Switching circuit

Abstract

The invention relates to a switching circuit (200) comprising a first and a second terminal (200A, 200B) and a control terminal (200C). A switching circuit (200) includes an integrated circuit (210) including a power supply terminal (210A), first and second output terminals (210B, 210C), first and second control terminals (210D, 210E), first and second MOSFETs (211, 212), and a control circuit (213). The source of each MOSFET (211, 212) is connected to a power supply terminal (210A). The drains of the first and second MOSFETs (211, 212) are connected to the first and second output terminals (210B, 210C) and then to the first and second terminals (200A, 200B). A control circuit (213) has first and second inputs connected to the first and second control terminals (210D, 210E) and then to the control terminals, and first and second outputs connected to the gates of the first and second MOSFETs (211, 212).

Description

Technical Field

[0001] This invention relates to a switching circuit, and more particularly to a switching circuit that prevents current backflow. Background Technology

[0002] MOSFETs are currently used in power switches. To prevent reverse current caused by a body diode between the source and drain, it is known to mount two MOSFETs back-to-back, such that current flows through the channels of both MOSFETs only when both MOSFETs are controlled to be "on". P-channel MOSFETs are easy to use due to their negative gate polarization, but P-channel MOSFETs have lower conductivity and are more expensive than N-channel MOSFETs. N-channel MOSFETs require additional control circuitry to control the MOSFET gate at the appropriate voltage, which requires more components.

[0003] Integrated circuits (ICs) can provide power switches that connect the output to the IC's power supply via an N-channel MOSFET. Several switches can be integrated in parallel on the same chip. However, traditional IC integrated switches cannot provide reverse current protection because the body diode is naturally forward biased with respect to the power supply. Therefore, such switches are inefficient in preventing current backflow that may occur when the switching load is inductive. Summary of the Invention

[0004] This invention changes the conventional use of power switches in integrated circuits to fabricate backflow prevention switching devices using the output MOSFETs of two power switches. This solution enables a significant reduction in the size of backflow prevention switching devices without requiring the design of specific integrated components. This invention provides a switching circuit including a first terminal, a second terminal, and a control terminal configured to receive a control signal for controlling an electrical connection between the first terminal and the second terminal, wherein the switching circuit includes an integrated circuit comprising at least: - Power terminals, - First output terminal and second output terminal - First control terminal and second control terminal - Connect to the grounding terminal for grounding voltage. - A first MOSFET and a second MOSFET, each having a drain, a source, and a gate, the source of the first MOSFET and the second MOSFET being connected to the power supply terminal, the drain of the first MOSFET being connected to the first output terminal and then to the first terminal, and the source of the second MOSFET being connected to the second output terminal and then to the second terminal. - A control circuit having a first input, a second input, a first output, and a second output, the first input and the second input being connected to the first control terminal and the second control terminal and then to the control terminal, the first output and the second output being connected to the gates of the first MOSFET and the second MOSFET (211, 212), the control circuit (213) controlling the gates of the MOSFETs (211, 212) according to the control signal.

[0005] When the integrated circuit is not adequately protected against overvoltage, the switching circuit may further include a first Zener diode connected in parallel between the first output terminal and the second output terminal. For the same reason, the switching circuit may further include a second Zener diode connected in parallel between the first output terminal and ground voltage.

[0006] Preferably, when the first terminal is connected to the battery, the threshold voltage of the second Zener diode must be higher than the nominal voltage of the battery (100).

[0007] When the second terminal is connected to a circuit with an inductive input, the threshold of the first Zener diode can be equal to the maximum voltage supplying the integrated circuit minus the nominal voltage of the battery.

[0008] In a preferred embodiment, the power supply terminal can be connected to the ground voltage via a capacitor, which is charged via a first terminal or a second terminal.

[0009] This invention is particularly significant for automotive applications, and further provides an automotive lighting device comprising light-emitting diodes connected to an LED driver intended to be powered by a vehicle battery. The automotive lighting device includes a switching circuit according to the invention connected between the battery and the LED driver, with a first terminal intended to be connected to the battery and a second terminal connected to the LED driver.

[0010] Preferably, the switching circuit and the LED driver are integrated on the same printed circuit board.

[0011] According to another aspect, the present invention provides a printed circuit board for an automotive lighting device, the printed circuit board including an LED driver and a switching circuit according to the invention, wherein the switching circuit is connected to the LED driver and is intended to be connected to a battery. Attached Figure Description

[0012] The invention will be described in detail with reference to the accompanying drawings, in which: Figure 1 This is a block diagram showing a circuit including the present invention, and Figure 2 This is an electrical diagram that details a preferred embodiment of the present invention. Detailed Implementation

[0013] Figure 1 A circuit is shown in which a switching circuit according to the present invention is used. Figure 1 The circuit includes a battery 100, a switching circuit 200, a DC / DC converter 300, and a load 400. This circuit can be used in many applications.

[0014] In a preferred embodiment, Figure 1 The circuit is the circuitry for a vehicle's lighting system. Battery 100 may be a 12V battery for vehicle accessories. Load 400 may be an LED constituting the headlight source of the vehicle. DC / DC converter 300 may be an LED driver 300, for example, a boost converter providing controlled DC current using an inductor. Switching circuit 200, LED driver 300, and LED 400 may be integrated in housing 500 to form the lighting system. Switching circuit 200 may also be integrated on the same printed circuit board 350.

[0015] Figure 2 The switching circuit 200 of the present invention is described in detail. The switching circuit includes a first terminal 200A, a second terminal 200B, and a control terminal 200C. The first terminal 200A can be configured to receive power from the battery 100 as input. The control terminal 200C receives a control signal for controlling the electrical connection between the first terminal 200A and the second terminal 200B. Figure 2 The diagram shows the input of the DC / DC converter 300 connected to a second terminal 200B, which, as an example, includes an inductor 310 mounted in series with a switch 320. The first input 200A is connected to... Figure 1 The battery shown is 100.

[0016] The switching circuit 200 primarily includes an integrated circuit 210, which is an integrated multi-channel power switch designed to switch at least two outputs to provide or not provide current from the power source of the integrated circuit. As an example, this integrated circuit could be an IC of model number TPS2HB16-Q1 manufactured and sold by Texas Instruments, but it could also be any other component with the characteristic details described below.

[0017] Integrated circuit 210 includes a power supply terminal 210A and a ground terminal 210F designed to supply power to integrated circuit 210. The integrated circuit includes a first output terminal 210B and a second output terminal 210C, which correspond to the sources of a first MOSFET 211 and a second MOSFET 212 located within integrated circuit 210, respectively. The drains of both the first MOSFET 211 and the second MOSFET 212 are connected to the power supply terminal 210A. The gates of the first MOSFET 211 and the second MOSFET 212 are connected to an internal control circuit 213. Integrated circuit 210 further includes a first control terminal 210D and a second control terminal 210E connected to the internal control circuit 213. In an example embodiment, the MOSFET may be an n-channel MOSFET. The internal control circuit 210 provides electrical signals to the gates of the first MOSFET 211 and the second MOSFET 212 in response to signals received from the first control terminal 210D and the second control terminal 210E.

[0018] According to the present invention, a first output terminal 210B is connected to a first terminal 200A, and a second output terminal 210C is connected to a second terminal 200B. Power terminal 210A is left floating, while ground terminal 200F is connected to ground. Power to integrated circuit 210 is provided through a parasitic diode of one of the first MOSFET 211 and the second MOSFET 212. A first control terminal 210D and a second control terminal 210E are connected to control terminal 200C to receive the same control signal. This connection transforms integrated circuit 210 into a switch with two back-to-back MOSFETs simultaneously controlled by the control signal; however, the control circuit and MOSFETs are both part of integrated circuit 210, and its size is smaller than that of two discrete MOSFETs and a control circuit.

[0019] During normal use, the output voltage of battery 100 is higher than the input voltage of the DC / DC converter. The parasitic diode of the first MOSFET 211 is conductive, and integrated circuit 210 is powered by the battery. When a control signal triggers the switch to turn it on, the control circuit provides a voltage that makes the second MOSFET 212 conduct and establishes a contact between the first terminal 200A and the second terminal 200B.

[0020] Those skilled in the art will note that when the voltage is higher than the battery voltage at the input of the DC / DC converter 300, and the switch remains on, current can flow through the parasitic diode of the second MOSFET 212 to power the integrated circuit 210. Then, the control circuit 213 can provide an adaptation voltage to the gate of the first MOSFET 211, and current can flow through the channel of the first MOSFET 211. Therefore, the switch of the present invention can also be used in other applications, such as recharging the battery 100 when needed.

[0021] When the inductive load is off, the voltage at the input of the DC / DC converter 300 increases significantly, and the integrated circuit 210 is powered through the parasitic diode of the second MOSFET 212. However, when the control signal indicates the off state, the control circuit 213 provides a voltage on the gate of the first MOSFET 211, thereby turning off the channel so that current cannot flow back to the battery.

[0022] During the turn-off period, the voltage at the inductor terminals can be very high, potentially causing an arc between the switching terminals. Typically, integrated circuits include electrostatic discharge (ESD) protection capable of suppressing the arc by switching the input or output to ground. However, the current supplied by the inductor may still exceed the current corresponding to an ESD event. Therefore, ESD protection can be enhanced by a first Zener diode 220 and a second Zener diode 230. The first Zener diode 220 is connected between the first terminal 200A and the second terminal 200B. The second Zener diode 230 is connected between the first terminal 200A and ground. The second Zener diode 230 is configured such that it is connected in parallel with the first output terminal 210B of the integrated circuit 210 and the first Zener diode 220.

[0023] In the example embodiment, the threshold voltage of the second Zener diode 230 is higher than the nominal voltage of the battery and less than the breakdown voltage of the battery 100, thereby preventing the battery 100 from being subjected to incorrect overvoltage protection. The threshold voltage of the first Zener diode 220 is equal to the difference between the maximum voltage supplying integrated circuit 210 and the threshold voltage of the second Zener diode 230, in order to limit the voltage at the second terminal to a value corresponding to the maximum voltage of integrated circuit 210.

[0024] As indicated, power terminal 210A is floating. To prevent high-frequency signals from entering the power supply of integrated circuit 210, power terminal 210A is connected to ground via capacitor 240. Capacitor 240 is an HF filter, but also a power filter that is charged via first terminal 200A or second terminal 200B.

[0025] This invention is not limited to the disclosed examples. As indicated, the switching circuit of this invention is a bidirectional switch, and the load may be different from the LED and may be a motor. The indicated integrated circuit may be replaced with any other integrated circuit having the same output circuit and at least two MOSFETs connected to the power supply terminals.

[0026] Furthermore, those skilled in the art will understand that this circuit is not limited to automotive applications. The invention can be applied to many other configurations, for which current return can be achieved in abnormal conditions.

Claims

1. A switching circuit (200) comprising a first terminal (200A), a second terminal (200B), and a control terminal (200C), the control terminal being configured to receive a control signal for controlling an electrical connection between the first terminal and the second terminal (200A, 200B), wherein, The switching circuit (200) includes an integrated circuit (210), which includes at least: - Power supply terminal (210A). - First output terminal (210B) and second output terminal (210C). - First control terminal (210D) and second control terminal (210E). - Connect to the grounding terminal (210F) for grounding voltage. - A first MOSFET (211) and a second MOSFET (212), each of the first MOSFET and the second MOSFET (211, 212) having a drain, a source, and a gate, the source of the first MOSFET and the second MOSFET (211, 212) being connected to the power supply terminal (210A), the drain of the first MOSFET (211) being connected to the first output terminal (210B) and then to the first terminal (200A), and the source of the second MOSFET (212) being connected to the second output terminal (210C) and then to the second terminal (200B), and - Control circuit (213) having a first input, a second input, a first output and a second output, the first input and the second input being connected to the first control terminal and the second control terminal (210D, 210E) and then connected to the control terminal, the first output and the second output being connected to the gates of the first MOSFET and the second MOSFET (211, 212), the control circuit (213) controlling the gates of the MOSFETs (211, 212) according to the control signal.

2. The switching circuit (200) as claimed in claim 1 further includes a first Zener diode (220) connected in parallel between the first output terminal (210B) and the second output terminal (210C).

3. The switching circuit (200) as claimed in claim 2 further includes a second Zener diode (230) connected in parallel between the first output terminal (210B) and the ground voltage.

4. The switching circuit (200) as described in claim 3, wherein, The first terminal (200A) is connected to the battery (100), and the threshold of the second Zener diode (230) is higher than the nominal voltage of the battery (100) and lower than the breakdown voltage of the battery (100).

5. The switching circuit (200) as described in any one of claims 2 to 4, wherein, The second terminal (200B) is connected to a circuit (300) with an inductive input, and wherein the threshold of the first Zener diode (220) is equal to the difference between the maximum voltage supplying the integrated circuit (210) and the nominal voltage of the battery (100).

6. The switching circuit (200) as described in any one of claims 1 to 5, wherein, The power terminal (210A) is connected to the ground voltage via a capacitor (240), which is charged via the first terminal (200A) or the second terminal (200B).

7. An automotive lighting device (500) comprising a light-emitting diode (400) connected to an LED driver (300) intended to be powered by a battery (100) of a motor vehicle, wherein, The automotive lighting device includes a switching circuit (200) according to any one of claims 1 to 6, the switching circuit (200) being connected between the battery (100) and the LED driver (300), the first terminal (200A) being intended to be connected to the battery, and the second terminal (200B) being connected to the LED driver (300).

8. The automotive lighting device (500) as claimed in claim 7, wherein, The switching circuit (200) and the LED driver (300) are integrated on the same printed circuit board.

9. A printed circuit board (500) for an automotive lighting device, the printed circuit board comprising an LED driver (300) and a switching circuit (200) according to any one of claims 1 to 6, wherein, The switching circuit (200) is connected to the LED driver (300) and is intended to be connected to the battery (100).

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