HV current limiting - help needed.

[DaleW]

I have a high voltage DC power supply, (180VDC), I am looking for a circuit that would allow me to control/limit the current from 1-15A, everything i can find is low voltage (less than 25VDC) and I don't know enough to modify them to work within my voltage/current requirements.

Producing a PCB isn't an issue however, a circuit design known to work because I don't have the ability to prototype it is pretty much a requirement.

The power supply is a toroidal transformer with 3 taps, 0 - 100VAC, 114VAC, 128VAC, a full wave bridge and filtering caps 4800uf@300VDC (4x1200uF) which gives me 140VDC, 160VDC and 180VDC after rectification and filtering but capable of delivering in excess of 40A.

Help in the way of a schematic would be greatly appreciated.

 

[KlausST]

Hi,

140V x 15A = 2100W of heat worst case (output shorted, supplied from lowest voltage tap ... expected to have automatic tap switching according output voltage.)

2100W of heat --> Nothing I would do using linear current limiting.

--> I´d use a switching circuit to reduce dissipated heat .. (maybe down to less than 1% w.r.t. a linear solution)

****
40A on a 4800uF gives a voltage drop of 8.3V per millisecond. .. or 83V per 50Hz half wave.
I don´t think it´s a stable bus voltage.

Also: check the ripple current specification of your capacitors.

Klaus

 

[dick_freebird]

A current mode controlled converter that has an "ISET" pin exposed, would give you a place to apply a variable limit-clamp.

This might look like "COMP" or "EAOUT", have to look at details (which seems to not be desired).

 

[Easy peasy]

Switch mode - i.e. buck would be the better solution to limit the current here . . .

 

[BradtheRad]

Help in the way of a schematic would be greatly appreciated.

Crude illustration of the buck converter. Transistors/mosfets which tolerate 180V are easier to find than IC's which tolerate 180V. By adjusting bias (as well as frequency, duty cycle) you adjust current through the system.