hybridfree/eevblog-posts huggingface dataset:
LED current mirror - Page 1
Forum section: electronics / beginners

author: deSitter
author_rank: Newbie
timestamp: February 27, 2017, 11:51:00 pm
content: Hello, first time poster, long time lurker.I'm working on a LED lighting solution and am looking for some feedback on my schematic. Due to certain constraints I've chosen to go with a single 1400mA constant current driver with suitable voltage to supply 8 parallel strings of 8 COB LED's each with ~0.175 A of current. I'm finding my biggest hurdle at the moment is dealing with current imbalances/thermal runaway in each string. I'm attempting to use a current mirror to resolve this problem, but this is the first time I've made a current mirror, so my confidence in the design is not that great. Does anyone have any thoughts or improvements on this design (see attachment image)? My electronics knowledge is limited to high-school physics, so please keep that in mind.I've simulated this schematic and everything appears to be working as intended under stable conditions. Though I am aware that a failure in all but the reference string will result in over-driving the remaining strings. Also, as for the resistors R1-R8, I'm not entirely convinced of their purpose. I somewhat understand their use for stability (thermal changes in the transistor?) with regards to DC biasing an amplifier circuit, but I'm not sure if the effect is the same in this case, nor am I sure of their value if they were to help.Thank you,

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: February 28, 2017, 01:23:50 am
content: yes the R are local negative feedback and definitely help balance the currents vs transistor heating and other parameter differencesfor this circuit an estimate of the amount of feedback has an interesting shortcut: feedback factor ~ V dropped by the R divided by 26 mVso sizing the R to drop > 260 mV makes the circuit very independent of the transistors - but do use all the same model number Q and stay within their power ratings

author: David Hess
author_rank: Super Contributor
timestamp: February 28, 2017, 03:56:03 am
content: It should work fine but I wonder if it is worth it. The reference transistor will drop a Vbe of 0.6 volts and about 0.3 volts for a reasonable R. So if an average of 0.9 volts drop for each current sink is assumed, would just replacing them with appropriate power resistors be good enough?Grading the transistors for Vbe will noticeably improve the matching with such a low emitter resistance but matters less as the value of R increases.
LED current - Page 1
Forum section: electronics / beginners

author: Unknown
author_rank: Unknown
timestamp: October 02, 2013, 04:10:03 am
content: Hi,I have a circuit shown below but I don't know how to calculate the LED current(I3). The Vs is 5V.Any ideas?Edit : I can solve this problem.

author: Bloch
author_rank: Unknown
timestamp: October 02, 2013, 04:45:00 am
content: Quote from: loga on October 02, 2013, 04:10:03 amI love to make you home workShow how you think it can be calculated.

author: IanB
author_rank: Super Contributor
timestamp: October 02, 2013, 04:54:37 am
content: Yes, that doesn't look like a practically useful circuit, it looks more like an exercise.What have you tried so far, and where did you get stuck?

author: Unknown
author_rank: Unknown
timestamp: October 02, 2013, 07:21:45 am
content: It's not my home work. It's a circuit that I see on the internet years ago and looks like a simple circuit but I can't figure out why no need a resistor on the LED branch. I just want to know how LED affect to current I1.If there is no LED I can solve my problem with KVL.Vs = I1*R1 + Vf + I1*R2 + I1*R3Vs = I1*(R1+R2+R3) + VforI1 = (Vs - Vf)/(R1+R2+R3)But when the LED is present in the circuit and I1 <> I2 but I1 = I2+I3.To IanB: this circuit come from $0.99 product from china.

author: Psi
author_rank: Super Contributor
timestamp: October 02, 2013, 07:37:01 am
content: Quote from: loga on October 02, 2013, 07:21:45 amR1 and R3 limit the total current in the circuit.The current through R2 further splits this current.So the LED is limited by the remainder.

author: ve7xen
author_rank: Super Contributor
timestamp: October 02, 2013, 07:42:25 am
content: Assume that Vf of both diodes is fixed, but they are not equal. D1 as a 1N4001 will have a lower Vf than the LED, so the LED Vf sets the drop across R2+D1. These assumptions should be enough to make KVL solvable.

author: AndyC_772
author_rank: Super Contributor
timestamp: October 02, 2013, 08:03:07 am
content: Combine R1 and R3 into a single resistor, located in the existing position for R1.Assume a constant forward voltage Vf for the LED, and a different constant voltage Vf for the diode.Call the battery -ve terminal GND. Now you know the voltages (with respect to GND) on both sides of both diodes.I2 = (Vf - Vf) / R2I1 = (Vs - Vf) / (R1 + R3)I3 = I1 - I2... and solve from there.

author: Unknown
author_rank: Unknown
timestamp: October 02, 2013, 10:25:38 am
content: Quote from: AndyC_772 on October 02, 2013, 08:03:07 amAt first I think as your solution. I must assume a constant forward voltage Vf for the LED and I can find I3.Butassume that we don't know Vfbut we know Vf say 0.7V.I simulated this circuit on LT Spice, I tested on breadboard but I can't find I3. with myself.That is why I asked how to calculate I3.

author: AndyC_772
author_rank: Super Contributor
timestamp: October 02, 2013, 10:33:54 am
content: You need to know Vf, it affects I3! You can't calculate one without knowing the other, or at least, the relationship between the two.
LED Dimming - Page 1
Forum section: electronics / beginners

author: dlad87
author_rank: Newbie
timestamp: April 12, 2021, 02:09:48 am
content: Hello,I’m looking to dim a standard 5mm led based on the position of a 100k volume pot.Not sure if it’s possible to do so using a single gang pot that is already controlling the volume of a mono audio circuit?I am also not opposed to using a 100k double gang pot (one side for volume and one for the led) but am still not sure how I would supply the right voltage range to the led with the 100k value pot. Not sure if there’s some kind of led driver that could do the job or some kind a CCS.The supply voltage is 9 volts.Thanks

author: ledtester
author_rank: Super Contributor
timestamp: April 12, 2021, 02:23:45 am
content: There are two ways to control the brightness of an LED:1 - control the current going through the LED2 - turn the LED on and off with a duty cycle between 0 and 100% (PWM dimming)Both methods will require extra circuitry.Here's a link to PWM dimming an LED with a 555 timer:https://www.electronicshub.org/pwm-led-dimmer-using-ne555/

author: dlad87
author_rank: Newbie
timestamp: April 12, 2021, 02:52:30 am
content: Thanks,I was reading that earlier. Would that circuit work with a 9V supply? And what effect would it have using a 100k pot instead of a 50k?

author: ledtester
author_rank: Super Contributor
timestamp: April 12, 2021, 04:42:50 am
content: I would just try it - you won't blow anything up.
LED Display multiplexing voltages and currents - Page 1
Forum section: electronics / beginners

author: LinkZ
author_rank: Contributor
timestamp: May 17, 2015, 07:50:04 pm
content: I've ordered this clock from aliexpress:http://www.aliexpress.com/item/0-56-Blue-LED-Meter-Electrical-Digital-Car-Motorcycle-Clock-Watch-DC-12V-24V-Time-Display/2019045353.htmlI want to use his circuit to drive a much larger display made from several 3mm leds, so i will drive the 3mm leds with transistor configured as switch. I've desoldered the original display from the clock to figure out if is a common cathode or common anode. It's a common cathode. So I tried to measure the voltages from the microcontroller outputs (where the original display was soldered) of the clock but I get positive voltages only from certain pins and the others (where you expect to read the same voltages) are negative and/or just too low to lit a LED display. I need those voltages because I have to calculate the Vbe to drive the transistor configured as a switch. What did I missed?
LED display out on Yamaha EMX512sc mixer - Page 1
Forum section: electronics / beginners

author: BluesCam
author_rank: Newbie
timestamp: December 30, 2015, 10:07:44 pm
content: Hello everyone. I have a Yamaha EMX512SC powered mixer. It seems to work OK, except the main output LEDs, both L&R do not light up when the signal is wide open. There are two LED drivers in there. Any ideas? Thanks
LED driver projects - Page 1
Forum section: electronics / beginners

author: smartone
author_rank: Newbie
timestamp: August 08, 2024, 10:46:59 pm
content: Hi,I am looking to make some LED light for my Garage / Workshop.Using some 2835 LED.Is there any good open source LED driver projects out there.Plus would be good for them to be dimmable.Thanks Stephen

author: PGPG
author_rank: Frequent Contributor
timestamp: August 09, 2024, 12:01:03 pm
content: Not sure if it will be very helpful as my task was different - to have problem solved once and for all.Since 20 years I had in the corridor a lamp designed for 2 halogen G9 60W bulbs. The lamp has no ventilation and a month or two after putting in 2 bulbs one always burned out. For the next 2 years one stayed. I tried to use 3W LED G9. Effect (with one being burned fast) the same but also I got strong stroboscopic effect (I have oscilloscope waveform of its light if someone is interested).Last month I have bought (about $3) 24W AC230 -> DC12V supply. Four 20cm pieces of 2835 LED type (more then 10W/m, 3 LEDs per 2.5cm) would give me enough light. But I used 8 times 20cm pieces and reduced its current 2 times (by reducing DC supply output voltage to 10.5V).That way I have got:- the same light as for 4 pieces,- about the same internal lamp temperature as for 4 pieces,- 2 times lower temperature difference between LED structure and internal lamp temperature.It is structure temperature what kills LEDs. I believe that reducing it may be 30°C I extended the life of the LEDs maybe 10 times.Regulating LED12V tape supply from may be 9V to 12V you regulate its light from 0 to 100%.

author: wasedadoc
author_rank: Super Contributor
timestamp: August 09, 2024, 12:17:14 pm
content: "Divers". Both times!Not to mention the grammatical error in a later sentence.

author: smartone
author_rank: Newbie
timestamp: August 09, 2024, 01:04:17 pm
content: up dated

author: smartone
author_rank: Newbie
timestamp: August 09, 2024, 01:20:26 pm
content: I was looking to make it a home project.Get some PCB made for the drivers and LED strips and building it all myself.Looking for some help with LED driver and see what I can do.I now have 3000x Lumileds L128-5090SA35A00G1 LED

author: wasedadoc
author_rank: Super Contributor
timestamp: August 09, 2024, 02:13:37 pm
content: Quote from: smartone on August 09, 2024, 01:04:17 pmOnly partly.And "update" is not two words.
LED - Downlights/Recessed Lights - Quality, Safety - Page 1
Forum section: electronics / beginners

author: Paranoid
author_rank: Newbie
timestamp: July 13, 2022, 07:00:02 pm
content: I been looking to upgrade old recessed can lights with "modern" LED slim potlights, Market is flooded with different brands.I went out and purchased a bunch of LED lights, removed the drivers, and snapped some pictures.And I'm blown away by how much the design varies between the cheapest and most expensive brands. While I don't understand any of the circuits, the amount of elements between brands is significant.I take SAFETY over longevity, as I have seen some pictures on Amazon of LED drivers catching on fire.I'm leaning toward thePS-B( Second picture ) as they are not the cheapest and not most expensive. The only concern is that the Driver enclosure is plastic (PBT) which is placed in metallic box where power terminates, other units have metal separation between wiring and driver.To get to the topic, my question: Could someone please explain to me why some of the boards have so few components? Is this a more modern design of the led driver, safety cost cutting?What safety elements should an exemplary LED driver have?

author: John B
author_rank: Frequent Contributor
timestamp: July 13, 2022, 08:29:22 pm
content: Some designs are like any other flyback DC power supply, but some LED drivers have to prioritise power factor for regulations etc, and so they use very low capacitance on the input and draw a sort-of sinusoidal current from the mains. The output usually has a fair bit of ripple.On the other hand, the last design isn't even isolated from the mains. Cheap - and higher risk depending on the application.

author: Paranoid
author_rank: Newbie
timestamp: July 13, 2022, 08:55:50 pm
content: Thank youI don't understand the answer fully I will do some searching but appreciate input ! happy to learn.Interesting about the last unitI'm leaning towards the PS-B ( second ) does not seem like they tried to skimp on components and its selectable colour.I was looking at circuits and one of the elements is CS98P171 - 8-bit GP-type Microcontroller with OTP ROMhttps://www.crmicro.com/Home/Products/IntelligentC/tyxmcu_en/Why would there be a need for MCU in Led Driver ?
LED Driver 900ma okay for 700ma LED? - Page 1
Forum section: electronics / beginners

author: robotic
author_rank: Contributor
timestamp: September 26, 2017, 12:40:51 am
content: So I'm planning on getting a 700ma 3W LED runs at 3.8V. I'm planning to buy a 21-38V 900ma (+-5%) LED driver.Will this work if I want to run 9 LEDs.Main question is can i get a 900ma driver for 700ma leds, I always assumed leds will draw as much current as needed. not sure the LEDs will draw more then needed and burn out.

author: sleemanj
author_rank: Super Contributor
timestamp: September 26, 2017, 12:59:12 am
content: No.LED are current controlled. You feed 700mA leds 900mA and they will gladly eat themselves to death.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 26, 2017, 01:09:17 am
content: Light Emitting Dog?

author: robotic
author_rank: Contributor
timestamp: September 26, 2017, 01:23:12 am
content: So 600ma Driver would be better? Just less light?

author: sleemanj
author_rank: Super Contributor
timestamp: September 26, 2017, 01:31:14 am
content: YesYou probably wouldn't even notice less light anyway, and it will be better for the LEDs, less current = less heat.

author: bjcuizon
author_rank: Frequent Contributor
timestamp: September 26, 2017, 02:41:31 am
content: Quote from: Alex Eisenhut on September 26, 2017, 01:09:17 amIf more than the usual, rated current is put into the led, then LED will stand for "Likelihood ofEarlierDeath".

author: Brumby
author_rank: Unknown
timestamp: September 26, 2017, 05:18:11 am
content: Quote from: robotic on September 26, 2017, 12:40:51 amNo. LEDs will draw as much currentastheycan.As said above, offering 700mA rated LEDs 900mA will guarantee their early demise.

author: robotic
author_rank: Contributor
timestamp: September 26, 2017, 10:59:40 pm
content: Thanks. I'll buy the 600ma driver =).
LED driver 9V at 220mA - is there a better way than NCR321Z? - Page 1
Forum section: electronics / beginners

author: aeberbach
author_rank: Regular Contributor
timestamp: July 18, 2021, 07:48:22 am
content: Got some answers for this project previously about switching various supply voltages with transistors and MOSFETs. I had a board made and it works great - now tuning the operation of various supply sections.I'm trying to drive a backlight for a LCD display and the panel datasheet says it wants a nominal 9V 220mA. I have a capable 9V supply. LED anode and cathode terminals are provided at the panel connector so I have the 9V supply on the anode and on the cathode, the the NCR321U in SOT457, driven by PWM*, to sink up to the maximum 220mA. It gets finger-burningly hot. I realise I should have used the NCR321Z, higher power sink in SOT223 package. Even so with a meter measuring current in place of the backlight I see this works fine. Is it just a fact of this panel's current requirement that things are going to get hot? A LM317 would be as good but without the PWM? I don't think I would expect the heat to be be any lower when the LEDs are in place, it's still the same current, right? Do I just provide plenty of copper for the SOT223 to stay as cool as possible?How would you do it?Link to device datasheet:https://au.mouser.com/datasheet/2/916/NCR320Z_NCR321Z-1599139.pdf*I like that I will be able to use PWM output from the FPGA to control panel brightness, using a rotary encoder.

author: Zero999
author_rank: Super Contributor
timestamp: July 18, 2021, 09:32:03 am
content: The NCR321Z is a linear regulator, which will dissipate the excess voltage drop, as heat. Your current meter hardly drops any voltage, compared to the LEDs, so it should run much cooler with the backlight connected.Your power supply voltage should be a little higher than the 9V required by the LEDs, otherwise the NCR321Z will not regulate the current properly.
LED Driver current setting of floodlight - Page 1
Forum section: electronics / beginners

author: Tantalum
author_rank: Regular Contributor
timestamp: January 20, 2022, 03:37:58 pm
content: HelloI have bought some cheap Chinese 12-24VDC "20W" floodlights and I wanted to add a module that would allow me to dim the brightness. Fortunately, the LED driver has a dedicated pin for that feature, it will be easy to modify.Now the problem.I was verifying the original PCB of the floodlight, and there are something strange with the current settings.It's a PT4115 LED driver, (NOT PT4115E), max 30VDC, 1.2A. The LEDs are 3.2V, 150mA max I thing.Datasheet:https://www.led-stuebchen.de/download/PT4115E.pdfI was checking the sens resistors, and realized that they were out of specs. There are 2 resistors in //, 91 & 82mOhm which makes an equivalent 43mOhm resistor, which is not enough according to the datasheet (minimum 82mOhm = 1.2A max).A 43mOhm resistor sets the current to 2.36A! Way too much for a 1.2A max led driver.When I analyze the led network, I can't figure out how much current is actually flowing through each LED.Can someone help me answering the following questions:Q1: Is this default setting a problem (=reliability issue)?Q2: How much current flow through each led?Q3: Is the giant ground loop a problem (V+ on the left, ground on the other side?Thank you

author: tunk
author_rank: Super Contributor
timestamp: January 20, 2022, 04:01:24 pm
content: Q2: Looks like there's two LEDs in series and 12 in parallell. Divide by 12 to get the average current.
LED Driver Dimming Simulation - Page 1
Forum section: electronics / beginners

author: merymery
author_rank: Contributor
timestamp: March 09, 2021, 08:58:45 pm
content: Hello everyone, I am working on SEPIC LED driver for my university project, I designed my LED driver in the simulation program. I used resistance as a load. I run it under PWM control by giving square waves from the signal generator. I get the output values I want in my simulation. Should I change the resistance value and duty value for LED dimming? I looked at the V-i characteristic graph from my LED catalog and entered the resistance value corresponding to the voltage-current values, calculated the new D value for the SEPIC converter according to the V value on V-i graph. When I enter the duty and resistance value in my simulation program, I cannot obtain the desired current and voltage value. I could not be sure whether my technique is wrong. This is my first experience with a Led driver, did I go the wrong way? I will be glad if you help

author: sigma_xi
author_rank: Contributor
timestamp: May 29, 2021, 06:40:13 am
content: Setting a fixed duty cycle is not going to work well. Usually LEDs are driven by a constant current. To do so, connect the LED in series with a current sensing resistor to your SEPIC output. Use the voltage across the resistor as feedback to automatically control the duty cycle of your driver.

author: Zero999
author_rank: Super Contributor
timestamp: May 29, 2021, 08:08:31 am
content: You need to control the current through the LED, not the voltage. Redesign your SEPIC converter so it regulates the current, rather than the voltage, by taking the feedback from a current sense resistor. Dimming can be implemented by PWMing the SEPIC converter on and off, at a much lower frequency, or by adjusting the LED current.
LED DRIVER ELP18X1CS - Page 1
Forum section: electronics / beginners

author: GHOSTKILLER1RO
author_rank: Newbie
timestamp: September 08, 2015, 10:36:55 am
content: Hi everyone! I'm new on this forum and I need some help. I recently bought two ELP18X1CS led drivers to power my 10w leds bought from ebay. After receiving the led drivers I was shocked that they are rated at 72V DC max. and a constant current of 350ma , while my leds are rated at 12V DC max. Can someone please tell me what can I do with these drivers, because I don't think I will manage to power my leds? What kind of leds are these designed for?Thanks! Sorry for my bad english.

author: cowana
author_rank: Frequent Contributor
timestamp: September 08, 2015, 11:01:57 am
content: LEDs are rated in terms of current - they require driving with a constant-current power source - the exact voltage drawn will depend on the batch, temperature, etc etc.For your LEDs, they will probably want a maximum current of 700mA, and this will correspond to a voltage somewhere around 12v.The ELP18X1CS LED driver will supply a constant current of 350mA at a voltage between 30 and 60v. This means it will happily drive a series string of three to five of your LEDs - although at a reduced power/brightness due to the reduced current.
LED Driver recommendation - Page 1
Forum section: electronics / beginners

author: scott216
author_rank: Regular Contributor
timestamp: November 03, 2013, 06:36:40 pm
content: I'd like to drive 4 RGB LEDs from an Arduino Pro-Mini (5V version) using the PWM output pins. The LEDs would all be wired together, I don't need to control them individually. The LEDs are common anode drawing 20mA/color, like this one:http://www.sparkfun.com/products/10821/.I'm looking for suggestions on how to do this. I guess I could get a little MOSFET for each color and use that with a resistor to drive the LEDs, but I know there are a whole bunch of LED driver chips available. When when I searched onDigikeyI was overwhelmed with the choices and didn't know where to start. Driver can be through-hole or SMD as long as the SMD can be hand soldered. I'd appreciate any suggestions.

author: mariush
author_rank: Super Contributor
timestamp: November 03, 2013, 06:56:41 pm
content: TLC5925, TLC59281 etc sounds like good chips to use.http://uk.farnell.com/texas-instruments/tlc5925idwr/led-driver-constant-current-soic24/dp/1858096http://uk.farnell.com/texas-instruments/tlc59281dbqr/led-driver-constant-current-ssop/dp/2323439serial in, 16 constant current out...

author: Kjelt
author_rank: Super Contributor
timestamp: November 03, 2013, 07:03:42 pm
content: Quote from: mariush on November 03, 2013, 06:56:41 pmHowever serial data in and TS asks for:Quote from: scott216 on November 03, 2013, 06:36:40 pm
LED driver specifications - Page 1
Forum section: electronics / beginners

author: Tantalum
author_rank: Regular Contributor
timestamp: May 27, 2022, 02:10:48 am
content: HelloThere is a specification of a led driver that I don't understand. It's about a TPS61196-Q1.Datasheet:https://www.ti.com/lit/gpn/tps61196-q1What does that mean "400mApulseoutput"Thank you

author: Zero999
author_rank: Super Contributor
timestamp: May 27, 2022, 08:43:45 am
content: It can supply a 400mA for a very short length of time, but only 200mA continuously. The duration of the pulse and the length of time between pulse should be specified elsewhere on the data sheet.

author: Tantalum
author_rank: Regular Contributor
timestamp: June 01, 2022, 11:09:17 am
content: Thank you
LED driver with BP2519  - Page 1
Forum section: electronics / beginners

author: deralbert
author_rank: Contributor
timestamp: January 21, 2023, 02:16:17 pm
content: Hello, I'm learning how to build a LED driver (in the end I will be able to control the circuit with my smart phone, so I want to build a kind of smart bulb, but unfortunately I'm not that far yet.). I have chosen a controller and am trying to understand the circuit from the datasheet. The link to the data sheet is here:https://datasheetspdf.com/pdf-file/1097656/BPS/BP2519/1.The circuit from the first page of the datasheet with my additional notes:https://www.linkpicture.com/q/Screenshot_1370.jpgI have a few questions about this circuit which I have summarized below:1. (Red) In the "Start Up" section of the datasheet it says that after the output voltage is built up it is used for the Vcc pin of BP2519. But what about the red marked resistor? Does the current stop flowing through this resistor at all after BP2519 is turned on?We see, there is a connection from full bridge rectifier through this resistor and a capacitor to GND. The current then should flow through this resistor from the output of the rectifier all the time! In other words: What prevents the rectifier current from flowing through this resistor after BP2519 has started?2. (Green) What is the purpose of this diode? Is it to prevent the full DC voltage from appearing at the output (let's say 230V DC coming from the rectifier)?3.(Blue) Several things come together at this point. The current flows through the transistor (if it is conducting) through the resistor Rcs (Current Sense resistor) to this point. Then there are two possibilities: Either the current flows to GND or to the inductor Lm. According to my naive opinion the current should flow entirely to GND and not even try to flow through Lm, at least because the resistance of the wire to GND is smaller as the (parasitic) resistance of Lm.In my opinion there shouldn't be a direct connection to GND to the left of the point, and everything should look like I painted it with the blue color. Is it correct? If not, and the circuit from the datasheet is correct, then why is the current flowing through Lm at all when there is a path to GND (with the smaller resistance)?4. (Purple) Why is the coil labeled Lm and not just L? Does this "m" say something special?5. (Orange) What is the purpose of this diode? Is it used to build a way back for the current from the output?6. (Light blue) In the circuit we see two different GNDs. What is GND in the middle in the circuit? What is this GND connected to? Are all three GNDs connected together somewhere? If I build a device according to this circuit and then connect it to the mains at home, I only have a GND in the socket and accordingly only one return path for the current. I don’t have another "second" GND.The datasheet and the circuit are also in attachments. Thank you in advance!
LED drivers with different V - Page 1
Forum section: electronics / beginners

author: matgube
author_rank: Newbie
timestamp: October 31, 2023, 03:27:51 pm
content: Hi all,I hope this is the right place to ask.I have two sets 7-segments digits, one mirroring the other, a sort of scoreboard with feedback to the user.One set needs to be very large and bright ("front" digits), the second small ("back" digits).I found suitable components, the front set works with 12V, the back one 5V.I was planning to use a LED driver like "Maxim Integrated MAX7219ENG+ PDIP Display Driver, 64 Segment, 24 Pin, 5.5 V". This works fine for the 5V LEDs, but not for the 12V. The idea is to be able to control one 5V digit and one 12V digit with the same output from the driver.What are my options? I'd like to go with something off the shelf rather than having to have a bunch of shift registers.Thanks!Matt

author: Terry Bites
author_rank: Super Contributor
timestamp: October 31, 2023, 03:39:59 pm
content: Here you go - direct from the MAXFOLK.

author: themadhippy
author_rank: Super Contributor
timestamp: October 31, 2023, 05:05:55 pm
content: QuoteULN2003 or ULN2803 driven by the 5v lines and controlling the 12v lines?
LED failure. LED is blinking - Page 1
Forum section: electronics / beginners

author: Stefan
author_rank: Contributor
timestamp: January 04, 2016, 02:17:32 am
content: I have a cheep LED flashlight. It consists of five white LEDs, one of which has started to blink. I'd guess about 10-20 times a sec or so, with a constant frequency, as far as I can tell. The odd thing is that the LED's are all wired in parallel and the others are working fine. The little PCB is in rather poor condition, but I don't think it is a slack joint, as the effect is constant no matter what I do to it.What kind of failure mode can cause that? What causes the oscillation? The cirquit is as simple as it gets. Two AA batteries in series connected to the LEDs. There isn't even a proper switch. The flashlight is turned on and off by losening or tighening the two parts of the housing that are screwed together (which causes the positive pole of the battery to push against a pad on the pcb).

author: djQUAN
author_rank: Frequent Contributor
timestamp: January 04, 2016, 02:31:31 am
content: The LED failed internally with the bond wires causing an intermittent connection.When cold, the bond wires make contact, when the die heats up, it opens and then the die cools down. Then repeat as long as power is on.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 04, 2016, 02:36:52 am
content: "If thine own right eye offends thee, pluck it out."

author: SeanB
author_rank: Super Contributor
timestamp: January 04, 2016, 05:56:12 am
content: Root cause is stress on the leads when soldering, likely the insertion into holes a little out of the tolerance, causing stress on the leadframe inside the case which then softened with the soldering, and started the bondwire cracking. Then with time and thermal cycling it cracked through to make the thermal oscillator you have. Get another LED the same colour and casing, or replace them all if you cannot get matching colour( pretty hard, they are generally using the reject units that failed colour binning there in any case)

author: Stefan
author_rank: Contributor
timestamp: January 04, 2016, 08:53:24 pm
content: Thanks, that makes perfect sense. A thermal-bond-wire-oscillator-switch. I'm gonna patent this and demand money everytime an LED is failingBeing short of white leds, I've followed Matthew and soldered the offending led out and casted it from me, I woudn't want the hole flashlight to go to hell, after all.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 04, 2016, 09:11:56 pm
content: I had a similar, though slower (e.g. 0.5 Hz) blinking in an IR LED used in wireless headphones. Here there where several LEDs in series and all turnd of due to partially failing LED.

author: Audioguru
author_rank: Super Contributor
timestamp: January 05, 2016, 01:03:45 am
content: I am lucky. I have a cheap Chinese flashlight with 24 LEDs in parallel and after replacing its Super Heavy Duty very weak battery cells with powerful name-brand alkaline cells it still works fine except its cheap on-off switch is intermittent.
How are LED Fairy lights are wired? - Page 1
Forum section: electronics / beginners

author: hamster_nz
author_rank: Super Contributor
timestamp: May 05, 2018, 03:56:41 am
content: Before I start cutting, does anybody know how inexpensive LED fairy lights are commonly wired?I've got a set of 100 LEDs , that are connected to a 31V controller using two wires. They can blink alternate LEDs for flashing effects. So I assume the LEDs are in alternating polarity.The string of 100 seems to be in 10 groups of 10, where there is a third wire running between them (9 links with three wires, than one with only two). The last 10 LEDs only have two wires.I assume means that they are 10 parallel strings of 10 LEDs in series, each string having 5 LEDs wired A-K the others wired K-A.So how exactly does that work? Without anything else, one set of LEDs will prevent current flowing into the other five. Does each LED have a standard diode back-to-backed with it, so current can still flow? What limits the current in a string? Is the PSU acting as a current source? Are the LEDs actually 'smart' in some way? THere doesn't appear to be anything else where the LED is connected? Is there special 'fairy light LEDs' that have an inbuilt reverse voltage bypass diode (the volumes made would be high enough to make them I guess)

author: tpowell1830
author_rank: Frequent Contributor
timestamp: May 05, 2018, 05:28:07 am
content: Very hard to answer, as they are different configurations. BigClive is always breaking these down.Hope this helps...

author: hamster_nz
author_rank: Super Contributor
timestamp: May 14, 2018, 09:05:19 am
content: Finally got some time to look at this. They are wired as 10 LEDs in parallel, repeated 10 times.Which is actually quite helpful - you can split them off into sets of ten, then drive them from 5V logic with about 100 Ohms or so of resistance to limit current.I'm somewhat abusing the outputs a 74HC04 to drive them, but it works quite well.
LED Flasher or pulse circuit - Page 1
Forum section: electronics / beginners

author: robertlopez925
author_rank: Contributor
timestamp: April 01, 2014, 08:05:26 am
content: so i need to make a led flash or pulse circuitit is going in a train and needs to be small around 1/2" up to 4" the power that will be feed to it is between 18-22V AC max i have seen some circuits fade on and give a pulse on the highest point of the fade then quickly fade down which will be nice to make... but a simple flasher circuit will also work i do have some clear led's with the specks listed below... i am pretty handy with a soldering iron so soldering is no issue any ideas?* Emitted Color : Warm White* Size: 3mm* Lens Color : Water Clear* Forward Voltage (V) : 3.2 ~ 3.4* Reverse Current (uA) : <=30* Luminous Intensity Typ Iv (mcd) : 12000* Life Rating : 100,000 Hours* Viewing Angle : 20 ~ 25 DegreeAbsolute Maximum Ratings (Ta=25°C)* Max Power Dissipation : 70mw* Max Continuous Forward Current : 20mA* Max Peak Forward Current : 75mA* Reverse Voltage : 5V* Lead Soldering Temperature : 240°C (<5Sec)* Operating Temperature Range : -25°C ~ +85°C* Preservative Temperature Range : -30°C ~ +100°C

author: mariush
author_rank: Super Contributor
timestamp: April 01, 2014, 02:46:51 pm
content: There are ready made leds that blink by themselves, so you'd only need a resistor to limit the current going into the led (and a diode + capacitor to make dc voltage).A 555 timer chip will make it easy to make a led blink and adjust how much time it stays on, how much it stays off but will require a few components (resistors and capacitors) and you'll also need to convert that to dc using a diode (or bridge) and then get the voltage down to 5v using a linear regulator perhaps.You can do lots of effects on a led with a PIC10 or PIC12 (or Attiny perhaps) microcontrollers and these don't require external components so they'll take less space. You'll only need to get the voltage down to 3-5v dc. However, you'll need a programmer and some basic C knowledge to program these microcontrollers.

author: Mr Smiley
author_rank: Frequent Contributor
timestamp: April 01, 2014, 06:40:58 pm
content: uni-junction transistor

author: robertlopez925
author_rank: Contributor
timestamp: April 02, 2014, 07:18:48 am
content: Quote from: mariush on April 01, 2014, 02:46:51 pmany good source for the flasher led's and i presume it would have to convert the power to dc of that led to work correct?
LED flasher project & PowerPoint-based template for enclosure drilling - Page 1
Forum section: electronics / beginners

author: JuiceKing
author_rank: Regular Contributor
timestamp: August 11, 2012, 01:33:09 pm
content: This 555-based LED flasher is very elementary and easy to put together on a breadboard in only a few minutes, but making a permanent version and precisely mounting it in an enclosure was a challenge and a good learning experience. Because I "winged it" and built this directly from the schematic, the soldered version you see here took at least 2 hours (and much desoldering wick) to get right, and then another 3-4 hours to make the box!My previous attempts to make enclosures with a freehand drill were very clumsy, so this time I planned ahead carefully and worked on better technique. I used a caliper to accurately measure screw hole distances and bolt diameters, and then drew templates using Microsoft PowerPoint, printed them, and taped them to the box to get the holes in just the right spots. This worked. Amazingly, the scaling of the printer was spot-on, first try. Without a drill press and calibrated stage, I can't think of another way to do this. I'd love to hear what others do.

author: T4P
author_rank: Super Contributor
timestamp: August 11, 2012, 04:30:58 pm
content: I print a template for my boxesBased on the 1590BB template for my 1590BB boxes

author: ftransform
author_rank: Frequent Contributor
timestamp: August 11, 2012, 06:36:48 pm
content: That looks like a quality box. I would recommend getting a 90$ harbor freight drill press though, they are not too bad.I feel like I learned to fly after using one for the first time. The days of tonguing the drill at the right angle were over!

author: Christopher
author_rank: Frequent Contributor
timestamp: August 11, 2012, 06:42:16 pm
content: I'd suggest not using an electrolytic cap, because of the high tolerance. Try a ceramic instead, your time value will be more accurate.

author: JuiceKing
author_rank: Regular Contributor
timestamp: August 11, 2012, 07:38:54 pm
content: Quote from: Christopher on August 11, 2012, 06:42:16 pmLOL. Also, that electrolytic cap will probably need to be replaced in 20-30 years!
LED for TX and RX of MAX232N - Page 1
Forum section: electronics / beginners

author: sean87
author_rank: Regular Contributor
timestamp: November 29, 2012, 10:20:21 pm
content: Hi all,I have made a PC serial to CMOS level circuit (if this kind of circuit all called this!) using MAX232. It works fine, but I want to add 2 LEDs so I can see data going out or coming in to the chip. I want this to the CMOS level side of chip (T2IN and R2OUT pins).Can I just hook up to LED's to this pins and ground? If not, what should I do? I looked in datasheet but didn't find anything on this regard.

author: digsys
author_rank: Unknown
timestamp: November 29, 2012, 11:13:20 pm
content: Assuming a 5V system, use 2K2-2K5 resistors (~2mA) and "good" leds. 50-100mcd (or high efficiency). Similar price to "cheap" leds.That way you won't load the signals at all. I wouldn't try to run 20mA on a standard led.OR IF you are not using the other 2 channels on the MAX232, link the 2 pairs together and use the 2nd pair just for leds.

author: sean87
author_rank: Regular Contributor
timestamp: November 29, 2012, 11:56:25 pm
content: Thanks, got the idea.

author: aluck
author_rank: Regular Contributor
timestamp: November 30, 2012, 01:15:54 am
content: Wouldn't it be better to put a small BJT to drive those LEDs?

author: Smokey
author_rank: Super Contributor
timestamp: November 30, 2012, 01:33:45 am
content: Logic level FETs are great for this kind of stuff. 2N7002LT1 or something like that.

author: hlavac
author_rank: Frequent Contributor
timestamp: November 30, 2012, 05:39:36 pm
content: If you want a nice visible indication even for a single bit you could build two pulse stretchersfrom single 74hct00 chip.Look at the right side of mylogic probe schematicto see what I mean...

author: sean87
author_rank: Regular Contributor
timestamp: December 04, 2012, 12:13:40 am
content: Thanks for ideas!I made the circuit. For TX/RX indicator LEDs I am facing a small or big problem! The CMOS level side of chip is always at 5v when idle. I connected a normal 5mm led to the GND and RX of cmos side and it is always on...when I send some data to chip, it slightly dims for a mili sec (I think it tries to show low bits !).Any idea how to invert this process?

author: kxenos
author_rank: Frequent Contributor
timestamp: December 04, 2012, 12:31:21 am
content: Connect the cathode of the LED to the signal and it's anode to Vcc.
LED HELP - Page 1
Forum section: electronics / beginners

author: robertlopez925
author_rank: Contributor
timestamp: March 29, 2015, 04:47:12 am
content: i am doing a project where i am needing to have a white and Red led on the same power source. But every time i connect them together the red led will work but not the white led will not. Can some one explain why this is happing and how to fix the issue.Thanksi am using a 3v warm white led and a 3v red/green led with a common cathode

author: IanB
author_rank: Super Contributor
timestamp: March 30, 2015, 11:26:22 am
content: Short summary of above post: use a separate current limiting resistor on each LED.

author: Simon
author_rank: Unknown
timestamp: March 30, 2015, 12:01:04 pm
content: And White and Blue want a smaller resistor not larger because they work at a higher voltage so have less left over for the resistor.R = (Vin-Vled) /Iled

author: Corporate666
author_rank: Unknown
timestamp: March 30, 2015, 01:59:19 pm
content: Quote from: robertlopez925 on March 29, 2015, 04:47:12 amYou need to give more information on how you have it connected now (a schematic), as well as what your power supply is.

author: Fat
author_rank: Regular Contributor
timestamp: March 31, 2015, 05:20:42 am
content: You need to give more information on how you have it connected now (a schematic), as well as what your power supply is.How are you wiring them? If they have a vf of 3 volts each and you put them in series, you need to provide 6 volts DC and the correct current to operate each different color. Most colors require differing amounts of current. My whites run at 1150 ma. The reds would die at this current. (We are running them as lighting over a saltwater fish tank).If you MUST have them run on the same supply you will need to determine the maximum vf and current for each, supply for the greatest and put something in place to limit the vf and current to the one requiring less of each.Best of luck.Fat
LED Holder Sizing - Page 1
Forum section: electronics / beginners

author: veedub565
author_rank: Frequent Contributor
timestamp: May 03, 2025, 09:16:28 am
content: Bit of a basic, possibly silly question. Does anyone know how the sizing works for LED holders ? I have a 7.6mm hole which I want to fit a 5mm LED into. It's panel mount and panel thickness is 3mmI've found a 7.6mm holder for 5mm LED's, but does that mean the holder is 7.6mm dia, or the hole cutout it fits into is 7.6mm dia ?Example herehttps://uk.rs-online.com/web/p/led-holders/1749669I've been trying to work out the datasheet for that one, it seems to suggest the dia of the holder is 7.6mm, panel hole size is 6.4mm and panel thickness is 3.2mmThere doesn't seem to be an easy way to sort by panel hole size

author: veedub565
author_rank: Frequent Contributor
timestamp: May 03, 2025, 10:21:10 am
content: Answered my own question I think. Looks like this will do the jobhttps://uk.rs-online.com/web/p/led-holders/2622999?gb=sIt's actually an 8mm hole, just the paint makes it 7.6mm. I'll file it out a bit and that holder should fit ok.
LED is not ESD protected..do we need to add anti-parallel diode? - Page 1
Forum section: electronics / beginners

author: ocset
author_rank: Super Contributor
timestamp: November 09, 2017, 06:25:58 am
content: Hello,We are using 100 of these LEDs on our LED PCB....Wicop2 Z8 Y19 LEDhttp://acrich.tw/_upload/Goods_Spec/Specification_Z8Y19_Rev5.2.pdfDo you think we need to add a diode in anti-parallel with each LED on the MCPCB? This will then protect us against ESD damage to the LEDs?

author: capt bullshot
author_rank: Super Contributor
timestamp: November 09, 2017, 07:14:47 am
content: I don't think you'll need them, given your finished product is encapsulated in a way that prevents ESD events from striking the PCB where the LEDs are mounted. Internal protection is handy for ESD protection at production time - which shouldn't happen if you know what you do. An external diode won't protect you then.BTW. For all the support you ask for here, you'll have to send one of your finished products to Dave (or me)

author: Ghydda
author_rank: Regular Contributor
timestamp: December 15, 2017, 11:51:09 pm
content: Quote from: capt bullshot on November 09, 2017, 07:14:47 amI offer a different opinion. LEDs are very susceptible to damage even from very small discharges.We never ever use LEDs without embedded esd-protection for lighting applications in our production.Cheers!
led lead for pipes - Page 1
Forum section: electronics / beginners

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: May 30, 2019, 08:54:38 am
content: What are those objects which clamp on to a THT LED lead to prevent it from warping or bending when used with a light pipe?

author: JackJones
author_rank: Regular Contributor
timestamp: May 30, 2019, 09:18:04 am
content: You mean things like this?https://www.digikey.com/product-detail/en/wurth-electronics-inc/705820100/732-11605-ND/7681950I think they're just called standoffs or spacers.

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: May 30, 2019, 09:25:13 am
content: Quote from: JackJones on May 30, 2019, 09:18:04 amThese are the same thing?https://datasheet.lcsc.com/szlcsc/Keystone-8324_C238181.pdf

author: JackJones
author_rank: Regular Contributor
timestamp: May 30, 2019, 09:30:51 am
content: Looks like a standard nylon led spacer, yeah.These are the kind of things you can get very cheaply from places like aliexpress if you don't mind waiting for the shipping time.

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: May 30, 2019, 09:49:39 am
content: Lens are far more costly than spacers even in aliexpress its far more expensive for panel mount THT lens compared with digikey.
LED Light Bulb Replacements and NTC or MOV? - Page 1
Forum section: electronics / beginners

author: metrologist
author_rank: Super Contributor
timestamp: March 26, 2021, 01:59:44 pm
content: I'm having a problem with my ceiling lighting. I thought I found good LED replacements, but they are starting to burn out too. I just can't find a suitable LED replacement bulb for the old CFL, which are very unreliable and have terrible performance, and are expensive anyway.The new LED bulbs that I bought to replace a burned out LED bulb do not work, and I do not know why. I tried a few new ones of the exact same mfg and model in working fixtures and they don't work anymore. I'm confused about that. Maybe just a bad batch?Out curiosity, the crispy device, is it more likely an NTC or MOV? I guess if it's in series it's an NTC and if in parallel a MOV?How would you fix this lighting issue?Note, I tried contacting info@feit.com asking why the new bulbs do not work and that their LED failed within the warranty and they told me that they do not make the CFL and to contact the manufacturer bulbconnection.com. Period.

author: floobydust
author_rank: Super Contributor
timestamp: March 26, 2021, 04:54:56 pm
content: The Feit bulb's input power is 11.3W and no way it can get rid of the heat decently. Just by looking at it - no heatsink fins, no vents or louvers. It seems to be an 'aggressive' design. If the light fixture is enclosed, e.g. with a globe then there can be even less airflow for cooling.Amazon reviewsare terrible and a few pics of them burning up"Bulb tried to burn house down, would have if it hadn’t failed loudly in the room I was in and I turned off power to it."I'm not sure what the burned up component is- but likely a consequence to the something shorting. Do not repair, throw in the garbage.

author: BrokenYugo
author_rank: Super Contributor
timestamp: March 26, 2021, 05:06:47 pm
content: IIRC at least with the long T12/T8 bulbs those florescent replacement LEDs require one to pay attention to what sort of ballast is used in the fixture, something like they don't get along with the old magnetic ballasts.