PDF TPS818 TPS818 5252 F 4-pin LX 5252 F ic 5252 F led 5252 led: 2000 - LX 5252 F ic. Abstract: 5252 F 'integrated circuit' Text: °) (5°) 3.0 5.0 0.3max 4-pin side-view clear plastic package Luminous efficiency correction. Original: PDF TPS818 TPS818 x22500 LX 5252 F ic 5252 F 'integrated circuit' 1997 - Not Available. Abstract: No abstract text available Text:.
CONTENTS for Model Railway Battery Monitor - amazing - The LED Flashlight - for cars and trucks 1,2,3 - LED and Piezo - a very good design INTRODUCTION This e-book covers the Light Emitting Diode. The LED (Light Emitting Diode) is the modern-day equivalent to the light-globe. It has changed from a dimly-glowing indicator to one that is too-bright to look at. However it is entirely different to a 'globe.' A globe is an electrical device consisting of a glowing wire while a LED is an electronic device. A LED is more efficient, produces less heat and must be 'driven' correctly to prevent it being damaged. This eBook shows you how to connect a LED to a circuit plus a number of projects using LEDs.
It's simple to use a LED - once you know how. INSIDE A LED: A 'Natural' or 'Characteristic' voltage develops across a LED when it is correctly connected in a circuit with a current-limiting resistor to allow a current between 1mA and 20mA. This voltage is shown in the table above and we normally use the lower value for each colour. However the table shows the voltage varies quite a lot and this depends on the actual crystalline construction of the crystal and the way it is manufactured. You cannot change this and that's why you need to measure the voltage across the LED when building some of the circuits. LED VOLTAGES Here is another table showing LED Voltages. The voltage across a LED depends on the manufacturer, the intensity of the colour and the actual colour.
LED VOLTAGES depend on many factors. You must test the LED(s) you are using. The voltage across some LEDs increases by 500mV (0.5v) when the current increases from about 10mA to 25-30mA and if you have 6 LEDs in series, this is an increase of 3v. If you are using a 12v supply, you cannot (should not) put 4 white LEDs in series as the 'characteristic voltage will be 3.6 x 4 = 14.4 and this is higher than the voltage from a 12v battery. You will need to remove one LED and fit a resistor to get the brightness you require. CONNECTING A LED A LED must be connected around the correct way in a circuit and it must have a resistor to limit the current. The LED in the first diagram does not illuminate because a red LED requires 1.7v and the cell only supplies 1.5v.
The LED in the second diagram is damaged because it requires 1.7v and the two cells supply 3v. A resistor is needed to limit the current to about 25mA and also the voltage to 1.7v, as shown in the third diagram. The fourth diagram is the circuit for layout #3 showing the symbol for the LED, resistor and battery and how the three are connected.
The LED in the fifth diagram does not work because it is around the wrong way. CHARACTERISTIC VOLTAGE DROP When a LED is connected around the correct way in a circuit it develops a voltage across it called the CHARACTERISTIC VOLTAGE DROP. A LED must be supplied with a voltage that is higher than its 'CHARACTERISTIC VOLTAGE' via a resistor - called a VOLTAGE DROPPING RESISTOR or CURRENT LIMITING RESISTOR - so the LED will operate correctly and provide at least 10,000 to 50,000 hours of illumination. A LED works like this: A LED and resistor are placed in series and connected to a voltage. As the voltage rises from 0v, nothing happens until the voltage reaches about 1.7v. At this voltage a red LED just starts to glow.
As the voltage increases, the voltage across the LED remains at 1.7v but the current through the LED increases and it gets brighter. We now turn our attention to the current though the LED.
As the current increases to 5mA, 10mA, 15mA, 20mA the brightness will increase and at 25mA, it will be a maximum. Increasing the supply voltage will simply change the colour of the LED slightly but the crystal inside the LED will start to overheat and this will reduce the life considerably. This is just a simple example as each LED has a different CHARACTERISTIC VOLTAGE DROP and a different maximum current. In the diagram below we see a LED on a 3v supply, 9v supply and 12v supply.
The current-limiting resistors are different and the first circuit takes 6mA, the second takes 15mA and the third takes 31mA. But the voltage across the red LED is the same in all cases.
This is because the LED creates the CHARACTERISTIC VOLTAGE DROP and this does not change. It does not matter if the resistor is connected above or below the LED. The circuits are the SAME in operation: HEAD VOLTAGE Now we turn our attention to the resistor.
As the supply-voltage increases, the voltage across the LED will be constant at 1.7v (for a red LED) and the excess voltage will be dropped across the resistor. The supply can be any voltage from 2v to 12v or more. In this case, the resistor will drop 0.3v to 10.3v. This is called HEAD VOLTAGE - or HEAD-ROOM or OVERHEAD-VOLTAGE.
And the resistor is called the CURRENT-LIMIT resistor. The following diagram shows HEAD VOLTAGE: The voltage dropped across this resistor, combined with the current, constitutes wasted energy and should be kept to a minimum, but a small HEAD VOLTAGE is not advisable (such as 0.5v). The head voltage should be a minimum of 1.5v - and this only applies if the supply is fixed. The head voltage depends on the supply voltage. If the supply is fixed and guaranteed not to increase or fall, the head voltage can be small (1.5v minimum). But most supplies are derived from batteries and the voltage will drop as the cells are used. Here is an example of a problem: Supply voltage: 12v 7 red LEDs in series = 11.9v Dropper resistor = 0.1v As soon as the supply drops to 11.8v, no LEDs will be illuminated.
(Sometimes the LEDs will illuminate because some LEDs will have a characteristic voltage that is slightly less than 1.7v and some will illuminate when the voltage is lower than 1.6v - but the brightness will reduce considerably.) Example 2: Supply voltage 12v 5 green LEDs in series @ 2.1v = 10.5v Dropper resistor = 1.5v The battery voltage can drop to 10.5v But let's look at the situation more closely. Suppose the current @ 12v = 25mA. As the voltage drops, the current will drop. At 11.5v, the current will be 17mA At 11v, the current will be 9mA At 10.5v, the current will be zero You can see the workable supply drop is only about 1v.
Many batteries drop 1v and still have over 80% of their energy remaining. That's why you need to design your circuit to have a large HEAD VOLTAGE. A large Head Voltage is also needed when a plug-pack (wall wart) is used. These devices consist of a transformer, set of diodes and an electrolytic. The voltage marked on the unit is the voltage it will deliver when fully loaded. It may be 200mA, 300mA or 500mA.
When this current is delivered, the voltage will be 9v or 12v. But if the current is less than the rated current, the output voltage will be higher. It may be 1v, 2v or even 5v higher. This is one of the characteristics of a cheap transformer. A cheap transformer has very poor regulation, so to deliver 12v @ 500mA, the transformer produces a higher voltage on no-load and the voltage drops as the current increases.
You need to allow for this extra voltage when using a plug-pack so the LEDs do not take more than 20mA to 25mA. Roger Mew contacted me asking for some suitable resistances for the HEAD VOLTAGE resistor. Here is a list: For 25mA current: Use 56R for 1.5v drop.
Use 82R for 2v drop Use 120R for 3v drop Use 150R for 4v drop Use 180R for about 5v drop TESTING A LED If the cathode lead of a LED cannot be identified, place 3 cells in series with a 220R resistor and illuminate the LED. 4.5v allows all types of LEDs to be tested as white LEDs require up to 3.6v. Do not use a multimeter as some only have one or two cells and this will not illuminate all types of LEDs.
In addition, the negative lead of a multimeter is connected to the positive of the cells (inside the meter) for resistance measurements - so you will get an incorrect determination of the cathode lead. CIRCUIT TO TEST ALL TYPES OF LEDs including blue and white IDENTIFYING A LED A LED does not have a 'Positive' or 'Negative' lead. It has a lead identified as the 'Cathode' or Kathode' or 'k'.
This is identified by a flat on the side of the LED and/or by the shortest lead. This lead goes to the 0v rail of the circuit or near the 0v rail (if the LED is connected to other components).
Many LEDs have a 'flat' on one side and this identifies the cathode. Some surface-mount LEDs have a dot or shape to identify the cathode lead and some have a cut-out at one end. Here are some of the identification marks: Note: the 3 leaded LED is different. The flat indicates the red LED and the other LED is green. See the diagram for the placement of the two LEDs.
LEDs ARE CURRENT DRIVEN DEVICES A LED is described as a CURRENT DRIVEN DEVICE. This means the illumination is determined by the amount of current flowing through it.
This is the way to see what we mean: Place a LED and 100R resistor in series and connect it to a variable power supply. As the voltage is increased from 0v, to 1v, the LED will not produce any illumination, As the voltage from the power-supply increases past 1v, the LED will start to produce illumination at about 1.6v to 1.7v (for a red LED).
As the voltage is increased further, the illumination increases but the voltage across the LED does not increase. (It may increase 0.1v) but the brightness will increase enormously. That's why we say the LED is a CURRENT DRIVEN DEVICE.
The brightness of a LED can be altered by increasing or decreasing the current. The effect will not be linear and it is best to experiment to determine the best current-flow for the amount of illumination you want. High-bright LEDs and super-bright LEDs will illuminate at 1mA or less, so the quality of a LED has a lot to do with the brightness. The life of many LEDs is determined at 17mA. This seems to be the best value for many types of LEDs.
1mA to 5mA LEDs Some LEDs will produce illumination at 1mA. These are 'high Quality' or 'High Brightness' LEDs and the only way to check this feature is to test them @1mA as shown below.
THE 5v LED Some suppliers and some websites talk about a 5v white or blue LED. Some LEDs have a small internal resistor and can be placed on a 5v supply. This is very rare. Some websites suggest placing a white LED on a 5v supply.
These LEDs have a characteristic voltage-drop of 3.6v and should not be placed directly on a voltage above 3.6v. If placed on a voltage below 3.6v, the LED will not glow very brightly.
If you have a voltage EXACTLY 3.6v, you can connect the LED, but most voltages are higher than 3.6v and thus you need a resistor. The only LED with an internal resistor is a FLASHING LED. These LEDs can be placed on a supply from 3.5v to 12v and flash at approx 2Hz. The LED is very weak on 3.5v but its flashing can be used to drive a powerful LED (see circuits section). It can also be used to produce a beep for a beeper FM transmitter. NEVER assume a LED has an internal resistor. Always add a series resistor.
Some high intensity LEDs are designed for 12v operation. These LEDs have a complete internal circuit to deliver the correct current to the LED. This type of device and circuitry is not covered in this eBook. If you don't know if a resistor is inside the device (such as a LED strip) you are testing, add a 100R and connect to a 12v supply.
Measure the current and if it less than expected, you can reduce the resistor to 47R and then 10R or remove it. Putting a LED on a high voltage will instantly destroy it and a 100R will prevent it being damaged. LEDs IN SERIES LEDs can be placed in series providing some features are taken into account. The main item to include is a current-limiting resistor.
A LED and resistor is called a string. A string can have 1, 2, 3 or more LEDs. Three things must be observed: 1. MAXIMUM CURRENT through each string = 25mA. The CHARACTERISTIC VOLTAGE-DROP must be known so the correct number of LEDs are used in any string. A DROPPER RESISTOR must be included for each string. The following diagrams show examples of 1-string, 2-strings and 3-strings: LEDs IN PARALLEL LEDs CANNOT be placed in parallel - until you read this: LEDs 'generate' or 'possess' or 'create' a voltage across them called the CHARACTERISTIC VOLTAGE-DROP (when they are correctly placed in a circuit).
This voltage is generated by the type of crystal and is different for each colour as well as the 'quality' of the LED (such as high-bright, ultra high-bright etc). This characteristic cannot be altered BUT it does change a very small amount from one LED to another in the same batch. And it does increase slightly as the current increases. For instance, it will be different by as much as 0.2v for red LEDs and 0.4v for white LEDs from the same batch and will increase by as much as 0.5v when the current is increased from a minimum to maximum. You can test 100 white LEDs @15mA and measure the CHARACTERISTIC VOLTAGE-DROP to see this range. If you get 2 LEDs with identical CHARACTERISTIC VOLTAGE-DROP, and place them in parallel, they will each take the same current.
This means 30mA through the current-limiting resistor will be divided into 15mA for each LED. However if one LED has a higher CHARACTERISTIC VOLTAGE-DROP, it will take less current and the other LED will take considerably more.
Thus you have no way to determine the 'current-sharing' in a string of parallel LEDs. If you put 3 or more LEDs in parallel, one LED will start to take more current and will over-heat and you will get very-rapid LED failure. As one LED fails, the others will take more current and the rest of the LEDs will start to self-destruct. The reason why they take more current is this: the current-limit resistor will have been designed so that say 60mA will flow when 3 LEDs are in parallel. When one LED fails, the remaining LEDs will take 30mA each.
Thus LEDs in PARALLEL should be avoided. Diagram A below shows two green LEDs in parallel. This will work provided the Characteristic Voltage Drop across each LED is the same. In diagram B the Characteristic Voltage Drop is slightly different for the second LED and the first green LED will glow brighter.
In diagram C the three LEDs have different Characteristic Voltage Drops and the red LED will glow very bright while the other two LEDs will not illuminate. All the current will pass through the red LED and it will be damaged. The reason why the red LED will glow very bright is this: It has the lowest Characteristic Voltage Drop and it will create a 1.7v for the three LEDs. The green and orange LEDs will not illuminate at this voltage and thus all the current from the dropper resistor will flow in the red LED and it will be destroyed. THE RESISTOR The value of the current limiting resistor can be worked out by Ohms Law. Here are the 3 steps: 1. Add up the voltages of all the LEDs in a string.
E.g: 2.1v + 2.3v + 2.3v + 1.7v = 8.4v 2. Subtract the LED voltages from the supply voltage. E.g: 12v - 8.4v = 3.6v 3. Divide the 3.6v (or your voltage) by the current through the string. For 25mA: 3.6/.025 =144 ohms for 20mA: 3.6/.02 = 180 ohms for 15mA: 3.6/.015 = 250 ohms for 10mA: 3.6/.01 = 360 ohms This is the value of the current-limiting resistor. Here is a set of strings for a supply voltage of 3v to 12v and a single LED: Here is a set of strings for a supply voltage of 5v to 12v and a white LED: Here is a set of strings for a supply voltage of 5v to 12v and two LEDs: CONNECTING A STRING OF LEDs Connecting 2, 3 or 4 or more LEDs to a voltage is easy. But you must follow these simple instructions: A LED circuit is designed around VOLTAGE.
This is the first thing you have to provide. You need to provide a voltage that is greater than the characteristic voltage of the LED or LEDs in the circuit (called a 'string'). This voltage will be at least 1.7v for a red LED and about 3.6v to 3.8v for a white LED. The voltage for each colour LED is discussed above. If you have more than one LED in the circuit, you need to add these 'characteristic voltages.' Suppose you get 3 x 3.8v = 11.4v for three white LEDs.
This is called the EXACT VOLTAGE you need to deliver. If you deliver 11v, none of the LEDs will illuminate.
If you deliver 11.8v, all the LEDs will be extremely bright and will burn out in a few minutes or hours. LEDs are not torch globes.
They are nothing like torch globes. So, you cannot think of them as torch globes. They are an ELECTRONIC device. They do not have a hot wire inside them that glows. They have a crystal that illuminates when a current flows from one contact, through the crystal to the other contact. When the LED illuminates, you know the voltage that will develop across the leads, by looking at the colour produced and then looking at the table above.
BUT you do not know the current required by the LED. The normal current is 17mA to 20mA, but some high-bright LEDs will produce very good brightness at 10mA or even 1 to 5mA. You need to find out how much current you want to flow through the string of LEDs. It might be low to conserve battery life or high to produce the maximum brightness. If you have a string of LEDs, the current flowing through the first LED will be same as all the other LEDs and this may produce different illumination if the LEDs are from different manufacturers or of different quality. The final step is to add a resistor to illuminate them.
This is called the CURRENT LIMITING RESISTOR. You can find the value of this resistor by mathematics, but this is pointless when you dont know the current required by the string. And the current can be anywhere from 1mA to 30mA. You need to have a supply that is at least 1v higher than the total characteristic voltage required by the LEDs, but you don't know this characteristic value. So, you know nothing.
But the answer is simple. Get a 12v supply and a 1k resistor. Connect all the LEDs in series and add the resistor. Connect this to the 12v.
Make sure the short lead (cathode lead) of the bottom LED goes to the black wire of the 12v. Make sure the short lead of the middle LED goes to the long lead of the bottom LED. And the same with the top LED. The long lead (anode) of the top LED goes to the resistor. See the following diagrams for examples: You MUST include the 1k resistor or all the LEDs will BLOW UP. If the LEDs do not come ON, try other LEDs (one may be damaged). You cannot connect more than 3 white LEDs to 12v.
FINAL STEP The final step is completely non-technical, because you cannot work out the value of the resistor needed to limit the current. You cannot work it out because the actual voltage across each LED will change slightly as the current increases, and this is an unknown value. And you don't know the value of current to produce the required brightness.
It is pointless going into any mathematics, when the answer is so simple. You need to supply a voltage higher than 11.4v and you must be sure the voltage will never drop below 11.2v as the LEDs will all turn off. This means a battery cannot be used as it will drop as low as 10.8v. The voltage (called the supply) can be 12v, 15v or even 20v. The supply voltage does not matter. As long as it is above 12v. When you use a high voltage supply, the CURRENT LIMIT RESISTOR may get hot and this is called WASTED ENERGY.
You can fix all these problems later when you get the string of LEDs illuminated and feel the resistor. All you have to do is get a 1k resistor and connect it between the supply and the string of LEDs and connect the bottom LED (the cathode of this LED) t the black wire (called the negative of the supply). It is really the 0v of the supply and the red lead is the positive of the supply. Now look at the brightness.
If it is not bright enough, use a 680R resistor then a 470R and 330R and then 220R, until the brightness is perfect. If some LEDs are too bright and others are not bright enough you will have to change them for other LEDs from different manufacturers, as some of the LEDs are high brightness and others are low brightness and some will be JUNK. You cannot fix this. Just try different LEDs. You can only connect the same 'quality LEDs in a string” if you want the same brightness. You can measure the current, if you like, but some LEDs work on 5mA, some on 20mA, while some may need 70mA and some 350mA.
You cannot mix LEDs with these huge differences. Each type must be on its own separate string. Some LEDs have a resistor inside the package and are designed to be connected to 12v. These LEDs are different again.
They are specially designed to connect to say a car (12v car). You can only work out all these things by starting with a 1k resistor and gradually reducing the value. This resistor is called a SAFETY RESISTOR and prevents the LEDs 'burning out.' Once you get the correct brightness the resistor becomes a CURRENT LIMITING RESISTOR. This is the ONLY safe way to tackle the problem.
Fiddling around with LEDs with no resistors will blow them up instantly. LEDS ON 12v - for cars and trucks When connecting LEDs to cars and trucks, you have to allow for an increase in voltage during the time when the battery is being charged. Normally the battery sits at 12.6v, but when charging, it can rise to 13.5v or slightly higher. If you put 3 white LEDs in series, the 'head' voltage will be about 1.8v when the battery is 12.6v, but increase to 2.7v when it is charging. This will increase the current through the LEDs by about 50% and will be noticeable as the brightness will increase considerably. The extra current may also damage the LEDs.
To keep an even brightness, we suggest using strings of LEDs with just two white LEDs and 220R 0.25watt resistors as shown in the following diagram. Red, green, orange, yellow and blue LEDs have a different characteristic voltage across them when illuminated and so you can have more LEDs in a single string, with a suitable current-limiting resistor.
Here is the answer for each colour: 25mA is the MAXIMUM for 3mm and 5mm ordinary, high-bright or Super-bright LEDs. LED series/parallel array wizard The LED series/parallel array wizard below, is a calculator that will help you design large arrays of single-colour LEDs. This calculator has been designed by Rob Arnold and you will be taken to his site: when you click: Design my array The wizard determines the current limiting resistor value for each string of the array and the power consumed. All you need to know are the specs of your LED and how many you'd like to use.
The calculator only allows one LED colour to be used. For mixed colours, you will have to use the 3 steps explained above.
The result is not always correct. Read the discussion below: ' THE DANGERS OF USING A 'LED WIZARD' to understand the word 'HEAD VOLTAGE.' The HEAD VOLTAGE should be as high as possible to allow for the differences in Characteristic Voltage and the variations in power supply voltage. Source voltage diode forward voltage diode forward current (mA) number of LEDs in your array View output as: ASCII schematic wiring diagram help with resistor colour codes Resistor Calculator Use this JavaScript resistor calculator to work out the value of the current-limiting resistor: Source voltage = LED forward voltage drop = LED current in milliamps = Current-limiting resistance in Ohms = Closest 5% Resistor = Resistor wattage = Actual current = Power dissipated by LED (watts) = Power dissipated by resistor (watts) =.