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Lf 198 sample and hold

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Shreehari

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I am rigging circuit sample and hold circuit using LF 198 but when i make S/H(BAR) low it is not holding the value of sampled..Pls suggest me a soln..I am using 0.01 m icro farad capacitance.
 

Yes I am operating as in datasheet.But can i change the capacitor value for better results?
 

The datasheet shows the circuit behaviour for capacitor values between 100 pF and 1 uF.
 
no man It didn't helped me ...circuit samples the DC VALUE but when it is held it varies as input varies..
 

So here is the brief description of my circuit


pin no 1 to 12v
pin no 2 NC
pin no3 to 2.4 V DC
pin no 4 to -12v
pin no 5 to Multimeter
pin no 6 to pin 7 Capacitor 0.01 microfarad
pin no 8 to +5v DC

Now I am getting 2.4 V dc at the output pin no 5.But when I make pin no 8 to 0v dc then also I am getting the same value.When I increase the input at here(while pin no 5 is still OV)then output follows input.It should not happen right?it should be same as 2.4V dc. I have a problem here.

---------- Post added at 07:24 ---------- Previous post was at 07:21 ----------
 
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oh sorry I didnt referred there... pin 7 is connected to ground..
 

Then I don't see a reason why the circuit isn't working. Maybe the device has been damaged.
 

I tried with 3 different ICS But there is no change in the observation.
 

It's a long time since I used the part in a design. But I never experienced any problems with it.
 

ok...is there any other simple idea to construct sample and hold circuits..if any pls provide me the information...
 

You can use an analog switch and two OPs, and build a circuit according to the LF198 block diagram.
 

wats there C1?
Click to expand...
Obviously it has to be connected, too.

P.S.: To answer more generally, I simply wanted to suggest the LF198 functional circuit as an example, how a S&H can be build. A specific detail of the LF198 is the feedback from output to the first stage. It's not the only way to realize a S&H, and it may need special measures in frequency compensation. A more basic circuit uses a simple OP buffer as first stage, and another buffer for the second stage.
See: Sample and hold - Wikipedia, the free encyclopedia
 
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hello FVM ..


I have problem with capacitor in building LF198 circuit..it is not charging aand discharging as i required?changed the capacitor but still have the same problem..
 

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