A lightning-proof overvoltage protection circuit and a protection device

Abstract

A lightning-proof overvoltage protection circuit and a protection device are disclosed, A protection circuit includes a first varistor sheet, a second varistor sheet, a transient suppression diode, apositive temperature coefficient thermistor sheet and a lead terminal, A positive temperature coefficient thermistor chip and a transient suppression diode are connected in series and then connected in parallel with the first varistor chip, and the series-parallel branch circuit is connected in series with the second varistor chip to form a single-port combined circuit, wherein, the performance ofthe first varistor chip 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 combination circuit is alow thermal resistance thermal conduction terminal, the positive temperature coefficient thermistor sheet and / or the second varistor sheet are thermally coupled with the low thermal resistance thermal conduction terminal, and the transient suppression diode can be replaced with a zener diode or a voltage switching type element.

Description

technical field [0001] The invention relates to the field of power supplies, in particular to a lightning protection and overvoltage protection circuit and 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 var...

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Problems solved by technology

[0005] However, there are still some defects in this solution. Because the action of the overheating disconnector needs to be delayed for a few seconds, and when the leakage current of the piezoresistor ceramic chip 1 enters the milliampere level and starts to accelerate the deterioration and heat generation, the defects inside the ceramic body are already very serious. The defects of some chips are so serious that the time from the start of heating to the breakdown and short circuit is very short, and the heat has not had time to conduct to the overheating disconnector to melt the low melting point alloy 5, and the short circuit accident occurs

Another situation that is not uncommon is that when the varistor ceramic chip 1 deteriorates to the vicinity of the accelerated deterioration zone, the leakage current of the varistor ceramic chip 1 is still less than the milliamp level, and the thermal stability can still be maintained. It maintains work under the working voltage of the power grid, but its varistor voltage value at this time has dropped significantly compared with the initial value when it was first put into use. At this time, the ability of the varistor ceramic chip 1 to resist surge impact It is already very fragile, and a power surge with not too much energy can directly break it down or close to it. At this time, its breakdown and short circuit speed is too fast, and the overheating disconnector has no time to respond to the action and cannot protect it.

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