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PICList Thread
'[EE] Cheap power supply'
2008\01\30@192718 by Listas de Correo

 I'm trying to find a solution for a power supply. It will supply power to
an appliance, so it should be as inexpensive as possible. It will also have
to be as small as possible since the design department says I have no more
room to play with :)

 The requirements are:

Vout1: 100Vdc 3A continuous and 10A peak (<5sec) to drive a DC motor

Vout2: 12~15V 15mA continuous to drive some mosfets

Vout3: 5V 15mA for a PIC

Ideally, it will be for 100~240 Vac input voltage, preferably but not
mandatory with automatic voltage selection.

A transformer is not viable, since there is no room for it.

The current design is very bad (not mine :P). It consists of a high power
series resistor that feeds a rectifier. The output of the rectifier has a
high ripple DC and then there are two zenners, the first one 15V and the
second 5V. It works (kind of) but I wish to:

a) reduce the ripple to 10% aprox (at Vout1)
b) improve the design to eliminate the resistor.



2008\01\30@234955 by Apptech

{Quote hidden}

You MUST say what sort of voolume you have available.

Who says that there is no room for a transformer.

The LV supplies require about 300 mW of power - extremely

Is the HV supply acceptable as is?

Why not use an eg TO92 sized or surface mount voltage


2008\01\31@071153 by Mauricio Jancic

The volume is high, aprox. 30K units/month.
The application is a hairdryer, and space is critical. They can't even put a
35x45 capacitor we were considering.

The LV supply is relatively easy to solve. The problem is the HV supply with
the high current requirements and the required ripple. What I'm trying to
avoid somehow is the large capacitor.


> {Original Message removed}

2008\01\31@075143 by Jake Anderson

If you can't put one large cap in then perhaps a bunch of smaller ones?

Look at inductors for your power storage, they seem to be "denser" in
terms of joules per cubic centimeter (and heavier, but thats not your
problem :->)

Given the racket a typical hair dryer makes i doubt a 50/60hz hum would
be noticed in a DC motor drive.

Mauricio Jancic wrote:
{Quote hidden}

>> {Original Message removed}

2008\01\31@080505 by Apptech

> The LV supply is relatively easy to solve. The problem is
> the HV supply with
> the high current requirements and the required ripple.
> What I'm trying to
> avoid somehow is the large capacitor.

You are liable to run into regulatory issues with power
factor and more. Why do you WANT to reduce the ripple? What
is it doing that is bad (eg motor hum or vibration or ...?)

Ideally you need to give us as complete as a description as
possible (and possibly some money from the 360,000 pa sales
:-) ) for us to be useful.

A "preregulator" would probably help -  either a Triac or
SCR or a FET in a bridge. The latter is very controllable.
Power factor wise "lumpy DC" at 2 x mains frequency may be
best. What does this do to your motor?

More details may lead to better solutions. And may not :-)


2008\01\31@090526 by Mauricio Jancic

I'm trying to start working with this customer and want to solve some of
their problems. The reduced ripple is to avoid motor hum.

I'm not familiar with your suggestion on using the FETs, do you have a
source I can look up?

I think I don't have much more details. The basic idea is to have the ps
with the mentioned ripple to avoid motor hum (which the user can hear).
That's the main thing. All of the above must be done considering the space


> {Original Message removed}

2008\01\31@145500 by Dwayne Reid

Hi there.

I *really* think that you need to talk to your motor supplier and manufacturer.

I suspect that the motor will run just fine from a bridge rectifier
between it and the AC line.  No filter cap needed.  If the motor is a
series-wound design (with field windings instead of permanent
magnets), you might not even need the bridge rectifier.

The rest of the circuit can use a capacitive power supply or one of
ST's VIP series off-line power supplies.

Why so much current for the PIC?


At 05:27 PM 1/30/2008, Listas de Correo wrote:
{Quote hidden}

Dwayne Reid   <>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
Custom Electronics Design and Manufacturing

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