Drive circuit

Abstract

To provide a drive circuit capable of preventing malfunction of a transistor that drives a load.SOLUTION: A drive circuit includes: a transistor having a power source side electrode to which an inductive load is connected, a ground side electrode and a control electrode; a first resistor connected to the control electrode; a line connected to the first resistor; a second resistor provided between the line and a ground; a first diode that has a cathode connected to the line and an anode and is connected in parallel with the second resistor; and a second diode having a cathode connected to the line and an anode. A capacitor in which a voltage for driving the transistor is generated is connected to the anode of the second diode.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a driving circuit. [Background technology]

[0002] BACKGROUND ART Igniters equipped with a transistor for driving a load such as an ignition device in an internal combustion engine of a vehicle or the like are known (see, for example, Patent Documents 1 to 4). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-176842 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-17512 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-45514 [Patent Document 4] Japanese Patent Application Publication No. 2023-43775 Summary of the Invention [Problem to be solved by the invention]

[0004] In some cases, a capacitor is connected to the output stage of a circuit that outputs a signal to control a transistor that drives a load. In such cases, when the transistor is turned off, the voltage on the ground side fluctuates, which can cause the capacitor to charge and discharge, potentially causing the transistor to malfunction.

[0005] The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a drive circuit that can prevent malfunction of a transistor that drives a load. [Means for solving the problem]

[0006] The drive circuit of the present invention, which solves the above-mentioned problems, comprises a transistor having a power supply side electrode to which an inductive load is connected, a ground side electrode, and a control electrode, a first resistor connected to the control electrode, a line connected to the first resistor, a second resistor provided between the line and ground, a first diode having a cathode and an anode connected to the line and connected in parallel to the second resistor, and a second diode having a cathode and an anode connected to the line, and a capacitor that generates a voltage for driving the transistor is connected to the anode of the second diode. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a drive circuit that can prevent malfunction of a transistor that drives a load. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram showing the configuration of an ignition system 1A using a general drive circuit 30A. [Figure 2] 1A and 1B are diagrams for explaining the operation of the ignition system 1A at the time of ignition. [Figure 3] 1 is a block diagram showing the configuration of an ignition system 1 using a drive circuit 30 of the present embodiment. [Figure 4] 10 is an explanatory diagram showing the state of the current flowing through the drive circuit 30 when the IGBT 32 is turned off. FIG. [Figure 5] 3 is a diagram for explaining the operation of the ignition system 1 at the time of ignition. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] At least the following matters will become clear from the description of this specification and the accompanying drawings.

[0010] In the following description, the same or equivalent components, members, etc. shown in each drawing will be denoted by the same reference numerals, and redundant explanations may be omitted as appropriate.

[0011] In this embodiment, unless otherwise specified, "connection" refers to a state in which two components are electrically connected. Therefore, "connection" includes not only cases in which two components are connected by wiring, but also cases in which two components are connected by, for example, resistors or terminals.

[0012] =====This embodiment===== Gasoline-fueled internal combustion engines for vehicles use an ignition system that ignites a mixture of fuel and air filled in the combustion chamber of the internal combustion engine at a predetermined timing to cause combustion.

[0013] Such an ignition system is provided with an igniter having a transistor that drives an ignition coil, such as an IGBT (Insulated Gate Bipolar Transistor).

[0014] Before describing the ignition system of this embodiment, a general ignition system (reference example) will be described.

[0015] <<<Reference example>>> 1 is a block diagram showing the configuration of an ignition system 1A using a general drive circuit 30A. The drive circuit 30A corresponds to an igniter for controlling ignition of an internal combustion engine. Hereinafter, the drive circuit 30A will also be referred to as the igniter 30A.

[0016] The ignition system 1A is for an internal combustion engine mounted on a vehicle, and includes an ECU (Electronic Control Unit) 10, an ignition device 20, and an igniter 30A.

[0017] <ecu10> The ECU 10 is a device that performs electronic control of the internal combustion engine, and includes a microcomputer 12, a PNP transistor Q1, and a capacitor C1.

[0018] A predetermined power supply voltage (e.g., 5 V) is applied to the emitter electrode of the PNP transistor Q1. The collector electrode of the PNP transistor Q1 is connected to a gate terminal (described later) of an igniter (here, igniter 30A) and is grounded via a capacitor C1.

[0019] The microcomputer 12 controls the on / off of the PNP transistor Q1 at appropriate ignition timing. Specifically, the microcomputer 12 outputs a high-level (hereinafter referred to as H level) or low-level (hereinafter referred to as L level) signal to the base electrode of the PNP transistor Q1. When the output of the microcomputer 12 is H level, the PNP transistor Q1 is turned off. When the PNP transistor Q1 is turned off, the capacitor C1 is not charged (as will be described later, the capacitor C1 is discharged via the igniter 30A). On the other hand, when the output of the microcomputer 12 is L level, the PNP transistor Q1 is turned on. When the PNP transistor Q1 is turned on, the capacitor C1 is charged.

[0020] The ECU 10 then outputs the voltage of the collector electrode of the PNP transistor Q1 (in other words, the charging voltage of the capacitor C1) to the igniter (here, the igniter 30A). An IGBT 32 (described later) of the igniter 30A is driven based on the output signal (hereinafter referred to as a control signal) from the ECU 10. That is, a voltage for driving the IGBT 32 is generated in the capacitor C1. The control signal also serves as a power supply voltage for the internal circuits of the igniter 30A (such as a control circuit 34 described later).

[0021] <Ignition device 20> The ignition device 20 is a device for igniting the air-fuel mixture in the combustion chamber of the internal combustion engine, and includes an ignition coil 22, a DC power supply 23, and an ignition plug 24.

[0022] The ignition coil 22 has a primary coil L1 and a secondary coil L2 with a larger number of windings than the primary coil L1. The ignition coil 22 is also called an ignition coil and corresponds to an "inductive load." However, the winding ratio is not limited to this.

[0023] One end of each of the primary coil L1 and the secondary coil L2 is connected to a positive terminal of a DC power supply 23. The negative terminal of the DC power supply 23 is grounded.

[0024] The other end of the primary coil L1 is connected to a C terminal (described later) of the igniter 30A.

[0025] The other end of the secondary coil L2 is connected to one electrode of the spark plug 24. The other electrode of the spark plug 24 is grounded.

[0026] An electromotive force (mutually induced electromotive force) is generated in the secondary coil L2 of the ignition coil 22 in response to the electromotive force generated in the primary coil L1. The secondary coil L2 then supplies the generated electromotive force to the spark plug 24, causing the spark plug 24 to discharge.

[0027] The DC power supply 23 is, for example, a vehicle battery, and supplies a voltage (for example, 12 V) to one end of the primary coil L1 and the secondary coil L2 of the ignition coil 22.

[0028] The spark plug 24 generates an electrical spark by discharging electricity. The spark plug 24 discharges electricity when a voltage of, for example, about 10 kV or more is applied thereto.

[0029] <Igniter 30A> The igniter 30A is a drive circuit that drives the ignition coil 22 based on instructions from the ECU 10. As shown in Fig. 1, the igniter 30A includes an IGBT 32, a control circuit 34, resistors R1 to R3, an NMOS transistor M1, a diode D1, a Zener diode ZD1, and a line LN. The igniter 30A also includes three terminals (a gate (G) terminal, a collector (C) terminal, and an emitter (E) terminal) corresponding to three electrodes (described below) of the IGBT 32. The igniter 30A is configured as a semiconductor integrated circuit, and is a so-called one-chip igniter in which the IGBT 32 and elements that control it are formed on the same substrate (i.e., on the same chip).

[0030] The IGBT 32 is an element for driving the ignition coil 22, and has a gate electrode, a collector electrode, and an emitter electrode. The collector electrode is connected to the ignition coil 22 (specifically, the primary coil L1) via a C terminal. The emitter electrode is grounded via an E terminal. The IGBT 32 corresponds to a "transistor." The gate electrode of the IGBT 32 corresponds to a "control electrode," the collector electrode corresponds to a "power supply electrode," and the emitter electrode corresponds to a "ground electrode." Here, an IGBT is used as the transistor, but this is not limiting, and a MOSFET, for example, may also be used. In the case of a MOSFET, the drain electrode corresponds to a power supply electrode and the source electrode corresponds to a ground electrode.

[0031] Resistor R1 is a high resistance (e.g., 10 kΩ) resistor that reduces the slope of the voltage applied to the gate electrode of IGBT 32 to prevent overshoot due to a steep rise in the collector terminal voltage. One end of resistor R1 is connected to the gate electrode of IGBT 32, and the other end is connected to line LN. Resistor R1 corresponds to the "first resistor."

[0032] The diode D1 is a speed-up diode that accelerates the turn-off of the IGBT 32. The anode of the diode D1 is connected to the gate electrode of the IGBT 32, and the cathode is connected to the line LN. In other words, the diode D1 has an anode connected to the gate electrode of the IGBT 32 and a cathode connected to the line LN, and is connected in parallel to the resistor R1. The diode D1 corresponds to a "third diode."

[0033] Resistor R2 is a pull-down resistor with a high resistance value (1 kΩ or more: for example, 3 kΩ) and is connected between line LN and terminal E (ground). Resistor R2 corresponds to the "second resistor."

[0034] The Zener diode ZD1 is an element that clamps an unintentional high voltage applied from the ECU 10 to a predetermined voltage (e.g., 7 V) to protect the control circuit 34, the NMOS transistor M1, and the like. Furthermore, the diode's parasitic capacitance absorbs high-frequency noise superimposed on the control signal from the ECU 10, preventing unintentional on / off of the IGBT 32. The cathode of the Zener diode ZD1 is connected to the line LN, and the anode is connected to the E terminal. In other words, the Zener diode ZD1 has a cathode connected to the line LN and an anode connected to the E terminal, and is connected in parallel to the resistor R2. The Zener diode ZD1 corresponds to the "first diode."

[0035] The source electrode of the NMOS transistor M1 is connected to the gate electrode of the IGBT 32, and the drain electrode is connected (grounded) to the terminal E. In addition, the output of a control circuit 34, which will be described later, is applied to the gate electrode of the NMOS transistor M1.

[0036] The control circuit 34 controls the NMOS transistor M1 to protect the IGBT 32 from overcurrent and overheating. The control circuit 34 receives the voltage from the line LN as a power source. A current-detecting resistor R3 is connected between the current sense terminal of the IGBT 32 and the E terminal. The voltage at the node between the current sense terminal of the IGBT 32 and the resistor R3 is input to the control circuit 34. When the IGBT 32 experiences an overcurrent, the control circuit 34 turns the NMOS transistor M1 on. This causes the gate electrode of the IGBT 32 to be at ground level, turning the IGBT 32 off. The igniter 30A also includes a temperature sensor (not shown), and when the temperature exceeds a predetermined level, the control circuit 34 turns the NMOS transistor M1 on. This turns the IGBT 32 off. This provides protection from overcurrent and overheating.

[0037] <About the operation of ignition system 1A> 2 is a diagram for explaining the operation of the ignition system 1A at the time of ignition. In Fig. 2, the gate terminal voltage indicates the voltage at the G terminal, the primary current indicates the current flowing through the primary coil L1 of the ignition coil 22, and the collector terminal voltage indicates the voltage at the C terminal.

[0038] Hereinafter, the operation of the ignition system 1A at the time of ignition will be described with reference to FIGS.

[0039] At time t0, the microcomputer 12 of the ECU 10 outputs an L-level signal to the base electrode of the PNP transistor Q1, and the PNP transistor Q1 is turned on.

[0040] When the PNP transistor Q1 is turned on, the G terminal of the igniter 30A becomes H level (a control signal of H level is input to the igniter 30A). Also, when the PNP transistor Q1 is turned on, the capacitor C1 is charged.

[0041] The control signal input to the igniter 30A is applied to the gate electrode of the IGBT 32 via the line LN and the resistor R1. As a result, the gate voltage of the IGBT 32 exceeds the threshold, turning on the IGBT 32 and causing a primary current to flow through the primary coil L1. Specifically, a current flows through the path of the DC power supply 23 → the primary coil L1 → the terminal C → the IGBT 32 → the terminal E → ground, and energy is stored in the ignition coil 22. Furthermore, when the line LN goes high, a power supply voltage is supplied to the control circuit 34 of the igniter 30A, and the control circuit 34 operates (monitoring the voltage at the connection node between the IGBT 32 and the resistor R3).

[0042] At time t1, the microcomputer 12 of the ECU 10 outputs an H-level signal to the base electrode of the PNP transistor Q1, turning off the PNP transistor Q1. Even when the PNP transistor Q1 turns off, the voltage at the G terminal (in other words, the voltage on the line LN) does not immediately reach zero but gradually decreases due to the charge stored in the capacitor C1 and the gate capacitance of the IGBT 32. The charge stored in the capacitor C1 is discharged through the G terminal → resistor R2 → E terminal → ground (the path indicated by the dashed arrow in Figure 1). The gate capacitance of the IGBT 32 flows through the diode D1 → resistor R2 → E terminal → ground.

[0043] Then, just before time t2, the gate voltage of the IGBT 32 falls below a threshold value (e.g., 2 V), turning the IGBT 32 off. This cuts off the primary current flowing through the primary coil L1, causing the primary current to begin to drop sharply. Following this drop in the primary current in the primary coil L1, the voltage across the primary coil L1 rises (see the voltage at terminal C in the diagram). At this time, a secondary voltage corresponding to the coil winding ratio is generated across the secondary coil L2.

[0044] Then, at time t3, the secondary voltage reaches a predetermined value (for example, several tens of kV), causing discharge in the spark plug 24. When the spark plug 24 discharges, the high voltage generated on the secondary side changes abruptly.

[0045] At that time, due to parasitic components such as the parasitic inductance of the emitter wiring and the parasitic capacitance between wirings, as shown in FIG. 1, the voltage of the E terminal may oscillate in the MHz order. Further, following the oscillation of the E terminal, as shown in FIG. 2, the G terminal and the C terminal also oscillate.

[0046] During the period when the voltage of the E terminal > the voltage of the G terminal, as shown by the solid-line arrow in FIG. 1, current flows through the path of E terminal → Zener diode ZD1 → G terminal → capacitor C1 → ground. That is, in order to charge the capacitor C1, the voltage of the G terminal rises. Note that by connecting a resistor R1 with a high resistance (for example, 10 kΩ) to the gate electrode of the IGBT32, current flowing through the gate electrode of the IGBT32 via the Zener diode ZD1 can be suppressed during this period.

[0047] On the other hand, during the period when the voltage of the E terminal < the voltage of the G terminal, as shown by the dashed-line arrow in FIG. 1, current flows through the path of capacitor C1 → G terminal → resistor R2 → E terminal → ground, and the charge of the capacitor C1 is discharged. At this time, since the resistor R2 has a high resistance (for example, 3 kΩ), the time required for discharge is longer than the charging time. Therefore, by repeating the oscillation, the voltage of the G terminal gradually rises.

[0048] As a result, at the time t4 when the oscillation subsides, the voltage of the G terminal becomes high, and the IGBT32 that should be turned off is turned on, and a primary current flows through the primary coil L1. Thus, there is a possibility that a malfunction occurs in which the IGBT32 is turned on after the discharge of the spark plug 24.

[0049] Therefore, in the present embodiment, malfunction is prevented even when the voltage of the E terminal oscillates during the discharge of the spark plug 24.

[0050] <<<This Embodiment>>> FIG. 3 is a block diagram showing the configuration of the ignition system 1 using the drive circuit 30 of the present embodiment. Note that the drive circuit 30 is also referred to as an igniter 30.

[0051] The ignition system 1 is used for an internal combustion engine mounted on an automobile or the like, similar to the ignition system 1A of the reference example, and includes an ECU 10, an ignition device 20, and an igniter 30.

[0052] <Configuration of Igniter 30> The igniter 30 differs from the igniter 30A of the reference example (FIG. 1) in that it includes a Zener diode ZD2. Note that the igniter 30, like the igniter 30A, is configured with a semiconductor integrated circuit.

[0053] The cathode of the Zener diode ZD2 is connected to the line LN and also to the cathode of the Zener diode ZD1, and the anode is connected to the G terminal. That is, the Zener diode ZD2 has a cathode connected to the line LN and an anode connected to the capacitor C1 that generates a voltage for driving the IGBT 32. The Zener diode ZD2 corresponds to the "second diode."

[0054] The Zener diode ZD2 is the same type of diode (Zener diode) as the Zener diode ZD1 and can be formed using the same semiconductor process as the Zener diode ZD1, which can suppress increases in the number of steps and costs required to form the Zener diode ZD2.

[0055] The forward voltage of the Zener diode ZD2 is, for example, 0.3 V, which is preferably smaller than the forward voltage (0.7 V) of a typical diode. This makes it possible to prevent the voltage applied to the gate electrode of the IGBT 32 from decreasing.

[0056] Furthermore, by providing the Zener diode ZD2, it is possible to prevent malfunctions such as the IGBT 32 being turned on at an unintended timing after the spark plug 24 discharges, as will be described later.

[0057] <About the operation of Ignition System 1> FIG. 4 is an explanatory diagram showing the state of the current flowing through the drive circuit (igniter) 30 when the IGBT 32 is turned off. FIG. 5 is a diagram for explaining the operation of the ignition system 1 at the time of ignition. Each of the times t10 to t14 in FIG. 5 corresponds to the times t0 to t4 in FIG. 2.

[0058] Hereinafter, the operation of the ignition system 1 of the present embodiment will be described with reference to FIGS. 4 and 5. Up to time t3, since it is the same as FIG. 2 of the reference example, the description is omitted. In the present embodiment, by providing the Zener diode ZD2, the voltage of the gate electrode of the IGBT 32 is lower by the forward voltage of the Zener diode ZD2 compared to the reference example. Therefore, in actuality, a slight deviation occurs after the time (time t12) when the IGBT 32 is turned off, but this deviation is ignored.

[0059] Also in the present embodiment, when the ignition plug 24 discharges (time t13), the voltage of the E terminal vibrates as shown in FIG. 4.

[0060] During the period when the voltage of the E terminal < the voltage of the G terminal, as indicated by the dashed arrow in FIG. 4, current flows through the path of capacitor C1 → G terminal → Zener diode ZD2 → resistor R2 → E terminal → ground. That is, the charge of the capacitor C1 is discharged.

[0061] On the other hand, during the period when the voltage of the E terminal > the voltage of the G terminal, as indicated by the solid arrow in FIG. 4, the current is stopped by the Zener diode ZD2, so the capacitor C1 is not charged.

[0062] Therefore, even when the E terminal vibrates, the capacitor C1 is not charged and only discharge occurs. For this reason, as shown in FIG. 5, at time t4 when the vibration subsides, the voltage of the G terminal is almost zero (the IGBT 32 is not turned on). Also, since the IGBT 32 is not turned on, no primary current flows through the primary coil L1.

[0063] In this way, in the igniter 30 of this embodiment, the Zener diode ZD2 is provided, so that it is possible to prevent the IGBT 32 from being turned on (malfunction) at an unintended timing.

[0064] ===Summary=== The drive circuit (igniter) 30 of this embodiment has been described above. The igniter 30 includes an IGBT 32, resistors R1 and R2, Zener diodes ZD1 and ZD2, and a line LN. The collector electrode of the IGBT 32 is connected to the primary coil L1 of the ignition coil 22. The gate electrode of the IGBT 32 is connected to a resistor R1, which is connected to the line LN. The resistor R2 is connected between the line LN and ground. The Zener diode ZD1 has a cathode connected to the line LN and an anode, and is connected in parallel to the resistor R2. The Zener diode ZD2 has a cathode connected to the line LN and an anode, and a capacitor C1, which generates a voltage for driving the IGBT 32, is connected to the anode. This prevents the capacitor C1 from being charged via the Zener diode ZD1 when the emitter electrode of the IGBT 32 vibrates, thereby preventing the IGBT 32 from malfunctioning and turning on at an unintended timing.

[0065] Furthermore, it is preferable that the forward voltage of the Zener diode ZD2 is smaller than the forward voltage (0.7 V) of a typical diode, which makes it possible to suppress a drop in the gate voltage when the IGBT 32 is turned on, for example.

[0066] Furthermore, the igniter 30 is configured with a semiconductor integrated circuit, and the Zener diodes ZD1 and ZD2 are formed in the same semiconductor process (they are the same type of diodes), which allows the Zener diode ZD2 to be provided without increasing the number of steps or costs.

[0067] Furthermore, each element (IGBT 32, resistors R1 and R2, Zener diodes ZD1 and ZD2, and line LN) that constitutes igniter 30 is formed in a semiconductor integrated circuit, which allows igniter 30 to be formed on the same substrate (e.g., a silicon substrate) (a one-chip igniter can be realized).

[0068] The igniter 30 has an anode connected to the gate electrode of the IGBT 32 and a cathode connected to the line LN, and includes a diode D1 connected in parallel to a resistor R1, the resistance value of which is greater than the resistance value of a resistor R2. The large resistance value of the resistor R1 can prevent current from flowing to the gate electrode of the IGBT 32 via the Zener diode ZD1, for example, when the voltage at the E terminal fluctuates (when the voltage at the E terminal is greater than the voltage at the G terminal). When turning off the IGBT 32, charge can be removed from the gate electrode via the diode D1 and the resistor R2, allowing the IGBT 32 to be turned off quickly.

[0069] The ignition coil 22 is an ignition coil, and the drive circuit 30 is an igniter for controlling ignition of the internal combustion engine, thereby making it possible to prevent malfunctions such as ignition at unintended timing in the internal combustion engine.

[0070] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. Furthermore, the present invention may be modified or improved without departing from the spirit thereof, and the present invention includes equivalents thereof.

[0071] Although the igniter 30 in the above-described embodiment is provided with the Zener diode ZD2, a type of diode other than a Zener diode (for example, a rectifier diode or a Schottky barrier diode) may be used. However, if the Zener diode ZD2 is provided, as described above, it can be formed using the same semiconductor process as the Zener diode ZD1, thereby suppressing increases in labor and costs. Furthermore, since the Zener diode has a smaller forward voltage than a rectifier diode, it can suppress a drop in the voltage applied to the gate electrode of the IGBT 32.

[0072] Furthermore, although the igniter 30 in the above-described embodiment is configured as a semiconductor integrated circuit, the present invention is not limited to this, and a part or the whole of the igniter 30 does not have to be configured as a semiconductor integrated circuit. [Explanation of symbols]

[0073] 1,1A ignition system 10 ECU 12 Microcomputer 20 Ignition system 22 Ignition coil 23 DC power supply 24 Spark plug 30,30A drive circuit (igniter) 32 IGBT 34 Control circuit C1 capacitor Q1 PNP transistor M1 NMOS transistor R1~R3 ​​resistance D1 Diode ZD1, ZD2 Zener diodes LN Line L1 primary coil L2 secondary coil

Claims

1. a transistor having a power supply electrode connected to an inductive load, a ground electrode, and a control electrode; a first resistor connected to the control electrode; a line connected to the first resistor; a second resistor provided between the line and ground; a first diode having a cathode connected to the line and an anode connected in parallel with the second resistor; a second diode having a cathode connected to the line and an anode; Equipped with The anode of the second diode is A capacitor is connected to generate a voltage for driving the transistor. Drive circuit.

2. 2. The drive circuit of claim 1, The forward voltage of the second diode is less than 0.7V. Drive circuit.

3. 2. The drive circuit of claim 1, the drive circuit is configured by a semiconductor integrated circuit, the first and second diodes are formed in the same semiconductor process; Drive circuit.

4. 4. The drive circuit according to claim 3, the first and second diodes, the first and second resistors, and the transistor; is formed in the semiconductor integrated circuit, Drive circuit.

5. 2. The drive circuit of claim 1, a third diode having an anode connected to the control electrode and a cathode connected to the line, the third diode being connected in parallel with the first resistor; The resistance value of the first resistor is greater than the resistance value of the second resistor. Drive circuit.

6. The drive circuit according to any one of claims 1 to 5, the inductive load is an ignition coil, The drive circuit is an igniter for controlling ignition of an internal combustion engine. Drive circuit.

Images