12V 5A DC power supply

pls can 0.33uF as input, CI and 0.1uF, Co, output capacitors withstand a 12V 5A DC SUPPLY! IF NOT, is there a calculator or formular for determining the values of input and output capacitors to be used in any DC supply circuit!

Your post is not clear.

snazzy c said:

pls can 0.33uF as input, CI and 0.1uF, Co, output capacitors withstand a 12V 5A DC SUPPLY! IF NOT, is there a calculator or formular for determining the values of input and output capacitors to be used in any DC supply circuit!

Click to expand...

As Nandhu told, your querry is not clear, but as i understood, you are asking about connecting the said two capacitors across the input and output of a regulator. And there is no direct relation with the capacitance used across a said power supply or its ampere ratings. If the capacitors are rated above the output / input voltage where it is connected, it should do its job. Its up to you now to decide what job you expect.
Cheers

Hi,

Your output capacitor calculations are depends on switching current requirements & not on contineous current requirements.
e.g. If you are having switching circuit on down side with 1ms on time & 2A current requirments, then you need to have a O/P capacitor which can deliver charge for 12V * 2A for 1ms time. after that you regulator will adjust to the requirements and provides additional current. You can find may articles on o/p capacitor selection. For selecting O/p capacitor voltage rating, ESR, capacity are major criterias

thanks for your reply. what am saying is this: i used 0.33uF, 50V (as input capacitor), 0.1uF, 50V (as output capacitor) and LM7820 Regulator ,with a 24V, 45AH battery to power a load of 19V, 2.1A. But the problems are: the regulator is heating very much (good heatsink was used), the load was tripping off after some times, the battery charger used was rated 24V, 170AH- 350AH and it's not automatic, measured input voltage on the battery (when charging) was 32.2V. I observed that the increases of the power loss (32v - 19v)*2.1A, i.e 27.3W, result in subsequent decrease in output voltage (from 19V to 17.85V). Are the values of the capacitors ok! Pls, i need solutions. Thanks!

snazzy c said:

thanks for your reply. what am saying is this: i used 0.33uF, 50V (as input capacitor), 0.1uF, 50V (as output capacitor) and LM7820 Regulator ,with a 24V, 45AH battery to power a load of 19V, 2.1A. But the problems are: the regulator is heating very much (good heatsink was used), the load was tripping off after some times, the battery charger used was rated 24V, 170AH- 350AH and it's not automatic, measured input voltage on the battery (when charging) was 32.2V. I observed that the increases of the power loss (32v - 19v)*2.1A, i.e 27.3W, result in subsequent decrease in output voltage (from 19V to 17.85V). Are the values of the capacitors ok! Pls, i need solutions. Thanks!

Click to expand...

Hi,

First of all , LM7820 isn't suitable for your application. Maximum Recommended Current for the 7820 is 1.5A. PEAK output current for 7820 @ 25C is 2.1 A (for a short time not continuous ), so you are trying to use this regulator at it's Maximum capabilities for a long time and this will happen.(even if you have a very good heatsink). your capacitors are fine,but i recommend to use at least one 10uf at input and one at output.

Again with this type of power dissipation/output current, you should go with a 3A Linear Regulator at least (Like LT1085 series) or at least something like LM317 (K Package, LM317K).if you don't want to use High current Linear Regulators,you have to use a High current PNP Transistor to Provide your output current and keep LM7820 current Low.

if i want to design this power supply for myself,i will use a switching regulator (Like LM2576,LM2676).it has more components ,but much better efficiency and lower power dissipation,unless you have some reasons that you don't want to use a switching regulator.