JP2016089674A - Igniter and vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an igniter, capable of soft shut off with a small circuit scale.SOLUTION: A voltage comparator 302 compares a voltage V, which corresponds to an ignition signal IGT, to a reference voltage V, and generates a determination signal S. An overvoltage protection element 206 is provided between the gate and the emitter of a power transistor 204. A soft shut off circuit 320 becomes enable state if assert level state of a determination signal Scontinues over predetermined energization protection time T, and in the enable state, the circuit makes output of a driving stage 300B high impedance, and supplies a correction current Ito the gate of the power transistor 204.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an igniter that controls an ignition coil connected to an ignition plug of an engine.

  FIG. 1 is a perspective view of an engine room 101 of a gasoline engine vehicle (hereinafter also simply referred to as a vehicle) 100. The engine room 101 accommodates an engine 110, an intake manifold 112, an air cleaner 113, a radiator 114, a battery 102, and the like. FIG. 1 shows a four-cylinder engine.

  The engine 110 is provided with a plug hole (not shown) for each cylinder, and a spark plug (not shown) is inserted into the plug hole. Each cylinder of the engine 110 is supplied with a mixed gas of air that passes through the air cleaner 113 and the intake manifold 112 and fuel from a fuel tank (not shown). The engine is started and rotated by igniting (sparking) the spark plug at an appropriate timing.

  FIG. 2 is a block diagram of a part of the electric system of the vehicle 100r. The electric system of the vehicle 100r includes a battery 102, an ignition coil 104, a spark plug 106, an ECU 108, and an igniter 200. ECU 108 periodically generates an ignition signal IGT instructing the ignition timing of ignition plug 106 in synchronization with the rotation of engine 110. The secondary coil L2 of the ignition coil 104 is connected to the spark plug 106. The igniter 200 controls the current of the primary coil L1 of the ignition coil 104 in accordance with the ignition signal IGT, thereby generating a high voltage of several tens of kV in the secondary coil L2 and discharging the spark plug 106 to The air-fuel mixture in 110 is exploded.

The igniter 200 includes a switch element 202 and a switch control device 300r. Switch element 202 is, for example, an IGBT (Insulated Gate Bipolar Transistor), the collector of which is connected to primary coil L1, and the emitter of which is grounded. The switch control device 300r controls the voltage of the control terminal (gate) of the switch element 202 according to the ignition signal IGT, and controls the on / off of the switch element 202. Specifically, the switch control device 300r turns on the switch element 202 while the ignition signal IGT is at a high level. When switch element 202 is turned on, battery voltage _VBAT is applied across both ends of primary coil L1, and the current flowing through primary coil L1 increases with time. When the ignition signal IGT is changed to a low level, the switch control unit 300r is turning off the switch element 202 instantaneously interrupts the current _{I L1} of the primary coil L1. At this time, a primary voltage V _L1 (= L · dI _L1 / dt) of several hundred volts proportional to the time differentiation of the current I _L1 is generated in the primary coil L1. At this time, a secondary voltage V _{S of} several tens of kV obtained by multiplying the primary voltage V _L1 by the winding ratio is generated in the secondary coil L2.

The switch control device 300r mainly includes a determination stage 300A and a drive stage 300B. The determination stage 300A receives the ignition signal IGT from the ECU 108, and determines its level (high / low). For example determination stage 300A includes a voltage comparator 302 that the voltage _{V IN} of the input line 301 is compared with a predetermined reference voltage _{V REF,} and generates a determination signal _{S DET} of the high-low binary.

Driving stage 300B in response to the determination signal _{S DET,} it switches on the switching element 202, and off. The delay circuit 304 gives a predetermined delay to the determination signal _SDET . This delay amount is set so that the time difference (delay) between the transition of the ignition signal IGT and the discharge time of the spark plug becomes a predetermined value. The pre-driver 306 and the gate driver 308 control the gate voltage of the switch element 202 according to the output of the delay circuit 304.

JP 2011-185165 A JP 2014-051904 A

  When the ECU 108 operates normally, the ignition signal IGT changes to a low level after an appropriate time has elapsed after the ignition signal IGT has become a high level, and the ignition plug 106 is ignited. However, if any abnormality occurs in the ECU 108, the ignition signal IGT does not transition to the low level and continues to maintain the high level, and the switch element 202 continues to be turned on. As a result, problems may arise such that the heat generated by the switch element 202 increases and a large current flows through the primary coil L1 of the ignition coil 104.

In order to solve this problem, an energization protection circuit 310 is provided. Energization protection circuit 310, an ignition signal IGT is turned off forcibly switching element 202 with a predetermined energization protection time from the transition to the high level T _P has elapsed, in which ignites the spark plug 106. FIG. 3A is a waveform diagram for explaining the operation of the energization protection circuit 310. Ignition signal IGT is turned on switching elements 202 transits to the high level, (the collector current of the IGBT) coil current _{I C} is increased. The energization protection circuit 310 includes a timer, and the timer measures the time during which the ignition signal IGT (determination signal S _DET ) is at a high level. And when the set value is reached the count value of the timer corresponds to the energization protection time T _P (##), to force off the switch element 202, to cut off the coil current I _C. In this case, the forced interruption of the coil current _{I C,} greatly changes the voltage of the secondary coil L2 of the ignition coil 104 (secondary voltage _{V S)} is, the spark plug 106 is to be ignited.

Depending on the type of engine or ECU, ignition of the spark plug 106 when the switch element 202 is forcibly turned off may not be preferable. In this case, as shown in FIG. 3 (b), gently off the switch element 202 after a power protection time T _P, soft shutoff function to reduce the coil current I _C slowly is required.

To prevent ignition by turning off the switching element 202 with the current protection, it is necessary to reduce the coil current I _C tens ms~ several hundred ms ones over a timescale T _SSO, the switching element 202 for the It is necessary to reduce the gate voltage from a high level voltage (for example, 5 V) to a low level voltage (0 V) on a time scale of several tens ms to several hundreds ms.

  However, in order to generate such a long time constant, a high resistance of several tens of MΩ is required, or a capacitor of several nF is required. Integration of these elements in the semiconductor chip of the switch control device 300r is not realistic from the viewpoint of size, and requires an additional external chip component, which causes an increase in cost and area.

  The present invention has been made in view of the above problems, and one of the exemplary purposes of an embodiment thereof is to provide an igniter capable of soft shut-off with a small circuit scale.

  One embodiment of the present invention relates to an igniter. The igniter includes a switch element connected to the primary coil of the ignition coil, and a switch control device that controls the switch element in accordance with an ignition signal from an ECU (Engine Control Unit). The switch element includes a power transistor and an overvoltage protection element provided between the gate emitter of the power transistor. The switch control device compares the voltage according to the ignition signal with a reference voltage, generates a determination signal, and when the determination signal is an assert level corresponding to ON of the switch element, the gate of the power transistor is at a high level. When a voltage is applied and the determination signal is at a negate level corresponding to turning off of the switch element, a drive stage that applies a low level voltage to the gate of the power transistor and a state in which the determination signal is at the assert level are predetermined energization protection And a soft shut-off circuit that is in an enable state when it lasts for a period of time and in which the output of the drive stage has a high impedance and supplies a correction current to the gate of the power transistor.

According to this aspect, by discharging the gate capacitance (parasitic capacitance) due to the leakage current of the overvoltage protection element, the gate voltage can be reduced with a sufficiently long time constant with a small circuit scale without externally attaching a large capacitance capacitor or high resistance. The soft shut-off without ignition can be realized. Further, since the effective discharge current is the difference between the leak current and the correction current, the time constant can be adjusted by the correction current.
Gate, emitter, and collector are convenient names, and may be read as base, source, and drain, respectively, depending on the type of power transistor.

The overvoltage protection element may include an anti-series diode pair connected in anti-series.
Thereby, the surge withstand voltage between the gate and source of the power transistor can be increased in both positive and negative.
The overvoltage protection element may include a plurality of diode pairs connected in series.

  The soft shut-off circuit may include a current source that is turned on in the enable state and supplies a correction current to the gate of the power transistor in the on state.

  The correction current may be larger as the battery voltage supplied to the ignition coil is larger. The higher the battery voltage, the greater the amount of heat generated by the power transistor and the higher the temperature of the power transistor. Since the leakage current of the protection element has a positive temperature characteristic, variation in time constant can be suppressed by increasing the correction current as the temperature rises.

  The correction current may be larger as the ambient temperature of the igniter is higher. The higher the igniter ambient temperature, the higher the power transistor temperature baseline. Since the leakage current of the protective element has a positive temperature characteristic, variation in time constant can be suppressed by increasing the correction current as the temperature increases.

The driving stage includes a gate driver including a high-side transistor and a low-side transistor provided in series between a power supply line and a ground line, and a pre-driver that controls on / off of the high-side transistor and the low-side transistor according to a determination signal , May be included. The soft shut-off circuit may supply the correction current using the high side transistor in the enabled state.
In this case, since the high side transistor can be used as a current source for generating a correction current, the circuit scale can be reduced.

The igniter may further include a current detection circuit that generates a detection voltage corresponding to the coil current flowing through the power transistor. The switch control device may further include an overcurrent protection circuit that adjusts the gate voltage of the power transistor so that the detection voltage does not exceed a predetermined threshold voltage. The overcurrent protection circuit may be disabled in the enable state of the soft shutoff circuit.
By providing the overcurrent protection circuit, it is possible to prevent the coil current (the collector current of the power transistor) from being clamped at a predetermined level and continuously rising when the switch element is kept on for a long time. Further, by disabling the overcurrent protection circuit while the soft shut-off circuit is enabled, it is possible to prevent the gate voltage from being adjusted by the overcurrent protection circuit and changing the discharge time constant.

The current detection circuit may include a current detection resistor provided between the emitter of the power transistor and the ground line, and the voltage drop of the current detection resistor may be the detection voltage. The overcurrent protection circuit may include a first transistor that is provided in parallel with the current detection resistor and is turned on in the enable state of the soft shutoff circuit and turned off in the disabled state.
Thereby, in the enable state of the soft shut-off circuit, the detection value corresponding to the voltage drop of the current detection resistor becomes substantially zero by turning on the first transistor, so that the overcurrent protection can be invalidated. By bypassing the current detection resistor, it is possible to prevent the current detection resistor from affecting the time constant.

  The current detection resistor may be a chip component, a resistance component of a bonding wire, or a resistor integrated in an IC of the switch control device.

The overcurrent protection circuit compares the detection voltage with the second transistor provided between the gate of the power transistor and the ground line and turns on the second transistor when the detection voltage exceeds the threshold voltage. And a comparator for performing.
According to this aspect, when the coil current exceeds a certain threshold level, the second transistor is turned on, and the gate voltage can be lowered to reduce the coil current.

  The soft shut-off circuit may be disabled when the determination signal transitions to the negate level. Thereby, the wasteful power consumption can be reduced by setting the correction current to zero during normal operation.

  The soft shut-off circuit may include a counter that starts a count operation when the determination signal transitions to the assert level, and may be enabled when the count value of the counter reaches a set value corresponding to the energization protection time.

  Another aspect of the invention also relates to an igniter. The igniter includes a switch element connected to the primary coil of the ignition coil, and a switch control device that controls the switch element in accordance with an ignition signal from an ECU (Engine Control Unit). The switch element includes a power transistor and a diode pair connected in reverse series between the gate emitter of the power transistor. The switch control device compares the voltage according to the ignition signal with a reference voltage, generates a determination signal, and when the determination signal is an assert level corresponding to ON of the switch element, the gate of the power transistor is at a high level. When a voltage is applied and the determination signal is at a negate level corresponding to turning off of the switch element, a drive stage that applies a low level voltage to the gate of the power transistor, and a state in which the determination signal is at the assert level is a predetermined energization protection time In the enable state, the output of the drive stage becomes high impedance, and the gate voltage of the power transistor is gently lowered by discharging the power transistor gate charge through the diode pair. Shut-off times And, equipped with a.

  Yet another aspect of the invention also relates to an igniter. The igniter includes a switch element connected to the primary coil of the ignition coil, and a switch control device that controls the switch element in accordance with an ignition signal from an ECU (Engine Control Unit). The switch element includes a power transistor and a diode pair connected in reverse series between the gate emitter of the power transistor. The switch control device compares the voltage according to the ignition signal with a reference voltage, generates a determination signal, and when the determination signal is an assert level corresponding to ON of the switch element, the gate of the power transistor is at a high level. When a voltage is applied and the determination signal is at a negate level corresponding to turning off of the switch element, a drive stage that applies a low level voltage to the gate of the power transistor and a state in which the determination signal is at the assert level is a predetermined energization protection time In the enable state, a correction current is supplied from the drive stage to the gate of the power transistor to discharge the charge of the gate of the power transistor with a differential current between the leakage current of the diode pair and the correction current. The power transistor gate Comprising a soft shutoff circuit allowed to lower the voltage slowly, the.

The switch control device may be integrated on a single semiconductor substrate.
“Integrated integration” includes the case where all of the circuit components are formed on a semiconductor substrate and the case where the main components of the circuit are integrated. A resistor, a capacitor, or the like may be provided outside the semiconductor substrate.

  Another aspect of the present invention relates to a vehicle. The vehicle includes an ignition coil having a gasoline engine, an ignition plug, a primary coil, and a secondary coil connected to the ignition plug, an ECU that generates an ignition signal instructing ignition of the ignition plug, an ignition signal The above-described igniter that drives the ignition coil according to the above may be provided.

  It should be noted that any combination of the above-described constituent elements, and those in which constituent elements and expressions of the present invention are mutually replaced between methods, apparatuses, systems, and the like are also effective as an aspect of the present invention.

  According to an aspect of the present invention, soft shutoff can be realized with a small circuit scale.

It is a perspective view of the engine room of a gasoline engine car. It is a block diagram of a part of electric system of vehicles. FIG. 3A is a waveform diagram for explaining the operation of the energization protection circuit, and FIG. 3B is a diagram for explaining soft shut-off. It is a circuit diagram of the igniter which concerns on embodiment. 5A to 5D are circuit diagrams illustrating configuration examples of the switch element 202. FIG. FIG. 5 is an operation waveform diagram of the igniter of FIG. 4. It is an equivalent circuit diagram of an igniter when the soft shut-off circuit is in an enable state. It is a circuit diagram which shows the 1st structural example of a switch control apparatus. It is a circuit diagram which shows the 2nd structural example of a switch control apparatus. FIGS. 10A and 10B are diagrams showing the time change of the junction temperature _TJ of the power transistor. The correction current I _S, is a view showing an example of the dependence of the ambient temperature Ta dependence and the battery voltage V _BAT. 12A and 12B are circuit diagrams showing modifications of the soft shut-off circuit and the gate driver.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A and the member B are connected” means that the member A and the member B are physically directly connected, or the member A and the member B are in an electrically connected state. Including the case of being indirectly connected through other members that do not affect the above.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as an electrical condition. It includes the case of being indirectly connected through another member that does not affect the connection state.

  FIG. 4 is a circuit diagram of the igniter 200 according to the embodiment. The igniter 200 receives the ignition signal IGT from the ECU 108 at its input terminal IN, and in response to the ignition signal IGT, the current (coil current or collector current) of the primary coil L1 of the ignition coil 104 connected to its output terminal OUT. Control).

  The igniter 200 includes a switch element 202 and a switch control device 300, and is modularized and accommodated in one package. The basic configuration of the switch control device 300 is the same as that of FIG. 1, and is a functional IC that includes a determination stage 300A and a drive stage 300B and is integrated on a single semiconductor substrate.

  The switch element 202 includes a power transistor 204 and protection elements 206 and 208, and is integrated on one semiconductor substrate manufactured by a high breakdown voltage process. The power transistor 204 is an IGBT (Insulated Gate Bipolar Transistor). The collector C of the power transistor 204 is connected to the OUT terminal, and the emitter E thereof is connected to the GND (ground) terminal. A MOSFET may be used as the power transistor 204. In this case, the emitter may be read as the source and the collector as the drain.

The protection element 206 is provided between the gate and emitter of the power transistor 204 for the purpose of overvoltage protection. For example, the protection element 206 may include a diode pair D1 and D2 connected in reverse series between the gate and emitter of the power transistor 204. In this case, if the positive over-voltage (surge noise) is applied between the gate-emitter, gate-emitter voltage V _GE is clamped by BV + V _F. Also when a negative overvoltage is applied between the gate emitter, gate-emitter voltage V _GE is clamped at -BV-V _F. BV is the reverse breakdown voltage of the diode, V _F is the forward voltage.

  The switch control device 300 includes a determination stage 300A, a drive stage 300B, and a soft shut-off circuit 320, and is a functional IC integrated on one semiconductor substrate.

  The determination stage 300A includes a voltage comparator 302. An ignition signal IGT from the ECU 108 is input to the input line 301. A high-frequency filter that removes high-frequency noise in the input line 301 may be inserted before the voltage comparator 302.

Voltage comparator 302, the voltage _{V IN} of the input line 301 is compared with the reference voltage _{V REF,} and generates a determination signal _{S DET.} In the present embodiment, the state of V _IN > V _REF is associated with the switch element 202 being on, and the state of V _IN <V _REF is associated with the switch element 202 being off. The determination signal _{S DET when} the V _{IN> V REF,} a high level _(asserted), low level when V IN _{<V REF} (negated), therefore, the high level of the determination signal _{S DET,} the switch element 202 is asserted level corresponding to oN, the low level of the determination signal S _DET is a negated level corresponding to the oFF of the switch element 202. Note that the assignment of high level, low level and assert, and negate is a design matter and may be replaced.

Driving stage 300B in response to the determination signal _{S DET} generated by the decision stage 300A, and controls on of the switch element 202, off. When driving stage 300B is the determination signal _{S DET} is asserted level corresponding to ON of the switching element 202 (high level), a high-level voltage _{V H} is applied to the gate G of the power transistor 204, the determination signal _{S DET} switch element When it is at the negate level (low level) corresponding to turning off 202, the low level voltage V _L is applied to the gate G of the power transistor 204. The high level voltage V _H is, for example, 5 V, and the low level voltage V _L is the ground voltage V _GND (= 0 V). The switch control device 300 may include a regulator that receives the battery voltage V _BAT and stabilizes it to generate the high level voltage V _H.

The drive stage 300B includes a delay circuit 304, a pre-driver 306, and a gate driver 308. The delay circuit 304 gives a predetermined delay to the determination signal _SDET . This delay amount is set so that the time difference (delay) between the transition of the ignition signal IGT and the discharge time of the spark plug becomes a predetermined value. The gate driver 308 through a GATE terminal has become the gate G of the power transistor 204 state phi _H for outputting a high level voltage _{V H,} the state phi _L that outputs a low level voltage _{V L} is switched. The pre-driver 306 controls the state of the gate driver 308 according to the delayed determination signal S _DET '. In addition to the two states φ _H and φ _L described above, the gate driver 308 is configured to be able to switch a state φ _{HZ in} which the output becomes high impedance (referred to as high impedance state).

Soft shutoff circuit 320, the state determination signal S _DET is asserted level becomes the enable state when sustained for a predetermined energization protection time T _P. Soft shutoff circuit 320 in an enabled state, switching the gate driver 308 from the state phi _H in a high impedance state phi _Z, the output of the drive stage 300B a high impedance. The soft shut-off circuit 320 supplies the correction current _ICMP to the gate G of the power transistor 204 in the enabled state.

For example, the soft shut-off circuit 320 includes a timer circuit that starts time measurement triggered by a positive edge of the determination signal _SDET , and when the time measured by the timer circuit reaches the energization protection time _TP , Good. The timer circuit may be an analog circuit or a digital circuit.

The soft shutoff circuit 320, the determination signal S _DET may become transits negates level disabled state. As a result, the wasteful power consumption can be reduced by setting the correction current _ICMP to zero during normal operation.

  5A to 5D are circuit diagrams illustrating configuration examples of the switch element 202. FIG. As described above, the protection elements 206 and 208 are provided between the gate emitter and the gate collector of the power transistor 204, and the protection elements 206 and 208 are respectively diode pairs D1 and D2 (also referred to as Dp) connected in reverse series. including. The diode pair D1, D2 may be a cathode common as shown in FIG. 4, or may be an anode common as shown in FIG. One of the protection elements 206 and 208 may be a cathode common diode pair, and the other may be an anode common diode pair.

  Each of the protection elements 206 and 208 may include a plurality of diode pairs Dp stacked in series. FIG. 5B shows a configuration in which a plurality of anode common diode pairs Dp are stacked, and FIG. 5C shows a configuration in which a plurality of cathode common diode pairs Dp are stacked. It is.

  The withstand voltage (Vf + BV) per diode pair Dp is typically several volts although it depends on the semiconductor process. For example, when the withstand voltage of the diode pair Dp is set to 7V and the gate-emitter voltage and the gate-collector voltage of the power transistor 204 are clamped to 420V or less, 60 stages (= 420/7) of diode pairs Dp may be stacked. .

  As shown in FIG. 5D, each of the diodes D1 and D2 in FIG. 4 may be configured by connecting a plurality of diodes in series. Similarly, each of the diodes D1 and D2 in FIG. 5A may be configured by connecting a plurality of diodes in series. The diodes D1 and D2 may be zener diodes.

The above is the basic configuration of the igniter 200. Next, the operation will be described.
FIG. 6 is an operation waveform diagram of the igniter 200 of FIG.
Before the time t0, the ignition signal IGT is at a low level, the gate driver (DR) 308 is a state phi _L, the gate voltage _{V G} of the power transistor 204 is at a low level voltage _{V L.} When the ignition signal IGT transits to a high level at time t1, and subsequently the input voltage _VIN exceeds the reference voltage V _REF at time t2, the determination signal _SDET becomes a high level. Thus, the gate driver 308 is switched to a state .phi.2, the power transistor 204 is turned on, go coil current I _C is increased.

The soft shut-off circuit 320 starts time measurement when the determination signal _SDET becomes high level. When energization protection time _{T P} has passed the enable state (t2). In FIG. 6, SSO indicates the state of the soft shutoff circuit 320. When the soft shut-off circuit 320 is enabled, the gate driver 308 is in the high impedance state _φHZ . The soft shut-off circuit 320 supplies a correction current _ICMP to the gate of the power transistor 204.

FIG. 7 is an equivalent circuit diagram of the igniter 200 when the soft shut-off circuit 320 is in an enabled state. A parasitic capacitance (gate input capacitance) exists between the gate emitter and the gate collector of the power transistor 204. This parasitic capacitance is denoted by Ci. Since a _{V H} <BV + V _F, the diode D2 of the protection element 206 is not broken down, the protection element 206, a small leakage current _{I LEAK.}

In this state, the parasitic capacitance Ci of the power transistor 204 is discharged by the leakage current I _LEAK of the protection element 206. At the same time, the gate capacitance Ci is charged by the correction current _{I CMP} from soft shutoff circuit 320. Thus the gate capacitance Ci is discharged at a discharging current _I DIS _{= I} LEAK _{-I CMP.}

At time t2, the charge amount Q stored in the gate capacitance Ci is given by equation (1).
Q = Ci × V _H (1)

The amount of charge when the capacitor Ci is discharged over the time T, which is the discharge current I _DIS , is given by equation (2).
Q = ∫ ₀ ^T I _DIS (t) dt (2)
For simplicity and ease of understanding of the description, the leakage current I _LEAK, the correction current I _CMP is constant with time. At this time, the discharge current I _DIS is also constant, and Equation (3) is obtained.
Q = T × I _DIS (3)

Equation (4) is obtained from equations (1) and (3). Equation (4) shows the amount of current I _DIS required to completely discharge the charge of the gate capacitance Ci in a certain time (referred to as soft shut-off time) _TSSO .
I _DIS = C _i × V _H / T _SSO (4)

The soft shut-off time _TSSO must be long enough that the spark plug 106 does not spark. For example, if T _SSO = 50 ms, V _H = 5 V, and Ci = 2 nF, the required discharge current I _DIS is I _DIS = 200 nA (= 0.2 μA). For example if the leakage current _{I LEAK} in a typical junction temperature _{T J} of the device is 1.6Myuei, the typical value of the correction current _{I CMP,} it may be set to I _{DIS -I} LEAK = 1.4μA.

Returning to FIG. When the output of the gate driver 308 becomes high impedance at time t2, the gate capacitance Ci is discharged with the discharge current I _DIS , and the gate voltage V _G is a sufficiently long time with a time constant corresponding to the discharge time (soft shut-off time) _TSSO. It will decrease over time. As a result, the coil current I _C can also be reduced gradually to suppress the variation of the secondary voltage V _S, the spark plug 106 can be prevented sparks.

The above is the operation of the igniter 200.
Thus, according to the igniter 200, soft shut-off can be realized by gently reducing the gate voltage by using the minute leak current _ILEK of the protection element 206 of the power transistor 204. Since the protection element 206 has another function of protecting the power transistor 204 from overvoltage, an increase in circuit area due to the addition of the protection element 206 is not essential.

As also circuitry, in addition to the conventional igniter 200 r, a circuit for switching the gate driver 308 in a high impedance state phi _HZ, it may be added only a circuit for generating a correction current I _CMP, when a long constant Since a large-capacitance capacitor and high resistance are not required to realize the above, soft shut-off can be realized with a small circuit scale.

  The present invention is understood as the block diagram / circuit diagram of FIG. 4 or extends to various circuits derived from the above description, and is not limited to a specific circuit configuration. A typical configuration will be described.

FIG. 8 is a circuit diagram illustrating a first configuration example of the switch control device 300.
Soft shut-off circuit 320 includes a current source 322 that is turned on in the enabled state. The current source 322 supplies the correction current _ICMP to the gate GATE of the power transistor in the on state. The switch 324 is provided to switch the current source 322 on and off. Note the position of the switch 324 is not particularly limited, on the correction current I _CMP, may be located anywhere off switched if. For example, a transistor corresponding to the switch 324 may be provided inside the current source 322.

Soft shutoff circuit 320 includes a counter 326. Counter 326 is above a timer which measures an energization protection time T _P, the determination signal S _DET starts counting of the clock signal CLK transits to assert level. Logic circuit 328, the count value of the counter 326 reaches the set value corresponding to the current protection time T _P, asserts the enable signal EN, the soft shutoff circuit 320 and the enable state. When the logic circuit 328 detects a negative edge of the determination signal _SDET , the logic circuit 328 negates the enable signal EN and disables the soft shutoff circuit 320.

The gate driver 308 includes a high side transistor M1 and a low side transistor M2 provided in series between the power supply line _VH and the ground line _VL . In order to optimize the slew rate (slope) of the gate voltage V _G, the resistors R1, R2 may be inserted.

The pre-driver 306 receives an enable signal EN. The pre-driver 306 controls the gate voltages of the transistors M1 and M2 according to the determination signal S _DET ′ when the enable signal EN is negated (that is, the soft shut-off circuit 320 is disabled). Further, when the enable signal EN is asserted (that is, the soft shutoff circuit 320 is enabled), the pre-driver 306 turns off the transistors M1 and M2 regardless of the determination signal _SDET ', and sets the output of the gate driver 308 to high. Impedance.

FIG. 9 is a circuit diagram illustrating a second configuration example of the switch control device 300. The switch control device 300 has an overcurrent protection function. Specifically, the igniter 200 further includes a current detection circuit 210. Current detecting circuit 210 detects a coil current _{I C} flowing in the power transistor 204. For example, the current detection circuit 210 includes a current detection resistor R _CS provided between the emitter E and the ground line of the power transistor 204 may output a voltage drop across the current detection resistor R _CS as the current detection value V _CS . The current detection value V _CS is input to the CS (current detection) terminal of the switch control device 300. The current detection resistor _RCS may be a chip component, a resistance component of a bonding wire, or a resistor integrated in an IC of the switch control device.

The switch control device 300 further includes an overcurrent protection circuit 330. The overcurrent protection circuit 330 adjusts the gate voltage V _G of the power transistor 204 so that the detected value V _CS of the coil current I _C does not exceed a predetermined threshold voltage V _TH . Overcurrent protection circuit 330 is disabled in the enabled state of the soft shutoff circuit 320 does not perform the adjustment of the gate voltage V _G.

By providing the overcurrent protection circuit 330, it is possible to prevent the coil current I _C (the collector current of the power transistor) from being clamped at a predetermined level and kept rising when the switch element 202 is kept on for a long time. Further, by disabling the overcurrent protection circuit 330 while the soft shut-off circuit 320 is in an enabled state, it is possible to prevent the overcurrent protection circuit 330 from adjusting the gate voltage V _{G and} changing the discharge time constant. .

The overcurrent protection circuit 330 includes a first transistor 332 that is provided in parallel with the current detection resistor _RCS and is turned on in the enable state of the soft shutoff circuit 320 and turned off in the disabled state. The overcurrent protection circuit 330 may adjust the gate voltage V _G of the power transistor 204 so that the detection value V _CS corresponding to the voltage drop of the current detection resistor R _CS does not exceed a predetermined threshold voltage V _TH. .

Thus, in the enabled state of the soft shutoff circuit 320, the detection value _{V CS} that corresponds to the voltage drop across the current sensing resistor _{R CS} by turning on the first transistor 332 becomes substantially _zero, and V CS _{<V TH} Therefore, overcurrent protection can be disabled. In addition, by bypassing the current sensing resistor R _CS, possible to prevent the current detection resistor R _CS affects the time constant.

The overcurrent protection circuit 330 compares the detection voltage V _CS with the second transistor 336 provided between the gate of the power transistor 204 and the ground line and the threshold voltage V _TH, and when V _CS > V _TH , And a comparator 334 that turns on the two-transistor 336. Thus, beyond a threshold level in which the coil current I _C, the second transistor 336 is turned on, it is possible to reduce the coil current I _C decreases the gate voltage V _G.

  The above is the second configuration example of the switch control device 300. According to the switch control device 300, overcurrent protection can be performed without disturbing soft shut-off.

Next, the correction current _ICMP will be described. The heat radiation performance of the igniter 200, a junction temperature _{T J} of the device (power transistor 204) is, and the ambient temperature Ta of the igniter 200, can vary greatly due to the influence of self-heating of the power transistor 204. When the protection element 206 is formed of a diode, the leakage current I _LEAK changes depending on the junction temperature T _J. Specifically, the higher the junction temperature T _J , the larger the leakage current I _LEAK . Therefore, due to variations in the junction temperature T _J, in order to suppress the variation in the discharge time of the gate capacitance Ci, depending on the junction temperature T _J, changing the correction current I _CMP, to keep the discharge current I _DIS constant Is desirable.

Here, if the switching control unit 300 and switch element 202 are integrated into separate semiconductor chips, the switch control device 300 side, which generates a correction current I _CMP, it is difficult to know the junction temperature T _J of the power transistor 204 directly . Therefore, the soft shut-off circuit 320 may change the correction current _ICMP as follows.

FIGS. 10A and 10B are diagrams showing the time change of the junction temperature _TJ of the power transistor 204. FIG. FIG. 10A shows the dependency of the ambient temperature Ta. Junction temperature T _J is starting at an ambient temperature Ta, gradually increases with a gradient corresponding to the power consumption P is the product of the collector-emitter voltage V _CE of the coil current I _C and the power transistor 204. Therefore, the higher the ambient temperature Ta, the higher the junction temperature _TJ , and the time integral value (discharge charge amount) of the leakage current I _LEAK also increases. Therefore, soft shutoff circuit 320, by increasing the correction current _{I CMP} higher ambient temperatures Ta, may suppress the fluctuation of the discharge current _{I DIS (= I LEAK -I CMP} ).

FIG. 10B shows the dependency of self-heating of the power transistor 204. If the overcurrent protection circuit 330 is provided to the switch control unit 300, the coil current I _C can be regarded as substantially constant. On the other hand, the collector-emitter voltage of the power transistor 204 increases as the battery voltage V _BAT increases. Therefore, the self-heat generation amount (that is, the slope of the junction temperature T _J ) of the power transistor 204 increases as the battery voltage V _BAT increases. Become. Therefore, the higher the battery voltage _VBAT , the higher the junction temperature _TJ , and the time integral value (discharge charge amount) of the leakage current _ILEAK also increases. Therefore, soft shutoff circuit 320 by the battery voltage _{V BAT} to increase the higher correction current _{I CMP,} may suppress the fluctuation of the discharge current _{I DIS (= I LEAK -I CMP} ).

Figure 11 is a diagram showing an example of the dependence of the dependence and the battery voltage V _BAT of the ambient temperature Ta of the correction current I _S.

A circuit that generates a current having a positive temperature characteristic is known, and the current source of the soft shut-off circuit 320 can be configured using such a known technique. For example, current sources having positive temperature characteristics include those using the temperature dependence of polysilicon resistance, diffusion resistance, and well resistance, those using a thermistor, and the base-emitter voltage of a bipolar transistor (forward voltage of the PN junction). ) which utilizes the temperature dependence of, but such as those using thermal voltage V _T is exemplified, the configuration is not particularly limited.

  A current source that generates a current corresponding to an arbitrary voltage is also known, and the current source of the soft shut-off circuit 320 can be configured using such a known technique. For example, the soft shut-off circuit 320 can be configured using a voltage / current conversion circuit, a gm amplifier, or the like.

According to those skilled in the art, there can be various variations in the current source for generating the correction current _ICMP having a positive temperature characteristic and / or having a positive dependence on the battery voltage _VBAT . It will be understood that variations thereof are within the scope of the present invention.

  The embodiments are exemplifications, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are within the scope of the present invention. . Hereinafter, such modifications will be described.

(First modification)
In the embodiment, the case where the soft shut-off circuit 320 includes the current source 322 that generates the correction current _ICMP has been described, but the present invention is not limited thereto. The capacitance value of the gate capacitance Ci of the power transistor 204, a combination of current amount of high-level voltage _{V H} and the leakage current _{I LEAK,} without supplying a correction current _{I CMP,} suitable for about suitable 10~100ms discharge Time may be available. In this case, the current source 322 may be omitted, and the correction current _ICMP may not be supplied.

(Second modification)
In includes a current source 322 that soft shutoff circuit 320 generates a correction current I _CMP, a case has been described of changing the correction current I _CMP according to the battery voltage V _BAT and the ambient temperature Ta invention embodiment It is not limited to it. Depending on the platform on which the igniter 200 is mounted, it is sufficient that the spark of the spark plug 106 can be prevented by the soft shutoff, and the soft shutoff time _TSSO may be allowed to vary. In this case, the correction current _ICMP may be constant, changed depending only on the ambient temperature Ta, or changed depending only on the battery voltage _VBAT .

(Third Modification)
The soft shut-off circuit 320 may generate the correction current _ICMP using the gate driver 308. 12A and 12B are circuit diagrams showing modifications of the soft shut-off circuit 320 and the gate driver 308. FIG. As shown in FIG. 12A, the high-side transistor M1 of the gate driver 308 may be configured with an N-channel MOSFET. The pre-driver 306 turns off the low-side transistor M2 when the soft shut-off circuit 320 is enabled. In the enable state soft shutoff circuit 320, the gate of the high side transistor M1, by providing the appropriate gate voltage V _G1, to generate a correction current I _CMP to the high side transistor M1. In FIG. 12A, the transistor M1 may be a P-channel MOSFET. Alternatively, the transistors M1 and M2 may be bipolar transistors.

As shown in FIG. 12B, the soft shutoff circuit 320 may include a transistor M3 and a current source CS1. The transistor M3 is of the same type as the high side transistor M1, and forms a current mirror circuit together with the high side transistor M1. Current source CS1 is turned on in the enabled state of the soft shutoff circuit 320 generates a current indicating the correction current I _CMP, supplied to the input side transistor M3 of the current mirror circuit. In FIG. 12B, the transistors M1 to M3 may be bipolar transistors.

(Fourth modification)
In the igniter 200 of FIG. 9, the current detection circuit 210 is configured by the current detection resistor _RCS , but the present invention is not limited thereto. As a means for detecting the coil current I _C, the current flowing through the power transistor 204 is copied by the current mirror circuit, may be detected copied current, the coil current by using the on-resistance of the power transistor 204 It may be detected. Alternatively, by adding an auxiliary winding in the ignition coil 104 may estimate the coil current I _C on the basis of the current flowing through the auxiliary winding.

  Although the present invention has been described based on the embodiments, it should be understood that the embodiments merely illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. It goes without saying that many modifications and changes in arrangement are allowed without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 100 ... Vehicle, 102 ... Battery, 104 ... Ignition coil, L1 ... Primary coil, L2 ... Secondary coil, 106 ... Spark plug, 108 ... ECU, 110 ... Engine, 112 ... Intake manifold, 113 ... Air cleaner, 114 ... Radiator , 200 ... igniter, 202 ... switch element, 204 ... power transistor, 206 ... protection element, 210 ... current detection circuit, 300 ... switch control device, 300A ... determination stage, 300B ... drive stage, 301 ... input line, 302 ... voltage Comparator, 304 ... Delay circuit, 306 ... Pre-driver, 308 ... Gate driver, 310 ... Current-carrying protection circuit, 320 ... Soft shut-off circuit, 322 ... Current source, 324 ... Switch, 326 ... Counter, 328 ... Logic circuit, _RCS ... Current detection resistor, 30 ... overcurrent protection circuit, 332 ... first transistor, 334 ... comparator, 336 ... second transistor.

Claims (15)

A switch element connected to the primary coil of the ignition coil;
A switch control device that controls the switch element in response to an ignition signal from an ECU (Engine Control Unit);
With
The switch element is
A power transistor;
An overvoltage protection element provided between the gate and emitter of the power transistor;
Including
The switch control device includes:
A voltage comparator that compares a voltage according to the ignition signal with a reference voltage and generates a determination signal;
When the determination signal is an assert level corresponding to turning on of the switch element, a high level voltage is applied to the gate of the power transistor, and when the determination signal is a negate level corresponding to turning off of the switch element, A drive stage for applying a low level voltage to the gate of the power transistor;
When the state in which the determination signal is at the assert level continues for a predetermined energization protection time, the enable state is enabled. In the enable state, the output of the drive stage is set to high impedance, and a correction current is applied to the gate of the power transistor. A soft shut-off circuit to supply,
An igniter characterized by including   The igniter according to claim 1, wherein the overvoltage protection element includes a diode pair connected in reverse series. The soft shut-off circuit is
3. The igniter according to claim 1, further comprising a current source that is turned on in the enable state and supplies the correction current to a gate of the power transistor in the on state.   4. The igniter according to claim 1, wherein the correction current increases as the battery voltage supplied to the ignition coil increases. 5.   The igniter according to any one of claims 1 to 4, wherein the correction current is larger as the ambient temperature of the igniter is higher. The drive stage is
A gate driver including a high-side transistor and a low-side transistor provided in series between a power supply line and a ground line;
A pre-driver that controls on and off of the high-side transistor and the low-side transistor in accordance with the determination signal;
Including
The igniter according to any one of claims 1 to 5, wherein the soft shut-off circuit supplies the correction current using the high-side transistor in the enable state. A current detection circuit for generating a detection voltage corresponding to the coil current flowing through the power transistor;
The switch control device further includes an overcurrent protection circuit that adjusts a gate voltage of the power transistor so that the detection voltage does not exceed a predetermined threshold voltage,
The igniter according to any one of claims 1 to 6, wherein the overcurrent protection circuit is disabled in an enable state of the soft shut-off circuit. The current detection circuit includes a current detection resistor provided between an emitter of the power transistor and a ground line, and a voltage drop of the current detection resistor is the detection voltage,
The overcurrent protection circuit includes a first transistor that is provided in parallel with the current detection resistor and is turned on in the enable state of the soft shutoff circuit and turned off in the disable state. The igniter described. The overcurrent protection circuit is
A second transistor provided between the gate of the power transistor and a ground line;
A comparator that compares the detected voltage with the threshold voltage and turns on the second transistor when the detected voltage exceeds the threshold voltage;
The igniter according to claim 7 or 8, characterized by comprising:   The igniter according to any one of claims 1 to 9, wherein the soft shut-off circuit is disabled when the determination signal transitions to a negate level.   The soft shut-off circuit includes a counter that starts a count operation when the determination signal transitions to the assert level, and enters the enable state when the count value of the counter reaches a set value corresponding to the energization protection time. The igniter according to any one of claims 1 to 10, wherein: A switch element connected to the primary coil of the ignition coil;
A switch control device that controls the switch element in response to an ignition signal from an ECU (Engine Control Unit);
With
The switch element is
A power transistor;
A diode pair connected in reverse series between the gate and emitter of the power transistor;
Including
The switch control device includes:
A voltage comparator that compares a voltage according to the ignition signal with a reference voltage and generates a determination signal;
When the determination signal is an assert level corresponding to turning on of the switch element, a high level voltage is applied to the gate of the power transistor, and when the determination signal is a negate level corresponding to turning off of the switch element, A drive stage for applying a low level voltage to the gate of the power transistor;
When the state in which the determination signal is at the assert level continues for a predetermined energization protection time, the enable state is enabled. In the enable state, the output of the drive stage is set to high impedance, and the charge of the gate of the power transistor is changed to the diode. A soft shut-off circuit that gently reduces the gate voltage of the power transistor by discharging through the pair;
An igniter comprising: A switch element connected to the primary coil of the ignition coil;
A switch control device that controls the switch element in response to an ignition signal from an ECU (Engine Control Unit);
With
The switch element is
A power transistor;
A diode pair connected in reverse series between the gate and emitter of the power transistor;
Including
The switch control device includes:
A voltage comparator that compares a voltage according to the ignition signal with a reference voltage and generates a determination signal;
When the determination signal is an assert level corresponding to turning on of the switch element, a high level voltage is applied to the gate of the power transistor, and when the determination signal is a negate level corresponding to turning off of the switch element, A drive stage for applying a low level voltage to the gate of the power transistor;
When the state in which the determination signal is at the assert level continues for a predetermined energization protection time, the enable state is enabled, and in the enable state, a correction current is supplied from the drive stage to the gate of the power transistor, thereby A soft shut-off circuit that gently reduces the gate voltage of the power transistor by discharging the charge of the diode pair with a differential current between the leakage current of the diode pair and the correction current;
An igniter comprising:   14. The igniter according to claim 1, wherein the switch control device is integrated on a single semiconductor substrate. A gasoline engine,
Spark plugs,
An ignition coil having a primary coil and a secondary coil connected to the spark plug;
An ECU for generating an ignition signal instructing ignition of the spark plug;
The igniter according to any one of claims 1 to 14, wherein the ignition coil is driven in response to the ignition signal.
A vehicle comprising:

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