Diode

-

 

Diode is a non-linear, polarized electronic component. The direction of connection of the diode therefore has an importance on the operation of the electronic circuit.

 It is a dipole that only allows electric current to flow in one direction. This dipole is called a rectifier diode when it is used to make rectifiers that transform alternating current into unidirectional current.

Diode Symbol


In the category of diodes, there are also regulation diodes, called zener diodes, which behave as a voltage source. This property will make it possible to develop around this simple component a whole series of assemblies delivering one or more direct voltages.

Operation

The diode is a switching component which has 2 operating modes:

• Diode in the state: On.

• Diode in the state: Blocked.

The diode can switch from on to off state.

Current-voltage characteristic of the diode:

Above a certain positive voltage Vd threshold Vo, the forward current increases very rapidly with Vd.

The threshold Vo depends on the basic intrinsic semiconductor used. It is around 0.2V for germanium and 0.6V for silicon.

The characteristic has the following form:

Current-voltage characteristic of the diode


This characteristic describes the evolution of the current flowing through the diode as a function of the voltage at its terminals in direct current.

Around zero:

The characteristic goes through the origin. For negative Vd, the current tends rapidly towards the limit -If (leakage current), because the diffusion current due to the majority carriers will cancel out.

Leakage current

When a diode is biased in reverse, it blocks the current but has a fault called the leakage current. In fact, the diode lets pass a tiny part of the current which is admitted to it in reverse. it does not block the current perfectly. This current is so weak from the nano-ampere nA) that it is negligible.

Inverse characteristic (Vd <0). Breakdown phenomenon:

When the applied voltage exceeds the value specified by the manufacturer, the current decreases very rapidly. If it is not limited by external elements, there is rapid destruction of the diode. Two phenomena are at the origin of this result:

avalanche phenomenon: 

when the electric field at the junction becomes too intense, the accelerated electrons can ionize the atoms by shocks, which frees other electrons which are in turn accelerated.There is a divergence of the phenomenon, and the current becomes important.

Zener phenomenon:

 the electrons are torn from the atoms directly by the electric field in the transition zone and create a current which quickly becomes intense when the voltage Vd reaches a value Vz known as the Zener voltage.

Half-wave rectification:

This is the simplest rectification possible: 

when the voltage of the power supply exceeds the threshold voltage of the diode, it conducts, allowing direct current to flow into the load. The voltage across the load Vout is then equal to the voltage across the power supply minus the forward voltage VF of the diode.

Filtering

Definition

The filtering of a rectified voltage consists in reducing the ripple as much as possible, therefore in having a voltage as constant as possible. This function can be performed by a capacitor.

Full-wave rectification at Graetz bridge

Circuit diagram:

Principle of operation:

diodes are assumed to be ideal.

During the positive alternation of Uin:

D1 and D3 lead, D2 and D4 blocked so u = Uin

During the negative alternation of Uin

D2 and D4 conduct, D1 and D3 blocked so u = - Uin

Signal diodes

The diodes previously studied involve non-negligible currents and voltages. The

Signal diodes are used in applications with low levels of currents and voltages.

Electrical Specifications :

- direct current: 75 to 500 mA;

- reverse breakdown voltage: 10 to 300 V;

- recovery time: 2 to 2000 ns.

Physical characteristics

Signal diodes do not need to withstand high reverse voltages: by construction, they

may have a low parasitic capacitance, and therefore operate at high frequencies.

These characteristics are obtained thanks to a reduced junction surface and a low doping

(decrease in stored charges).


Comments

Post a Comment

Popular posts from this blog

7 segments display

-
Image
The 7-segment displays are displays that allow you to view a figure or a number using luminous segments. The light sources are internal. It is almost always this type of display which is used on radio clocks when the color of the digits is green or red.  The 7-segment displays mostly emit a red or green light, but there are also some that glow in the blue. to display a number between 0 and 9, at least seven segments are needed, and these segments have been conventionally assigned the first seven letters of the alphabet: A, B, C, D, E, F and G. Common anode: Here is the principle of common anode displays: (Diagram of the inside of the box) To use its displays, you must always follow the instructions for supplying the LEDs. the (+) of the power supply on the anode and the (-) on the cathode. Just like the LEDs, you will need to add a resistor (220 ohms if the power supply is equal to 5v) to reduce the current on each segment of the display. Otherwise you risk toasting the segment...
Read more

Mosfet

-
Image
Metal-oxide semiconductor field-effect transistor (mosfet) is the second type of field-effect transistor. The mosfet gate is a channel isolated by a layer of silicon dioxide (Si02). The drain and the source are made from substrate materials. they are connected to the gate by a narrow channel. Transistor has type of metals. The first is called the mosfet at depletion and the second is called the   enhancement mosfet (E). The MOSFET transistor is different from the JFET in that the gate is isolated from the channel. Like diodes, these elements are most often made of silicon. They are used to make amplifiers. The enhancement MOSFET In the absence of a control signal at the Gate (Vgs = 0V), the Mosfet is blocked regardless of the type of channel (N or P).Conduction only begins to manifest from a threshold:+ Vth for Drain an N-channel MOS and –Vth for a P-channel MOS. N-channel   enhancement mosfet is a positive voltage applied to the input. The positive charge sticks...
Read more

LM35 Temperature Sensor

-
Image
  The LM35 temperature sensor is an analog temperature sensor .This integrated circuit has 3 pins and generates an output voltage in linear relation with the temperature expressed in degrees Celsius The LM35 sensor is able to measure temperatures ranging from (-55 ° C to + 150 ° C) in its most precise version and with the right mounting, enough to measure any temperature. The analog output of the sensor is proportional to the temperature. It suffices to measure the voltage at the output of the sensor to deduce the temperature. Each degree Celsius corresponds to a voltage of + 10mV. The LM35 does not require any external calibration or size and maintains an accuracy of (+ / -0.4 ° C) at room temperature and (+ / - 0.8 ° C) over a range of 0-100° C. The temperature measured by the sensor is given by the relation: T = Vout / 10 with: T: Temperature [° C] Vout: Output voltage [mV]   DHT22 sensor The DHT22  temperature and humidity sensor communicates with ...
Read more