What is a Power Diode – Construction, Types & Its Applications

The diode is a simple semiconductor device that includes two layers, two terminals & a single junction. The junction of normal diodes can be formed through semiconductors like p-type and n-type. The terminal at p-type is known as anode whereas the terminal at the n-type is known as the cathode. There are different kinds of diodes are available in the market. Each type has its application. This article discusses an overview of the power diode. Ideally, a diode must have no reverse recovery time. But, the deigning cost of such diode may change. In various applications, the reverse recovery time effect is not important so low-cost diodes can also be used.

What is a Power Diode?

Definition: A diode that has two terminals like anode & cathode and two layers like P & N, used in the power electronics circuits is known as power diode. This diode is more complex in construction as well as in operation because low power device has to change to make them appropriate in high power applications.

In power electronic circuits, this diode plays an essential role. It can be used as a rectifier in converter circuits, voltage regulation circuits, flyback / freewheeling diode, reverse voltage protection, etc.

These diodes are related to signal diodes except for a slight disparity in its construction. The doping level in signal diode for both P-layer & N-layer is the same whereas, in power diodes, the junction can be formed among a heavily doped P+ layer & lightly doped N– layer.

Construction

The construction of this diode includes three layers like the P+ layer, n– layer and n+ layer. Here the top layer is the P+ layer, it is heavily doped. The middle layer is n– layer, it is lightly doped and the last layer is n+ layer, and it is heavily doped.

Here p+ layer acts as an anode, the thickness of this layer is 10 μm & the level of doping is 10¹⁹ cm^-3.

The n+ layer acts as a cathode, the thickness of this layer is 250-300 μm & the level of doping is 10¹⁹ cm^-3.

The n- layer acts as a middle layer/drift layer, the thickness of this layer mainly depends on the breakdown voltage & the level of doping is 10¹⁴ cm^-3. Once this layer width increases then breakdown voltage will be increased.

Working Principle of Power Diode

The working principle of this diode is similar to the normal PN junction diode. When the voltage of the anode terminal is high than the voltage of the cathode terminal, the diode conducts. The range of forwarding voltage drop in this diode is very small approximately 0.5V – 1.2V. In this mode, the diode works as a forward characteristic.

If the voltage of the cathode is high than the voltage of anode, the diode performs as blocking mode. In this mode, the diode performs like the reverse characteristic.

Types of Power Diode

The classification of these diodes can be done based on the reverse recovery time, the process of manufacturing & the depletion region penetration in reversed bias condition.

The power diodes depending on the reverse recovery time as well as the process of manufacturing are classified into three types such as

• General Purpose Diodes
• Fast Recovery Diodes
• Schottky Diodes

General Purpose Diodes

These diodes have huge reverse recovery time around 25μs; therefore they are applicable in low frequency (up to 1 kHz) & low-speed operations (up to 1- kHz).

Fast Recovery Diodes

These diodes have quick recovery act due to their very small reverse recovery time less than 5μs, used in high-speed switching applications

Schottky Diodes

Please refer to this link to know more about Schottky diodes

The power diodes depending on the penetration of the depletion region are reversed biased condition are classified into two types such as

• Punch through Diodes
• Non-Punch through Diodes

Punch through Diodes

Diode, where the width of the depletion region at the breakdown enters into the n+ layer, is known as a punch-through diode.

Non-Punch through Diodes

A diode where the width of a depletion region at the breakdown doesn’t go through into the adjacent n+ layer is usually called non-punch-through diodes.

In this mode, the drift region’s width is extra than the highest width of the depletion region, therefore the depletion region cannot enter into the adjacent n + layer.

How to Select?

The selection of power diode can be done based on the IF (forward current) & VRRM (the peak inverse) voltage.

These diodes are protected by using snubber circuits from the spikes of overvoltage. This may occur while doing the process of reverse recovery. A snubber circuit used for power diode mainly includes a resistor & a capacitor that is connected in parallel with the diode.

V-I Characteristics

The V-I characteristics of a power diode are shown below. Once the forward voltage increases then the forward current will be increased linearly.

An extremely less amount of current leakage will supply in the reverse bias condition. This current is independent of the applied reverse voltage.

The leakage current mainly supplies because of the minority charge carriers in the diode. As the reverse voltage gets the reverse breakdown voltage, then the breakdown of an avalanche will occur. When the reverse breakdown arises, the reverse current will also be raised drastically with less increase in reverse voltage. The reverse current can be controlled by an external circuit.

Advantages and Disadvantages of Power Diode

The advantages and disadvantages of power diode include the following.

• The PN-junction region of this diode is large & can supply huge current, however, the capacitance of this junction can also be large, which works at a lower frequency & it is generally used for rectification only.
• It will resolve AC at high current and a high voltage.
• The main disadvantage is its size & probably needs to be fixed to a heat sink while conducting a high current.
• It needs specialized hardware for installing and insulating from the metal frames which are available in the surrounding.

Applications

The applications of power diode include the following.

• This diode provides uncontrolled power rectification
• It is used in different applications like DC power supplies, for charging the battery, inverters and AC rectifiers.
• These are used like snubber networks and free-wheeling diodes due to their characteristics like voltage & high-current.
• These diodes are used as feedback, freewheeling diodes, and high-voltage rectifier.
• In reverse breakdown condition, when the current and voltage of this diode are huge, the power dissipation can be high so the device can be destroyed.

FAQs

1). What is the function of a power diode?

It is a type of crystalline semiconductor, used to change AC to DC and this process is called rectification.

2). What are the applications of power diode?

These diodes are used where high voltages & larger currents are involved.

3). What are the types of power diodes?

They are fast recovery, Schottky & general purpose diodes.

4). What is the difference between power & normal diode?

Power diode is applicable for where high current & voltage are used like inverter whereas normal diode is applicable for small-signal applications.

Thus, this is all about an overview of a power diode that plays an essential role in the circuits of power electronics. These diodes are used in converter circuits, as flyback diode, voltage regulation circuits, freewheeling diode or protection of reverse voltage, etc. Here is a question for you, what are the disadvantages of power diode?