Current Source

Hi,

I want to know what will the value of the "V4" that keeps the difference bewtween the inverting and non inverting inputs zero.

http://www.ecircuitcenter.com/Circuits/curr_src1/curr_src1.htm

jess

 

[John Fields]

On Mon, 23 Dec 2013 13:46:13 -0800 (PST), jsscshaw88@gmail.com
wrote:

Hi,

I want to know what will the value of the "V4" that keeps the difference bewtween the inverting and non inverting inputs zero.

http://www.ecircuitcenter.com/Circuits/curr_src1/curr_src1.htm

jess

---
Vin + Vbe(Q1)

 

[Maynard A. Philbrook Jr.]

In article <9287c88b-d08d-4f1e-84ba-075ccb5d1223@googlegroups.com>,
jsscshaw88@gmail.com says...

Hi,

I want to know what will the value of the "V4" that keeps the difference bewtween the inverting and non inverting inputs zero.

http://www.ecircuitcenter.com/Circuits/curr_src1/curr_src1.htm

jess

Not sure what node you are referring to, so I will assume it is #4 which
is the op-amp output node.

Transistors have an average band gap of ~650mV at room temperature and
it should be 650 mV more than what is at the emitter.

With that, you should be able to construct the rest. Good luck with
your home work.

Jamie

 

[Ian Field]

"Maynard A. Philbrook Jr." <jamie_ka1lpa@charter.net> wrote in message
news:MPG.2d229e9cdd98eed898971f@news.eternal-september.org...

In article <9287c88b-d08d-4f1e-84ba-075ccb5d1223@googlegroups.com>,
jsscshaw88@gmail.com says...

Hi,

I want to know what will the value of the "V4" that keeps the difference
bewtween the inverting and non inverting inputs zero.

http://www.ecircuitcenter.com/Circuits/curr_src1/curr_src1.htm

jess

Not sure what node you are referring to, so I will assume it is #4 which
is the op-amp output node.

Transistors have an average band gap of ~650mV at room temperature and
it should be 650 mV more than what is at the emitter.

Its basically a voltage follower developing a fixed voltage across the
current sense resistor, that voltage is within Voffset of the op-amp minus
the forward bias drop in the BE junction.

The fixed voltage developed across the fixed resistor forces a predictable
current to flow - this current (minus the transistor's base current) also
flows through the collector load resistor.

 

[Ian Field]

"Maynard A. Philbrook Jr." <jamie_ka1lpa@charter.net> wrote in message
news:MPG.2d229e9cdd98eed898971f@news.eternal-september.org...

In article <9287c88b-d08d-4f1e-84ba-075ccb5d1223@googlegroups.com>,
jsscshaw88@gmail.com says...

Hi,

I want to know what will the value of the "V4" that keeps the difference
bewtween the inverting and non inverting inputs zero.

http://www.ecircuitcenter.com/Circuits/curr_src1/curr_src1.htm

jess

Not sure what node you are referring to, so I will assume it is #4 which
is the op-amp output node.

Transistors have an average band gap of ~650mV at room temperature and
it should be 650 mV more than what is at the emitter.

Its basically a voltage follower developing a fixed voltage across the
current sense resistor, that voltage is within Voffset of the op-amp minus
the forward bias drop in the BE junction.

The fixed voltage developed across the fixed resistor forces a predictable
current to flow - this current (minus the transistor's base current) also
flows through the collector load resistor.