# What's this circuit is used for?

#### evandro bubiak

Joined Aug 4, 2015
12
I'm trying to figure out the usage of this part of the circuit.

Could someone help me?

#### DickCappels

Joined Aug 21, 2008
6,580
It looks a little bit like a sample-and-hold circuit. The voltage across the 2.2 nf capacitor as long as the current sources are powered by the + and - drive signals and when those signals are removed the capacitor (tends to) maintain the same voltage until the next time to take a sample.

#### evandro bubiak

Joined Aug 4, 2015
12
Reading another document, It says something about limiting the du/dt of the control signal. I'm still confused about it.

#### DickCappels

Joined Aug 21, 2008
6,580
You can use it for that too if the + and - signals are DC.

#### AlbertHall

Joined Jun 4, 2014
10,388
What's the rest of the circuit, what is it part of?

#### evandro bubiak

Joined Aug 4, 2015
12
You can use it for that too if the + and - signals are DC.
Yes, they are +- 15Vdc. But why don't use a simple RC circuit instead of those BJT?

#### DickCappels

Joined Aug 21, 2008
6,580
Because by limiting the charging current to a constant value the output changes linearly with time, in other at a rate of some number of volts per second, a opposed to the logarithmic curve of an RC circuit. I think this is common in industrial controls.

#### evandro bubiak

Joined Aug 4, 2015
12
Because by limiting the charging current to a constant value the output changes linearly with time, in other at a rate of some number of volts per second, a opposed to the logarithmic curve of an RC circuit. I think this is common in industrial controls.
Thank you!!! You opened my eyes!

#### evandro bubiak

Joined Aug 4, 2015
12
What's the rest of the circuit, what is it part of?
This circuit is part of a voltage controller board. The rest of the circuit are juste simple gaind circuit.

#### Ramussons

Joined May 3, 2013
871
My memory tells me It is an Analog Switch that uses a Diode Bridge Network.
When the diodes are Forward biased (conducting state), signals from the Left are transmitted to the Right.
When the Diodes are Reverse Biased, the transmission is blocked.
The 2 BJT's form a Constant Current Source.