A surge protection circuit and a surge protection device

Abstract

A surge protection circuit and a surge protection device are disclosed, A protection circuit includes a first varistor sheet, a second varistor sheet, a third varistor sheet, a positive temperature coefficient thermistor sheet, a gas discharge tubes and a lead-out terminal, A first varistor sheet is connected in series with a gas discharge tube, The positive temperature coefficient thermistor chipis connected in series with the third varistor chip, and two series branches are connected in parallel with the second varistor chip in series to form a single-port combined circuit. The performanceof the first varistor chip and the gas discharge tube against surge shock is better than that of the second varistor chip against surge shock. At least one of the two lead-out terminals of the single-port combined circuit is a low thermal resistance thermal conductive terminal, a second varistor sheet, a third varistor sheet and a positive temperature coefficient thermistor sheet form a thermal coupling, and the low thermal resistance thermal conductive terminal and the second varistor sheet and one or both of the positive temperature coefficient thermistor sheets are simultaneously thermallycoupled to each other.

Description

technical field [0001] The invention relates to the field of power supplies, in particular to a surge protection circuit and a surge protection device. Background technique [0002] Surge protector (SPD for short), as a standard low-voltage electrical appliance, is widely used in low-voltage transmission and distribution lines. Quality and ensuring the safety of electrical appliances have obvious effects. [0003] The core component of the SPD is a surge suppression component, the most commonly used is a varistor ceramic chip. Due to the long transmission distance of power transmission and distribution lines and their exposure to the open air, they are more likely to suffer from high-energy surge pulses than indoor electrical equipment. During the design life of the SPD, the varistor ceramic chips are more likely to be damaged beyond the rated specifications The multiple impacts of the high-energy surge caused the deterioration and failure of the varistor. Since the varis...

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Problems solved by technology

[0007] But this scheme still has some serious defects, at first because of the current-limiting effect of the positive temperature coefficient ceramic thermistor sheet 12, no matter how badly the piezoresistor sheet 11 deteriorates, the heating temperature is only maintained at the center of the thermistor sheet 12. Near the middle point temperature, it will not be disconnected from the grid and quit working until the varistor voltage value of the varistor sheet 12 deteriorates to about 1 / 2 of the peak value of the grid operating voltage. After the connection, the too low varistor voltage value clamps the grid current that is constantly following, so that the gas discharge tube 13 cannot return to the disconnected state, and the thermistor sheet 12 will be short-circuited, and the protection circuit will fail. At this time, the varistor sheet 11 will Immediate breakdown short circuit, causing serious short circuit fault

Theoretically, most varistors will fail in this way if there are no other protective measures

The other failure process is similar to the situation of scheme 1, that is, when the varistor sheet 11 deteriorates to a certain extent, even if it has not entered the accelerated deterioration zone, but because its internal structure has been severely damaged, its ability to withstand surge shocks The ability has been greatly reduced. At this time, a surge can break it down or nearly break it down. At this time, the gas discharge tube 13 is also in the conduction state, and the piezoresistor sheet 11 that is broken down or near the breakdown is also lost. The ability to clamp off the following current of the grid leads to the failure of the protection circuit of the thermistor sheet 12, resulting in a serious short-circuit fault

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