TECHNICAL FIELD

The present disclosure relates to the technical field of power supply, in particular to an input detection and protection circuit.

BACKGROUND

Development of power supply technology including electronic ballast, LED driver, power bank and the like has started many years ago, and applications on such technology are becoming more and more mature, especially in agriculture and in energy-saving renovation of street lamp recently. The differences in diversified demands of the market have promoted a huge product family, with a wide variety of products, a common power ranges from 70 W to 1000 W, and common voltages including 120 V, 208 V, 220 V, 230 V, 240 V, 277 V, 347 V, 380 V, 400 V, 480 V, etc. due to different standards of voltages in different countries. It is not hard to see from the above voltage specifications that the power distribution environments where various power supplies locate could be complex, so attention must be paid to the rated voltage range of products and the environments of grid during installation.

To be further understood, the use environment can be divided into household use at single voltage, medium-scale power supply to motors, and grid distribution in large-scale industrial applications. Therefore, the voltage environments of the grid are complex. When In use, an input surge voltage is monitored to reach several kilovolts, and the fluctuation and instability of the grid reach more than 30% when, far exceeding the designed withstand voltage of products, thus the main cause for failures is such rugged grid environments. According to failure analysis, there are several main causes as follows for a large number of damages:

One cause is the misuse of two live wires in the 3-phase 4-wire power distribution, where the actual input voltage is 1.7 times the nominal value. For example, when a product with a nominal rated voltage of 230 V is connected to a wrong wire, it has a voltage of up to 400 VAC, which greatly exceeds a withstand voltage thereof. A second cause is that the grid has a voltage surge exceeding the withstand voltage of internal devices of the product, due to its instability of the grid, resulting in damage to electrolytic capacitors and MOS transistors. A third cause is the three-phase imbalance caused by neutral line phase loss, where one phase voltage exceeds an input rating, resulting in damage to internal electrolytic capacitors and MOS transistors. A fourth cause is a surge voltage induced at the moment of lightning or of switching on. A fifth cause is a rapid change of high current when the input capacitor is charged, which results in an induced high voltage generated when the current reduces.

After an observation of a long-term usage, it can be found that the damage caused by abnormal input voltage accounts for more than 60% of all failure rates, wherein the failure rate in the household use environment is obviously lower than that in industrial applications since there is no multiple service voltages in the household use environment. The failure rate in the usages of motor is significantly higher than that in the usages of grid. The probability of damage at the moment of switching on and off is greater than that in normal operation, and the failure rate in the thunderstorm weather is higher than that in the sunny weather.

Therefore, the present disclosure proposes improvements in view of the above problems.

SUMMARY

The present disclosure aims to provide an input detection and protection circuit as improvements with respect to the prior arts.

In order to address the above issues, a technical scheme according to the present disclosure is provided as follows:

An input detection and protection circuit, wherein the input detection and protection circuit includes a power input circuit, an input voltage acquisition circuit, a pull-in circuit for a relay, a PFC circuit and an MCU chip.

The power input circuit performs a first limitation to an input surge voltage, and then performs a second limitation to a residual voltage from the first input surge voltage limitation; the input voltage acquisition circuit feeds back an input voltage to the MCU chip, the pull-in circuit for a relay is connected to a relay in the power input circuit, and the MCU chip controls the PFC circuit to switch on and off according to voltage values input by the input voltage acquisition circuit, and controls pull-in and drop-out of the relay through the pull-in circuit for the relay.

As an improvement of the input detection and protection circuit according to the present disclosure, the power input circuit includes: a first varistor, a second varistor, a thermistor and the relay, and the input surge voltage is firstly limited by the first varistor and then secondly limited by the second varistor and the thermistor.

As an improvement of the input detection and protection circuit according to the present disclosure, the power input circuit further includes a third varistor connected in parallel to both ends of the thermistor.

As an improvement of the input detection and protection circuit according to the present disclosure, the input voltage acquisition circuit includes:

a first diode, a second diode, a first capacitor, a second capacitor, a first resistor and a second resistor; one end of each of the first and second diodes is connected to the power input circuit and the other end thereof is connected to the MCU chip through the first and second capacitors and the first and second resistors.

As an improvement of the input detection and protection circuit according to the present disclosure, when the input voltage is within a safe range, the MCU chip controls the pull-in of the relay through the pull-in circuit for the relay, and when the input voltage is out of the safe range, the relay is dropped-out.

As an improvement of the input detection and protection circuit according to the present disclosure, the input voltage acquisition circuit includes: a third resistor, a fourth resistor and a third capacitor; one end of the third capacitor is connected to the PFC circuit and the other end thereof is connected to the MCU chip through the third resistor and the third capacitor.

As an improvement of the input detection and protection circuit according to the present disclosure, when the input voltage is within a safe range, the MCU chip controls the PFC circuit to be switched on; and when the input voltage is out the safe range, the MCU chip controls the PFC circuit to be switched off.

As an improvement of the input detection and protection circuit according to the present disclosure, the pull-in circuit for the relay includes a triode, a fifth resistor, a sixth resistor and a fourth capacitor, a collector of the triode is connected to the relay, and the collector and an emitter of the triode are electrically connected to the MCU chip through the fifth resistor, the sixth resistor and the fourth capacitor.

As an improvement of the input detection and protection circuit according to the present disclosure, the input detection and protection circuit further includes a power supply module that supplies power to the relay and the MCU chip.

As compared with existing technologies, the present disclosure has beneficial effects that the input detection and protection circuit according to the present disclosure can provide protection against abnormalities due to extremely high input voltage, such as phase loss from the grid, incorrect wire connection during installation, high surge voltage at the moment of switching on, impulses by continuous lightning. According to the present disclosure, the input detection and protection circuit acquires a charging voltage of a capacitor of a subsequent stage, and enables the pull-in of the relay according to the internal setting in order to effectively reduce surge current and impact. Meanwhile, the input detection and protection circuit monitors the input voltage, such that protection can be provided when the voltage is extremely high or low, wherein the relay can be dropped-out in case of an abnormality, and a standby current can be provided to the MCU by PTC to indicate such abnormality.

