Rectifier questions

[CTho9305]

I found one of these and was wondering how exactly it would be used. If I'm understanding the datasheet correctly (looking at the column for 4J), if I put 400V AC on the inner two pins, I'd get DC out... but I don't know what that voltage would be. 600V?

Also, I assume this could handle wall current directly? What would the output voltage be then?

Thanks.

 

[Evadman]

You should get out .707 of what you put in ( If I remember correctly ) That is just telling you the max that it is rated for.

 

[CTho9305]

so this rectified could be safely connected to wall power, and the output would be about 77 volts? interesting.

 

[Evadman]

That rectifier is made for up to 400 volts in, so 120 or 240 is not a problem. Don't quote me on that .707 figure, it has been a while 🙂 Find someone who is 100% sure 🙂

 

[CSoup]

Yeah, SQRT(2) is one of the factors, there is a factor of 0.5 in addition which gives about 0.707. Been a while here also. You can put one of these together with fairly common parts. You need about 4 diodes for a diode bridge that will essentially flip the negative part of the AC signal up. Lets say your AC was 120V peak to peak, now you have a bunch of hills from 0 to 60 V. This signal is smooth to DC through feed back I think.

Also, if you do find the actual equation for this rectifier, make sure you use the right number for the input voltage since the power line is rated at 120V RMS, but that is actually something more like 168V peak-to-peak.

 

[Demon-Xanth]

600V is the max revese voltage, a 120VAC waveform has 340V peak to peak. It wouldn't work for 240VAC

You will NOT get DC out. What you will get out is a waveform that is like a bunch of half cycles in the same direction peaking at Vpeak-1V.

This can be filtered to 119VDC (120VAC is RMS, about 170V peak)

note: 1V is dropped in the rectifying diodes, they have a 4A limit (average current), you might want to mount it to a metal plate or case if you're pulling that much.

Connection wise you'll want to put the AC in on the terminals w/ a sinewave symbol or "AC", the negative is negative and positive is positive (duh). To filter it start out with a huge ass capacitor and you can get more creative after that. If you want a DC voltage that's easier to work with use a step down transformer on the input.

 

[CTho9305]

so if I want some 119V DC, I put the wall current to the sine-wave-labelled pins, and can draw up to 4 amps from the +/- pins. there is already a heatsink on it (pulled from a monitor). to actually get a somewhat constant voltage, I take these two caps: (220uF, 200V max and 220uF, 160V max) and put them from the + pin to the - pin. correct?

 

[Demon-Xanth]

Getting a constant voltage depends on the definition of constant as well as the load. Typically under 4A or so you're gonna want caps in the 10,000-100,000 uF range and there's some other filtering that you can do as well (add a choke for example)

 

[CTho9305]

<< Getting a constant voltage depends on the definition of constant as well as the load. Typically under 4A or so you're gonna want caps in the 10,000-100,000 uF range and there's some other filtering that you can do as well (add a choke for example) >>


:Q don't have any of those. anyway, the whole point would be to charge up a 390uF (400V) capacitor to a fairly high voltage, so it doesn't need to be very stable, as long as it doesn't drop too far.

 

[Demon-Xanth]

<< don't have any of those. anyway, the whole point would be to charge up a 390uF (400V) capacitor to a fairly high voltage, so it doesn't need to be very stable, as long as it doesn't drop too far. >>



That's the reason for the large cap. larger==more stable. More current==less stable (in a simple setup such as this)