Can I get away with using 400v caps instead of 450v in a LCD TV switch mode power supply? These 2 caps are the main filter ones. I'm asking because I can get the 400v ones locally but have to wait 2 weeks for the 450volt ones.

 

Depends on the voltage in the circuit. Generally, you don't want to go lower and it is better to go higher, especially if you are replacing a bad cap.

So I would say the answer is NO. Go with a higher voltage. 600V would be better.

 

It depends on the circuit design.

"Some" SMPS are made for 120v and 220 volt countries and can take either at the input. They incorporate a larger voltage cap to match the largest possible input allowed.

You would need to reverse engineer the circuit to see what's happening or measure the peak voltage on the old caps. Is it coming straight off a bridge or are they using some doubling circuit.

However, any alterations would change the validity of any sticker info applied to the device. Ie. if the sticker says 110 -240 Vac input and your in a 120 volt country and adjust the cap voltage rating down for such and then someone, someday sees the sticker and hooks up to 240.. then poof.

cheers

 

If you can manage to find and fit the right combination of caps, you can always rig up an equivalent cap from smaller caps. Say, two caps with half the rated voltage you want but twice the capacitance, you can just put them in series.

Or, if you find caps that are of half the capacitance but have high enough voltage ratings, you can put them in parallel.

 

I do not recommend putting capacitors in series in order to double the operating voltage. Since the node joining the two capacitors is floating there is no guarantee the capacitors will share the operating voltage equally.

 

Can I get away with using 400v caps instead of 450v in a LCD TV switch mode power supply? These 2 caps are the main filter ones. I'm asking because I can get the 400v ones locally but have to wait 2 weeks for the 450volt ones.

I have a SMPS design partly pinched from the L6565 datasheet and that uses 400v capacitors.