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Strange Behaviour of PSpice LM317 Model

  • Thread starter Klaus Vestergaard Kragelund
  • Start date
K

Klaus Vestergaard Kragelund

Jan 1, 1970
0
Hi

I'm using Orcad Capture 9.1 and was just showing a friend what is possible
with spice. But I couldn't get this enormously simple circuit to behave.
Anyone got an idea of what is going wrong?

I have tried with several different models of the LM117 - this one shows a
schematic of the 7805 circuit with node voltages and currents:

http://www.microdesign.dk/strange.jpg

Thanks

Klaus
 
J

Jim Thompson

Jan 1, 1970
0
Hi

I'm using Orcad Capture 9.1 and was just showing a friend what is possible
with spice. But I couldn't get this enormously simple circuit to behave.
Anyone got an idea of what is going wrong?

I have tried with several different models of the LM117 - this one shows a
schematic of the 7805 circuit with node voltages and currents:

http://www.microdesign.dk/strange.jpg

Thanks

Klaus

Your schematic is a misuse of a 7805. What do you get with an LM117?
(And try reading the data sheet :)

...Jim Thompson
 
K

Klaus Vestergaard Kragelund

Jan 1, 1970
0
Jim Thompson said:
Your schematic is a misuse of a 7805. What do you get with an LM117?
(And try reading the data sheet :)

...Jim Thompson

Hi Jim

I know its a misuse, but I reverted to that one because the results of the
LM317 was even more strange. But I guess my friends Spice installation is
bad because at my station I get the correct values for the LM317
circuit..... I'll try to get his olb/lib files and se if I can find the
error (on previous occations I have downloaded models in which the pin
references were wrong - so I think this may be the error)

Cheers

Klaus
 
K

Klaus Vestergaard Kragelund

Jan 1, 1970
0
Jim Thompson said:
Your schematic is a misuse of a 7805. What do you get with an LM117?
(And try reading the data sheet :)

Hmm - I should have waited until I could get his files on the LM117. I'll
try to get them tomorrow - what we saw was e.g 5V accross the Output/ADJ
pins - and that should stay at 1.25V with low bias current....

Thanks

Klaus
 
K

Klaus Vestergaard Kragelund

Jan 1, 1970
0
Klaus Vestergaard Kragelund said:
shows

Hmm - I should have waited until I could get his files on the LM117. I'll
try to get them tomorrow - what we saw was e.g 5V accross the Output/ADJ
pins - and that should stay at 1.25V with low bias current....

Thanks

Klaus

Problem solved - model of the LM117 had switched legs and the problem was
compounded by using the LM7805 afterwards without proper biasing :-(

Just goes to shows on should not drink beers and simulate circuits .....

Cheers

Klaus
 
J

Jim Thompson

Jan 1, 1970
0
Problem solved - model of the LM117 had switched legs and the problem was
compounded by using the LM7805 afterwards without proper biasing :-(

Just goes to shows on should not drink beers and simulate circuits .....

Cheers

Klaus

I thought it was wine that did it ;-)

...Jim Thompson
 
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