filter caps

[Snaz]

as far as power supplies, is there a process to determine what is needed after a bridge rectifier? most of the ones i have seen are 220uF 160V. where did they get this?

 

[JKF1000]

I am asuming you mean the smoothing capacitor used after the rectifier and before the regulator, there is a general rule of thumb, for effective smoothing you need to use at least 2000uF per ampere, more is better, as for voltage rating, always allow at least 50% headroom above your operating voltage, as a example, for a 12v circuit, you would rate your caps at no less than 18v(more likely 25v due to avaliability)
Hope this helps, Karl.

 

[Snaz]

actually it leads to more questions lol. as per hte amps thing.. is the current loss from the voltage loss in a transformer? i guess i'm wondering how you know how many amps you will have after the transformer?

Also i have been reading that by placing an inductor after the filter cap, you wont lose as much energy. is there a rule on how many uH you need for this inductor?

 

[Leftyretro]

In the 80s I use to work with and repair if needed tons of small linear regulated open frame DC power supplies from firms like Lambda, Power Standard, etc.

I had noticed that there was a commonality among the brands as to the sizing of the main filter capacitors. All the 5VDC supplies tended to use around 2,000 MFD per AMP of output current, so a supply rated at 3 amp 5vdc would use a 6,000 MFD cap. The next popular voltage were the 12VDC supplies where the commonality was around 1,000MFD per amp output.

Later I actually found an article about sizing and calculating for the required amount of filtering capacitance. It had to do with defining the maximum allowable ripple voltage (such that the lower peak was above the regulator drop off voltage) when delivering it's maximum rated current. I didn't keep the article but I'm sure someone may have a link somewhere.

So there is basic engineering to figure out the amount of filtering required for a given DC power supply output to maintain good linear regulation. Of course such a formula would be different for full wave rectification then for half wave but you knew that already, right

 

[saturn1bguy]

So there is basic engineering to figure out the amount of filtering required for a given DC power supply...

Vpp = Iload(dt/C),

Specify the output ripple voltage (Vpp) you can live with, and solve for C (dt for full wave rectification = 8ms).