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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16
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2answers
1k views

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 ...
2
votes
2answers
78 views

Mixed forward voltage LEDs in series with constant current driver

I've been looking for answers for a few weeks, so now I'll actually voice my question! My plan is to power 109 LEDs in series off of one constant current driver. The goal is to create supplemental ...
6
votes
2answers
119 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 ...
0
votes
1answer
42 views

Constant Current IC Driving a String of ICs

I have been having difficulty wrapping my head around the ideas of constant current and constant voltage. Basically I have assembled this circuit with an arduino. Now, imagine that I wanted to ...
0
votes
1answer
70 views

Multiple TLC5940s on PCB “dropping out” when many outputs turned on

I've designed a PCB to connect 12 TLC5940s to an 8x8x8 RGB LED cube through 3 64-pin headers, which I will include screenshots of below. I have a separate board for controlling the anodes for ...
5
votes
3answers
308 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 ...
1
vote
1answer
47 views

Buck controller MOSFET drive voltage

I am trying to design a switching regulator for LEDs, which uses the LM3405 as controller. This IC uses the BOOST pin to power the internal MOSFET driver, which controls an internal MOSFET. There are ...
0
votes
1answer
40 views

How to programme constant current of a LED Driver for various current levels?

I need to design a backlight unit that will change its duty cycle and constant LED current via a microcontroller. My supply is a SMPS with 12V - 20A output. I need to drive 16 * 16 = 256 LEDs(seperate ...
0
votes
2answers
61 views

Charging lead acid battery using boost/buck converter

I plan on permanently connecting a 12v lead acid battery to my home made wind turbine (dc). I already have a dc-dc buck/boost converter so I wonder if i can use that to charge the battery. ...
0
votes
1answer
88 views

Automatic switching of a constant current circuit

I'm running 14 ~3W (700mA) LEDs in series on a constant current LED Driver that handles between 36-65V output. The driver runs the LEDs at 600mA. The heatsinks I've attached are pretty small, and if ...
-1
votes
1answer
30 views

Adjust the power of laser diode on both CW and pulsed mode

I am working on my graduation project to build a laser unit, i am supposed to control the power of laser diode when operating in pulsed mode and continuous mode. firstly, i had the pulses from ...
3
votes
1answer
132 views

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 ...
0
votes
0answers
72 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 ...
-4
votes
1answer
133 views

Is there a way to get dc out of a capacitor? [closed]

The voltage and current during discharge of a capacitor is describe with an e function. I assume that thus a separate component is necessary (since ...
0
votes
2answers
198 views

constant current source circuit

I am designing a constant current source(35mA) circuit using transistor.Thought of usingthis below circuit but the problem with that is my resistance R is fixed( 2.3 ohm ) which I could not change due ...
0
votes
1answer
83 views

How do “Inverter” or “IGBT” welders control CC and CV output?

I have a question on welding units. A lot of the newer units these days have "Dependable Fairchild or Infineon IGBT (non module)", "MOSFET design for Hobby use" and I can't tell if all of this stuff ...
1
vote
0answers
51 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 ...
1
vote
2answers
126 views

How can I make a Fuse Blown Indication LED circuit with variable voltage input?

I'm creating a power supply with an input fuse and and output fuse, and I'd like to have blown fuse indicators. However, the circuits I have found typically have set voltages and thus set resistors, ...
2
votes
1answer
71 views

Mirroring constant current

I'm trying to draw a constant 60mA from a battery but I get a draw that is too high with the following setup. Does anyone know what I'm doing wrong? Regards EDIT: Sorry I added the wrong measures. ...
4
votes
2answers
112 views

Why sample current via lopsided resistive divider?

I'm studying the constant-current circuit of the Agilent E3610A 15V 30W DC Bench Power Supply. The entire schematic is at the end of the user manual, but I've redrawn the parts of interest here for ...
0
votes
3answers
153 views

High Side Constant Current Source

I am trying to create a constant current source of 100mA to charge a single cell Li-ion battery. I see the LM317 thrown around a lot as a solution, but I'm looking for something that does not require ...
0
votes
1answer
63 views

Instrumentation Amplifier output mysteriously increases upon connecting across a resistor, compared to connecting the same voltage directly across it

I am designing a simple resistance measurement circuit. Resistance range is from \$10m\Omega\$ to \$10k\Omega\$ and desired accuracy is 0.1%. The circuit provides constant current to the resistance ...
1
vote
2answers
151 views

Is it possible to build non-linear resistor using linear potentiometer

I have CAT4101 constant current LED driver and I need to control LED current. My idea is to use microcontroller and digital potentiometer (MCP41010) to control the current. While the potentiometer I ...
1
vote
1answer
138 views

7805 for 4-20mA current injector

I'm trying to setup a low cost current injector for testing certain I/O modules. I found a rather simple design for a current source using 7805. simulate this circuit – Schematic created ...
0
votes
1answer
152 views

MOSFET as constant current source?

This circuit is being called a constant current source, how can this be? Since the gate and the source are both connected together their isn't a potential difference between them. Doesn't' this mean ...
0
votes
1answer
48 views

Advice on driving the DRL leds

I'm going to be using 2 sets of three 12v 9W leds, purchased from that well known auction site so that's all the info I have, as daylight running lights. Obviously I could simply connect them up (in ...
1
vote
1answer
130 views

LED constant current driver

I need a constant current of 400-500mA for each color of a 10W rgb LED. Each color consists of 3 1W chip is series. for 3 LEDs in series I'll need about 11 Volts for blue and 8 volts for green. So far ...
2
votes
2answers
128 views

Puzzled with the result of LM317 constant current

So, LM317 can be used as a constant current regulator by adjusting the voltage in the Adj pin. The internal voltage reference is 1.25V, and so using a 1.25/0.900 ~= ...
1
vote
0answers
80 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 ...
3
votes
1answer
115 views

Multiple power supplies in home-made circuit

I'm planning to build an ebb-and-flow hydroponic system (nope, not for weed) and as my electronics skills are close to zero, I'm trying to put things together before soldering anything. I'm a decent ...
0
votes
1answer
139 views

LM317 constant current load

Would this work as a constant current load since I don't have a high power pot? Is there a better way to do it? simulate this circuit – Schematic created using CircuitLab
0
votes
1answer
55 views

TPS40211 PWM LED driver topology

I've recently been trying to figure out an LED driver circuit for my 32V, 0.7A CoB emitter. I settled on the TPS40211, since it ticked all the boxed in terms of input voltage range, output, etc. I ...
1
vote
2answers
154 views

Limiting current through Zener shunt reference by PNP current source

I've got an unregulated input voltage of 5V..20V from which I need to drive a shunt reference LM4040 at 3.3V. According to my calculations a shunt resistor of 1.5kOhm would result in a peak current of ...
7
votes
1answer
462 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 ...
1
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0answers
37 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 ...
1
vote
1answer
120 views

12V regulator for 100W LED

I want to make a 100W high power LED headlight for bike, but the problem is that LED releases a lot of heat, and I'm using a 150W boost converter to convert 12V to 30V ( minimum operating voltage of ...
0
votes
0answers
100 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 ...
0
votes
0answers
52 views

Battery powering two LED's with a led driver

Currently I am working on an application that is battery powered. I have two reflective sensors (RPR220 and RPR220-PC30N) which I am comparing to eachother. As a power supply I use 4 AA none ...
2
votes
1answer
157 views

Discrete LED Driver Topology

I have drawn the above schematic by reverse engineering a locally available LED Bulb. I was expecting to find an IC in the driver board but instead found this discrete circuit. Googling "Discrete ...
-1
votes
1answer
52 views

Current Regulator IC/Transistor [duplicate]

Can anyone suggest a Current Regulator that can bring down 2A to 40mA... I'll be needing 40mA to power my arduino... I'm not that keen in electronics so pls use simple terms in explaining things to me ...
0
votes
3answers
191 views

Driving an LED with a low amplitude square wave as an input of MOSFET switch

I am trying to drive an LED with a square wave. I've made a circuit like below: The problem is, an equiment can generates a square wave with a limited amplitude up to 1.7 V. After some experiments, ...
2
votes
1answer
885 views

Why use a transistor for getting a Constant Current Source in a circuit with an op amp?

I have used the above simple circuit for a constant source where \$V_{\text{in}} = -5\$V, \$R_{\text{in}} = 390\Omega\$, \$R_f\$ is the load which ranges from \$110\$ to \$170\Omega\$....would using ...
0
votes
0answers
53 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 it's ...
2
votes
2answers
95 views

please help choose mosfet, npn, pnp, diode for my circuit

I developed a circuit which uses charge pump to supply a current mirror. Simulation works, I was able to get 40V and constant 10 mA at load < 4k. I breadboarded each charge pump and current ...
0
votes
1answer
67 views

How to get constant current across varying Rload in h bridge

My I is a constant source of 10 mA from Vsupply of 50V, so my Rload can max at 5k at 10mA. I load is going both directions. My Isource is constant, but Iload is changing with varying Rload, why is ...
1
vote
1answer
116 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
112 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
502 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
43 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 ...
1
vote
1answer
99 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 ...