First of all: Yes I know, you should always measure the performance of a power supply under load. BUT:
I just conjured up a little +/- 12 V supply with a 7812 and a 7912. After soldering the thing together I just hooked it up to my 30V lab suplly (which has only one channel, hence the need for this) and checked the output with my multimeter. I thought that is fine because I wasn't interested in any noise measurement or the exact output voltage. I just wanted to see if we were in the ballpark.
Oddly enough the positiv output was perfectly fine but ne negative one showed -3 V. So I quickly turned it off and looked intensely for faulty wiring. With nothing to be found in that respect I replaced the 7912 with a spare one I had orderd along with it. But that gave me exactly the same behaviour.
When testing the 7912 parts in an isolated environment (pure -12V supplied with -15V) it showed up fine, so no defective parts. After several hours of frantic resoldering and looking for bad or false connections I came up with the idea of hooking up a little load (just two 4.7k resistor because I had it handy) and all of a sudden the ba***rd gave me +12 V and -12 V.
So I guess there is a lesson to be learned here: ALWAYS always always put a load on if you want to measure output voltage.
Here is my question however: Since I am relatively new to electronics I wanted to ask if this behaviour is normal or have I found a slightly strange version of the 7912?
Like I said I would have expected maybe something from -11 V to -13 V or so since there was no load (apart from the 1Meg in the multimeter) but I really didn't expect a discrepancy as high as almost 10V!
Here is the datasheet for the exact 7912 I used: http://cdn-reichelt.de/documents/datenblatt/A200/TS7900#TSC.pdf
Thanks in advance!
I just conjured up a little +/- 12 V supply with a 7812 and a 7912. After soldering the thing together I just hooked it up to my 30V lab suplly (which has only one channel, hence the need for this) and checked the output with my multimeter. I thought that is fine because I wasn't interested in any noise measurement or the exact output voltage. I just wanted to see if we were in the ballpark.
Oddly enough the positiv output was perfectly fine but ne negative one showed -3 V. So I quickly turned it off and looked intensely for faulty wiring. With nothing to be found in that respect I replaced the 7912 with a spare one I had orderd along with it. But that gave me exactly the same behaviour.
When testing the 7912 parts in an isolated environment (pure -12V supplied with -15V) it showed up fine, so no defective parts. After several hours of frantic resoldering and looking for bad or false connections I came up with the idea of hooking up a little load (just two 4.7k resistor because I had it handy) and all of a sudden the ba***rd gave me +12 V and -12 V.
So I guess there is a lesson to be learned here: ALWAYS always always put a load on if you want to measure output voltage.
Here is my question however: Since I am relatively new to electronics I wanted to ask if this behaviour is normal or have I found a slightly strange version of the 7912?
Like I said I would have expected maybe something from -11 V to -13 V or so since there was no load (apart from the 1Meg in the multimeter) but I really didn't expect a discrepancy as high as almost 10V!
Here is the datasheet for the exact 7912 I used: http://cdn-reichelt.de/documents/datenblatt/A200/TS7900#TSC.pdf
Thanks in advance!