Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

lm324 voltage follower o/p behaviour

Status
Not open for further replies.

sabu31

Advanced Member level 1
Joined
Jan 28, 2011
Messages
408
Helped
12
Reputation
24
Reaction score
12
Trophy points
1,298
Activity points
4,796
Hi

I am using LM324 as a voltage follower. The Supply to opamp is 5V and -ve supply is ground 0. Two strange behaviours i am getting from the opamp.

When i directly connect the probes to o/p of opamp, there is amplification of input spikes. The voltage follower behaves normally, when a 100ohm load is connected, but it gets saturated at around 2.65V, ie.. o/p does not increase even if input is increasing. In datasheet its mention that o/p short circuit current of opamp is 50mA, but 2.65V at 100ohm is 26.5mA.
The saturation is avoided if I use 300ohms resistor . and if use a lesser value resistor like 20 ohms , it gets saturated at around 1V and there is amplification of spikes. I feel there is something related to loading, but not clear. Can somebody clarify this. Thanking you.
 

The sink/source currents are given at 15V supply, so don't expect them to be near those values at 5V ..
The output won't go higher than, say, Vcc-1.5V and lower than GND+0.9V ..
If you want an opamp to perform well within the supply voltage range you have to select one that is rated for rail-to-rail (output, input or both) operation ..

:wink:
IanP
 
  • Like
Reactions: sabu31

    sabu31

    Points: 2
    Helpful Answer Positive Rating
Hi

Thanks for the reply. Does that mean, that it will be linear upto 3.5 and then start saturating . Or the output will saturate as it tends to towards Vcc-1.5V, say from 3V onwards (in case of 5V Vcc).
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top