Electron gun power supply issues: Stumped by a current meter

[gcewing]

Are you sure your rectifier is actually doing full-wave and not half-wave for some reason?

[ChristofferB]

The rectifier bridge is doing something strange, that's for sure. Bridge output to the meter is a 100 Hz sine wave shifted up to be all positive.

This then makes sense that the meter only shows about half, but I still don't get the bridge behavior..

Increasing the capacitance across the meter/bridge to 10 uF gives some DC component, but not much..

The RMS voltage across the meter is close to 100 mV, which would translate into 0.5 mA through the meter, which would give the expected reading, so the current transformer and meter are working as expected.

 

[ChristofferB]

Looping the high current lead once more through the transformer gives much more predictable results!

I now see the exact output one would expect from a rectifier, so I guess at 6V primary, the induced voltage in the secondary had trouble turning on the diode junctions.

The scale is now reading slightly too high, however. 0.7 FS (supposed to be 0.7A) with 0.5A input. I guess I could make all the resistors trimpots and just set it.

[NiHaoMike]

Might want to try a voltage doubler with Schottky diodes.

[Kleinstein]

The current transformers have a limited voltage. It depends on the number of turns, and with a relatively low number of turns the diode drop may be already on the high side. So a rectifier with shottky diodes may be more suitable.

[ChristofferB]

That's what I figured, eventually.

I just made two turns through the current transformer and replaced the resistors with trimmers to set the readout to a known value. A bit of a kludge but it's working as intented.

Thanks for all your advice and happy new year!