Bipolar power supply

[SimonFrisendal]

Hey everyone. I have designed this bipolar power supply that i will use to drive two bandpass filters that will then trigger a relay to trigger an alarm at a specific frequency.
It can be seen in the attached pdf.
The dioensret is a diode rectifier.

Can anyone see if i have made any mistakes?

 

[Reloadron]

At a glance it looks OK. I would likely make C2 & C4 10uF (Adjustment Bypass Caps). I would also add some output filtering depending on load current.

Ron

 

[SimonFrisendal]

The load current shouldn't be too big. A couple of operational amplifiers and two relays that need 18 mA to "switch". So i think this should be enough. C2 and C4 are values i took from the application note for the lm317.

Simon.

 

[ronsimpson]

Are the two big capacitors after the bridge backwards?

 

[SimonFrisendal]

Both are electrolytic. The top has the positive terminal on the plus voltage, and the bottom one has the negative terminal on the negative voltage if that makes sense.

 

[atferrari]

D1-D3 and D2-D4, are they right?

Seems to me that some of them should be reversed but not sure which ones.

Maybe D3 & D2?

 

[ronsimpson]

I think your ele caps are wrong.

 

[unclejed613]

D1 and D2 are backwards and so are forward biased. they should be reverse biased.

btw, good form putting the diodes in. even though you don't have electrolytics after the regulators. if you do end up putting some there, the diodes will protect the regulators from them discharging back through the regulators.

 

[SimonFrisendal]

Thanks. I didn't even see that myself. It's definitely D1 and D2 that are placed wrong. That's what happens when you copy and paste

This thread also shows that the ele caps are placed right and that D1 and D2 should be reversed.
https://www.electro-tech-online.com/threads/variable-bipolar-power-supply.24291/

 

[Reloadron]

Duh, looked at the lower supply knowing it was negative, looked at the protection diodes and looked right over them. Not like they are small and hard to see.

Ron

 

[ronsimpson]

Picture attached

 

[SimonFrisendal]

Thanks for the update, but i have already fixed it. Thanks for all the replies

 

[audioguru]

I guess the original schematic in this thread is corrected so the replies about things backwards are now meaningless.

Look at the datasheet for the LM317 and LM337. All schematics use 240 ohms for the more expensive LM117 and LM137. The LM317 and LM337 use 120 ohms for R1 and R2 (and half the value for the other resistors) so that their output does not rise when there is no load.

 

[SimonFrisendal]

I guess the original schematic in this thread is corrected so the replies about things backwards are now meaningless.

Look at the datasheet for the LM317 and LM337. All schematics use 240 ohms for the more expensive LM117 and LM137. The LM317 and LM337 use 120 ohms for R1 and R2 (and half the value for the other resistors) so that their output does not rise when there is no load.

But the datasheet that i am using from Texas Instruments specifies that 240 ohm resistors are to be used. Which one are you using?