JPH0555732U - Protection circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention relates to a protection circuit for preventing overcurrent to a device that conducts current in both forward and reverse directions, and aims to perform normal energization without impairing the protection function when switching energization. [Constitution] Diode D ₁ and PTC thermistor R _TH1
And a second series circuit 5b formed of a thermistor R _{TH 1} and a diode D ₂ connected in reverse polarity to the diode D ₁ and connected in parallel.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to a protection circuit, and more particularly, to a protection circuit that prevents an overcurrent from flowing in both forward and reverse directions.

[0002]

[Prior Art]

 FIG. 3 shows a circuit configuration diagram of a conventional example. In the figure, reference numeral 1 denotes a DC (direct current) motor. One end of the coil of the DC motor 1 is directly connected to the other end through a PTC (Positive Temperature Coefficient) thermistor 2 for preventing coil burnout of the DC motor 1. It is connected to the drive circuit 3.

Therefore, the current from the drive circuit 3 is supplied to the DC motor 1 via the PTC thermistor 2.

When a current is continuously applied to the DC motor 1, the current causes the coil of the DC motor 1 to burn. However, conventionally, the PTC thermistor 2 prevents the burn.

The operation of preventing burnout will be described below. The PTC thermistor 2 generates heat when an electric current flows, its temperature rises, and its resistance increases. Therefore, when a current flows through the coil of the DC motor 1, the PTC thermistor 2 generates heat in this current to increase its resistance and suppress the current flowing through the coil.

Therefore, an overcurrent does not flow in the DC motor 1, and the DC motor 1 can be protected from the overcurrent.

[0007]

[Problems to be solved by the device]

 However, the conventional protection circuit has a structure in which the PTC thermistor is simply connected in series between the motor and the drive circuit. Therefore, when the motor is energized in the forward direction and then the forward / reverse mode is switched and the motor is energized in the reverse direction, the PTC thermistor has a resistance value corresponding to the energization in the forward direction. It is the resistance value when power is applied in the positive direction.

Therefore, for example, in the case where the overcurrent is supplied by the energization in the forward direction and the resistance of the PTC thermistor is sufficiently large, the motor does not operate at all for the energization in the reverse direction. There was a problem.

The present invention has been made in view of the above points, and an object of the present invention is to provide a protection circuit that can perform normal energization without deteriorating the protection function when switching energization.

[0010]

[Means for Solving the Problems]

 The present invention is a protection circuit for protecting a protected device by limiting a current to a protected device which is energized in both forward and reverse directions, and a first rectifying element for energizing the protected device in a forward direction, And a first series circuit in which a first protection element whose resistance changes in accordance with the current is connected in series, a second rectifying element for energizing the device to be protected in the reverse direction, and a first series circuit And a second series circuit in which a second protection element whose resistance changes is connected in series is connected in parallel.

[0011]

[Action]

 The first series circuit and the second series circuit are connected in parallel, and the first rectifying element forming the first series circuit and the second rectifying element forming the second series circuit are opposite to each other. Is energized in the opposite direction. A first protection element is provided in the first series circuit and a second protection element is provided in the second series circuit.

Therefore, a current flows through the first series circuit during energization in the forward direction, and a current flows through the second series circuit when energized in the reverse direction.

Therefore, the current to the protected device is suppressed by the first protection element when the current is applied in the forward direction, and the current to the protected device is suppressed by the second protection element when the current is applied in the reverse direction. To be done.

As described above, by switching the resistance element that suppresses the current to the protected device by energizing in the forward direction and the reverse direction, the current to the protected device is switched to the protected device during the forward / reverse switching. Since the power can be supplied without being suppressed, the protected device can be operated in a normal state.

[0015]

【Example】

 FIG. 1 shows a circuit configuration diagram of an embodiment of the present invention. In the figure, 4 is a protected device, a DC (direct current) motor, 5 is a protection circuit, and 6 is a drive circuit.

The DC motor 4 is connected to the drive circuit 6 via the protection circuit 5. The drive circuit 6 energizes the DC motor 4 in the forward direction or the reverse direction.

The DC motor 4 rotates in the forward direction when energized in the forward direction by the drive circuit 6, and rotates in the reverse direction when energized in the reverse direction.

The protection circuit 5 is formed by connecting a first series circuit 5a and a second series circuit 5b in parallel. The first series circuit 5a is formed by connecting a diode D ₁ which is a first rectifying element and a PTC thermistor R _TH1 which is a first protective element in series. The diode D ₁ is connected such that the side connected to the DC motor 4 is the cathode and the side connected to the drive circuit 6 is the anode.

The second series circuit 5b has a configuration similar to that of the first series circuit 5a, and a diode D ₂ which is a second rectifying element and a PTC thermistor R _TH2 which is a second protection element are connected in series. It becomes. However, in the second series circuit 5b, the diode D ₂ is connected such that the side connected to the DC motor 4 is the anode and the side connected to the drive circuit 6 is the cathode.

FIG. 2 is a sectional view showing an embodiment of the present invention. The DC motor 4 is housed in a case 7, and a pinion 4b is fixed to a rotary drive shaft 4a of the DC motor 4.

The pinion 4 b meshes with a tooth portion 8 a formed on the outer periphery of the gear 8. A spiral inner screw 8b is formed on the inner circumference of the gear 8, and the inner screw 8b engages with a spiral out task screw 9a formed on the outer circumference of the output shaft 9.

The gear 8 is rotated by the pinion 4 b as the DC motor 4 rotates. When the gear 8 rotates, the inner screw 8b and the outer screw 9a of the gear 8 cooperate with each other to move the output shaft 9 in the arrow C direction.

The case 7 also houses a circuit board 11 having a DC motor 4 and a protection circuit 5 formed thereon. The DC motor 4 and the protection circuit 5 are connected inside the case 7.

Further, the protection circuit 5 is connected to the drive circuit 6 provided outside by a connection cord 12 extending outside the case 7.

Here, returning to FIG. 1, the operation will be described. Due to the diodes D ₁ and D ₂ , current flows from the drive circuit 6 side to the DC motor 4 side in the first series circuit 5a, and current flows from the DC motor 4 side to the drive circuit 6 side in the second series circuit 5b. Flows.

In other words, a current flows through the first series circuit 5a when the drive circuit 6 energizes the DC motor 4 in the positive direction (direction of arrow A), and the second series circuit 5b drives. When the circuit 6 is energized in the reverse direction (direction of arrow B) to the DC motor 4, a current flows.

As described above, the first series circuit 5a composed of the diode D ₁ and the PTC thermistor R _TH1 and the second series circuit composed of the diode D ₂ and the PTC thermistor R _TH2 connected in reverse polarity to the diode D ₁ are connected. When the circuit 5b is connected in parallel to form the protection circuit 5, and when energized in the positive direction, the PTC thermistor R _TH1 of the first series circuit 5a protects the DC motor 4 due to overcurrent and energizes in the reverse direction. In this case, the PTC thermistor R _TH2 of the second series circuit 5b can protect the DC motor 4 from overcurrent. The PTC thermistor R _TH1 returns when energized in the reverse direction, and the PTC thermistor R _TH2 returns when energized in the forward direction to prepare for the next switching of the energizing direction.

Therefore, even if the resistance of the PTC thermistor R _TH1 is increased due to overcurrent when the drive circuit 6 switches the energization direction of the DC motor 4 from the forward direction to the reverse direction, Since it is protected by the PTC thermistor R _TH2 , the influence of the PTC thermistor R _TH1 does not appear in the energization in the reverse direction, and the normal operation can be performed.

Although the present embodiment is used as a protection circuit for the DC motor 4, the present invention is not limited to this, and may be applied to any device that energizes in both forward and reverse directions.

[0030]

[Effect of the device]

 As described above, according to the present invention, by providing the resistance element that suppresses the current for each energizing direction, even when the energizing direction is switched, the protection function remains the same and the influence of the state of the resistive element before switching is not affected. It has features such as being able to immediately perform normal energization.

[Brief description of drawings]

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

FIG. 2 is a sectional view of an embodiment of the present invention.

FIG. 3 is a circuit configuration diagram of a conventional example.

[Explanation of symbols]

4 DC Motor 5 Protection Circuit 5a First Series Circuit 5b Second Series Circuit D ₁ , D ₂ Diodes R _TH1 , R _TH2 PTC Thermistor

Claims (1)

[Scope of utility model registration request] 1. A protection circuit for protecting a device to be protected by limiting a current to the device to be protected which is energized in both forward and reverse directions. A first series circuit in which a rectifying element and a first protective element whose resistance changes according to the current are connected in series; a second rectifying element that energizes the protected device in the opposite direction;
A protection circuit having a configuration in which a second series circuit in which a second protection element whose resistance changes according to a current is connected in series is connected in parallel.