Minggu, 18 September 2011

semiconductor diode



Physical function
An LED is a special type of semiconductor diode.
Like a normal diode, an LED consists of a chip of semiconducting material is fully charged, or in-bulb, with impurities to create a structure called a pn junction.
-Charge carriers - electrons and holes flow into the junction from electrodes with different voltage.
When an electron meets a hole, he fell into a lower energy level, and release energy in the form of photons.


Light emission
The wavelength of light emitted, and therefore its color, depending on the difference in the energy band of the material that forms a pn junction.
A normal diode, typically made of silicon or germanium, emits visible light near infrared, but the material used for an LED have a difference between the energy band near infrared light, visible, and near ultraviolet.

Substrate LED
LED development began with infrared and red devices made with gallium arsenide.
Perkembagan in materials science have enabled the production of tools with shorter wavelengths, producing light with varied colors.

Conventional LEDs are made from inorganic mineral that varies, resulting in the following colors:
* Aluminum gallium arsenide (AlGaAs) - red and infrared
* Gallium aluminum phosphide - green
* Gallium arsenide / phosphide (GaAsP) - red, orange-red, orange, and yellow
* Gallium nitride (GaN) - green, pure green (or emerald green), and blue
* Gallium phosphide (GaP) - red, yellow, and green
* Zinc selenide (ZnSe) - blue
* Indium gallium nitride (InGaN) - turquoise and blue
Aluminum gallium indium phosphide * - orange-red, orange, yellow, and green
* Silicon carbide (SiC) - blue
* Diamond (C) - ultraviolet
* Silicon (Si) - blue (under development)
* Sapphire (Al2O3) - blue

Positive voltage phase of the first forwarded by D1, while the next phase which is passed through D2 to the load R1 with transformer CT as a common ground .. Thus the load R1 gets a full wave voltage supply like the picture above. For some applications such as for supply to a small dc motor or dc incandescent lamps, the shape of this voltage is sufficient. Although the voltage ripple seen here from the second series of the above is still very large.
series of half-wave rectifier with filter capacitor C is parallel to the load R. Apparently with this filter out the voltage waveform can be flat. Figure-4 shows a DC voltage output from circuit half-wave rectifier with capacitor filter. Bc line is approximately straight line with a certain slope, which in this state for the load current supplied by voltage capacitor R1. Actually the line bc is not a straight line but exponential in accordance with the nature of discharging the capacitor.
Bc depends on the slope of the curve of current (I) which flows to the load R. If the current I = 0 (no load) then the curve will form a horizontal line bc. But if the load currents greater, the slope of the curve bc will be more sharp. The voltage that comes out will be shaped with a sawtooth ripple voltage of magnitude are:

VR = VM-VL

and dc voltage to the load is Vdc = VM + Vr / 2

A good rectifier circuit is a circuit that has a ripple voltage (Vr) the smallest. VL is the voltage discharge or discharge the capacitor C, so it can be written:

VL = VM e -T/RC

If equation (3) disubsitusi to formula (1), then diperole

VR = VM (1 - e -T/RC)

If T <


For example, you design a full wave rectifier circuit of the power supply 220V/50Hz grid to supply the load of 0.5 A. What is the value capacitors are necessary so that this circuit has a voltage ripple of not more than 0.75 Vpp. If the formula (7) turned upside down then obtained.

C = I.T / Vr = (0.5) (0.01) / 0.75 = 6600 UF

For capacitors that are widely available for elco type that has a maximum working voltage polarity and specific. Working voltage capacitors used must be greater than the power supply output voltage. You may now understand why you created a series of audio buzzing, trying to check the power supply rectifier circuit that you created, if the voltage ripple is quite disturbing. If the market is not available such a large capacitor, it could with two or three pieces paralel capacitor.

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