Making Symmetric power supply - 78XX/79XX - first Time

Thread Starter

Mikuda

Joined Mar 23, 2017
10
Hello! I'm making power supply for waveform generator (based on MAX038).
I'ts gonna be +5v -5v output.
I have a question about acceptable tolerance.
My breadboard prototype works well but it gives +5.1v and -4.95v.
It's barely 0.15v difference but I have no idea if it's significant or not.
So, is it normal? And if not what can be the cause? How can I troubleshot and or tweak that output to be exactly +5 -5 (if it's necessary of course)?
 

AlbertHall

Joined Jun 4, 2014
9,824
A longer answer. Below is a section from the 7805 datasheet. You can see that even with the junctions in the chip at room temperature you can expect the output voltage to be anywhere between 4.8V and 5.2V. Over an extended temperature range it might be anywhere between 4.75V and 5.25V. For all except very demanding applications this variation will not cause any problems.

upload_2017-9-27_14-3-10.png
 

AnalogKid

Joined Aug 1, 2013
8,440
Next, check the datasheet for the MAX038 to see what its tolerance is for power supply variations. If it can handle +/-5%, then you're good to go. If it needs tighter balancing between its supplies, then there are other regulators with better performance.

ak
 
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