ElectroPhile
New Member
Dear All,
I recently built a power supply which works well. It uses the classic LM317T with 4 MJ2955 power transistors as pass transistors and will run a 60W halogen car headlight globe at 13 volts. The pass transistors are mounted on a large 3mm sheet of aluminium. I have built smaller power supplies before, but this is the 1st I have built with pass transitors. I am fairly new to it, but with its two panel meters it looks the part. I was quite proud of it, it is useful as a bench power supply, I built it primarily to power a Jacobs Ladder I had built some years before.
The Jacobs Ladder is the old September 1995 "Silicon Chip" design using a modified electric fence circuit built around a 555 timer and MJ10012 transistor running a 12V automotive coil.
Previously I had run the Jacobs Ladder from a car battery but lugging a car battery in and out and having it on the kitchen table was displeasing my wife...
So I built the power supply, it regulates very well, I tried all different types of loads on it, the regulation was excellent.
I connected the Jacobs Ladder, the arc rose, then silence. On checking over the power supply, the regulator LM317 appeared to have died. In went another, I also added a diode to the 12V input of the Jacobs Ladder, thinking voltage spikes are going back into my power supply.
The 2nd test ran a little longer, but the same problem. Another cooked LM317T.
In powering any other device my power supply is fine. I suspect voltage spikes are making their way back from the Jacobs Ladder, or perhaps the very agressive switching provided by the MJ10012 in the Jacobs Ladder is part of the problem. There was a 16 volt Zener in the Jacobs Ladder across the input terminals. There was, until I accidentally burnt it out when I got the porlarity back the front.
Is it likely to be the switching or is the LM317 receiving the emf from the Jacobs Ladder? Would some capacitance across the output of my power supply help?
I'd be most grateful for any ideas.
Electrophile
I recently built a power supply which works well. It uses the classic LM317T with 4 MJ2955 power transistors as pass transistors and will run a 60W halogen car headlight globe at 13 volts. The pass transistors are mounted on a large 3mm sheet of aluminium. I have built smaller power supplies before, but this is the 1st I have built with pass transitors. I am fairly new to it, but with its two panel meters it looks the part. I was quite proud of it, it is useful as a bench power supply, I built it primarily to power a Jacobs Ladder I had built some years before.
The Jacobs Ladder is the old September 1995 "Silicon Chip" design using a modified electric fence circuit built around a 555 timer and MJ10012 transistor running a 12V automotive coil.
Previously I had run the Jacobs Ladder from a car battery but lugging a car battery in and out and having it on the kitchen table was displeasing my wife...
So I built the power supply, it regulates very well, I tried all different types of loads on it, the regulation was excellent.
I connected the Jacobs Ladder, the arc rose, then silence. On checking over the power supply, the regulator LM317 appeared to have died. In went another, I also added a diode to the 12V input of the Jacobs Ladder, thinking voltage spikes are going back into my power supply.
The 2nd test ran a little longer, but the same problem. Another cooked LM317T.
In powering any other device my power supply is fine. I suspect voltage spikes are making their way back from the Jacobs Ladder, or perhaps the very agressive switching provided by the MJ10012 in the Jacobs Ladder is part of the problem. There was a 16 volt Zener in the Jacobs Ladder across the input terminals. There was, until I accidentally burnt it out when I got the porlarity back the front.
Is it likely to be the switching or is the LM317 receiving the emf from the Jacobs Ladder? Would some capacitance across the output of my power supply help?
I'd be most grateful for any ideas.
Electrophile