Microcontroller power source

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haneya

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Hello, this is my first post here, I hope that it is on the right section.
I am working on a project based-on microcontroller, I completed the design on a simulation software(ISIS), its known that ISIS neglecting the voltage source, so I dont know how to provide the voltage supply to microcontroller (my power source is ATX PC power supply), I know that 5VDC should be connected to microcontroller through resistance the problem is that I don't know how to calculate the required resistance.

I will attach the schematic design for my project, I need some help with the required resistance.



Am using PIC 16F877A
Power supply specifications: red 5v 20A, purple 5vsb 2A, yellow 12v 8A.

Thanks.
 

More than anything else, while connecting low-current circuits, such as yours, to high-current power supply, such as ATX, you need a protection circuit, not just A RESISTOR ..
An example of such a device is called PolyZen, see details here:
**broken link removed**

If you can’t get hands on that stuff you can consider a small-ohm, low-wattage resistor followed by 5.6V Zener diode ..
Resistor, for example 0.5ohm/0.5W, will act as a fuse and the Zener diode will protect your circuit against any overvoltage situation ..

Rgds,
IanP
 

Thanks IanP, I do have a regulator to provide a stable 5v an 1A, if thats what do you mea, but now is it ok to connect 5v (from regulator) directly to MCU ar it should be connected to a resistor ?



Thanks
 

The voltage regulator produces nice&clean +5V and that’s enough ..
Direct connection between the regulator and the microcontroller is all what’s required ..

Rgds,
IanP
 

    H

    haneya

    Points: 2
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Hi,
Pls remember your regulators dissipation-they need good cooling!
With 1A & max 28V inp = 23W is to dissipate!:-(
ATX delivers 12V too >> then is your dissipated pwr. only ca. 30% from that_ ~7W

As I know PC-Power supplies/switchers needs in all case (pre)load resistor on +5V``:-((
If you dont have it; is danger is that will bourns out....

Other side:
I belief that some small AC-Adapter (for ex.a 5V/ 10W switcher, as for scanner, lap tops...) is the best supply solution for yourt application.
K.
 

Thanks guys for the replies, I have a question, Is it necessary to use capacitors on the regulators and between VDD,VSS ?
Another problem I want your help with, what if I want to use the purple line (5vsb 2.0A) should I add any extra components that is connected to Microcontroller ?


Thanks.

Anas
 

Hi haneya,
I would recommend:
by supplying external is every time a serial diode to design into (anode is to the external connector) a circuit, as false poling protection....
If you have only an external power adapter:
forget then 5V regulator, C2,C3 & put C1 (100 uF, but min 10-22uF) direct to uP, II with 100nF_C4.
If you have the internal 5V regulator to:
You should have all as is + the recommended serial diode in external 5V connection.
K.
 

@ betwixt , I did thanks.

@ karesz, can you please draw a how the connections will lock like?

I am now even more confused, because am forced to use the 5Vsb 2.0A (purple line), that means the regulator will not work (at least 8v required).

@ IanP

can you show me a drawing that show the connection to micocontroller.


Am sorry if I ask for to much. Thanks
 

OK;
What version do you need pls?
K.
 


This one
 

Also, the cicuit from IanP?
On it I see purple for Uinp upto max 28V!
& two times red; at pin 7& 20 by ATmega & at pin2 from 5V regulator.
What is 5Vsb 2A please?
Is it instead Vin max +28V to find?
K.
 

On it I see purple for Uinp upto max 28V!
& two times red; at pin 7& 20 by ATmega & at pin2 from 5V regulator.
Click to expand...
No I didn't mean the purple line form IanP, I mean a purple wire that provides 5Vsb (stands for stand by voltage), it a wire that provide a 5V always, I mean even without running power supply.

Am using ATX PC power supply for my project.

Thanks.
 

Hli,
OK, yet did I understand what your purple wire is....
I belief, the scene is clear:
Your purple/+5Vsb put pls to the uP pins7&22 + C4 100nF, red signed as "from Vout +5V ", additional apply an10--100uF parallel with your C4_practically the existent C3.
Then you can eliminate C1 /C2 & the 7805V regulator_ this was what I wished to suggest for you, but my simple english:-(
K.
 

Thanks karesz, I guess this will work with me, am sorry I didn't understand you at the first post. when It comes to English then we are on the same boat
 

That is life!... Important is only: we wish understand us...
And dont forget pls: as I know, must PC pwr-supplies need a +5V load!!
YOu must search for that,I dont know what is the minimal load, but I do become 2 from my examplares dead, then I didnt applyd some (basic)load...
Good luck!
K.
 

    H

    haneya

    Points: 2
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