Powering 16F628 From Stable 12vDC

Hello boys and girls,

I would to know which is the best way to supply my pic with 5VDC/300mA from 12VDC/5,2A.

A Step-Down DC-DC Regulator(like max726) is the best way to do that?

Best regards
Nikos Geronikolos

LM7805 and some capacitors is also a good alternative.
Also much cheaper.

I make a mistake!!
I want to step-down my supply from 24vDC to 5vDC.

Dear Mat I try to use LM317 from 24V TO 8V and then with lm7805 from 8v to 5V but the LM is getting too much hot.I do not understand the reason why!!
The LM has output current 1,5A.My current consuption is 300mA.

Hi N' geron'

24v- 5 v = 19 v

19v x .3a = 5.7 Watts

With no heatsink :

temp raise is ~ 70°C/ Watt for a TO 220 case ...

so, your regulator should raise to 400°C ( LoL !!! ) ... if there were no Thermal Shutdown !!! ( 130°C )

So, you MUST use a 5 to 7°C/Watt heat sink ...

( or better a switching supply ... with a nice glitch filter !!! )

Alain

When you take 300 mA and the voltake over the LM317 is 24 - 8 = 16 volt. The power into the LM317 is 16 x 0,3 = 4.8 watt.
So you have to cool that power down. The power in the LM7805 is less 0,3 x 3 = 0.9 watt. For this power you need also cooling.
LM2578 is may be usable

Hi Acetronics,

Could you please suggest me a common switching supply.
Do you mean dc-dc step down converter?

Quote:

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Originally Posted by ngeronikolos

Hi Acetronics,

Could you please suggest me a common switching supply.

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That's the kind of question I CAN'T answer : you live in a different country with a widely different market !!!

> Do you mean dc-dc step down converter ?

Yes, National has lots of down converters, in the LM 25xx series you mentionned.
And the Datasheet is really crystal clear for components around ...
do not forget a small ( LoL ) heatsink will also be necessary ...

Alain

I use for a lot of applications the LT1933. (Linear Technology)

A very small device, external a few resistor, diode and 1 coil of 22uH.

See the internet for specs.

We currently use th LM2574-5.0 just for this reason. Our 5V line require around 200mA-300mA which when run through a linear regulator I could probably heat my house since our source voltage is 24VAC which comes up to around 30-35VDC. The regulator works quite nice and is pretty cheap. I've run it up to about 350mA-400mA and it does get warm to the touch but not hot by any means.