Hello. I'm obeying schematic rules but can't get 5V from the AMS1117 5V regulator with this schematic (see the attachment please). Input and output capacitors are 22uF and here the results:

R1=1K, R2=3K -> 1.6V~
R1=47, R2=150 -> 2.55~ and R2 is so hot.

If I dont use resistors, the output is 5V for a few seconds and then decreased to 1.6V and then the regulator is burning.

What is wrong with this cheap regulator?

 

hi,
How did you calculate R1 and R2.??
The Vref requires only 50uAmps.
What is the input voltage and the load resistance.??
E

 

I calculated by this page:
http://www.daycounter.com/Calculators/Voltage-Regulator-Resistor-Divider-Calculator.phtml

Input is 12V and there is no load, I just measuring the output with multimeter.

 

Check with the datasheet that you have correctly identified the pins on the regulator.

 

I cant say I wasnt in doubt about the pins. I dont know my regulator brand, bought from China, I checked a lot of datasheet and the pinout shown as in the attachment. The regulator packaging ia SOT223 and I used left pin as GND, center and tab as OUT and right one as IN.

 

Must be a wrong connection or wrong resistor somewhere. If Vout=2.55V, then even if R1 were shorted the maximum power dissipation in R2 would be 2.55^2/150 = 43mW. R2 would hardly get warm.

 

I used left pin as GND, center and tab as OUT and right one as IN.

That would be for the fixed voltage version, according to the datasheet. Yours is the adjustable voltage version!

 

The pinout is only the alternative I found so far but didnot try. See the attachment please. But if so, how I can get 5V without resistor even for a short time?

 

I cant say I wasnt in doubt about the pins. I dont know my regulator brand, bought from China, I checked a lot of datasheet and the pinout shown as in the attachment. The regulator packaging ia SOT223 and I used left pin as GND, center and tab as OUT and right one as IN.

Note the connections are different depending on whether it is the fixed or variable voltage version of the regulator. You are using the connections for the fixed voltage regulator, but the fixed voltage version doesn't need the resistors. The GND pin should be connected directly to ground.
What is the marking on the regulator? What characters (if any) follow the ASM1117?

 

Note the connections are different depending on whether it is the fixed or variable voltage version of the regulator. You are using the connections for the fixed voltage regulator, but the fixed voltage version doesn't need the resistors. The GND pin should be connected directly to ground.
What is the marking on the regulator? What characters (if any) follow the ASM1117?

All the text is:
AMS1117
5 H517

 

Check this list, you seem to have a 5V version.??

 

Please clarify. Have you got the fixed 5V output version or the variable output voltage version of the regulator?

 

I m not sure it is fixed or not. It just writes

AMS1117
5.0 H517

On the chip. I wasnt know pinout could be different between fixed or adjustable since the documentation is single for all types and there is only 1 pinout. Now it seems it is adjustable because it is burning when I connect GND pin to ground directly.

 

But I really confused. How could I positive voltage if pinout is wrong? The alternative pinout that I attached before is totally opposite of I applied.

 

I tried alternative pinout without resistor and burned again! Nonsense!!

 

What is wrong with this cheap regulator?

being incorrectly used?

I calculated by this page:

that's for the adj version.

you should really read the datasheet.

 

I read already. Maybe I did not understand or missed some important thing since my english is not so good. I tried lots of combination and I got 3.7V max. I m sure this is absolutely adj version, coz I need absolutely a resistor on gnd pin. Try to read datasheet again! So there is another schema with protection diode,what about it?

 

hi,
If you are confident that its a adjustable, make R1 a 220R, R2 a 620R and use a 9V dc input, don't forget the 10uF across R2.
What is the 5v driving into, ie: load resistance.?
E

 

this is absolutely adj version

Wire it accordingly then.

Ground the gnd pin, what output voltage do you get?

 

I would check the authenticity of the chip. I have a Chinese chips 74xx and 4xxx that dont work under feedback configurations that should work with real parts.
I suspect there is a chance that your regs are faulty.