# 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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Disclaimer: I'm no electronics engineer and I have no experience in this kind of circuit! I do occasionally design simple analog circuits and PCBs, barely messing with opamps. Context: I'm about to ...
91 views

### Calculate the junction temperature of a MOSFET during pulse

Hi all I have a question regarding using a MOSFET for a constant current source. I have found this question with some answers but it wasn't clear to me yet. I want to create a constant current LED ...
365 views

### Driver selection for high power LEDs

I'm currently working in a project where I need to control the intensity of 24 high power LEDs in 5 levels. I'm planning to use LumiLeds L1CU-BLU1000000000 (https://www.lumileds.com/uploads/705/PB198-...
879 views

### Improved Howland Current Source not providing less than 1mA

I've learning a lot about op amps and constant current sources lately. I've implemented the above Improved Howland VCCS. Found it on page 6 of TI's "A Comprehensive Study of the Howland Current Pump": ...
54 views

### Calculating constant current buck converter ripple current

For building a constant current LED driver, I'm looking at the TI LM3407 datasheet: https://www.ti.com/lit/ds/symlink/lm3407.pdf For calculating the necessary inductor, there's several things I don't ...
84 views

### 22V 2A current limiter circuit

I need to build a simple circuit to limit the current of a 22-25V input (from two car batteries) to 2 amperes - to avoid frying a battery charging circuit. I found this one - "General Purpose&...
35 views

### Step up in series with step down DC DC and led driving

I'm having an issue that I can't seem to resolve. I have 100 watts rgb leds that I'm driving with constant current drivers (https://www.amazon.com/gp/product/B019W4C5IE/ref=...
65 views

### Constant current driver and undervoltage protection for lipos

I'm searching for a way to drive a couple LEDs with a single-cell LiPo battery, such that the LEDs will be cut off completely when the LiPo voltage drops below, say, 3.3V. PCB space, component count ...
75 views

### Designing a PID control with plant controlled using relays

I am working on a project to design a Controlled (Constant Current) DC Battery Charger. The charger has a variable transformer (Plant). The output of which is fed to the batteries to charge them via a ...
59 views

### (ARC WELDING) Why does voltage DROP with increasing current?

I hope I'm asking in the right place! I worked with automated TIG (GTAW) welding equipment. I'm confused about how the welding power supply controls the current applied through the work piece. If the ...
82 views

### What's the best way to control DC current in a circuit from 1mA-20mA at 15-30V input with a microcontroller?

I’m trying to create a circuit for iontophoresis that I can control the current of with a raspberry pi or eventually a microcontroller. What would be the best way to control the current? ...
154 views

### LED driver high current and voltage

For a project I have to design a led beacon that will consist of +400 LEDs. These LEDs will be driven only a short amount of time maximum of 3% duty cycle (frequency: 100Hz, pulse: 300us). The LEDs ...
610 views

### Constant Current LED Driver Output Control using PWM

I want to control the brightness of a led which is powered by a constant current driver. On utilizing a MOSFET and pwm signal from an arduino uno the led starts to fade in as the duty cycle ...
120 views

### Designing a constant current pulse circuit

I'm looking for help designing a constant current pulse through a variable load impedance of 10-100k (R4). The ideal response is shown below. This waveform was measured from an off the shelf ...
2k views

### Constant Current Led Driver (non dimmable) to work with PWM

I have 18W lamps that came with non dimmable led drivers. Ive found datasheet for the main chip (ws3441), which included schematics: and internal block scheme of the chip: I'd like to add dimming ...
79 views

### 20 mA current loop speed/distance trade offs?

By 20 mA current loop, I'm referring to digital current loop communications, e.g. the standard used by old Model 33 teletypes. (Image credit: By Rama & Musée Bolo - Own work, CC BY-SA 2.0 fr, ...
120 views

### Calculating dissipation of a CCR powered via a full bridge rectifier

I'm putting together a string of UV/purple LEDs for photoetching purposes. The idea is the following: simulate this circuit – Schematic created using CircuitLab The 80 LEDs are in series, ...
111 views

### Commercial 1.5m / 5' LED light fitting parallel LED arrangement

I am reviewing LED light fittings for an industrial premises refit. As with most of the experienced users on this site I like to understand what I'm purchasing and have opened up a sample fitting to ...
320 views

### Constant current source - unexplained issues

I have been puzzling over this for days now, and cannot for the life of me figure it out... I have a constant current source set up to use as an analog dimmer for my LM3429 LED driver. I have made ...
592 views

### Designing Buck Converter with Adjustable Output Current and Output Voltage

I am currently attempting to design a buck converter where both the output current and output voltage can be simultaneously adjusted. I will be utilizing an Arduino for control. I figured some sort of ...
487 views

### Overcharging LiPo with current source

What would happen if I charge a LiPo battery with a constant current source? I know that properly it should be charged constant-current until 4.2V and then constant-voltage mode, but what if I just ...
40 views

### Robust central stop in harsh conditions

There is 5 kilometers long cable with numerous (possibly many) central stop buttons in series. The cable is laid around machinery and other cabling at a production plant. The buttons are SPST-NC (...
436 views

### Constant current source to heat thermistor rapidly

My goal is to heat a thermistor as rapidly as possible. The thermistor has a resistance value of 10k Ohms at 25 degrees C, and a negative temperature coefficient. If I apply a constant voltage of ...
207 views

### AC current amplifier with pwm current control

I'm starting to build a piece of test equipment to test a trip device for switch gear breakers. I need to amplify an AC current source. When the breaker is in service the trip device receives its ...
54 views

### help with auto shutoff circuit with negative voltages

I have a circuit that has constant current but the load drops in resistance over time. I need to be able to shut off the circuit once a voltage level drop is reached. The voltage starts at -95vdc and ...
120 views

### Triangular wave generation using consant current

I am trying to design a circuit, that will generate a triangular wave from charging/discharging a capacitor with a constant current, but am stuck. I have a power supply of +-12V and +5V, the circuit ...
104 views

### Portable LED Power Supply & Driver

I have a question about power a portable LED light source. I understand the various ways to power an LED array but my question is more about the best practical approach. I have created a portable “...
51 views

### PWM Switching of 0-200mA Laser diode driver

My main goal is to create constant current source as laser diode driver between 0-200mA, controllable by 0-3.3V analog input from MCU, And can be modulated (ON/OFF only) by square 0/3.3V PWM signal (...
28 views

### Is backfeeding BD9C601EFJ buck converter IC a problem?

So I've got a circuit like that [Values are completely random, I didn't set them yet, the question is only about topology]: The circuit is intended to charge a 2S battery through F3, however when the ...
19 views

### Charging 18v Ni-CD battery pack with DROK voltage regulator

I have an 18v 2000mAh black and decker drill battery that I want to charge and use in the mean time while I wait for a proper charger to arrive. I have a DROK Voltage Regulator/Buck converter (https://...
86 views

### Current limiting rectifier with capacitive reactance (isolated)

[UPDATE] I have answered my own question with links to experimental data and theory. Please expand on that answer if you can for the reference of future readers. Thanks for replies so far and ongoing....
53 views

### How to reduce noise Buck converter at constant current mode ACT4088

Hello i am using a ACT4088US-T (datasheet here) Buck converter and i made it to run in constant current mode 500[mA] through a Diode (D5): Everything works fine. It draws 500mA no matter the load i ...
61 views

### OpAmp current source does not work as expected

I'm trying to build a constant current source for 2mA (IEPE accelerometer). The simulation works as expected: But the real circuit is sourcing only about 240µA. Vgs is around 2V; I thought this will ...
45 views

### Constant current regulator enable when current and voltage reached

I have constant current regulator which consists of one transistor, two diodes, enable transistor (1.5k ohm) and resistor connected from emitter to GND (~15-20ohm) as visible in schematic. It limits ...
58 views

### What voltage to charge a single NiCd cell?

Ok. I have researched and not found any results abt this question. What is the voltage range for charging a single NiCd cell? I also have another question: what is the recommended constant current ...
83 views

### Powering a constant current strip with a constant voltage supply

I have an application where I have the following components installed. 277 Vac to 48 Vdc Constant Voltage Driver (MeanWell) -> 48 Vdc CV PWM dimming interface controlled by 0-10 V -> constant ...
47 views

### How to strobe high power led while maintaining constant current

I am trying to make a high power tv-be-gone. For those who don't know, it uses arduino or attiny to run through every IR power code for most tv brands. I have made regular ones that use several 5mm IR ...
77 views

### Understanding constant current source in amplifier stage

I am teaching myself electronics in my spare time and I am trying to look at circuits and understand how they work. I am currently studying amplification and transistor basics, and I have started ...
49 views

### 2 N-MOSFETs in series

I'm trying to design a circuit to charge a capacitor bank with constant (limited) current and then discharge the capacitors through an LED. I've come up with the circuit in the schematic below, ...
32 views

### Is there any CC Led Driver IC that has common GND between led cathode and VIN-?

I have a project that has as 3W (using 500mA) Led and an I2C sensor at the end of a cable, and I need 6 wires for it. (4 to the I2C sensor) and 2 for the led. I’m using the PT4115 CC led driver CI, ...
53 views

### Can you use LM5117 as a CC/CV LiPo charger for a 1mAh LiPo cell?

I am trying to build a LiPo charger for a custom 1mAh LiPo cell. The cell is rated for charging with 0.5C, so 0.5mA max charging current. I cannot find any off-the-shelf ICs that can charge with such ...
309 views

### Help with a constant voltage led driver

Maybe the title could be better chosen. Hello, I have a 33V 0.8A constant voltage led driver (see picture below, the item no. is GL-1201C-8 if that can help) which no longer works. I searched online ...
71 views

### Create specific resistances across a constant current source

I'd like to emulate the controls on a garage door circuit programmatically. As far as I can tell the circuit acts like a constant current source and sends out 10mA to the wall console. I'd like the ...
36 views

### Effect of op-amp's input offset voltage on stability of constant current load

I'm designing a simple circuit to have a constant current load with good short term stability. The exact current value is not important, as long as it's stable short-term (10 seconds). R1 is the load -...
108 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 ...
64 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 ...
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### Yet another constant current LED driver design, almost

I am about to design a constant current LED driver, with the following requirements: The LED string is fed with 24 V The FPGA interface is 3.3 V The system consist of 8 LEDs in a row, with ...
44 views

### first order circuits

I solved this circuit for the current in the 3 ohm resistor and I thought that the current would be continuous but it's not. The circuit is first at stable state, then we turn the switch off and the ...