# Tagged Questions

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 ...

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### BJT Current Source and Current Doubler - Identification and Analysis

Identification: Is there a name for the following NPN BJT Current Source with three identical BJTs, which doubles the reference input current? Analysis: If $R_L = \frac{1}{2} R_1$ as shown in the ...
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### high side variable current source

I want to design a high side variable current source: Power source (Vacc) is an accumulator whose output varies between 9V and 7V. I need output DC current values between 10mA and 100mA. I need it ...
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### Help with burning inductor in an LM2576 regulator [closed]

I was helping a friend to design a constant 3A current source using an LM2576 to drive a load. Problem is that the 100uH inductor keeps burning every time the circuit is switched on. One option is to ...
67 views

### Convert a dual supply op amp circuit to single supply

I have made a dual supply circuit as above. This circuit is a variation of Howland current pump. The circuit output (at R18) is connected to battery pack of 6.5 Volts and the pack negative terminal is ...
294 views

### Why isn't this opamp working correctly?

I am working on an adjustable current source. In a thread awhile back, various circuits were discussed: simple adjustable current source for LED string ... but as I have settled on one option, and ...
64 views

### Oscillations in Precision Voltage to Current Converter Design

I am trying to re-design the TI Precision Design - Low Level (5uA) V-to-I Converter. My design goals are: Increase bandwidth from around 1kHz to 100kHz (ideally 1MHz in the future) Increase output ...
41 views

### Reverse Current in N Channel Power Mosfet

I am designing a bidirectional current source to drive a large (~60A) current through a large inductive load (100's mH) and facilitate very fast switching times (as close to an 1A/us as possible). My ...
1k views

### op amp+mosfet = current source.Why do we need a feedback resistor?

The feedback resistor is needed to compensate for the error of the input currents? How to choose the resistance R2. Circuit source Resistor R2. Can I use this circuit, op-amp with differential ...
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### Power supply: How to diferentiate current source and voltage source

I found a power supply in my workshop that is marked as 12v@2A it is the typical Chinese power supply to drive leds so it is supposed to be Current Source, but I'm not sure at all, so I would like to ...
44 views

### Bi-colour LED temperature indicator. Varying brightness. Thermistor as sensor

I want to make a temperature indicator using a bi-colour (reg/green) LED and a thermistor. GREEN should be fully on (20mA) at 25C (thermistor = 10K) and RED off (0mA), and at 100C (thermistor = 1K) ...
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### What causes the common mode gain in MOS differential amplifier

I went through many of the past questions in this forum and also a lot of other sites but none answered my question, so I made up my mind to post it here. What exactly causes the common mode signal ...
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### What are the underlying physical principles of a constant current power source?

I´m currently looking for a led driver to drive a 34,25 W High-Power LED at 38.06 V / 900 mA. Browsing trough various online shops i found a constant current source and i don`t get how it works. The ...
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### Why is the Schmitt Trigger output fed back to the current source in NE 566 (VCO)?

I understand the working of the circuit, a Voltage Control Oscillator, except the part where the inverted square wave from the Schmitt Trigger gets fed to the Constant current source/sink. Pins 5 and ...
114 views

### Designing a 1A current source with high-side current sense

I want to design a 1A current source on a PCB. I have bunch of MAX9611 chips laying around. In their datasheet it says it can be configured as inrush current limiter and current source (in a closed-...
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### Why a diode is in parallel with the current source in the equivalent circuit of a solar cell?

The model of a solar cell has a diode in parallel to the current source: (source) Why is the diode in parallel and not in series with the current source?
116 views

### Paralleling op-amps for more current?

I'm trying to design a current source / sink that will be a part of a step generator that will drive a BJT base. I only intend to drive small BJT transistors so a max base current of 10mA was decided ...
148 views

### How is the current through resistor same as collector current in this circuit?

My textbook says that the current through resistor will be same as the collector current when the diode shown matches with the base-emitter diode internal to the transistor. Could somebody kindly ...
147 views

### what is the easiest trick to check whether a transistor is used as a switch or current amplifier?

Newbie in electronics here. I think I know the basic theory behind transistors.I would like to know based on the schematic how you can know whether the transistor is used as a switch or an amplifier ...
107 views

### How to calculate the output impedance of this circuit?

This is a hybrid-pi model of a BJT, and I want to know its output impedance: simulate this circuit – Schematic created using CircuitLab I know that I should short the input ports, place ...
55 views

### I do not completely understand the intuition behind equivalent sources used in source transformations

My book states that two circuits can be considered equivalent if they produce the same voltage and current in any resistor connected to the two ends of the circuit. The book then goes about proving ...
29 views

### Need help understanding the concept of “Circuit model of a discharging RL circuit”

I don't understand the statements for t<0 and t>0. Why does this happen?
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### simulating a photo diode response- how to make use of pulsating current sources

Currently my photo diode is exposed to pulsed laser with Pulse width : 10ns < tw < 150ns Pulse repetition rate : 1Hz < PRF < 70Khz Expected peak current : 50mA so when i ...
124 views

### Cheap, low-quality constant-current sink over wide voltage range

I'm looking for a cheap (as in: low component count, low PCB area, low component cost) way to put >= 1mA of load on a voltage that may be anything from 1.2 to 17 volts (minimum required load on a LDO ...
94 views

### RS485 current source/sink

I'm looking at using the RS485 to communicate between two Arduinos. I'm trying to wrap my head around the current requirements though... If I connect a driver to a receiver through a differential pair,...
119 views

### Battery discharge current

What is the meaning of standard discharge current mentioned on the datasheet of lithium batteries. Does it represent the maximum current load can take or it represent the instantaneous current battery ...
47 views

### Why is the dependent current source ignored?

I need to find i1 / v1 when i2 = 0. According to the solution manual, the KVL is -V1 = 2kOhms*i1 + 1kOhms(i1 + i2), and since i2 = 0 they get -V1 = 3000i2. Are they forgetting the dependent ...
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### Are there any circuits to get output as a sum of a set of current sources?

I have 3 current sources (I1, I2 and I3) and I need to get an output of linear summation of the current of these sources. Iout = aI1+bI2+cI3 where a,b and c are gain factors (like 1 to 10 and are ...
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### FET Current limiter 30A and overload detection

I plan to make a module for my motorbike to replace fuse by current limiters and overload detection system. I've heard nice things to do with J-FET. It should work up to 12V 30AMP. The detection ...
99 views

### Follower current source?

I need advice on a problem I'm having I need a follower to transmit an AC signal into a low impedance load which is the cathode of a triode but I also need it to be an adjustable current source to ...
50 views

### Current step generator - ideas for completing the implementation?

I'm working on a circuit that can act as a current sink or source. The goal is to control it using some digital means so it can output the required current. Right now I am not sure about the ...
167 views

### Is it OK to PWM a current source?

I want to control power RGB LEDs, for efficiency and safety they are better to be driven by a current source. I can use either linear or buck converters. I made a linear current source using ...
50 views

### How to connect multiple ACM 7135 to one ATtiny? [closed]

One ACM 7135 provides 350mA. Nine can fully power Cree XM-L2 U3. But that's 10W. ACM7135 only have Vin, Vout and GND pins. People are using them with ATtiny (example), apparently without any other ...
92 views

### Switching a ~10 μA current at ~10 kHz

I would like to inject 10 μA into my load, and to be able to switch the current on/off at up to 10 kHz. My first attempt is just based on the transistor current source in Horowitz/Hill. ...
47 views

### serially connected current source and resistor

In source conversion we can simplify circuit by shorting resistor in case of resistor and current source are serially connected and open resistor in case of voltage source and resistance are parallel ...
201 views

### simple adjustable current source for LED string

I want an simple adjustable current source that can drive a string of up to 9-10 LEDs at up to 350ma, with typical forward voltage of 2.85v, from a 30vdc power supply. I know there are off-the-shelf ...
152 views

### Current source with low-side LOAD

Why does this work? simulate this circuit – Schematic created using CircuitLab But this doesn't. simulate this circuit In the second schematic, V2 is adjustable. Is there a ...
104 views

### is there any way to get current from vibration?

I was wondering if you have something that vibrates , is there any way that you can make some power out of it?
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### What is this circuit called? (Dual of a boost converter)

A boost converter is a circuit that uses power from a voltage source, to act as another voltage source with a greater voltage. To conserve power, it draws more current from the input than it provides ...
71 views

### Current Source Transformation

So my question is: Can I transform the current source I1 with R5 into a voltage source? I know for sure that if R3 was not in between them I could, but does it make a difference? I am not sure. ...
93 views

### Bipolar Voltage to Current Converter

I need a circuit or component which converts bipolar voltage to bipolar current. I have found the XTR111 from Texas Instruments and the 1B22 from Analog Devices. However, they only convert 0-10 V to 0-...
125 views

### PT1000 2 wire probe. Can I add third wire?

I'v got 2 wire (81 cm) PT1000 probe which I want to utilize in a project. I would like to use current source and couple of opamps to make the measurement through ADC (uC) just like described here: ...
98 views

### audio-taper potentiometer in 50-100 ohm range [closed]

Anyone know where to source an audio or logarithmic taper potentiometer in the 50 or 100'ish ohm range ? Mouser and Digikey don't show anything, even non-stocked. I'd like to build an adjustable ...
155 views

### question about transistor matching circuit

I'm studying this transistor matching circuit provided initially by Bob Moog. I think I mostly understand how it works, the op amp, bjt not under test and resistors form a current source, which stays ...
42 views

### Possible calculation error using current divider rule on a non ideal current source circuit

I am going through my notes in preparation to an exam, the following was taken straight from the board as my lecturer wrote it. As far as im aware the current divider rule should be I1 = It * (...
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### Voltage regulator Current regulation

I want to understand the concept of current regulation in the circuit, In my research I came across the following link Boosting Regulator Current for IC 78xx by MJ2955 where in the circuit schematic ...
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### How do I calculate the voltage in this circuit?

I have the following circuit: I am a beginner at this stuff, so... ;) Ok, the question is to calculate the voltage across the terminals A and B? I have no clue how to do that? You can't just take ...
120 views

### Can an opamp be neither in linear region nor saturated?

I'm trying to build a voltage controlled DC current source. For this, I built this circuit: A little bit of context. The voltage supply is 5V. Current range must be from 0mA to 30mA or so. Load ...
95 views

### Wide Input Voltage Range Constant Current Source

I would like to design a Constant Current Source of 25mA, With Input varying from 2V to 50V. Please provide just an idea how to get about this.