A double-check needed

[Speakerguy]

Hey guys,

I am using the L6384 600V half bridge driver. It is fed power from the HV line through a resistor to the VCC pin which has an internal clamp to set the voltage to ~15.6V typ @ 5mA, and the absolute max current it can handle per the data sheet is 25mA. I am using isolated and rectified line voltage (170VDC here in the US). Here is the half bridge driver data sheet:

http://www.stmicro.fr/stonline/products/literature/ds/5651/l6384.pdf

I want to supply it with enough current to do it's job, as well as POSSIBLY feed an optoisolator.

What wattage and size resistor would you use? I've done the calculations myself, I just want a completely independent verification for safety purposes.

 

[dknguyen]

Isn't there other LV stuff in the circuit that is being powered either off the HV line or by a separate means. Since you don't mention any I assume all those that exist are safe. Couldn't you just tap power off of that?

If you're really after safety shouldn't you just use a Adum1234? Or an opto-isolator? And an isolated LV supply? Because a resistor that lets by 5mA of high voltage is enough to do harm. Also remember that if the silicon fails short (which silicon seems to do when it does fail), the resistor won't protect you. It just seems to me that having burning off that energy is wasteful and having a resistor running at 80C is a bit needless toowhen a tiny step-down transformer and another diode rectifier would be, be safer, run cooler and be more efficient.

 

[Speakerguy]

The LV side will be running off of an isolated and regulated 15V supply. Either a small wall-wart or some 9V batteries.

The L6384 says not to feed it from a low impedance voltage supply because it is meant to be run off a HV supply through a resistor to the clamp regulator, and if you feed it (for example) 15.2V from a low source impedance and the clamp kicks in at its min 14.6V it goes kablooey due to overcurrent (25mA max).

I guess I could keep my LV side isolated through an optoisolator, and use two nine volt batteries and a series resistor to power the L6384 and keep it isolated and happy while the FET's do their own thing with the HV.