Switching from full to half wave rectification

Question

The Context:

Multiple manufacturers of electro-magnetic brakes offer rectifier modules to switch their DC brakes with an AC feed. This can often be tied to the same phases turning the motor, so that the brake lifts when the motor is powered:

(Image from Mayer document linked below)

They often also offer these modules with an "over-excitation" option. The idea being that half wave rectification provides enough power to lift the brake, but by briefly using full wave rectification, the RMS voltage is higher and the brakes lift more quickly.

Both Mayr and Precima offer the same sort of module:

Precima (p.g. 5 of the pdf)

Mayr (p.g. 4 of the pdf)

The Question:

Using only a 2 phase supply, how do you switch from full wave rectification to half wave after a specified time period? So far, a thyristor seems like a fairly good choice for switching 'off' the full wave rectifier. In the example below, if the switch is closed, the thyristor conducts as a diode, when open, it blocks current both ways.

^{simulate this circuit – Schematic created using CircuitLab}

Tested here (as Circuit Lab cannot simulate thyristors): Falstad Circuit

How can I add some sort of RC network/similar to the thyristor's control pin that would allow operation similar to the devices talked about above, with a resistor value setting a time for the full wave rectification to be active before the 'switch' opens and the thyristor turns off?

Answer 1

Using only a 2 phase supply, how do you switch from full wave rectification to half wave after a specified time period?

It's probably conceptually easier if you always use a full wave rectifier and then, on the DC side, use a MOSFET to activate the brake solenoid, and, after a short while, deactivate the MOSFET for every other half cycle.

If you see the reasoning here; the "control" circuit is located on the DC side of the rectifier and you can more easily derive a logic supply for a timer so that after a short while of operating full-wave, you revert to half wave. It also means that you can control back-emfs more reliably compared to the situation of your control circuit being on the AC side of the rectifier.