Dear mkelly
Hi
If you want create simultaneous supply for your opamp , there is a classic way available : use a RCD voltage multiplier , before your rectifier , and then limit it's amplitude with a simple zener diode , thus you'll have two voltages (+-) , as well .
Best Wishes
Goldsmith
Hello, I am attempting to build a linear voltage regulated power supply with the following requirements:
-3 outputs:
- 1 Variable 0-30Volts output up to 1A
- + / - matched (tracked) output for powering various op-amps (up to 22V for ua741)
I have the following design that only does the first variable output, and I think this part of the design is pretty solid:
http://i.imgur.com/N53PD.png
-Note that the second switch off the secondary of the transformer is basically used to control heat dissipation in the LM317. I will hit the switch when I need high current at low voltage to reduce the voltage drop across the regulator.
I'm wondering how I could modify this to include + / - supplies for powering op-amps. I want to be able to adjust them from say 15V up to 22V, and I want them to be tracked (adjust them both with 1 pot)
Would a second transformer be the best (easiest) solution?
Since the transformer has a center tap, use the center tap as the ground (0V). Connect the other 2 ends to the bridge rectifier. The + output of the rectifier will be +VDC. The - output of the bridge rectifier will be -VDC. Connect the LM317 input to +VDC. The circuit gnd shown in the circuit will now be the transformer center tap. With -VDC input, use an LM337. The circuit will be similar to the LM317 circuit. Download the datasheet. You can also find a lot of circuits online. To have a matched output, use a dual potentiometer so that adjusting the position of the knob adjusts the resistance of two variable resistors together (one in LM317 circuit, one in LM337 circuit). Something like this:
**broken link removed**
Hope this helps.
Tahmid.
---------- Post added at 01:39 ---------- Previous post was at 01:19 ----------
Here's what you want:
**broken link removed**
goldsmith said:See my previous post , i told you the correct way and simplest way .
Hi mkelly,
I dodn't understand why you have 2 diodes D4 and D5 on the output. They will just degrade your load regulation and make your output voltage very inaccurate. Also from the LM317 datasheet I see https://www.ti.com/lit/ds/symlink/lm317.pdf the Theta jA is 53C/W so with an ambient temperature of even 50C you can only dissipate (150-50)/53 ~ 2W. Take at least a 10% margin on that so say 1.8W. So with 5V 1A even your first scheme will cause too much dissipation on the LM317. One option is to use a multiple tap transformer if you have one, another I think more elegant way is to use a switching regulator.
The diodes were put there to be a quick fix for the LM317 to regulate down to zero volts.
I'm using the TO-220 package for the LM317, so I can dissipate a bit more power than what you've mentioned but it still won't be enough. Is it very difficult to use a switching regulator?
Since the transformer has a center tap, use the center tap as the ground (0V).
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