current-limitingtoroidaltransformer
This component was inside an isolation transformer. It's obviously for limiting inrush current, but how does it work and what is inside?
I believe it's a relay of some sort, switching a resistor in series with the input or something like that. When voltage are applied to it's input i can hear the relay inside oscillating, so clearly somethings wrong. Makes me wonder how it triggers on the inrush current and why they didn't go for a NTC current limiter.
Thanks 🙂
Switching an inductor may make it work like a boost converter, and thus temporarily generate a higher voltage.
One way of making sure that the input voltage to the LM338 converter is no higher than allowed, is to wire a high-wattage (between 600W and 5 kW) TVS diode with an appropriate clamping max voltage biased against the input voltage and ground.
Also, if you're switching on the measured/actual output voltage, then you can get into oscillation. It would be safer to switch on "desired" output voltage, and let the regulator make sure it gets there. You could perhaps feed the bias voltage from the regulator ADJ into your microcontroller with a resistive divider to achieve this. Or you could just use a comparator with a pre-set trip point to drive/un-drive the relay.
A current limiter is a current source with a limited voltage compliance. All practical current sources have this limitation, so they are current limiters.
Consider the humble current-limited lab supply. Set its current limit to 20 mA, and voltage at 5 V, and now it's a constant-current source for testing LEDs.
(answers with pictures get upvotes!)
Best Answer
It's almost surely some kind of impedance (a power resistor or an NTC thermistor) with a time-delay relay contact shunting the resistance.
That way the power consumption in steady state is small- perhaps 0.4W- mostly just the relay coil and the control circuitry.
The relay contact simply closes a short time after power is applied.