Hey everyone!
I'm designing a DC power supply as a project. Not from scratch, though I'm expanding on the original design(s) quite a bit.
Here's the original design: http://www.qsl.net/yo5ofh/projects/vps/vps.htm
Mine will be a bit more complex due to the homemade voltmeter/ammeter on the output, though that's not really related to my question.
Rather, my problem is at an earlier stage. I'm simulating the supply in LTSpice, but I'm not happy with the results. Even though the LM317 should be capable of ~1.5 amps, I'm only getting a maximum of 0.8 A. If I try to use up more (by lowering the load resistor), the output voltage simply drops so that it stays around 800 mA... though more ripple is added.
AFAIK my simulated transformer should be able to handle this easily, the diodes in the full-wave rectifier are rated for 3 A, and after that I find only the LM317 that could possibly limit anything further...? The schematic is in the pictures below.
The voltage (between the upper and lower nodes towards the right) is at 13 V with a 100 ohm resistor for the load.
Here's a picture with a slighly larger, but still OK load at 25 ohm (+ 1 ohm) = ~0.5 A: link
... and here's one with a larger load that is far from OK, 10.5 ohm (+ 1 ohm) = ~1.1 A (in theory): link - note that the output voltage dropped from ~13 to ~8 volts.
R5 is the load, and R2 is a way-too-big shunt resistor for the ammeter (which is really aa ugly, but cheap, design). R2 doesn't cause any problems though as I've tried without it.
Due to the LM317 component not being part of the LTSpice project, I'll only upload it if asked for (you'd need to install the component as well, unless I learn how to include it "inline").
Any advice on what I should check? According to the LM317 data sheet, as far as I understand it anyhow, this shouldn't happen.
Now, of course, the simulated model isn't identical to the real thing, but I'd sooner blame myself than the simulation at this point, as I'm still a beginner.
I'm designing a DC power supply as a project. Not from scratch, though I'm expanding on the original design(s) quite a bit.
Here's the original design: http://www.qsl.net/yo5ofh/projects/vps/vps.htm
Mine will be a bit more complex due to the homemade voltmeter/ammeter on the output, though that's not really related to my question.
Rather, my problem is at an earlier stage. I'm simulating the supply in LTSpice, but I'm not happy with the results. Even though the LM317 should be capable of ~1.5 amps, I'm only getting a maximum of 0.8 A. If I try to use up more (by lowering the load resistor), the output voltage simply drops so that it stays around 800 mA... though more ripple is added.
AFAIK my simulated transformer should be able to handle this easily, the diodes in the full-wave rectifier are rated for 3 A, and after that I find only the LM317 that could possibly limit anything further...? The schematic is in the pictures below.
The voltage (between the upper and lower nodes towards the right) is at 13 V with a 100 ohm resistor for the load.
Here's a picture with a slighly larger, but still OK load at 25 ohm (+ 1 ohm) = ~0.5 A: link
... and here's one with a larger load that is far from OK, 10.5 ohm (+ 1 ohm) = ~1.1 A (in theory): link - note that the output voltage dropped from ~13 to ~8 volts.
R5 is the load, and R2 is a way-too-big shunt resistor for the ammeter (which is really aa ugly, but cheap, design). R2 doesn't cause any problems though as I've tried without it.
Due to the LM317 component not being part of the LTSpice project, I'll only upload it if asked for (you'd need to install the component as well, unless I learn how to include it "inline").
Any advice on what I should check? According to the LM317 data sheet, as far as I understand it anyhow, this shouldn't happen.
Now, of course, the simulated model isn't identical to the real thing, but I'd sooner blame myself than the simulation at this point, as I'm still a beginner.