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LED Basics For beginners.

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LED Basics For beginners.

Post by assassin on Fri Aug 11, 2017 2:59 am

This is an introductory guide to making LED’s and using them, it isn’t a full description of circuit design or how to make up an LED circuit, it is simply to show that LED circuits are very simple and cheap to make and with a little basic knowledge anyone can design and build an LED circuit. Where would anyone need to use an LED circuit? In reality LED lighting can be used anywhere where lighting is required which may be for problematic car lights to outdoor security lights, for off grid lighting to a remote outbuilding without power, or even as internal mains or battery powered emergency lighting.

LED’s can be powered by a variety of means and the most common are mains power or battery power, but an LED needs its maximum power to be delivered to the LED in DC form and batteries are DC power, while mains power is in AC form. LED’s come with a voltage rating called the “forward voltage” and this may be given as a range such as 3.2 – 3.6V forward voltage which is often abbreviated to “Vf” in electronic circuits.

Every LED has a current consumption and this is in “milliamps” (Ma) and one milliamp is 1/1000th of one amp; therefore an LED rated at 30Ma consumes 30/1000th of an amp when it is lit or 0.030 amps. If we use our example above we can see we need a power capability of 3.6V at 0.03 amps for maximum brightness of our LED, and both the Vf and Ma rating are essential to correctly designing a circuit as you cannot and should not over rate the maximum voltage of an LED.

LED’s come in a range of types, styles, and voltages and the most popular are the single LED’s with an input rating ranging generally from1.2 - 5 volts and come in a range of a variant called the dome top, which means its body is round and its top is domed. These come in a variety of sizes and colours and the main sizes are 2mm, 3mm, 5mm, 8mm, and 10mm which are the standard sizes, they also come in a range of shapes such as square, rectangular, triangular, and a range of styles such as top hat and simply looking at a picture will show the difference. These types of LED will have two power pins and as an LED is polarity sensitive you must connect them the correct way round or they won’t work and may blow, so we use the power pins to identify polarity, most 2 pin LED’s have one pin which is longer and this is the positive (+) terminal, some may have equal length pins with a flat pressed onto the positive (+) pin.

Our next type of LED is called the SMD or “surface mount discrete” which are usually round or square, both types come without the power pins and come with two tags which are designed to be soldered directly to a circuit board. Two main types exist generally, and the round type usually have a single LED called a “chip” which is surrounded by a series of very small mirrors; the next popular type are the type with a square face, usually yellow in colour, and these have multiple LED chips connected in series or parallel, or a combination of both. Both types usually have an input voltage range and this can be anything such as 9 – 12 volts or even 30 – 36 volts as they usually have some form of voltage regulation built into their circuits, and they will always be a DC voltage.

We have to be aware of some other things which apply to LED’s and these are:

Viewing Angle – and this is the angle the light is emitted, many LED’s may have the same output or light rating but their viewing angle defines how the light is emitted and can range from 120˚ for a wide angle LED to as little as 8˚ for a longer range LED, so what does this mean. A wide angle LED such as the 120˚ LED will emit a light over a wide angle but for a short distance, similarly a narrow angle LED will emit its light over a very narrow angle but for a much longer distance.

MCD – this is the amount of light an LED will produce and a low powered LED may produce a light of 5000MCD which may be fine for a car key to illuminate a door key hole on the driver’s door, while a high powered LED will be well in excess of 100,000 MCD and be suitable for security or other lighting. By using multiple LED’s we can use both the viewing angle and MCD together to produce a high powered light for a security light for example as the area in front of the light doesn’t need illuminating, but areas away from the light do.
Powering an LED:

How do we power them? It’s a reasonable question and we can power them from the mains using a transformer, and for this example we will assume we are making a power supply to supply 12 volts as this is a common voltage, and it can also be used in automotive applications. We begin by using a mains transformer to supply an output of 15 volts? So why 15 volts, basically as it is above the 12 volts DC we require and in transforming voltage down we also need to rectify it by converting it to DC voltage and each stage has a voltage loss across it.
With a 240 volt input and a transformer output of an unregulated voltage of 15 volts AC we need to rectify it to DC voltage and to do this we use by using something called a “bridge rectifier” which is sometimes called a “Wheatstone Bridge” and this is a four pin integrated circuit. These use four diodes connected together so voltage can only run forwards and if you have diodes you can make your own bridge rectifier.
Diodes are basically a one way valve which allow voltage to run in one direction only and then prevents it running in the reverse direction so it takes two pulses from AC voltage and allows one power pulse to run forwards from one direction and then the power pulse from the other wire to do the same.
Bridge rectifiers are a readily bought integrated circuit and cost pennies to buy, they come with four pins and two are marked with the symbol ~ and the third pin is marked with a + symbol, while the fourth pin is marked with a – symbol. We take our two 15 volt AC wires from our transformer and solder one to one of the pins marked ~ and solder the other wire to the remaining pin marked ~ we have changed our AC transformed current to DC current at a fluctuating 15 volts.

Now we have to stabilise our voltage at a specific voltage and to do this we use something called a “voltage regulator” and these come in a variety of styles and packages and regulate our voltage output from an unregulated DC output of the bridge rectifier to a regulated fixed voltage of 12 volts.
Voltage regulators come in a package and there are numerous packages available and my preference is for a package called a “TO 220” package, you can get many other packages such as LM 317 for example, but the package denotes the pin layout and every TO 220 package has the same pin layout or configuration. By sticking to one package of voltage regulator you only have to learn one pin layout and this simplifies the pin layout and standardises component layouts.
Regulator styles are another type or designation of the voltage regulator and the most popular were the type 78 regulator which are still readily available and have been superseded by the newer type 79 regulator which offers better performance, but in reality either will suffice and they are cheap due to their popularity.
Voltage regulators can be denoted by their identification number and if we stick to the TO 220 package these are a 5 digit number and these will be 78X05 or 79X12 and we have to understand the numbers by breaking them down.

If we break these numbers down we can see the 78 refers to a 78 package and the 79 refers to a newer 79 package. The X as the third number can be anything and is often a letter as opposed to a number, and the last two numbers denote its regulated output voltage.
Therefore a 78X12 denotes a 78 style of voltage regulator with a regulated output of 12 volts.
Similarly a 79X18 denotes a 79 style of voltage regulator with a regulated voltage of 18 volts.
Voltage regulators come in two main types which are positive regulators or negative regulators and we always use a positive voltage regulator, and totally avoid the negative voltage regulators.

Pin layouts are always the same for 78 and 79 series voltage regulators and this assumes you are looking at the front view, the back of the voltage regulator is always flat while the front has a square bulge and the writing is printed onto it. Below is the pin layout of the regulators.



As we can see we have three clearly denoted pins but at the top we have a hole, and on the rear there is a metal or conducting surface which is connected to metal around the hole which is also an earth or ground, so be aware of this.

If we take a wire and solder it to the + marked pin on the bridge rectifier and run it to pin 1 denoted as input on the above drawing we have power to it, if we run another wire from the – marked pin on the rectifier to the pin marked ground we have a regulated output. By running a wire from the output terminal and another wire from ground we have the positive and negative wires running to an application at a regulated 12 volts DC.

NOTE – all voltage regulators come with either a maximum milliamp or amp rating and if you exceed more than 50% or half its ampere rating you need to connect a heatsink to the back of it; heatsinks are shaped aluminium extrusions designed to give surface area to conduct away heat. You cut a piece of heatsink extrusion longer than the back of the voltage regulator and align it so it covers the whole back of the heatsink and extends higher than the top, locate the regulator onto it and mark the hole and drill it. You then cover the back of the regulator with thermal grease and bolt it to the heatsink and the metal to metal contact conducts the heat away, and the thermal grease conducts the heat from the regulator to the heatsink.

But we have a 12v supply to power a 3.6 v LED and this will blow it? Yes it will and we have to match the LED to the voltage by using a resistor of the correct value, so how do we do it? We use a resistor which come in a range of set values, and they never match our exact requirement so we move up to the next value above what we need, so how do we do it, basically we cheat and use an online resistor calculator site.

http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator

This is the site I use as it gives the resistor value for a single LED, LED’s wired in series, and LED’s wired in parallel and all we do is put in the information and click on calculate and it does it all for us, it gives the exact resistor value and the next standard resistor value. Are resistors expensive? No, less than 1 pence each if you buy them in rolls of 100 resistors.

This site comes in three sections and if we refer to our LED specifications we see it is rated at 3.2 – 3.6 volts at 30Ma so this is what we enter in the single LED section.

Supply Voltage 12 volts
Voltage Drop Across LED 3.6
Desired Current in milliamps 30Ma
Click on the calculate button and it tells us the optimum resistance is 280 ohms, but the next standard resistor value is 330 ohms and we should use a standard 330Ω resistor.

If we move to the LED’s in series:

Supply Voltage 12 volts
Voltage Drop Across LED 3.6
Desired Current in milliamps 30Ma
Number of LED’s Connected 3
Click on the calculate button and it gives us the optimum resistor of 40Ω, but the next standard resistor is 47Ω and we should use the 47Ω resistor.

If we move to the LED’s parallel.

Supply Voltage 12 volts
Voltage Drop Across LED 3.6
Desired Current in milliamps 30Ma
Number of LED’s Connected 3
Click on the calculate button and it gives us the optimum resistor of 93.33Ω, but the next standard resistor is 100Ω and we should use the 100Ω resistor.

What is series and parallel? Basically it is two ways of wiring an LED or even LED chips.

When you wire a series of LED’s in series you place them in position and for the sake of clarity we will use 3 LED’s, you connect the cathode (-) pin of the first LED to the anode (+) pin of the second diode, then connect the cathode (-) pin of the second LED to the anode (+) pin of the third LED. Normally they are in close proximity and you can simply bend the pins over and solder them together but sometimes they may need the pins trimming, but always overlap them for a good soldered connection.

We are now left with two free pins, one is the anode (+) pin of the first LED and the second free pin is the cathode (-) pin of the third LED, and we solder the ground or earth wire directly to this cathode; on the first pin of the first LED we solder one end of a resistor (47Ω) and then the wire to the other end of the resistor and we have a circuit.

If we wire in parallel we run two conductors side by side with sufficient space between them to insert our LED’s, we solder the anode (+) of the first LED to the positive rail and the cathode to the negative rail. We place our second LED alongside our first LED and leave a little space and solder the anode to the positive rail and the cathode to the negative rail, and repeat with our third LED, this gives us three LED’s sat alongside each other as opposed to end to end as we have in series. We then solder our ground or negative wire from the voltage regulator to our negative rail and solder one end of a 100Ω resistor to out positive rail and our positive wire to the other end of our resistor.

Voltage regulators come in a range of fixed voltages and are called “fixed voltage regulators” and come in standard sizes of 5v, 6v, 8v, 9v, 12v, 15v, 18v, and 24v regulated output, but other voltages are available.
Voltage regulators also have a wide range of voltage inputs and a fairly standard voltage regulator would require you to find out this from the manufacturers data sheet or your component supplier, and a typical regulator would range from 12-30 volts, but they do vary so check before buying. Another little cheat is to avoid buying the 240/15 volt transformer and opt for the more popular 240/18 volt transformer as they are more popular and cheaper to buy, and if your voltage regulator can handle the 18v input (most can but check) then this is another option


If you use battery power such as that from a vehicle, or from another alternative source of power such as solar or water power which uses a storage battery we can omit the transformer and the bridge rectifier as a battery is already a DC supply with a voltage of 12 volts. Why do we still need the voltage regulator? Because any battery is rated as a NBV rating which is its Nominal Battery Rating and is only an average value. In a car or other automotive application the true value of the battery is around 12.6 – 12.8 volts, but this can rise as high as 14.6 when the engine is running and charging the battery. In an alternative power source battery the charging voltage can rise to 16 volts or higher and all we are doing is using a voltage regulator to stabilise this voltage to a fixed level.

In our example we have used three LED’s so why? Because if we add up the forward voltage of 3.6v + 3.6v  + 3.6v it gives us 10.8 volts as a total, and we never exceed the power source voltage as we cannot power the LED’s at maximum efficiency. If we were to add a fourth LED in series it would a total forward voltage of 14.4 volts which exceeds our supply voltage of 12.6 volts and undersupply our LED’s meaning they may work, but be dimmer.
Doing The Maths:

We need to work out voltage, current in amps (and milliamps) and watts and we use a simple formula to do this, but note that amps are always calculated in amps and not milliamps.

VOLTS X AMPS = WATTS

WATTS ÷ AMPS = VOLTS

WATTS ÷ VOLTS = AMPS

From these equations we can work out everything we need to know.
Always convert milliamps to amps for each calculation, e.g. our 30 Ma power consumption would be 0.03 amps for calculation purposes.

Costs:

Buying components can be a chore and if we search for a competitive supplier we can get some good prices, my suppliers costs are as follows.

Transformer 240 volt to 18 volt with 250Ma output £3.94
Bag of 50 3mm diameter LED’s in bright white £1.74 (3.48p each)
Bag of 5 79X12 voltage regulators £1.75 (35p each)
Bag of 5 bridge rectifiers (1 amp rated) £1.50 (30p each)
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Re: LED Basics For beginners.

Post by assassin on Fri Aug 11, 2017 6:13 pm

Many thanks Lopsum.
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Re: LED Basics For beginners.

Post by Waffle on Sat Aug 12, 2017 5:25 pm

This is a really good post, we should all be using LED's for many reasons.

Coupling them with off grid systems has huge benefits when managing your own micro energy generation. I think some LED's claim to be up to 90% savings, the energy savings are matched with the greenhouse savings (if you believe in that).

Here is a short video of how to make your own LED lantern, roughly 8 coughs of light and powered only by salt water. Yes we are all lied to, there is no need for a new nuclear power plant, or maybe thats why the power plant is being built on the coast, salt water......

https://www.youtube.com/watch?v=5vOuj_feM2s&feature=share


Last edited by Waffle on Sat Aug 12, 2017 7:38 pm; edited 1 time in total

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Re: LED Basics For beginners.

Post by assassin on Sat Aug 12, 2017 7:24 pm

Mine in my poly tunnels must emit greenhouse gasses?
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Re: LED Basics For beginners.

Post by assassin on Sat Aug 12, 2017 7:28 pm

Seriously though, I run a compact water turbine and generate my own electricity, but anyone can produce their own power using wind power as it has much more generating capacity than the much more expensive solar power which was another taxpayer funded scam right from the start.

Mini wind turbines can produce a lot of power and are better matched to the UK's climate as we consume more power in winter when the windier weather is abundant, they work during the day and at night unlike solar, and with storage batteries you can generate while you sleep.
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Re: LED Basics For beginners.

Post by Lopsum on Sat Aug 12, 2017 8:03 pm

waffle ,that would be an expensive way to generate that amount of electricity.Its a galvanic cell it is very old tech and certainly is not hidden knowledge. Galvanic corrosion will eat the copper and aluminum so it would need replacing after a while , its ok in small scale it you want a few leds but the amps we get from the grid would need a vast amount of copper for them to use it to supply us with.
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Re: LED Basics For beginners.

Post by Waffle on Mon Aug 14, 2017 9:53 pm

I couldn't help but feel like it had been hidden from when I saw it, I never knew we didn't need batteries for a light like that........ Maybe I just have my conspiracy head on too often




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Re: LED Basics For beginners.

Post by assassin on Wed Aug 16, 2017 2:31 am

Waffle, you can do it two ways, with power storage or without power storage.

If you run without power storage and are directly connected you will get huge power fluctuations running LED lighting which isn't good.

Batteries are storage and also a buffer as they absorb power to act as a buffer against dips and surges associated with most power generation forms and if you run a wind or water turbine which produce at anytime within the 24 hour cycle why would you waste what you produce while you are snoring, most people wouldn't.

On a more practical note many companies install alternative power systems, solar panels being the most popular followed by the much more effective wind turbines for both a tax loss and to reduce their carbon footprint on paper which both have financial benefits in the short to medium term. One client ran several of their computers from the 12V supplied by the solar panels and looked at running all their IT equipment from a 12v supply from alternative power, and we installed two compact wind turbines and a different charge controller to accept both sources of power and charge their batteries.

During hot summer months they ran fine from solar, but in Autumn, Winter, and Spring they were lacking, and the addition of the wind turbines charged their batteries through the night and now they run all their IT equipment from 12V without running their batteries flat, and recently they had a mains power failure and they continued to work.
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Re: LED Basics For beginners.

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