Over-voltage protection device

1. Field of the Invention

The present invention relates to an over-voltage protection device. In particular, this invention relates to a circuit device that restrains the spike voltage and protects the over-voltage for a power adapter or a hand-held device.

2. Description of the Related Art

Reference is made to FIG. 1 . When an electric equipment 20 (such as a laptop or a LCD etc.) that operates in DC power is providing power from an AC power, a power adapter 21 is required to convert the AC power into DC power. In FIG. 1 , power adapter 21 obtains the AC power from an AC power plug 22 , and converts the AC power into DC power for electric equipment 20 . The structure in FIG. 1 has a problem. When electric equipment 20 is turned on or AC power plug 22 of power adapter 21 is plugged into the AC power socket (not shown in the figure), a large spike voltage easily occurs to generate spike current. The large spike current makes the AC power socket and the switch generate a spark or interfere with other electric equipments. The power quality is affected.

Moreover, when the AC power received by power adapter 21 is unstable (such as when the voltage is too high), power adapter 21 converts the over-voltage into over-voltage DC power, and delivers the over-voltage DC power to electric equipment 20 . The over-voltage DC power will burn down electric equipment 20 . Therefore, power adapter 20 needs a spike voltage restraining circuit and an over-voltage protection circuit to overcome the above problems.

One particular aspect of the present invention is to provide an over-voltage protection device that can be used in a power adapter and has the spike voltage restraining function and an over-voltage protection function.

In the first embodiment, the over-voltage protection device has a voltage input terminal and a voltage output terminal. The over-voltage protection device includes a comparison module, a first switch, a second switch and an output switch. The comparison module obtains an input voltage from the voltage input terminal, and compares the input voltage with a threshold voltage and outputs a control signal according to the comparison result. The first control terminal of the first switch is coupled with the comparison module. The first drain terminal is coupled with the voltage input terminal. The first source terminal of the first switch is coupled with a grounding terminal. The first switch is controlled by the control signal. The second control terminal of the second switch is coupled with the first drain terminal. The second source terminal of the second switch is coupled with the grounding terminal. The second switch is controlled by the output signal of the first source terminal. The third control terminal of the output switch is coupled with the second drain terminal. The third drain terminal of the output switch is coupled with the voltage output terminal. The third source terminal of the output switch is coupled with the voltage input terminal. The output switch is controlled by the output signal of the second drain terminal to cut off the input voltage or pass the input voltage to the voltage output terminal.

In the second embodiment, the over-voltage protection device further includes a first spike voltage restraining device and a second spike voltage restraining device. The first spike voltage restraining device is coupled with the voltage input terminal and the second control terminal to turn off the second switch according to a spike voltage. The second spike voltage restraining device is coupled between the third control terminal and the third source terminal to turn off the output switch according to the spike voltage.

When an over-voltage is inputted, the comparison module determines whether the voltage is too high or not, and turns off the output switch to achieve the over-voltage protection if the voltage is too high. At the same time, when the spike voltage occurs, the first spike voltage restraining device guides the spike voltage into the grounding terminal; and the second spike voltage restraining device will short-circuit the control terminal and the source terminal of the output switch in order to cut off the voltage and thus achieve the spike voltage restraining function.

For further understanding of the invention, reference is made to the following detailed description illustrating the embodiments and examples of the invention. The description is for illustrative purpose only and is not intended to limit the scope of the claim.

The drawings included herein provide a further understanding of the invention. A brief introduction of the drawings is as follows:

FIG. 1 is a block diagram of the power adapter of the prior art;

FIG. 2 is a schematic diagram of the over-voltage protection device of the present invention;

FIG. 3 is a circuit diagram of the over-voltage protection device of the first embodiment of the present invention;

FIG. 4 is a circuit diagram of the over-voltage protection device of the second embodiment of the present invention;

FIG. 5A is a waveform diagram of the output voltage when the over-voltage protection device of the present invention operates under a normal input voltage;

FIG. 5B is a waveform diagram of the output voltage when the over-voltage protection device of the present invention operates under an over-voltage input voltage; and

FIG. 5C is a waveform diagram of the output voltage when the over-voltage protection device of the present invention operates under a spike voltage.

Reference is made to FIG. 2 , which shows a schematic diagram of the over-voltage protection device of the present invention. The over-voltage protection device 1 has a voltage input terminal T 1 and a voltage output terminal T 2 . The over-voltage protection device 1 obtains an input voltage Vin from the voltage input terminal T 1 , and outputs an output voltage Vout via the voltage output terminal T 2 . When the input voltage Vin is inputted into the over-voltage protection device 1 and the input voltage Vin is larger than a predetermined value, the over-voltage protection device 1 will cut off the input voltage Vin. Moreover, when a spike voltage occurs, the over-voltage protection device 1 will also cut off the input voltage Vin.

Reference is made to FIGS. 2 and 3 . FIG. 3 shows a circuit diagram of the over-voltage protection device of the first embodiment of the present invention. The over-voltage protection device 1 includes a comparison module 10 , a first switch Q 1 , a second switch Q 2 and an output switch Q 3 . The comparison module 10 obtains an input voltage Vin from the voltage input terminal T 1 , and compares the input voltage Vin with a threshold voltage Vth to output a control signal S 1 according to the comparison result. The first control terminal of the first switch Q 1 is coupled with the comparison module 10 . The first drain terminal of the first switch Q 1 is coupled with the voltage input terminal T 1 . The first source terminal of the first switch Q 1 is coupled with a grounding terminal G. The first switch Q 1 is controlled by the control signal S 1 .

Reference is made to FIGS. 2 and 3 again. The second control terminal of the second switch Q 2 is coupled with the first drain terminal of the first switch Q 1 . The second source terminal of the second switch Q 2 is coupled with the grounding terminal G. The second switch Q 2 is controlled by the output signal S 2 of the first source terminal of the first switch Q 1 . The third control terminal of the output switch Q 3 is coupled with the second drain terminal of the second switch Q 2 . The third drain terminal of the output switch Q 3 is coupled with the voltage output terminal T 2 . The third source terminal of the output switch Q 3 is coupled with the voltage input terminal T 1 . The output switch Q 3 is controlled by the output signal S 3 of the second drain terminal of the second switch Q 2 to cut off the input voltage Vin or pass the input voltage Vin to the voltage output terminal T 2 .

Reference is made to FIGS. 2 and 3 again. The first switch Q 1 is a NMOSFET, the second switch Q 2 is a NMOSFET, and the output switch Q 3 is a PMOSFET.

Reference is made to FIGS. 2 and 3 again. The comparison module 10 includes a parallel constant voltage regulator 101 , a voltage-divide unit 102 , and a comparator 103 . The parallel constant voltage regulator 101 includes a Zener diode D 1 , an input capacitor C 1 and an input resistor R 1 . The Zener diode Z 1 is coupled with the input resistor R 1 in serial and is coupled with the input capacitor C 1 in parallel. The parallel constant voltage regulator 101 is coupled with the voltage input terminal T 1 to generate the threshold voltage Vth according to the input voltage Vin. The voltage-divide unit 102 is coupled with the voltage input terminal T 1 to receive the input voltage Vin and generate a divided input voltage V 1 . The non-invert input terminal of the comparator 103 receives the divided input voltage Vin, the inverted input terminal of the comparator 103 receives the threshold voltage Vth, and the output terminal of the comparator 103 outputs the control signal S 1 .

Reference is made to FIGS. 2 and 3 again. The designer can use the different Zener diode D 1 with different operation voltage range to obtain the threshold voltage Vth. Furthermore, by designing the resistance of the resistors R 2 and R 3 in the voltage-divide unit 102 , the over-voltage protection range is set. When the input voltage Vin is conducted to into the over-voltage protection device 1 , the Zener diode Z 1 breaks down to generate a stable threshold voltage Vth. The resistor R 3 in the voltage-divide unit 102 generates the divided input voltage V 1 according to the input voltage Vin.

When the input voltage Vin is normal, the divided input voltage V 1 is not larger than the threshold voltage Vth. This means that the divided input voltage V 1 is lower than the protection voltage range of the over-voltage protection device 1 . At this time, the comparator 103 outputs a low level control signal S 1 to turn off the first switch Q 1 . Because the first switch Q 1 is in the turn-off status, the input voltage V 1 is delivered to the second control terminal of the second switch Q 2 via the first resistor R 4 to turn on the second switch Q 2 . The turn-on second switch Q 2 guides the third control terminal of the output switch Q 3 to the grounding terminal G to turn on the output switch Q 3 . At this time, the input voltage Vin passes through the turn-on output switch Q 3 and outputs from the voltage output terminal T 2 of the over-voltage protection device 1 to form the output voltage Vout. Reference is made to FIG. 5A , which shows a waveform diagram of the output voltage Vout when the over-voltage protection device of the present invention operates under a normal input voltage Vin. In FIG. 5A , the output voltage Vout is 6V.

When the input voltage Vin is too high, the divided input voltage V 1 is larger than the threshold voltage Vth. This means that the divided input voltage V 1 is larger than the protection voltage range of the over-voltage protection device 1 . At this time, the comparator 103 outputs a high level control signal S 1 to turn on the first switch Q 1 . The turn-on switch Q 1 guides the second control terminal of the second switch Q 2 to the grounding terminal G in order to turn off the second switch Q 2 . The turn-Off second switch Q 2 makes the third control terminal of the output switch Q 3 to become floating status in order to turn off the output switch Q 3 . The turn-off output switch Q 3 cuts off the input voltage Vin so that the over-voltage input voltage Vin cannot not be delivered to the over-voltage protection device 1 . Reference is made to FIG. 5B , which shows a waveform diagram of the output voltage Vout when the over-voltage protection device of the present invention operates under an over-voltage input voltage. In FIG. 5B , after a transient period t 1 passes, the output voltage Vout becomes 0V.

Reference is made to FIGS. 2 and 4 . FIG. 4 shows a circuit diagram of the over-voltage protection device of the second embodiment of the present invention. The elements in second embodiment that are the same as ones in the first embodiment are labeled by the same labels. The operation principle and the effect of the second embodiment are the same ones of the first embodiment. The difference is: the over-voltage protection device 1 ′ further includes a first spike voltage restraining device 12 and a second spike voltage restraining device 14 . The first spike voltage restraining device 12 is coupled with the voltage input terminal T 1 and the second control terminal of the second switch Q 2 in order to turn off the second switch Q 2 according to a spike voltage. The second spike voltage restraining device 14 is coupled between the third control terminal and the third source terminal of the output switch Q 3 in order to turn off the output switch Q 3 according to the spike voltage.

Reference is made to FIGS. 2 and 4 again. The first spike voltage restraining device 12 includes a first resistor R 4 and a first capacitor C 2 that are coupled together in serial. The first terminal of the first resistor R 4 is coupled with the input voltage terminal T 1 . The second terminal of the first resistor R 4 is coupled with the first drain terminal of the first switch Q 1 , the second control terminal of the second switch Q 2 , and the first terminal of the first capacitor C 2 . The second terminal of the first capacitor C 2 is coupled with the grounding terminal G. The second spike voltage restraining device 14 includes a second resistor R 5 and a second capacitor C 3 that are coupled together in parallel. The first terminal of the second capacitor C 3 is coupled with the input voltage terminal. The second terminal of the second capacitor C 3 is coupled with the second drain terminal of the second switch Q 2 , and the third control terminal of the output switch Q 3 .

Reference is made to FIGS. 2 and 4 again. The spike voltage is a high frequency AC noise. According to formula (1), when the spike voltage occurs, first capacitor C 2 and second capacitor C 3 form a short circuit status (the impedance is equal to zero) due to the high frequency AC spike voltage.

In formula (1), Xc is the impedance of the capacitor, ω is the frequency, and the C is the capacitance of the capacitor. When a high frequency AC noise occurs, the impedance Xc of the capacitor is equal to 0. Therefore, the capacitor is short circuited.

According to formula (1), when the spike voltage occurs, the first capacitor C 2 of the first spike voltage restraining device 12 becomes short circuited to guide the spike voltage to the grounding terminal G. At this time, the short circuited first capacitor C 2 is connected between the second control terminal and the second source terminal of the second switch Q 2 in order to turn off the second switch Q 2 . The turn-off second switch Q 2 makes the third control terminal of the output switch Q 3 to become floating status in order to turn off the output switch Q 3 . Moreover, when the spike voltage occurs, the second capacitor C 3 of the second spike voltage restraining device 14 also becomes short-circuited. The short circuited second capacitor C 3 is connected between the third control terminal and the third source terminal of the third switch Q 3 in order to turn off the output switch Q 3 . The turn-off output switch Q 3 cuts off the input voltage Vin so that the input voltage Vin cannot be delivered to the over-voltage protection device 1 . Reference is made to FIG. 5C , which shows a waveform diagram of the output voltage when the over-voltage protection device of the present invention operates under spike voltage. In FIG. 5C , when the spike voltage occurs, the output voltage is 0V.

Reference is made to FIG. 4 again. The second switch Q 2 , the output switch Q 3 and the second spike voltage restraining device 14 form a standard soft-start circuit. When the spike current occurs, the spike current charges the second capacitor C 3 in the soft-start circuit so that the current flowing through the output switch Q 3 is not too sharp. Thereby, the spike current protection effect is achieved.

The over-voltage protection device of the present invention has a spike voltage retaining function and an over-voltage protection function. When an over-voltage is inputted, the comparison module determines if the voltage is too high and turns off the output switch to achieve the over-voltage protection function if the voltage is too high. At the same time, when the spike voltage occurs, the first spike voltage restraining device guides the spike voltage into the grounding terminal. The second spike voltage restraining device short circuits the control terminal and the source terminal of the output switch in order to cut off the voltage to achieve the spike voltage restraining function.

The description above only illustrates specific embodiments and examples of the invention. The invention should therefore cover various modifications and variations made by herein-described structure and operations of present invention, provided that they fall within the scope of the invention as defined in the following appended claims.