JP2000105614A - Power control unit for electric equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To block voltages at both the terminals of a field effect transistor(FET) from exceeding a voltage resistance value and to attain the protection of this transistor by turning on an operation signal just for a while even when a driving signal for driving electric equipment is turned off. SOLUTION: The power control unit 11 is composed of an FET 4 serially connected to a driving coil 3, a snubber circuit 12 and an operation signal output part 17 and the operation signal output part 17 is composed of a driving signal generating circuit 18, a Vds detecting circuit 19, a voltage resistance discriminating circuit 20, an OR circuit 21 and an element operating circuit 22. When turning off a driving signal V1 and absorbing a counter electromotive force generated in the driving coil 3 through the snubber circuit 12, an operation signal V3 is turned on just for a while so that a detecting voltage Vds can not exceed the voltage resistance value of the FET 4, and the detecting voltage Vds is lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric motor for driving an electric device having an inductance component represented by an electric motor, an electromagnetic valve, an electromagnetic clutch, an electromagnetic relay or the like. The present invention relates to a power control device for a device.

In particular, the present invention relates to a power control device for an electric device having an element protection circuit for preventing a switching element from being destroyed by a back electromotive force generated in an inductance component when a drive signal is switched from on to off.

[0003]

2. Description of the Related Art In general, electric equipment having an inductance component includes an electric motor, an electromagnetic valve, an electromagnetic clutch, an electromagnetic relay, and the like. For example, as an electromagnetic valve used for controlling an engine of an automobile, an air-fuel ratio of an engine during idling is used. An idle control valve that controls the flow rate of air to compensate for this, and controls the flow rate of this gas when a part of the exhaust gas from the engine is introduced into the intake side of the engine to reduce the combustion temperature of the engine. There is an EGR control valve and the like. In addition, as such an electromagnetic valve, a valve that can freely set a valve opening in order to control the flow rate of each gas with high accuracy is used.

In order to electronically control the solenoid valve,
A power control device is provided together with a control unit for mounting on a vehicle, and the power control device supplies a drive coil (an inductance component) of the solenoid valve with a drive signal based on an operation signal input from the control unit,
The flow rate of each gas is controlled by increasing and decreasing the valve opening of the solenoid valve. A pulse wave is used as a drive signal output from the power control device to the drive coil of the solenoid valve.

Here, in a drive coil of an electromagnetic valve or the like, when a drive signal is switched from on to off, a back electromotive force stored in the drive coil is generated as a large surge voltage, and the surge voltage is generated by the switching element. There is a risk of dielectric breakdown.

[0006] Therefore, there is a power control device of this kind in the related art provided with an element protection circuit as shown in FIGS. 8 to 10. Here, an example in which a solenoid valve is controlled will be described. I do.

[0007] 1 is a DC voltage E to a power control device 2 described later.
The battery 1 outputs, for example, a DC voltage E of 12 V.

Reference numeral 2 denotes a power control device according to the prior art. The power control device 2 includes a field effect transistor 4 as a switching element connected in series to a drive coil 3 of an electromagnetic valve.
An operation signal output unit 5 for outputting a pulse-like operation signal to the gate of the field effect transistor 4; and a snubber circuit for preventing breakdown of the field effect transistor 4 when a back electromotive force is generated in the drive coil 3. 6 are roughly constituted. The drive coil 3 has an inductance L and a resistance value R. The field effect transistor 4 has a drain connected to the drive coil 3 and a source connected to the negative side of the battery 1. Further, in the field effect transistor 4, the voltage between the drain and the source is Vds, and the maximum voltage value that can be applied between the drain and the source is a withstand voltage value Vdss.

Reference numeral 6 denotes a snubber circuit as an element protection circuit.
The snubber circuit 6 includes a capacitor 8 connected in parallel between the drain and the source of the field-effect transistor 4 and connected via a diode 7, and a connection point 9 between the capacitor 8 and the diode 7. Battery 1 for drive coil 3
And a resistor 10 connected between the positive side and the positive side.

The capacitance of the capacitor 8 is represented by Cs, the resistance of the resistor 10 is represented by Rs, and as shown in FIG.
Let iL be the current flowing through the drive coil 3, i be the current flowing between the drain and source of the field effect transistor 4, iD be the current flowing through the diode 7 of the snubber circuit 6, and VC be the voltage of the capacitor 8. 9 and 10, the current ip indicates the peak value of the current i flowing from the drain to the source of the field-effect transistor 4, and the voltage Vdsp indicates the final value of the voltage Vds.

Here, the operation of the power control device 2 for the solenoid valve will be described. When a pulse-like operation signal is input to the gate of the field effect transistor 4 from the operation signal output unit 5, the signal causes the field effect transistor 4 to operate. 4 is closed between the drain and the source, a pulse-like drive signal corresponding to the operation signal is output to the drive coil 3, and the drive coil 3 generates an electromagnetic force by the supplied current, To work.

On the other hand, when the operation signal output from the operation signal output unit 5 is switched from on to off, the connection between the drain and the source of the field effect transistor 4 is opened, and the drive signal is turned on in the drive coil 3. Is switched to off, and the electromagnetic force by the drive coil 3 is eliminated.

However, as described above, since the power is stored in the inductance L of the drive coil 3 by the drive signal at the time of ON, the back electromotive voltage VR corresponding to the time change of the current is generated at both ends of the inductance L. I do. The back electromotive voltage VR is expressed by the following equation (1).

[0014]

(Equation 1)

The back electromotive voltage VR may be superimposed on the DC voltage E of the battery 1 and destroy the field effect transistor 4. Therefore, the power control device 2 is provided with a snubber circuit 6.

Here, the circuit operation of the snubber circuit 6 will be described with reference to the characteristic diagrams of FIGS.

Now, when the operation signal output from the operation signal output section 5 is turned off from on to off and turned off, the voltage Vds becomes less than the DC voltage E + VD (the forward voltage of the diode 7). Since the rate of change di / dt is large, the back electromotive voltage VR sharply increases. But,
Thereafter, the current iD starts to flow through the diode 7,
The current change rate di / dt decreases, and the voltage Vds applied to the field-effect transistor 4 gradually increases to suppress the surge voltage. On the other hand, the capacitance Cs of the capacitor 8
Is set such that the final attained value Vdsp of the voltage Vds is smaller than the withstand voltage Vdss of the field-effect transistor 4.
R is absorbed.

Further, a safe operation area curve shown in FIG.
The peak value ip of the current i and the final attained value Vdsp of the voltage Vds can be located in the SOA curve as shown in the SOA curve) and the current-voltage characteristic locus at the time of turn-off. Thus, the field effect transistor 4 can be protected.

Next, the setting of the capacitance Cs of the capacitor 8 constituting the snubber circuit 6 and the resistance value Rs of the resistor 10 will be described.

First, when the field effect transistor 4 is in the on state immediately before the turn off, the power WL stored in the drive coil 3 is expressed by the following equation (2).

[0021]

(Equation 2)

Since all of the power WL must be absorbed by the capacitor 8, the following equation (3) is established from the relation of power.

[0023]

(Equation 3)

Equations (2) and (3) are transformed to obtain the capacitance Cs
Is calculated, Equation 4 is obtained.

[0025]

(Equation 4)

The function of the resistor 10 is to discharge the accumulated charge in the capacitor 8 until the field-effect transistor 4 performs the next turn-off operation. Therefore, for example, the accumulated charge is accumulated before the next turn-off operation. When the resistance value Rs is set under the condition of discharging 90% of the following equation, the following equation (5) is obtained.

[0027]

(Equation 5) Where f is the switching frequency of the field effect transistor 4

Here, if the resistance value Rs of the resistor 10 is set to a value that is too small, the current iD of the snubber circuit 6 will oscillate. Therefore, it is better to set the value as large as possible within a range that satisfies Equation 5.

[0029]

The power control device 2 according to the prior art is provided with a snubber circuit 6 for protecting the field effect transistor 4, and the snubber circuit 6 charges the back electromotive voltage VR. A capacitor 8 for the The capacitance CS of the capacitor 8 is:
As described above, the voltage Vds is equal to the withstand voltage Vdss.
Is set so as not to exceed, so that a relatively large capacitance is required.

On the other hand, in the power control device 2, it is necessary to quickly supply the current to the drive coil 3 at the time of driving, and to stop the current quickly at the time of cutoff.
The back electromotive voltage VR generated in the drive coil 3 must be charged quickly. However, in the capacitor 8 according to the prior art, the charging time is wasted because the capacitance CS is increased for the above-described reason. For this reason, the power control device 2 has a problem that when the drive signal is turned off, the current cannot be stopped quickly, and the performance of the electric device cannot be improved.

The present invention has been made in view of the above-described problems of the prior art, and the present invention provides a small capacitance by appropriately turning on an operation signal for activating a switching element even when a drive signal is in an off state. It is an object of the present invention to provide a power control device for electric equipment that can protect a switching element by absorbing a back electromotive force generated at the time of turn-off even with a capacitor.

[0032]

In order to solve the above-mentioned problems, a power control apparatus for an electric device according to the present invention includes a switching element which is connected in series to an electric device having an inductance component and operates by inputting an operation signal; A capacitor connected in parallel with the switching element and connected via a diode; a resistor connected between a connection point between the capacitor and the diode and a power supply side of the electric device; And an operation signal output unit that outputs an operation signal to the switching element to operate the element.

According to the first aspect of the present invention, the operation signal output section includes a drive signal generating means for generating a drive signal for driving the electric device, and a voltage detection circuit for detecting both ends of the switching element as a detection voltage. Means for outputting a determination signal for activating the switching element only for a short time when the detected voltage detected by the voltage detection means exceeds a withstand voltage determination value set near the withstand voltage value of the switching element. The switching element is activated when at least one of a withstand voltage judging means for outputting the judgment signal output from the withstand voltage judging means and the driving signal output from the driving signal generating means is output. Signal output means for outputting a signal.

As described above, the diode and the capacitor connected to both ends of the switching element, and the resistor connected between the connection point between the diode and the capacitor and the power supply side of the electric device constitute the element protection circuit. Therefore, when the drive signal applied to the electric device is switched from on to off, the back electromotive force generated in the inductance component of the electric device is absorbed by the element protection circuit, and the switching element is protected.

When the drive signal is turned off, the back electromotive force stored in the inductance component of the electric device flows through the switching element, and the voltage across the switching element connected in parallel with the capacitor rapidly increases. At this time, since the detection voltage detected by the voltage detection means exceeds the withstand voltage determination value, the withstand voltage determination means and the signal output means output an operation signal which is turned on only for a short time to the switching element. For this reason, even when the drive signal for driving the electric device is in the off state, the detection voltage can be reduced before the withstand voltage of the switching element is exceeded, for example.

Further, for example, by setting the withstand voltage determination value to a value smaller than the withstand voltage value, the value can be set smaller than the capacitance of a conventional capacitor.

According to the second aspect of the present invention, the minute time is set as a time until the electric device substantially starts the load start even when the operation signal is input to the switching element.

With this configuration, even if the drive signal for driving the electric device is in the off state and the operation signal for activating the switching element is in the on state, the load of the electric device is substantially started. Without switching, the switching element can be protected.

According to the third aspect of the present invention, the withstand voltage determining means includes:
A determination signal output start means for starting to output a determination signal when the detection voltage rises above a withstand voltage determination value; and when the detection voltage falls below a startup determination value at which the electric device substantially starts load startup. And a determination signal output stopping means for stopping the output of the determination signal.

With this configuration, the determination signal output from the determination signal output start means and the determination signal output stop means can be turned on for a short time. For this reason, even if the switching element is operated only for a short time by the determination signal, the current flowing through the electric device can be set to a value lower than the current value at which the electric device substantially starts the load start, and the drive signal is turned off. In this case, the switching element can be protected without driving the electric device.

According to a fourth aspect of the present invention, an avalanche diode is connected in parallel to both ends of the switching element, and the withstand voltage judgment value used in the withstand voltage judgment means is set to a value lower than the withstand voltage value of the avalanche diode. It is in.

With this configuration, even if the operation signal is turned off and the current due to the back electromotive force stored in the inductance component flows through the switching element,
By appropriately operating the switching element according to the withstand voltage determination value set to a value lower than the withstand voltage value of the avalanche diode, the voltage across the switching element is prevented from exceeding the withstand voltage value of the avalanche diode. Protection of the diode and the switching element can be achieved.

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a power control device according to the present invention will be described below in detail with reference to FIGS. In the present embodiment, the same components as those of the above-described related art are denoted by the same reference numerals, and description thereof will be omitted.

First, the first embodiment will be described with reference to FIGS.
A case where the solenoid valve is controlled based on the above will be described as an example.

Reference numeral 11 denotes a power control device used in the present embodiment. The power control device 11 includes a drive coil 3 for an electromagnetic valve.
A field-effect transistor 4 as a switching element connected in series to the switch, a snubber circuit 12 for preventing the field-effect transistor 4 from being destroyed when a back electromotive force is generated in the drive coil 3, It is roughly constituted by an operation signal output section 17 described later for inputting an operation signal V3 to the gate.

The snubber circuit 12 has a field effect transistor 4 similar to the snubber circuit 6 according to the prior art.
A capacitor 14 having a capacitance C0 connected in parallel between the drain and the source of the driving coil 3 and having a capacitance C0 connected through a diode 13; a connection point 15 between the capacitor 14 and the diode 13; And a resistor 16 having a resistance value R0 connected therebetween.

Reference numeral 17 denotes an operation signal output unit applied to the present embodiment. The operation signal output unit 17 is constituted by, for example, electronic components, and the operation signal output unit 17 is provided with a drive signal generation circuit 18 described later. , Vds detection circuit 19, withstand voltage determination circuit 20, OR circuit 21, and element operation circuit 22.

Reference numeral 18 denotes a drive signal generation circuit as drive signal generation means. The drive signal generation circuit 18 generates a pulsed drive signal V1 as shown in the upper part of FIG. The drive signal V1 is output repeatedly at the switching frequency f in order to operate the solenoid valve.

Reference numeral 19 denotes a Vds detecting circuit as a voltage detecting means for both ends. The Vds detecting circuit 19 detects a voltage between the drain and the source of the field effect transistor 4 by a detecting voltage Vds.
Is detected.

Reference numeral 20 denotes a withstand voltage determination circuit as withstand voltage determination means. The withstand voltage determination circuit 20 includes a withstand voltage determination value VA set to a value lower than the withstand voltage value Vdss of the field effect transistor 4. And a start determination value VB at which the solenoid valve starts substantial load start. The withstand voltage determination circuit 20 compares the detection voltage Vds input from the Vds detection circuit 19 with the withstand voltage determination value VA and the activation determination value VB, as shown in the second stage in FIG. The detection voltage Vds is changed from the withstand voltage determination value VA to the activation determination value V.
The determination signal V2 as shown at the third stage in FIG. 2 is output to the OR circuit 21 only during the short time .DELTA.T when descending toward B.

Reference numeral 21 denotes an OR circuit. The OR circuit 21 has an input side to which the drive signal generation circuit 18 and the withstand voltage determination circuit 20 are connected, and an output side to which an element operation circuit 22 is connected. In the OR circuit 21, when at least one of the drive signal V1 and the determination signal V2 is turned on, the on signal is turned on by the element operation circuit 22.
Output to

Reference numeral 22 denotes an element operation circuit comprising a driver circuit. The element operation circuit 22 receives an output signal from the OR circuit 21 and outputs an operation signal V3 for operating the field effect transistor 4 to the field effect transistor 4. 4 is output to the fourth gate. Note that the OR circuit 21 and the element operation circuit 22 constitute a signal output unit according to the present invention.

Next, the power control device 1 according to the present embodiment
The circuit operation of No. 1 will be described with reference to the characteristic diagram of FIG.

First, when the drive signal V1 output from the drive signal generation circuit 18 for operating the solenoid valve is in the ON state, the OR circuit 21 receives the ON drive signal V1 and the OFF state determination signal V2. Since they are respectively input, the OR circuit 21 and the element operation circuit 22 output an operation signal V3 in an ON state toward the gate of the field effect transistor 4. Then, in the field effect transistor 4, the connection between the drain and the source is closed, and a drive signal is output to the drive coil 3 to drive the solenoid valve.

On the other hand, when the drive signal V1 output from the drive signal generation circuit 18 is turned off from on to off and turned off, the OR circuit 21 receives the off-state drive signal V1 and the off-state determination signal V2, respectively. Is entered,
From the OR circuit 21 and the element operation circuit 22, an OFF operation signal V3 is output to the gate of the field effect transistor 4. Thereby, in the field-effect transistor 4,
The opening between the drain and the source is opened, and the drive coil 3 is opened.
To eliminate the electromagnetic force caused by

When the drive signal V1 is turned off, the detection voltage Vds becomes the DC voltage E + VD (diode 7
Until the voltage reaches the forward voltage), the current change rate di /
Since dt is large, the back electromotive voltage VR sharply increases. However, thereafter, since the current iD starts flowing through the diode 13 and the capacitor 14 starts to be charged, the current change rate d
i / dt decreases, and the detection voltage Vds applied to the field effect transistor 4 gradually increases.

Further, when the detected voltage Vds rises and exceeds the withstand voltage determination value VA, the withstand voltage determination circuit 20 outputs an ON state determination signal V2 to the OR circuit 21 and the element operation circuit 22 outputs the ON state. Is output to the field effect transistor 4. Then, by closing the field effect transistor 4, a current flows through the drive coil 3 and the detection voltage Vds decreases.

Thereafter, when the detection voltage Vds falls below the activation determination value VB, an off-state operation signal V3 for opening the field effect transistor 4 is output from the element operation circuit 22, and the field effect transistor 4 is opened. Then, the capacitor 14 starts charging and the detection signal Vds rises again.

Here, the detected voltage Vds is equal to the withstand voltage determination value VA.
The period from a further rise to a fall below the activation determination value VB is set to a minute time ΔT. This minute time ΔT
Is that even if the operation signal V3 is input to the field effect transistor 4 and the field effect transistor 4 is temporarily closed, the solenoid valve substantially starts to start the load (starts to open by excitation). It is set as the time until. As described above, although the current iL flows through the drive coil 3 of the solenoid valve during the minute time ΔT, the solenoid valve does not exceed the current value im at which the load starts to be started. I have.

This operation is repeated until the back electromotive force of the drive coil 3 is absorbed by the capacitor 14, and thereafter, the detection voltage Vds falls below the activation determination value VB.

This operation becomes a characteristic diagram as shown in FIG. 2, and even if the drive signal V1 is off, the detection voltage V
When ds is falling from the withstand voltage determination value VA to the start determination value VB, the activation signal V3 is turned on only for a short time ΔT, so that the detection voltage Vds becomes the withstand voltage value Vdss.
Prevent from crossing.

On the other hand, after the drive signal V 1 is turned off, the current iD due to the back electromotive force stored in the drive coil 3
Flows toward the diode 13 and charges the capacitor 14. This charging is performed when the operation signal V3 is in the off state and is not performed when the operation signal V3 is in the on state. Therefore, the current iD changes with the on / off operation of the operation signal V3.
In addition, since the back electromotive force flows through the field effect transistor 4 when it is turned on and is prevented from flowing when turned off, the current i flowing through the field effect transistor 4 also changes. Then, the back electromotive force of the drive coil 3 is charged in the capacitor 14 and discharged through the resistor 16, so that the current iD decreases.

Further, in order to clarify the operation of the operation signal output unit 17, its operation will be described with reference to the flowchart of FIG.

First, in step 1, the drive signal generation circuit 1
It is determined whether or not the drive signal V1 output from 8 is in the off state. If the determination is "NO", it is determined that a normal signal for operating the solenoid valve is input, and the routine proceeds to step 2. In step 2, the operation signal V3 is turned on and output to the gate of the field effect transistor 4. Then, by closing the field effect transistor 4, an electromagnetic force is generated in the drive coil 3. Further, the process returns in step 13.

On the other hand, if "YES" is determined in step 1, the driving signal V1 is in the off state,
Assuming that the back electromotive force has been generated in the drive coil 3, the processing after step 3 is performed.

In step 3, the detection voltage Vds is read from the Vds detection circuit 19, and in step 4, it is determined whether the detection voltage Vds is higher than the activation determination value VB. If the determination in step 4 is "NO", , The detection voltage Vds is lower than the activation determination value VB. Therefore, step 5
Then, the decision voltage V2 is turned off, that is, the output of the decision signal V2 is stopped. In step 6, the off-state activation signal V3 is output to the field effect transistor 4. Then, the field effect transistor 4 is opened, and the process returns to the step S13.

On the other hand, if "YES" is determined in the step 4, the detection voltage Vds is higher than the activation determination value VB, and the process proceeds to a step 7.

In this step 7, it is determined whether or not the detected voltage Vds is lower than the withstand voltage determination value VA. If "NO" is determined, the detected voltage Vds exceeds the withstand voltage determination value VA. It is. Therefore, in step 8, the determination signal V2
Is turned on, that is, the output of the determination signal V2 is started. In step 9, the on-state operation signal V3 is output to the field effect transistor 4. And the field effect transistor 4
Is closed, and the routine returns to the step S13.

On the other hand, if "YES" is determined in the step 7, it means that the detected voltage Vds is lower than the withstand voltage determination value VA, and the process proceeds to the step 10. This step 1
0, it is determined whether or not the determination signal V2 is in the off state, and "Y
If "ES" is determined, although the detection voltage Vds is between the activation determination value VB and the withstand voltage determination value VA, but has not yet exceeded the withstand voltage determination value VA, the activation signal V3 is turned off in step 11. Then, the process returns to step 13.

On the other hand, if "NO" is determined in the step 10, the detection voltage Vds is between the activation determination value VB and the withstand voltage determination value VA, and has exceeded the withstand voltage determination value VA in some cases. From step 1 to step 12
In step 2, the operation signal V3 is turned on and output to the field effect transistor 4, and the process returns in step 13.

As described above, in the present embodiment, even when the drive signal V1 is in the off state, the operation signal V3 output from the operation signal output unit 17 is turned on for only a short time ΔT, thereby detecting the detection voltage Vds Can be prevented from exceeding the withstand voltage value Vdss.

As a result, the SOA (safe operation area) shown in FIG.
As shown by the curve and the current-voltage characteristic locus at the time of turn-off, the peak value ip of the current i and the final attained value Vdsp of the detection voltage Vds can be located in the SOA curve, and the field effect transistor 4 is protected. be able to.

Next, the setting of the capacitance C0 of the capacitor 14 and the resistance R0 of the resistor 16 constituting the snubber circuit 12 will be described.

As described above, when the withstand voltage determination value VA smaller than the withstand voltage value Vdss is exceeded, the field effect transistor 4 is closed. The capacitance C0 of the capacitor 14 can be set smaller than the capacitance Cs.

On the other hand, the capacitance C 0 of the capacitor 14 is
As shown in FIG. 2, when the drive signal V1 is in the off-state, the on-state operation signal V3 is output to the field-effect transistor 4, and the field-effect transistor 4 is closed.
The current iL flowing through the drive coil 3 is set to a value not exceeding the current value im at which the solenoid valve starts operating.

From the above points, the capacitance C0 of the capacitor 14 used in the present embodiment is set as shown in Equation 6. Note that the left side is a condition for the solenoid valve not to operate even when the current iL is supplied to the drive coil 3, and the right side is a condition for turning the drive signal V1 off and the determination signal V2 on.

[0077]

(Equation 6)

The function of the resistor 16 is to discharge the electric charge stored in the capacitor 14 until the field-effect transistor 4 performs the next turn-off operation.
For example, when the resistance value R0 is set under the condition that 90% of the accumulated charge is discharged before the next turn-off operation, the following equation is obtained.

[0079]

(Equation 7)

Thus, in the power control device 11 according to the present embodiment, the voltage (the detection voltage Vds) across the field-effect transistor 4 is monitored by the operation signal output unit 17 and the detection voltage Vds becomes the withstand voltage determination value VA. When the voltage exceeds the threshold voltage Vds, the detection signal Vds can be lowered before exceeding the withstand voltage value Vdss by appropriately turning on the operation signal V3 for a very short time ΔT, thereby protecting the field effect transistor 4. be able to.

When the detection signal Vds exceeds the withstand voltage determination value VA, the withstand voltage determination circuit 20 in the operation signal output unit 17 closes the field effect transistor 4 so that the detection voltage Vds becomes the withstand voltage value. Since it is prevented from exceeding Vdss, the capacitance C0 of the capacitor 14 can be set smaller than the capacitance CS of the capacitor 8 according to the prior art. As a result, the capacitor 14 receives the drive signal V1
, The back electromotive force generated at the time of turn-off can be quickly charged, and the current i at the time of off can be quickly stopped, and the performance of the solenoid valve used as an electric device can be improved.

The power control apparatus 1 according to the present embodiment
When the electric device 1 is used for an electric motor or the like having the same drive coil, the electric power control device 11 must be provided for each drive coil. By reducing C0,
These power control devices 11 can be reduced in size.
Moreover, in the power control device 11, the time required for the detection voltage Vds to reach the final attainment value Vdsp can be reduced as compared with the related art, so that the switching frequency f can be increased.

Further, in this case, the operation signal output unit 1
The operation signal output unit 17 can be constituted by a microcomputer instead of individually constituted by electronic components.

Next, a second embodiment will be described with reference to FIGS. 5 to 7. In the present embodiment, an avalanche diode is built in between a drain and a source of a field-effect transistor. is there. It is to be noted that the same components as those of the above-described first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

Reference numeral 31 denotes a power control device according to the present embodiment. The power control device 31 has substantially the same configuration as the power control device 11 according to the first embodiment, but includes a field-effect transistor 32 and a capacitor 34. , The resistance 35 and the withstand voltage determination circuit 36 of the operation signal output unit 17 are different.

Reference numeral 32 denotes a field-effect transistor as a switching element connected in series to the drive coil 3. An avalanche diode 33 is connected in parallel between the drain and the source of the field-effect transistor 32. The avalanche diode 33 It is built into the field effect transistor 32. And the avalanche diode 33
If the avalanche voltage as the withstand voltage value of is VAR,
The avalanche diode 33 prevents a voltage higher than the avalanche voltage VAR from being applied to the field effect transistor 4.

A capacitor 34 constitutes a part of the snubber circuit 12. The capacitor 34 is connected between the drain and the source of the field effect transistor 32 by a diode 13
Connected through. The capacitance of the capacitor 34 is set to C0 '.

Reference numeral 35 denotes a resistor which constitutes a part of the snubber circuit 12. The resistor 35 is connected between the connection point 15 between the capacitor 34 and the diode 13 and the positive side of the drive coil 3. The resistance of the resistor 35 is set to R0 '.

Reference numeral 36 denotes a withstand voltage judging circuit which constitutes the operation signal output unit 17. The withstand voltage judging circuit 36 is substantially the same as the withstand voltage judging circuit 20 according to the first embodiment, and the Vds detecting circuit 19 and the OR gate. Although connected to the circuit 21, the withstand voltage determination circuit 36 has a withstand voltage set to a value higher than the withstand voltage Vdss of the field-effect transistor 4 and lower than the avalanche voltage VAR of the avalanche diode 33. A voltage judgment value VA 'and a start judgment value VB' are built in. As shown in the second stage in FIG. 6, the detection voltage Vds input from the Vds detection circuit 19 is changed from the withstand voltage judgment value VA 'to the start judgment value. A minute time ΔT 'when descending toward VB'
The determination signal V2 as shown in the third stage is
Output to 1.

The withstand voltage of the field effect transistor 32 is set by the avalanche voltage VAR of the avalanche diode 33 which is higher than the withstand voltage Vdss up to now. As a result, the final attained value Vdsp of the detection voltage Vds of the field effect transistor 32 becomes lower than the avalanche voltage VAR of the avalanche diode 33, so that the capacitance C0 'of the capacitor 34 is set correspondingly. do it.

That is, the capacitance C0 'of the capacitor 34 used in the present embodiment is set as shown in Expression 8.

[0092]

(Equation 8)

The function of the resistor 35 is to discharge the accumulated charge of the capacitor 34 until the field-effect transistor 32A performs the next turn-off operation. Therefore, for example, the accumulated charge is discharged before the next turn-off operation. Of 90
%, The resistance value R0 'is set as shown in equation (9).

[0094]

(Equation 9)

As described above, also in the power control device 31 according to the second embodiment, the protection of the field-effect transistor 32 can be more reliably achieved as in the first embodiment described above. As shown in FIG.
The back electromotive force generated at turn-off of
The battery can be charged quickly, and the performance of electrical equipment can be improved. Further, as shown in FIG. 7, the peak value ip and the final attained value Vdsp can be located in the SOA curve, and the field effect transistor 32 and the avalanche diode 33
Can be protected.

In the first embodiment, step 7 in the flowchart shown in FIG. 3 is a specific example of the determination signal output start means, and step 4 is a specific example of the determination signal output stop means.

In each of the embodiments, even when the drive signal V1 is in the off state, the detection voltage Vds is not changed to the withstand voltage determination value VA.
The activation signal V3 is turned on only for a short time ΔT when the voltage falls from (VA ′) to the activation determination value VB (VB ′). However, the present invention is not limited to this. Of course, the activation signal V3 may be set to be turned on only for a predetermined fixed short time when it exceeds.

In each of the embodiments, a field effect transistor is used as a switching element. However, the present invention is not limited to this, and a switching transistor, a triac, or the like may be used.

[0099]

As described above in detail, according to the first aspect of the present invention, the drive signal is turned off, the back electromotive force stored in the inductance component of the electric device flows through the switching element, and the voltage across the switching element is obtained. Rises sharply.
At this time, since the detection voltage detected by the voltage detection means exceeds the withstand voltage determination value, the withstand voltage determination means and the signal output means output to the switching element an activation signal which is turned on only for a short time. Therefore, even when the drive signal for driving the electric device is in the off state, for example, the detection voltage can be reduced before the withstand voltage of the switching element is exceeded, and the switching element can be protected.

Also, for example, by setting the withstand voltage determination value to a value smaller than the withstand voltage value, the value can be set smaller than the capacitance of a conventional capacitor, and the time required for the capacitor to be charged is reduced. It is possible to quickly stop the current flowing through the electric device when the operation signal is turned off, thereby enhancing the performance of the electric device.

According to the second aspect of the present invention, the minute time during which the switching element is operated by the withstand voltage determination means is a time until the electric device substantially starts load driving even when an operation signal is input to the switching element. When the drive signal for driving the electric device is in the off state, the switching device is protected for a short period of time without turning on the electric device, even if the operation signal for activating the switching device is in the on state for a short time. Can be.

According to the third aspect of the present invention, the withstand voltage determining means includes:
A determination signal output start means for starting to output a determination signal when the detected voltage rises above a withstand voltage determination value, and outputting a determination signal when the detected voltage falls below a start determination value at which the electric device starts load driving practically The determination signal output from the withstand voltage determination means, the determination signal output from the withstand voltage determination means can be turned on for a short time,
When the drive signal is in the OFF state, the switching element can be protected without substantially starting load starting of the electric device.

According to the fourth aspect of the present invention, an avalanche diode is connected in parallel to both ends of the switching element, and the withstand voltage judgment value used in the withstand voltage judgment means is set to a value lower than the withstand voltage value of the avalanche diode. Even if the drive signal is turned off and the back electromotive force stored in the inductance component flows through the switching element, the switching element is appropriately driven by the withstand voltage determination value set to a value lower than the withstand voltage value of the avalanche diode. This prevents the voltage at both ends from exceeding the withstand voltage value of the avalanche diode and protects the avalanche diode and the switching element.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a power control device according to a first embodiment.

FIG. 2 is a characteristic diagram illustrating a drive signal, a detection voltage, a determination signal, an operation signal, and a current in the power control device according to the first embodiment.

FIG. 3 is a flowchart illustrating an operation of a drive signal output unit.

FIG. 4 is a characteristic diagram showing a safe operation area curve and a current / voltage characteristic trajectory at the time of turn-off according to the first embodiment.

FIG. 5 is a circuit diagram showing a power control device according to a second embodiment.

FIG. 6 is a characteristic diagram showing a drive signal, a detection voltage, a determination signal, an operation signal, and a current in the power control device according to the second embodiment.

FIG. 7 is a characteristic diagram showing a safe operation area curve and a current / voltage characteristic locus at the time of turn-off according to the second embodiment.

FIG. 8 is a circuit diagram showing a power control device according to the related art.

FIG. 9 is a characteristic diagram showing an operation signal, a voltage, and a current in the power control device according to the related art.

FIG. 10 is a characteristic diagram showing a safe operation area curve and a current / voltage characteristic locus at the time of turn-off.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Battery (DC power supply) 3 Drive coil 4, 32 Field effect transistor (switching element) 11, 31 Power control device 12 Snubber circuit 13 Diode 14, 34 Capacitor 15 Connection point 16, 35 Resistance 17 Operation signal output part 18 Drive signal Generation circuit (drive signal generation means) 19 Vds detection circuit (voltage detection means at both ends) 20, 36 Withstand voltage determination circuit (withstand voltage determination means) 21 OR circuit (signal output means) 22 Element operation circuit (signal output means) 33 Avalanche Diode VA, VA 'Withstand voltage judgment value VB, VB' Start judgment value ΔT, ΔT 'minute time

Claims (4)

[Claims] A switching element connected in series to an electric device having an inductance component and operated by input of an operation signal; a capacitor connected in parallel with the switching element and connected via a diode; A resistor provided between the connection point therebetween and the power supply side of the electrical device, and an activation signal output unit that outputs an activation signal to the switching device to activate the switching device. In the power control device, the operation signal output unit includes a drive signal generation unit that generates a drive signal for driving the electric device, a voltage detection device that detects a voltage across the switching element as a detection voltage, A detection voltage detected by the both-ends voltage detection means is set near a withstand voltage value of the switching element. Withstand voltage determination means for outputting a determination signal for operating the switching element only for a short time when the withstand voltage determination value is exceeded, a determination signal output from the withstand voltage determination means, and output from the drive signal generation means A power output device for outputting an operation signal to the switching element when at least one of the drive signal is output. 2. The small time is set as a time until the electric device substantially starts a load start even when an operation signal is input to the switching element.
A power control device for an electrical device according to claim 1. 3. The withstand voltage determination means includes: a determination signal output start means for starting to output a determination signal when the detected voltage rises above a withstand voltage determination value; 3. The power control device for an electric device according to claim 1, further comprising: a determination signal output stop means for stopping the output of the determination signal when the load value falls below a start determination value for starting load startup. 4. An avalanche diode is connected in parallel to both ends of the switching element, and a withstand voltage judgment value used by the withstand voltage judgment means is set to a value lower than the withstand voltage value of the avalanche diode. Item 6. An electric power control device for an electric device according to Item 1, 2, or 3.