Questions tagged [current-mirror]

Current mirror circuits enable the mirroring of the current flowing somewhere else in the circuit onto a path of interest. Typically used in non intrusive load current measurements.

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Is a current mirror necessary if LEDs are binned?

I have a 20VDC input with a buck CC LED driver, driving 48 LED strings of 6 x 3V LEDs in series. I am underdriving the LEDs at 60% of rated power. Each LED string consumes ~33mA. The LEDs are ...
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How does the attack / release element of this audio compressor function?

This is an audio compressor circuit based on (and designed by the makers of) the THAT 4301. U2B converts the AC input to RMS, which is then inverted by U2D. When there is no signal input to the ...
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How does current flow when you short base and collector in a current mirror?

I am studying analog electronics and I don't understand how current flows in a current mirror when you short base and collector together. Electrons are being injected from the emitter into the base ...
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Constant current power supply and 4 unique loads that I would like to individually control via PWM. Loads are to be driven at varying currents

I have a 1400ma constant current power supply (plenty of power to drive all loads at 100% duty), and I want to PWM 4 separate loads that are all driven optimally at either 350ma, 700ma, or 1400ma. The ...
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Current increase in a Current mirror

I am watching lectures by Behzad Razavi. In one of his lectures he shows this circuit and explains that as the current increases in Ma the current also increases in Mb, due to which Mb will push more ...
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How does the current mirror stabilize tail current in an op amp?

Op amps often use the "slave" side of a current mirror to provide the tail current for the input transistor pair, such as in this simple op amp voltage follower schematic: The "gates&...
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Why this 4-bjt current miror got better precicion?

I just wonder how precise of 2-bjt current mirror circuit then I found this circuit from link form circuitlab.com My question is How much we can rely on 2-bjt how to determine how precision there ...
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Designing current mirror

I have a 105V/3A output current source, and I am trying to get a current mirror circuit to pass 10-100 uA DC across 5 lanes that have very high impedance (around 1 MOhm). What is the best/quickest way ...
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Can't understand how the Zener voltage reference works

I've built a small amplifier circuit in which I've wanted to use a Zener diode as a reference but I can't figure out how it works. Knowing that the negative rail is -5V and the Zener breakdown ...
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How to drive dozens of LEDs with the same current without a constant current LED drive IC?

Let's say I have an array of many indicator LEDs that I need to turn on/off independently; the LED current is about 1 mA. In the past I used constant sink LED driver ICs such as the TLC5916 as shown ...
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How can a current mirror be adjusted to create a ratio between the reference and the output current?

I am working on a project were I need to pass a current through a load and a larger multiple through a different load. Hence if I pass 100mA through this load I need to pass approx 10A through the ...
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Voltage Controlled (w/ op amp) Wilson Current Mirror Can't Actually Mirror (Missing something)

I'm working on a current mirror circuit and I'm in a little bit of a problem. I have a current mirror circuit, which is supposed to, well, mirror the current, except that the current in the "copy&...
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Long tail amplifier using current mirrors

I have built this in the Multisim simulator and it works there as desired. Now I have built it on a "lame" breadboard. Is the upper PNP current mirror correct? Since the "left" ...
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Can current mirror branches be connected to different sources

Can the branches within a current mirror be connected to different sources as shown below? The aim is to provide the high voltage required by each LED but reduce the voltage across the resistor R1 in ...
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How to ensure the correct supply voltage when using a current mirror

I am trying to design a current mirror with a constant current source and 2 parallel LEDs (I have to connect the LEDs in parallel and cannot use a separate current source for each LED). If each LED ...
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Will a current mirror prevent thermal runaway of these LEDs in parallel

The source is a constant current LED driver. I found that connecting the LEDs in parallel caused thermal runaway with one LED consuming nearly all of the current with its temperature constantly ...
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Why use diode connected BJT (and not just connect two BJT back-to-back) for current mirror circuit?

I have been studying about current mirror circuits using BJTs. The circuit I have is this: For the left BJT, it says: IC1 = Io(e^(Vbe1/Vt)) This is understandable ...
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PMOS current mirror acting wonky in Simscape

I am trying to model a current mirror, seen below, solely built upon PMOS. This should not be a hard task because the theory and implementation are straightforward. What I do get when I model it in ...
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Qualitatively and quantitatively finding the transient response of a current mirror

In a current mirror circuit, when Iss is doubled or multiplied by a factor, it takes some time to clone those values and reach the steady state. I varied the width of the transistor and found that the ...
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3 votes
3 answers
711 views

Current mirror LED circuit with constant current source

I am trying to temporarily fix a current mirror circuit for driving 40 LEDs. Each LED in the circuit represents a custom LED strip that has a forward voltage of roughly 145V and a forward current of ...
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Error: Multiple analyses requested in LTSpice

I am running the following simulation in LT spice but I am getting the following error: Multiple analyses requested .trans 0 100m 90m 1m .op Here is my circuit. ...
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Current Mirror Controlled Switch

I'm trying to understand how Vg is calculated in this circuit below. I understand the current mirror is meant to protect the SMPS from current flowing into the output of J2 if the 12V source is not ...
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1 answer
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The load resistance in a MOSFET current mirror vs CMOS

In class I have learned that in a MOS current mirror like the one below, we can say that the load seen by M1 is equal to r_o of M2. This makes sense to me since I have drawn the small signal model and ...
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1 answer
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How do I find CMRR?

How do I find the common-mode rejection ratio, CMRR for this circuit? I know I have to find differential gain and common-mode gain as 'differential mode gain/commonmode gain' but with current mirrors ...
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Can anyone explain these conditions for the current mirror?

An important feature of the current mirror is a relatively high output resistance which helps to keep the output current constant regardless of load conditions. Another feature of the current mirror ...
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Question about diode connected transistor (BJT) with current source

I'm trying to find ΔV for this circuit, but I'm having a bit of trouble doing so. I think the current on the right BJT will be n times greater than the left, but I'm not sure about that either. It ...
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Potential In VA

I'm trying to find VA and I don't get something, is Ic1 = V+/20k, and then this current splits through emitters of Q1 and Q2? If so, then the voltage VA is 0? Also, I know that Q3 and Q4 are a ...
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3 votes
2 answers
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What is the point / name of this circuit? Reverse voltage protection + current mirror?

I stumbled across this circuit on page 8 of the Nano Pi Duo 2. What purpose does it serve? I recognize the MOSFET arrangement to be a reverse voltage protection circuit and the PNP transistors form a ...
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Op-amp with voltages in both inputs

I'm trying to solve a practice problem, which is represented by the schematic below. simulate this circuit – Schematic created using CircuitLab We are asked to relate the voltages \$V_1,V_2\$ ...
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2 votes
2 answers
703 views

Differential pair active load contradiction

I'm confused about one current-based explanation for why the active current mirror restores a differential pair's gain by letting each differential input reinforce the other. The explanation (from ...
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Low-voltage cascode current mirror biasing circuit

On the left is a low voltage cascode current mirror and on the right is a circuit whose left branch generates \$V_b\$ for the mirror. Razavi (Design of Analog CMOS Integrated Circuits 2nd edition, ...
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Huge current mirror circuit

I have a question about the circuit above. In the first place we can measure the current IR2 in given values, then using the current mirror topologies we can express IC7, IC8, IC3, IC11 and the other ...
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High Power BJT Current mirror

I am trying to find an example of BJT current mirror with high power consumption. Any advice concerning the setup , or an example design will be appreciated.
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what is current mirror?

I was looking for a high-level explanation about the current mirror but couldn't find it. Can someone explain what is current mirror using simple words? What does it do? and what is the real ...
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1 vote
1 answer
212 views

Why is the output current not equal to the input current in this current mirroring circuit?

Why is the output current not equal to the reference current in this current mirroring circuit? (I have been explicitly told that they are not equal). Both of the transistors are equal and in the ...
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789 views

BJT Current Mirror Problem

Problem: A simple current mirror is set up with two NPN transistors. \$V_{CC}=12\$ Volts \$+V_{in}= 30\$ Volts. Load resistance \$R_L\ =\ 1\ K\Omega \$. What is the resistance value interval for ...
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2 answers
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Problem in the output current of an PNP current mirror

I have a problem in the implementation of a current source, based on an OPAMP voltage-to-current converter followed by a PNP current mirror (see picture). Indeed, the output currents are identical to ...
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3 answers
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Built difference amplifier "tail" vs. SPICE models

I am working on a difference amplifier example lab 5L.1 from Art Of Electronics Hands on Lab Course (I am not a student). I simulated three types of "tail" circuits using SPICE. Then I built ...
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Differential Amplifier - Active Load Current MIrror Logic

I'm trying to wrap my head around the workings of a differential amplifier when a current mirror is used as an 'active load' With reference to this Youtube video leecture: here My understanding so ...
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3 answers
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How this current mirror act as a replacement to resistor Rc?

In this differential amplifier: The PNP transistor Q6 acts as an active load resistor and as a current mirror. Since current source Q6 has nearly infinite impedance, we will be able to have very ...
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Current mirror collector voltage

I'm trying to get the VGS of DMHC4035PMOS. Based on the simulation, I'm supposed to get -5.53V but I'm getting -8.2V on my PCB. Is there anything wrong with the design? What is the collector voltage ...
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A kind of current mirror design

Recenlty I saw a kind of current mirror circuit used to provide bias current for a differential amplifier. The circuit is posted below and I don't understand its working mechanism, as well as the ...
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438 views

MOS current mirror region of operation

The mosfet M1 is clearly in saturation as gate and drain terminals are shorted. Why we take M2 also in saturation? I know Vgs1 = Vgs2 and they are identical MOS but i cant justify why M2 should be in ...
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1 vote
3 answers
498 views

Is the transistor Q4 in the wide swing cascode current mirror operating in linear region?

In the wide swing cascode current mirror shown below, the transistor Q4 is in the linear region of operation according to the voltages at gate and drain. Is it not necessary for transistor to operate ...
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1 vote
3 answers
440 views

Matched biasing transistor vs. emitter resistor in current mirror

If adding emitter resistors can reduce the temperature variation in \$V_{BE}\$, why do we still need to find a matched pair of transistors to construct a current mirror?
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Specific current mirror explanation-source

I am trying to understand the following current mirror, though I haven't found any book that describes it. Is there any source in which I can see how it works and its pros and cons? The drawing is ...
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4 votes
1 answer
65 views

Current mirror configuration analysis in LM393

I've been trying to figure out how this comparator (LM393) works. So far I can recognize the sections: Q8, Q9, Q10, Q12 form the differential amplifier. Q15 and Q16 are the output transistors. Q1, ...
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1 vote
1 answer
512 views

Current Mirror Circuit

Below is a sample current mirror circuit. I understand that If the transistor Q1 is connected in a diode connected BJT configuration and the Transistor Q1 and Q2 have identical transistor parameters, ...
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1 vote
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DC voltage at the output of push pull stage

I have an output stage. The circuit diagram is as shown: In DC condition, the node X has a DC voltage of Vdd/2. The node Z has a voltage of about 1.26 volts. Vdd = 3.3 volts. Transistors M7 and M5 ...
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Modified Current mirror principle

Could somebody explain to me the principle of this current mirror? I don't understand why I throughout my R2 and R3 is not dependent on R1 (R bias)? My goal is to have 0,8V voltage drop on R3. Many ...
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