to deliver the required load for a long time, you may consider a switched regulator (as Tim suggested). This type of regulators require reasonable experience.

If it is a commercial project, you may consider contracting somebody that is into MOSFET class D, E amplifiers (as sine wave output is required). They have a high efficiency (over 85%) and therefore do not need much cooling provisions.

Best regards,

Wim PA3DJS

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(Dutch)

Reply to
Wimpie

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