How to start designing an AC to DC power supply?

AC to DC ?

Hi all

I want to design a AC to DC power,but I have no idea how to start,is there any related data or reference circuit ?
AC input : 85V ~ 250V
DC output : 4.5V ,1A

Thanks

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chmr

Re: AC to DC ?

For such a requirements you should use switching power supply but for a beginner it is not easy to make it. May be it would be easier to by 5V supply and modify it for 4.5V.

Re: AC to DC ?

Good starting point will be to analyse some examples.
This article contains some examples of switching power supplies:

http://www.merictech.com/Meric/datasheets/IPS10_Rev7_March03.pdf

Re: AC to DC ?

You need a transformer reducer 250V to 24V approx. a rectifyer, caps, LM7805 and a diode to reduce 5VDC to 4.4VDC X 1A. approx.

Re: AC to DC ?

Hi Ianp

I found a circuit,is it the same with you gave ?

Re: AC to DC ?

www.powerint.com

if you require only one converter you can bye a standard 5 Volt supply and put a schotky rectifier in series which will drop the voltage to 4.5 volt.

Re: AC to DC ?

Dear chmr,

You can use a simple AC-DC conversion circuit.
http://www.kpsec.freeuk.com/powersup.htm

You need the following:

1. A power transformer to step down 240Vac. You can easily purchase a transformer that can step down to as low as 12Vac. Most power transformers operate at 1A and higher.

2. A bridge rectifier to rectify a 12Vac to approximately 9Vrms.

3. An electrolytic capacitor (2000µF, 50Vdc) as reservoir and smoothing capacitor

4. An electrolytic capacitor (330µF, 25Vdc) as reservoir and smoothing capacitor

5. A Linear Voltage Regulator (LM294 or 7805) with 1A output current rating.


This simple chained AC-DC conversion gives 5Vdc and 1A. Since you need 4.5Vdc, there are a number of possible ways:

1. A simple voltage divider, such that the resistive ratio gives you 4.5Vdc

2. A simple zener voltage regulator at 4.5Vdc

3. You can modified (1) to an Linear Voltage Regulator by means of a Comparator using an Op-amp referenced to 4.5Vdc.

NB: Connect some 100nF or 0.1µF Ceramic capacitors as de-coupling capacitors in parallel to the Output Voltage and Ground, either close to the Voltage Regulator or the ICs.

Re: AC to DC ?

Thanks all

The circuit that I post was my boss give,but it can't work,the MOSFET is not switching.It seens there has some problems in the photo coupler circuit.

Can anyone tell me how to modify the circuit,but the only and most important is "cost".

Thanks a lot

----------------
chmr

Re: AC to DC ?

I have some doubts about the circuit that controls diode in optocoupler. In fact there is no protection on the bath Emiter/Base/Zener Diode and almost no current limit (except for 2Ω7) for the optocoupler diode.

My suggestion is that you have a look again at section on TL431 (application 2, Page 8 and 9) in: h**p://www.merictech.com/Meric/datasheets/IPS10_Rev7_March03.pdf