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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135 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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246 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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902 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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4answers
1k 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
131 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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124 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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174 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
2k 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
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 ...
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208 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 ...
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3answers
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 ...
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2answers
2k views

BJT Constant current LED driver

I need to build a constant current driver for a LED with a forward voltage of 3.4V and 350mA maximum current. The driver will be controlled by a PWM signal from a 3.3V MCU. Reading this post and ...
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1answer
425 views

Need help on creating the most stable LED possible [closed]

I am currently trying to make a circuit to drive an LED with smallest amount of fluctuation as possible. Background: Using an LED and spectrometer together to analyze small molecules. I can use the ...
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3answers
617 views

Can a Li-ion battery be discharged in CV mode?

I have a load which can also be set to "Battery test". I can easily discharge a Li-ion battery using the CC (contant-current) mode, which is also a condition recommended by the manufacturers. For ...
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52 views

Constant dump current and OVP simplest

I'm on the hunt for a circuit which is simply to dump 3A (+/- 0.5A) cc to ground if it receives a signal from an Arduino or if the voltage exceeds 5.5 V on the load it should clamp it for up to 5A (+/-...
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2answers
758 views

Adjustable Voltage Regulator that operates in the uA region as a Precision Current Regulator?

I've been looking at all sorts of voltage regulators to suit my needs, I'm arranging an adjustable voltage regulator in such a way that I'm actually using it as a precision current source. Turns out I ...
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1answer
2k views

LM317T with weird pinout?

So, some time ago I bought some LM317T voltage regulators. Today, I made a 50mA constant current circuit like this: Now, before you tell me that my circuit is wrong and that it should be wired in ...
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0answers
878 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": ...
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3answers
214 views

Understanding constant current circuit

I've been learning about different constant current circuit designs and just recently stumbled upon this one. All I know is that the highlighted resistor is the load resistor and when varied, like a ...
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0answers
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, ...
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3answers
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) ; ...
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2answers
266 views

Simple Constant Current Circuit Acting Strange on Occasion

I have a simple constant current source driven by a DAC. Very low frequency, less than 100 Hz changes on the input. I have had trouble once in a while when the transistor either fails or temporarily ...
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1answer
166 views

Limiting output range of Buck Converter

I bought one of these cheapo Ebay toys from China. It's a buck converter with a Constant Current function. I plan on using to drive LEDs from an 18.5v 18650 li-ion battery pack. One of the ...
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1answer
331 views

Need help with LM317 (500 mA) out of 3 volts supply Calculations [closed]

Does LM317 regulate a constant current of 500 mA out of 3 volts supply (Vin) ? Need help with its associated calculations please. !
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3answers
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 ...
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1answer
364 views

Problem with Constant Current power supply

I built this schematic recently. The Constant Voltage mode works as a treat, stable as it needs to be. When I insert the LM311 comparator, the circuit works fine for about 30 seconds, then something ...
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3answers
151 views

Controlling multiple LEDs down to 0.25mA

I need to drive 50 (standard 5mm) LEDs, controlling the brightness of each LED individually, down to only 0.25mA and up to 25mA. I started using TI's TLC5947 to drive these LEDs. This chip, as many ...
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2answers
128 views

AC constant current (6 A rms) to 12 V DC

How to convert AC Constant current 6 A rms to 12 V DC (or 24 V DC) ? I want this circuit for LED power supply. In addition the circuit has 2 steps to control illumination of LEDs.
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1answer
775 views

Constant Current Driver with a Step-Up Regulator IC

First of all, although I couldn't find any similar question(s), excuse me if one has been asked before. I want to make an LED driver for 2 different LED strips. One needs about 45 VDC and the other ...
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2answers
1k views

How to make amplifier (almost) Beta independent?

There are several ways to bias the quiescent point of transistor, when used as an amplifier. Among which voltage divider is best known for its improvements (improved temperature drift and beta ...
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3answers
454 views

LED Parallel Forward Voltage Higher Than Indvidual LEDs Vf

I measured the forward voltage of two CoB LEDs at 600mA then wired them in parallel driven by 1200mA. Why is the parallel Vf higher than the individual forward voltages? Forward Voltages: ...
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2answers
239 views

Reducing heat dissipation in linear current source used for driving a LED

I'm currently using a linear current source to drive a single LED as in here. In my case (following the notation in the link), VDD is directly connected to a single cell lithium polymer battery, i.e. ...
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1answer
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 “...
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1answer
54 views

Change current of bandgap

Here is my bandgap,and i want to change the current "I" ,according to the formula: I=\$\frac{nk\times lnK}{qR}\$, n,k and q are constant So i can only change \$ lnK \$ and R to adjustment the ...
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2answers
255 views

Protecting laser diode that is transmitting an audio signal

I would like to first state that I do not really know anything about circuit design- I am very much a beginner. That being said, I am working on a project where I am using a laser to play music. I ...
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0answers
406 views

PTC Thermistor - Schematic Analysis

I am developing a redesign of a current PCB which uses the attached circuit in order to evaluate the temperature using a PTC thermistor (which is R3 in the given image). The circuit is connected to ...
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1answer
940 views

Lab power supply CC with comparator: principle

I'm building a lab bench supply, and it uses a current sensing resistor and a comparator for shunting out the input of the drive circuit when switching to CC mode. I'm having trouble understanding ...
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2answers
111 views

Drive PLCC6 LED

have a question about PLCC6 LEDs. All three of them in one housing are white. I want to drive them with the Infineon LED driver BCR402U and a 12V powersupply. Since one package houses three LEDs, is ...
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1answer
248 views

Improved Differential Amplifier

I made this circuit as shown below: simulate this circuit – Schematic created using CircuitLab After those improvements with current mirror and constant current source were considered, this is ...
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2answers
1k views

Transistor Current Source Biasing

I'm reading Art of Electronics, and in the section Transistor Current Source, they mention "The base voltage can be provided a number of ways. A voltage divider is OK as long as it is stiff enough. As ...
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1answer
319 views

LM317T outputs current on Adjust pin with nothing connected between adjust and Vout?

I have a LM317T-based simple circuit and I'm using a 12V battery to power it. I connected the Vin to + 12V and made a constant current circuit as shown here. Now, I'm using a variable resistor of 100k ...
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3answers
2k views

Constant Current Source using Fixed Voltage Regulator

I was in the process of building a 2W laser diode driver and I realized after some debugging that I had a 3.3V constant voltage LM1086 chip instead of an adjustable voltage regulator. I intended to ...
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1answer
267 views

generate constant current from raspberry pi

Hi i'm embedded programmer but not good enough at the electrical side. Two electrodes are put in a material. I need to drive 50 micro amp current to the electrode and measure the voltage created. (...
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2answers
860 views

Can a diode prevent backwards current flow from a constant current source?

I'm trying to make a AA battery replacement battery for a vintage computer because its actual battery has gone bad. Its of the NiMH type and I'm pretty sure those are charged with a constant current. ...
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1answer
2k views

Does a rated 5V, 2.1/1A charger provide a constant current? [closed]

I use power banks often to charge my iPhone. The default charger is a 5V/1A charger (which I assume provides constant current). However, the power bank has 2 output ports - able to provide 5V=1A and ...
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2answers
82 views

Question about voltage ratings on constant current LED Drivers

I have a 50W LED chip, 28-32V, 1400mA max current. I'm looking at a 60W, 1400mA constant current LED Driver but it's output voltage is rated 25V to 43V. Will this driver work as is, or do I need to ...
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2answers
141 views

Effects of current/voltage limiting of LEDs

First of all, I have read many articles about the non-linear effects of voltage vs current of LEDs. I also know that current will rise as temperature rises, batteries have resistance, LEDs brightness ...
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1answer
205 views

Using a single resistor for constant current load

I have a super capacitor (1000F) laying around and I want to measure ESR and it's capacitance. I have access to a 8V/500A power supply and various meters. If I wanted to charge/discharge the ...
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0answers
304 views

how to convert 0 to 5 V signal into 4 to 20mA current transmitter [duplicate]

i want to make a voltage to current converter which is also known as current transmitter. i want to convert 0 to 5v into a 4 to 20mA current loop which can be received by a powered load. i want to ...
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1answer
267 views

I want to convert 0-5 volt to 4 to 20 mA current loop through a self powered load

I have done this circuit diagram in Multisim where the R1 is the variable voltage source and the load is represented by the black box. There are two problems: If I change the load resistance the ...

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