How to design power supplies? help!

[Tomby]

I would like to design my own power supply to power some of my designs but am not sure where to start. Can anyone please tell me where is a good place to start designing efficient power supplies for DC? I would like to design an efficient stable DC power supply that has an AC input voltage. Thanks in advance!!

 

[WA]

I don't know if you have 50 or 60 cycles per second outlet from wall and voltage (110 or 220).

I'll guess 110/60hz

1. what voltage do you need?

you need to know what output you want (5 volts) for example.

2. you will need a step-down transformer to around 6-7 volts.

3. you'll need a rectifier circuit (most commonly sold in electronics parts store).

4. finally you'll need a regulator circuit. For 5v I believe the part number is a 7805. Again these are common in electronics parts store.

5. Most electronics books will show how a power supply is built.

I've started this conversation and I know there will be many other members who might even have a schematic to help there, along with other helpfull tips.

Hope this helps somewhat.
WA

 

[penrico]

Remember, power of transformer must be the double of power in DC in your circuit.

Power Of Transformer = 2 * Icc * (Vsecundary-1.4)*1.4142

If current in DC is low (up to 300mA), you can use a full wave rectifier with middle point transformer. But in upper currents, is better to use a bridge rectifier.

DC voltage for a bridge rectifier is:

(Secundary voltage - 1.4) * 1.4142

For a 78xx regulator, this DC voltage is advisable to be 2v over output voltage of your source. For example, if you need 5V DC at output, secundary voltage of your transformer, must be over 7V or more.

 

[tom_hanks]

let me know your proper requirement.
like this...

1. what output voltage ?
2. maximum current consumption of load?
3. any power sequencing for output voltage?
4. normal fluctution on input side?
5. required output voltage stablilty(tolerance)?
6. input voltage?
7. do u need short circuit protection?

i can help you..

 

[dung]

Buy a switching power supply of PC . The schematic you can search in elektroda, you can modify to have any voltage between 3V - 24V

 

[Tomby]

Thanks for the quick reply guys

I am looking to build an efficient power supply from scratch with specs:
20Watts or 40 Watts power
100-120V input AC voltage
roughly 10% input voltage fluctuation
5-10% output DC voltage stability
12V or 24V output voltage
with built in short cct protection

Is it possible to acheive efficiency of 90% or higher with this?

In response to tom_hanks, unfortunately I am not quite sure as to what you mean by power sequencing, please explain a bit more. Thanks!