7805 variable regulator

[shreyas_patel21]

thank you DXNewcastle,
I need two outputs 5V and 12V
and current for both should be 1 to 1.3A; I want to use it for cd-drive power supply.

 

[shreyas_patel21]

thank you DXNewcastle,

I understood it,

but what should I do if 1-1.3 A current for 5V and 12V is required at output of 7805 and 7812 respectively..?

I want to make power supply for a CD drive.
and I have adapter that gives 22V 1A.

thank u

 

[DXNewcastle]

shreyas, I am confused.
You posted earlier that you needed 1 milli Amps from the regulators at 5 volts and the same at 12 volts. Now you have posted that you want 1 - 1.3 Amps at 5 volts plus 1 - 1.3 Amps at 12 volts.
But you want to use a 22 volt supply which can only provide a maximum of 1 Amp.
Its not possible to achieve 2 - 2.6 Amps output from a 1 Amp input.

It really would be easier and more efficient if you could use a transformer with 3 secondary windings that supplies (approximately) 7.5 volts each. You would use one of them for the 5 volt supply and both in series for the 12 volt supply. Or you could use a simpler transformer with a 15 volt secondary and supply the 2 regulators from that.

But if you are determined to use a 22v DC supply then you must use one which can supply the current you need (nearly 2.5 Amps).
The circuit you have supplied should be re-drawn so that the current for the 5v does not have to pass through the 12volt regulator first.
Use the two regulators, without any 'voltage dividing' resistors, with proper decoupling capacitors on their input and output pins, with their inputs directly connected to the 22v supply and their outputs connected to your load.
The 78xx regulators are available in several power ratings. Make sure that you use devices capable of 1.5Amps each. You will probably need to mount them on heatsinks.

I hope this helps

 

[KJ6EAD]

I think Shreyas meant 1A at 5V and 1.3A at 12V. 22V at 1A = 22W available, and 5W + 15.6W = 20.6W needed (0.94A from 22V), leaves only 1.4W (60mA from 22V) of overhead for losses/inefficiency. I don't think that's nearly enough.

 

[luben111]

If using inductor step down regulator (when using inductor) it's possible to get from 24V/1A a 12V/2A output (transforming the power)