Using two transistors to create regulator?

[realflow100]

Can I use overkill capacitors or would I need only the right values instead? because I have two 4uF 250V non-polar capacitors..
I have a 2F 16V capacitor to block noise from the power supply if necessary?

 

[spec]

Can I use overkill capacitors or would I need only the right values instead? because I have two 4uF 250V non-polar capacitors..
I have a 2F 16V capacitor to block noise from the power supply if necessary?

Hi real,

If you have a look at the circuit in post 17, you will see a schematic for a stabilized 5V power supply using the LM7805 three terminal regulator to give 0A to 1A current output.. It is similar to the circuit suggested by ronsimpson and MikeAI. The data sheet list below the schematic shows alternative three terminal regulators to give 3A or 5A output current.

Input and output capacitors are shown. These are minimum values. Any values more than the minimum will be suitable. If the 2F (Farads) is correct for those two capacitors they should not be used as they will be the wrong types (HI-Caps). The two 4uF capacitors will be fine, but for the 3A and 5A regulators a 10 uF input capacitor, or over, would be better.

The regulator chip will remove any low frequency noise and the capacitors will decouple the high frequency noise, so you do not need to worry about that.

This circuit will provide you with a highly stabilized 5V supply which will be both over current and over temperature protected and will be ideal for powering a USB hub. It will also be simple to build and will not cost you the earth.

spec

 

[realflow100]

I have two 3,300uF capacitors rated 50V is that too much or would that be alright? I'd like ultra stable voltage output that doesnt drop with increase in load. but I want to use a high power 3-5A regulator so i have plenty of headroom with less heat generated by the regulator.
Can it work like that?

 

[spec]

I have two 3,300uF capacitors rated 50V is that too much or would that be alright? I'd like ultra stable voltage output that doesnt drop with increase in load. but I want to use a high power 3-5A regulator so i have plenty of headroom with less heat generated by the regulator.
Can it work like that?

One 3,300uF capacitor on the input would be good and would ensure that the ripple voltage at the input would be low. But you would still need a 330nF low loss capacitor (ceramic, polycarbonate) in parallel with a big capacitor like that to handle the high frequency filtering. Let us know which of the regulator chips you are going to use and we will be able to work out a definitive design for you. The two higher current regulators, being low dropout types, as ronsimpson said, are much more touchy about capacitors than the 7805.

 

[AnalogKid]

I want to use a high power 3-5A regulator so i have plenty of headroom with less heat generated by the regulator.

Nope. The heat generated by the regulator is calculated with Watt's Law, P = E x I, and is be exactly the same no matter what the current capability of the devices. In a linear regulator, the majority of the heat dissipated is the voltage across the pass devices times the current through them. So if the regulator has a 12 V input and a 5 V output, and makes 1.5 A, then the power dissipated is (12-5)x1.5 = 7 x 1.5 = 10.5 watts. 3 amp part, 10 amp part - don't care.

You will get better long-term reliability if you use a 3 A part in a 1 A circuit, but the heat will not change.

ak

 

[spec]

Hi real,

Here is a 5V voltage regulator that uses a variable 5A three terminal regulator which is less critical of capacitance values than the low drop out (LDO) types. Although the LM338 is not a LDO regulator it will still have a comparably low drop out voltage at currents up to around 2A.

So long as you fit the two capacitors shown, which must be ceramic types, you can fit whatever additional capacitors you wish.

Being adjustable, later on you can set the output voltage to 5.25V which, when line drops are taken into account, is best for a USB source voltage. That will give you better charging of USB devices, mobile phones etc.

The LM338 voltage regulator costs around the £2 UK mark.

spec

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ERRATA

NOTES

DATA SHEETS
(1) LM338 Voltage Regulator 5A
**broken link removed**