Download Zener diode and regulators

Zener
Diode
Zener diode and regulators
Zener diodes are used to maintain a fixed voltage. They are
designed to 'breakdown' in a reliable and non-destructive way so
that they can be used in reverse to maintain a fixed voltage
across their terminals. The diagram shows how they are
connected, with a resistor in series to limit the current.
Cont.…
• A Zener Diode is a special kind of diode which
permits current to flow in the forward direction
as normal, but will also allow it to flow in
the reverse direction when the voltage is above a
certain value - the breakdown voltage known as
the Zener voltage.
• Commonly available Zener diodes are available
with breakdown voltages (“Zener voltages”)
anywhere from 1.8 to 200 V.
History of Zener
The device was named after Clarance Melvin
Zener, who discovered the Zener effect. Zener
reverse breakdown is due to electron
quantum tunneling caused by a high strength
electric field.
Zener V-I characteristics
Cont.…
The illustration above shows this phenomenon in a
Current vs. Voltage graph. With a zener diode connected
in the forward direction, it behaves exactly the same as a
standard diode - i.e.
a small voltage drop of 0.3 to 0.7V with current flowing
through pretty much unrestricted. In the reverse
direction however there is a very small leakage
current between 0V and the Zener voltage - i.e. just a tiny
amount of current is able to flow. Then, when the voltage
reaches the breakdown voltage (Vz), suddenly current
can flow freely through it.
For example if you pass a reverse 5V through a 3V zener
diode and measure the voltage across the zener diode,
that voltage will be 3V.
Cont.…
• The Zener voltage of a standard diode is high, but if a
reverse current above that value is allowed to pass
through it, the diode is permanently damaged.
• Zener diodes are designed so that their zener voltage
is much lower - for example just 2.4 Volts. When a
reverse current above the Zener voltage passes through
a Zener diode, there is a controlled breakdown which
does not damage the diode.
• The voltage drop across the Zener diode is equal to the
Zener voltage of that diode no matter how high the
reverse bias voltage is above the Zener voltage.
Cont.…
• Zener diodes can be distinguished from ordinary
diodes by their code and breakdown voltage
which are printed on them.
• Zener diode codes begin BZX... or BZY... Their
breakdown voltage is printed with V in place of a
decimal point, so 4V7 means 4.7V for example.
• Zener diodes are rated by their breakdown
voltage and maximum power:
•The minimum voltage available is 2.4V.
•Power ratings of 400mW and 1.3W are common.
Circuit symbol and construction
Circuit symbol
Physical identification
Cont.…
If the zener diode’s voltage is 12.6 volts and the power
supply’s voltage is 45 volts, there will be 32.4 volts
dropped across the resistor (45 volts - 12.6 volts = 32.4
volts). 32.4 volts dropped across 1000Ω gives 32.4 mA of
current in the circuit.
Uses of Zener Diodes
• Since the voltage dropped across a Zener
Diode is a known and fixed value, Zener diodes
are typically used to regulate the voltage
in electric circuits.
• Using a resistor to ensure that the current
passing through the Zener diode is at least 5mA
(0.005 Amps), the circuit designer knows that
the voltage drop across the diode is exactly equal
to the Zener voltage of the diode.
Types of Zener Diodes
• There are many different kinds of Zener diodes. At
Future Electronics we stock many of the most common
types categorized by power dissipation, nominal
working voltage, forward (drive) current, forward
voltage, packaging type and maximum reverse current.
• The parametric filters on our website can help refine
your search results depending on the required
specifications.
• The most common values for nominal working voltage
are 5.1 V, 5.6 V, 6.2 V, 12 V and 15 V. We also carry
Zener diodes with nominal working voltage up to 1 kV.
Forward (drive) current can have a range from 200 uA
to 200 A, with the most common forward (drive)
current being 10 mA or 200 mA.
Applications for Zener Diodes:
• Zener diodes can be found in several applications.
Some of these are: voltage stabilizers or regulators (in
shunt mode), surge suppressors for device protection,
peak clippers, switching operations, reference elements
and in meter protection applications.
• The constant reverse voltage of a Zener diode renders it
a very useful component in regulating the output
voltage against variations in the load resistance or
variations in the input voltage from an unregulated
power supply. The current through the Zener diode will
change in order to keep the voltage within the
threshold limits of Zener action and the maximum
power that it can dissipate.
Waveform clipper
Two Zener diodes facing each other in series will act to
clip both halves of an input signal. Waveform clippers can
be used to not only reshape a signal, but also to prevent
voltage spikes from affecting circuits that are connected
to the power supply.
Voltage shifter
A Zener diode can be applied to a circuit with a resistor to
act as a voltage shifter. This circuit lowers the input
voltage by a quantity that is equal to the Zener diode's
breakdown voltage.
Voltage regulator
A Zener diode can be applied to a circuit to
regulate the voltage applied to a load, such as in a
linear regulator.
Choosing the Right Zener Diode:
• When you are looking for the right Zener diodes, with the
FutureElectronics.com parametric search, you can filter the
results by various attributes: by Forward (Drive) Current (200
uA, 10 mA, 200 mA, 250 mA, 1A,…), Forward Voltage (700 mV,
900 mV, 1.1 V, 1.2 V, 1.5V,…) and Power Dissipation (from 100
mW to 1.5 kW) to name a few.
• You will be able to find the right semiconductor chip when
designing a circuit that requires a Zener diode regulator, power
Zener diode, 5v Zener diode, 12v Zener diode, 18v Zener diode,
24v Zener diode, high voltage Zener diode, low voltage Zener
diode, Zener diode rectifier, 3v Zener diode or for designing any
Zener diode circuits.
Voltage clamps: Limiting signals with Zener diodes
Thank you for listening