7908 voltage regulator

[juh]

I have newly purchased 7908 voltage regulators. I want to test them first before installing them to the circuit. I supplied -14V dc, 1A. I should expect an output of -8V right? but instead, i keep getting an output of 13V. what could be the problem? thank you!

 

[(*steve*)]

Place a small load on the output, say a 1k resistor.

 

[juh]

Place a small load on the output, say a 1k resistor.

nothing changed. i still got 13V.

 

[(*steve*)]

Show is the circuit diagram, and maybe a photo of how you've built it.

Do you have an input and output capacitor?

 

[davenn]

I have newly purchased 7908 voltage regulators. I want to test them first before installing them to the circuit. I supplied -14V dc, 1A. I should expect an output of -8V right? but instead, i keep getting an output of 13V. what could be the problem? thank you!

You have probably wired it incorrectly, Did you check the device pinouts with the datasheet ?
as Steve said we need to see a photo of your construction to confirm that

Dave

 

[juh]

http://www.ehow.com/how_7345520_test-to_220-voltage-regulators.html
http://www.learningaboutelectronics.com/Articles/How-to-test-a-voltage-regulator

i followed the instructions there. it worked for my 7805 voltage regulators but not with the 7908. yes, i've checked the datasheet. but sorry, i can't provide a photo right now. i don't have any camera with me.

 

[davenn]

you did realise/notice that the pin connections are different for the 78xx compared to the 79xx regulators ??

Dave

 

[juh]

yes. the middle pin would be the input for the 79xx regulator.

 

[Harald Kapp]

Do you have the capacitors in place as described in the datasheet?
Without these caps the regulator may show all sorts of strange behavior.