5V voltage regulator problem

Thread Starter

ksp1717

Joined Oct 30, 2008
13
Hi

I am not sure where to put this topic but here it goes.

I am using a -5V and +5V voltage regulators.


PTN78000AAZ for -5V,1.5A
LD1086D2T50TR for 5V,1.5A

I am using a 12V,1.5A supply to power both the devices. I have followed their datasheets PTN78000 and LD1086 to make the basic application circuits.

Now here is the problem. When I power up the circuit, the PTN78000 functions as expected and gives me ~-5V, but the LD1086 also gives me negative voltage of ~-3.5V as output. The LD1086 also gets hot and soon if I measure the voltage at input it drops to ~2.8V instead of 12V and I am measuring 0.4V from PTN78000 and 1.7 from LD1086.

Can some one explain me what is going on. I am also attaching the full schematic.

The power supply directly is connected to only these two devices. All others are downstream.

Thanks for your help
ksp
 

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mlog

Joined Feb 11, 2012
276
The schematic is difficult to read, but it looks like the +5v power supply ouput is connected to the collector of a PNP transistor (Q1), while the negative power supply output is connected to the collector of a NPN transistor (Q2).
 

Audioguru

Joined Dec 20, 2007
11,251
Why is there schematic drawing software available that makes the schematic a negative covered in dots and makes the numbers too small to see??

EDIT: It also makes crossed lines all over the place.
 

Thread Starter

ksp1717

Joined Oct 30, 2008
13
HI

Thank You for your replies. The problem was not with the devices mentioned but with the transistor matching as mentioned by mlog. I have swapped the transistors and now it is working as it should. Thank you all

Btw sorry for the schematic image. I made those pins small :( on purpose. I should have made them large.

ksp
 

bountyhunter

Joined Sep 7, 2009
2,512
Hi


I am using a -5V and +5V voltage regulators.




Now here is the problem. When I power up the circuit, the PTN78000 functions as expected and gives me ~-5V, but the LD1086 also gives me negative voltage of ~-3.5V as output. The LD1086 also gets hot
Sometimes with dual polarity supplies, one side will yank the other output to the wrong polarity on turn-on and it will latch up (and get hot). Thats why they show diodes on the outputs with reverse polarity.
 
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