led driver circuit presentation

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LIGHT EMITTING DIODEs Driver circuit By Dr.M.Srinivasan Dept of EEE 1

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Page 1: Led Driver Circuit Presentation

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LIGHT EMITTING DIODEs Driver circuit

By Dr.M.SrinivasanDept of EEE

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A light emitting diode (LED) is essentially a PN junction opto-semiconductor that emits a monochromatic (single color) light when operated in a forward biased direction.

LEDs convert electrical energy into light energy. They are frequently used as "pilot" lights in electronic appliances to indicate whether the circuit is closed or not.

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About LEDs (1/2)The most important part of a light emitting diode (LED) is

the semi-conductor chip located in the center of the bulb as shown at the right. The chip has two regions separated by a junction. The p region is dominated by positive electric charges, and the n region is dominated by negative electric charges. The junction acts as a barrier to the flow of electrons between the p and the n regions. Only when sufficient voltage is applied to the semi-conductor chip, can the current flow, and the electrons cross the junction into the p region.

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How Does A LED Work? (1/2)

When sufficient voltage is applied to the chip across the leads of the LED, electrons can move easily in only one direction across the junction between the p and n regions.

In the p region there are many more positive than negative charges.

When a voltage is applied and the current starts to flow, electrons in the n region have sufficient energy to move across the junction into the p region.

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How Does A LED Work? (2/2)Each time an electron recombines

with a positive charge, electric potential energy is converted into electromagnetic energy.

For each recombination of a negative and a positive charge, a quantum of electromagnetic energy is emitted in the form of a photon of light with a frequency characteristic of the semi-conductor material (usually a combination of the chemical elements gallium, arsenic and phosphorus)..

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Testing LEDs

Never connect an LED directly to a battery or power supply! It will be destroyed almost instantly because too much current will pass through and burn it out.

LEDs must have a resistor in series to limit the current to a safe value, for quick testing purposes a 1k resistor is suitable for most LEDs if your supply voltage is 12V or less.

Remember to connect the LED the correct way round!

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How Much Energy Does an LED Emit?

The energy (E) of the light emitted by an LED is related to the electric charge (q) of an electron and the voltage (V) required to light the LED by the expression: E = qV Joules.

This expression simply says that the voltage is proportional to the electric energy, and is a general statement which applies to any circuit, as well as to LED's. The constant q is the electric charge of a single electron, 1.6 x 10-19 Coulomb.

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Finding the Energy from the Voltage

Suppose you measured the voltage across the leads of an LED, and you wished to find the corresponding energy required to light the LED. Let us say that you have a red LED, and the voltage measured between the leads of is 1.71 Volts. So the Energy required to light the LED is

E = qV or E = 1.6 x 10-19 (1.71) Joule,

since a Coulomb-Volt is a Joule. Multiplication of these numbers then gives

E = 2.74 x 10-19 Joule.

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Applications

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Illumination (1/2)

Architectural Lighting Signage (Channel Letters) Machine Vision Retail Displays Emergency Lighting (Exit Signs) Neon Replacement Bulb Replacements Flashlights Outdoor Accent Lighting - Pathway, Marker Lights

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Illumination (2/2)

LEDs not only consume far less electricity than traditional forms of illumination, resulting in reduced energy costs, but require less maintenance and repair. Studies have shown that the use of LEDs in illumination applications can offer: Greater visual appeal Reduced energy costs Increased attention capture Savings in maintenance and lighting replacements

As white LED technology continues to improve, the use of LEDs for general illumination applications will become more prevalent in the industry.

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Types of LED Products

1.LED Retrofit 2.LED Fixture

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2.LED Fixture

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WHAT IS A DRIVER AND WHAT IS IT USED FOR? Operating an LED module always requires

control gear (a ballast), which in the field of LEDs is called a driver.

Current can only flow in one direction through an LED (diode).

LED modules can be operated with one of two different supply sources (drivers) depending on gearshift assembly:• a constant current source• a constant voltage source

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CONSTANT VOLTAGE OPERATION

If an LED module is operated using a constant voltage source but without current limitation, the current will increase up to the thermal destruction of the LED.

To avoid this effect, LED modules for operation with constant voltage are fitted with integrated current control.

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When operating an LED using a constant current source, the current operating the LED is kept at a constant level, with current control being integrated in the driver.

Constant current sources can feature either transistors or integrated circuits.

The use of a constant current source is more efficient.

CONSTANT CURRENT OPERATION

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Constant voltage driver A constant voltage driver is used in areas where you

may have a variable amount of fixtures, such as a cove (LED tape) or under-cabinet light.

They typically have 12 V or 24 V outputs, although other output voltages are possible.

Constant voltage drivers can only be dimmed via a PWM method.

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Constant current drivers

Constant current drivers provide a constant current, such as 700mA, to a specific LED module that is designed to operate at that current level.

LED fixtures that use only one LED module per driver (much like a fluorescent lamp with its associated ballast)

Note that some drivers support multiple currents, making them more flexible when the manufacturer is designing a fixture

For constant current drivers, there are two different dimming methods for adjusting the output current when dimming: pulse-width modulation (PWM) and constant-current reduction (CCR)

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Driving Techniques

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Driving Techniques

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Driving LEDs

Analog LED Drive Circuits Digital LED Drive Circuits                               

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Analog LED Drive Circuit

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Digital LED Drive Circuits

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::The END::Thank you for

your Attention!