Dear Sir/ Madam,
I am Using LM1117 adj regulator for my project application.When i testing the circuit output I am getting voltage from 1.43 upto 4.93 Volts.
But the problem is when i came to check the current its showing '0'. The circuit connected as follows.
20V ,4.5A from SMPS to 1.33K Resistor to reduce to less than 15v.
Positive terminal to Pin no 3 of LM1117.
Ground to Pin 1.
from pin 3 to 1 having 10uf tantalum capacitor.
pin 2 has 100e resistor and its connected to 10 pot. The other end of pot is grounded.
And Having one more capacitor of 10uF Tantalum on output pin no 2 to ground.
Checking the output across second capacitor capacitor.
My application need 2.5v ,250 mA .
Please help to get the required output.
See Figure 1 in the LM1117 data sheet for connections for the '-ADJ' version. Note that the LM1117 GND/ADJ pin does not go to GND in the adjustable configuration
You did not mention exact package type, but the pin#'s narrowed the possibilities. For your application, the connections should look like this ...
Pin 1 = ADJ feedback pin
Pin 2 & TAB = Vout pin
Pin 3 = Vin pin
The seemingly low values for R1 and R2 are correct and are to ensure that the minimum load current requirement is always met, and keeps voltage errors due to the Iadj current at a minimum. The TAB=Vout is the same as Pin 2=Vout on the TO-220, TO-263 and SOT-223 packages, do not connect the TAB to GND.
I think the problem is on the resistor it self which is using to reduce less than 15v. because that emitting only 0.02A i think.. let me check and tell you what is happening ...
I am agreeing my connection also have error.. Thank you for clearing the path..
My apologies for not including a suggestion for the series R to drop voltage from 20V to 15V at 250mA
Vdrop = ( 20V -15V ) = 5V
I = 250mA (for load) + 10mA for regulator bias = 260mA
R = 5V / 260mA = 19.2 ohms
W = 5V x 260mA = 1.3 Watts
So, that's ~20 ohms, rated at 1.5W minimum
Thank you very much...
but one doubt....
Does it compulsory to connect the Tab pin to pin no 2 as per the diagram (Package TO-220)??
Pin 2 and the tab are connected internally on the device.It is not necessary to connect to both.
Regards,Ronald MichallickLinear Applications
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That query for confirmation. because in previous post it is connected to output.
Thank you for the support.
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