Trick of White LED. Circuit Clinic 6


WHITE-LED

Introduction of White LED created a revolution in electronics field to replace the Fluorescent lamps in lighting systems. High power White LEDs are now widely used to make Ceiling lamps, Flood lights, Vehicle lamps, surgical instruments, Projectors etc. When compared to ordinary White LED, the high power LED consumes around 200-300 milli ampere and mounted on heat sink for heat dissipation. Majority of high power White LEDs are flat chips that will be easily destroyed if the voltage and current exceeds. So LED driver circuit is used for the  stable operation of the LED. The theory and working of LED is given in the previous post, so only the relevant facts about White LED is given here.
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The world of LED Circuit Clinic 5


LED

I think, without an LED, the circuit will be incomplete. It is used as visual indicator in most of the circuits to confirm the working of a particular section. It is a simple diode with light emitting property and hence the name Light Emitting Diode. Its encapsulation has two electrode posts with a chip. When the chip is energized, it emits photons in the form of visible light. The colour of the light depends on the material in the chip. LED works in very low voltage as low as 1 volt. But the new generation White and Blue LEDs require minimum 3 volts to get sufficient brightness. Introduction of the white LED, created a White revolution in the field of LED lighting. Due to its low current consumption, modern lighting system is gradually changing to LED lighting. In addition to White LED, various other types like, Pink LED, Bicolour LED, Multi colour LED etc are also in use . Infrared LED emits light in the Infrared region and hence invisible to eye.
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Zener and Voltage regulation Circuit Clinic 4


CLINIC-3

Zener is not an obsolete device as some designers think. Even though voltage regulator ICs are used widely for precision voltage regulation, Zener diodes are still in use to drop voltage at some sections of the circuit board. Zener is a simple semiconductor device and looks like the glass rectifier diode 1N4148. It generates a fixed voltage output depending on its value. It is designed to operate in the reverse breakdown region. It is always connected in the reverse biased mode with the cathode to the positive supply. Zener diode requires a series resistor to limit current across it, without which the device will be damaged. Zener diodes are available in various voltage ratings from 1.1 volt to 68 volt. Power Zener diodes are also available for industrial applications. They can handle high voltage and current. It’s lead identification is similar to other diodes. The lead near the black or white band is cathode which goes to the positive supply.

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Diode in action Circuit Clinic 3


CLINIC-3-DIODE

What is the function of a diode in the circuit? It  simply act as a switch to pass current only in one direction from Anode to Cathode. So it is essential in all most all circuits. Diodes are semiconductor devices with a p-n junction to allow the one way flow of current. This condition is the forward biasing. If the current flow is reversed, the diode enters into the reverse biased mode and prevents the flow of current. Diodes perform many functions in an electronic circuit like rectification, clamping, protection, voltage multiplication, signal detection etc. Major types of diodes are power diodes, signal diodes, zener diodes, photo diodes, LED etc. Schottky diodes are fast recovery diodes ideal for switching applications.
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Selection and use of Capacitors Circuit Clinic 2


CIRCUIT-CLINIC-2

Let us move to the world of capacitors. You can see a number of capacitors scattered here and there in the circuit board starting from the front end to the last. These capacitors are doing lot of job in the circuit like smoothing, filtering, coupling, de-coupling, buffering etc. You can also see the size and shape difference. The capacitors may be electrolytic or disc but the structure is identical in both having two electrodes separated by a dielectric material. But the functions will be different. For example, a Smoothing capacitor in the power supply section will remove ripples from AC to give a clean DC while a capacitor in the audio circuit acts as the noise filter. So the selection of capacitor and its use in the different parts of the circuit is important. Electrolytic capacitors are polarized so always connect with correct polarity otherwise, it will explode. Disc capacitors are non polarized so they can be connected either way round.
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Resistor Selection Circuit Clinic 1


CIRCUIT-CLINIC-1

Starting a series of articles to explain the circuit design considerations and troubleshooting to cure defects. When we see a circuit, sometimes we think that how these components are selected? Why some additional components are included to make the circuit over designed? Why a specific value component is selected. All these are some of the common doubts arise when we see a circuit. Circuit design is an art which has many aims. First is its proper working and second is its compactness. In addition to this, we have to use rare components not easily seen in common circuits for the purpose of introducing their working to hobbyists. Another important thing to remember while selecting a component, especially ICs, transistors, sensors etc, is the ultimate result of the circuit to satisfy our needs.

A circuit can be designed in different ways according to the idea of the designer. Some designers design the circuit using only a few components with a concept that this is sufficient and it is easy to describe. The circuit will work but we cannot study anything from it. If the circuit is slightly complicated, the performance will be more accurate and a student can analyze the working of each section in the circuit. See, a hobbyist or a circuit designer is not designing the circuit for the purpose of commercial sale but to understand the basics of electronics. For commercial applications, the design is entirely different and the only aim is to satisfy the needs, low cost and low size. You can see the power supply in china make low cost LED light. They are using only a capacitor and a diode to convert AC to DC. So, design the circuit as per your idea, interest and purpose.

Do not try to follow others because each person has his own ideas and the way of designing. Do not under estimate other’s designs because it is their design according to their mind. But the ultimate aim should be proper working of the circuit. We can light an LED with a series resistor starting from 100 ohms to 1 kilo ohms with a 12 volt supply. Take your own value depending on the forward voltage of the LED. Only difference is change in brightness and current consumption. If you use a high value resistor, brightness will be reduced. So it is your choice according the requirement.

If a circuit is not working, don’t throw it away. Find out the error and make it working. There lies your skill and ability. Experimentation is always better than too much theory and calculations using paper and pen.
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