Rectifier diode tutorial

How does Rectifier Diode work? – Construction and Rectify Definition

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Rectifier diodesemiconductor diode designed for rectifying alternating current (mostly with low power frequency – 50 Hz at high power emitted during load). To “rectify” the meaning of this component, its main task is the conversion of the alternating current (AC) into direct current (DC) through the application of rectifier bridges. The variant of rectifier diode with the Schottky barrier is particularly valued in digital electronics.

rectifier diode symbol

Rectifier diode symbol

The most typical rectifier diodes are made from silicon (semiconductor crystal). They are able to conduct high values of electric current,and that can beclassified as its basic feature. There are also less popular, but still used semiconductor diodes made from germanium or gallium arsenide. Germanium diodes have much lower permissible reversed voltage and a smaller permissible junction temperature (Tj = 75 ° C for germanium diodes and Tj = 150 ° C for a silicon diode). The only advantage that germanium diode has over silicon diode is lower threshold voltage value during operating in a forward-bias (Vf (IO) = 0.3 ÷ 0.5V for germanium and 0.7 ÷ 1.4V for silicon diodes).

Rectifier diode is capable of operating on current values varying from several miliamperes to few kiloamperes and voltages up to few kilovolts.

Rectifier diode

We distinguish two groups of technical parameters of the rectifier diode, but they apply to other diodes too:

  • permissible limit parameters,
  • characteristic parameters.

A rectifier diode is characterized by following permissible limiting parameters:

  • IFN – rated current in the forward bias (also known as a maximum average current of the diode),
  • IFRM – peak, repeatable current diode conduction (for example, for the pulses with duration of less than 3.5 ms and a frequency of 50 Hz),
  • IFSM – peak, non-repeatable current conduction (eg. for a single pulse with a duration of less than 10 ms),
  • VRWM – peak, reverse voltage operation (or average, reverse voltage during diode operation in wave rectifier with load),
  • VRRM – peak, repetitive reverse voltage,
  • VRSM – peak, non-repetitive reverse voltage,
  • PTOT – the total value of the power dissipated on that electronic component,
  • Tj – maximum temperature of diode’s junction
  • Rth -thermal resistance under operating conditions,
  • a maximum instantaneous current of the diode (it determines resistance for overloads)

High current rectifier diode

An example of a high-performance diode is a double high current rectifier diode with a current of 2x 30A.

STM offers a double high voltage rectifier diode called STPS60SM200C. The diode is best suited for base stations, welders, AC / DC power supplies and industrial applications.

High current rectifier diode

High current rectifier diode STPS60SM200CW

The value of VRRM breakdown voltage is 200V, conduction voltage 640mV, and its current memory is 2x30A. An additional safeguard is from a discharge called ESD to 2kV.

The operating temperature range is -40 degrees Celsius to 175 degrees Celsius. Such temperature values allow the diodes to be used under all conditions in the base stations.

Characteristical parameters of rectifier diode:

  • VF forward voltage with determined IF forward current (usually with a maximum average rectified current, also known as rated current IFN),
  • IR reverse current at VRWM peak reverse voltage operation.
rectifier diode characteristics

Current-Voltage characteristics of the Rectifier Diode

Half-Wave Bridge Rectifier and Full-Wave Bridge Rectifier

Bridge rectifiers are divided into different types due to:

  • Structure and number of phases of supply voltage: single phase bridge rectifier, the multi phase bridge rectifier (three phase rectifier bridge, two phase rectifier bridge).
  • A number of half wave rectification voltage: single bridge (half wave rectifier), double bridge (full wave diode rectifier). We can create the combined circuit like single phase full wave bridge rectifier or 3 phase full wave rectifier. You can combine the number of phases with full or half wave rectifiers.
  • Load type: resistive, capacitive, inductive.

Properties of Bridge Rectifiers:

  • Supply voltage V
  • Component constant output voltage V0s, I0s
  • Maximum output current I0smax
  • Energy efficiency Nip
  • Circuit ripple factor
  • Maximum reverse voltage Vrm

Half-Wave Bridge Rectifier:

Half-Wave Bridge Rectifier is the simpliest circuit that can convert alternating current (both signs, + and -) to a current of one sign (+). After further filtering the obtained output current, it can be changed to the direct current.

On the output of this circuit we will obtain a sine wave with only positive half of its period and this is why it is actually called a Half-Wave Rectifier. There will be no “negative part” of the sine wave, because rectifier diode conducts only when it is forward-biased (positive voltage). The current flows through the resistive load only in one direction in a pulsating manner.

Example of simple half-wave bridge rectifier diode circuit is shown below:

half_wave_rectifier

Half-wave rectifier diode circuit

Characteristics of a Half-Wave Bridge Rectifier:

half wave bridge rectifier

Time characteristics of the Half-Wave Bridge Rectifier

Full-Wave Bridge Rectifier

The Full-Wave Bridge Rectifier circuit is shown below. It is often called the Graetz Bridge.

full_wave_rectifier

Full-Wave Bridge Rectifier circuit (Graetz Bridge)

Operation principle of the Full-Wave Bridge Rectifier is as follows. The picture below (red) shows the path of the current, two red diodes are forward-biased (conducting current), while other two are reverse-biased (not conducting current). Current is flowing from the supply through first red diode. Then from the first red diode through the load. After it passes the load it will flow through the second red diode and after that back to the power supply.

full_wave_rectifier_forward

Full-Wave Bridge Rectifier circuit (alternating current, forward-bias)

While the supply voltage changes its polarity, situation described above will be opposite (blue circuit below). Two blue diodes are forward-biased (conducting current), while other two are reverse-biased (not conducting current). Current is flowing from the supply through first blue diode. Then from the first blue diode through the load. After it passes the load it will flow through the second blue diode and after that back to the power supply.

full_wave_rectifier_reverse

Full-Wave Bridge Rectifier circuit (alternating current, reverse bias)

Characteristics of the Full-Wave Bridge Rectifier are shown below:

full wave bridge rectifier

Time characteristics of the Half-Wave Bridge Rectifier

How to test Rectifier Diode?

The simpliest multimeters can be used to determine the polarity of a rectifier diode (where is the anode and where is the cathode). There are at least three ways of doing this but I will show two easiest ways to do that:

a) Using ohmmeter (2kΩ range):

How to test Rectifier Diode

Forward-bias: Ohmmeter will indicate the approximate value of the forward voltage of the diode (near 0,7V)

How to test Rectifier Diode

Reverse-bias: Ohmmeter indicates “1”, which means its very high resistance (electric valve off)

A “diode check” function will give the same result as using method mentioned above.

b) Using VDC measurement function:

How to test Rectifier Diode

Forward-bias: Multimeter should show voltage drop of about 0,7V for silicon diodes

How to test Rectifier Diode

Reverse-bias: Multimeter will indicate the approximate full voltage value of the supply (Note: Here diode is inserted in opposite way compared to the example above. In reality, I would change the polarity of the Power Supply, because you can’t unmount “with your hands” once soldered component, unless you desolder it. Of course, we don’t want to do that to the good operating component. I just wanted to show you an example, that you should also pay attention to correct component placement at your PCB or Breadboard)

Three phase rectifier bridge

The use of a three phase diode rectifier bridge (full wave rectifier bridge) is possible in any of the three phase voltage circuits. In this case, the output voltage has a minimum ripple. Power sources use the power of the circuit in its greatest extent. Three phase bridge rectifiers often have the ability to control the output current.

Below you can observe three phase rectifier circuit schematic which shows you how it can be built.

Three phase rectifier bridge

Three phase rectifier bridge schematic and characteristic

Three phase bridge rectifier calculations

Down below is an example of three phase bridge rectifier calculations with equations and values for the given scheme. Results are shown in the table below.

Pd – Power output

Vd – Average value of the rectified voltage

Id = Pd / Vd – Average value of the rectified current

R = Vd / Id – System resistance

three phase bridge rectifier calculations

Three phase rectilinear bridge rectifier

 

Formulas

Three phase bridge rectifier resultsNotes
Vd/Vf2,34Vf – transformer phase voltage
Vd/V121,35V12 – phase-to-phase transformer voltage
I/Id0,82I – effective value on the secondary side of the transformer
VRRM/Vd1,05VRRM – Peak back voltage, repetitive
IF(AV)/Id0,333IF (AV) – average conduction current
IFRMS/Id0,58IFRMS – effective value of conduction current
Pu=PdR* Id2Output power
S2/PdProcessing power of the secondary winding of the transformer
S1/PdThe computing power of the primary transformer winding
St/Pd1,05Typical transformer power

Full bridge rectifier as the integrated circuit

The full bridge rectifier is commonly seen as a one-chip integrated circuit. It is built of four rectifier diodes in the Graetz bridge system. It can be used for a THT and SMD mounting. Using this solution is the most popular, economical and saves space on the Printed Circuit Board.

full bridge rectifier ic

Picture above shows the connectors that are in each rectifier bridge circuit integrated circuits. The (+) sign corresponds to the + VDC output, the (-) sign corresponds to the – VDC output, the characters (~) correspond to the VAC connection. The proper voltage connection is made by connecting the VAC input to the + VDC output horizontally, and the VAC output to the – VDC output horizontally.

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