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8 votes
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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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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
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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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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
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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
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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
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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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0 votes

BJT Push-Pull explained

Just a visualization change will help..visualize the capacitor as impedance(resistor symbol connected to ground and the high frequency harmonics of pulse causing current to flow in it, in turn ...
dhuwarkesh's user avatar
0 votes

How to improve gain for CC-CE-CC amplifier

When designing discrete transistor amplifiers, it is helpful if the oscilloscope is set to DC coupling so you can see where the DC bias are. The gain of the middle stage needs to take in to ...
qrk's user avatar
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0 votes

How to improve gain for CC-CE-CC amplifier

Several things: You have three stages, but only one has gain. You're trying to design it to get a particular amount of gain. It's likely that the gain drop you see when adding the third stage is ...
GodJihyo's user avatar
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0 votes

NPN transistor as a switch configuration

Will this configuration values will okay in the long run or is a fail? and max \$I_C\$ current from 50-60 mA. It comes down to how low you want the saturation voltage to be. Consider this data ...
Andy aka's user avatar
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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
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0 votes

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

The transistor creates no energy. It sources current into a load that provides the energy. In common emitter configuration, with a resistive load R connected to voltage V, the transistor will saturate ...
John Doty's user avatar
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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
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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
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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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7 votes
Accepted

BJT four-resistor bias circuit analysis, parallel resistors

Thevenin's theorem applies as follows:
Franc's user avatar
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2 votes
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Class-A power amplifier magnitude and phase

then to compare the phase, the sample is going down then sudden increase, then going down again, whereas in my simulation, the phase is just going down. The graph jumps from -180° to +180° and ...
Andy aka's user avatar
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1 vote
Accepted

Bipolar Junction Transistor operating modes

1.) Definition of saturation: The voltage drop across the collector resistor (caused by the collector current Ic) must be large enough to make Vb>Vc. That means: The base-collector-junction now is ...
LvW's user avatar
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2 votes

Reconciling High Drain Voltage with Typical V_BE Drop in nMOS+PNP IGBT Configuration

The IGBT is indeed constructed as as per the bottom diagram on your question. The NMOS transistor does indeed block the full voltage that is across the IGBT output terminals. A simple equivalent ...
Fabio Barone's user avatar
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0 votes

How to find the output impedance for the unbypassed Common-Emitter Emitter bias configuration when ro presents?

The equation you give matches perfectly equation (27) from the book that you presumably are referring to. However, there seems to be a problem with either that equation or the circuit drawn in which ...
HarryH's user avatar
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