power for led's  - Page 1
Forum section: electronics / beginners

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 09, 2014, 08:08:27 pm
content: hello noob here again.how could i power 25 of the leds i have in the sources and still using the schematic bellow or something better to make the leds flash to the music.thanks again eevblog community.rather ask first than do it wrong.sources:http://dgpy.en.alibaba.com/product/777127977-218310298/5mm_Violet_UV_DIP_Led.html

author: electronics man
author_rank: Frequent Contributor
timestamp: February 09, 2014, 08:13:47 pm
content: Put them in parallel whith a resistor for each

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 09, 2014, 08:16:14 pm
content: i know i need to put them in parallel but how would i need to change the schematic and how much power do i need coming in if i change it to 25.

author: electronics man
author_rank: Frequent Contributor
timestamp: February 09, 2014, 08:18:22 pm
content: What voltage are you using and what voltage do the LEDs need

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 09, 2014, 08:19:55 pm
content: Quick DetailsType: LEDPackage Type: Through HoleMax. Forward Voltage: 3.0-3.4VMax. Reverse Voltage: 5VMax. Forward Current: 15-20mAMax. Reverse Current: 15-20mAEmitting Color: Red,Green,Blue,Yellow,Orange(Amber),Purple,White,multicolor,FlashingSize: 3mm,5mm,8mm,10mmLens: Water clear,colored diffused,color transparenti took this straight fromhttp://dgpy.en.alibaba.com/product/777127977-218310298/5mm_Violet_UV_DIP_Led.html

author: electronics man
author_rank: Frequent Contributor
timestamp: February 09, 2014, 08:26:35 pm
content: You supply must be able to supply 25x15 = 375mA, the resistor you will need should be worked out acording to the voltage used but you probably don't realy need to calculate it just estimate

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 09, 2014, 08:29:28 pm
content: alright but do i need to change the schematic any (beside psu) like the transistor because i am changing the amount of leds being used.

author: electronics man
author_rank: Frequent Contributor
timestamp: February 09, 2014, 08:36:13 pm
content: The circuit you have is a series one you need a parallel one with a resistor on each one.

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 09, 2014, 08:41:31 pm
content: alright i know what i need for my project now.electronics man check your pm inbox pls

author: Marco
author_rank: Super Contributor
timestamp: February 09, 2014, 08:48:47 pm
content: You can just make multiple parallel strings of 4 and leave off the resistor, if the MOSFET is too good (low resistance) and the voltage a little high you'll blow the LEDs though. If you want to use a current limiting resistor you need to make parallel strings of 3 with a ~200 Ohm resistor in each string.I can't say if your MOSFET can handle it because you didn't give us the MOSFET, not going to trawl the video for it.

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 09, 2014, 08:52:14 pm
content: TIP31 transitor

author: Marco
author_rank: Super Contributor
timestamp: February 09, 2014, 09:05:09 pm
content: With a 12 Volt supply, a TIP31 and 4 LEDs in a string I'd be amazed if you get more than a couple mA through those LEDs ... the voltage is simply too low.At 10 mA those LEDs probably take around 3.25 volt, the saturation voltage (Vcesat) of the transistor is around 1.2 ... with 3 LEDs that leaves about 1 volt for the current limiting resistor, so at 20 mA that would be 50 Ohms. So I'd make 8 parallel strings of 3 LEDs in series with a 50 Ohm resistor each.The transistor can easily handle that (because the diodes don't conduct at low voltages it's never going to see much power and it can handle far more current than the 150 mA your LEDs might use).PS. you can use 25 leds in parallel with a ~400 Ohm current limiting resistor each as well ... but you need more resistors and it's less efficient (you burn 2.5 Watts combined in all the resistors).

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 09, 2014, 09:18:37 pm
content: alright so the resistors i would use is 8 50ohm resistors in each row.what if i were to use 2 9volt batteries.( sorry for being so dumb about this .)p.s check your pm inbox marco

author: mariush
author_rank: Super Contributor
timestamp: February 09, 2014, 10:06:44 pm
content: Ok, let's take separate this into 2 separate things and get you to understand things better.1. How do you turn leds on and off and how do you connect them ?LEDs don't work like normal lightbulbs. There are two important things you have to know about a LED: the forward voltage and the current.The forward voltage is the minimum voltage from which the LED starts working. The current is how much energy has to go through the LED to be bright as the manufacturer designed it to be. The current can be lower and then the LED will simply be dimmer.In your case, you have this:Max. Forward Voltage: 3.0-3.4VMax. Reverse Voltage: 5VMax. Forward Current: 15-20mAMax. Reverse Current: 15-20mAThis tells you that most of the LEDs you buy from that seller will light up when there's around 3-3.4v on them and that you shouldn't allow more than 20mA to go through them otherwise the LEDs will die sooner and the color will be uglier (you get orange instead of red, stuff like that).Now, when you want to turn on or off several leds at the same time, you can connect leds in series (like christmas tree ornaments) or in parallel. In both cases, you want to make sure the maximum current that will go through the circuit will not go over the current of the leds.LEDs in series :+V -----> [ limit current ] -------[ led 1 ] ------ [ led 2 ] ----- [ led 3 ] ---- - GNDIf you connect LEDs in series, the voltage you need to power this string of leds must be equal or higher than the minimum forward voltage of the leds, times how many leds you have in the chain. The current remains the same as each led current, 15-20 mA or the amount of current you want the leds to have.So for example, if you have 3 leds with a maximum forward voltage of 3-3.4v you can't power them from 5v, but you can power them from 12v because the leds need 3 x 3.4v = 10.2 voltsSo if you have 3 leds powered from 12v, then they will light up, but you will need to somehow limit the current going through them, otherwise they will consume so much current they will blow up.You can limit the current going through this chain of LEDs by placing a resistor before or after the leds. In series, there is a rule saying the current remains the same on all components in the series of components. So, if the resistor restricts current to 10 or 20mA, each led in the chain will also be limited to that current.The formula to determine the value of that resistor is very simple, based on Ohm's law which says V = I x R (voltage = current x Resistance)So the value of the resistor is R = [ Input Voltage - ( number of leds x max forward voltage ) ] / Current (A).With 12v input voltage and 3 leds with a forward voltage of 3.4v and 20 mA (0.020 A) we would have R = (12-10.2)/0.02 = 140 ohm and we can round this up to a standard value of 150 ohm (the current will be a bit lower, about 18-19mA).So these three leds with a 150 ohm resistor will work just fine from 12v and will use 20mA to work.LEDs in parallel:So if you have the same 3 leds with forward voltage 3-3.4v and 20mA per led and you connect the leds like in the picture above, your power supply needs to give you at least 3.4v (just the forward voltage of a single led) but now it has to be able to give 60 mA of current.You still need to limit the energy using a resistor, but now you have to allow up to 60 mA ( 3 x 20) and your input voltage may be lower. For example, let's do the math now for 5v input voltage, because it's larger than the minimum 3.4vR = (5v - 3.4v) / 0.06 A = 26.6 ohm or 27 ohm which is a standard value.Now, you don't see this configuration often because some leds are built better than others and this way, you only limit the current to all leds. One led may use a bit less current, other may use more, so one may be brighter than another. Also, in this configuration, if one led burns out, then the whole current goes through the remaining leds ( 60mA / 2 = 30mA which is more than the maximum of 20mA) and then the other leds may also die. In series, if one led dies, the circuit is interrupted and the leds simply no longer light up until you replace the led.So now let's go to your problem ... you say you want to light up 25 leds. Let's make it 24 because it's easier this way.If you'd put all 24 leds in series, the minimum input voltage will have to be at least 24 x 3.4v or about 81.6v and the whole string will use 20 mA.If you put them all in parallel, you'd need a power supply with at least 3.4v input voltage, but the power supply will need to provide 20mA x 24 = 480 mA.What you can do is make 8 separate strings of 3 leds and then connect these in parallel - each string of 3 leds will have its own resistor limiting the current to 20mA, and the 8 strings in parallel can run from 12v and will use in total 20 mA x 8 = 160 mA.2. How does the circuit workThe circuit looks like this :Here's what happens. You notice there are two TIP31 transistors, one for each channel. Here's the datasheet for them :http://www.hobbytronics.co.uk/datasheets/TIP31.pdfThese chips act like a sort of valve/tap/faucet. The more energy comes through one of the pins (base), the more energy the chip lets through from second pin (collector) to the third pin (emmiter).So as the volume of your music increases, more current is allowed to go through it. When the volume decreases, the transistor reduces the current going through it.If you have one of those strings of 3 leds with a resistor to limit the maximum current to 20mA then if the volume is large enough, the transistor will let 20mA go through it and the string will light up to the maximum. If the sound intensity is smaller, it will only allow a smaller amount of current so the LEDs in the string will be dimmer.The transistor is made to allow a certain amount of energy go between collector and emitter for a certain amount of energy coming into its base bin. That parameter is called hFe and you can find it in the datasheet at the bottom of page 2. There are actually two values, but you can see there a minimum value of 25 and a typical value of 50.What this means is that if you have 2 mA of energy coming into the base pin, you will have anything between 2x25 = 50mA and 2 x 50 = 100mA going from collector to emitter. If you have 10mA on the base, you may have anything between 10x25 = 250mA and 10x50 = 500mAThis is important to understand because if you put 3 leds like in the Kipkay circuit, 20 mA is not a problem for this chip. But, if you put 24 leds that use 160mA in total, you may need to play music loud ( get enough current into the base pin) to have the leds bright (allow 160mA to go through the transistor).Another thing that you should understand is that batteries can not provide a lot of current and work for long periods of time. 9v batteries in particular are kind of weak, if you want them to last you shouldn't draw more than around 50mA from them. If you put two in series to get 18v, you don't get more current so you still shouldn't connect something that demands more than around 50mA. Connecting those 24 LEDs to the 2 9v batteries is not a good idea, because those leds will use 160mA, more than what the batteries should be used for. The batteries will last maybe a couple of hours and they'll be dead then.

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 09, 2014, 10:25:28 pm
content: Oh my thank you so much this actually helped me alot.Make sure you check your pm inbox

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 09, 2014, 11:42:14 pm
content: so i needat least 24 leds12v 160ma psu8 150 ohm resistors2 tip31 transistorwireand an audio plugor

author: mariush
author_rank: Super Contributor
timestamp: February 10, 2014, 12:39:16 am
content: Pretty much.Keep in mind that you don't have to run the leds at 20mA each, they may be bright enough for you at currents as low as 10mA. So don't get stuck at searching for exactly a 12v 160mA power supply. It can be more than 160 mA, it can be a bit lower.You can also search for a 7.5v or a 9v adapter and just change the layout of the leds and change the resistor value - instead of series of 3 leds and 12v, just change it to have series of 2 leds and suitable resistor - you have the formula in my post above.The TIP31 transistor can work with voltages higher than 12v as well, for example you could make series of 5 leds and a suitable resistor and power them from a 19v laptop charger/adapter.But you should have no problem finding one of those adjustable dc adapters, one that looks like this:Resistors are super cheap, you can get 20-50 for a dollar. Those eBay leds are also super cheap, probably better to just get 50 or 100.Since you're in US, you could just order from Digikey or Mouser.com..Here you go , leds from 0.1$ each :http://www.digikey.com/product-search/en?FV=fff40008%2Cfff801b9%2C1140050%2C11402b2&mnonly=0&newproducts=0&ColumnSort=1000011&page=1&stock=1&pbfree=0&rohs=0&quantity=10&ptm=0&fid=0&pageSize=25pick the led, write down the forward voltage and the current, decide how many you want in a series ( 3, 4, 5 etc) and based on the input voltage you'll use determine the resistor value to limit the current in each series of leds.Resistors from 0.05$ each :http://www.digikey.com/product-search/en?FV=fff40001%2Cfff80482&mnonly=0&newproducts=0&ColumnSort=1000011&page=1&stock=1&pbfree=0&rohs=0&quantity=10&ptm=0&fid=0&pageSize=25TIP31 ..http://www.digikey.com/product-search/en/discrete-semiconductor-products/transistors-bjt-single/1376376?k=TIP31Power supplies :http://www.digikey.com/product-search/en?FV=fff40009%2Cfff8004a&mnonly=0&newproducts=0&ColumnSort=1000011&page=1&stock=0&pbfree=0&rohs=0&quantity=&ptm=0&fid=0&pageSize=25Mouser.com should have pretty much the same prices.No need to bother with eBay and waiting weeks for parts to come.

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 10, 2014, 02:49:33 am
content: it is worth the price to be able to get it in two days with prime WHILE prototyping because like really i am not going to spend 100 dollars right now lolhttp://www.amazon.com/HQRP-BC12V300-SBC12V300-Controlled-Training/dp/B008O4AZU4/ref=sr_1_6?ie=UTF8&qid=1392000282&sr=8-6&keywords=ac+adapter+200ma+12vhttp://www.amazon.com/microtivity-IL188-Assorted-Resistors-Colors/dp/B0060FGA8A/ref=pd_sim_indust_6http://www.amazon.com/gp/product/B0002ZPZYO/ref=s9_psimh_gw_p328_d0_i1?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-2&pf_rd_r=1CWXZS2JSH75FSKW8XWC&pf_rd_t=101&pf_rd_p=1688200382&pf_rd_i=507846so this in theory for now is the perfect order because i will get it in 2 days so yea thank you could some one be as so polite and check it for me to see if i got it right

author: mariush
author_rank: Super Contributor
timestamp: February 10, 2014, 03:41:38 am
content: Digikey.com and Mouser.com will ship it to you in pretty much 2-3 days, if you're in US.I already gave you the links above to various things.ex. your power adapter is 10$ , here's 2 for around 5$ each :9v 300mA :http://www.digikey.com/product-detail/en/PSM03A-090-R/993-1234-ND/403187912v 230mA :http://www.digikey.com/product-detail/en/PSM03A-120-R/993-1232-ND/40318836$ for about 80 leds and 20 resistors ... on Digikey they're 10 leds for 1$ , 20 resistors for 1$, overall just a bit more expensive...The TIP31 is 60 cents on Digikey at the link I posted above, they're 4.5$ on amazon. Just put the money on leds instead on Digikey.Just pick, put in basket and buy all at once from same online store - Digikey and Mouser are reliable and used by lots of people here, it's safe to buy from there.If you just put the US flag in your profile to screw we us, I can recommend other such online stores that will ship cheaply within Europe.

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 10, 2014, 03:45:07 am
content: oh i tough dig-key or others you have mentioned would only let me buy like 1000 at a time guess i should have checked first i will be back on the next notice on this project thanks to every one who had helped so far

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 14, 2014, 03:10:30 am
content: i odered products pm if you want to see me build it, it may not be interesting to you but any help is loved with this newb

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 14, 2014, 03:00:03 pm
content: how would i "my self" find a heat sink for this :http://www.digikey.com/product-detail/en/TIP31C/TIP31CFS-ND/458805: whats the math in it what do i need to figure out.

author: mariush
author_rank: Super Contributor
timestamp: February 14, 2014, 04:55:46 pm
content: Your transistors probably won't need any heatsink, or you could just cut a few square inches of metal sheet and screw each one on a separate piece of metal.If you really want heatsinks, something like this would work (one for each)http://www.digikey.com/product-detail/en/507002B00000G/HS112-ND/5846http://www.digikey.com/product-detail/en/V7236C1/AE10840-ND/3511408http://www.digikey.com/product-detail/en/504102B00000G/HS104-1-ND/5832As for how to calculate, the datasheet is very weak, it has no information about how well the heat transfers to a heatsink through the metal tab of the IC. But generally, these transistors can work at up 150c internally so you could safe they're safe to use at up to around 100c on the outside of the chip.Those heatsinks above will heat up by about 20c above ambient temperature for each watt of power dissipated on the transistor, so if your room temperature is 30c, the heatsink will be about 50c warm if the transistor wastes about 1 watt in it. Your circuit shouldn't waste so much power so it should be fine with it.There's some parameters that are usually required to determine the minimum heatsink parameters for a part, like junction to air, junction to case etc and the datasheet for tip31 doesn't have them. Maybe datasheets for the same chip but made by other companies will have them (and they're usually fairly close between manufacturers).There's a page with a calculator that can help you with the math, if you know these parameters and at the bottom of the page it also explains how the formulas are used:http://www.ef-uk.net/data/heatsinking.htm

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 14, 2014, 05:11:04 pm
content: alright this is going to be running for hours at a time so i wanted to be safe...

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 18, 2014, 01:46:17 am
content: alright so i have my design done and every thing. but i cant deal with just wire's its just everywhere should i just get a PCB or just a perfboard. whats easier. would it be easier just to order PCB so i can just hook it up and see it work. ( i am only going to make around 20 of themhttps://www.eevblog.com/forum/beginners/power-for-led%27s/

author: electronics man
author_rank: Frequent Contributor
timestamp: February 18, 2014, 11:31:03 am
content: for quantaties of 20 you would have to order some custom boards and that costs a lot.

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 18, 2014, 09:47:05 pm
content: ah guess i will just get some perfboard

author: electronics man
author_rank: Frequent Contributor
timestamp: February 18, 2014, 09:49:52 pm
content: yeah its good for a prototype but not for a product

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 18, 2014, 10:16:10 pm
content: wait so a PERFBOARD isnt good for final product so what should i buy. i do not want to stick with wires

author: electronics man
author_rank: Frequent Contributor
timestamp: February 18, 2014, 10:19:49 pm
content: profesional pcb but it is expensive its the only way you can do it.

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 18, 2014, 10:21:23 pm
content: i mean i guess but my limit its 10$per board/with componets

author: electronics man
author_rank: Frequent Contributor
timestamp: February 18, 2014, 10:34:53 pm
content: i dont kown what your pcb size is but im not sure you could do it for that price especialy for 20 boards

author: mariush
author_rank: Super Contributor
timestamp: February 18, 2014, 10:43:27 pm
content: 12cm x 18cm prototyping boards (basically 2500 holes with pads to solder parts to)... pack of 10 = 15$ :http://www.ebay.com/itm/10x-Prototyping-PCB-Universal-Printed-Circuit-Board-12x18CM-Prototype-Breadboard-/200992229492?pt=LH_DefaultDomain_0&hash=item2ecc120874http://www.ebay.com/itm/10x-Prototyping-PCB-Universal-Printed-Circuit-Board-Prototype-Breadboard-12x18CM-/331073356732?pt=LH_DefaultDomain_0&hash=item4d158283bchttp://www.ebay.com/itm/10x-Prototyping-PCB-Universal-Printed-Circuit-Board-Prototype-Breadboard-12x18CM-/360787058695?pt=LH_DefaultDomain_0&hash=item540095a007You can get smaller sizes as well, like 9cm x 15 cm (1440 holes), 10 boards for 8$ :http://www.ebay.com/itm/10x-Prototyping-PCB-Universal-Printed-Circuit-Board-Prototype-Breadboard-9x15CM-/360787055803?pt=LH_DefaultDomain_0&hash=item54009594bbor even smaller 7cm x 9 cm (720 holes) , 10 boards for 3-5$ :http://www.ebay.com/itm/10PCS-Prototyping-PCB-Universal-Printed-Circuit-Board-5x7CM-Prototype-Breadboard-/360798860977?pt=LH_DefaultDomain_0&hash=item540149b6b1http://www.ebay.com/itm/10PCS-Prototyping-PCB-Universal-Printed-Circuit-Board-Prototype-Breadboard-5x7CM-/350937931578?pt=LH_DefaultDomain_0&hash=item51b587df3ahttp://www.ebay.com/itm/10PCS-Prototyping-PCB-Universal-Printed-Circuit-Board-Prototype-Breadboard-7x9CM-/400603662383?pt=LH_DefaultDomain_0&hash=item5d45d6c82fand you can cut any of these in smaller strips if you want to solder the leds on a long strip or something like that. The material is phenolic paper, paper in a rosin, so you can cut it easily with a sharp blade or using a small woodsaw.

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 18, 2014, 10:46:24 pm
content: yea it didnt even sound like it to me ether i am just going to buy some huge perfboards and break them up into tiny pieces. and also i bought tip31C instead of just tip31 i saw other people just using tip31c so i thought it would also work for me.. what did i do wrongoh you posted exactly what i had to say first lol

author: mariush
author_rank: Super Contributor
timestamp: February 18, 2014, 11:06:45 pm
content: For what you're trying to do, TIP31 or TIP31C is the same thing.The difference is basically in the maximum voltage allowed on the collector pin. TIP31 = 40v, TIP31A = 60v, TIP31B=80v, TIP31C = 100v.. you're going to work with 12v or close to 12v, so it makes no difference what version you have, all support at least 3 times your voltage.QuoteHe means for a hobby, for something you're going to use by yourself and maybe give to a few friends, it's good enough.If you want to sell it in a store, give warranty, advertise etc etc, you should make a real pcb.

author: noah_fakelastnamelike_bob
author_rank: Regular Contributor
timestamp: February 18, 2014, 11:09:14 pm
content: well alrighty i am going to shut up now. i ma work on my project