Timeline for LM2596 inverting mode to generate -5v
Current License: CC BY-SA 3.0
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| Nov 3, 2014 at 22:21 | comment | added | gratefulfrog | Thanks again! I have read and re-read the datasheet, in fact many versions of the datasheet. That's why I'm asking questions here ;-) I tried the circuit as you suggested, with C1,R1,R2 setting delayed startup on pin5, R3=1k, R4=3k, and two 9v batteries in parallel to supply more current. Then, with feedback pin4 to ground, I get -1.23v as before. With feedback pin4 connected to the R3/R4 junction, I get 0.2v output and the LM2596 gets burning hot! I am at a loss as to what is wrong, still - but THANKS for your HELP! I really appreciate it! | |
| Nov 3, 2014 at 17:47 | comment | added | Bruce Abbott | 33k is too high. R3 should be between 1k and 5k (R3=1k and R4=3K is OK). In this configuration the LM2956 can draw a lot of current when starting up, perhaps too much for your battery. You should use the recommended delayed startup circuit (C1, R1, R2) on pin 5. Read the datasheet! | |
| Nov 3, 2014 at 10:58 | comment | added | gratefulfrog | When I tried the above circuit with LM2956 feedback pin connected to gnd, I get -1.23v. But if I connect the feedback pin to the output of the voltage divider, I get +0.58v output and the lm2596 heats up. The circuit is powered from a 9v battery which also heats up if I connect the voltage divider, but not if the feedback is connected to battery gnd. Any thoughts would be very welcome :-) | |
| Nov 3, 2014 at 8:34 | comment | added | gratefulfrog | Are you saying that to get -5v output, with R3 = 1K, then R4= 1((5/1.23)-1) = 3k? I have been using 100k and 33k for my +5v psu, do you think that these values will work? Thanks for your help, sorry to be so ignorant, still...sigh... | |
| Nov 2, 2014 at 19:45 | history | answered | Bruce Abbott | CC BY-SA 3.0 |