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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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Driving 8 x 117W COB LEDs

I am currently attempting to design a LED grow light using the following LEDs but I am having a very hard time finding a sufficient power supply. 8 x Lumileds - SunPlus CoBs DataSheet 51.7 V, ...
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4answers
101 views

Capacitor bank as a constant current source?

Can a capacitor bank of high power density, be integrated to a circuit such that it acts as a constant current source to a load? Even for a short duration of time.
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4answers
192 views

Constant current source gets heated

I am trying to control some power LEDs using a microcontroller. For this I plan to use a transistor based constant current source to protect the LEDs from getting damaged and PWM on the base of the ...
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2answers
89 views

Why constant current led driver is not used in parallel led strip? [closed]

I know that the constant current led driver is not used in the parallel led strip. and constant voltage led driver is not used in the series led strip. can anyone explain me with the example that why ...
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1answer
58 views

AL8860 LED driver does not output required constant current

The LED driver circuit i've made here does not output a constant 1A current. With an input voltage of 12V and 9V total Vf on the three LEDs (CREE LED star), the current is only 0.65A. Am I ...
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0answers
50 views

Calculating value of a current limiting resistor in a constant current circuit?

I am using 12 leds in series with 3.0-3.4 v forward voltage and 400-500mA forward current (these values are from the datasheet). I am using a constant current led driver(24-40v and 580mA). My problem ...
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4answers
92 views

Inductor with constant current source

Hii can anyone explain how to do this. Its Given Answer as 6A. What exactly happens when a constant current source in series with inductor? TIA
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3answers
52 views

Constant Current Load fails to recover after setting load to zero

I'm trying to design a Constant Current load for testing battery cells using the TLC070 Op Amp (what I happen to have on hand) and a low pass filtered (150Ohm + 470uF cap) PWM input from an Ardiuno. ...
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1answer
53 views

Constant current circuit load and without load for voltage measurement?

How can I control the constant current block? What I need? I need to calculate voltage with constant current load (I = 100ma and after some time I need to calculate voltage without load (I = 0), for ...
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2answers
43 views

Zener Shunt Regulator Question

I want an alternative low component, transformerless power supply for low power DC projects, I have used Shunt Regulators in the past but never with AC. Below I have proposed a AC to DC shunt type ...
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0answers
61 views

Current Pump Circuit

I found this circuit diagram in an academic paper, however, there are no values associated with any of the passive components. The authors claim that this circuit can deliver 1-120mA across a load of ...
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0answers
54 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 ...
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1answer
124 views

Analyzing a constant current source

I'm looking at some old chemistry education literature where a constant current source was proposed (J. Chem. Ed. 1969, 46(9) p613, link). I am trying to better understand the circuit and could use ...
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1answer
63 views

Analysis of a modified Howland Current Pump

I am trying to do an analysis of the following modified howland current pump based on the circuit description in the datasheet of the LMP7701. This is a voltage controlled current pump that is driven ...
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1answer
58 views

Laser pointer circuit

I've got a small red laser pointer from a chinese ultrasonic distance meter, which has a small regulator circuit (6mm x 7mm) with SMD components. I guess that is a constant current to drive the laser,...
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1answer
180 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 ...
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3answers
304 views

Understanding constant current LED drivers (ac to DC)

I am trying to understand the way constant current LED drivers work. Lets say I have a driver with these specs: Description: Power: 18W Output Voltage: DC 36-63V Output Current; 300mA Input ...
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0answers
84 views

Laser Diode Driver and Cooling

I am a newbie at analog design, and trying to design a laser diode driving circuit and TEC cooling circuit for a 14 pin laser diode, such as P1550-ADF-B: 1550NM ADF LASER DIODE which has forward ...
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1answer
70 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-...
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2answers
96 views

Voltage doesn't add up in LED circuit

The circuit consists of following: simulate this circuit – Schematic created using CircuitLab And video on this link. Summary: When there is no current flow on the circuit, supply voltage is ...
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2answers
63 views

Over-voltage on a current regulator

Let's say I have a current regulator, or a LED driver, set at 4V that can sink 20mA. If I connect a white LED rated 20mA at 4V to it, then everything is fine. But what happens if I replace, in the ...
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2answers
66 views

High power LED array

I’m designing SLA 3D printer and I need to design UV LED array for LCD screen backlight. Preliminary design is 5x3 (5 parallel lines with three LEDs in each). All LEDs will be soldered on PCB. The ...
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1answer
47 views

Help Powering 2x10W LED using a 15v 1A power supply

Beginner here, trying to build a lighting using two 10W SMD LED'S. Please advise me for a better and efficient setup. Here are my specs. Power Supply DC 15v 1A LED specs: Input voltage 9-12v ...
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2answers
65 views

LEDs + Constant Current Driver - Discharging the Circuit

I have a project where I made a series of high power Osram OSLON blue leds using custom boards on aluminium PCB. I just put 16 LEDs in series and joined them to an appropriate constant current supply. ...
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2answers
115 views

Current-limiting for LED when Vf = Vdd [duplicate]

I need to drive several indicator LEDs at <2mA. Each LED has a nominal Vf between 3.2V and 3.3V (Vf max up to 4V). In the past I've had the luxury of (a) current-limiting resistors or (b) ...
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2answers
192 views

NPN transistor as variable resistor for cc LED operation

I want to build a simple circuit, to control a chain of LEDs via an external PWM signal but limit their current. Unfortunatly I'm not aware of all the effects that the transistor would introduce to ...
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5answers
191 views

BJT Constant Current, Resistor Equations

I am looking to design a simple constant current circuit to draw a precise load from a variable voltage rail. The voltage rail (V+) should be 10V-20V in normal conditions, but it is possible for V+ ...
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4answers
223 views

Driving 10W RGB LED Red Channel Issue

Been a while since I have been on here but I do not know where else to turn for help! This is more of a hardware issue than anything so i do hope that I am in the correct forums to be asking, if ...
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3answers
252 views

Converting appliance LEDs from constant current to constant voltage to allow for dimming

I'm trying to implement dimming control for the lights in my kitchen hob extractor. The lights are 4x LED spotlights which are each 3v 700mA (2.1W). They are currently wired in series to a 700mA 10W ...
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2answers
389 views

How to calculate this two transistors Constant Current Source circuit?

I came across a constant current source calculator at Electronic Product website:enter link description here For example, for a 13.5V input, 300mA output, it comes out the following parameters: <...
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1answer
118 views

~40 uA current sink… what current mirror topology to use?

I need to sink a constant 20-60 microamps from the inverting input terminal of an op-amp in order to shift the output voltage upwards a bit. This is a pretty low-speed circuit, with little spectral ...
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2answers
176 views

Add constant current to an XL6019 module

I need to add a circuit to an XL6019 module to get a constant current (adjustable) source to drive some SMD LEDs. I'm no expert in complex circuits and my level of knowledge in electronics is basic. ...
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1answer
160 views

Building a VCCS with AD8220 Instrumentation Amplifier

This question is to help me with my work in building a VCCS for the excitation signal of an Electrical Impedance Tomography measurement set-up to use with EIDORS. I have only basic knowledge in ...
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0answers
60 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, ...
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1answer
222 views

LM317 intermittent current source

I need a 50 mA current source despite the load value (resistor LOAD), and I need the current flowing just when the microcontroller says so. It works fine with LOAD = 0 ohm and IL = 50 mA, but when I ...
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4answers
285 views

RTD sensor circuit design

Design Criteria For a project I'm making I want to measure temperature using a 10 bit ADC on a MCU. I don't care for absolute accuracy but I would like precision down to around 1/10th of a degree C. ...
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1answer
120 views

What is the operating principle of this single-transistor constant current source?

Sorry if this has been asked before; I'm still learning about electronics and probably don't have the right vocabulary to describe this part's functionality. I came across an interesting part made by ...
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1answer
59 views

Constant Current Load op-amp ref voltage limit

I am trying to build a constant current load circuit described in DIY-Constant-Current-load I wanted a 20mA CC load, so I chose 4V at R2-pin2 and 200ohm for R1. After constructing the circuit, i ...
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1answer
161 views

How do i get this constant current circuit stable?

Im making a battery tester / discharger. For this i'm using a constant current circuit made with an opamp and a mosfet. I built and tested the circuit by itself with around 3-4A and it was stable. I ...
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0answers
26 views

Help me set constant current to 1.5mA output and LED to 20mA [duplicate]

I don't understand enough to accomplish this, constant current output to 1.5mA LED current to 20mA its simply been too long since I learned these things. Im only modifying an existing (likely popular) ...
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1answer
105 views

Is LED properly implemented in the constant current circuit?

Consider this simple constant current source. The voltage is 27 V, yet the indicator LED is rated to a much lower reverse breakdown. Is the LED safe? Will the LED draw current away from the output ...
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1answer
117 views

Voltage oscillates continously in USB Li-ion charger. Anomaly or CC/CV behavior?

I have purchased two USB boards for charging Li-ion batteries and it should have a CC/CV charging regime. So I connected the board to a 5V USB source (computer first then solar panel) and the voltage ...
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2answers
393 views

PWM equivalent for a constant current source and load

I am working with LED drivers and compatible LED lights. They look somewhat like this: These come in two versions: (1) Constant voltage type and (2) Constant current type I am implementing a circuit ...
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2answers
269 views

Issue with Constant Current Sink

I'm having a problem with my constant current sink circuit [see below]. As I increase the variable voltage, the Voltage across my 22 Ohm resistor remains relatively constant (0.7V). However, the ...
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2answers
58 views

Can a CD74HCT4094E shift register output 20mA?

I want to drive IV-9 numitron tubes with a shift register. These have 8 segments which each need about 4V/20mA DC to light up. I’m considering to use the CD74HCT4094E shift register, but am unsure if ...
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1answer
59 views

Clamp the output of constant current source and capacitor to particular voltage

How do I need to saturate the output to 891mV? The current source is 1uA and the capacitor value is 3.76n I need the output to ramp up till 3.35ms then saturate to 0.891V
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90 views

3 watt LED driver

is this schematic good for driving a 3 W LED (700 mA, 3.3 V)? P1 is a 12V lead-acid battery input, P2 output.
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3answers
641 views

Arduino 4-20mA transmitter

Looking to build an Arduino controlled current-loop transmitter for driving 4-20 mA over an ~100 Ohm non-inductive resistance with 24V power supply. Also the Arduino should drive ideally 4 independent ...
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2answers
947 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 ...
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3answers
119 views

Current sink for microcontroller port not constant

I have designed a two-transistor current sink for my application. I need it to keep the current constant which flows through an IR-LED: simulate this circuit – Schematic created using ...