# Questions tagged [current-source]

An electronic component that sources current - if it sinks current it is called a current sink but both devices (sinks and sources) can be called sources. An IDEAL current source will supply current , maintain high voltage compliance (i.e. adapt it's output voltage to match the network it is supplying current to) and have an infinite output impedance. In non-ideal implementations current sources have limited operating ranges and finite output impedances.

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63 views

### Op amp controlled LED current

I'm trying to implement a simple current control circuit for an LED from here: https://www.allaboutcircuits.com/technical-articles/the-basics-behind-constant-current-led-drive-circuitry/ The ...
40 views

### Current source resistor values in differential amplifier

In this circuit How measure input impedance this differential amplifier in LTspice? the OP has used a 4ma current source in a differential amplifier. I'm taking it apart to learn how it works. I see ...
96 views

### Trying to better understand voltage and current sources

I feel like I am going a little crazy here because the more and more I read about these things the less I understand them. So I understand that an ideal voltage source has no output impedance, no ...
37 views

### I have found the Rth=10 ohms, However i can't find the thevenin's voltage(between a &b)

*I converted the wye network into a delta and found the equivalent resistances in parallel and series and got it to be 10 ohms. However i am stuck at trying to find Vth. I tried applying mesh analysis ...
40 views

### Why does a source transformation not work in this case?

Circuits 2 and 3 give 3.8 mA as the current through R1 [2k Ohm resistor]. However, why is it not possible to transform circuit 3 to circuit 1? what I did: I tried simulating circuits 2 and 3 below to ...
50 views

### Find all currents with mesh analysis

Can anyone help with this priblem?
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### I don't understand current source, voltage source, infinite resistance, zero resistance etc

When I google things like voltage source and current source they talk about things like maintaining a particular level, having infinite output resistance, or zero output resistance, etc. I don't ...
693 views

### Reversed DIP Switch

Simple question, why does the LED lights up when the switch is off
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### Can we explain the differential pair in terms of resistances?

It has always been a big challenge for me to find the most general ideas behind great circuit solutions that can be illustrated by simple electrical concepts... and even by non-electrical analogies ...
68 views

### Would this photodiode sensor work better in series or parallel?

I am working on a photodiode small object sensor that detects and records signatures of objects passing through an array of photodiodes facing an array of IR LEDs. I am connecting the photodiodes to ...
188 views

### Current controlled bridge amplifier

This circuit essentially takes a control input and then doubles it when presenting it to the load. I would like a circuit that controls the current to the load. How would I modify the circuit to do ...
154 views

### How to emulate a capacitor discharge curve using a microcontroller output pin?

I require a configurable amount of capacitance, without using a bank of dozens of actual capacitors and some kind of complicated switchboard, like this: Not only would this be an unwieldy solution, ...
89 views

### Can power outlet be taken as a current source?

Consider a situation where I have a power outlet and I am completely unaware of the internal circuits and the fact that the electricity comes from an ac voltage source supplied by some company. I just ...
37 views

### How do these current pull-up sources work?

I'm looking at the data sheet for the TPS54160 (https://www.ti.com/lit/ds/symlink/tps54160.pdf). The UVLO feature mentions the use of current pull-up sources l1 and ...
53 views

### Working out theveni. Voltage with no voltage source

How do i get the thevenin voltage having worked out the load impedance and obtained it as 3.415 -j0.7317 ohms
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### BJT Common Emitter - Active Load Biasing

I'm experimenting with/learning about the use of active-loads with a common emitter and I've hit a wall. When using a resistor in the collector it makes sense how the output voltage bias can be set to ...
42 views

### Control capacitor charge current with a GPIO?

I have drawn the following schematic: Vp/Vm are +/-12V rails. The capacitor charges through R1. A 3.3V pulse is produced at regular intervals on an MCU GPIO to turn Q1 "on", short C1 and ...
44 views

### LM13700 control current appearing as voltage at output?

I've got an LM13700 in this VCA configuration, and for whatever reason the gain control input (I'm applying a triangle LFO, ranging from 2-7v) is appearing as a voltage at the output. Does anybody ...
353 views

### 1.2V AAA rechargeable batteries, voltage for almost full charged cell

Some weeks ago, I bought a new pair of AAA rechargeable batteries, Ni-MH. Its package shows "Panasonic eneloop" model with up to 800mAh. First I connected them in series and connected two ...
61 views

### Thevenin Equivalent Circuit of Ideal Independent Current Source

This is dual to <Norton Equivalent Circuit of Ideal Independent Voltage Source>. I have wrote it to answer a problem <click here> but I need to make it independent which requires ...
69 views

### Norton Equivalent Circuit of Ideal Independent Voltage source

For some purpose I need to derive the equivalent Norton circuit of an ideal independent voltage source. I found that it is impossible to do it. I describe the way I found it below and need comments, ...
79 views

### One milliamp current source for RTD

I am trying to design a one milliamp current source (Howland current source) with a precision of +/- 1 uAmp. The current source will be used to measure temperature with a 3 wires RTD sensor (H-T-01-12-...
67 views

### Working of op-amp based current source

Can anyone please explain me the working of the circuit attached? I believe the op-amp U1 is connected to provide a stable DC voltage at the non inverting terminal of U3. Is my approach correct? The ...
56 views

### Problems regarding KCL & KVL

Question: Below figure represents an approximate equivalent circuit of a field effect transistor amplifier. Using KCL find the output voltage $v_2$ in terms of input voltage $v_1$. My try: I ...
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### Oscillations in parallel-RLC network with a limiting VCCS

Here is a parallel-RLC network (where G = 1/R is the admittance) with a limiting VCCS. The characteristic of the VCCS is shown in Fig (b), where the slope is G1. The problem asked is as follows: Find ...
2k views

### How can I make a current source that can supply 1uA?

Is there anyway I can make a constant current source which has an output of 1uA or can I get it from the market? The load is around 200kOhms, and I need accuracy to 1%.
90 views

### Why can we bias MOSFET with current source?

My question is: If I have properly set VGS to prevent MOS from turning off, then if we biase a MOSFET with a constant current source, how can we conclude that it is working at saturation region? How ...
73 views

### Two independent current sources with one opamp?

simulate this circuit – Schematic created using CircuitLab The above circuit delivers a predetermined current to the load: $$i_L=-\frac{u_s}{2R}$$ Is it possible to extend it, so that it does ...
48 views

### What is causing the DC Offset in Mirrored Howland Current Pump Circuit

I am creating a current source to try to expand my knowledge about electronics design. After some research I decided to build the Howland setup since I want to develop a bipolar current source. The ...
28 views

### dependent current source polarity

In this question, I apply the current cycle law, I find the current i1 to 25uA. I find the voltage on the dependent current source -2 volts. When I go through the formulas, there is no problem here. ...
53 views

### op amp - current source - voltage output

I have the electronic schematic bellow composed with two op amp and I want to determine the voltage output of the X2 op Amp. I m a little bit confusing about the aim of using the zener diode D1 in ...
410 views

### Why is the voltage drop created by a current source added?

A few days ago a similar question was asked for the simple circuit below consisting of three elements in series (voltage source, resistor and current source). Despite professional explanations, the OP ...
41 views

### Underdamped RLC with CCCS, calculating capacitor voltage

Referring to "Electrical Circuits" Nilsson/Riedel 10th Edition. I have a classic underdamped RLC circuit with a CCCS (Current Controlled Current Source) with a current multiplication factor ...
48 views

### [op amp - Gain current source - current reference]

I have a question about the formula to consider for calculation of the gain for the electronic bellow. Thanks for your support.
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### op amps comparator or differential amplifier

I have a part of electronic schematic as described bellow, I'm a little bit confusing about the function of the LM321 amplifier. In this case, can we say that is a differential amplifier or just a ...
52 views

### Need help for pointing out, source follower circuit with current source, designing NMOS

I'm not sure did I solve this problem right. I made $r_{o2}$ , which is resistance looking at Q2 drain. So I can get $$g_{m,Q3} = 1.8m(A/V)$$ from A_v = \frac{r_{o2} || r_{o3}}{1/g_m + (r_{o2} ...
55 views

### LM317LM as a current source

I have been using LM317L as a current source for generating 2-50mA current for a load, by following the datasheet, P14: So far so good, but now I have come across LM31L-n, particularly LM317LM/NOPB, ...
72 views

### Opamp input bias current and current sources

I have a current source connected to a load and I want to measure the voltage at the output of the source, and therefore I would like to buffer this voltage. In this configuration, I am under the ...
52 views

### Circuit for OpAmp-MOSFET based constant current source for 0.2 - 1.5A

I'm a beginner in electronic circuit design and have designed my first Voltage based constant current source using OpAmp driven MOSFET (based on this). The intended current output needs to be ...
35 views

### JFET Constant Current Source (CRD alternative)

Today I have build constant current source based on J111. To drain I connected VCC it's 24VDC from laboratory power supply, then I connected resitor 470Ohm between gate and source. To source pin i ...
46 views

### PMOS and NMOS Current loads in Common Source Stage

I am new to the concept of Single Stage amplifiers design using CMOS. In that, I came across a concept of using current source as loads in design of Common Source Stage, where it was mentioned in a ...
55 views

### Fixed current source

Thank you for reading this question and forgive me if I sound naive. I am working with a device that uses 4-20mA as set-point, I need 3 fixed values to work with this device: (4mA, 12mA, 20mA) The ...
27 views

### Measuring current output of a diode driver

I have a laser diode driver chip that can produce DC currents up to 200mA. The current is adjusted by a potentiometer on the driver chip. The driver chip has four pins: inputs: GND, SUPPLY outputs: ...
67 views

### Constant current source with MOSFETs

I have a question regarding this constant current source circuit: I have seen this circuit with two BJTs (like in the figure), but sometimes T2 is a MOSFET (I assume for lower Rdson resistance and ...
69 views

### Meaning of “A voltage source ālikesā an open-circuit load”

I read a book "The Art of Electronics" by Paul Horowitz, Winfield Hill. In the book, I saw some phases. A voltage source ālikesā an open-circuit load and āhatesā a short-circuit load A current ...
2k views

### What are some practical examples of a constant current source?

Please don't state the obvious that nothing is a perfect constant current source. And please do not give examples of how to create them from components. I looked at this SE Q/A which stated the ...
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### Efficient current drive with arbitrary waveform

I need to drive a defined, arbitrary current waveform into an output with a load impedance that may not be constant. Currently, I am using this: The 100V is created from 9V dc using a standard boost ...
71 views

### Oscillations in voltage-controlled current source with MOSFETs and opamp feedback — Why?

I have a circuit that should operate as a voltage-controlled push-pull current driver, able to source or sink at least 2A (into a 1 ohm load). It has unexpected oscillations on the output current. ...
51 views

### 4mA-20mA loop behaviour when out of range

I have a temperature sensor that records temperatures from 10ĀŗC to 30ĀŗC, but in my project they only want temperatures to be read in the range of 15-25 with 4ma when 15 and 20ma when 25.My problem is ...