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# LM317: Output voltage observed even after input is made 0

Part Number: LM317

Hi,

I am using LM317 to convert 5V to 3.6V (schematic shown below)

When I made input 5V to 0 after some time, still i am getting 1.5 V at the output which is present for some 2-3 seconds before getting 0. Please let me know the reason for it and ways to make it 0

• Hi Manish,

Remember that capacitors usually charge to a certain voltage, it looks like you are getting some delay to fully discharge. Can you provide some of the curves showing this issue to further analyze this?

Best,

Edgar Acosta

• Hi Edgar

Blue curve : output of LM317

Yellow curve: Input of LM317

when supply is turned off, at that instant, input also doesn't goes to 0. it holds at 1.25V for certain duration, and during that time output stays at 1.04V.

I tried putting a diode between output to input, same observation was there.

Please tell me how to make it 0.

Case 1:

Input capacitor: 10uF and 0.1uF at input

Output capacitor: 10uF

case 2:

Input capacitor: 1uF and 0.1uF at input

Output capacitor: 1uF

case 3:

Input capacitor:  0.1uF at input

Output capacitor: 1uF

In all three cases, i am getting similar results.

Thanks

Manish Sharma

• Hi Manish,

It seems your output is tracking your input. You need to discharge faster. This can be done by adding a bleeder resistor between Vout and GND. Overall, your capacitors are not discharging fast enough. Please try using the bleeder resistor. If you have more doubts or problems please let me know.

Regards,

Edgar A.

• Hi Edgar,

Tried by putting a bleeder resistor (1Mohm, 10Kohm) at output of LM317.

in this case , the output is not building up.

Regards

• Hi Manish,

Sincerely,

Edgar Acosta

• Hi Manish,

Is it possible to get more detailed images from the oscilloscope showing Vin, Vout, and possible Iout?

Regards,

Edgar Acosta

• HI Edgar,

Above picture is having Vin and Vout image.

Regards

• Hi Manish,

My apologies, I meant a new picture depicting the output not building up and showing V/div.

Best,

Edgar Acosta