Withstand 300VAC surge for 5 seconds

[rahul.shah]

Hi,

I want to design a LED driver with one specification. "can withstand 300VAC surge for 5 seconds".

It is a constant current drive.
current is 250mA.
LED driver is driven through AC mains of 230V/110V AC.
Output power = 18 watts. => voltage dropped (consumed) = 75V

Which MOV can do this work? Or is there any else design that I should consider?

how to make a selection? any calculation sheet with an example will be of a great help.

Regards and Thank you,
Rahul Shah

 

[chuckey]

If your kit is connected to the mains and the mains goes from 230 to 300V for 5 seconds then your MOV would have to conduct enough current to drop the mains by 70V, which is not practical. So you would have to put a resistor in series with the supply and the increased current through it when the MOV conducts will drop this voltage. The voltage drop across this resistor would would be a waste of power in ordinary running, so it would be best if it was a PTC, so as it took more current it would heat up and drop more voltage. These devices look OK.:- https://en.wikipedia.org/wiki/Resettable_fuse.
So it is matching the time constants of these devices, so the PPTC goes open circuit before the MOV goes bang!
Frank

 

[rahul.shah]

Hi Frank,
Putting a PPTC is a good idea. But how will it ensure that my after circuit will not be damaged? Do you have any formula that can be used to calculate parameters for part selection for 5 seconds sustainability?

Thanks,
Rahul

 

[mtwieg]

MOVs are more suited to suppressing a 6kV surge down to <500Vac, not suppressing a 300Vac surge down to <250Vac. A TVS diode is more suitable for such precise clamping levels. A TVS diode + PTC may be feasible, depending on how much power the LED driver normally has to draw and how much voltage the PTC has to drop. But I think that just designing the LED driver with a higher voltage tolerance would be much more robust, and have a smaller impact on efficiency.

 

[RAJAT AGGARWAAL]

In my led panel, used inducter
try it rahul.. it this time not damaged near 1 week... lol
b4 i ve burnt many..
used metalise polyster cap supply with bleeder resistor, then bridge, then inducter, then cap, then clamping, then mosfet timer with cap charge timing delay on, now here is my sweet white leds.. yup cheapo chinese
now don.t think anybody here can tell u exact design coz we not has your led. try some sets with lil diff n chk for some days.....
n yea. it ll burn in cheap invertor... just happy in sinewave coz capacitive supply.. n surge woah... i guess inducter can solve it vd a proper near 300v mov.
hope my work help u..

 

[mtwieg]

A choke is only effective for spikes shorter than one AC cycle, it wouldn't do anything for a five second surge. Unless the choke's resistance was huge, which would make it no better than a series resistor.

 

[schmitt trigger]

In North America, there is a very common industrial voltage of 277 volts which may go to 305 volts.

This voltage is very widely used for lighting applications, and therefore all of the major US semiconductor houses (Texas Instruments, Fairchild, Onsemi, etc) offer reference designs that will handle that high voltage continuously and forever.

Check their websites.