[SOLVED] output of lm358 is less than 3v!!!

[prasanthceg]

i made an ir sensor for line tracing using lm358 as a comparator.. i am getting the lm358 output as 2.5v.. so naturally when i connect it to the microcontroller, mc does not respond to the sensor.. can anyone suggest a solution for increasing the output voltage of lm358.. i dont wish to change the comparator further..

 

[FvM]

You didn't mention the supply voltage.

 

[albejanon]

Hi, LM358 is not a rail to rail opamp... I recommend you to use a rail to rail opamp to get full voltage. Any manufacturer designed rail-to-rail opamps you only have to search and you'll find... I hope this would help you.

 

[prasanthceg]

You didn't mention the supply voltage.

my supply voltage is 5v.. i tried increasing the supply voltage but in vain..

 

[FvM]

LM358 is not a rail to rail opamp

No, but it can drive logic level in most cases, though. Depending on the logic standard, a pull-up resistor may be required.
P.S.:

my supply voltage is 5v

Refer to the LM358 data sheet. You can expect about 3.8 V for the unloaded output. 2.5 V means the device is either defective or you're drawing more than 20 mA from the output, which wouldn't be a good idea. Check your circuit!

 

[prasanthceg]

You can expect about 3.8 V for the unloaded output. 2.5 V means the device is either defective or you're drawing more than 20 mA from the output, which wouldn't be a good idea. Check your circuit!

can u pls help me out for decreasing the current from the output??

 

[FvM]

If you show your circuit...

 

[prasanthceg]

If you show your circuit...

here is my circuit:

 

[FvM]

It seems absolutely correct. Did you try to drive the microprocessor pin from a resistor, if it's actually configured as input?

If the regular unloaded LM358 output high voltage of about 3.8 V isn't sufficient to drive the input, you can connect a pull-up resistor of 5 - 10k.

 

[prasanthceg]

thanks mate.. my problem solved..