# Questions tagged [constant-current]

Questions regarding Constant Current supplies, devices and applications. As opposed to Constant Voltage supplies. Voltage will vary while Current remains the same. Common in LED lighting applications.

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### What is the dual of a diode?

A diode has an exponential I-V curve. To a first approximation, it will pass whatever amount of current is required to keep the voltage across it constant. Is there a passive component that will (...
3k views

### What's the intuition for reading transistor/resistor circuits?

The below circuit supposedly provides constant current to an LED. I tested using everycircuit.com and that seems correct (used R = 70 ohm for example). What's a step by step way of thinking about the ...
3k 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 ...
5k views

### Usefulness of constant current limiting in bench power supply

I'm building a bench power supply as my introductory project to electronics. When it comes to adjustable voltage it's easy to see the usefulness of such feature but I can't figure out what is the ...
15k views

### How does this constant current sink actually work?

I have implemented a constant current source and it works wonderfully, but I was just hoping to try and understand it a little bit more! Here is the circuit in question: I have tried doing some ...
3k views

### Need for Temperature Compensation of Current Mirror

I am currently learning about current mirror configurations. I have made two of them so far. Both of them worked as desired but, when heated or cooled, the current through the right side (the side ...
8k views

### Precision CC CV circuit or power supply

I want to design a CC/CV (constant current/constant voltage) circuit in which I can set the voltage limit or current limit with DAC's 0 to 5V range. I know how to design variable CC circuits and CV: ...
2k views

### Explanation of LED driver circuit

I've been reading up on LED drivers and found some common connection schemes. Yet, I recently came across the following LED driver circuit at this URL: I tried to find out what exactely was going on ...
2k views

### can leds take varying voltage > listed voltage, with constant current?

My confusion stems from a an led that shows: Input(DC): 600mA-700mA / 3V-3.4V. the product suggests a constant current led driver (same brand as LED) that shows: Output: Current 600mA (Constant) ; ...
940 views

### Buffering a constant current source IC to increase maximum voltage rating

The actual question: Which of these configurations, if any, is the most effective for my goal of increasing the maximum voltage rating of the outputs of a constant-current driver IC? As established ...
11k views

### Adjustable linear led driver? Linear, not PWM

I'm working on a product that requires an led to output currents varrying from 0mA to 350mA and as many possible levels in between (~1000 would be sufficient I suppose). I CANT output a PWM signal to ...
10k views

### Constant current circuit with transistors/MOSFETs design comparison

There are a few designs out there for constant current devices, but most of them use a certain chip. I was looking for a way to build my own constant current supply from parts that I have available. ...
8k views

### LM317 µA Constant Current source possibility?

I want to create an adjustable µA Constant Current source using a LM317. It is typically stated to have a 5mA to 10mA minimum current for proper regulation. The On-Semi version linked above shows a ...
6k views

### Why does this buck converter output such low current?

I'm making my first attempt at building a buck converter, as a constant-current supply for a 700ma LED, from a 5V or 12V supply. I have it working with the parts I had on hand, at about 88% ...
554 views

### Probing with Oscilloscope Stops ADC Fluctuation

I've gone back to my constant current project to fix an annoying fluctuation in the required current display. See schematics below. The entire circuit consists of a CCS section with signal outs for ...
17k views

### Standard current and discharge current

I've been looking into batterie's datasheets and don't understard what 2 of the specifications mean: continuous standard current and maximum continuous discharge current. Could someone explain this to ...
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### Why do the inputs of this CC circuit op-amp need clamping?

I'm studying the constant current circuit of the HP E3610A DC Bench Power Supply. I'm building a supply of similar topology using surface mount components and the LF442 isn't available in a SOIC-8 ...
8k views

### Efficient constant-current regulator for 700ma LEDs

I'm building a lamp with twelve 3x700ma RGB LEDs in it, that need to be individually PWM controlled (100-200Hz), so they can display different colours from each LED. To do this then, I think I need a ...
262 views

### Voltage Controlled Current Source - help needed

I am designing a voltage controlled current generator for the currents in a range from 0 - 2.5mA. The load resistance is within the range of 0 - 5k Ohms. I decided to go with difference amplifier ...
1k views

### Microcontroller Adjustable 2A 24V Constant Current Source

I need to come up with a method to provide a microcontroller-adjustable, regulated current ranging from 0-2A at ~24V to a load in a closed-loop fashion. I have been researching this issue for awhile ...
5k views

### Why can't electronic systems use constant current power source and vary the voltage as power consumption varies?

Today, electronic systems use constant voltage power source. Current consumption varies as power consumption varies. Why can't electronic systems be designed the other way round? Using constant ...
792 views

### How to calculate the tolerance of this constant current circuit?

I am using the circuit below to provide constant current to th LEDs. I request your suggestion on how to calculate the tolerance of current (minimum and maximum variation of set current) due to ...
853 views

### Constant current circuit

How does the red (rot) LED at the input to the base provide a constant current to the other two LED's after the collector, via the transistor? (I have been told that the NPN transistor here has a ...
3k views

### What is causing the oscillation in the feedback loop of an SMPS?

I am trying to make a switching constant current regulator for a Ni-MH charger. It accepts a current set input from the microcontroller using a PWM DAC. I basically want to source 2000mA and 200mA for ...
19k views

### Why N-channel MOSFETs are better than P-channel MOSFETs?

Besides the reason that electron mobility is higher than hole mobility, what are the other reasons of preferring an N-channel over a P-channel MOSFET?
16k views

### Make adjustable mosfet constant current source

I want to modify this circuit below so the current can be trimmed. The problem is the variations in base-emitter voltage of the NPN transistor. According to datasheets, it is between 0.55V and 0.7V ...
7k views

### Beginner information related to constant current dummy loads

I am beginning an electronics design project to build a constant current load to drive testings for batteries, bench power supplies etc. I have been hard trying to locate some black-on-white ...
823 views

### microamp constant current sink

I'm trying to put together a constant current sink circuit for discharging small Lithium-Ion coin cells. I need to be able to sink from about 200 uA to 12 mA. My first thought was to use some voltage ...
10k views

### Why is PWM used to control LEDs even when they're only used On or Off?

I've noticed on cars with LED tail lights that they have a flicker to them - I presume because they're PWM controlled. But I've seen it on vehicles where brake lights and tail lights are separate ...
3k views

### Schematic for common buck/boost converter designs

Does anybody know the schematics of these common LM2596 buck converter with current adjustment and buck-boost converters from ebay? I know I can easily buy it cheap but I like making my own modules ...
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### How do I build the current regulator circuit referred to on the LM337 datasheet?

What I would like to accomplish: I am trying to add current regulators into a home built dual rail linear regulated power supply. I previously asked this question about transformer fusing and ...
2k views

### How to improve current control loop in power supply?

I'm working on MCU programmable bench power supply. Its range is 0-50V and 0-3A programmed in 10mV and 10mA increments. It will be published as open hardware and source code that anyone can use it if ...
2k views

### 'Leftover' voltage when using constant current

I came across this circuit, simulate this circuit – Schematic created using CircuitLab Which states that the current through the LED is equal to 0.5*R2/1000. I'm not 100% sure how to come to ...
3k views

### Looking for a Constant Voltage/ Constant Current power supply schematic

I would like to create as an hobbistic project a power supply circuit allowing to switch between a Constant Voltage mode and a Costant Current one. When Voltage Mode is on, Current regulation should ...
2k views

### Low Overhead Constant Current LED Driver

I have a 3V3 rail and want to run an LED with a Vf=3.1V at 10mA with a constant current source. I'm used to circuits like the one below but the problem is that I only have 200mV of overhead and ...
4k views

### Parallel Transistors in Constant Current Load

I'm designing a constant-current dummy load for testing my power supplies. This load should be able to handle a maximum of $2\mathrm{A}$ at $24\mathrm{V}$. My current design, so far, is loosely ...
17k views

### LM317 to create constant current of 2mA?

I have a circuit where I want to have a constant current of 2mA through a variable resistor. I've been told that I could probably use a LM317 as a current regulator, with one resistor on the ouput. ...
2k views

### Using a TLC5940 to control LEDs with different forward voltages

I am trying to build an LED matrix (64x32) of RGB LEDs using a TLC5940 current sink LED driver. The forward voltages of the LED components for each RGB LED are: R: 1.8V G: 2.8V B: 2.8V The driver ...
2k views

### Component usage in this constant-current source circuit

In the April 2014 edition of Elektor magazine, they present a circuit for a high-precision current source device (page 42). It allows the user to select a constant-current between 10nA and 20mA. They ...
11k views

### How to dim an LED with constant current supply?

I have a power RGB led with 350 mA max per color. If I get 3x 300-350 mA constant power supplies will I be able to dim each individual color from 0 to 100% power with Arduino (with NPN transistors)? ...
590 views

### BCR402R - what is the purpose of Rext in this LED driver?

I'd like to know what is(are) the purpose(s) of Rext in the BCR402R LE driver circuit. The BCR402R is a 20 mA constant current LED driver. The application circuit (see below) shows an external ...
2k views

### LED current driver

I am trying to regulate the current across an LED so that I can tightly control its intensity since I will be using this light as a source of illumination for a sensor. I am using a CAT4002A-D LED ...
20k views

### Capacitor Discharge through Constant Current Source

I was just thnking of how to model the voltage decay from a fully charged capacitor through a constant current source (CCS). A good approximation to this would be to model the constant current source ...
870 views

### Digital Current limiting with MCU

All current limiting circuits I've found until now use some sort of analog Logic with Op-Amps to limit/control the current. (Why) is no digital current limiting used? I would imagine a shunt resistor ...
846 views

### Powering RGB LED's and using a PWM chip; series or parallel?

I'm working on a hobby project where I will be using an Arduino board and a TLC 5940 to control 5 different groups of RGB LED's. The number of LED's in any particular group will not necessarily match ...
935 views

### Basic schematic help

I'm trying to design a lighting circuit for an indoor garden, and I'm not understanding things that seem like they're really basic, so I need some help. The schematic I'm referencing is: I have a 24V ...
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### SMPS Constant Current Source only works with low resistance loads

I'm looking for any advice that can be given to solve this issue. I followed the design idea from here: buck regulator to CC source and it appears to work pretty well until I started raising the load ...