Hello, I am new in electronics and I would like to understand the function of the circuit with ref195. Is there anyone who can explain it to me please?
The schema is in the picture. I would like to use the NPN 2n3903 (OFF/ON voltage 0 V/5 V) instead of PNP.

 

hi hra'
Welcome to AAC
To use a NPN to control Sleep mode.
Pull up resistor to Vcc in place of the PNP
and use a NPN in place of the resistor, to pull /Sleep to 0V,
Do you follow OK.?
E
EDIT:
Please post the remainder of the original circuit, it appears that you are trying to generate a negative voltage reference.!!!

Reading the d/s shows that for correct Sleep control the transistor must be PNP.

 

Thank you for your respone.
Well and if i want to use the PNP, which on/off voltage should i use?
I did a simulation in microcap. I have to use Vs=12 V
It looks I must use 12 V for OFF and 0 V for ON. Is it possible?


Can you explain me the function of the rest of the circuit please? Thank you

 

hi,
The problem is that REF195 is connected with its Gnd at -5Vref.
If you are using a Vs of +12v, I do not see how the d/s can claim, /Sleep control using TTL voltage levels.???
The 2N3906 would never be switched Off.

You would have to use a 12V/0V levels to control the PNP.

One option would be to add an NPN transistor that controls the 2N3906.

I will check your circuit.

E

 

It looks I must use 12 V for OFF and 0 V for ON. Is it possible?

Thats correct.

If you use a pullup to Vsupply PNP base, then an open drain MOSFET or open
collector driver to the PNP base will allow a much lower logic swing to shut off
the PNP. In case of MOSFET that would be 0 to Vgson, NPN would be 0 to .7V.

The integrator basically operates as a servo loop to control gnd rail of ref to
force differential voltage of ref output to ground to stay fixed at Vref. Its used
open loop, eg. gain very high, but integrated to limit noise generated by the
control loop.

Regards, Dana.

 

The scheme is from datasheet of ref195 (http://www.analog.com/media/en/technical-documentation/data-sheets/REF19xSeries.pdf page 22, you can check it). It's a school project and I would like to know how the circuit works.

 

Can you explain me the function of the rest of the circuit please?

When the circuit starts, the Ref Output is positive.
Since the integrator (+) input is at circuit common, this causes the integrator output to start going negative, which also pulls the Ref Gnd negative.
When the integrator output equals the Ref Output-t0-Gnd reference voltage, the Ref Output to circuit common is 0V and the integrator output stops (which is now at a voltage equal to the negative of the Ref-to-Gnd voltage).

The same function could also be done with a simple two-transistor inverting opamp configuration, but its accuracy is determined by the resistor tolerance, and resistors with better than 1% tolerance are expensive.
The integrator circuit's only inaccuracy is the input offset voltage of the integrator op amp.
It would require perfectly matched resistors to get the same accuracy in the inverting circuit.