What is Snubber Circuit and How does it work?

What is meant by Snubber circuit?

• Basically, a series-connected resistor and capacitor are linked across a device is called as a snubber circuit.
• Snubbers are devices that are employed to inhibit phenomenon like voltage transients in electrical systems, pressure transients in fluid systems, or excess force or quick movement in mechanical systems
• Circuit protection against voltage spikes, ringing, and oscillation effects are provided by snubbers.
• Snubber performs the same function or clamps voltage spikes without changing the ringing frequency.
• The rate of rise of forward voltage, or dv/dt, across the thyristor must be suppressed by a snubber circuit in order to prevent damage to the device.

Purpose of Snubber Circuit

• The primary goal of the Snubber circuit is to avoid unintentional SCR or thyristor triggering caused by a rapid rise in voltage, or high dv/dt.
• We already know that if the SCR’s anode to cathode voltage rises quickly, erroneous triggering may result. Commonly referred to as dv/dt triggering
• Snubbers absorb or clamp high-voltage spikes, preventing them from reaching the semiconductor device.
• Snubbers limit the rate of voltage change across the device, reducing the risk of unintenional turn-on or damage.
• Snubbers help to damp oscillations that can occur during switching, improving the stability of the circuit.

Components and Construction of Snubber Circuits

The construction of a snubber circuit depends on the desired configuration, with the most common being the RC snubber. In this type, a resistor (R) and a capacitor (C) are connected in series across the device that needs protection. The resistor limits the current flow, while the capacitor absorbs energy from voltage spikes, thereby suppressing the rate of voltage rise. Selecting appropriate values for R and C is crucial for effectively reducing transient spikes.

In the RCD snubber configuration, a diode is added in parallel with the resistor and capacitor. This diode provides a low-impedance path for discharge currents, particularly useful in circuits with inductive loads.

Components of a Snubber Circuit:

Resistor:

Limits the current flow through the snubber circuit and dissipates energy.

The resistance value is chosen to balance the need to minimize power dissipation while effectively damping voltage transients.

Capacitor:

Stores and releases energy, helping to smooth out voltage spikes and suppress high-frequency noise.

The capacitance value and voltage rating are chosen based on the magnitude and duration of voltage transients. Capacitors with low equivalent series resistance (ESR) are preferred to minimize losses and improve transient response.

Diode:

Provides a low-impedance discharge path when connected in parallel with the RC combination. The diode starts conducting when the voltage across it exceeds its forward voltage drop, allowing transient currents to bypass the protected device.

The diode is selected based on its forward voltage drop and reverse recovery time to ensure it responds quickly and effectively to transients.

By carefully selecting and configuring these components, snubber circuits can effectively protect power semiconductor devices from voltage transients and improve the overall reliability of the circuit.

Working Principle of Snubber Circuits

Snubber circuits work by absorbing energy from voltage transients and limiting the rate of voltage change across a diode. When a diode connected to an inductive load is switched off, it can cause a rapid rise in voltage, leading to spikes that may damage the diode or other components in the circuit.

The most common snubber circuit is the RC snubber, which consists of a resistor (R) and a capacitor (C) connected across the diode. The resistor controls the current flow through the capacitor, while the capacitor absorbs the energy from the voltage spikes. This absorption prevents the voltage from reaching dangerously high levels, protecting the diode and other components.

In an RCD snubber circuit, an additional diode is added to the RC combination. This extra diode provides a low-impedance path for discharging the transient current, enhancing the circuit’s ability to control voltage spikes.

By managing voltage transients, snubber circuits improve the reliability of the system, reduce electromagnetic interference (EMI), and extend the lifespan of the components

What are the functions of a snubber circuit

• It is possible to reduce or get rid of voltage or current spikes.
• Limitations for dI/dt or dV/dtshape the load line to keep it inside the safe operating area.
• It distributes the switch’s power onto a resistor or another suitable load.
• Overall switching losses may be reduced.
• It can lower EMI by lessening voltage and current ringing.

Types of Snubbers

• Snubbers circuits are divided into passive and active types.
• Passive parts make up the passive snubber (resistor, inductor, capacitor & diode).
  • RC Snubber
  • RCD Snubber
  • Diode Snubber
• The semiconductor switch was used to build the active snubbers circuit.

What is meant by RC Snubber?

• A small resistor (R) and a tiny capacitor are connected in series to create an easy RC snubber (C). By restricting the rate of rise in voltage (dV/dt) across the thyristor to a value that will not activate it, this combination can be used to suppress the rapid rise in voltage across a thyristor and prevent the thyristor from being accidentally turned on.
• Both DC and AC loads can be utilised with an adequately made RC snubber.
• Common applications for this kind of snubber include inductive loads like electric motors.
• Because a capacitor’s voltage cannot change instantly, a decreasing transient current will flow through it for a brief period of time when the switch is opened, causing the voltage across the switch to rise more gradually.
• Determining the voltage rating can be difficult due to the nature of transient waveforms.
• However, it can be identified by the application and the power rating of the snubber components alone.
• RC snubbers can be constructed as a single component or individually.

Example of RC Snubber Circuit – Boost Converter with RC Snubber circuit

• When the high-side switch is turned ON or OFF, the energy that has accumulated in the parasitic inductors causes resonance in the input loop.
• Due to resonance frequencies for parasitic elements exceeding several hundred MHz at relatively low values, EMI characteristics decrease.
• RC snubber circuits are widely employed to reduce this high-frequency noise.
• To lessen high-frequency noise, a simple RC network might be added to the switch.

What is meant by RCD Snubber ?

• Some designers referred to this as an RCD clamp rather than an RCD snubber.
• RCD clamps are widely used as it is a low impedance circuit. It does so because the voltage spikes will actually be clamped without changing the spike or ringing frequency.
• The components of an RCD snubber are a resistor, capacitor, and diode.
• Resistor will release energy from the leaking stored power, Capacitor provides a low ripple DC source and diodes function in only one direction.

Example of RCD Snubber circuit

• For low-power DC/DC conversions, the forward converter continues to be the backbone of the industry
• An early attempt to enhance reset was the Forward Converter with an RCD Snubber Circuit. The transformer is reset using an RCD network.
• This strategy has a low cost. It is still a wise choice for affordable designs.
• A diode D and a capacitor C clamp the voltage at a level set by the input voltage and duty ratio when the switch is off. The capacitor is reset by a resistor R. The drawback of R is that it loses power. This dissipation leads to a difficulty with the thermal design in addition to decreasing efficiency.
• This is especially true for offline converters because the resistor’s power dissipation is proportional to the input line

Diode Snubber

• A simple rectifier diode is typically employed as a snubber when a DC current is flowing.
• The snubber diode is linked in parallel with an inductive load (such as a relay coil or electric motor).
• The diode’s installation prohibits it from conducting under normal conditions.
• When the external driving current is interrupted, the inductor current takes its place and passes through the diode.
• The energy held in the inductor is gradually released by a combination of the diode voltage drop and the resistance of the inductor.
• A basic rectifier diode’s disadvantage when used as a snubber is that it permits current to pass for a time, which causes the inductor to run somewhat longer than is desirable.
• This delay in the actuator dropping out must be taken into account when designing circuits.
• The diode must quickly convert to forward conduction mode when the driving current is interrupted.
• The majority of common diodes, including “slow” power silicon diodes, may turn on relatively quickly, in contrast to their delayed reverse recovery durations. This work well for getting around electromechanical components like relays and motors.

Snubber Circuits for Thyristor Protection

• A snubber circuit is made up of a parallel thyristor and a series combination of capacitance C_s and resistance R_s.
• To stop unauthorized dv/dt triggering of the SCR, a capacitor C_s connected in parallel with the device is adequate.
• A sudden voltage emerges across the circuit when switch S is closed. As a result of the capacitor C_s‘s short circuit-like behavior, the voltage across the SCR is zero. Because voltage across Cs rises up slowly over time, dv/dt across C_s and therefore across SCR is lower than the device’s maximum dv/dt rating.
• In order to keep dv/dt within acceptable bounds, R_s, C_sand the load circuit characteristics normally create an underdamped circuit. Snubber circuit characteristics are designed in a very complicated way. In order to achieve a good performance of the power electronics system, intended snubber parameters are in actuality increased or decreased in the final completed power circuit.

Selecting criteria of R_s, C_s

         In actual usage, R_s, C_s, and the parameters of the load circuit should be chosen so that the dv/dt across C_s during its charging falls below the SCR’s stipulated dv/dt rating and the discharge current upon SCR turn-on is within reasonable bounds.

Why use Rs in series with Cs if Cs is sufficient to prevent dv/dt from accidentally turning on the device?

• C_s charges to its maximum voltage V_s before the gate pulse activates the SCR.
• The capacitor discharges through the SCR when the SCR is turned on, sending a current equal to V_s / (resistance of the local path formed by C_s and SCR).
• Due to the relatively low resistance, the turn-on di/dt will typically be high, which could lead to SCR destruction.
• A resistance R_s is connected in series with C_s to limit the amount of discharge current.
• The initial discharge current V_s/R_s is now relatively small when the SCR is turned on, and the turn-on di/dt is decreased.

Response of Switching converter with and without RC Snubber

         To reduce the voltage spike on the switching device to a safe level, RC snubbers are frequently utilized in switching converters. In order to avoid more problems, the voltage spike should not only be clamped, but also the spike frequency or ringing behavior should be changed.

         The RC snubber reduces the voltage spike level while also altering the ringing frequency. The resistor operates as a discharge channel, and the capacitor serves as a charge storage device.

Snubber circuits in power electronics

• When a power semiconductor switch turns on or off in a simple power switching network with a resistive load, device voltage and current are high. The device loses energy and dissipates power.
• In high-voltage switching circuits, peak power dissipation is 25% of maximum voltage and current. Inductive loads dissipate more.
• However, a semiconductor-connected snubber reduces turn-off losses. When the switch opens, the uncharged snubber draws current. This diversion reduces switch voltage build-up, lowering current before switch voltage rises considerably. Slowly increasing switch voltage reduces switching energy loss.
• Power electronics snubbers can operate at high frequencies and low switching losses. The charged snubber must release its energy. A tiny resistor limits the discharge current of the snubber when the switch is closed at the start of its conduction angle.

Advantages of Snubber Circuits

1. Reduction of Voltage Spikes: Snubber circuits effectively reduce voltage spikes that occur during the switching process of diodes, protecting them from potential damage.
2. Increased Reliability: By mitigating voltage transients, snubber circuits enhance the reliability of the system, reducing the risk of unexpected failures and downtime.
3. Minimized Electromagnetic Interference (EMI): Snubber circuits dampen voltage spikes, thereby minimizing electromagnetic interference and reducing radio frequency interference (RFI) generated by diodes during switching.
4. Protection Against Transient Overvoltages: Snubber circuits provide protection against transient overvoltages that may result from sudden changes in load conditions, safeguarding the circuit components.
5. Improved Voltage Regulation and Efficiency: By reducing voltage spikes and transient voltages, snubber circuits help improve voltage regulation in power supplies, leading to enhanced overall efficiency.
6. Prevention of Ringing and Oscillations: Snubber circuits prevent ringing or oscillations that can occur due to voltage spikes, ensuring stable and smooth operation of the system.
7. Reduction of Switching Noise: Snubber circuits effectively reduce the switching noise generated during the diode switching process, contributing to a quieter and more reliable circuit operation.

What are the disadvantages of using snubber circuits?

While snubbers are beneficial, they also have some disadvantages:

• Snubber circuits dissipate energy, leading to power loss, which can be significant in high-power circuits.
• Adding snubbers increases the complexity and cost of the circuit.
• Additional components may require more space on the PCB, which can be a limitation in compact designs.

What is disadvantages of RC snubber over RCD snubber?

         The RC snubber has the drawback of increasing the amount of current the transistor must carry when it goes on without taking into account whether the switch node voltage is growing or lowering. To make an RCD snubber for higher power applications, you can connect a diode in series with the RC.

Explain the snubber circuit in terms of mechanical systems

• Snubbers are used to restrict movement in pipe and equipment during unexpected circumstances including earthquakes, turbine trips, and safety/relief valve closure.
• Snubbers constrain a component in irregular situations yet allow for free thermal mobility under normal circumstances.
• Pipe deflection is possible using a hydraulic snubber under typical operating circumstances.
• The snubber becomes activated and works as a restraint to prevent pipe movement when it is subjected to an impulse load.
• A mechanical snubber applies the constraint force using mechanical means.

How do you test a Snubber circuit?

The charged snubber must release its energy. A tiny resistor limits the discharge current of the snubber when the switch is closed at the start of its conduction angle.The snubber capacitor is to lessen the parasitic inductance of electrical cable. It is a capacitor that is linked to a large-current switching node. Turn off the power, remove the external snubber capacitor from the circuit, and measure the capacitance between its two leads.

How inspection done in Snubber?

• This may be the cause of resets or strange relay point shutdowns on a job site.
• Before testing, unplug control power to the controller and relays.
• If you receive a bad reading, switch test leads and try again.

Step 1: Measure capacitance with a capacitance metre with all control power off and relay output connectors disconnected. Set the capacitance dial. Measure capacitance between “common (COM)” and “Normally Open (NO)” on the board. The meter should read between.08μF and.120μF.

Repeat for each Relay Output. The board must be replaced if any Snubber Capacitors are out of range.

Step 2: Checking “Normally Closed (NC)” is more complicated. Turn off control power and remove the panel board first. Only power the board’s power terminal on a test bench. Power the board up and manually switch each relay on, then read the capacitance again, this time between “Common (COM)” and “Normally Closed (NC)” on the board, where you should again read between.08μF and.120μF on the meter. Turn off the power, remove the external snubber capacitor from the circuit, and measure the capacitance between its two leads.

What factors should be considered when designing a snubber circuit?

When designing a snubber circuit, consider the following:

• Power Rating: Ensure the resistor can handle the power dissipated during transients.
• Capacitor Voltage Rating: The capacitor should be rated for a voltage higher than the expected transient voltage.
• Time Constant: The RC time constant (R × C) should be selected based on the characteristics of the transient to be suppressed.
• Circuit Impedance: The impedance of the snubber circuit should match the circuit to ensure effective damping.

How the Snubber circuit protects the MOSFET?

• Power MOSFET the RC snubber is connected in parallel with a power MOSFET.
• Cutting off a current in a circuit causes its voltage to increase sharply due to stray inductances.
• The snubber damps this surge voltage to protect the power MOSFET as well as components in its vicinity.
• A circuit used to prevent voltage spikes and voltage oscillations across a MOSFET during device turn-off.
• The large peak current handling capability of the MOSFET and the fact that its switching speed can be easily controlled by controlling the gate current eliminates the need for a turn-on snubber in most cases.

FAQ on Snubbers

What is the purpose of a snubber?

A snubber is used to protect electronic components, particularly in power circuits, from voltage spikes and transients. It typically helps to absorb or dissipate the energy of the transient, reducing the risk of damage to sensitive components like semiconductors.

What is the snubber circuit in SCR?

In a Silicon-Controlled Rectifier (SCR) circuit, a snubber is a network (usually an RC circuit) connected across the SCR to limit the rate of voltage rise (dV/dt) across it. This prevents the SCR from being accidentally triggered by a rapid increase in voltage, ensuring it only turns on when intended.

How does a snubber capacitor work?

A snubber capacitor works by absorbing the energy from a voltage spike. When a sudden change in voltage occurs, the capacitor charges up, reducing the spike’s magnitude. This action protects the components in the circuit by smoothing out the transient and preventing it from reaching sensitive devices.

How to use an RC snubber?

To use an RC snubber, connect the resistor (R) and capacitor (C) in series, then place this series combination across the device you want to protect, such as a relay, motor, or SCR. The resistor limits the current through the capacitor, while the capacitor absorbs the voltage spikes, thus protecting the circuit.

What is a snubber circuit used for?

A snubber circuit is used to suppress or minimize voltage transients and protect electronic components from overvoltage conditions. It is commonly used in power electronics, relays, motors, and any circuit where inductive loads or switching transients may cause voltage spikes.

What is the application of snubber?

Snubbers are widely used in power electronics, motor drives, switch-mode power supplies, and circuits containing inductive loads. They protect semiconductors, extend the life of relays and contactors, and improve overall circuit reliability by reducing the stress caused by transients.

Can snubbers be used in AC circuits?

Yes, snubbers can be used in AC circuits to protect against transients caused by inductive loads, switching operations, or lightning strikes. In AC circuits, the design of the snubber must account for the continuous operation and the varying nature of the AC waveform.