Troubleshooting the Milestag Circuit

[duffman]

I am building a circuit and finished only to find a couple problems. I have an initial suspicion as to what the problem is however, if this doesnt work then ill lay it all out. I have soldered an lm7805. After powering up, applying the two ends of a 12 volt lamp, it lights up between the first pin and seoncd pin. duh. Its the pin that is getting external power, and the ground. However, i put the lamp between the second pin and the third and there is no light. This is strange because I am expecting a 5 volt output. However, there is none. Has anyone had a similar situation or know whats goign on? THe component seems fine, and the joints are all ok. I was under the impression that lm 7805s were cut and dry too. Just add voltage thats above 5 to pin 1, ground two, then three is 5 volts.

 

[Oznog]

I am building a circuit and finished only to find a couple problems. I have an initial suspicion as to what the problem is however, if this doesnt work then ill lay it all out. I have soldered an lm7805. After powering up, applying the two ends of a 12 volt lamp, it lights up between the first pin and seoncd pin. duh. Its the pin that is getting external power, and the ground. However, i put the lamp between the second pin and the third and there is no light. This is strange because I am expecting a 5 volt output. However, there is none. Has anyone had a similar situation or know whats goign on? THe component seems fine, and the joints are all ok. I was under the impression that lm 7805s were cut and dry too. Just add voltage thats above 5 to pin 1, ground two, then three is 5 volts.

Forgive the obvious question, but will your 12v lamp light at all on 5v?

A voltage regulator may oscillate if the required capacitance is not included on the pins near the regulator. So... don't leave out the caps.

 

[duffman]

**broken link removed**
the setup is in the top left corner
Yes, it will light, but it certainly isnt as bright as if it were connected to twelve volts.

Assuming I had one of the electrocaps in the setup backwards and turned it on, would the electrolytic capacitor blow, or would the lm7805? There were 3 caps in the setup. A 100 uf, a 10 uf and a .1 uf. I returned the 10 uf cap to the right orentation, and it still does not work. Which components could plausiibly be damaged by the mixup? (the .1 uf cap is nonpolar)[/img]

 

[Optikon]

**broken link removed**
the setup is in the top left corner
Yes, it will light, but it certainly isnt as bright as if it were connected to twelve volts.

Assuming I had one of the electrocaps in the setup backwards and turned it on, would the electrolytic capacitor blow, or would the lm7805? There were 3 caps in the setup. A 100 uf, a 10 uf and a .1 uf. I returned the 10 uf cap to the right orentation, and it still does not work. Which components could plausiibly be damaged by the mixup? (the .1 uf cap is nonpolar)[/img]

The LM7805 has over current protection and likely thermal shutdown as well. Is the part hot to the touch? Can you measure the output pin?
Can you pull the 7805 out and supply 5V external - all work ok?
Double check the pinout and connections..

Just some things to think about.

 

[Roff]

What voltage are supplying to the input?