Constant current confusion - Page 1
Forum section: electronics / beginners

author: tyguy2
author_rank: Unknown
timestamp: July 14, 2016, 11:11:50 pm
content: I'm working on a project that needs to drive 4 100ma LEDs with a 12v supply (along with a micro and a few jellybean parts)(Datasheethttp://www.mouser.com/ds/2/602/DS146-748694.pdf). Not only this, but each LED needs to be able to turn on and off independently from the others (ie, LED1 needs to be on while LEDs2-3 need to be off). I looked into using an LM317 as a constant current source, but I couldn't find any information on multi LED configurations. I thought about using Darlington transistors to allow the micro controller to control each LED, but other than that, I'm stumped. Any ideas?

author: MosherIV
author_rank: Super Contributor
timestamp: July 14, 2016, 11:36:37 pm
content: HiSo, you want to turn LEDs on/off by micro control. The LEDs are driven by 12VThe easiest way is outlined on this pagehttp://www.w9xt.com/page_microdesign_pt7_transistor_switching.htmlJust use ohms law to set the current throught the LED, ie work out R2.(R2 = 12V - 1.4V /desired current)R1 is pretty easy, just work out what value will push say 5mA into the base, turns transistor full on.This will give rough constant curent control, but good enough for driving LEDs.If you really must do accurate constant current control, look at thishttp://electronics.stackexchange.com/questions/141935/opamp-misbehaving-in-constant-current-source-circuitTo set a fixed current by the micro, make Rset = Viohigh/desired current.

author: tyguy2
author_rank: Unknown
timestamp: July 14, 2016, 11:56:00 pm
content: Quote from: MosherIV on July 14, 2016, 11:36:37 pmFirstly, a resistor with a fix voltage is a horrible way to current limit a high power LED. It has no feedback whatsoever, and is highly inefficient, not to mention I'll have to use high wattage resistors for the LED's. As for the opamp, I'm looking for something that can drive multiple LED's in parallel (so they operate independently), not something I can duplicate 4 times over (unless I have to, in which case I'd probably go with the LM317 solution). It looks to me like the opamp design only drives 1 load, unless I'm reading it wrong (which I probably am, I pretty new to constant current and LED drivers)

author: Brumby
author_rank: Unknown
timestamp: July 14, 2016, 11:56:59 pm
content: If you want to control 4 LEDs independently, you will need 4 separate current control circuits - one for each.If you only want to have one current source, then have all 4 LEDs in series with each other and the current source, with a mechanical switch across each LED - like this:Presuming there is sufficient voltage.Don't know about MCU control, though.

author: tyguy2
author_rank: Unknown
timestamp: July 15, 2016, 12:04:56 am
content: Perhaps I could use darlington transistors or BJT's to replace the switches? Are you sure the switch method with 1 constant current source will work? Also, speaking of enough voltage, what about the voltage drop across each LED. The forward voltage of each LED is ~2.3 volts -I'm using 3 different colors of LED, 3 have a FV of ~2.3, the other has a FV of ~3.3. If I do the math, that's 10.2 volts. Should I increase the voltage of my power supply, which is currently (pun not intended) 12 volts?

author: MosherIV
author_rank: Super Contributor
timestamp: July 15, 2016, 12:14:50 am
content: QuoteNot really, classic way for doing simple current control. Correct there is no control of the current, it works because the load does not change much which it should not do for LEDs. It use to be the way to do simple cc control for battery charging. Yes, the resistors will need to be power resistor but probably max 1 watt, you need to work out the power dissipation.QuoteCorrect, 1 opamp will be needed per LED. This is a simple to understand cc control circuit. You can do it with transistors only but it is more complicated and harder to understand (for me at least, hate all the calculatiins needed to bias transistors properly)The problem with LM317 is it does not have any way to turn on/off the cc. It is just a regulator.Feel free to look at alternatives, just throwing you some ideas.

author: tyguy2
author_rank: Unknown
timestamp: July 15, 2016, 12:44:34 am
content: Quote from: MosherIV on July 15, 2016, 12:14:50 amIt's not a problem that the cc can't be turned off on the LM317, because I should be able to control the LED's directly via a transistor of some sort.

author: tyguy2
author_rank: Unknown
timestamp: July 15, 2016, 12:45:55 am
content: Do you really think that a 1 watt resistor would work? Would I need a heat sink of some sort for the resistor?

author: Buriedcode
author_rank: Super Contributor
timestamp: July 15, 2016, 01:02:59 am
content: Quote from: tyguy2 on July 15, 2016, 12:45:55 amWork it out. You've mentioned that "a resistor is a horrible way to limit current" and for large voltage differences between supply and LED forward voltage, yes, its less than ideal - but it also proves you understand ohms law. You can work out the power dissipation of any resistor you use and rate it accordingly.As for have control over individual LED's then the suggestions posts so far pretty much cover it, unless you want to get into using buck regulators. You could just use a single buck that is capable of providing > 500mA to provide a lower voltage and use transistors to switch the LED's - preferably just above the maximum Vf of the LED's so the power dissipation in the current limiting resistors is smaller. Ebay and even amazon have plenty of buck modules that are quite efficient in the 200-500mA range (but crap at <100mA and> 2A).

author: tyguy2
author_rank: Unknown
timestamp: July 15, 2016, 01:20:50 am
content: Oh, I like the idea for the buck converter. What kind of IC would I use for that? I'm putting this into a PCB, so I can't really use anything from Ebay.

author: Monkeh
author_rank: Super Contributor
timestamp: July 15, 2016, 01:29:50 am
content: Allow me to just pull a 4-bit constant-current LED driver out of a hat:http://www.digikey.com/product-detail/en/stmicroelectronics/STP04CM05XTTR/497-6942-1-ND/1880319Linear mind you.I take it these are fairly high forward voltage LEDs?

author: tyguy2
author_rank: Unknown
timestamp: July 15, 2016, 01:40:05 am
content: Quote from: tyguy2 on July 15, 2016, 12:04:56 amForward Voltages^Hmmmmm, I'm looking at the driver, and it looks a bit too complex for my taste. I think I should just go for the resistor set up...

author: Monkeh
author_rank: Super Contributor
timestamp: July 15, 2016, 01:43:48 am
content: So you're talking about dumping a watt each for those three. Abandon 12V unless you want a space heater.Grab a buck reg, run it at about 3.6V, and you might even be able to run your micro off it.There's way, way too many for me to come up with a recommendation off the top of my head right now, so.. go nuts:http://www.digikey.com/product-search/en/integrated-circuits-ics/pmic-voltage-regulators-dc-dc-switching-regulators/2556570

author: tyguy2
author_rank: Unknown
timestamp: July 15, 2016, 01:49:40 am
content: Would this generate a lot of heat on the IC? Anywhere else I would need to know?

author: Monkeh
author_rank: Super Contributor
timestamp: July 15, 2016, 01:50:32 am
content: Quote from: tyguy2 on July 15, 2016, 01:49:40 amNo, that's the whole point of using a buck converter.They are layout sensitive. Be careful.

author: tyguy2
author_rank: Unknown
timestamp: July 15, 2016, 01:52:16 am
content: Thanks for bearing with me, I appreciate the help!

author: Connoiseur
author_rank: Regular Contributor
timestamp: July 15, 2016, 02:15:25 am
content: If you are using a micro, then why not PWM the leds?The attached picture shows the basic idea.Adjust duty cycle in a loop till required current is obtained (get the current through ADC as shown).You can simply double the reference value for two leds and keep on increasing it; as the number of leds turned ON increases; in software.PS: use a rail to rail opamp or a dedicated current sense amplifier for acceptable results.

author: MK14
author_rank: Super Contributor
timestamp: July 15, 2016, 04:06:35 am
content: Quote from: Connoiseur on July 15, 2016, 02:15:25 amAre you sure about that particular circuit ?There is apparently no resistor (ignoring the very low valued Rsense resistor) between the LEDs and the 12V power supply. Therefore a potentially huge current would attempt to flow, during the on parts of the PWM cycles. This could easily exceed the LEDs datasheet specifications. The transistors will probably limit the current to an extent, depending on the base resistor values, but that would be very hit and miss.A quick look at the LEDs datasheet, seems to say that there would be about 2 volts (depending on colour) across them (at about 100 ma), and around 300 ma (pulsed) is the maximum.You would probably see amps flowing (depending on the 12V and other things), in your circuit, as it stands.I guess a series resistor could be included to fix that issue.

author: Brumby
author_rank: Unknown
timestamp: July 15, 2016, 04:16:25 am
content: Quote from: tyguy2 on July 15, 2016, 12:04:56 amYes (Again, assuming the voltage available is adequate). There's always a current path, so whether all 4 switches are open (4 LEDs lit) or all are closed (short circuit and no LEDs lit) the same current will flow.QuoteIf Vce of the transistor < Vf of the LEDs, then I would think so. You'd have to account for the varying offset of the base voltages for each transistor, but for off/on operation then that's not too onerous.

author: David Hess
author_rank: Super Contributor
timestamp: July 15, 2016, 04:42:07 am
content: Unless you pulse width modulate the LEDs, controlling the current is going to require heat dissipation in a current limit resistor or transistor or both.You do not say what voltage your microcontroller is operating at however you have everything you need to make simple switched constant current sources using one bipolar transistor and output port per LED. Put the current limiting resistor in series with the emitter of each transistor to ground and drive the bases directly from the output ports. Connect the LEDs between +12 volts and the transistor collectors.With 5 volt outputs, the voltage across the resistors will be 5 - 1 Vbe = 5 - 0.6 or 4.4 volts. 4.4 volts / 100 milliamps = 44 ohms @ 440 milliwatts so use 1 watt resistors. Transistor dissipation will be 12 - 4.4 - Vled = 12 - 4.4 - ~3 = 4.6 volts * 100 milliamps so 460 milliwatts. You might get away with 625 milliwatt 2N4401 transistors but I would use something in a TO-126/TO-225 package like a 2N4921/2N4922/2N4923 or BD135/BD137/BD139.If you do want to use TO-92 transistors (or SOT-23s, whatever), add another resistor in series with the collectors to take up some of the heat dissipation. Alternatively, lower the +12 volt supply to the LEDs.

author: MK14
author_rank: Super Contributor
timestamp: July 15, 2016, 05:01:26 am
content: Quote from: tyguy2 on July 15, 2016, 01:20:50 amYou are better off converting (lowering) the voltage (as you are mentioning above) or using a low voltage supply to begin with. Then the circuitry will be much easier for you, and you will have much less wasted heat energy produced.PWM produces about the same amount of wasted power in the form of heat, as a non-PWM solution. For loads such as your LEDs, with series resistors.I.e. 12V down to about 2V, wastes power and produces heat in the resistors and/or transistors, regardless of PWM or DC. You have to use switching voltage converters (such as the buck converter), to minimize wasted energy, which causes heating in the components.Alternatively putting all four LEDs in series, would also save a lot of energy (when all four are simultaneously on). But it would be very difficult to switch them on and off, via the MCU, without rather complicated circuitry. So I don't think it is a good solution, unless you are happy with the mechanical switches, someone shows earlier in this thread.

author: rudika79
author_rank: Regular Contributor
timestamp: July 15, 2016, 05:30:23 am
content: You can use switch mode led driver IC. At any part distributor you can found hundreds of different type. I design once RGB led driver with three led driver. You have one control pin for adjusting brightness and switch on/off the LED. Later when I will be at my workplace I can give you the part number and the circus diagram if you want.

author: MK14
author_rank: Super Contributor
timestamp: July 15, 2016, 05:58:57 am
content: Quote from: rudika79 on July 15, 2016, 05:30:23 amThat sounds like a very good idea!It will be very efficient, easily handle the 12 volt supply. Accurately control the LED currents, producing low amounts of heat, and four channel ones in a single IC are available. I don't know which is the best one for your purposes.Example:https://www.maximintegrated.com/en/products/power/led-drivers/MAX16814.html

author: rudika79
author_rank: Regular Contributor
timestamp: July 15, 2016, 06:59:06 am
content: See attached picture for schematic. I use ZXLD1350 IC. It's comming in sot23-5 type package. On R-LED pin ypu can switch on/off and supply PWM signal for brightnes. LED you connectrd to J1 connector. I had three off this IC on PCB.

author: Brutte
author_rank: Frequent Contributor
timestamp: July 15, 2016, 08:07:33 am
content: I'd use 4 x jelly bean BJTs in current sink configuration. The SOT23 would be more than adequate for 100mA. This way the LED current would be independent of supply voltage and beta.If you want to be super accurate then there are SOT23-4 current mirrors available (a pair of BJTs).

author: tyguy2
author_rank: Unknown
timestamp: July 16, 2016, 04:01:47 am
content: I've attached a schematic of a possible LED driver circuit that I want to make sure is correct. I'm using thehttp://www.diodes.com/_files/datasheets/AP3211.pdfas a buck converter at 2.4v. It has a Feedback voltage of 0.81v, so I set R1 and R2 to 10k ohms and 5.1k ohms respectively. This should give me a power output of 2.4v, just above the forward voltage of the LED's at 2.2v. The MCU controls the LED's via BJT's that sink the current to ground. Does anyone see anything wrong with my design? Is a 0.5 amp diode ok to use if the circuit will be drawing between 400-500ma? Did I do the math correctly on the resistors?

author: MK14
author_rank: Super Contributor
timestamp: July 16, 2016, 06:02:46 am
content: Quote from: tyguy2 on July 16, 2016, 04:01:47 amYou seem to be progressing it nicely.The voltage drop across an LED (Vf) is not rigidly fixed. It varies from device to device, with temperature and LED colour, so trying to give itexactlythe right voltage is not the best of ways of doing it. You need to use something which controls and limits the current, or use resistors and a partially higher drive voltage, to give the resistors some headroom.That's the advantage of switch mode LED drivers. As well as the buck converter, they regulate the current for you as well, for all 4 channels. But they are a bit harder to use, so I understand if you want to avoid them.If you raise the voltage to about 3.5V (but a bit too low and tight), 4V or more. You can then calculate resistors (in series with each LED) which will give the desired current (100mA). The datasheet you supplied gives thetypicalforward voltages. You will probably need different resistors, depending on LED colour, as the Vf changes, ideally you want different resistor values.Here is an online LED resistor calculator, or better still do it yourself.http://ledcalc.com/Opinions will probably vary as to how much more voltage you need, if using resistors.Also the transistors will have a bit of voltage drop across them, depending on how saturated the transistor is, with whatever the base current is and what transistor they are. (See its datasheet).

author: MK14
author_rank: Super Contributor
timestamp: July 16, 2016, 06:21:57 am
content: Or as another post said earlier, you could make constant current generators. But then it is getting so much more complicated, that the all in one, switch mode LED driver chip(s), becomes increasingly attractive.

author: Brutte
author_rank: Frequent Contributor
timestamp: July 16, 2016, 07:27:23 am
content: Quote from: tyguy2 on July 16, 2016, 04:01:47 amDude, you are heading in exactly opposite direction we are pointing you atHopeless, concerning number of hints given.

author: MosherIV
author_rank: Super Contributor
timestamp: July 16, 2016, 09:00:49 am
content: QuoteFirstly, the LEDs are the wrong way round.Second, not sure you understand the idea behind constant current throught the LEDs, your circuit could potentially burn out the LEDs. The switcher is controlling voltage and there is nothing to control the current through each LED.Thirdly, if it takes 2.4V to drive the LED then they will not light up, the BJTs will drop 1.4V.Raise the switcher voltage to 5V.Put the LEDs the right way round.Add current limiting resistors to each LED, at 5V supply, 5V - 2.4V - 1.4V = 3.8V, this gives a current limiting resistor of around 38Ohms sorry if you saw my first post with 1.4 ohms, do not know what I was thinking. I realised my mistake while brushing my teeth

author: MK14
author_rank: Super Contributor
timestamp: July 16, 2016, 09:22:48 am
content: Quote from: MosherIV on July 16, 2016, 09:00:49 amWell spotted that the LEDs are the wrong way round.Unfortunately I missed that, so I feel a bit foolish, as I should have noticed it as well.What makes you think BJTs will drop 1.4 Volts ?It should be a fair bit less than that, lots less if suitably saturated. E.g. 0.2 V (saturated) or a diode drop (not especially saturated), approx.Maybe you are thinking of darlington transistors, which do have higher voltage drops, because of the second transistor ?1.4 Ohms?That seems amazingly low, can you show your calculation ?Maybe you accidentally put the decimal point in the wrong place or something ?It's going to more like 25 Ohms, depending on the supply voltage. I.e. about 10 Ohms per volt dropped, for 100mA.Also "5V - 2.4V - 1.4V = 3.8V", actually it is = 1.2V, ignoring that I don't agree with the voltages either.But it is very easy to miss-key a calculator.

author: tyguy2
author_rank: Unknown
timestamp: July 17, 2016, 02:52:07 am
content: Quote from: Brutte on July 16, 2016, 07:27:23 amWell then, what would you recommend? The 4 bit constant current LED driver IC? I appreciate your concern and patience, as well as the additional help you've added to this thread.As for the rest of the comments:Whoops, didn't notice the LED's were switched. I assumed that because the LED's forward voltage requirements were met, they would draw the correct amount of current, but I didn't consider voltage drop across the transistors. I've seen people drive high power LED's from a very specific voltage before without current limiting (from a bench power supply), but maybe I'm missing something. So if I set the DC-DC buck converter to 5v, then I should add ~25 ohm resistors (depending on the voltage drop across the transistor and the current draw of the LED) to limit current, so long as the transistor is saturated.

author: Monkeh
author_rank: Super Contributor
timestamp: July 17, 2016, 02:55:14 am
content: Quote from: tyguy2 on July 17, 2016, 02:52:07 amYou need to meet their forward voltage requirement very precisely, and it varies per-LED, with current, with temperature.. This is why you use constant current, not constant-voltage.What voltage will your micro run from?

author: tyguy2
author_rank: Unknown
timestamp: July 17, 2016, 02:58:23 am
content: Quote from: Monkeh on July 17, 2016, 02:55:14 amIt's a 5v micro, so I plan on running that on the same power rail (if I go with a 5 volt config)

author: Monkeh
author_rank: Super Contributor
timestamp: July 17, 2016, 02:59:08 am
content: Quote from: tyguy2 on July 17, 2016, 02:58:23 amOr.. just use a buck converter to get 5V and run the LEDs from it too.

author: tyguy2
author_rank: Unknown
timestamp: July 17, 2016, 03:00:42 am
content: Whoops, didn't notice that. I'm a bit tired right now

author: MosherIV
author_rank: Super Contributor
timestamp: July 17, 2016, 10:53:31 am
content: QuoteDiodes (including LEDs) must have current flowing anode to cathode or they will not work. They are commonly used to stop current flowing in the wrong direction eg rectifier diodes in linear power supply.If the voltage drop for the transistor is not taken into account, the calculation for the current limiting resistor will give a value that is too high. At lowish LED currents, it may not light at all. The 100mA that you are looking for, you probably would not notice a difference.My background is an embedded software eningeer, so I usually use LED as indicators. Not interrested in brightness, so I useally use 2 diode drops for the voltage across a BJT and 20 to 30mA for LED current, the calcualtion works for me.As for some people driving LEDs from psu without current limit, LEDs can be abused for short periods of time and survive, not sure how long they will last though.I took another closer look at the data sheet for the LED. You have not said which colour you are using, hence it is not clear what the max current is for the LED.Why are you driving the LED at 100mA?This is going to produce a VERY bright LED output. If this is just for an indication for someone to look at, it will be very unconfertable, will leave bright spots in their vision. If they are being used to light up dark areas then ok.I would not class these as the high power LEDs. 100mA is near the top limit of normal LEDs these days.

author: tyguy2
author_rank: Unknown
timestamp: July 17, 2016, 06:29:22 pm
content: The colors I'm using are Red, Red-Orange, and Green, which all have the same max currents (125ma) (see page 4http://www.mouser.com/ds/2/602/DS146-748694.pdf) I'm diffusing these LED's over a larger area (they are going to act as a large wall mounted indicator, hence red, orange, and green, each LED will light a circle about 40 cm in diameter), so it shouldn't be too bad, right? I could also reduce the current being provided to it by changing the resistor of the LED to reduce brightness.

author: tyguy2
author_rank: Unknown
timestamp: July 17, 2016, 07:07:23 pm
content: So I fixed the LEDs, and added the resistors to limit current, set the supply voltage to 5v, and put the resistors on the collectorsto 330 ohm to saturate the BJT.

author: MosherIV
author_rank: Super Contributor
timestamp: July 17, 2016, 08:28:15 pm
content: QuoteNear full power spread over 40cm diameter, still might be too bright. Try it and see.Yes, if it is too bright, you just adjust the resistor which controls the LED brightness.The circuit looks ok now.

author: tyguy2
author_rank: Unknown
timestamp: July 17, 2016, 08:29:19 pm
content: Thanks

author: MK14
author_rank: Super Contributor
timestamp: July 17, 2016, 10:05:17 pm
content: I don't know if you've seen thishttp://www.diodes.com/_files/product_app_note_pdfs/AN1063.pdfBut it explains how to select (and calculate the required ratings) the right diode for D1.How are you planing to "cool" the LEDs ?The app note (have you seen it ?), explains that it needs to be done, as is typical for LED lights, where there is quite a task to do (PCB wise), to keep them cool.Via a metal layer built into the PCB, or multi-layer PCB boards. If I understood it correctly.

author: tyguy2
author_rank: Unknown
timestamp: July 17, 2016, 10:11:24 pm
content: Yes, I saw the application note on cooling the LEDs. I'm cooling them with a copper pour around each LED on both layers of the PCB with Vias to connect them (as well as possible heat sinks on the back of the board). Thanks for the info on diodes.

author: MK14
author_rank: Super Contributor
timestamp: July 17, 2016, 10:15:43 pm
content: Quote from: tyguy2 on July 17, 2016, 10:11:24 pmGood.http://www.lumileds.com/uploads/403/AB203-pdfAlso you can control the brightness via PWMing the MCU outputs, if you are handy enough with software. Hardware (changing the resistors, as mentioned above by another poster) would work as well.

author: MK14
author_rank: Super Contributor
timestamp: July 17, 2016, 10:21:46 pm
content: R7 to R10, 330 Ohms, is fairly low. You might want to check that the microcontroller has outputs, rated at high enough current (a touch under 15 mA's, assuming still 5V supply for MCU). Many will have enough, but not all. If it is too high for them, then just use higher value resistors. At such a relatively low output current to the LEDs, you should still have plenty of Hfe (gain if you like) in the transistors, to give a suitably low voltage drop across the transistors.

author: tyguy2
author_rank: Unknown
timestamp: July 17, 2016, 11:00:12 pm
content: The MCU I'm using can provide 45 ma per pin, so it should be fine.

author: MK14
author_rank: Super Contributor
timestamp: July 17, 2016, 11:37:50 pm
content: Quote from: tyguy2 on July 17, 2016, 11:00:12 pmWow 45 mA's.Can I be curious and ask what it is then ?I've only seen ones that go up to about 25 mA's, such as some PICs, if I remember correctly.EDIT:It's ok, you are talking about Arduino I think.Google was my friend.I think the later MCU's (which I was thinking of) have a smaller feature size, so they are not so good at giving maximum output current capabilities (but there may be exceptions). But older chips which I suspect you are using, still might.

author: Monkeh
author_rank: Super Contributor
timestamp: July 17, 2016, 11:47:56 pm
content: Quote from: MK14 on July 17, 2016, 11:37:50 pmOne of the AVRs, I imagine. They do have rather robust pin drivers.

author: MK14
author_rank: Super Contributor
timestamp: July 17, 2016, 11:49:50 pm
content: Quote from: Monkeh on July 17, 2016, 11:47:56 pmThanks!45mA's is rather amazing, because you can do a heck of a lot with that. It's almost enough to drive those LEDs on its own.It must save needing external small signal transistors on the outputs, in many cases.

author: tyguy2
author_rank: Unknown
timestamp: July 18, 2016, 12:59:44 am
content: It's an Atmega1280, I believe.

author: MK14
author_rank: Super Contributor
timestamp: July 18, 2016, 01:24:26 am
content: Quote from: tyguy2 on July 18, 2016, 12:59:44 amThanks for letting me know.A quick look at the datasheet, seems to indicate that it will supply 20mA (which is more than enough for your circuit, as shown) per pin (maybe a bit more, it would take longer to find that value), with a limit on the overall current paths.Disclaimer: The datasheet covers a large number of devices. It is very easy to look up the wrong chip. So please take care, before using the following values.The 40mA it mentions is the Absolute Maximum, which is best avoided at all costs, as that is the level which may unfortunately break/damage the chip and/or see it misbehave.QuoteQuotehttp://www.atmel.com/Images/Atmel-8272-8-bit-AVR-microcontroller-ATmega164A_PA-324A_PA-644A_PA-1284_P_datasheet.pdf

author: tyguy2
author_rank: Unknown
timestamp: July 18, 2016, 01:54:06 am
content: Whoops, 1280

author: MK14
author_rank: Super Contributor
timestamp: July 18, 2016, 02:43:24 am
content: Quote from: tyguy2 on July 18, 2016, 01:54:06 amAn easy mistake to make.A super quick look, seems to say my previous post, is about right with the currents, or not very far, from the revised cpu number.Also, you had no choice but to include the wrong one, initially.Otherwise you would have got into trouble, for being off-topic, the topic title being 'confusion'.

author: tyguy2
author_rank: Unknown
timestamp: July 18, 2016, 04:17:06 am
content: Oh, putting confusion in the title isn't allowed? My bad, I'll remember for next time

author: Brumby
author_rank: Unknown
timestamp: July 18, 2016, 04:19:30 am
content: Putting 'confusion' into the title isn't a bad thing ... but since you did, citing the wrong chip number was a good move. It kept the thread 'on topic'.

author: MK14
author_rank: Super Contributor
timestamp: July 19, 2016, 08:33:41 am
content: Quote from: tyguy2 on July 18, 2016, 04:17:06 amSorry. I was joking, as explained by:Quote from: Brumby on July 18, 2016, 04:19:30 amThanks for explaining it.The joke was that "Confusion" in the topic title, meant that you HAD to create the mistake on purpose, otherwise you would be off-topic. N.B. I was joking.Also take care, as previously mentioned, the VERY BRIGHT LEDs can potentially damage your eye sight. Eyes can't handle overly bright light sources too well. Unlike a faulty component, where you can just buy a new one. Eyes are not so easily replaced.

author: David Hess
author_rank: Super Contributor
timestamp: July 19, 2016, 08:02:36 pm
content: Quote from: MK14 on July 19, 2016, 08:33:41 am"Do not look into bright LED with remaining eye" just does not have the right ring to it.

author: tyguy2
author_rank: Unknown
timestamp: July 19, 2016, 08:18:48 pm
content: "Eye" see what you did there.

author: MK14
author_rank: Super Contributor
timestamp: July 19, 2016, 08:28:42 pm
content: Related, but different example (lasers rather than LEDs). Warning: Unpleasant details!http://www.americanews.com/story/health/2015/11/06/teen-permanently-lose-75-percent-vision-due-one-little-toy