Definition of pulse and surge

Resistors that are resistant to pulse and surge are required in circuits where the current limiting against instantaneous flow of large current is critical, and in the circuits where the static electricity (ESD) becomes a serious concern.

Here, for convenience, overloads with high power and relatively long duration (high energy) are referred to as "pulse", and overloads with high voltage but short duration such as ESD are referred to as "surge".

 

 

What are high pulse-resistant and surge-resistant resistors?

Pulse/surge resistant resistors are resistant to damage caused by instantaneous applications of large power or high voltage.

Among SMD type resistors, thick film chip resistors(metal glaze film type) are generally more pulse resistant than metal-film chip resistors. Thick film chip resistors with special construction, SG73, SG73P, SG73G and WG73 are made more pulse resistant or surge.

Also, metal plate chip resistors for current sensing have strong resistance to pulse and surge because their resistive bodies are made of metal plates.

For the leaded type resistors, wire-wound type resistors with the metal resistive wire around the insulator such as CW, CW-H, RW, BGR and BWR are relatively stronger in pulse resistance than metal film or carbon film resistors with resistor film formed on the surface of the insulator.

Solid type ceramic resistors HPC and PCF with ceramic resistive body have extremely strong pulse resistance.

Resistor that are strong against surge are resistant to instantaneous high voltage such as ESD. SG73S with guaranteed ESD resistance falls under this category.

Pulse Resistance Level by resistor type(image)

Snubber circuits

Snubber circuits have a function of absorbing surge energy generated by switching and are connected to both ends of an element that generates surge voltage. Snubber circuits include series circuits of resistors and capacitors (RC snubbers), and circuits that connect a diode for clipping the tip of surge voltage in addition to RC. Snubber circuits are circled in the figure below.

Rectifier diodes on the secondary side of the switching power supply become the source of surge upon the occurrence of the abrupt voltage and current changes while switching ON/OFF. RC snubber circuits are used to absorb this surge voltage. Please note that the surge resistance is required especially for the resistors used in RC snubber circuits.

Snubber circuits are required to absorb noise without increasing the energy loss, and resistors used in these circuits require both the optimized constant and the consideration for safety. Depending on the switching voltage and the constant of snubber circuits, flame-retardant type resistors are required to prevent the resistor from emitting fume or catching fire when capacitors or semiconductors are short-circuited.

Metal oxide film resistors MOS are suitable for the use in snubber circuits because of the flame retardant coating, in addition to the advantage that smaller types can be used if the allowable power matches since they have high heat resistance..

Chip type surge resistant resisters SG73, SG73S, SG73G and WG73 are recommended for surface mount power supply circuits.