JP2001238348A - Protection circuit for power supply for inductive load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a closed circuit for absorbing a surge current of an inductive load with an element having relatively low power consumption and for an inductive load which does not require a backflow prevention diode having a large current capacity in a main power supply circuit. Obtain a power supply protection circuit. A protection circuit for an inductive load power supply device for energizing an inductive load 5 with a battery 1 through a Pch MOSFET 2P includes an Nch MOSFET 12N connected in parallel to the Pch MOSFET 2P or the inductive load 5.
When the PchMOSFET2P is turned off, the NchMOS
The FET 12N detects a surge voltage of the inductive load 5 and conducts to form a current closed circuit, and absorbs a surge generated in the inductive load 5 by the current closed circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for an inductive load power supply device for energizing an inductive load such as an induction motor through a switching element such as a field effect transistor.

[0002]

2. Description of the Related Art In an inductive load power supply, when the energizing current is suddenly cut off when the switching element is turned off, a high voltage surge is generated in the inductive load, and this surge voltage may damage the switching element. Was. As a conventional protection circuit against such a surge voltage, there is, for example, a conventional example A shown in FIG. Here, a battery 1 which is a DC power source is switched to a power switching element P
Channel MOS type field effect transistor (hereinafter, Pc
Abbreviated as hMOSFET. ) Inductive load 5 through 2P
PchM as a protection circuit for the power supply main circuit
A constant voltage diode 6 having a Zener voltage lower than the withstand voltage of the PchMOSFET 2P is connected in parallel with the OSFET 2P.

[0006] The conduction of the PchMOSFET 2P is controlled by a drive circuit 7. When a surge voltage equal to or greater than the Zener voltage value is generated in the inductive load 5 by turning off the Pch MOSFET 2P, a current path is formed by conducting the constant voltage diode 6, and the surge is absorbed in this current path.

FIG. 8 shows another conventional example B in which a diode 8 is connected in anti-parallel to an inductive load 5 and a surge voltage between both terminals of the inductive load 5 is absorbed by the diode 8 when a surge voltage occurs. I am trying to do it. When the battery 1 is reversely connected by mistake, the diode 8 and the PchMOS
Since a forward voltage is applied to the parasitic diode 3 of the FET 2P, a diode 9 is inserted in the power supply main circuit to prevent a reverse voltage short circuit.

[0005]

However, according to the configuration of the conventional example A, when the zener voltage of the constant voltage diode 6 is, for example, 40 V, the conduction start voltage of the constant voltage diode 6 due to the surge voltage becomes 40 V, and therefore, When a surge occurs, if the constant voltage diode 6 has a large peak power, that is, if the current of the power supply main circuit is 10 A, 4
Since power consumption of 00 W (40 V × 10 A) is generated, an expensive element with a high withstand voltage is required as the constant voltage diode 6. Further, according to the configuration of the conventional example B, an expensive large-current diode that can withstand the large current of the power supply main circuit is required as the diode 9 for preventing reverse voltage short circuit. Further, there is a problem that a loss is caused by a forward voltage drop of the diode 9.

The present invention has been made in view of the above problems, and can be constituted by an inexpensive element having relatively low power consumption, and does not require a diode for a large current for preventing backflow. An object is to provide a protection circuit for a device.

[0007]

According to a first aspect of the present invention, there is provided a protection circuit for an inductive load power supply unit for inducing an inductive load with a DC power supply through a switching element. A protection element consisting of a field-effect transistor connected in parallel to the switching element, a source of the protection element is connected to a series connection point of the switching element and the inductive load, and a gate and a drain of the protection element are respectively set to a predetermined potential. When the switching element is turned off, the protection element conducts due to the potential fluctuation of its source to form a current closed circuit, and the surge generated in the inductive load at turn off is absorbed by the current closed circuit. It was done.

According to a second aspect of the present invention, the switching element according to the first aspect of the present invention is particularly configured by a Pch MOSFET, a source of the switching element is connected to a positive electrode potential of a DC power supply, and a drain of the switching element is induced. The protection element is connected to the negative potential of the DC power supply through a load, and the protection element is an N-channel MOS field effect transistor (hereinafter abbreviated as NchMOSFET).
And the drain of the protection element is connected to the positive potential of the DC power supply, and the gate of the protection element is connected to the negative potential of the DC power supply.

According to a third aspect of the present invention, the switching element according to the first aspect of the present invention is particularly configured by an N-channel MOS field effect transistor (hereinafter abbreviated as an Nch MOSFET), and the source of the switching element is a direct current. The switching element is connected to the negative potential of the power supply, the drain of the switching element is connected to the positive potential of the DC power supply through an inductive load, and the protection element is formed of a P-channel MOS field effect transistor (hereinafter abbreviated as PchMOSFET). And the drain of the protection element is connected to the negative potential of the DC power supply, and the gate of the protection element is connected to the positive potential of the DC power supply.

According to a fourth aspect of the present invention, there is provided a protection circuit of an inductive load power supply device for energizing an inductive load with a DC power supply through a switching element, wherein the protection element comprises a field effect transistor and a backflow prevention device connected to a drain side thereof. It has a series circuit with a diode, the series circuit is connected in parallel to the inductive load, the source of the protection element is connected to the series connection point of the switching element and the inductive load, and the gate of the protection element and the backflow prevention The drain through the diode is connected to a predetermined potential, and when the switching element is turned off, the protection element conducts due to the potential fluctuation of its source to form a current closed circuit. Is absorbed by the closed current circuit.

According to a fifth aspect of the present invention, the switching element according to the fourth aspect of the present invention is particularly configured by a Pch MOSFET, a source of the switching element is connected to a positive electrode potential of a DC power supply, and a drain of the switching element is induced. While connected to the negative electrode potential of the DC power supply through a load, the protection element is configured by an Nch MOSFET, the drain of the protection element is connected to the negative electrode potential of the DC power supply through a backflow prevention diode, and the gate of the protection element is connected. It is connected to the positive potential of the DC power supply.

According to a sixth aspect of the present invention, the switching element according to the fourth aspect of the present invention is particularly configured by an Nch MOSFET, a source of the switching element is connected to a negative potential of a DC power supply, and a drain of the switching element is induced. While connected to the positive electrode potential of the DC power supply through a load, the protection element is configured by a PchMOSFET, the drain of the protection element is connected to the positive electrode potential of the DC power supply through a backflow prevention diode, and the gate of the protection element is connected. It is connected to the negative potential of the DC power supply.

[0013]

According to the first aspect of the present invention, since the protection element which detects and conducts a surge generated in the inductive load when the switching element is turned off forms a current closing circuit for absorbing the surge, the conduction is made. It can be constituted by an inexpensive element having a low starting voltage, that is, relatively low power consumption. Further, since the protection element is directly connected between both terminals of the switching element, highly reliable protection for the switching element can be obtained.

Further, according to the second aspect of the present invention, the protection element is N
Since the switching element is constituted by a chMOSFET, a PchMOSFET is used as a switching element, and the switching element is placed on the positive side of a DC power supply with respect to an inductive load, so-called high-side drive can be performed.
Since a short-circuit current does not pass between the drains due to the insulating structure, a diode for preventing reverse voltage short-circuit is not required in the main power supply circuit.

According to the third aspect of the present invention, the protection element is P
Since the switching element is constituted by a chMOSFET, an NchMOSFET is used as a switching element, and the switching element is placed on the negative electrode side of a DC power source with respect to an inductive load, so-called low-side drive can be performed.
Since a short-circuit current does not pass between the drains due to the insulating structure, a diode for preventing reverse voltage short-circuit is not required in the main power supply circuit.

According to a fourth aspect of the present invention, a current closing circuit for absorbing a surge is formed by a protection element that detects and conducts a surge generated in an inductive load when the switching element is turned off. Similarly to the above, it can be constituted by an inexpensive element having a low conduction start voltage, that is, relatively low power consumption.

According to the fifth aspect of the present invention, since the protection element forming the current closing circuit for absorbing surge is connected between both terminals of the inductive load, not only protection of the switching element but also protection of the switching element is achieved.
The effects of surges on others can also be prevented. Further, since the protection element is constituted by an NchMOSFET, a PchMOSFET is used as a switching element, and the switching element is placed on the positive side of a DC power supply with respect to an inductive load, so-called high-side drive can be performed. In addition, an insulating structure is provided between the gate and drain of the NchMOSFET. In addition, since a short-circuit current is not passed, a diode for preventing reverse voltage short-circuit is not required in the main power supply circuit.

According to the sixth aspect of the present invention, since the protection element forming the current closing circuit for surge absorption is connected between the two terminals of the inductive load, the same as in the fifth aspect of the invention, if only the protection of the switching element is provided. In addition, it is possible to prevent the influence of the surge on others. Further, since the protection element is constituted by a PchMOSFET, an NchMOSFET is used as a switching element, and the switching element is placed on the negative side of a DC power supply with respect to an inductive load, so-called low-side drive can be performed. In addition, an insulation structure is provided between the gate and drain of the PchMOSFET. In addition, since a short-circuit current is not passed, a diode for preventing reverse voltage short-circuit is not required in the main power supply circuit.

[0019]

Embodiments of the present invention will be described below with reference to examples. FIG. 1 shows a protection circuit of an inductive load power supply device according to a first embodiment of the present invention. In this circuit, a power Pch MOSFET 2P as a switching element is connected in series with the inductive load 5 so as to be located on the positive electrode side of the battery 1, so that the so-called inductive load 5 is driven on the high side. The source of the Pch MOSFET 2P is connected to the positive electrode potential of the battery 1, and its drain is connected to the inductive load 5
, And the gate is connected to the drive circuit 7. Also, the NchMOSFET12N is replaced with the PchMOSFET2P
Are connected in parallel, the gate of the Nch MOSFET 12N is connected to the negative electrode side of the battery 1, and the source is
It is connected to a series connection point A between the chMOSFET 2P and the inductive load 5.

Next, the operation of this circuit will be described with reference to FIG. The output voltage E7 of the drive circuit 7 is a Pch MOSFET
2P is turned off in the period T1, for example, turned on in the period T2,
Turn off with 3. When the Pch MOSFET 2P is off, the source and the gate of the Nch MOSFET 12N are both connected to the negative potential of the battery 1, so that the Nch MOSFET
The MOSFET 12N is turned off, and the NchM
No current flows through the OSFET 12N.

When the Pch MOSFET 2P is on, the potential of the gate of the Nch MOSFET 12N is lower than the potential of the source.
N is turned off, and the Nch MOSFET 12N
No current flows through The current IL of the inductive load 5 is PchMO
In response to the rise of the current IS of the SFET 2P, it rises rapidly at the beginning of the period T2 and reaches a steady state.
The sharp decrease starts from the end of the period T2.

That is, when the Pch MOSFET 2P is turned off from the on state, an induced voltage in the same direction as the voltage of the DC power supply 1 is generated at both terminals of the inductive load 5 by the inductive component of the inductive load 5, so that the potential of the connection point A EA is a potential lower than the negative potential of the battery 1. At this time, NchMO
The source potential of the SFET 12N is also a negative potential (ΔV in the figure) lower than the negative potential of the battery 1, and this negative potential is NchM
When the voltage becomes equal to or lower than the threshold voltage of the OSFET 12N, the Nch MOSFET 12N is turned on during the potential decrease period αT, and the Nch MOSFET 12
The current IH flows to the connection point A through N, and furthermore, a current closed circuit is formed to reach the DC power supply 1 through the inductive load 5, so that the inductive load surge is absorbed. Such NchM
By the function of OSFET12N, PchMOSFET2
P is protected without being damaged by the surge voltage caused by the induced voltage. In this embodiment, the Nch MOSFET 12N
Constitute the protection element of the present invention.

At this time, the Nch MOSFET 12N
Assuming that the voltage of the battery 1 is 12V, the threshold voltage of the Nch MOSFET 12N is 1.5V, and the current IL flowing through the inductive load 5 is 10A, (12V + 1.5V) × 10A = 135W Become.
When the battery 1 is reversely connected by mistake, the NchMO
Since no current flows between the gate and the drain and between the gate and the source of the SFET 12N due to the structure of the MOS field-effect transistor, no short-circuit current flows through the NchMOSFET 12N.

FIG. 3 is a diagram showing a second embodiment of the present invention. In this circuit, as in the first embodiment, the power PchMOSFET 2P drives the inductive load 5 as a switching element on the high side. A series circuit of an Nch MOSFET 12N and a backflow prevention diode 15 is connected in parallel with the inductive load 5. NchMOS
The drain of the FET 12N is connected to the cathode of the diode 15, and the anode of the diode 15 is connected to the negative electrode of the battery 1. The gate of the Nch MOSFET 12N is connected to the positive electrode of the battery 1, and the source is PchMO.
Series connection point A between the drain of SFET 2P and inductive load 5
It is connected to the. The rest is the same as the first embodiment.

Next, the operation of this circuit will be described. The voltage-current characteristics of this circuit are the same as those of the first embodiment shown in FIG. When the PchMOSFET 2P is off,
The source of the NchMOSFET 12N is connected to the negative potential of the battery 1, and the gate thereof is connected to the positive potential of the battery 1 and has a potential higher than the potential of the source. Therefore, the NchMOSFET 12N is turned on.
Since there is no potential difference between the source of the NchMOSFET 12N and the anode terminal of the diode 15, the NchMOSF
No current flows through the ET 12N and the diode 15.

When the Pch MOSFET 2P is on, the source potential of the Nch MOSFET 12N becomes the same as the positive potential of the battery 1 at the gate potential.
The chMOSFET 12N is off. Note that N
Since a potential difference is generated between the source of the channel MOSFET 12N and the anode terminal of the diode 15, the parasitic diode 1
3, the current does not flow through the Nch MOSFET 12N and the diode 15 due to the backflow prevention diode 15.

Next, when the Pch MOSFET 2P is turned off from the on state, the potential of the connection point A becomes a negative potential lower than the negative potential of the battery 1 due to the characteristics of the inductive load 5. At this time, the source potential of the Nch MOSFET 12N also becomes a negative potential equal to or lower than the negative potential of the battery 1, and its gate is connected to the positive potential of the battery 1.
The MOSFET 12N is turned on, and the voltage at the connection point A becomes [(negative electrode potential of the battery 1) − (on resistance of the Nch MOSFET 12N × current) − (forward voltage of the diode 15)].
, The diode 15 and the NchM
A current flows through the OSFET 12N to the connection point A and returns to the inductive load 5 to form a closed current circuit, thereby absorbing the inductive load surge. By the function of the Nch MOSFET 12N, the Pch MOSFET 2P is protected without being damaged by the surge voltage due to the induced voltage, as in the first embodiment. In this embodiment, the Pch MOSFET 12
P constitutes the protection element of the invention.

In the second embodiment, the NchMOS
The peak power instantaneously generated in the surge absorbing current closed circuit composed of the FET 12N and the diode 15 is NchM
The on-resistance of the OSFET 12N is 0.1Ω and the diode 1
Assuming that the forward voltage of No. 5 is 0.6 V and the current flowing through the inductive load 5 is 10 A, (0.1Ω × 10 A + 0.6 V) × 1
0A = 16W, which is relatively low power.

When the battery 1 is reversely connected in the second embodiment, the source of the Nch MOSFET 12N is connected to the positive potential of the battery 1,
The 2N gate is connected to the negative potential of the battery 1 and
The chMOSFET 12N is turned off. Also, N
The parasitic diode 13 of the chMOSFET 12N is also in the opposite direction to the battery. For this reason, NchMOSFE
No short-circuit current flows through T12N.

FIG. 4 is a diagram showing a third embodiment of the present invention. In this circuit, unlike the first embodiment, an Nch MOSFET 2N is used as a switching element, and the Nch MOSFET 2N drives the inductive load 5 as a switching element on the low side. Nch
The Pch MOSFET 12P is connected in parallel with the MOSFET 2N, and the gate of the Nch MOSFET 2N is connected to the drive circuit 7 '. The drain of the Pch MOSFET 12P is connected to the negative electrode of the battery 1, and the gate is connected to the positive electrode of the battery 1. Also, PchMOSFE
The source of T12P is connected to a series connection point A between the drain of the NchMOSFET 2N and the inductive load 5.

Next, the operation of this circuit will be described with reference to FIG. Here, the voltage waveform of the output voltage E7 'of the drive circuit 7' has the opposite polarity to that of the first embodiment, but the NchMO
For example, the SFET 2N is turned off in the period T1, turned on in the period T2, and turned off in the period T3. In this case, the current IL flowing through the inductive load 5 rapidly rises at the beginning of the period T2 and reaches a steady state in response to the rise of the current IS of the NchMOSFET 2N, but starts to drop sharply from the end of the period T2.

When the Nch MOSFET 2N is off, the source and the gate of the Pch MOSFET 12P are connected to the positive potential of the battery 1, and the Pch MOSFET
Since T12P is off, the Pch MOSFET
No current flows through 12P. In addition, NchMOSFET2
Even when N is on, the gate potential of the Pch MOSFET 12P is higher than the source potential and the Pch MOSFET 12P
Since P is off, the Pch MOSFET 12P
No current flows through

Next, when the Nch MOSFET 2N is turned off from the on state, the node A becomes a positive potential higher than the positive electrode potential of the battery 1 due to an induced voltage (surge voltage) due to the characteristics of the inductive load 5. At this time, PchMOSFET1
The source potential of the 2P also becomes a positive potential higher than the positive potential of the battery 1, and the positive potential of the battery 1 + ΔV (PchMOS
When the threshold voltage of the FET 12P) is reached, the PchMO
The SFET 12P is turned on, and the PchMOSF
A current flows to the negative electrode potential of the battery 1 through the ET 12P, and a current closed circuit from the battery 1 to the inductive load 5 is formed, so that the inductive load surge is absorbed. The induced voltage disappears and the potential EA at the connection point A becomes the positive potential 12 of the battery 1.
When the voltage returns to V, the source potential of the Pch MOSFET 12P also returns to the original. By the function of the Pch MOSFET 12P, the Nch MOSFET 2N is protected without being damaged by the surge voltage caused by the induced voltage. In this example,
The Pch MOSFET 12P constitutes the protection element of the present invention.

It should be noted that also in the third embodiment, Pc
The peak power instantaneously generated in the hMOSFET 12P is, as in the first embodiment, the voltage of the battery 1
V, the threshold voltage of the Pch MOSFET 12P is 1.5
V and the current flowing through the inductive load 5 is 10 A, (12
V + 1.5V) × 10A = 135W. Further, when the battery 1 is reversely connected in the third embodiment, a MOS transistor is provided between the drain and the gate and between the source and the gate of the Pch MOSFET 12P as in the first embodiment.
Since no current flows due to the structure of the field effect transistor,
A short current does not flow through the Pch MOSFET 12P.

FIG. 6 is a diagram showing a fourth embodiment of the present invention. In this circuit, unlike the case of the third embodiment,
The inductive load 5 is driven low side by the Nch MOSFET 2N. A series circuit of a Pch MOSFET 12P and a backflow prevention diode 15 is connected in parallel with the inductive load 5. The drain of the Pch MOSFET 12P is connected to the anode terminal of the diode 15, and the cathode terminal of the diode 15 is connected to the positive electrode of the battery 1. Pch
The gate of the MOSFET 12P is connected to the negative electrode of the battery 1, and the source is connected to a series connection point A between the drain of the Nch MOSFET 2N and the inductive load 5. NchM
The gate of the OSFET 2N is connected to the drive circuit 7 '.

The voltage-current characteristics of this circuit are the same as those of the third embodiment shown in FIG. NchMOSFET2
When N is off, the source of the Pch MOSFET 12P is connected to the positive potential of the battery 1,
The gate of the ET 12P is connected to the negative electrode potential of the battery 1, and the Pch MOSFET 12P is in an ON state.
Since there is no potential difference between the cathode terminals of PchMO
No current flows through the SFET 12P and the diode 15. When the NchMOSFET 2N is on, the Pch
The source potential of the MOSFET 12P is substantially equal to the negative potential of the battery 1, and there is no potential difference between the source and the gate of the Pch MOSFET 12P.
T12P is turned off. On the other hand, PchMOSFET12
Since a potential difference occurs between the source and the drain of P, a current tries to flow through the parasitic diode 13.
No current flows through T12P.

Next, when the Nch MOSFET 2N is turned off from the on state, the connection point A has a positive potential equal to or higher than the positive potential of the battery 1 due to the characteristics of the inductive load 5. At this time, the source potential of the Pch MOSFET 12P also becomes a positive potential higher than the positive potential of the battery 1, and the Pch MOSFET 12P
Since the gate of 12P is connected to the negative potential of the battery 1, the Pch MOSFET 12P turns on and the connection point A
Is the positive electrode potential of the battery 1 + ΔV [(PchMOS
When the ON resistance of the FET 12P × current) + (forward voltage of the diode 15)], the P-channel MOS
A current flows to the positive electrode of the battery 1 through the FET 12P and the diode 15, and absorbs an inductive load surge. With the function of the PchMOSFET 12P, the NchMO
The SFET 2N is protected without being damaged by the surge voltage due to the induced voltage, as in the third embodiment. Also in this embodiment, the Pch MOSFET 12P constitutes the protection element of the present invention.

In the fourth embodiment, the peak power instantaneously generated when the surge is absorbed is equal to the peak power P as in the second embodiment.
Assuming that the on-resistance of the chMOSFET 12P is 0.1Ω, the forward voltage of the diode 15 is 0.6V, and the current IL flowing through the inductive load 5 is 10A, (0.1Ω × 10A + 0.
6V) × 10A = 16W. Also, PchMOSF
Since no current flows structurally between the drain and the gate of the ET12P, even if the DC power supply 1 is reversely connected by mistake,
No short-circuit current flows.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is an operating voltage / current characteristic diagram in the first embodiment.

FIG. 3 is a circuit diagram of a second embodiment.

FIG. 4 is a circuit diagram of a third embodiment.

FIG. 5 is an operating voltage / current characteristic diagram in the third embodiment.

FIG. 6 is a circuit diagram of a fourth embodiment.

FIG. 7 is a circuit diagram of a conventional example A.

FIG. 8 is a circuit diagram of a conventional example B.

[Explanation of symbols]

Reference Signs List 1 battery 2N N-channel MOS field effect transistor (NchMOSFET) 2P P-channel MOS field effect transistor (PchMOSFET) 5 Inductive load 7 Drive circuit 12N N-channel MOS field effect transistor (NchMOSFET) 12P P-channel MOS field effect transistor (NchMOSFET) PchMOSFET) 13 Parasitic diode 15 Backflow prevention diode

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Isao Oya, Inventor F-term (reference) 5G053 AA10 CA05 EC03 FA04 5H740 BA12 BB06 BB07 BB10 BC01 BC02 JB01 MM01

Claims (6)

[Claims] 1. A protection circuit for an inductive load power supply device for energizing an inductive load with a DC power supply through a switching element, comprising: a protection element including a field-effect transistor connected in parallel to the switching element. Is connected to a series connection point of the switching element and the inductive load, and the gate and the drain of the protection element are connected to respective predetermined potentials, and the protection element is turned off when the switching element is turned off. A current closed circuit is formed by conducting with a potential change of a source, and a surge generated in the inductive load at the time of turn-off is configured to be absorbed by the current closed circuit. Protection circuit. 2. The switching element is a P-channel M.
An OS type field effect transistor, the source of the switching element is connected to the positive potential of the DC power supply, the drain of the switching element is connected to the negative potential of the DC power supply through the inductive load, The protection element is formed of an N-channel MOS field effect transistor, the drain of the protection element is connected to the positive potential of the DC power supply, and the gate of the protection element is connected to the negative potential of the DC power supply. 2. The protection circuit for an inductive load power supply according to claim 1, wherein: 3. The switching element is an N-channel M
An OS type field effect transistor, the source of the switching element is connected to the negative potential of the DC power supply, the drain of the switching element is connected to the positive potential of the DC power supply through the inductive load, The protection element is formed of a P-channel MOS field effect transistor. The drain of the protection element is connected to the negative potential of the DC power supply, and the gate of the protection element is connected to the positive potential of the DC power supply. 2. The protection circuit for an inductive load power supply according to claim 1, wherein: 4. A protection circuit for an inductive load power supply device for energizing an inductive load with a DC power supply through a switching element, comprising: a protection element comprising a field effect transistor; and a backflow prevention diode connected to a drain side of the protection element. Having a series circuit, the series circuit is connected in parallel to the inductive load, a source of the protection element is connected to a series connection point of the switching element and the inductive load,
The gate of the protection element and the drain through the backflow prevention diode are each connected to a predetermined potential, and when the switching element is turned off, the protection element conducts due to the fluctuation in the potential of the source, thereby closing the current. Wherein the surge generated in the inductive load at the time of the turn-off is absorbed by the current closing circuit. 5. The switching element is a P-channel M.
An OS type field effect transistor, the source of the switching element is connected to the positive potential of the DC power supply, the drain of the switching element is connected to the negative potential of the DC power supply through the inductive load, The protection element is formed of an N-channel MOS field effect transistor, the drain of the protection element is connected to the negative potential of the DC power supply through the backflow prevention diode, and the gate of the protection element is connected to the positive electrode of the DC power supply. 5. The protection circuit for an inductive load power supply according to claim 4, wherein the protection circuit is connected to a potential. 6. The switching element is an N-channel M
An OS type field effect transistor, the source of the switching element is connected to the negative potential of the DC power supply, the drain of the switching element is connected to the positive potential of the DC power supply through the inductive load, The protection element is formed of a P-channel MOS field effect transistor, the drain of the protection element is connected to the positive potential of the DC power supply through the backflow prevention diode, and the gate of the protection element is connected to the negative electrode of the DC power supply. 5. The protection circuit for an inductive load power supply according to claim 4, wherein the protection circuit is connected to a potential.