How to get 3 power supply ?

[guest3]

I want to get 3 power supply 5v/2A, +15v/0.3A, -15v/0.3A from ac 220v.
I think I should use transformer first(tranform to 15v or 5v?), and then rectify it. And then what should I do? and which regulator could provide 5v/2A? Thanks.

 

[djalli]

I want to get 3 power supply 5v/2A, +15v/0.3A, -15v/0.3A from ac 220v.
I think I should use transformer first(tranform to 15v or 5v?), and then rectify it. And then what should I do? and which regulator could provide 5v/2A? Thanks.

Yes you need a transformer. To at least 15 not 5volts. Unless from 5volts you want to go back at 15 and make your power supply more complex.

You can do it without transformer but it is not reccomendable.

Search this board, I bet you would find tens of design you can copy and implement.

 

[Bluechem]

to get an output with good stability, you should make sure that input voltage of regulator is not less than minimum input voltage specified in datasheet.using something like 20 volt unregulated DC to get 2A 5V is rather unwise because it leads to much unnecessary power dissipation. you can use a transformer which has multiple taps.

 

[guest3]

Search this board, I bet you would find tens of design you can copy and implement[/quote]
I have serached before submitting this post, I havn't found them. I use the key words: regulator, power.


using something like 20 volt unregulated DC to get 2A 5V is rather unwise because it leads to much unnecessary power dissipation. you can use a transformer which has multiple taps.[/quote]
Is the unnecessary power is: (20-5)*2=30W? so huge!
And the transformer itself power is (220-20)*2.6=520W???

 

[guest3]

I want to use 18v 30VA transformer, and then send the voltage to three ICs, 7815, 7915, LM2576-5, is it ok?
I worry the power consumption of LM2576 itself, because 18v input, and 5v output while 2A current. The power is 26W, could the heatsink abosrt the heat fully?

 

[guest3]

I want to use 18v 30VA transformer, and then send the voltage to three ICs, 7815, 7915, LM2576-5, is it ok?
I worry the power consumption of LM2576 itself, because 18v input, and 5v output while 2A current. The power is 26W, could the heatsink abosrt the heat fully?

 

[guest3]

I want to use 18v 30VA transformer, and then send the voltage to three ICs, 7815, 7915, LM2576-5, is it ok?
I worry the power consumption of LM2576 itself, because 18v input, and 5v output while 2A current. The power is 26W, could the heatsink abosrt the heat fully?

 

[Bluechem]

Is the unnecessary power is: (20-5)*2=30W? so huge!
And the transformer itself power is (220-20)*2.6=520W???

your calculation is wrong. in a transformer Pin is almost equal to Pout.
if you want to waste the energy and complicate matters for yourself, be my guest ; but it is not a good practice.

 

[guest3]

I want to use common inductance first, and get into bridge rectifier, and then high frequency transformer. I want to let the transformer output 3 volts. 10v, 18v, -18v. Is this resonable? 5v supply is LM2576,the other two are 7815/7915.

 

[Bluechem]

what voltage you want to make from 3V ? you shoud read datasheet of parts you mentioned to make sure that the input voltage is appropriate for them.you mean you want switching power supply?

 

[IanP]

I would suggest that you use +18V for the 5V output and +15V output.
The LM2576-5 has approximately 75% efficiency so at 2A we are talking here of approx. 7W of heat.
If you allow sufficient heatsink, say 2.5degC/W, it will be heated up by only less then 20 deg above ambient temperature, and this is perfectly fine.
This will simplify your circuit and you will be taking full advantage of using switch mode voltage regulator...