JP6371739B2 - Inductive load drive - Google Patents

Description

  The present invention relates to an inductive load driving device.

  When performing drive control by energizing an inductive load, a switching element such as a field effect transistor (FET) is connected to the inductive load in series, and the switching element is turned on / off to control inductivity. Perform drive control of the load. At this time, if the switching element is controlled from on to off, a counter electromotive voltage is generated at both ends of the inductive load, and an excessive voltage exceeding the rated voltage is applied to the switching element, and the switching element and the peripheral connected thereto May cause circuit failure.

  For this reason, conventionally, there is a case in which a freewheeling diode is connected in parallel to the inductive load to suppress the flyback voltage generated across the inductive load. However, since it takes time until the load current flows back through the inductive load and the freewheeling diode and decreases, the switching response of the inductive load is inferior (see, for example, [Problem to be Solved by the Invention] in Patent Document 1).

  In a low-side drive circuit with a FET as a switching element downstream of an inductive load, a Zener diode and a diode are connected between the gate and source of the FET, and the switching element is turned on when the applied voltage to the switching element exceeds a predetermined voltage. As a result, a method of clamping the drain and source to a predetermined voltage may be used (see, for example, Patent Document 2). This method is generally called an active clamp circuit or a dynamic clamp circuit, and has a faster switching time and a better switching response than the case where the freewheeling diodes are connected in parallel.

JP 2014-238022 JP 2009-118620

  In the technique disclosed in Patent Document 2, there is a problem that the clamp voltage of the active clamp circuit overshoots the set voltage at a low temperature and exceeds the rated voltage between the drain and source of the switching element and cannot be protected. In addition, there has been a problem that an IC (Integrated Circuit) that monitors the drain voltage exceeds the rated voltage or a failure due to latch-up occurs in order to diagnose a failure of the inductive load driving device at a low temperature.

  An object of the present invention is to provide an inductive load driving device capable of generating a predetermined clamp voltage without overshooting the clamp voltage of an active clamp circuit even at a low temperature.

In order to achieve the above object, an inductive load driving apparatus according to an example of the present invention is connected in series to an inductive load, and a switching element that turns on / off a current supplied to the inductive load according to a control signal; A drive control unit for supplying the control signal to the gate terminal of the switching element; a first resistor connected in series from the drive control unit to the gate terminal of the switching element; the inductive load; and the switching element. A Zener diode connected in series from the first connection point to a second connection point between the first resistor and the gate terminal of the switching element, a first diode in a direction opposite to the Zener diode, and the Zener When a current supplied to the inductive load is turned off and connected to a third connection point between a diode and the first diode, a Zener current is An inductive load driving device including a circuit that discharges at a high frequency , wherein the circuit is connected in parallel to the capacitor charged by the Zener current supplied from the third connection point, And a second resistor for discharging the charge charged in the capacitor .

  According to the present invention, a predetermined clamp voltage can be generated without overshooting the clamp voltage of the active clamp circuit even at a low temperature. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is a figure which shows the basic composition of the inductive load drive device by the 1st Embodiment of this invention. It is a figure for demonstrating the structure of the breakdown promotion circuit shown in FIG. It is a figure which shows the drive waveform in the inductive load drive device shown in FIG. It is a figure which shows the clamp voltage waveform in the low temperature in the inductive load drive device without the breakdown promotion circuit shown in FIG. It is a figure which shows the clamp voltage waveform in the low temperature in the inductive load drive device with the breakdown promotion circuit shown in FIG. It is a figure which shows the structure of the inductive load drive device by the 2nd Embodiment of this invention. It is a figure which shows the drive waveform in the inductive load drive device shown in FIG. It is a figure which shows the clamp voltage waveform in the low temperature in the inductive load drive device without the breakdown promotion circuit shown in FIG. It is a figure which shows the clamp voltage waveform in the low temperature in the inductive load drive device with the breakdown promotion circuit shown in FIG. It is a figure which shows the structure of the inductive load drive device by the 3rd Embodiment of this invention. It is a figure which shows the typical circuit example of an active clamp circuit.

  Hereinafter, the configuration and operation effects of the inductive load driving device according to the first to third embodiments of the present invention will be described with reference to the drawings. In each figure, the same numerals indicate the same parts.

(Comparative example)
First, as a comparative example, a typical circuit example of an active clamp circuit is shown in FIG.

  In FIG. 9, a Zener diode (112) between the drain and gate generates a clamp voltage described later. The diode (113) connected in series with the Zener diode (112) is for preventing the gate-source voltage from being lowered via the Zener diode (112) when the FET (107) is turned on.

  In other words, the Zener diode (112) and the diode (113) opposite to the Zener diode (112) are connected to the resistor (104) and the FET from the connection point (P1) between the inductive load (110) and the FET (107). A connection point (P2) with the gate terminal of (107) is connected in series.

  The series resistance (hereinafter referred to as the gate resistance (104)) between the diode (113) and the gate drive circuit (push-pull circuit (901)) is that the drive control unit (103) turns off the FET (107), that is, a low signal. During output, the Zener current (902) flows through the gate resistance (104) and the drive control unit (103) during the clamping, thereby raising the gate voltage (105) of the FET (107) to the ON threshold voltage (107 ) For half-on.

  In other words, the gate resistance (104) is connected in series from the drive control unit (103) to the gate terminal of the FET (107).

  The gate-source resistor (106) is for fixing the gate of the FET (107) to the ground potential and keeping it off when the output signal of the drive control unit (103) is indefinite, but at the same time during the clamping In addition, part of the Zener current (902) is energized to the ground to raise the gate voltage (105) to the half-on threshold voltage. Therefore, the back electromotive voltage generated by the load (110) turns on the FET so that the gate-source voltage of the FET (107) is maintained at the half-on threshold voltage, so that the drain-source voltage is the same as that of the Zener diode (112). Clamped to the sum of the Zener voltage, the forward voltage of the diode (113), and the half-on threshold voltage of the FET (107).

  Thus, in order to generate the clamp voltage, the Zener voltage (breakdown voltage) of the Zener diode (112) provided between the drain and gate of the FET (107) is indispensable. However, when the current flowing through the Zener diode 112 is small at a low temperature (for example, −40 ° C.), the Zener diode 112 may not break down and the Zener voltage may once rise.

  This is because the breakdown of a Zener diode requires an avalanche effect that causes free electrons to collide with the silicon crystal and eject covalently bonded electrons, which continuously increase the free electrons. This is because free electrons are not easily emitted from.

  In order to increase the zener current (902) and promote breakdown, it is possible to reduce the resistance between the gate-source resistance (106) and the gate resistance (104), but the gate-source resistance (106) 103) is generally several tens to several tens of kilohms due to restrictions on current supply capability and on-resistance, and a Zener current sufficient to promote breakdown does not flow.

  As for the gate resistance (104), the drive control section (103) is usually composed of a CMOS (Complementary MOS) push-pull circuit (901), and its on-resistance is about several tens of ohms. Even if the resistance of (104) was lowered, breakdown could not be promoted according to the experiment results of the present inventors. Therefore, lowering the gate resistance (104) is not sufficient to promote breakdown.

(First embodiment)
FIG. 1 shows a basic configuration of an inductive load driving apparatus 1A according to a first embodiment of the present invention. As shown in FIG. 1, the inductive load driving apparatus 1A includes an inductive load (110) and an N-channel FET (107) as a switching element connected in series between a battery power source (109) and a power source ground (108). A low-side drive circuit that performs on / off control of the FET (107) by driving the gate signal (105) of the FET (107) by the drive control unit (103) of the control device (101).

  That is, the FET (107) as a switching element is connected in series to the inductive load (110), and turns on / off the current supplied to the inductive load (110) according to the gate signal (105: control signal). The drive control unit (103) supplies a gate signal (pulse voltage) to the gate terminal of the FET (107).

  Between the drain gate of the FET (107), a Zener diode (112) for setting the clamp voltage, and a block for preventing the gate signal (105) output by the drive controller (103) from dropping when the FET (107) is on A diode (113) is provided.

  Then, a Zener diode breakdown promoting circuit (114) is connected to a connection point between the Zener diode (112) and the diode (113). The breakdown promoting circuit (114) is connected to the connection point (P3) between the Zener diode (112) and the diode (113), and the current supplied to the inductive load (110) is turned off. (115) is discharged at high frequency. Details of the breakdown promoting circuit (114) will be described later with reference to FIG.

  In order to diagnose the failure state of the inductive load driving device in a vehicle-mounted control device or the like, as shown in FIG. 1, the drain voltage (116) of the FET (107) is used as the diagnosis unit (102) of the control device (101). May be monitored.

  FIG. 2 shows a specific example of the breakdown promoting circuit (114) of the Zener diode (112) of FIG. 1, and FIG. 3 shows its operation waveform.

  The capacitor (201) of the breakdown promoting circuit (114) in FIG. 2 generates a high voltage at the drain terminal of the FET (107) due to the back electromotive force of the inductive load (110) when the FET (107) is turned off. At the same timing (304, 305), the anode of the Zener diode (112) is grounded to the ground via the capacitor (201) at high frequency, so that the Zener current (115) is increased and the Zener diode (112) This is to promote the free electron emission, the avalanche effect, and the breakdown, thereby suppressing the overshoot of the Zener diode (112).

  That is, the breakdown promoting circuit (114) increases the Zener current (115) and promotes the breakdown of the Zener diode (112). The breakdown promoting circuit (114) includes a capacitor (201) charged by a Zener current (115) supplied from the connection point (P3).

  The diode (202) is for preventing the electric charge charged in the capacitor (201) by the Zener current (115) from being discharged by the drive control unit (103). This is to prevent the switching time from on to off of the gate signal (105) from slowing down when the current drive capability of the drive control unit (103) is small.

  That is, the breakdown promoting circuit (114) further includes a diode (202) connected in series from the connection point (P3) to one end of the capacitor (201).

  A resistor (203) connected in parallel to the capacitor (201) is for discharging the electric charge charged in the capacitor (201). That is, the breakdown promoting circuit (114) includes a resistor (203) that is connected in parallel to the capacitor (201) and discharges the electric charge charged in the capacitor (201). Here, one end of the capacitor (201) is grounded.

  In order to enable overshoot suppression of the Zener diode (112) at the next off-timing (305) by selecting a constant that will allow sufficient discharge within the drive cycle (303) of the FET (107). belongs to. In other words, the resistance value of the resistor (203) is set so that the discharge is completed within the period of the gate signal (control signal).

  FIG. 4-1 shows the timing when the FET (107) is turned off from the on state in the case of the active clamp circuit (comparative example shown in FIG. 9) without the Zener diode breakdown promotion circuit (114) in the low side drive circuit shown in FIG. This is a waveform when (304) is observed in the time axis direction.

  As shown in FIG. 4-1, in the active clamp circuit of FIG. 9, the breakdown of the Zener diode (112) at low temperature is delayed, resulting in an overshoot voltage (401). On the other hand, FIG. 4-2 shows a waveform when the break promoting circuit (114) of the Zener diode (112) is used, and the Zener diode (112) is clamped to a predetermined set voltage (301) without overshooting.

  As described above, according to the present embodiment, a predetermined clamp voltage can be generated without overshooting the clamp voltage of the active clamp circuit even at low temperatures. As a result, the switching element and the peripheral connection circuit element can be prevented from exceeding the rated voltage and causing a failure.

(Second Embodiment)
FIG. 5 shows a basic configuration of an inductive load driving apparatus 1B according to the second embodiment of the present invention. As shown in FIG. 5, the inductive load driving apparatus 1B includes a P-channel FET (507), which is a switching element, and an inductive load (510) in series between a battery power source (509) and its power supply ground (508). And a high-side drive circuit that performs on / off control of the FET (507) by driving the gate signal (505) of the FET (507) by the drive control unit (503) of the control device (501).

  Basically, the operation principle is the same except that the polarity is reverse to that of the first embodiment. FIG. 6 shows the operation waveform. Similarly to FIG. 4-1, FIG. 7-1 shows that the drain voltage (516) of the FET (507) undershoots in the high side drive circuit shown in FIG. 5 without the Zener diode breakdown promoting circuit (517). Figure 7-2 shows the waveform when the drain voltage becomes the undershooted voltage (701) .Figure 7-2 shows the waveform when the breakdown promoting circuit (517) is used, and the Zener diode (512) does not undershoot. The waveform clamped to voltage (601) is shown.

  As described above, according to the present embodiment, a predetermined clamp voltage can be generated without overshooting the clamp voltage of the active clamp circuit even at low temperatures.

(Third embodiment)
FIG. 8 shows a basic configuration of an inductive load driving apparatus 1C according to the third embodiment of the present invention. FIG. 8 shows the same low-side drive circuit as in the first embodiment of the present invention, but an embodiment in which a different breakdown promoting circuit (801) is applied.

  In this breakdown promotion circuit (801), a capacitor (802) is connected in series to the battery power supply (109) of the inductive load (110) from the connection point between the active clamp Zener diode (112) and the diode (113). ing.

  The anode of the Zener diode (112) connects the capacitor (802) at the timing when the FET (107) is turned off and the high voltage is generated at the drain terminal of the FET (107) due to the back electromotive voltage of the inductive load (110). Through a high-frequency short circuit to the battery power supply (109), thereby increasing the Zener current (815) and promoting free electron emission, avalanche effect, and breakdown in the Zener diode (112). This is to suppress the overshoot.

  In other words, one end of the capacitor (802) is connected to a battery power supply (109) that supplies current to the inductive load (110).

  Similar to the first embodiment and the second embodiment, the diode (803) prevents the charge charged in the capacitor (802) from being discharged to the drive control unit (103), and the gate signal (105) This is to prevent the switching time from on to off from slowing down. The resistor (804) is for discharging the electric charge charged in the capacitor (802) by the next clamp timing.

  As described above, according to the present embodiment, a predetermined clamp voltage can be generated without overshooting the clamp voltage of the active clamp circuit even at low temperatures.

  In addition, this invention is not limited to above-described embodiment, Various modifications are included. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. In addition, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment. The signal polarity shown in the timing chart is an example, and the present invention is not limited to this. In addition, part or all of the above-described configurations may be realized by, for example, one integrated circuit or a plurality of integrated circuits.

  In the above embodiment, the breakdown promotion circuit (114, 517, 801) includes the capacitor (201, 518, 802), the diode (202, 519, 803), and the resistor (203, 520, 804), but at least the capacitor (201, 518, 802) may be provided. The inductive load driving device (1A to 1C) includes at least FET (107, 507: switching element), gate resistance (104, 504: first resistance), Zener diode (112, 512), diode (113, 513: first diode) and a breakdown promoting circuit (114, 517, 801) may be provided.

  Further, each of the above-described configurations, functions, and the like may be realized by hardware by designing a part or all of them with, for example, an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by interpreting and executing a program that realizes each function by the processor. Information such as programs, tables, and files for realizing each function can be stored in a recording device such as a memory, a hard disk, or an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

  In addition, the following aspects may be sufficient as embodiment of this invention.

(1) Between the power source driving the inductive load and the power source and the ground,
With inductive load,
A switching element provided in series with the inductive load for on / off control of energization of the inductive load;
A drive control unit that outputs a control signal to perform on / off control to a control signal input terminal of the switching element;
A series resistor provided between a control signal output terminal of the drive control unit and a control signal input terminal of the switching element;
A diode in the opposite direction of a Zener diode is connected in series between the control signal input terminal of the switching element from the connection point of the inductive load and the switching element, and is induced by the breakdown voltage of the Zener diode when the inductive load is cut off. In the inductive load driving device in which the back electromotive voltage generated by the capacitive load is clamped to a predetermined voltage between the switching terminals of the switching element,
An inductive load drive characterized by having a circuit that increases the energizing current of the Zener diode to promote breakdown when the inductive load is cut off at the connection point between the Zener diode and the diode in the reverse direction. apparatus.

  (2) In the circuit for promoting the breakdown of the Zener diode of (1), a capacitor is provided in series with the clamping Zener diode, and at least an inductive load, a Zener diode and a capacitor constitute a closed loop circuit, and the inductive load is energized. An inductive load driving device that promotes breakdown of a Zener diode by causing a high-frequency current to flow through the Zener diode when the current is cut off.

  (3) In the circuit for promoting breakdown according to (1) and (2), a diode is provided in series so that only a high-frequency current that flows when energization of an inductive load is interrupted to the capacitor is provided. An inductive load driving device characterized in that a circuit for promoting down is electrically separated from a control signal circuit of a switching element.

  (4) In the circuit for promoting breakdown according to (1) and (2), the charge charged in the capacitor by the high-frequency current has a time constant that can be sufficiently discharged within the switching cycle of the inductive load. An inductive load driving device characterized in that a constant-selected resistor is provided in parallel to the capacitor.

  The present invention is applicable to inductive load driving circuits such as in-vehicle / aviation / marine equipment, refrigeration / refrigeration equipment, outdoor equipment, etc. that can be used in a low temperature environment.

1A, 1B, 1C ... Inductive load drive
101, 501 ... Control device
102, 502 ... Diagnostic Department
103, 503 ... Drive control unit
104, 504 ... Gate resistance
105, 505 ... Control signal
106 ... Control signal pull-down resistor
107, 507 ... Switching element
108,508 ... Grand
109,509… Battery power
110, 510 ... Inductive load
111,511… Load current
112, 512 ... Zener diode
113, 513 ... Diode
114, 517, 801 ... Breakdown promotion circuit
115, 515, 815, 902 ... Zener current
116, 516 ... Drain signal
201, 518, 802 ... capacitors
202, 519, 803 ... diode
203, 520, 804 ... discharge resistance
204, 521, 805 ... Capacitor potential
301,601… Clamp voltage
302,602 ... Capacitor charging voltage
303, 603 ... Switching cycle
304, 604 ... Inductive load off timing
305, 605 ... Off timing of next inductive load
401… Overshoot voltage
505 ... Control signal pull-up resistor
701: Undershoot voltage
901 ... Push-pull circuit

Claims (6)

A switching element that is connected in series to the inductive load and turns on / off a current supplied to the inductive load in response to a control signal;
A drive controller for supplying the control signal to the gate terminal of the switching element;
A first resistor connected in series from the drive control unit to the gate terminal of the switching element;
A Zener diode connected in series from the first connection point of the inductive load and the switching element to the second connection point of the first resistor and the gate terminal of the switching element and the reverse of the Zener diode A first diode in the direction;
Connected to said third connection point between the zener diode and the first diode, when a current supplied to the inductive load is turned off, the induction comprising a circuit for discharging the Zener current to high frequency, the A capacitive load drive device,
The circuit is
A capacitor charged by the Zener current supplied from the third connection point;
An inductive load driving device comprising: a second resistor connected in parallel to the capacitor and discharging the charge charged in the capacitor . The inductive load driving device according to claim 1,
The circuit is
An inductive load driving device characterized in that the Zener current is increased to promote breakdown of the Zener diode. The inductive load driving device according to claim 1 ,
The circuit is
The inductive load driving device further comprising a second diode connected in series from the third connection point to one end of the capacitor . The inductive load driving device according to claim 1 ,
One end of the capacitor is grounded. An inductive load driving device, wherein: A switching element that is connected in series to the inductive load and turns on / off a current supplied to the inductive load in response to a control signal;
A drive controller for supplying the control signal to the gate terminal of the switching element;
A first resistor connected in series from the drive control unit to the gate terminal of the switching element;
A Zener diode connected in series from the first connection point of the inductive load and the switching element to the second connection point of the first resistor and the gate terminal of the switching element and the reverse of the Zener diode A first diode in the direction;
An induction circuit connected to a third connection point between the Zener diode and the first diode and discharging the Zener current at a high frequency when the current supplied to the inductive load is turned off. A capacitive load drive device,
The circuit includes a capacitor charged by the Zener current supplied from the third connection point,
One end of the capacitor is connected to a power source that supplies current to the inductive load. The inductive load driving device according to claim 1 or 3 , wherein
The resistance value of the second resistor is
The inductive load driving device is characterized in that the discharge is set to be completed within a period of the control signal.

Images