# Help with power source

Discussion in 'General Electronics Chat' started by art_12345, Mar 26, 2015.

1. ### art_12345 Thread Starter New Member

Mar 26, 2015
4
0
Hi, I am new to this forum, and also I want to apologize for my bad english.
I am trying to buil a power source where I can get +12v dc, -12v dc, 5vdc, and a full rectified signal of 12v like the following:

I am using a transformer with central tap and the following circuit to get all the dc voltages:

but I want to know if there is a way to get also the full rectified signal without using another transformer?

File size:
919 bytes
Views:
18
File size:
919 bytes
Views:
19
2. ### Papabravo Expert

Feb 24, 2006
10,338
1,850
Once the capacitors are placed on the output of the bridge rectifier the rectified AC is GONE.
You can run the output of the +12v to a 7805. If you pull significant current it will get very hot according to
(12V - 5V)* (0.5 Ampere) ≈ 3.5 Watts

A better solution is a multitap secondary or a third secondary winding.

3. ### MikeML AAC Fanatic!

Oct 2, 2009
5,450
1,066

Last edited: Mar 26, 2015
art_12345 and cmartinez like this.
4. ### cmartinez AAC Fanatic!

Jan 17, 2007
3,695
2,747
Bullseye Mike... I was trying to solve the OP's conondrum, until I saw your post.... it's met all of the KISS's requirements...
@art_12345, the full answer is in Mike's post.

5. ### ScottWang Moderator

Aug 23, 2012
4,924
776
If the D5,D6,R4 used for the input of 5V regulator, do you think is that too high?

6. ### cmartinez AAC Fanatic!

Jan 17, 2007
3,695
2,747
The standard 7805 can handle up to 35V, I think. So he should be alright.

7. ### ScottWang Moderator

Aug 23, 2012
4,924
776
20Vac is too high for a liear 7812,7912 regulator.
I'm not talking about input rated voltage, it should care about the power consumption of 7805, when the input voltage is too high then all the waste power will turn to the heat in the 7805, it may reducing the using life of 7805.

8. ### cmartinez AAC Fanatic!

Jan 17, 2007
3,695
2,747
Oh... I think I understand now. The 7805 is a linear regulator, so maybe he should be using a switching one instead?

Jan 17, 2007
3,695
2,747
10. ### art_12345 Thread Starter New Member

Mar 26, 2015
4
0
Thanks Mike, this is what I was looking for, I will change the7812 for the switching regulator also, Thanks to all

11. ### cmartinez AAC Fanatic!

Jan 17, 2007
3,695
2,747
Yes, the same brand I posted handles the same switching regulator at other voltages. Just check it out.

Aug 23, 2012
4,924
776
13. ### ScottWang Moderator

Aug 23, 2012
4,924
776
I just checked the R-78C5.0-1.0 online store in Taiwan, only one I can find and it charges NT\$350 close to US\$11.17, wow, it can be buy a small arduino to play.