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That's what's supposed to happen. You won't get another charge cycle until you turn CHARGE off and then ON again.
This part is for when you need to charge up a capacitor for something like a camera flash unit. If you want a continuous output, this is the wrong tool for the job.
If you can tolerate a 2.5V minimum voltage drop, there are these new two-terminal constant current linear regulators from Diodes, Inc.
https://www.digikey.com/en/product-highlight/d/diodes/al5809-constant-current-linear-regulator
These are intended for driving LED strings, and come in 15 mA...
There are devices for that. See, for example,
**broken link removed**
This is a MOSFET switch which turns off if the current exceeds 5A. It stays turned off until power cycled. On resistance is about 0.130 ohm. It's a MOSFET, so it has on-resistance, not a diode drop.
(OK, so "Upload image" and "Manage Attachments" are completely different systems. Whatever.)
Successful LT3750 layout.
U1 is the LT3750. The big MOSFET above is its switch. The transformer is to the left.
All the passive components it needs are tightly clustered around it. The traces in that...
I've successfully built a capacitor charger using a LT3750. It works well, but board layout and bypass capacitors matter a lot. My first PC board didn't work at all; the LT3750 wouldn't switch. It took a while to find a layout that would work.
(Unable to upload image due to bad forum...
If you're blowing out sense resistors R20, etc., then F6 must not be turning off soon enough. The way these power supplies work, if the MOSFET stays turned on after the transformer has saturated, there's a short circuit. You're always a few microseconds from burnout.
Put scope probes on the...
**broken link removed**
Completely new design
I've gone to a completely new design. It's more complex, but it works.
This circuit uses an LT3750 capacitor charger controller. I'd been avoiding that, because I didn't want to deal with soldering 0.5mm pitch components. But with more practice...
L3 is probably saturating. Its saturation current is 270mA. LTSpice's default inductor model doesn't model saturation at all. When the current drops low enough that the inductor comes out of saturation, the ringing starts.
I tried shorting out R18 and L3. That's just noise filtering to prevent...
As requested, transformer primary current scope traces.
Current through L1, simulated.
Voltage across R18, actual (inverted).
R18, 2.2Ω, is in series with the high end of the primary of the transformer. So, per I = E/R, 1v on the scope = 0.45A. We only have about 1A in the real world...
Just discovered that the default LTSpice inductor model cannot saturate. The "Peak Current" parameter doesn't do anything. Wrote to Coilcraft to see if they have a SPICE model of the transformer. They have SPICE models for their two-terminal inductors, but not their transformers.
And, finally, what's going on with the secondary.
Voltage across the secondary.
Huge excursions on the downward side. Strange effects as the cap charges up.
Here's the real world.
Voltage across secondary
The key point here is that the voltage isn't rising fast enough. It's only at 60v...
OK, as requested, measured waveforms from an oscilloscope vs. simulated waveforms from LTSpice.
First, cap charging. This is measured between test points W3 and W5.
This is what's supposed to happen. The cap charges to 120V in 17ms; then the 120V Zener stops further charging.
What actually...
Will make voltage measurements at the transformer windings and post pictures of the scope traces, to compare with the sim. I can get a value for primary side current by measuring the voltage across R18.
The current limiting device does go into current limit as the filter caps charge. But once...
That design is scary.
The relays are not rated for 480 volts. The contacts may arc, burn out, or weld.
The traces are too close together for 480 volts.
There are no fuses.
The way that circuit is set up, if the controller fails while the contactor is closed, the contractor will remain closed...
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