Snubber
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A snubber is a device used to suppress ("
snub A snub, cut or slight is a refusal to recognise an acquaintance by ignoring them, avoiding them or pretending not to know them. For example, a failure to greet someone may be considered a snub. In Awards and Lists For awards, the term "snub" ...
") a phenomenon such as voltage transients in
electrical Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
systems, pressure transients in fluid systems (caused by for example
water hammer Hydraulic shock (colloquial: water hammer; fluid hammer) is a pressure surge or wave caused when a fluid in motion, usually a liquid but sometimes also a gas is forced to stop or change direction suddenly; a momentum change. This phenomenon com ...
) or excess force or rapid movement in
mechanical Mechanical may refer to: Machine * Machine (mechanical), a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement * Mechanical calculator, a device used to perform the basic operations of ...
systems.


Electrical systems

Snubbers are frequently used in electrical systems with an inductive load where the sudden interruption of
current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...
flow leads to a large
counter-electromotive force Counter-electromotive force (counter EMF, CEMF, back EMF),Graf, "counterelectromotive force", Dictionary of Electronics is the electromotive force (EMF) manifesting as a voltage that opposes the change in current which induced it. CEMF is the EMF c ...
: a rise in
voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...
across the current switching device that opposes the change in current, in accordance with Faraday's law. This transient can be a source of electromagnetic interference (EMI) in other circuits. Additionally, if the
voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...
generated across the device is beyond what the device is intended to tolerate, it may damage or destroy it. The snubber provides a short-term alternative current path around the current switching device so that the inductive element may be safely discharged. Inductive elements are often unintentional, arising from the current loops implied by physical circuitry like long and/or tortuous wires. While current switching is everywhere, snubbers will generally only be required where a major current path is switched, such as in
power supplies A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a res ...
. Snubbers are also often used to prevent
arcing An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma; the plasma may produce visible light. An ...
across the contacts of relays and
switches In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
, or the electrical interference, or the
welding Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as bra ...
of the contacts that can occur (see also arc suppression).


Resistor-capacitor (RC)

A simple RC snubber uses a small resistor (R) in
series Series may refer to: People with the name * Caroline Series (born 1951), English mathematician, daughter of George Series * George Series (1920–1995), English physicist Arts, entertainment, and media Music * Series, the ordered sets used in ...
with a small
capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...
(C). This combination can be used to suppress the rapid rise in
voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...
across a
thyristor A thyristor () is a solid-state semiconductor device with four layers of alternating P- and N-type materials used for high-power applications. It acts exclusively as a bistable switch (or a latch), conducting when the gate receives a current ...
, preventing the erroneous turn-on of the thyristor; it does this by limiting the rate of rise in voltage ( dV/dt ) across the thyristor to a value which will not trigger it. An appropriately designed RC snubber can be used with either DC or AC loads. This sort of snubber is commonly used with inductive loads such as
electric motor An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate for ...
s. The voltage across a
capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...
cannot change instantaneously, so a decreasing transient current will flow through it for a fraction of a second, allowing the voltage across the switch to increase more slowly when the switch is opened. Determination of voltage rating can be difficult owing to the nature of transient
waveforms In electronics, acoustics, and related fields, the waveform of a signal is the shape of its graph as a function of time, independent of its time and magnitude scales and of any displacement in time.David Crecraft, David Gorham, ''Electron ...
, and may be defined simply by the
power rating In electrical engineering and mechanical engineering, the power rating of equipment is the highest power input allowed to flow through particular equipment. According to the particular discipline, the term ''power'' may refer to electrical or me ...
of the snubber components and the application. RC snubbers can be made discretely and are also built as a single component (see also
Boucherot cell : ''This article relates to loudspeaker driving. See Zobel network for a more general description of telecommunications usage.'' A Boucherot cell (or Zobel network) is an electronic filter, used in audio amplifiers to damp high-frequency oscil ...
).


Diodes

When the current flowing is DC, a simple rectifier diode is often employed as a snubber. The snubber diode is wired in parallel with an inductive load (such as a
relay A relay Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts An automotive-style miniature relay with the dust cover taken off A relay is an electrically operated switch ...
coil or
electric motor An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate for ...
). The diode is installed so that it does not conduct under normal conditions. When the external driving current is interrupted, the inductor current flows instead through the diode. The stored energy of the inductor is then gradually dissipated by the diode
voltage drop Voltage drop is the decrease of electrical potential along the path of a current flowing in an electrical circuit. Voltage drops in the internal resistance of the source, across conductors, across contacts, and across connectors are undesirab ...
and the resistance of the inductor itself. One disadvantage of using a simple rectifier diode as a snubber is that the diode allows current to continue flowing for some time, causing the inductor to remain active for slightly longer than desired. When such a snubber is utilized in a relay, this effect may cause a significant delay in the ''drop out'', or disengagement, of the actuator. The diode must immediately enter into forward conduction mode as the driving current is interrupted. Most ordinary diodes, even "slow" power
silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ta ...
diodes, are able to turn on very quickly, in contrast to their slow reverse recovery time. These are sufficient for snubbing
electromechanical In engineering, electromechanics combines processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focuses on the interaction of electrical and mechanical systems as a whole and how the two systems ...
devices such as relays and motors. In high-speed cases, where the switching is faster than 10
nanoseconds A nanosecond (ns) is a unit of time in the International System of Units (SI) equal to one billionth of a second, that is, of a second, or 10 seconds. The term combines the SI prefix ''nano-'' indicating a 1 billionth submultiple of an SI unit ( ...
, such as in certain switching power regulators, "fast", "ultrafast", or
Schottky diode The Schottky diode (named after the German physicist Walter H. Schottky), also known as Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltag ...
s may be required.


Resistor-capacitor-diode

More sophisticated designs use a diode with an RC network.


Solid-state devices

In some DC circuits, a
varistor A varistor is an electronic component with an electrical resistance that varies with the applied voltage. Also known as a voltage-dependent resistor (VDR), it has a nonlinear, non- ohmic current–voltage characteristic that is similar to that ...
made of inexpensive metal oxide , called a Metal Oxide Varistor (MOV) is used. They may be unipolar or bipolar, like two inverse-series silicon
Zener diode A Zener diode is a special type of diode designed to reliably allow current to flow "backwards" (inverted polarity) when a certain set reverse voltage, known as the ''Zener voltage'', is reached. Zener diodes are manufactured with a great var ...
s, but are prone to wear out after about a dozen max-rated joules of energy absorption such as lightning protection, but are suitable for lower energy. Now with lower series resistance (Rs) in semiconductors they are generally called Transient Voltage Suppressors (TVS), or Surge Protection Devices (SPD). Transient Voltage Suppressors (TVS) may be used instead of the simple diode. The coil diode clamp makes the relay turn off slower ( T=L/R ) and thus increases contact arc if with a motor load which also needs a snubber. The diode clamp works well for coasting a uni-directional motor to a stop, but for bi-directional motors, a bipolar TVS is used. A higher voltage zener-like TVS may make the relay open faster than it would with a simple rectifier diode clamp, as R is higher while the voltage rises to the clamp level. A
Zener diode A Zener diode is a special type of diode designed to reliably allow current to flow "backwards" (inverted polarity) when a certain set reverse voltage, known as the ''Zener voltage'', is reached. Zener diodes are manufactured with a great var ...
connected to ground will protect against positive transients that go over the Zener's breakdown voltage, and will protect against negative transients greater than a normal forward diode drop. Transient-voltage-suppression diodes are like Silicon Controlled Rectifiers (SCRs) which trigger from overvoltage then clamp like Darlington transistors for lower voltage drop over a longer time period. In AC circuits a rectifier diode snubber cannot be used; if a simple RC snubber is not adequate a more complex bidirectional snubber design must be used.


Mechanical and hydraulic systems

Snubbers for
pipes Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circula ...
and equipment are used to control movement during abnormal conditions such as earthquakes, turbine trips,
safety valve A safety valve is a valve that acts as a fail-safe. An example of safety valve is a pressure relief valve (PRV), which automatically releases a substance from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds ...
closure,
relief valve A relief valve or pressure relief valve (PRV) is a type of safety valve used to control or limit the pressure in a system; pressure might otherwise build up and create a process upset, instrument or equipment failure, or fire. The pressure is re ...
closure, or hydraulic fuse closure. Snubbers allow for free thermal movement of a component during regular conditions, but restrain the component in irregular conditions. A
hydraulic Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counte ...
snubber allows for pipe deflection under normal operating conditions. When subjected to an
impulse Impulse or Impulsive may refer to: Science * Impulse (physics), in mechanics, the change of momentum of an object; the integral of a force with respect to time * Impulse noise (disambiguation) * Specific impulse, the change in momentum per uni ...
load, the snubber becomes activated and acts as a restraint in order to restrict pipe movement. A mechanical snubber uses mechanical means to provide the restraint force.Snubbers: A General Overview
Piping Technology & Products, (retrieved February 2012)


See also

*
Shunt (electrical) In electronics, a shunt is a device that creates a low- resistance path for electric current, to allow it to pass around another point in the circuit.Rudolf F. Graf, ''Modern dictionary of Electronics'', Mc-Graw Hill, 1968 Library of Congress 68- ...
*
Transient-voltage-suppression diode A transient-voltage-suppression (TVS) diode, also transil or thyrector, is an electronic component used to protect electronics from voltage spikes induced on connected wires. Description The device operates by shunting excess current when the ...


References


Further reading

* *{{cite book , last1=Horowitz , first1=Paul , last2=Hill , first2=Winfield , title=The Art Of Electronics , edition=2nd , date=1989 , publisher=Cambridge University , isbn=0-521-37095-7 , url-access=registration , url=https://archive.org/details/artofelectronics00horo


External links


Designing RC snubbers
- NXP app note Electronic circuits