Guidance for building 12V & 5V 1A regulator using LM317

Thread Starter

peterson2

Joined Nov 17, 2017
3
Hi Team,

I have a query to build 12V & 5V regulator circuit using LM317. I have one 15V transformer for input Vin both the voltage regulators.
Regulator circuit taken from http://www.electronics-tutorials.ws/blog/variable-voltage-power-supply.html

Here is my query, If i create 2 separate regulator circuit for 12V & 5V output with input 15V. Will there be huge heat for 5V regulator because the Vin and Vout voltage difference is high or Shall i connect the both regulator in serial.

Actually i created 2 parallel regulator using 7812 & 7805 but heat dissipation from 7805 is high even with heat sink. This circuit has to up 24/7 through out the year. Afraid it might burn out within few days.

Please give me a suggestion, is there any other way to create 12V & 5V 1amp regulator circuit with less heat.
 

dl324

Joined Mar 30, 2015
12,212
Welcome to AAC!

Here is my query, If i create 2 separate regulator circuit for 12V & 5V output with input 15V. Will there be huge heat for 5V regulator because the Vin and Vout voltage difference is high or Shall i connect the both regulator in serial.
If the current from the 5V regulator is 1A, you probably don't want to have it's input be from the 12V regulator.

With a 1A load from the 5V regulator, dissipation in that regulator will be about 15 watts; depending on how the AC is rectified. To reduce that, you can use a power zener diode (or a power transistor/low power zener equivalent) to lower the input to about 8V. That will give you about 3W of dissipation in that regulator, but the other 12W will still be dissipated by the zener diode or power transistor.

A switching regulator would reduce wasted power.
 

Thread Starter

peterson2

Joined Nov 17, 2017
3
Dear dl234,

Thanks a lot for your suggestion. So i think i have change my circuit design to use only 8V Transformer so the 3V will be dissipated from the regulator IC.

Thanks agian.
 

dl324

Joined Mar 30, 2015
12,212
So i think i have change my circuit design to use only 8V Transformer so the 3V will be dissipated from the regulator IC.
Transformers are rated in RMS VAC. An 8VAC transformer won't give you enough headroom for a 12V supply and it won't give 8VDC after rectification.

You should also plan on the secondary being rated for about twice the total load current. Can't be more specific until you specify rectifier type.
 

Thread Starter

peterson2

Joined Nov 17, 2017
3
I m redesigning the circuit, replacing 12V coil type relay to Solid state relay with operates on 3V. SSR relay is quiet expensive but for this heat problem i think there is no other option.
 
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