kk so as the title says i am making a dual rail power supply however i have been met with some confounding problems. My circuit is a typical dual rail with the bridge rectifier leading to 2 capacitors which connect to ground. comming from the capactitor to an adjustable regulator (lm317t and lm337 ) i also have a tip41 and tip42 surrounding the regulators to help with heat dissipation. kk, so my confounding problem is.. at first i had a -14 on my negative rail (which is fine) but positive was like 30 volts.. which basically means somethings wrong.. after i while i had a dif problem (same circuit left over night problem suddenly changed..) where after plugging in the center tap 24v transformer... i wud see my positive voltage decrease slowly from like over 20v whilst my negative voltage increase slowly from a low number... so basically i have no clue whats wrong.. my circuit is basically the same as this one : http://www.circuitstoday.com/wp-content/uploads/2008/02/dual-supply.jpg

except as stated earlier i have a tip41 and 42 for heat dissipation. and also instead of 4 caps on in and 4 on out i just have 2 on in and 2 on out... so no biggie...

any assistance welcome plz...

 

When you measure the voltage, do you have a load on the output, or is it open? Try measuring the voltage with a 5K load.
Also, how do you have the transistors connected and do you have any resistors?
Google 'high current voltage regulator circuit' and read through a few of the web pages.

 

Are you sure your transformer center tap is connected?

 

Yes, It sure sounds like the center tap is not connected.
The schematic is not drawn consistently. There are no 'dots' on many of the required connections along the ground line. Might be a silly question, but these are connected, correct?

 

I recently built the same circuit. At max I am getting +/- 18 volts.

 

There are no 'dots' on many of the required connections along the ground line. Might be a silly question, but these are connected, correct?

Yes they connect.

I note 4 places where I see a dot needed to indicate a connection between ground and the center of 4 cap pairs.

When I draw my schematics I take great care to never connect 4 wires in an X plus a dot. On my schematic wires always connect in a T and cross in an X so even without dots there is never any confusion.

 

To clarify, I was asking the op if they had these connected (as they should be) on their circuit.

 

ty for all the responses guys. and sorry im late replying i kinda crashed and slept.
kk in response to do i have a load. no i dnt i just used a open wire. so i guess ill test that when i go up to school either today or monday. also i have the ground connected as shown meaning. with the capacitors and with regulators etc. so thats fine.

lastly the trasnsistors are connected. with basically collector at the input for the regulator the base connected to the output of the regulator. and i take my output at the emitter. its there to pass the current thru it rather than the regulators to lessen heat.

i had asked a guy about the rise and sink problem .. and he said that means ground is changing which makes sense (if ground is 0 for eg and went up to 1 that means my + wud sink by 1 whilst my - wud rise by 1...) but idk how thats even possible.

im googling the high current thing right now so ill respond after reading up on that
/edit/ ye so i kno what that circuit is it uses zener voltage to reference thus regulating... ye i learned about that but how does that rlly apply to my problem here tho?

 

bump!. plz dnt quit on me guys ...

 

I know you said all the grounds are connected, but check the attached schematic to be sure you didn't miss any.
Look for bad solder joints, broken wires, cut traces, etc.

 

its in a breadboard so.. no bad solder joints or anything.. as for broken wires.. hmmm not possible because i have the capacitors directly into ground.. and the same for the resistors stretched directtly to ground... well actually i guess its a possibility still.. but i mean its unlikely.

 

With NO power to the circuit check the breadboard connections with an ohm meter.
Measure between the transformer center tap and other ground connections, make sure you have very close to zero ohms.

EDIT: Breadboards can easily have bad connections. And, sometimes the buss strips for power and ground
are split in the middle.

 

Can you post a photo of your breadboard?

 

i can ill try and take one now and see if i can post it up b4 i head up to school. (gonna test all the things posted here when ireach)

 

umm so this is the best i can do right now but i realise it s dark and u cant rlly see the wires... my current webcam that i used to take this pic is pretty shitty tho ... 1 thing to note is the caps are 1kuF 50v. however i have two 4.7uF 50v caps i use otherwise.

 

well i didnt get to go to school today but i will be there on monday for sure. so...ill check out the stuff yall said. like broke wires and such.... but if theres any other suggestions feel free to post them guys.

 

Are all 4 caps 1000uF? What is the significance of the 4.7uF caps? Where are they connected?

 

what i mean is . rather than 4 caps as shown in schematic. i have only 2 on the input to the regulators. however in the image i posted the 2 caps shown are two 1kuF 50v caps. I usually however use two 4700uF 50v caps... however as they are big the picture would show even less so i just swapped them with those shown (either should work anyways).

 

What are the values of the components used in the circuit? I need to to implement it on proteus.