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.

learn more… | top users | synonyms

1
vote
1answer
65 views

Understanding this LPF in opamp feedback loop

I'm using a basic opamp driven mosfet to implement a precision low current sink for an LED: This seems to work just fine within the range that I want it (10mA or so). I've seen other circuits that ...
3
votes
1answer
78 views

How to drive a sensitive, constant-current, 1MHz resistive device?

I am currently working with sensors which are mostly resistive (100 to 600 ohms on average) and need to be fed with a controllable bidirectional constant current (from -1mA to +1mA with a resolution ...
4
votes
3answers
277 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 ...
1
vote
0answers
27 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 ...
0
votes
1answer
63 views

rgb led current limit

I am working with RGB LED, my question is will it burn up / get damaged I have already chosen resistors proper for each color of R G B to draw 20mA, but running R G and B at same time draws lots of ...
0
votes
1answer
47 views

how to calculate solar panel size needed to run circuit

Iam doing a project and want to calculate what size solar panel to use to run my circuit. the only thing is that I have some size constraints involved cant be bigger and \$5\times5\$ in. I have a ...
0
votes
1answer
29 views

Current Regulation in LED Driver and PFC Circuit

Datasheet: http://diodes.com/datasheets/AL6562.pdf I am trying to understand how this IC works block by block and I am confused about over-voltage protection in the error amplifier - specifically ...
0
votes
2answers
114 views

Powering LED Strips with a Constant Voltage Supply and Constant Current Driver

I have a LED strip (16ft Hitlights Luma5 warm-white high-density) powered by a constant voltage supply. I'm considering adding PWM dimming with a Maxim MAX16820 constant current driver. The PWM signal ...
0
votes
2answers
93 views

Help please! I need to give constant current to an LED from a Lipo battery

I'm trying to drive an LED from a Lipo battery. The useable voltage range of the Lipo goes from 4.2V down to 3.4V, and the forward voltage of the LED is 3.2V. With a resistor in series with the LED, ...
1
vote
3answers
137 views

Discharge constant 2A-3A current from a battery

I am supposed to drain a constant current of 2A or 3A from a battery (most probably a NiMH battery). What could be a possible way to do that ? Purpose of doing it is to calculate the battery's Energy ...
2
votes
1answer
114 views

Did Capacitative Loading Kill My Op Amp?

I've been playing with various constant current source configurations to help control the current output of my bench power supply and my latest efforts centred around the op amp and MOSFET approach. ...
1
vote
1answer
73 views

Can I cross the output inductor trace with input power line?

I'm attempting to learn a little more about SMPS design while referring to existing designs and posts such as this one: SMPS PCB Design Critic I'm implementing an AL8805 based constant current buck ...
0
votes
2answers
51 views

CNC stepper motor driving CC vs CV

I am trying to design a small CNC maching for milling PCBs. I am using unipolar stepper motors driven by a microcontroller, but I am unsure of what tehnique to use to drive them. I once read that ...
3
votes
3answers
477 views

How do I build a 10uA current source/limiter?

I need a constant current of 10uA through a variable resistor in the 100k values. I need to inject the current into that resistor and I need the resistor to be connected to Ground such that I can ...
0
votes
0answers
69 views

Charging Batteries in Series

So I am working on charging 2 batteries in series, and have an odd situation that I'm hoping to get answered. I have a single bank charger that outputs 8A and a dual bank charger that is 20A total ...
3
votes
4answers
186 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 ...
7
votes
2answers
351 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 ...
1
vote
1answer
86 views

Facing to real world feedback designs (here, Constant Current Generator)

I still work on a current generator made with 2 opamps and a nMOS. If I find the bias point to understand how much my LED can be driven, I still have problems to find an affordable way to derive the ...
0
votes
1answer
59 views

Meaning of TLC59281 LED supply voltage rating

TL;DR: Does the max VO of 17V refer to the LED supply voltage or only to what's left after the diode drops? TI's TLC59281 is more or less a device that combines two 74HC595-like shift registers with ...
0
votes
1answer
92 views

Practicality of driving LEDs with high voltage?

After watching someone build a fairly wasteful project, I wondered if there was a better way. The LEDs are cheap chinese variety, with a forward voltage of around 34-36V @3A, and they throw off about ...
0
votes
1answer
80 views

Calibrating buck LED driver by altering Vsens

Many switch mode buck LED drivers use a current mode scheme with a sense resistor back to a Vsens or Current Sense input on the chip. A good example is the LM3404. Here's the typical use circuit: I ...
0
votes
1answer
115 views

Driving an infrared LED from a coin cell

I am designing a remote-control type IR transmitter that will be powered by a coin cell battery (i.e. CR2032) and commanded by a microcontroller. The LED is pulsed at around 40kHz. How can I ensure ...
1
vote
0answers
68 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 ...
4
votes
1answer
288 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 ...
1
vote
3answers
88 views

Can I get constant current at the output of a buck convertor (to drive a LED)?

I want to drive a LED with a buck converter circuit as shown in the schematic below. In order to keep the circuit simple, the system will run open-loop (i.e.; there won't be any voltage or current ...
0
votes
1answer
85 views

Capacitors vs buck/boost converters

I'm trying to drive high power LEDs with a laptop power supply, and wondered if I should use resistors to limit the extra current, or something like this to limit the current. If I did use that ...
0
votes
0answers
1k views

Can I turn an LM2596 switch mode PSU into a constant current source?

I have a cheap LM2596 switch mode regulator from eBay: Which I can power with a dual cell LiIon supply (6 to 8.4V). I would like to use this supply to create a variable current source for an LED ...
2
votes
2answers
279 views

Sourcing current with sink LED driver

I'm using an existing keypad with 8 LEDs that source power. I was hoping to use and LED driver of sorts, but all of the ones I find only refer to sinking power. Is it possible to use these drivers to ...
1
vote
2answers
238 views

Constant Current Square Wave through LED

I am running a somewhat powerful LED, on the order of 3.5V 500mA, off of an ~11V battery using a constant current switched mode power supply from Ebay that uses the LM2596. What I need to do now is ...
2
votes
3answers
410 views

How do I keep my constant current source constant?

So I am trying to created a current source that will be used to drain a battery at specific time intervals for a specified duration. simulate this circuit – Schematic created using ...
0
votes
0answers
90 views

Calculating power draw for LEDs and driver (TLC5941)

I am designing a backlit keyboard with 61 white LEDs. These will be individually driven by a TI current limited PWM driver (TLC5941). LEDs: 61 x Osram LCW JNSH.PC (Datasheet) Drivers: 4 x Texas ...
3
votes
1answer
198 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 ...
1
vote
3answers
174 views

how to create a high current source?

I'm looking to observe magnetizing offsets of various current sensors. The idea is that when you pass a high current pulse (close to the rating of the device) through a current sensor and then return ...
0
votes
1answer
133 views

Constant current LED driver min / max current rating explanation

I currently have a 150-1500mA led driver that I sue to power a 30W LED. Driver has adjustable maximum current pins that I can use to change to match the maximum current. I have it set to 1050mA. I am ...
-1
votes
1answer
138 views

Back EMF and Source EMF, stabilizing current?

In a circuit where there is change in a magnetic flux, Back EMF is induced. When back EMF is increases it reduces the source EMF( or oppose it) and therefore, the current is reduced, in order to ...
0
votes
0answers
113 views

3x CAT4101 parallel with CREE LEDs

I've tested the LEDs with one CAT4101 and they work great, but now it's time to dial it up a notch. I've now got three CAT4101's wired up in parallel to give me 3A to drive two 10W CREE LEDs in ...
0
votes
1answer
211 views

Switched-mode constant current supply with Schmitt Trigger

I'm planning on building a small constant current power supply for charging lithium-ion batteries on the go. While they normally use constant current AND constant voltage, I've elected not to include ...
0
votes
2answers
67 views

How can I tell if my current is continuous in a first order DC circuit with a switch

Assuming this circuit has been running for a long time (switch SW1 is closed), and in t=0 the switch (SW1) opens, and I'm being asked about the current that runs through the inductor L1. I know that ...
4
votes
5answers
436 views

Constant current circuit

I'm back for another question, this time shorter than the wall of text I posted last time! Here is my question: How does the red (rot) LED at the input to the base provide a constant current to ...
6
votes
2answers
749 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 ...
-1
votes
1answer
619 views

Is it possible to increase voltage without changing the current? [closed]

If we have a certain power applied to a circuit, and we would only like to increase the voltage applied by large factors... can this be done? Maybe by increasing only the resistance? Or maybe by ...
-2
votes
2answers
399 views

Constant current led drivers shared ground

I have 4 constant current led drivers with PWM. Here's 300-1500mA LED Driver datasheet. I want to use 3 of these drivers to power each color of a 90w rgb led. I was under assumption that I could ...
0
votes
0answers
104 views

Controlling a TLC5927 LED Driver

I am trying to control TLC5927, with no success. I have read the whole datasheet, but I still can't figure it out. I tried to simulate it, with no success too. Can someone draw me a timing diagram ...
0
votes
0answers
212 views

Keeping current constant during PWM dimming of a LED string

simulate this circuit – Schematic created using CircuitLab I'm looking for a good control method for PWM dimming a string of LEDs and keeping the current through the LEDs at a constant ...
0
votes
1answer
77 views

Differences between a LM317AHVT and a LM317T

Is there any practical difference between the LM317AHVT and LM317T vis-a-vis regulating a 900mA, 9-12V LED?
0
votes
1answer
322 views

Constant current driver LED over-voltage effects [duplicate]

I have a 90W RGB led. Voltage range is 32-34V for green and blue but it's 22-24v for red. To what extent does the voltage matter if the current output is limited to let's say 30W (max for single ...
-2
votes
2answers
94 views

Increasing current [closed]

Here an interesting challenge. You have a 3 volt 50uAh battery. How many would it take to create a device that can supply 3 volts at 1mAH. Would you connect them in parallel or series or a ...
3
votes
4answers
336 views

Ideal constant current source?

I've developing an LED fixture for my aquarium to grow plants. To do so, I've selected several high powered LED's. I'm currently considering driving them with LM317's because I know how to use those ...
0
votes
1answer
123 views

Can I use constant current LED driver as input to Buck regulator?

I have an 100W constant current LED driver that I bought in error but maybe I can use it in another way. I want to use 3 buck regulators to pwm control each individual color of 90W RGB LED. Can I ...
0
votes
1answer
248 views

Is there any benefit of making lamps with high wattage LEDs but low wattage driver circuits other than cost?

Over the past few years I have bought a number of GU10 mains voltage LED bulbs and have generally been disappointed with their brightness. The 9W LED bulbs I bought (supposedly 460-590 Lumen) produce ...