JP2018191150A - Switching circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching circuit capable of constructing at a low cost.SOLUTION: A switching circuit comprises: a high-side switch Q1; a low side switching circuit 12 including a first low-side switch Q21 and a second low-side switch Q22 serially connected; a first bootstrap capacitor C1; a second bootstrap capacitor C2; a charging circuit 13 that includes a charging capacitor C3 which is charged when the first low-side switch Q21 is turned OFF and the second low-side switch Q22 is turned ON, and that charges the bootstrap capacitor C1 with the electric charge charged to the charging capacitor C3 when the first low-side switch Q21 is turned ON and the second low-side switch Q22 is turned OFF; and a low-side switch driving circuit 15 which alternately turns ON/OFF the first low-side switch Q21 and the second low-side switch Q22.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a switch circuit that is used, for example, for turning on / off a power supply line from a power source to a load device, and in particular, turning on / off a high side with an N channel MOS field effect transistor (FET).

  For example, in a switch circuit for turning on / off a power supply line for supplying power from a power source constituted by an assembled battery or the like to a load device using a high-side switch, a MOSFET is often used as the high-side switch. In such a switch circuit, the characteristics of the high side switch are required to have a high breakdown voltage, a large current, and a low ON resistance. In addition, MOSFETs satisfying such requirements have an overwhelmingly large number of N-channel MOSFETs in general-purpose products such as driver ICs that are generally distributed. Therefore, in the switch circuit as described above, an N-channel MOSFET is often used as a high-side switch.

  When an N-channel MOSFET is used as a high-side switch, in order to turn on the N-channel MOSFET, a voltage higher than the power supply voltage needs to be applied between the gate and the source due to its nature. For this reason, a gate drive circuit for a high-side switch including a charge pump circuit that generates a boosted voltage to be applied to the gate of the high-side switch is known as a conventional technique using an N-channel MOSFET as a high-side switch (for example, Patent Documents). 1 paragraphs 0006-0013, FIG. 3).

JP 2007-306708 A

  However, since the above-described conventional technology uses a P-channel MOSFET for the charge pump circuit, there is a case where a switch circuit cannot be configured using a general-purpose driver IC or the like, which makes it difficult to reduce the cost. is there.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a switch circuit that can be configured at low cost.

  The present invention includes a high-side switch, a low-side switch circuit including a first low-side switch and a second low-side switch connected in series, a first bootstrap capacitor that is a bootstrap capacitor of the high-side switch, 2 Charged while the low-side switch is ON, the second bootstrap capacitor that is the bootstrap capacitor of the first low-side switch, the first low-side switch is OFF, and the second low-side switch is ON A charging capacitor that is charged between the first bootstrap capacitor and the first bootstrap capacitor with the charge charged in the charging capacitor while the first low-side switch is on and the second low-side switch is off. A charging circuit for charging; Serial and high-side switch driver circuit the high-side switch to ON / OFF, and the low-side switch driving circuit for ON / OFF alternately the first said low side switch second low-side switch is a switch circuit comprising a.

  The first bootstrap capacitor, which is the bootstrap capacitor of the high side switch, is charged by alternately turning on / off the first low side switch and the second low side switch. Further, since the first low side switch and the second low side switch are alternately turned on / off and do not turn on at the same time, they can be turned on / off independently of the ON / OFF of the high side switch. Therefore, by repeating the operation of alternately turning on / off the first low-side switch and the second low-side switch with the high-side switch turned on, the high-side switch can be always turned on.

  The switch circuit according to the present invention further includes a second bootstrap capacitor that is a bootstrap capacitor of the first low-side switch. Therefore, the switch circuit according to the present invention can be configured using N-channel MOSFETs for the high-side switch, the first low-side switch, and the second low-side switch. Accordingly, the switch circuit according to the present invention can be easily configured at low cost using a general-purpose driver IC or the like.

  Furthermore, in the switch circuit according to the present invention, the charging capacitor and the second bootstrap capacitor are charged simultaneously by turning on the second low-side switch. That is, the second low-side switch doubles as a charging switch for the charging capacitor and a charging switch for the second bootstrap capacitor. Accordingly, the switch circuit according to the present invention can be efficiently configured with fewer circuit elements.

  As a result, according to the present invention, it is possible to provide an effect of providing a switch circuit that can be configured at low cost.

  ADVANTAGE OF THE INVENTION According to this invention, the switch circuit which can be comprised at low cost can be provided.

The circuit diagram of the switch circuit concerning the present invention. 3 is a timing chart illustrating the operation of the switch circuit according to the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In addition, this invention is not specifically limited to the Example demonstrated below, It cannot be overemphasized that a various deformation | transformation is possible within the range of the invention described in the claim.

The configuration of the switch circuit according to the present invention will be described with reference to FIG.
FIG. 1 is a circuit diagram of a switch circuit according to the present invention.

  The switch circuit according to the present invention includes a high-side switch Q1, a first bootstrap capacitor C1, a high-side driver 11, a low-side switch circuit 12, a charging circuit 13, a bootstrap circuit 14, and a low-side switch drive circuit 15.

  The high side switch Q1 is an N-channel MOSFET. The high side switch Q1 has a drain connected to the input power source Vin and a source connected to the output terminal Vout. That is, the high side switch Q1 is provided between the input power supply Vin and the output terminal Vout, and is a switch for turning on / off the power supply line from the input power supply Vin to the output terminal Vout.

  The high-side driver 11 as a “high-side switch drive circuit” is a driver that turns on / off the high-side switch Q1. The first bootstrap capacitor C1 is a bootstrap capacitor of a high side switch. The high side driver 11 has an input terminal connected to the signal input terminal P1, and an output terminal connected to the gate of the high side switch Q1. The high-side driver 11 has a positive power supply terminal connected to one end of the first bootstrap capacitor C1, and a negative power supply terminal connected to the source of the high-side switch Q1 and the other end of the first bootstrap capacitor C1. Has been.

  The low-side switch circuit 12 is a switch circuit provided on the low side, that is, a switch circuit provided between the output terminal Vout and the ground terminal GND. The low side switch circuit 12 includes a first low side switch Q21 and a second low side switch Q22 connected in series. The first low-side switch Q21 and the second low-side switch Q22 are both N-channel MOSFETs. The drain of the first low-side switch Q21 is connected to the output terminal Vout. The source of the first low side switch Q21 is connected to the drain of the second low side switch Q22. The source of the second low side switch Q22 is connected to the ground terminal GND.

  The charging circuit 13 includes two diodes D1 and D3 and a charging capacitor C3. The diode D1 has an anode connected to the logic power supply 5V and a cathode connected to one end of the charging capacitor C3. The diode D3 has an anode connected to one end of the charging capacitor C3 and a cathode connected to one end of the first bootstrap capacitor C1. The other end of the charging capacitor C3 is connected to a connection point between the source of the first low side switch Q21 and the drain of the second low side switch Q22. The charging capacitor C3 is preferably a capacitor having a capacity larger than that of the first bootstrap capacitor C1 in order to more stably maintain the high-side switch Q1 in the ON state.

  The bootstrap circuit 14 includes a diode D2 and a second bootstrap capacitor C2. The second bootstrap capacitor C2 is a bootstrap capacitor of the first low side switch Q21. The diode D2 has an anode connected to the logic power supply 5V and a cathode connected to one end of the second bootstrap capacitor C2. The other end of the second bootstrap capacitor C2 is connected to a connection point between the source of the first low side switch Q21 and the drain of the second low side switch Q22.

  The low side switch drive circuit 15 includes a first low side driver 151, a second low side driver 152, and an inverter 153. The first low-side driver 151 is a driver for turning on / off the first low-side switch Q21, and its output terminal is connected to the gate of the first low-side switch Q21. The first low-side driver 151 has a positive power supply terminal connected to one end of the second bootstrap capacitor C2, and a negative power supply terminal connected to the other end of the second bootstrap capacitor C2. The second low-side driver 152 is a driver that turns on / off the second low-side switch Q22, and has an input terminal connected to the signal input terminal P2 and an output terminal connected to the gate of the second low-side switch Q22. The second low-side driver 152 has a negative power supply terminal connected to the ground terminal GND. The inverter 153 is a NOT gate circuit that inverts the logic of the signal at the signal input terminal P2 and outputs the inverted signal to the first low side driver 151. The input terminal is connected to the signal input terminal P2, and the output terminal is the first low side driver 151. Connected to the input terminal.

Next, the operation of the switch circuit according to the present invention will be described with reference to FIG. 1 and with reference to FIG.
FIG. 2 is a timing chart illustrating the operation of the switch circuit according to the present invention.

  The low-side switch drive circuit 15 alternately turns on / off the first low-side switch Q21 and the second low-side switch Q22 in accordance with a signal input to the signal input terminal P2. While the first low-side switch Q21 is OFF and the second low-side switch Q22 is ON, the charging capacitor C3 is charged through the path illustrated by the symbol A in FIG. 1 and illustrated by the symbol B in FIG. The second bootstrap capacitor C2 is charged through the path (timing T1-T2, T3-T4, T5-T6, T7-T8 in FIG. 2). On the other hand, while the first low-side switch Q21 is ON and the second low-side switch Q22 is OFF, the charge charged in the charging capacitor C3 is transferred to the first bootstrap through the path indicated by the symbol C in FIG. The capacitor C1 is discharged to charge the first bootstrap capacitor C1 (timing T2 to T3, T4 to T5, T6 to T7, T8 to T9 in FIG. 2).

  That is, the first bootstrap capacitor C1, which is the bootstrap capacitor of the high side switch Q1, is charged by alternately turning on / off the first low side switch Q21 and the second low side switch Q22. After the first bootstrap capacitor C1 is charged until the voltage becomes equal to or higher than the predetermined voltage (after timing T9 in FIG. 2), the high side switch Q1 is turned on at a desired timing (timing T10 in FIG. 2) at any time. Can do.

  The first low-side switch Q21 and the second low-side switch Q22 are alternately turned on / off and do not turn on at the same time. Therefore, the operation of alternately turning on / off the first low-side switch Q21 and the second low-side switch Q22 can be repeated while the high-side switch Q1 is ON. As a result, the first bootstrap capacitor C1 is repeatedly charged while the high side switch Q1 is ON. Therefore, the voltage of the first bootstrap capacitor C1 is maintained at a predetermined voltage or higher to maintain the high side switch Q1. Can always be turned on.

  The switch circuit according to the present invention further includes a second bootstrap capacitor C2 that is a bootstrap capacitor of the first low-side switch Q21. Therefore, the switch circuit according to the present invention can be configured using N-channel MOSFETs for the high-side switch Q1, the first low-side switch Q21, and the second low-side switch Q22. Accordingly, the switch circuit according to the present invention can be easily configured at low cost using a general-purpose driver IC or the like.

  Further, in the switch circuit according to the present invention, the charging capacitor C3 and the second bootstrap capacitor C2 are simultaneously charged by turning on the second low-side switch Q22. That is, the second low-side switch Q22 serves both as a charging switch for the charging capacitor C3 and a charging switch for the second bootstrap capacitor C2. Accordingly, the switch circuit according to the present invention can be efficiently configured with fewer circuit elements.

DESCRIPTION OF SYMBOLS 11 High side driver 12 Low side switch circuit 13 Charging circuit 14 Bootstrap circuit 15 Low side switch drive circuit C1 1st bootstrap capacitor C2 2nd bootstrap capacitor C3 Charging capacitor Q1 High side switch Q21 1st low side switch Q22 2nd low side switch

Claims (1)

A high-side switch,
A low-side switch circuit including a first low-side switch and a second low-side switch connected in series;
A first bootstrap capacitor that is a bootstrap capacitor of the high-side switch;
A second bootstrap capacitor that is charged while the second low-side switch is ON and is a bootstrap capacitor of the first low-side switch;
Including a charging capacitor that is charged while the first low-side switch is OFF and the second low-side switch is ON, while the first low-side switch is ON and the second low-side switch is OFF A charging circuit for charging the first bootstrap capacitor with an electric charge charged in the charging capacitor;
A high-side switch driving circuit for turning on and off the high-side switch;
A switch circuit comprising: a low-side switch drive circuit that alternately turns on and off the first low-side switch and the second low-side switch.

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