8 votes
Accepted

Why is the frequency and voltage of my Colpitts oscillator lower on breadboard than LTSpice?

A breadboard will have capacitance between the connection rows. The jumper wires will have inductance. Real components will have parasitic resistance, inductance and capacitance that a simulation may ...
GodJihyo's user avatar
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6 votes

BJT four-resistor bias circuit analysis, parallel resistors

Let me provide a different way of looking at it. It may be simpler to see your question with regard to \$R_1\$ and \$R_2\$ using math. Let's keep the BJT base current in place and assume that it is ...
periblepsis's user avatar
  • 9,055
4 votes

BJT Push-Pull explained

Each bipolar transistor, by itself, is a voltage follower. The upper transistor pulls up to Vin-0.6V, and the lower to Vin+0.6V. With this kind of circuit it is impossible for both transistors to be ...
hacktastical's user avatar
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4 votes

I don't understand how transistors are used as a switch

In this case the transistor allows a small current to switch a larger current, so a switch with a lower rating can be used. This could also be done with a relay, but transistors are much smaller and ...
GodJihyo's user avatar
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2 votes

Simulated 741 op amp has unexpectedly small output swing

First of all, the 741 needs dual supply. With +/- 15 V power, the output range is +/- 14 V according to its datasheet, or -13.3 V to 14.3 V according to simulation. Also, in your first LTspice ...
Shuo Chen's user avatar
2 votes

BJT Push-Pull explained

First of all, you can have a potential without any current flowing. Even if the emitter is "floating", it will still have a potential, notably, 1 diode drop different from the transistor ...
MOSFET's user avatar
  • 3,110
2 votes

BJT four-resistor bias circuit analysis, parallel resistors

The answer to your question depends on the node which is used to "look" into the circuit. 1.) When you look into the circuit from the upper node (Vcc) you see a resistor which equals a ...
LvW's user avatar
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2 votes
Accepted

What is the difference between using op amp and transistor for small signal amp?

A typical opamp has a differential input with high impedance, very high voltage gain, and very low output impedance. This is useful for many applications; for voltage amplification specifically it ...
vir's user avatar
  • 18.5k
2 votes

Why is the frequency and voltage of my Colpitts oscillator lower on breadboard than LTSpice?

I changed some components and I retain ultimately this behavior.
Antonio51's user avatar
  • 13.4k
1 vote

Multi-Stage Amplifier Help

I would start with designing the output stage; this would be a voltage follower unity-gain stage (an emitter follower, or common-collector). I would prefer to use split power supplies because that ...
Fabio Barone's user avatar
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1 vote

What is the difference between using op amp and transistor for small signal amp?

You mentioned two (2) applications that are very different; for these two applications, let's compare the pros and cons of using (a) a simple transistor solution (using only 1 or 2 transistors), and (...
Fabio Barone's user avatar
  • 2,369
1 vote

I don't understand how transistors are used as a switch

In the circuit you showed us, the transistor isn't really doing anything that you couldn't achieve with just a switch, and as such it doesn't demonstrate the real benefits of transistors. The purpose ...
Simon Fitch's user avatar
  • 35.2k
1 vote

I don't understand how transistors are used as a switch

In your "simple voltage source-switch-resistor-lamp" circuit, the switch has to carry the entire current of the lamp. Depending on how much current the lamp takes, that could be a very big ...
Hearth's user avatar
  • 32.6k
1 vote

I don't understand how transistors are used as a switch

The 25 W lamp in your 24 V circuit will draw 1 A from the power supply. What happens if you want to switch this on using a tiny touch button capable of 50 mA max? The transistor in this circuit ...
Transistor's user avatar
  • 176k
1 vote

NPN transistor as a switch configuration

The rule of thumb for transistor switches is to make the base current 1/10th of the collector current to force it into saturation. This would put you at around $$ R1 = \frac{V_{in}-V_{BE}}{I_B} = \...
GodJihyo's user avatar
  • 23.4k
1 vote

If a BJT can be modelled as a current-controlled current source, is there any limit to the load resistance?

The premise of the question is wrong. It would be correct to say that a BJT can sometimes be modeled as a current-controlled current source. As far as "when" is concerned- it depends.
Fred's user avatar
  • 356
1 vote

Simulated 741 op amp has unexpectedly small output swing

As Shuo Chen pointed out in his answer, R3 in your first schematic should be 4.5 k\$\Omega\$, not 4.5 \$\Omega\$. A simple non-inverting amplifier has two resistors in the feedback network. These are ...
Math Keeps Me Busy's user avatar

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