TWI746319B - Switch unit - Google Patents

Abstract

A switch unit is configured to provide reverse current protection. The switch unit comprises an input terminal, an output terminal, a switch device, an operational amplifier, and a voltage difference circuit. The switch device is coupled between the input terminal and the output terminal. The voltage difference circuit receives the voltage of the output terminal for generating a first signal, where the first signal is greater than the voltage of the output terminal. The operational amplifier is coupled to the input terminal and the first signal for generating a second signal to control the switch device.

Description

Switch unit

The present invention relates to a switch unit, in particular to a switch unit that can provide reverse current protection.

With the development of portable devices in recent years, in order to save power and extend the use time, power management integrated circuits and switching elements have become indispensable. Generally speaking, the switching element is a power supply channel part arranged between a power supply and a load. The system can determine whether to provide power to the load by controlling the on-state of the switching element. In order to improve the reliability of the switching components, the designer can add a reverse current protection circuit to protect the peripheral components of the power supply.

Figure 1 is a schematic diagram of a conventional switch unit 10. The switch unit 10 has an input terminal Vi, an output terminal Vo, a switching element 100, a comparator 110, and a control circuit 120. When the voltage at the output terminal Vo is greater than the voltage at the input terminal Vi, the switching current Isw will flow backward from the output terminal Vo to the input terminal Vi. In order to prevent the occurrence of reverse current, when the voltage of the output terminal Vo is greater than the voltage of the input terminal Vi, the comparator 110 will make the control signal Vc to a low level through the control circuit 120 to turn off the switching element 100. Since the magnitude of the reverse current depends on the input compensation voltage and speed of the comparator 110, the switch unit 10 cannot accurately detect the time point when the reverse current is generated, and the reverse current is likely to be too large.

In view of the foregoing problems, the object of the present invention is to provide a switch unit that can reduce the reverse current.

The switch unit is provided according to the present invention. The switch unit has an input terminal, an output terminal, a switch element, an operational amplifier, and a voltage difference circuit. The switch element is coupled between the input terminal and the output terminal. The switching element has a switching current Isw, where the switching current Isw refers to a current flowing from the input terminal through the switching element to the output terminal. The input terminal can have a high voltage (for example, 24V) for a high voltage circuit. The switching element can be an N-type power metal oxide semi-transistor. The drain of the N-type power MOSFET is coupled to the input terminal and the source of the N-type power MOSFET is coupled to the output terminal. The voltage difference circuit receives the voltage at the output terminal to generate a first signal, wherein the first signal is greater than the voltage at the output terminal. The difference between the first signal and the voltage of the output terminal may be a predetermined value Vp, wherein the predetermined value Vp may be a relatively small value (for example, about 20 mV). The operational amplifier has a non-inverting input terminal coupled to the input terminal and an inverting input terminal coupled to the first signal for generating a second signal to control the conduction state of the switching element.

When the switching element is in a normal operating state, the voltage at the input terminal is greater than the voltage at the output terminal. In order to speed up the determination of the reverse current, an embodiment of the present invention replaces the conventional comparator with the operational amplifier. When the switching element is in a light load mode, if the difference between the voltage of the input terminal and the voltage of the output terminal is too small, the operational amplifier will modulate the second signal so that the voltage of the input terminal and the voltage of the output terminal are different from each other. The voltage difference is maintained at least at the predetermined value Vp. At this time, the on-resistance of the switching element is equal to Vp/Isw. When the load of the switching element is lighter, it means that the on-resistance of the switching element is greater. When the switching element is in a no-load mode, the switching element will be turned off, so no reverse current will be generated. Therefore, through the combination of the operational amplifier and the voltage difference circuit, when the switching element is in the light load mode, the switching unit can activate a reverse current protection mechanism early to reduce the reverse current by modulating the on-resistance of the switching element. Current.

10: Switch unit

Isw: Switching current

100: switching element

110: Comparator

120: control circuit

Vi: input

Vo: output

Vc: control signal

20: Switch unit

200: switching element

210: Operational amplifier

220: Voltage difference circuit

V1: The first signal

V2: second signal

Figure 1 is a schematic diagram of a conventional switch unit.

Figure 2 is a schematic diagram of a switch unit according to an embodiment of the present invention.

The following description will make the purpose, features, and advantages of the present invention more obvious. The preferred embodiments according to the present invention will be described in detail with reference to the drawings.

Figure 2 is a schematic diagram of a switch unit 20 according to an embodiment of the present invention. The switch unit 20 has an input terminal Vi, an output terminal Vo, a switching element 200, an operational amplifier 210, and a voltage difference circuit 220. The switching element 200 is coupled between the input terminal Vi and the output terminal Vo. The switching element 200 has a switching current Isw, where the switching current Isw refers to a current flowing from the input terminal Vi through the switching element 200 to the output terminal Vo. The input terminal Vi can have a high voltage (for example, 24V) for a high voltage circuit. As shown in Figure 2, the switching element 200 can be an N-type power MOSFET. The drain of the N-type power MOSFET is coupled to the input terminal Vi and the source of the N-type power MOSFET is coupled to the output terminal Vo. The voltage difference circuit 220 receives the voltage at the output terminal Vo to generate a first signal V1, wherein the first signal V1 is greater than the voltage at the output terminal Vo. According to an embodiment of the present invention, the difference between the voltage of the first signal V1 and the output terminal Vo may be a predetermined value Vp, wherein the predetermined value Vp may be a relatively small value (for example, about 20 mV). The operational amplifier 210 has a non-inverting input terminal coupled to the input terminal Vi and an inverting input terminal coupled to the first signal V1 for generating a second signal V2 to control the conduction of the switching element 200.

Specifically, when the switching element 200 is in a normal operating state, the voltage at the input terminal Vi is greater than the voltage at the output terminal Vo. In order to speed up the determination of the reverse current, an embodiment of the present invention replaces the conventional comparator with an operational amplifier 210. When the switching element 200 is in a light load mode, if the difference between the voltage at the input terminal Vi and the voltage at the output terminal Vo is too small, the operational amplifier 210 will modulate the second signal V2 The difference between the voltage at the input terminal Vi and the voltage at the output terminal Vo is maintained at least at the predetermined value Vp. At this time, the on-resistance of the switching element 200 is equal to Vp/Isw. When the load of the switching element 200 is lighter, it means that the on-resistance of the switching element 200 is greater. When the switching element 200 is in a no-load mode, the switching element 200 will be turned off, so no reverse current will be generated. Therefore, through the combination of the operational amplifier 210 and the voltage difference circuit 220, when the switching element 200 is in the light load mode, the switching unit 20 can activate a reverse current protection mechanism early by modulating the on-resistance of the switching element 200 to reduce the reverse current. Current.

According to an embodiment of the present invention, when the switching element 200 is in the light load mode, the switching unit 20 can activate the reverse current protection mechanism early. When the switching element 200 is in the no-load mode, the switching element 200 will be turned off, so no reverse current will be generated. In addition, the switch unit 20 can be applied to a high-voltage circuit.

Although the present invention has been described with the preferred embodiment as an example, it should be understood that the present invention is not limited to the disclosed embodiment. On the contrary, the present invention is intended to cover various modifications and similar configurations that are obvious to those familiar with the art. Therefore, the scope of the patent application should be based on the broadest interpretation to include all such modifications and similar configurations.

The foregoing descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made in accordance with the scope of the patent application of the present invention shall fall within the scope of the present invention.

20: Switch unit

Isw: Switching current

200: switching element

210: Operational amplifier

220: Voltage difference circuit

V1: The first signal

V2: second signal

Vi: input

Vo: output

Claims (10)

A switch unit includes: an input terminal; an output terminal; a switch element coupled between the input terminal and the output terminal; a voltage difference circuit for receiving a voltage of the output terminal to generate a first signal, The first signal is greater than the voltage at the output terminal; and an operational amplifier, coupled to the input terminal and the first signal, is used to generate a second signal to control the switching element, and the switching unit is used to provide A reverse current protection. The switch unit described in item 1 of the scope of patent application, wherein the switch unit is applied to a high-voltage circuit. For the switch unit described in item 1 of the scope of patent application, when the switch element is in a no-load mode, the switch element is turned off. The switch unit described in the first item of the scope of patent application, wherein when the switch element is in a light load mode, the switch unit activates a reverse current protection mechanism early. The switching unit described in the first item of the scope of patent application, wherein the switching element is an N-type power metal oxide semi-transistor. The switch unit described in item 5 of the scope of patent application, wherein a drain of the N-type power MOSFET is coupled to the input terminal, and a source of the N-type power MOSFET is coupled to the output end. As for the switch unit described in claim 1, wherein a difference between the first signal and the voltage of the output terminal is a predetermined value. For the switch unit described in item 7 of the scope of patent application, the predetermined value is a relatively small value. For the switch unit described in item 7 of the scope of patent application, the predetermined value is about 20mV. For the switch unit described in item 7 of the scope of patent application, when the switch element is in a light load mode, if the difference between a voltage of the input terminal and the voltage of the output terminal is too small, the operational amplifier will The second signal is modulated so that the difference between the voltage at the input terminal and the voltage at the output terminal is maintained at least at the predetermined value.

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