Community hub
0 subscribers7 pages, 0 posts
Recent from talks
All channels
Be the first to start a discussion here.
Be the first to start a discussion here.
Be the first to start a discussion here.
Be the first to start a discussion here.
Contribute something
Welcome to the community hub built to collect knowledge and have discussions related to Snubber.
Nothing was collected or created yet.
Snubber
View on Wikipediafrom Wikipedia
 | This article needs additional citations for verification. (April 2011) |
A snubber is a device used to suppress ("snub") a phenomenon such as voltage transients in electrical systems, pressure transients in fluid systems (caused by for example water hammer) or excess force or rapid movement in mechanical systems.
Electrical systems
[edit]Snubbers are frequently used in electrical systems with an inductive load where the sudden interruption of current flow leads to a large counter-electromotive force: a rise in voltage 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 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. Snubbers are also often used to prevent arcing across the contacts of relays and switches, or electrical interference, or the welding of the contacts that can occur (see also arc suppression).
Resistor-capacitor (RC)
[edit].PNG)
A simple RC snubber uses a small resistor (R) in series with a small capacitor (C).[1] This combination can be used to suppress the rapid rise in voltage across a thyristor, preventing the erroneous turn-on of the thyristor; it does this by limiting the rate of rise in voltage ( ) 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 motors. The voltage across a capacitor 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, and may be defined simply by the power rating 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).
Diodes
[edit]When the current flowing is DC, a simple rectifier diode is often employed as a snubber.[2] The snubber diode is wired in parallel with an inductive load (such as a relay coil or electric motor). 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 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 diodes, are able to turn on very quickly,[3] in contrast to their slow reverse recovery time. These are sufficient for snubbing electromechanical devices such as relays and motors.
In high-speed cases, where the switching is faster than 10 nanoseconds, such as in certain switching power regulators, "fast", "ultrafast", or Schottky diodes may be required.[4]
Resistor-capacitor-diode
[edit]More sophisticated designs use a diode with an RC network.[5]
Solid-state devices
[edit]In some DC circuits, a varistor 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 diodes, 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 ( ) and thus increases contact arc[clarification needed] 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 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
[edit]Snubbers for pipes and equipment are used to control movement during abnormal conditions such as earthquakes, turbine trips, safety valve closure, relief valve closure, or hydraulic fuse closure. Snubbers allow for free thermal movement of a component during regular conditions, but restrain the component in irregular conditions.[6] A hydraulic snubber allows for pipe deflection under normal operating conditions. When subjected to an impulse load, the snubber becomes activated and acts as a restraint in order to restrict pipe movement.[7] A mechanical snubber uses mechanical means to provide the restraint force.[8]
See also
[edit]References
[edit]- ^ Ott, Henry W. (1976). Noise Reduction Techniques in Electronic Systems. John Wiley. pp. 189–192. ISBN 0-471-65726-3.
- ^ Ott 1976, p. 193; diode protects transistor driver from overvoltage.
- ^ cliftonlaboratories.com
- ^ cds.linear.com
- ^ Ott 1976, p. 192–193: "The R–C–D network provides optimum contact protection, but it is more expensive than other methods and cannot be used in an ac circuit."
- ^ Hydraulic & Mechanical Snubbers Piping Technology & Products, (retrieved February 2012
- ^ Hydraulic Snubber Piping Technology & Products,(retrieved January 2012)
- ^ Snubbers: A General Overview Piping Technology & Products, (retrieved February 2012)
Further reading
[edit]- Ott, Henry (1988). Noise Reduction Techniques in Electronic Systems (2nd ed.). Wiley. ISBN 978-0471850687.
- Horowitz, Paul; Hill, Winfield (1989). The Art Of Electronics (2nd ed.). Cambridge University. ISBN 0-521-37095-7.
External links
[edit]- Designing RC snubbers - NXP app note
Snubber
View on Grokipediafrom Grokipedia
Fundamentals
Definition and Purpose
A snubber is a device or circuit designed to suppress voltage, current, or mechanical transients—such as spikes, oscillations, or sudden shocks—in electrical, fluid, or mechanical systems, thereby protecting components from damage due to excessive stress.[3] In electrical contexts, snubbers mitigate rapid changes in voltage or current during switching operations, while in mechanical applications, they restrain excessive motion or force during dynamic events like impacts or vibrations.[7] This suppression prevents phenomena like arcing in contacts, component overheating, or structural failure, ensuring safer and more stable system operation.[8] The origins of snubber technology trace back to 19th-century electrical engineering, where French physicist Armand Fizeau demonstrated an early capacitive snubber in 1853 by placing a capacitor across switch contacts to reduce arcing during inductive load disconnection.[9] By the early 20th century, snubbers had evolved as essential tools for managing inductive load switching in emerging power systems, including applications in vacuum tube amplifiers and early electronic circuits.[10] These developments addressed the challenges of electromagnetic induction discovered by Michael Faraday in the 1830s, adapting protective measures to practical engineering needs as electrification expanded.[9] The primary purposes of snubbers include absorbing excess energy from transients to prevent voltage or mechanical overloads on sensitive elements, thereby reducing electromagnetic interference (EMI) that could disrupt nearby circuits or signals.[3] They also extend the operational lifespan of components by minimizing wear from repeated stress and enhance overall system reliability in environments prone to disturbances, such as power conversion or seismic activity.[11] In practice, snubbers find general use in relays to suppress back-EMF during coil de-energization, in motors to dampen startup surges, and in power supplies to stabilize output against load variations, averting failures like contact welding or insulation breakdown.[12]Operating Principles
Snubbers address transient phenomena that arise during the switching of electrical circuits, particularly those involving inductive elements. When a switch opens or closes rapidly, the current through an inductor cannot change instantaneously, leading to voltage spikes governed by the relation , where is the inductance and is the rate of change of current. This inductive kickback generates high-voltage transients, often exacerbated by parasitic inductances in wiring or components, which can exceed the ratings of switches like transistors or diodes and cause device failure. Similarly, capacitive discharge in circuits with parasitic or load capacitances can produce current spikes during switching, contributing to overall transient stress, though inductive effects predominate in most power electronics scenarios.[13][4] The core mechanism of a snubber involves absorbing the energy stored in these transients and dissipating it safely, typically as heat. For an inductor, the stored magnetic energy is given by , where is the current at the moment of switching; without mitigation, this energy manifests as destructive voltage or current excursions. Snubbers redirect this energy into a dissipative element, such as a resistor, converting it into thermal form rather than allowing arcing or breakdown across the switch. This absorption prevents excessive stress on circuit components, ensuring reliable operation by limiting peak voltages and currents during transients.[4][13] Beyond mere absorption, snubbers provide damping to suppress oscillations that arise from the interaction between inductance and capacitance in the circuit. These ringing effects, often underdamped LC oscillations, prolong transients and amplify stress; snubbers achieve critical or overdamping to minimize this by introducing controlled energy decay. In resistive-capacitive configurations, the time constant determines the rate of voltage decay across the snubber, allowing the transient to settle exponentially without prolonged ringing—typically aiming for a response where the oscillation frequency is significantly higher than the switching rate to ensure effective suppression. This damping role is essential for maintaining system stability and extending component lifespan in high-frequency applications.[4]Electrical Snubbers
RC Snubbers
An RC snubber consists of a resistor and capacitor connected in series, typically placed across the switching device or the inductive load to mitigate voltage transients generated during switching operations. When the switch opens, the inductive load releases stored energy, causing a rapid voltage rise; the capacitor charges to absorb this spike, limiting the rate of voltage change (dV/dt), while the resistor restricts the inrush current during charging and enables controlled discharge of the capacitor, ultimately dissipating the energy as heat in the resistor. This setup provides bidirectional damping suitable for both AC and DC circuits.[2] The primary advantages of RC snubbers lie in their simplicity, low cost, and effectiveness in protecting components from overvoltages in applications involving inductive loads, such as relays, transformers, contactors, and motor drives. By reducing voltage overshoots and ringing, they minimize arcing at switch contacts, lower electromagnetic interference (EMI), and enhance overall circuit reliability without requiring active components. For instance, in motor drive systems, an RC snubber can suppress inductive kickback to prevent contactor arcing, extending the lifespan of switching elements.[4][14] Despite these benefits, RC snubbers introduce limitations, notably continuous power loss through I²R heating in the resistor, which degrades efficiency particularly at higher switching frequencies or voltages, and practical constraints on component size and ratings for high-voltage environments, where larger capacitors and resistors may be needed to handle the energy. These dissipative characteristics make them less ideal for high-power applications exceeding a few hundred watts.[2][4] Design of an RC snubber begins with selecting the capacitor value to adequately absorb transient energy or limit dV/dt, often using the relation , where is the peak load current, is the switching rise time, and is the allowable voltage excursion (approximating an optimal in energy-based variants for peak conditions, where is the parasitic inductance, the peak current, and the peak voltage). The resistor is then chosen to match the circuit's characteristic impedance, typically where is parasitic inductance, ensuring critical damping while keeping the RC time constant below the switching period. Power dissipation in the resistor is calculated as , where is the switching frequency, representing the average energy loss per cycle (equivalent to in certain low-frequency approximations for the resistive drop). These parameters must balance transient suppression against thermal management to avoid overheating.[2][4][15]Diode-Based Snubbers
Diode-based snubbers, also known as freewheeling or flyback diodes, are primarily employed to protect switching devices from voltage transients generated by inductive loads in DC circuits. The simplest configuration places a single diode in parallel with the inductive load, oriented in reverse bias during normal conduction; its anode connects to the load's lower potential side and cathode to the higher potential side relative to the switch. This setup allows the diode to become forward-biased when the switch opens, providing a low-impedance path for the inductor's stored energy to dissipate gradually.[12][16] For applications requiring bidirectional current flow, such as in certain power inverters or motor drives, an antiparallel diode configuration is used, consisting of two diodes connected back-to-back across the inductive load to handle current continuity in both directions. This arrangement ensures protection against flyback in either polarity without blocking the primary current path.[17] In operation, when the switch turns off, the inductor attempts to maintain its current by inducing a high reverse voltage according to ; the diode conducts almost immediately, limiting this voltage spike by offering a path where the inductor voltage drops to approximately the diode's forward voltage drop , typically 0.7 V for silicon diodes. The peak clamped voltage across the switching device is thus . This process allows the inductive current to decay exponentially through the diode, preventing destructive overvoltages.[18][16] These snubbers offer significant advantages, including minimal power dissipation—limited primarily to the diode's forward conduction loss during current recirculation—making them far more efficient than RC snubbers, which incur resistive heating. They are particularly suited for DC circuits driving solenoids, relays, or motors, where simplicity and low losses enhance overall system efficiency.[4][2] However, diode-based snubbers have limitations; they are ineffective against capacitive transients, as they do not absorb or dissipate capacitive energy but merely redirect inductive currents. In AC applications, a single diode fails to provide protection across alternating polarities without additional components, necessitating bidirectional setups or alternatives.[19][20] Diode snubbers have been commonly used in automotive relays since the 1960s, coinciding with the rise of transistor-based switching in vehicle electronics to suppress spikes from coil inductance.[21] In transistor switches, such as those using MOSFETs or BJTs to control inductive loads, the freewheeling diode prevents avalanche breakdown by clamping the drain-source or collector-emitter voltage below the device's breakdown threshold, thereby extending component lifespan and reliability.[22][12] For cases with residual ringing, a small RC network may be added in parallel with the diode to damp oscillations, though this is secondary to the diode's primary clamping role.[2]Advanced Electrical Types
RCD snubbers combine a resistor, capacitor, and diode to provide clamped reset functionality, primarily in flyback converters where they absorb energy from the transformer's leakage inductance during switch turn-off, limiting voltage spikes on the primary-side MOSFET.[23] This configuration directs the leakage current through the diode to charge the capacitor, with the resistor dissipating excess energy to maintain a stable clamp voltage over multiple cycles.[24] In switched-mode power supplies (SMPS), RCD snubbers prevent transformer saturation by clamping drain voltages below critical levels, avoiding core flux imbalance from prolonged high-voltage excursions.[23] The clamp voltage rise above the input voltage, , is given bywhere is the peak switch current, is the leakage inductance, and is the clamp capacitor value; this equation ensures the total clamp voltage remains within the MOSFET's rating, typically setting to half the reflected output voltage for optimal design.[24] RL snubbers, the dual of RC snubbers, consist of a resistor and inductor in series, typically placed in series with the switching device to limit current transients and control the rate of current rise (dI/dt). They are useful in applications where fast voltage switching must be paired with gradual current changes to reduce EMI and stress on components.[2] Nonlinear snubbers employ devices with voltage-dependent resistance for precise clamping, such as metal oxide varistors (MOVs), which exhibit high impedance below a threshold voltage and low impedance above it, effectively shunting transients to ground.[8] MOVs are rated by their energy absorption capacity, often in joules (e.g., up to 220 J for industrial variants like the V1000LA80AP), allowing them to handle repetitive surges without degradation in power electronics applications.[8] Transient voltage suppressor (TVS) diodes complement MOVs in nonlinear setups, offering sub-nanosecond response times for fast transients while clamping voltages to safe levels, though with lower energy handling compared to MOVs.[8] These devices provide advantages in efficiency over linear RC networks by minimizing power dissipation during normal operation, ideal for protecting IGBTs and thyristors in high-power circuits.[8] Solid-state advancements enable snubberless designs through MOSFETs with integrated protection features, such as avalanche-rated silicon or enhanced gate drivers that tolerate transients without external components.[25] Active clamping circuits further evolve this by using auxiliary MOSFETs and capacitors to resonantly recycle leakage energy, replacing dissipative RCD snubbers and achieving near-zero voltage stress in synchronous rectifiers.[25] For instance, in phase-shifted full-bridge converters, active clamps limit rectifier voltages to under 45 V at 400 V input, supporting frequencies up to 500 kHz with 45% smaller transformers due to reduced losses.[25] The rise of silicon carbide (SiC) and gallium nitride (GaN) devices since the early 2010s has diminished reliance on traditional snubbers, as their superior switching speeds (e.g., GaN at 200 kHz versus silicon's 50-80 kHz) and lower parasitic inductances minimize overshoots and EMI, enabling compact, efficient topologies with fewer auxiliary circuits.[26] SiC adoption accelerated post-2010 with cost reductions from $1,200 to $600 per wafer, while GaN HEMTs entered commercial power electronics in 2010, boosting system efficiency by up to 12% in supplies and reducing cooling needs.[26]