JP2009291026A - Relay contact protection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a relay contact protection circuit which allows voltages on primary side and secondary side to be similar while preventing the rush currents from the primary side to the secondary side, at a manufacturing cost lower than an example in the prior art. <P>SOLUTION: The relay contact protection circuit protects a contact point by reducing a voltage difference between contact points of a relay that supplies an electric current to a load by pre-charging before driving the relay to reduce the current flowing between contact points. It includes a capacitor connected parallel to the load, a first semiconductor switch which performs secondary charging to the capacitor by a voltage stepped up from a power supply voltage, a voltage measuring part which measures a voltage charged to the capacitor and outputs a measurement voltage, and a pre-charge control part which turns on the first semiconductor switch for secondary charging when the measurement voltage comes to a primary charge voltage set in advance. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a relay contact protection circuit that protects contacts by preventing sparks and the like that occur when an electric relay is turned on and off.

The electrical relay has a large voltage difference between the voltage on the primary side (power supply side) and the voltage on the secondary side (power supplied side), and an element (for example, a capacitor) that accumulates charges on the secondary side is connected. In such a case, an inrush current flows from the primary side to the secondary side, and sparks are generated due to sparks or the like, resulting in problems of contact welding (permanent contact) or contact failure.
Therefore, in order to reduce the contact current flowing on the secondary side, the inrush current is obtained by precharging the secondary side and bringing the voltage of the element that accumulates the charge close to the voltage on the primary side and then turning on. (For example, refer to Patent Document 1).

However, in the precharge circuit described in Patent Document 1, for example, like the precharge circuit 100 shown in FIG. 3, the capacitors C1 and C2 are preliminarily connected via the resistor 14 by turning on the switch 13. In the case of charging, a diode 12 is provided to protect the precharge circuit from a negative surge voltage superimposed on the power supply voltage output from the battery B1, and the precharge result is obtained by the forward voltage ΔV of the diode 12. As a result, the voltage on the secondary side (point P) drops from the primary side.
Therefore, even if the switch 13 is turned on and the capacitors C1 and C2 are precharged, only the voltage lower by the forward voltage ΔV of the diode 12 can be charged, so that the inrush current to the capacitors C1 and C2 can be completely reduced. Can not. Therefore, by providing a diode in series on the contact side of the relay 2 in correspondence with the diode 12 of the precharge circuit and reducing it by the forward voltage ΔV, the precharged voltage and the relay 2 are supplied in the ON state. Is used to equalize the voltage (see, for example, Patent Document 2).
JP 2007-19293 A JP 2003-143709 A

  However, in the protection method disclosed in Patent Document 2, the voltage charged by the precharge circuit is the same as the voltage supplied while the relay 2 is turned on, and an inrush current flows to charge the capacitors C1 and C2. However, as the current capacity supplied to the load 31 increases, it is necessary to increase the current capacity of the diode that is connected in series with the relay 2 and decreases by the forward voltage ΔV. In addition, this diode becomes a very expensive part, and the manufacturing cost of the protection circuit increases.

  The present invention has been made in view of such circumstances, and the voltages on the primary side and the secondary side are made the same from the primary side to the secondary side at a lower manufacturing price than the conventional example. An object of the present invention is to provide a relay contact protection circuit that suppresses the inrush current.

  The relay contact protection circuit of the present invention reduces the voltage difference between the contacts of the relay that supplies current to the load by precharging before driving the relay, thereby reducing the through current flowing between the contacts. A relay contact protection circuit for protecting the contact, wherein the capacitor is connected in parallel with the load, and the capacitor is subjected to secondary charging with a voltage obtained by boosting the power supply voltage of the power supply. 1, a voltage measuring unit that measures the voltage charged in the capacitor and outputs the measured voltage, and when the measured voltage reaches a preset primary charging voltage, the first semiconductor switch is turned on. And a precharge control unit for performing secondary charging.

The relay contact protection circuit of the present invention further includes a second semiconductor switch that performs primary charging to the capacitor from the power source applied to the relay via a rectifying element,
When the measured voltage reaches a preset primary charging voltage, the second semiconductor switch is turned off.

  The relay contact protection circuit of the present invention is characterized in that the precharge control unit turns off the first semiconductor switch when the measured voltage becomes a voltage value of a power source applied to the relay.

  In the relay contact protection circuit of the present invention, the contact point of the relay is actually turned on after the precharge control unit has a measurement voltage applied to the relay and a signal to turn on is input to the relay. The first semiconductor switch is turned off with a time delay, and the precharge is terminated.

The relay contact protection circuit according to the present invention is characterized in that a current limiting resistor is interposed between an output terminal of the first semiconductor switch and a capacitor.
The relay contact protection circuit according to the present invention corresponds to a voltage difference between the measured voltage and a voltage value of a power source applied to the relay contact when the precharge control unit turns on the first semiconductor switch. Then, PWM control is performed.

  As described above, according to the present invention, the first-stage precharge through the diode and the second-stage precharge in which the forward voltage of the diode is increased by the booster circuit. In order to precharge the secondary side, the voltage on the secondary side (supplied side) is set to the same value as the voltage on the primary side (supply side), and the voltage is lowered by the forward voltage of the diode in the first stage. The voltage is increased by charging the capacitor at high speed, and is adjusted to the voltage on the secondary side in the second stage. Therefore, the voltage on the secondary side is changed to the voltage on the primary side at the same speed as the conventional example. When the relay is turned on, the inrush current flowing through the load (especially the capacitor) can be reduced as compared with the conventional one, and an expensive component (for example, a large-capacity rectifying element: Diode) Fried, it can be constructed without increasing the cost.

Hereinafter, a relay contact protection circuit according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a relay contact protection circuit according to the embodiment.
In this figure, the relay contact protection circuit includes diodes 12 and 22, switch 13 (corresponding to the second switch), resistors 14 and 16, control unit 17, switch 19 (corresponding to the first switch), charge pump. The circuit 20 and the voltage detection circuit 21 are comprised. In addition, one end of the switch 11 in FIG. 1 is connected to the + side of a power source (DC power source, hereinafter referred to as a battery) B1. For example, when driving a car, when an ignition switch is turned on, the switch 11 is turned on. It becomes.

  The control unit 17 is supplied with power for driving from the battery B1 via the diode 22 (protects the internal circuit of the control unit 17 from negative surge), and when the switch 11 is turned on, the precharge at the first stage is performed. (Details are described in detail in the explanation of the operation).

The diode 12 has an anode connected to the other end of the switch 11 and a cathode connected to the input side of the switch 13 to suppress the influence of a negative voltage surge superimposed on the output voltage of the battery B1, that is, It is provided for circuit protection in the switch 13.
The switch 13 has a control terminal connected to the control unit 17, an input side connected to the cathode of the diode 12, an output side connected to one end of the resistor 14, and performs a first-stage precharge in the ON state. Is increased to a voltage value lower than the voltage value VB of the battery B1 by a voltage drop ΔV of the diode 12 (see FIG. 2). The other end of the resistor 14 is connected to the connection point P.

The switch 19 has an input side connected to the charge pump circuit 20, an output side connected to one end of the resistor 14 via the resistor 16, a control terminal connected to the control unit 17, and the control terminal connected to the control unit 17 from the control unit 17. In the ON state, the second stage precharge is performed by the boosted voltage of the charge pump circuit 20, and the voltage at the connection point P is increased to a voltage value similar to the voltage value VB of the battery B1. .
The voltage detection circuit 21 detects the voltage value at the connection point P and outputs the detection value to the control unit 17.

The circuit using the relay 2 whose contact is protected by the relay contact protection circuit 1 has the following configuration.
The relay 2 is an electromagnetic relay, and opens and closes a contact G that connects a drive circuit (transistors 32 to 35 to be described later) and capacitors C1 and C2 that supply power for driving the load 31, and the battery B1, and the contact G. The coil L is comprised.
The coil L has one end connected to the cathode side of the diode 22 and the other end connected to the control unit 17, and is driven and not driven by the control signal S5 to open and close the contact G, and to connect the power source PVB and the load. 31 is connected to or disconnected from the drive circuit.

The capacitors C1 and C2 are connected in parallel with a drive circuit (transistors 32-35) that drives the load 31, so that the voltage at the connection point P does not change suddenly due to an inrush current that flows when driving the load. , Provided to store electric energy by accumulating electric charges.
When the charge pump circuit 20 is driven by the control signal S4, it boosts the voltage VB of the battery B1 and outputs the boosted voltage Vp.

Examples of the load 31 include a DC motor.
The motor drive circuit for driving the DC motor is composed of N-channel MOS transistors (hereinafter referred to as MOS transistors) 32, 33, 34, and 35 for driving a DC motor as a load.
Here, the drain of the MOS transistor 32 is connected to the connection point P, the control signal SM <b> 2 from the control unit 17 is input to the gate, and the source is connected to the drain of the MOS transistor 33.

In the MOS transistor 33, the control signal SM3 from the control unit 17 is input to the gate, and the source is grounded.
In the MOS transistor 34, the drain is connected to the connection point P, the control signal SM 4 from the control unit 17 is input to the gate, and the source is connected to the drain of the MOS transistor 35.
In the MOS transistor 35, the control signal SM5 from the control unit 17 is input to the gate, and the source is grounded.

The control unit 17 sets the control signals SM2 to SM5 to the “H” level and the “L” level, respectively, so that the transistors 32 to 35 are turned on and off to control the rotation of the motor. For example, the control signals SM2 and SM5 are set to “H” level, the MOS transistors 32 and 35 are turned on, while the control signals SM3 and SM4 are set to “L” level, the MOS transistors 33 and 34 are turned off, and the R direction The DC motor 31 is rotated by passing an electric current.
When rotating in the direction opposite to the rotation direction in the above-described control, the control signals SM3 and SM4 are set to the “H” level, the MOS transistors 33 and 34 are turned on, while the control signals SM2 and SM5 are set to “L”. ”Level, the MOS transistors 32 and 35 are turned off, a current is passed in the Q direction, and the DC motor 31 is rotated.

Next, the operation of the relay contact protection circuit 1 according to the present embodiment will be described with reference to FIGS. 1 and 3. FIG. 3 is a waveform diagram for explaining an example of the operation of the relay contact protection circuit 1. The vertical axis indicates the voltage (VC) at the connection point P, and the horizontal axis indicates time t. The following operation will be described from the time when the switch 11 is turned on and the relay contact protection circuit 1 starts driving.
At time t1, the switch 17 is turned on, and after a predetermined time, the control unit 17 outputs the control signal S2 to turn on the switch 13 in order to perform the precharge operation at the connection point P.

As a result, the first-stage precharge operation is started and the switch 13 is turned on, whereby a current to the connection point P flows through the diode 12 and the resistor 14, and charges are accumulated in the capacitors C1 and C2. As a result, the battery is charged and the potential at the connection point P gradually increases.
When the first-stage precharge operation is started, the control unit 17 determines whether or not the detection voltage VC input from the voltage detection circuit 21 exceeds a preset threshold voltage Vt1 at a predetermined cycle. The process to detect is started. This threshold voltage Vt1 is set to a value obtained by subtracting the forward voltage ΔV of the diode 12 from the voltage VB of the battery B1.

At time t2, when the control unit 17 detects that the detection voltage VC input from the voltage detection circuit 21 exceeds a preset threshold voltage Vt1, the control unit 17 starts a second-stage precharge operation. Therefore, the control signal S3 instructing the driving state is output to the switch 19, the switch 19 is driven, and the boosted voltage Vp is applied to one end of the resistor 14 via the resistor 16. The charge pump circuit 20 is driven by the control signal S4 when the relay contact protection circuit 1 starts driving, and the boosted voltage Vp is output.
Then, after the control unit 17 outputs the control signal S4 that instructs the switch 19 to drive, the time when the switch 19 is turned on and the boosted voltage Vp is applied to one end of the resistor 14 is measured in advance. Is set, the control signal S4 is output to the switch 19, the time is counted by the counter, and after the time has elapsed, the control signal S2 for turning off the switch 13 is output.
Then, when the switch 13 is turned off and the switch 19 is turned on, the first-stage precharge operation is completed, and the second-stage precharge operation is started.

  Here, as described above, the switch 19 is turned on, and the boosted voltage Vp is supplied to the connection point P via the resistor 16 and the resistor 14. Here, the resistor 16 is provided to limit the current flowing from the charge pump circuit 20 to the connection point P. That is, if the potential at the connection point P suddenly rises, voltage control cannot be performed and the secondary side voltage becomes higher than the primary side. In order to improve the controllability of the potential at the point P, the current is limited by the resistor 16.

  When the second stage precharge operation is started, the control unit 17 detects whether or not the detection voltage VC input from the voltage detection circuit 21 exceeds a preset threshold voltage Vt2 at a predetermined cycle. The process to start is started. Here, the threshold voltage Vt2 is set to the voltage VB of the battery B1 (that is, the voltage of the power source PVB).

At time t3, when the control unit 17 detects that the detection voltage VC input from the voltage detection circuit 21 exceeds a preset threshold voltage Vt2, a current is passed through the coil L, and the contact G is turned on. The relay 2 is driven so as to change from the open state (open) to the connected state (closed), the power source PVB and the connection point P are connected, and the drive current for the load 31 is supplied from the battery B1.
At this time, since there is no voltage difference between the voltage VB of the battery B1 on the primary side and the connection point P on the secondary side, no inrush current flows and no sparks occur, and the contact G of the relay 2 Suppresses deterioration.

At this time, the control unit 17 sets the control signal S5 to the state in which the coil L is driven, and after passing a current through the coil L, the contact point G is in the connected state and the time during which the positive side of the battery B1 is applied to the point P is preset. The measured value is set, the control signal S5 is output to the coil L, the time is counted by the counter, and the switch 19 is turned off after the time of the measured value has elapsed. The signal S2 is output.
Then, the control unit 17 outputs a control signal S4 that deactivates the charge pump circuit 20, and stops the operation of the charge pump circuit 20. With the above-described processing, the second-stage precharge operation is completed, and the precharge operation for the connection point P is completed.
The threshold voltages Vt1 and Vt2 described above are stored in advance in the storage unit in the control unit 17 as described above.

Further, in the relay contact protection circuit 1 described above, a PNP bipolar transistor is used as the switch 19 and the potential of the control signal S3 to be turned on / off is adjusted to control the value of the current flowing through the base, thereby connecting the connection point from the charge pump circuit 20. The current flowing in P may be adjusted, the collector of the bipolar transistor and the output of the charge pump circuit 20 may be connected without providing the resistor 16, and the collector and the output side of the switch 13 may be directly connected. .
Also, the current flowing from the charge pump circuit 20 to the connection point P is adjusted by controlling the value of the current flowing through the base by using a PNP bipolar transistor for the switch 19 and making the control signal S3 into a pulse shape and performing PWM control. As such, without providing the resistor 16, the emitter of the bipolar transistor and the output of the charge pump circuit 20 may be connected, and the collector and the output side of the switch 13 may be directly connected. Alternatively, a PNP bipolar transistor may be used as the switch 13, the emitter and the cathode of the diode 12 are connected, and the collector may be connected to one end of the resistor 14.
Further, when a charge pump circuit is provided in another circuit, the boosted voltage is inputted from the charge pump circuit, and the switch 19 controls whether or not the boosted voltage is supplied to the connection point P. good.

As described above, the relay contact protection circuit 1 according to the present embodiment increases the potential of the connection point P to be precharged directly from the battery B1 via the diode 12 in the first stage, When the voltage VC detected by the voltage detection circuit 21 exceeds the set threshold voltage Vt1, it is detected that the precharge from the battery B1 is at a limit, that is, a state where no voltage increase is expected, and the first stage pre-charge is detected. The charge process ends.
After the first-stage precharge operation is completed, the relay contact protection circuit 1 according to the present embodiment starts the second-stage precharge, starts precharge with the boosted voltage from the charge pump circuit 20, and sets the threshold value. Precharging is performed until the voltage Vt2 is exceeded, that is, until the connection point P becomes the voltage VB of the battery B1 (that is, until the potential difference between the primary side and the secondary side becomes “0”).

Then, the relay contact protection circuit 1 according to the present embodiment is configured to drive the relay 2 after the precharge is completed by the processing described above, and therefore, the precontact corresponding to the potential in real time according to the potential of the connection point P. Since the charging operation is performed, there is no waste of time from the start of precharging to the drive of the relay, so that the precharging operation that is actually performed with a fixed amount of time is provided as in the conventional case. Compared with, high-speed precharge can be performed.
Moreover, the relay contact protection circuit 1 according to the present embodiment does not use expensive parts such as a diode, and can reduce the manufacturing cost.

It is a block diagram which shows the structural example which protects the relay contact which drives the load 3 (DC motor drive circuit) using the relay contact protection circuit 1 by one Embodiment of this invention. It is a wave form diagram which shows the operation example of the relay contact protection circuit 1 of FIG. It is a block diagram which shows the structural example which protects the relay contact which drives the load 3 (DC motor drive circuit) in a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Relay contact protection circuit 2 ... Relay 11, 13, 19 ... Switch 12, 22 ... Diode 14, 16 ... Resistor 17 ... Control part 20 ... Charge pump circuit 21 ... Voltage detection circuit 31 ... Load (DC motor)
32, 33, 34, 35 ... MOS transistors (N-channel MOS transistors)
B1 ... Battery C1, C2 ... Capacitor

Claims (6)

A relay that protects the contact by reducing the voltage difference between the contacts of the relay that supplies current to the load by precharging and reducing the through current flowing between the contacts before driving the relay. Contact protection circuit,
A capacitor connected in parallel to the load;
A first semiconductor switch that performs secondary charging of the capacitor with a voltage obtained by boosting a power supply voltage of a power supply;
A voltage measuring unit for measuring a voltage charged in the capacitor and outputting a measurement voltage;
A relay contact protection circuit, comprising: a precharge controller that turns on the first semiconductor switch to perform secondary charging when the measured voltage reaches a preset primary charging voltage. The capacitor further includes a second semiconductor switch that performs primary charging from the power source applied to the relay via a rectifying element,
The relay contact protection circuit according to claim 1, wherein the second semiconductor switch is turned off when the measured voltage becomes a preset primary charging voltage.   3. The relay contact protection circuit according to claim 1, wherein the precharge control unit turns off the first semiconductor switch when the measured voltage becomes a voltage value of a power supply applied to the relay. 4. .   The precharge control unit delays the first contact point by the time when the relay contact is actually turned on after the measurement voltage becomes a voltage value to be applied to the relay and a signal to turn on is input to the relay. 4. The relay contact protection circuit according to claim 2, wherein the semiconductor switch is turned off to end the precharge. 5.   5. The relay contact protection circuit according to claim 1, wherein a current limiting resistor is interposed between an output terminal of the first semiconductor switch and a capacitor.   When the precharge control unit turns on the first semiconductor switch, the precharge control unit performs PWM control corresponding to a difference voltage between the measurement voltage and a voltage value of a power source applied to a contact of the relay. The relay contact protection circuit according to any one of claims 1 to 4.

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