Speakerguy
Active Member
..in electronic neon sign power supplies? The really light weight SMPS types. I cut one open and took out the transformer. It looks like a ferrite core, with one side wound with standard magnet wire. The other side is enclosed in a plastic box and is potted, so I can't see inside, but it has the high voltage lead wires coming out of it.
I thought this would have been some sort of standard transformer, but it behaves oddly.
I am driving it with a 555 timer into a half-bridge FET driver connected to two power FETs, 27V Vdd for the FETs. I use a pot on the 555 in astable mode to sweep frequency from 25kHz to 40kHz. The output of the FETs is a 27V square wave, fed to a 20ohm power resistor to limit current and then into the primary of the transformer (the magnet wire portion). So far so good.
Measuring the secondary (unloaded), I get a resonant response. At 33kHz, I get just over 10kV out of the secondary. At 25kHz and 40kHz, it drops significantly (only a few kV). Also, the output looks like a really good sine wave. All the harmonics of the square wave it is being fed with are almost totally rejected.
Anyone have any idea what kind of transformer this is, or what else they might have inside that potted plastic box? I'm hesitant to start slicing it into sections on the band saw to find out.
I thought this would have been some sort of standard transformer, but it behaves oddly.
I am driving it with a 555 timer into a half-bridge FET driver connected to two power FETs, 27V Vdd for the FETs. I use a pot on the 555 in astable mode to sweep frequency from 25kHz to 40kHz. The output of the FETs is a 27V square wave, fed to a 20ohm power resistor to limit current and then into the primary of the transformer (the magnet wire portion). So far so good.
Measuring the secondary (unloaded), I get a resonant response. At 33kHz, I get just over 10kV out of the secondary. At 25kHz and 40kHz, it drops significantly (only a few kV). Also, the output looks like a really good sine wave. All the harmonics of the square wave it is being fed with are almost totally rejected.
Anyone have any idea what kind of transformer this is, or what else they might have inside that potted plastic box? I'm hesitant to start slicing it into sections on the band saw to find out.
