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power supply 2A output

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leonel

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What value of capacitor should i put in the rectifier capacitor to achive a 2A output?
470uF 35V it's enough?
I will use 3A diodes in the bridge rectifier!
I want 24VAC to 24VDC having an 2A output.
 
Depends on what your running off of it and how much Ripple is acceptable.
 
The value of capacitor depends on allowed voltage ripple. Calculate:
C=I*t/Urip
t is discharging time of capacitor and it is about 8ms for fullwave rectifier and 50Hz mains frequency
I is max load current
Urip is peak-peak ripple voltage, you define it.
 
With just a bridge and a capacitor, 24V AC becomes roughly 36V DC, and 470uF is no where near big enough either - as a MINIMUM, stick a '0' on the end for 4700uF. But as suggested, a LOT depends on what you're wanting to feed, how critical it's supply is, and how much ripple it can stand.
 
Hi Leonel

Tweaking power supplies?
Hmmm...
First step is to make a life insurance and insurance contract on your house for fire.
Alternatively, a fuse of appropriately low amp rating could do (on the primary of the transformer).

After rectifying and then filtering, the 24VAC (effective voltage) will be about 34VDC without load. The mains voltage is not guaranteed to be exactly 230V. If it is higher, then the 34VDC also increases and may exceed 35V. So in theory you could make a cap with 35V rating suffer a little bit.
 
Leonel - as already stated the size of the capacitor determines the amount of ripple. I struggled with the question of how much ripple is acceptable and unfortunately it depends on the application. I am an amateur radio operator and wondered what equipment manufacturer's would say about ripple requirements for their amateur equipment. I was not able to get a good answer from Yaesu, Kenwood or Icom. I was able to find people who provided the AC power supplies (all rigs run on nominal 12 vdc) and they said their normal spec was 100 millivolts. At the time I did not clarify if they meant peak to peak or rms so I'd assume peak to peak. In several amateur radio handbooks I've seen statements about ripple requirements but the information is for various sections of a receiver or transmitter. It goes from 5% down to 1% - and it just appears like it's info that applies to vacuum tubes. In my "Practical Electronics for Inventors" book the author makes some reference to staying below 200 mv ripple - because of some industry standard for IC operation. Keep in mind that an IC voltage regulator has some ripple rejection capabilities.

All I've addressed so far is ripple. The net result of a rectifier and capacitor filter might be a DC voltage that is too high so you might need to reduce it or regulate it down to suit your needs.

Sorry for the long post but I wanted to leave you with some info so you could set a goal for sizing the capacitor.
 
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