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crissty 23rd August 2005 07:46 AM

Regulated power supply
 
I have made and tested chip amp from 3886 by National Semi, and tested it with 20V-0-20V 100Va transformer.

Actually now i got a transformer rated @35V-0-35V rail, but after bridge i get 50V DC rails.

How can i use a regulator for getting 35v. I dont wanna go in for linear regulator design as it will have quite high losses & heat dissipation.

I need a schematic design of SMPS, using 3525/3524 and mosfets, to get regulated +-35V 4-5Amps

mateo88 23rd August 2005 09:10 PM

An lm338 or lt1084 are surprisingly efficient and don't require a big heatsink, either. I would reccomend giving one of those a shot, since the circuit will be very simple and very cheap (and very good, too!).

h_andree 23rd August 2005 09:19 PM

I think the LM338 can get hot. I have them
regulating 38V down to 29V. I've attached
them to a 2" heatsink. You can touch the
heatsink but not too long.

Harry

carlmart 23rd August 2005 10:18 PM

Quote:

Originally posted by h_andree
I think the LM338 can get hot. I have them
regulating 38V down to 29V. I've attached
them to a 2" heatsink. You can touch the
heatsink but not too long.

If you can't keep your hand on the heatsink then you need more heatsink or a fan.

A hand's touch is usually a good judge when a part is being stressed by heat.

If you don't pay attention to that, the part may have quite a short life.


Carlos

mateo88 24th August 2005 02:08 AM

Hmmm, that's odd. My lm338's don't get hot at all, and really are barely even warm on 1.5" x 1/4" pieces of aluminum. They're regulating 35v to 26v.

peranders 24th August 2005 04:57 AM

Quote:

Originally posted by mateo88
An lm338 or lt1084 are surprisingly efficient and don't require a big heatsink, either. I would reccomend giving one of those a shot, since the circuit will be very simple and very cheap (and very good, too!).
This type of regulator is UNEFFECIENT by nature and can go down to almost 0% effeciency. How much heat you must burn away has to do with the load and how much voltage drop you have.

crissty 24th August 2005 02:17 PM

Please..... I need schem for SMPS type.

jan.didden 24th August 2005 03:14 PM

Quote:

Originally posted by carlmart


If you can't keep your hand on the heatsink then you need more heatsink or a fan.

A hand's touch is usually a good judge when a part is being stressed by heat.

If you don't pay attention to that, the part may have quite a short life.


Carlos


Calos,

I you can touch it but not hold it, it is probably close to 50 degrees Celcius. Nothing to worry about!

Jan Didden

jan.didden 24th August 2005 03:16 PM

Quote:

Originally posted by peranders

This type of regulator is UNEFFECIENT by nature and can go down to almost 0% effeciency. How much heat you must burn away has to do with the load and how much voltage drop you have.


Corretc. The dissipation in Watts depends on the product of voltage the regulator has to drop times the current it is passing. Different implementations have different dissipation requirements. One man's cool chip can become another man's burning hell ;)

Jan Didden

carlmart 24th August 2005 06:46 PM

Quote:

Originally posted by janneman

I you can touch it but not hold it, it is probably close to 50 degrees Celcius. Nothing to worry about!


You are certainly right. I am probably exaggerating in my heat concern on electronic parts.

Some say a bit of temperature is good for the sound.

Bottom line: it's important to see if the heatsink metal close to the part is about the same temperature as the part itself, to see if the heat transfer is being properly done.


Carlos


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