Jump to content
Electronics-Lab.com Community
Sign in to follow this  
audioguru

was Re:Ir-remote Now is: Op Amp discussion

Recommended Posts

Kevin,
I don't understand you.
You didn't attach a sketch of whatever you are talking about.
In my last reply, I posted the data sheet for a 741 opamp. It doesn't have the diodes that you are talking about, and it uses transistor current sources instead of the collector resistors that you are talking about. Its input stage doesn't have a base resistor.
Did you see it? Would you like to discuss it?

Share this post


Link to post
Share on other sites

RI is your base resistor. The emitter resistance of the other transistor sees this base resistor. The impedance, looking at the emitter of a transistor, is resistance of the base divided by beta. RF is a collector resistor as seen by the output stage. You are right, there are no diodes. But there are PN junctions in parallel with the resistors that can be used to calculate the current.

You may not believe me when I tell you there is a different version of that circuit you posted. It's missing 2 diodes and a connection point. Anyways, the currents subtract with the upper current being higher and the load gets the rest of the current.

Share this post


Link to post
Share on other sites

Kevin,
You keep thinking that an opamp is a transistor. They are not the same.
An opamp is a complete amplifier with a voltage gain of about 200,000, a low-impedance symmetrical push-pull output and a high-impedance differential input. It doesn't need a resistor at its output to a supply voltage, like a transistor needs for its collector current. An opamp with + and - supply voltages usually uses 0V as ground. Its load is also usually connected to ground since its output is symmetrical.
The voltage gain of a complete opamp circuit is determined by the ratio of its external negative feedback resistors. Since the voltage gain of an opamp without feedback is so high, its output will swing to a voltage level that is controlled by its input voltage and feedback resistors, so that the voltages at its inputs are practically the same.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

×
×
  • Create New...