36
votes
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What does this transistor circuit do?
The circuit topology is that of a capacitance multiplier designed to remove ripple from a 'dirty' regulated power supply. The name stems from the fact that the value of the capacitance seen from the ...
- 4,129
18
votes
What does this transistor circuit do?
"Capacitance multiplier" is a striking but somehow confusing name for beginners who can take it literally. So it needs to be well clarified what exactly this circuit does.
At first glance, ...
- 19.5k
14
votes
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How to design a good common-collector amplifier?
The problem is that the NPN transistor can only "source" the current and cannot "sink" current (current can only flow out of the emitter and never flow into emitter).
In your ...
- 15.7k
12
votes
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What is the basic idea behind the so-called "diamond buffer"?
Here are my thoughts after taking a good look at the diamond buffer.
To simplify things, I'll assume a load at the output is sinking current to ground, so that the lower half (the "pushing" ...
- 47.3k
11
votes
Why does the emitter follower clip?
The emitter follower can only pull the output voltage up (positive), it can't push the output down.
Rload and Re form a voltage divider between Ground and -12V. If the transistor wasn't there, the ...
- 60.8k
10
votes
Down-converting voltage
It should work within the limitations of the opamp and the transistor.
The opamp limitations include its power supply range, input and output voltage range, and output current capability.
The ...
- 315k
10
votes
What does this transistor circuit do?
No, it is not a capacitance multiplier.
In order to be one, it needs a voltage divider to ensure enough Vce for the transistor.
Here, we don't have one and cannot reliably keep the transistor in ...
- 9,686
9
votes
Transistor Driver - what is the purpose of Q2 on the included schematic?
Q2 is not simply a B-E diode, it is an emitter follower.
Without Q2, R1 pulls up with about 10mA, driving the load rather modestly. This is okay for small loads, like logic-level inputs, or even ...
- 45.6k
8
votes
Emitter follower voltage regulator misbehaving
An emitter-follower operates on the principal that the base-emitter voltage of a forward biased transistor is approximately equal to 0.6 or 0.7 V. So for some input voltage on the base, the emitter ...
- 3,062
8
votes
What does this transistor circuit do?
This circuit is a low-pass filter (R and C) followed by a voltage buffer. Some people call it a capacitance multiplier, but it does not multiply the capacitance.
There are three problems with the ...
- 1,407
8
votes
What is the basic idea behind the so-called "diamond buffer"?
Referring to this schematic:
The basic idea is a zero-offset follower. Consider just the top half for example (T1, T2, IE1, V+, RLOAD). Note that T1 emitter is VBE above Vin, and only sinks current;...
- 45.6k
8
votes
Unity Gain Amplifier Purpose
Unity gain generally refers to the voltage gain of an amplifier, but there is also current and power gain to consider.
The typical use for a unity gain buffer is to amplify the current while keeping ...
- 27.9k
7
votes
Accepted
How to select resistor for emitter follower when driving speaker?
As you know, the peak AC input signal for delivering any particular power into any particular speaker load is:
$$V_\text{P}=\sqrt{2\:R\:P}$$
In your case, with \$1\:\text{W}\$ and \$R_\text{SPKR}=4\:...
- 78.7k
7
votes
Transistor Driver - what is the purpose of Q2 on the included schematic?
Compare the performance with and without Q2 (100kHz with 0.6Ω resistive load):
Without Q2 (specifically with Q2 connected as a diode) there is only the 1k resistor to charge the gate capacitance. So ...
6
votes
Designing a stiff voltage source using an emitter follower
First, we know that \$V_{base} \approx V_{emitter} + 0.6V\$ and that the exercise is asking us to keep \$V_{emitter}\$ within 5 and 4.75V (5% tolerance) when \$V_{base}\$ is driven from a voltage ...
- 391
6
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(logic level) Gating the output of a 900hz (5v p2p) oscillator
I think I'll just answer b):
is there a different approach for generating a logic enabled 900hz audio tone ? (…for fastish logic switching from the mcu)
You already have an MCU. Practically all ...
- 100k
6
votes
What does this transistor circuit do?
I've seen this used as a "super capacitor", to provide slightly lower VDDs, but with much cleaner (much less 60 Hz and 60,000 Hz supply ripple). In particular, this was in a set of RF ICs ...
- 35k
6
votes
Accepted
Why do I have clipping in this emitter follower
The output voltage can only go negative by the transistor reducing its current and allowing current from the 8-ohm resistor Re to flow through the load. But as it does so the current through Re will ...
- 34.2k
6
votes
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Emitter follower as single-ended power amplifier
Can't we use only a single transistor in emitter follower configuration to have a single-ended class A power amplifier
Sure we can, I guess you mean something like this:
simulate this circuit –...
- 81.4k
6
votes
Unity Gain Amplifier Purpose
It means buffering the same signal out but with stronger current-providing ability, without loading the weak source signal by applying too much load.
For example if you have a weak source like a ...
- 172k
5
votes
Accepted
Linear regulator using emitter follower and operational amplifier
An emitter follower has a minimum voltage drop below the Vout of the op-amp of about 700mV. If the op-amp can be supplied with a higher supply voltage than input voltage you can reduce that to tens or ...
5
votes
Art of Electronics: Emitter-Follower Zout
As pointed out earlier to the OP, when you "delta" a constant, it disappears without a trace. I am a learner too and I have been battling with this part of the same book. I don't understand why the ...
- 229
5
votes
The need for a current source in an emitter follower
When biasing a transistor, you want to Q point to be stable. Since \$\beta\$ varies a lot, you want to design in such a way that changes in \$\beta\$ do not disturb the bias point.
By placing a ...
- 5,784
5
votes
Why does the emitter follower clip?
It might be easier for you to understand why output voltage is clipping at -2.1V if we redraw the circuit and change the reference point (GND) position.
As you can see I moved the GND and I hope ...
- 15.7k
5
votes
(logic level) Gating the output of a 900hz (5v p2p) oscillator
Just use the reset pin on the 555.
- 10.1k
5
votes
Accepted
Why is the base resistance suggested to be one-tenth of the emitter resistance times beta?
The factor of 1/10 is a crude, rule-of-thumb rule used to design voltage-dividers, where a load resistor may be connected to the output.
If you want your voltage-divider to maintain a certain output ...
- 11k
5
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Why is the base resistance suggested to be one-tenth of the emitter resistance times beta?
@wbeaty already gave an answer in regard to the voltage divider, and why you don't want to load it too much. But here's another way to look at it, and I think is relevant in BJT biasing. \$\beta\$ is ...
- 5,784
5
votes
Accepted
Op amp Power supply splitter with totem pole
But while I was looking at it, I noticed that since both transistors need to be (almost/close to) half way open, they will act like a resistor and will just sink current to GND (the original GND) even ...
- 19.5k
5
votes
What is the basic idea behind the so-called "diamond buffer"?
I was curious to see just how this diamond buffer performs, so I made this LTspice simulation. I adjusted the bias resistors R1 and R2 to just barely exhibit clipping with a 4.5 V sine wave and 5 VDC ...
- 7,645
5
votes
Accepted
Emitter Follower - Normal BJT vs Phototransistor
In a phototransistor, light falling on the base region generates electron-hole pairs which control current flowing through the transistor just like B-E voltage would do in a standard transistor.
In ...
- 81.9k
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