Zeebit
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Today, I was finally able to put together the bench power supply I've been building. But yes, it failed. I'll explain what happened below but here is the schematic of the circuit. Its based on the circuit on the LM317 datasheet with some modifications.
When I turned it on for the first time, nothing started to smoke so I was a bit relieved. :crackup: Both voltage and current adjustment pots were zeroed at this time. I switched on the output and the minimum voltage was about 1.8V. Its supposed to be 1.25 but the voltage pot did not go all the way to zero ohms. I cranked it all the way up and it went to about 24V.
The voltage was doing ok so I thought I'd test the current next.
I got my multimeter set to amps and connected the leads to the output. The current adjustment pot(its 5K) was at minimum (it also did not go all the way down to zero) at this time. I gave it a small turn and my multimeter and the panel meter displayed around 3.5A. I was surprised so I quickly turned the power supply off because it wasn't supposed to do that.
I zeroed both pots and turned it on again. This time, the voltage was stuck at about (negative) -1 volt. I probed the output pin of the LM317 and sure enough it was producing that voltage. I also noticed that the fuse for the main rectifier section was blown. I used a 4 amp rated fuse there.
I replaced the fuse and the LM317. The voltage is now ok. It goes from 1.8V to 24V. The problem is that a slight turn of the current pot from minimum caused the CC led to light up even if nothing is connected to the output. I tried to measure the output current and again, it was at around 3.5A.
I'm not sure what is happening here. No components have released the magic smoke yet.
I would like to ask help from the electronic geeks here in finding out what is wrong.
BTW, big thank to djQUAN for helping me on this project.
When I turned it on for the first time, nothing started to smoke so I was a bit relieved. :crackup: Both voltage and current adjustment pots were zeroed at this time. I switched on the output and the minimum voltage was about 1.8V. Its supposed to be 1.25 but the voltage pot did not go all the way to zero ohms. I cranked it all the way up and it went to about 24V.
The voltage was doing ok so I thought I'd test the current next.
I got my multimeter set to amps and connected the leads to the output. The current adjustment pot(its 5K) was at minimum (it also did not go all the way down to zero) at this time. I gave it a small turn and my multimeter and the panel meter displayed around 3.5A. I was surprised so I quickly turned the power supply off because it wasn't supposed to do that.
I zeroed both pots and turned it on again. This time, the voltage was stuck at about (negative) -1 volt. I probed the output pin of the LM317 and sure enough it was producing that voltage. I also noticed that the fuse for the main rectifier section was blown. I used a 4 amp rated fuse there.
I replaced the fuse and the LM317. The voltage is now ok. It goes from 1.8V to 24V. The problem is that a slight turn of the current pot from minimum caused the CC led to light up even if nothing is connected to the output. I tried to measure the output current and again, it was at around 3.5A.
I'm not sure what is happening here. No components have released the magic smoke yet.
I would like to ask help from the electronic geeks here in finding out what is wrong.
BTW, big thank to djQUAN for helping me on this project.
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