circuit connection of OPA860

1072.OPA860 IQ.TSCHello,

Can you please send a schematic of the circuit you are using along with some information on what kind of load the VCCS is driving. Please see the attached example of a split supply VCCS using the OPA861 which is very similar. We can modify this as we go along based on your needs.

-Samir

HI samir,

Thanks for the reply,

I dont have tina latest software, i cont able to see what you attatched. kindly attach PDF.

I am attaching the reference circuit of mine, in which i connected -vss to ground in buffers and opa860. the capacitor 2nd terminal is my load.

Is my circuit is ok if not suggests me changes.

Thanks in advance,

Rajesh

Hello,

 In your circuit you used a dc blocking cap on the C-Output. You then use some kind of servo to loop back into the E-input. There are 2 issues with this:

1. The E-input does not have a known dc bias on it since the dc information has been blocked by the 4.7u cap.

2. The C-Output will not be able to settle to a dc point since there is no dc path for the current from its output.

It is important to also comply with the voltage ranges for the 3-inputs of the OTA.

You need to download TINA from here to simulate your circuit. You can then use the TINA circuit I sent the last time to start playing around with the circuit.

I am not sure what the dc input on the B-pin is. Once that is known and you ensure that is in the compliance range (3.7V to 1.3V when using +5V and 0V supplies), we can then move on to ensuring the bias on C and E are also within compliance.

-Samir

Thanks for the reply,

my circuit working for split supply only i get to see that by using CRO, but  i want to to measure current and i want to control the current. In OPA860 what is the essential element to control current and also concerns  to my circuit. I removed dc blocking capacitor for DC bias as you suggested. my doubt is the circuit i attached above works as VCCS or not.

Thanks in advance,

Rajesh

This reply is continuation of previous reply,

'The input um giving is 1.69v sine pulse voltage(with various frequency range).

Hello samir,

Thanks for the reply,

In the software i'm unable to find OPA860, i think it is not there. Whether i check with the IC that u sent me

Vbe = 1.65v

and at the output im connecting resistors for up to 3.3k the output vp-p is ok if i increased the range of the resistor then the peaks are clipping.

On which factor that voltage depends can i decrease the vp-p by using RE or Riq.

Yes please use the TINA file I sent you to run the simulations. If you look through the datasheet and the characteristic curves it will clue you in on what settings are needed to get the right transconductance (V to I). Both Re and Riq can be used to set this transconductance value.