# Linear power supply design circuit [help]

#### Teklucifer

May 14, 2016
4
Hello everyone,

I am building a power supply with 24v 5A transformer to compensate the voltages dropped by diodes and other components. I have posted a design earlier however it had too many conflicts. I redesigned it again without current limiting, but I'd like to add an adjustable current regulator. I am not sure of where to put it! The design is made to decrease the ripples [
]. Please do criticize, and tell me what can I make to make it better or fix it.

I know that the lm338 dissipates alot of heat so i will use a radio heatsink laying around with a fan [https://farm6.staticflickr.com/5641/22741611580_ed371c13ca_b.jpg]

A couple of questions:

How can i determine the best values for caps?
How can i improve the circuit?
Where can i find Vripple in datasheets?
Is there any other way of adding a precise adjustable current limit?

Sincerely,

teklucifer

EDIT:
"P.S: I may not be able to reply fast due to time-zone difference - I apologize in advance for my inactivity"

#### davenn

Moderator
Sep 5, 2009
14,142
How can i determine the best values for caps?

C1 ... for main smoothing cap ... general rule is 1000uF / 1A of current
so your minimum would be 5000uF in reality I would use 6800uF or 10000uF

C2 ... 100nF ( 0.1uF) would be fine and also for C3 and C5

C4 ... 100uF would be fine

your blue error arrow ... not sure what your were specifically thinking,?

Where can i find Vripple in datasheets?

your ripple voltage is primarily determined by the C1 and C2 values Vs the current being drawn
the datasheet has load regulation figures as well as ripple rejection info for the IC
look in the electrical characteristics table

Dave

#### Teklucifer

May 14, 2016
4
Will the power supply limit the current or my design is incorrect I am also thinking to move the current limiting after voltage regulation. One more thing is, someone told me that RV2 is wrong position for voltage regulation.

#### davenn

Moderator
Sep 5, 2009
14,142
One more thing is, someone told me that RV2 is wrong position for voltage regulation.

R3 is connected incorrectly

look at the datasheet

#### Teklucifer

May 14, 2016
4
Another question,

Since the lm33 dissipates alot of heat, can i use this heatsink to cool the regulator? (with forced air cooling)

#### Alec_t

Jul 7, 2015
3,330
If D1 is a zener diode (it's shown as a normal diode) then RV1 will control the input voltage to the 338. R2/Q2 provide fixed current-limiting.

#### davenn

Moderator
Sep 5, 2009
14,142
Another question,

Since the lm33 dissipates alot of heat, can i use this heatsink to cool the regulator? (with forced air cooling)

The middle style of those 3 in the pic is the one you want ... doesn't need to be that big tho

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