EMF Prevention for SSRs

When working with Silicon-Controlled Rectifiers (SCRs) or other types of thyristors, also known as Switch-Mode Rectifiers (SMRs) or Switch-Mode Switches (SMS), in inductive-load applications, it is crucial to {prevent|protect} the device from the voltage {spikes|surges|increases} generated when the device turns off, which is also known as {Back EMF|Back Electromotive Force|Counteracting Force}.

Back EMF occurs due to the {sudden|rapid} current {interruption|disruption|cut-off} in the {inductive|reactive} load, which causes a reverse voltage to appear across the thyristor. This reverse voltage can be {several|hundreds} {volts|voltage} units, potentially {damaging|harmful|detrimental} the device or causing it to fail {catastrophically|critically|viciously}. The severity of the Back EMF can vary greatly depending on the {characteristics|features|properties} of the load, the maximum current it can handle, and the load's {inductance|reactance|resistance}.

To mitigate this issue, switching devices are equipped with a protection circuit known as Back EMF protection or {snubber|absorber} circuit. A snubber circuit is usually a simple RC network that consists of a {resistor|ohm} and a capacitor connected in series or parallel with the switching device. The RC network {absorbs|neutralizes} the energy generated by the Back EMF, preventing it from being applied across the switching device.

Choosing the right value for the {resistor|ohm} and capacitor in a snubber circuit is {critical|vital|essential} to its {effectiveness|efficiency|performance}. Factors to consider include the maximum reverse voltage across the device, the peak current that the load can draw, رله ssr the desired snubber energy, and the switching device's {characteristics|features|properties} such as its current ratings, voltage ratings, and capacitance.

Typically, a snubber {resistor|ohm} between {100|500} ohm is recommended for applications with loads of around {100|1000} milliseconds in {inductance|reactance}. Increasing this {resistance|ohm} can sometimes improve the protection but {degrade|deteriorate|reduce} the switching performance of the device. This also holds for the choice of snubber {capacitor|capacitance}.

When calculating the snubber {capacitor|capacitance} value, it's {vital|essential|important} to take into account the stored energy in the inductive load. For applications with high stored energy and long inductive load time, a larger snubber {capacitor|capacitance} may be necessary to prevent device failure. Values between {100|1,000} nF and {1|10} uF are typical. However, as smaller inductive loads require smaller energy storage, this value decreases to about {10|50}nF and {10|50}pF.

While these guidelines should serve as a good starting point for choosing the snubber values, designers may prefer running simulations using advanced SPICE {software|program|utility} to precisely calculate the optimal values for their specific application.

Designers and engineers should also explore the option of using more advanced protection techniques such as input-output (I/O) and blocking diodes integrated in the overall power supply, {snicker|bootstrap} or {snubber|absorber} circuits. This helps mitigate high-voltage {phenomena|events|occurrences} and drastically improves total system {reliability|dependability|efficiency}.

By including a snubber circuit, you can improve the {reliability|dependability|efficiency} and safety of power electronic systems by preventing thyristor device failure.