Circuit protection

Common Type

Overcurrent Protection

(over current)

is automatically powered off when the current is too large, preventing the circuit The components are damaged due to exceeding the rated current.

Overvoltage protection

(over-Voltage Protection)

Mainly prevents damage to electronic components from DISCHARGE SUPPRESSION. Widely used in a variety of electronic systems such as telephone, fax machine and high-speed transmission interface (USB, IEEE1394, HDMI, SATA), especially electronic communication devices, how to avoid abnormal voltage (Over-Voltage or EOS) -Stress)) or electrostatic discharge (ESD) is especially important for electronic preparation.

Over temperature protection


Temperature protection components have passed the commodity, have passed a berice, and the over-temperature protection components are widely used in pairs The temperature has special requirements. Such protection components can be divided into chemical pharmaceutical active types, low-temperature alloys, and the main feature of chemical pharmaceuticals can be made of low-temperature products (have done 48 ° C), but the structure is more complicated, the cost is high; the low-temperature alloy type is mainly a large diameter low-temperature fuse to conduct a conduction effect, and must ensure that the heat generated by the rated current does not melt the fuse, This low-temperature fuse is generally adjusted by regulating the ratio of ingredients such as tin (Sn), copper (Cu), silver (Ag), bismuth (Bi), indium (IN).

Over-temperature overcurrent protection


In recent years, with the application of the application, the simple temperature protection function is not satisfied with the Japanese and new moon. The needs of motor, motor, and 3C product safety protection, therefore re-developing components that can monitor and promptly protected simultaneously with temperature, current, and voltage abnormalities, and the rise of this component is mainly based on lithium ion batteries and lithium polymer batteries. To maximum application.

Overcurrent overpressure


Circuit protection

With the complexity of modern electronic products, the requirements for protecting components are also increasing, such as protection Comprehensive, limited reserved space, etc. With these requirements, the protection assembly community set off a combination package, as mentioned above, it is mentioned in combination package, but throughout Most of the pressure protection combination package products are still in the development stage, and there is no mature commercial product.

Protection importance

In various electronic products, the trend of setting overcurrent protection and overvoltage protection components is increasing, and the reason is, which mainly has the following Factors:

(1) With the demand for electronic products, the function of IC is getting stronger and stronger, and its "worth" is naturally more and more expensive, and it needs to be strengthened.

(2) In order to reduce power consumption, reduce heat generation, extend the service life, the working voltage of the semiconductor components and ICs is getting lower and lower, according to the statistics of the SIA (US Semiconductor Industry Association), the working voltage is about 1.5V By 2004, it will drop to 1.2V or less, so the ability of its anti-overcurrent / overvoltage needs to adapt to new protection requirements.

(3) Mobile electronics increasingly, such as handheld, PDA, laptop, video recorder, digital camera, optical drive, etc., these electronic products require battery components as in batteries Components and battery chargers must be equipped with protection components.

(4) In modern luxury cars, the equipment has more and more electronic equipment, and the working conditions are more bad than the general electronic products, such as car driving conditions and environmental changes, the car will produce Very large instant peak voltage, etc. Therefore, in the power adapter for these electronic devices, it is generally necessary to install overcurrent and overvoltage protection elements at the same time.

(5) Many electric / electronic products need to prevent lightning strikes and the intersection of power cords and telephone lines to ensure normal communication and user personal safety. Therefore, with the development of electric / electronic products, the demand of overcurrent / overvoltage protection components has a rise.

(6) According to statistics, 75% of the failure of electronic products is due to overcurrent / overvoltage. IBM has analyzed the cause of the computer power supply, of which 88.5% is caused by overcurrent / overvoltage. With the demanding of electronic product quality, manufacturers must use circuit protection components in order to improve market competitiveness.


Overvoltage protection

overvoltage Cause

1 Operation over voltage: from the pull gate, closing, fast The overvoltage caused by the electromagnetic processes in the regular operation of the DC switch.

2 surge over pressure: caused by accidental causes of lightning strikes, from the grid to the overvoltage of the converter.

3 power electronics turn off overvoltage: overvoltage generated during power electronic devices.

4 In the power electronic converter - motor speed control system, since the motor feedback brake causes an overvoltage generated by the DC side DC voltage, it is also referred to as a pump lifting voltage.

The basic principle of overvoltage protection is to add different additional circuits according to different parts generated in the circuit, and automatically open the additional circuit when reaching the ratio, so that the overvoltage is attached. The circuit forms a pathway, consumes an overvoltage stored electromagnetic energy, so that the energy of the overvoltage does not add on the main switching device to protect the power electronics.

Overcurrent protection

Reason for overcurrent

When a device breakdown or short circuit inside the power electronic converter, the trigger circuit or control circuit is faulty, Overload, DC side short circuit, the reversible transmission system generates a loop or inverter failure, and the AC power supply voltage is too high or too low, and phase loss, etc., can cause the current of the components in the converter to exceed normal operating current, that is, overcurrent. Since the current overload capacity of the power electronics is much different than that of the general electrical equipment, the converter must be appropriately overcurrent protection. The overcurrent of the converter is generally divided into two categories: overload overcurrent and short circuit overcurrent.

Overcurrent protection method

(1) AC adapter reactor, or uses a rectifier transformer with a leakless resistance to limit the short circuit current. However, there is a large AC pressure drop in normal operation.

(2) current detecting device. When the excess is sent, the overcurrent signal can block the trigger circuit on the one hand, so that the fault current of the converter quickly drops to zero, thereby effectively suppressing the current. On the other hand, the over-electric relay is controlled, so that the AC contactor contacts are jumped and cut off the power. However, overcurrent relays and AC contactors need to have a certain time (100 ~ 200ms), so this protection can only work only if the current is not large.

(3) DC fast switch. For large, medium-capacity converters, the rapid fuse is high and the replacement is inconvenient. In order to avoid overcurrent, the fast fuse is blown, and the DC fast switch with only 2ms of the operation time is used, which can protect the power electronics before the fast fuse action.

(4) Fast fuse. Fast fuses are the last line of defense that prevents overcurrent damage of the converter. In the thyristor converter, the fast fuse is the most common overcurrent protection measures, which can be used in the AC side, DC side, and the main circuit. Among them, the AC side quick fuse can protect the thyristor element short circuit and the DC side short circuit, but when normal operation is required, the fast fuse current quota is greater than the current quota of the thyristor, so that the protection of the short circuit fault of the component is more Difference.

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