## Basic Voltage reg circuit.

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Hi All,

Can someone please take a quick look at this basic circuit to make sure it will work before I go out and buy the parts to test it.

I have 32V AC supply and need to convert to 24V DC and approximately 4A current.

Craig

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You will need a biiiig capacitor at B+ terminal

Oh ok how big are we talking?? 4700uF??

Depends how much ripple you can tolerate at the output. If it is to charge a battery, then 4700uF is adequate.

Please read 7824 datasheet. It has example schematics. I don't think these examples have two resistors, just one between base-emitter, through which the regulator input current flows. In your schematic R1 would be removed to a shortcut.

Peak voltage output is 32*1.414V or about 45V minus diode drops (plus increased voltage when there is no load). I think absolute maximum input voltage is 35V. You cannot use 7824 unless you find one that accepts up to 45V or bigger voltage.

And regulator input must have at least 26-27 volts to give out 24V, so calculating max ripple is easy. 45V-27V=18V max ripple at 4A current. Rest is up to your mains frequency. About 2700uF 60V might do it, but might not in extreme cases (low mains voltage), so maybe 3300uF.

I think you will be better off using a switching regulator to get better efficiency and less heat.
For 24v output 4A and input of 34v you will get 40W of heat which is a lot.

Consider a solution like http://www.ti.com/product/lm2587 or http://www.ti.com/product/lm2679 and try to use an input voltage that is not too far from the intended output.

Alex

"For every effect there is a root cause. Find and address the root cause rather than try to fix the effect, as there is no end to the latter."
Author Unknown

Thanks very much for the help. I will look into the Switching type regulators. Looks like what I might need to go for. I have no choice on the input voltage as it comes from a transformer in a 1000V cabinet.

If you are making something to hook up to inside a cabinet, why invent it yourself? Phoenix Contact among many other distributors sells proven solutions.

cwilson wrote:
Thanks very much for the help. I will look into the Switching type regulators. Looks like what I might need to go for. I have no choice on the input voltage as it comes from a transformer in a 1000V cabinet.
If this device is going to reside INSIDE that cabinet I am sure there are regulatory standards that have to be met(in the USA Underwriters Lab).

An off the shelf encapsulated product that has the proper agency approvals is a safer route to follow.

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