Power Electronics

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2. POWER DIODES AND ITS TYPES
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Thristors
Line Commutated
BCT
TRIAC
GTO IGCT
MCT
LASCR
GATT
RCT ETO
MTO
Schottky
Fast Recovery
General Purpose
Power Semiconductor Devices
Power Diodes Power Transistors
Power BJT’s
Power MOSFET
IGBT
SIT
SITH

4. Power diode
Diodes are the main building blocks of rectifier section of ac and dc
converters.
The rectifier diode has a smaller voltage drop in the forward bias
state and small leakage current in the reverse bias state.
The forward bias characteristics of the power diode is approx linear,
which means that the voltage drop is proportional to the ohmic
resistance and current.

5. • Power diode consists of three layers. Top
layer is a heavily doped P+ layer. Middle
layer is lightly doped n– layer and the last
layer is a heavily doped n+ layer.
• The heavily doped p+ layer act as an anode.
The thickness of this layer is around 10 μm
and doping level is 1019 cm-3
• Last layer of the heavily doped n+ act as a
cathode. The thickness of this layer is
around 250 to 300 μm and doping level is
1019 cm-3.
• Middle layer of lightly doped n– is known as
a drift layer. The thickness of the drift layer
depends on the required breakdown
voltage. The breakdown voltage increases
with an increase in the width of the drift
layer. If the width of the drift layer
increased, then the on-state voltage drop
increase therefore power loss is more.
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6. • Operating Principle of Power diode:
• The operating principle of power diode is same as the conventional
PN junction diode. A diode conducts when the anode voltage is
higher than the cathode voltage. The forward voltage drop across the
diode is very low around 0.5V to 1.2V. In this region, the diode works
as a forward characteristic.
• If the cathode voltage is higher than the anode voltage, then the
diode works as blocking mode. In this mode, diode works according
to the reverse characteristic.
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7. I-V characteristic of Power Diode:
• The forward current increase linearly
with an increase in forward voltage.
• A very small amount of leakage current
flows in the reverse bias (blocking
mode). The leakage current is
independent of the applied reverse
voltage.
• The leakage current flows due to the
minority charge carriers.
• When the reverse voltage reaches the
reverse breakdown voltage, avalanche
breakdown occurs. Once the reverse
breakdown occurs, the reverse current
increase drastically with small increase
in reverse voltage. The reverse current
can control by an external circuit.
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8. Application of Power Diode in Power Electronics:
• High voltage rectifier
• As freewheeling diode
• As feedback diode
• In the case of reverse breakdown, As the voltage and current of the
diode are large, the power dissipation is dangerously high and it can
destroy the device.
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9. Types of Power Diode
GENERAL PURPOSE DIODE:
Voltage/Current Ratings: 10KV/5KA
Switching Time (µS): 25
On Voltage/Current: 1.6V/10KA
Are generally manufactured by diffusion
High reverse recovery time
Use in low speed applications where recovery time is not critical
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10. • General Purpose Diodes:
• This kind diodes have high reverse recovery time. It will be in the
range of 25μs.
• The diode current rating will be from 1A to several thousand
amperes.
• The voltage rating will be from 50V to 5kV. Some of the applications
of the general purpose diodes are battery charging circuits,
uninterruptible Power Supplies(UPS) and electrical traction etc.
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11. Types of Power Diode
FAST RECOVERY DIODE:
Voltage/Current Ratings: 3000V/1000A
Switching Time (µS): 2-5
On Voltage/Current: 3V/3KA
Low recovery time
Use in choppers & inverters where the speed of
recovery time is of critical importance
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12. •As the name indicates, these diodes have very
low reverse recovery time. It will be less than
5μs.
•They are mainly used in switching circuits like
choppers, commutation circuits, switching mode
power supplies etc.
•The current rating of the diode will be from 1A to
several thousand amperes.
•The voltage rating will be from 50V to 3kV.
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13. Types of Power Diode
SCHOTTKY DIODE:
Voltage/Current Ratings: 100V/300A
Switching Time (µS): 0.23
On Voltage/Current: 0.58V/60A
Have low on state voltage
Very small recovery time (typical of nanoseconds)
The leakage current increases with the voltage ratings & their
ratings are limited to 100V
These are ideal for high current & low power voltage dc chopper
supplies
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14. • Schottky Diodes:
• In this type of diodes, instead of P-N junction ( semiconductor to
semiconductor) metal to semiconductor junctions used.
• The Schottky diodes have very fast recovery time and low forward
voltage drop.
• The current flow will be done by only majority carriers.
• So the time delay due to reverse recombination is avoided.
• The drawback with Schottky diode is they have low voltage ratings (
around 100V) and forward current ratings(upto 300A)
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15. Schottky Diode Basics:
• Here the semiconductor (N-type) will be normally silicon.
• The metal will be typically gold, silver, aluminium, nickel, chromium,
platinum, tungsten, or alloys of exotic metals
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16. VI-Characteristics:
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17. • As the diode conducts using majority carriers, it has lower forward
voltage drop (typically 0.35V) than the silicon diode(typically 0.6V).
• It is a unipolar device (current conduction will happen due to
majority carrier only).
• Schottky diodes have lower on-state losses than pn-junction diodes
but also have low maximum reverse voltage rating (typically 50V to
200V).
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18. • Why Schottky diode is suitable for Switching circuits?
(OR)
• Why Schottky diode switching faster than bipolar Junction Diode?
• In this diode, the electrons are the majority carriers on both sides of
the junction (ie, in the N-type semiconductor as well as in the metal).
• So depletion layer is not formed near the junction. (Ie no stored
charge carriers in the junction)
• This scenario will give the following benefits:
With reverse bias condition, there is no significant current from the
metal to the semiconductor.
Thus the time delay existing in the junction diodes due to hole –
electron recombination is absent in schottky diode.
• Hence, the schottky diode can switch OFF faster than a bipolar diode.
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19. Principle Ratings for Diodes
Peak Inverse voltage (PIV):
Maximum reverse voltage that can be connected across a
diode without breakdown.
If PIV rating is exceeded , the diode begin to conduct in the
reverse direction and can be immediately destroyed.
It is also called Peak Reverse Voltage (PRV) or breakdown
voltage VBR.

20. Principle Ratings for Diodes
Maximum Average Forward Current (If (avg)max):
it is maximum current a diode can safely handle when forward
biased.
Reverse Recovery Time (Trr):
A real diode does not instantaneously switch from a conduction
to a non conduction state, instead a reverse current flows for a
time , and the diode does not turn off until the reverse current
decays to zero.
Graphically one can describe the reverse recovery time of the diode as
the total time which starts from the instant at which the reverse current
starts to flow through the diode to the time instant at which it reaches to
zero

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22. Maximum Junction Temperature Tj (max)
•Maximum junction temperature that a diode can withstand
without failure. Diodes are mounted on heat sink to improve
their temperature rating.
Maximum Surge Current (IFSM)
•Maximum current that the diode can handle as an occasional
transient or from a circuit fault.

23. THANKS
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