Abstract:
A relay switch has a coil such that a predetermined voltage is imposed on one end thereof and the other end is grounded with a resistor therebetween, and when the voltage of the coil is at least a predetermined value, the relay switch is turned on and a power source is supplied to an electronic apparatus. A transistor causes the voltage of the coil to be at least the predetermined value by means of drawing in the current flowing through the coil and causing the current to flow to the ground without passing through the resistor when starting the supply of the power source, and after the start of supply of the power source, gradually decreases the amount drawn in of the current flowing through the coil, causing a decrease in a manner so that the voltage of the coil does not fall below the predetermined value.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a relay drive apparatus that controls supply of electric power to an electronic device. 
       BACKGROUND ART 
       [0002]    Relay drive apparatuses that drive a relay to supply electric power to an electronic device have been known heretofore (for example, Patent Literature (hereinafter, referred to as “PTL”) 1. In the relay drive apparatus of PTL 1, a voltage of coil  6  of relay  8  is temporarily increased in a case where relay  8  is turned ON. The voltage of coil  6  is temporarily increased because an operation of relay  8  is likely to become unstable in a case where the relay drive apparatus is used in a high-temperature environment such as a vehicle-mounted charging apparatus, and relay  8  should be surely turned ON even in such cases. In the relay drive apparatus of PTL 1, an ON signal is output to first transistor  3  from first output terminal  2   a  of control circuit  2  so that first transistor  3  is put into a conduction state. In the relay drive apparatus of PTL 1, the voltage of coil  6  of relay  8  can be temporarily increased in this manner. 
         [0003]    Meanwhile, the relay drive apparatus of PTL 1 lowers the voltage of coil  6  to reduce the power consumption after relay  8  is turned ON. 
         [0004]    In other words, in the relay drive apparatus of PTL 1, first transistor  3  is maintained in an ON state from time t 0  to time t 1  as illustrated in  FIG. 1 . First transistor  3  is turned OFF after time t 1  inclusive. In addition, in the relay drive apparatus of PTL 1, the voltage of coil  6  of relay  8  is high from time t 0  to time t 1  and is low after time t 1  inclusive as illustrated in  FIG. 2 . 
       CITATION LIST 
     Patent Literature 
     PTL 1 
       [0000]    
       
         Japanese Patent Application Laid-Open No. HEI 10-255627 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    In PTL 1, however, the current flowing through coil  6  of relay  8  cannot be rapidly changed when first transistor  3  is switched from ON to OFF. As a result, in PTL 1, the current flowing through coil  6  flows to resistor  5  after first transistor  3  is turned OFF, and the voltage of coil  6  temporarily decreases. Relay  8  is turned OFF in a case where the temporarily decreased voltage becomes less than open voltage  51  of relay  8  as illustrated in  FIG. 2 . 
         [0007]    An object of the present invention is to provide a relay drive apparatus capable of preventing a relay from being turned OFF when the voltage of a coil is lowered, by gradually reducing a drawing amount of a current that flows through the coil to reduce the voltage of the coil in a case where the current flowing through the coil of the relay is drawn to increase the voltage of the coil. 
       Solution to Problem 
     Advantageous Effects of Invention 
       [0008]    A relay drive apparatus according to the present invention is a relay drive apparatus that controls supply of electric power to an electronic device, the relay drive apparatus including: a relay switch that includes a coil and that is turned ON when a voltage of the coil is equal to or greater than a predetermined value to supply the electric power to the electronic device, the coil having one end to which a predetermined voltage is applied and having another end grounded via a resistor; and a voltage adjusting section that increases the voltage of the coil to a value equal to or greater than the predetermined value by drawing a current which flows through the coil and allowing the current to flow to a ground not via the resistor when the supply of the electric power starts and that reduces the voltage of the coil to a voltage not below the predetermined value by gradually reducing a drawing amount of the current which flows through the coil after the supply of the electric power starts. 
         [0009]    According to the present invention, it is possible to prevent a relay from being turned OFF when the voltage of a coil is lowered, by gradually reducing a drawing amount of a current that flows through the coil to thereby reduce the voltage of the coil in a case where the current flowing through the coil of the relay is drawn to increase the voltage of the coil. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a diagram illustrating ON-OFF switching timing of a transistor of the related art; 
           [0011]      FIG. 2  is a diagram illustrating a time course of a voltage of a coil of a relay switch of the related art; 
           [0012]      FIG. 3  is a diagram illustrating a configuration of a relay drive apparatus according to Embodiment 1 of the present invention; 
           [0013]      FIG. 4  is a diagram illustrating ON-OFF switching timing of a transistor according to Embodiment 1 of the present invention; 
           [0014]      FIG. 5  is a diagram illustrating a time course of a voltage of a coil of a relay switch according to Embodiment 1 of the present invention; 
           [0015]      FIG. 6  is a diagram illustrating a configuration of a relay drive apparatus according to Embodiment 2 of the present invention; 
           [0016]      FIG. 7  is a diagram illustrating a configuration of a relay drive apparatus according to Embodiment 3 of the present invention; 
           [0017]      FIG. 8  is a diagram illustrating a time course of change in a resistance value of a variable resistor according to Embodiment 3 of the present invention; and 
           [0018]      FIG. 9  is a diagram illustrating a time course of a voltage of a coil of a relay switch according to Embodiment 3 of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       Embodiment 1 
     Configuration of Relay Drive Apparatus 
       [0020]    A configuration of relay drive apparatus  100  according to Embodiment 1 of the present invention will be described with reference to  FIG. 3 . Relay drive apparatus  100  is disposed in a vehicle-mounted charging apparatus mounted on a vehicle that runs on electric power of a storage battery, examples of which include a hybrid electric vehicle (HEV), a plug-in electric vehicle (PEV), and an electric vehicle (EV). 
         [0021]    Control section  101 , transistor  102 , relay switch  103 , resistor  104 , time constant circuit  105 , and transistor  106  mainly constitute relay drive apparatus  100 . Control section  101 , time constant circuit  105 , and transistor  106  constitute a voltage adjusting section. 
         [0022]    Terminal  301  of control section  101  outputs a control signal for switching between conduction and non-conduction of transistor  102  to transistor  102 . Terminal  301  of control section  101  outputs the control signal to time constant circuit  105  when supply of electric power to an electronic device (not illustrated) starts, and stops outputting the control signal after a predetermined time passes from the start of the output of the control signal. The predetermined time herein is, for example, one second from the start of the output of the control signal. 
         [0023]    A base of transistor  102  is connected to terminal  301  of control section  101 . An emitter of transistor  102  is connected to a power supply. A collector of transistor  102  is connected to one end of coil  201 . 
         [0024]    Relay switch  103  has coil  201  and switch  202 . The one end of coil  201  is connected to the collector of transistor  102  and the other end of coil  201  is grounded via resistor  104 . When transistor  102  conducts, a predetermined voltage is applied by the power supply to the one end (power supply side) of coil  201  via transistor  102 . Coil  201  generates a magnetic force when a current flows. Switch  202  opens and closes connection between the power supply and the electronic device (not illustrated) and supplies electric power to the electronic device when turned ON. In a case where the voltage of coil  201  is equal to or greater than a predetermined value, switch  202  is turned ON by being affected by the magnetic force from coil  201 . In addition, switch  202  is turned OFF when the magnetic force generated by the coil  201  goes away. 
         [0025]    Resistor  104  is inserted in series between coil  201  and the ground. Resistor  104  is a resistor for adjusting the voltage of coil  201 . 
         [0026]    Resistor  401  and capacitor  402  are used to constitute time constant circuit  105 . Time constant circuit  105  is disposed between terminal  302  of control section  101  and transistor  106 . Time constant circuit  105  delays a control signal that is input from terminal  302  of control section  101  and outputs the control signal to a base of transistor  106 . When the output of the control signal from terminal  302  of control section  101  stops, time constant circuit  105  causes a transient change in the control signal. Then, time constant circuit  105  outputs the control signal in which the transient change is caused to the base of transistor  106 . 
         [0027]    Transistor  106  adjusts the voltage of coil  201 . The base of transistor  106  is connected to resistor  401 . A collector of transistor  106  is connected to the other end (ground side) of coil  201 . An emitter of transistor  106  is grounded. Transistor  106  conducts when a control signal is input to the base from time constant circuit  105 , and performs a drawing operation by drawing the current that flows through coil  201  and allowing the current to flow to the ground not via resistor  104 . After the output of the control signal from terminal  302  of control section  101  stops, the control signal in which the transient change is caused by time constant circuit  105  is input to the base of transistor  106 , and transistor  106  gradually reduces the drawing amount of the current flowing through coil  201 . 
         [0028]    &lt;Operation of Relay Drive Apparatus&gt; 
         [0029]    An operation of relay drive apparatus  100  according to Embodiment 1 of the present invention will be described with reference to  FIGS. 3 to 5 . 
         [0030]    First, control section  101  supplies a control signal from terminal  301  to the base of transistor  102  in order that transistor  102  conducts at time t 0  as illustrated in  FIG. 4 . In addition, control section  101  supplies the control signal from terminal  302  to the base of transistor  106  in order that transistor  106  conducts. 
         [0031]    Then, the current that is supplied from the power supply flows in the order of transistor  102 , coil  201 , transistor  106 , and the ground. In other words, the current flowing through coil  201  is drawn to transistor  106  and flows to the ground via transistor  106 . In this case, a potential difference between the one end and the other end of coil  201  increases, so that the voltage of coil  201  increases. For example, the voltage of coil  201  is v 10  as illustrated in  FIG. 5 . 
         [0032]    Then, control section  101  stops the output of the control signal from terminal  302  at time t 10  that is when a predetermined time passes from time t 0 . In this case, time constant circuit  105  causes a transient change in the control signal and outputs the control signal in which the transient change is caused to the base of transistor  106 . As a result, switching of transistor  106  from ON to OFF can be moderated as illustrated in  FIG. 4 , and the drawing amount of the current flowing through coil  201  can be gradually reduced. In other words, the current that flows in the order of the power supply, transistor  102 , coil  201 , transistor  106 , and the ground gradually goes away. 
         [0033]    As described above, the current flowing through coil  201  flows to the ground via transistor  106  for a while after time t 10 , and thus a rapid decrease in the voltage of coil  201  can be prevented. Accordingly, the voltage of coil  201  does not fall below relay open voltage Vr after time t 10  inclusive as illustrated in  FIG. 5 . As a result, relay switch  103  is not turned OFF after time t 10  inclusive. 
         [0034]    The current flowing through coil  201  flows to the ground via resistor  104  in a case where transistor  106  does not conduct. Accordingly, the voltage of coil  201  is maintained at voltage V 11 . 
         [0035]    &lt;Effects of Embodiment 1&gt; 
         [0036]    In this embodiment, relay switch  103  can be prevented from being turned OFF when the voltage of coil  201  is lowered, by gradually reducing the drawing amount of the current flowing through coil  201  to reduce the voltage of coil  201  in a case where the current flowing through coil  201  of relay switch  103  is drawn to increase the voltage of coil  201 . 
         [0037]    In addition, according to this embodiment, the voltage of coil  201  is increased when the supply of the electric power starts. Accordingly, an ON operation of relay switch  103  can be surely performed even in a case where relay drive apparatus  100  is disposed in a high-temperature environment such as a vehicle-mounted charging apparatus. 
         [0038]    In addition, according to this embodiment, the voltage of coil  201  is reduced after a predetermined time passes from the start of the supply of the electric power, which enables power saving. 
       Embodiment 2 
     Configuration of Relay Drive Apparatus 
       [0039]    A configuration of relay drive apparatus  600  according to Embodiment 2 of the present invention will be described with reference to  FIG. 6 . Relay drive apparatus  600  is disposed in a vehicle-mounted charging apparatus mounted on a vehicle that runs on electric power of a storage battery, examples of which include an HEV, a PEV, and an EV. 
         [0040]    Compared to relay drive apparatus  100  according to Embodiment 1 illustrated in  FIG. 3 , relay drive apparatus  600  illustrated in  FIG. 6  includes no transistor  102 , but includes transistor  602  and also includes control section  601  instead of control section  101 . In  FIG. 6 , the same reference numerals as in  FIG. 3  are used to refer to the same parts and description thereof will be omitted. 
         [0041]    Relay switch  103 , resistor  104 , time constant circuit  105 , transistor  106 , control section  601 , and transistor  602  mainly constitute relay drive apparatus  600 . Time constant circuit  105 , transistor  106 , and control section  601  constitute a voltage adjusting section. 
         [0042]    Terminal  701  of control section  601  outputs a control signal to time constant circuit  105  when electric power is supplied to the electronic device (not illustrated). Terminal  702  of control section  601  outputs a control signal for switching between conduction and non-conduction of transistor  602  to transistor  602 . 
         [0043]    One end of coil  201  of relay switch  103  is connected to the power supply and the other end of coil  201  of relay switch  103  is grounded via resistor  104  and transistor  602 . A predetermined voltage is applied to the one end of coil  201  by the power supply. The configuration of relay switch  103  other than what is described above is identical to that in Embodiment 1 described above. Thus, description thereof will be omitted. 
         [0044]    Resistor  104  is inserted in series between coil  201  and transistor  602 . 
         [0045]    A base of transistor  602  is connected to terminal  702  of control section  601 . A collector of transistor  602  is connected to resistor  104 . An emitter of transistor  602  is grounded. 
         [0046]    Time constant circuit  105  is disposed between terminal  701  of control section  601  and transistor  106 . Time constant circuit  105  delays the control signal that is input from terminal  701  of control section  601  and outputs the control signal to the base of transistor  106 . After the output of the control signal from terminal  701  of control section  601  stops, time constant circuit  105  causes a transient change in the control signal. The configuration of time constant circuit  105  other than what is described above is identical to that in Embodiment 1 described above. Thus, description thereof will be omitted. 
         [0047]    &lt;Operation of Relay Drive Apparatus&gt; 
         [0048]    An operation of relay drive apparatus  600  according to Embodiment 2 of the present invention will be described with reference to  FIGS. 4 to 6 . ON-OFF switching timing of transistor  106  is identical to that in  FIG. 4  and a time course of change in the voltage of coil  201  is identical to that in  FIG. 5 . Thus, the operation of relay drive apparatus  600  will be described with reference to  FIGS. 4 and 5  as well as  FIG. 6 . 
         [0049]    First, control section  601  supplies the control signal from terminal  702  to the base of transistor  602  in order that transistor  602  conducts at time t 0  as illustrated in  FIG. 4 . In addition, control section  601  supplies the control signal from terminal  701  to the base of transistor  106  in order that transistor  106  conducts. 
         [0050]    Then, the current that is supplied from the power supply flows in the order of coil  201 , transistor  106 , and the ground. In other words, the current flowing through coil  201  is drawn to transistor  106  and flows to the ground via transistor  106 . In this case, the potential difference between the one end and the other end of coil  201  increases, so that the voltage of coil  201  increases. For example, the voltage of coil  201  is v 10  as illustrated in  FIG. 5 . 
         [0051]    Then, control section  601  stops the output of the control signal from terminal  701  at time t 10  that is when a predetermined time passes from time t 0 . In this case, time constant circuit  105  causes the transient change in the control signal and outputs the control signal in which the transient change is caused to the base of transistor  106 . As a result, switching of transistor  106  from ON to OFF can be moderated as illustrated in  FIG. 4 , and the drawing amount of the current flowing through coil  201  can be gradually reduced. In other words, the current that flows in the order of the power supply, coil  201 , transistor  106 , and the ground also goes away gradually. 
         [0052]    As described above, the current flowing through coil  201  flows to the ground via transistor  106  for a while after time t 10 , and thus a rapid decrease in the voltage of coil  201  can be prevented. Accordingly, the voltage of coil  201  does not fall below relay open voltage Vr after time t 10  inclusive as illustrated in  FIG. 5 . As a result, relay switch  103  is not turned OFF after time t 10  inclusive. 
         [0053]    The current flowing through coil  201  flows to the ground via resistor  104  and transistor  602  in a case where transistor  106  does not conduct. Accordingly, the voltage of coil  201  is maintained at voltage V 11 . 
         [0054]    &lt;Effects of Embodiment 2&gt; 
         [0055]    In this embodiment, relay switch  103  can be prevented from being turned OFF when the voltage of coil  201  is lowered, by gradually reducing the drawing amount of the current flowing through coil  201  to lower the voltage of coil  201  in a case where the current flowing through coil  201  of relay switch  103  is drawn to increase the voltage of coil  201 . 
         [0056]    In addition, according to this embodiment, the voltage of coil  201  is increased when the supply of the electric power starts. Accordingly, an ON operation of relay switch  103  can be surely performed even in a case where relay drive apparatus  600  is disposed in a high-temperature environment such as a vehicle-mounted charging apparatus. 
         [0057]    In addition, according to this embodiment, the voltage of coil  201  is reduced after a predetermined time passes from the start of supply of the electric power, which enables power saving. 
       Embodiment 3 
     Configuration of Relay Drive Apparatus 
       [0058]    A configuration of relay drive apparatus  800  according to Embodiment 3 of the present invention will be described with reference to  FIG. 7 . Relay drive apparatus  800  is disposed in a vehicle-mounted charging apparatus mounted on a vehicle that runs on electric power of a storage battery, examples of which include an HEV, a PEV, and an EV. 
         [0059]    Compared to relay drive apparatus  100  according to Embodiment 1 illustrated in  FIG. 3 , relay drive apparatus  800  illustrated in  FIG. 7  includes no transistor  102 , time constant circuit  105 , and transistor  106 , but includes variable resistor  802  and transistor  803  and also includes control section  801  instead of control section  101 . In  FIG. 7 , the same reference numerals as in  FIG. 3  are used to refer to the same parts and description thereof will be omitted. 
         [0060]    Relay switch  103 , resistor  104 , control section  801 , variable resistor  802 , and transistor  803  mainly constitute relay drive apparatus  800 . Control section  801  and variable resistor  802  constitute a voltage adjusting section. 
         [0061]    Terminal  901  of control section  801  changes a resistor value of variable resistor  802  by outputting a control signal to variable resistor  802  when and after supply of electric power to the electronic device (not illustrated) starts. Terminal  902  of control section  801  outputs a control signal for switching between conduction and non-conduction of transistor  803  to a base of transistor  803 . 
         [0062]    One end of coil  201  of relay switch  103  is connected to the power supply and the other end of coil  201  of relay switch  103  is grounded via resistor  104  and transistor  803 . A predetermined voltage is applied to the one end of coil  201  by the power supply. The configuration of relay switch  103  other than what is described above is identical to that in Embodiment 1 described above. Thus, description thereof will be omitted. 
         [0063]    Resistor  104  is inserted in series between coil  201  and transistor  803 . 
         [0064]    One end of variable resistor  802  is connected to the other end of coil  201  and the other end of variable resistor  802  is grounded. When the supply of electric power to the electronic device starts, variable resistor  802  performs a drawing operation including changing the resistance value in accordance with control made by the control signal that is input from control section  801 , drawing the current flowing through coil  201 , and allowing the current to flow to the ground not via resistor  104 . After the supply of the electric power to the electronic device starts, variable resistor  802  changes the resistance value in accordance with the control made by the control signal that is input from control section  801 , and gradually reduces the drawing amount of the current flowing through coil  201 . 
         [0065]    A base of transistor  803  is connected to terminal  902  of control section  801 . A collector of transistor  803  is connected to resistor  104 . An emitter of transistor  803  is grounded. 
         [0066]    &lt;Operation of Relay Drive Apparatus&gt; 
         [0067]    An operation of relay drive apparatus  800  according to Embodiment 3 of the present invention will be described with reference to  FIGS. 7 to 9 . 
         [0068]    First, control section  801  supplies a control signal from terminal  902  to the base of transistor  803  in order that transistor  803  conducts at time t 0  as illustrated in  FIG. 8 . In addition, control section  801  supplies the control signal from terminal  901  to variable resistor  802  in order that the resistance value of variable resistor  802  is reduced to XΩ. Resistance value X is much smaller than the resistance value of resistor  104  (resistance value X&lt;&lt;resistance value of resistor  104 ). 
         [0069]    Then, the current that is supplied from the power supply flows in the order of coil  201 , variable resistor  802 , and the ground. In other words, the current flowing through coil  201  is drawn to variable resistor  802  and flows to the ground via variable resistance  802 . In this case, the potential difference between the one end and the other end of coil  201  increases, so that the voltage of coil  201  increases. For example, the voltage of coil  201  is V 20  as illustrated in  FIG. 9 . 
         [0070]    Then, control section  801  supplies the control signal from terminal  901  to variable resistor  802  at time t 20  that is when a predetermined time passes from time t 0 , and gradually increases the resistance value of variable resistor  802  from XΩ to Y(X&lt;Y)Ω as illustrated in  FIG. 8 . As a result, the drawing amount of the current flowing through coil  201  can be gradually reduced by variable resistor  802 . In other words, the current that flows in the order of the power supply, coil  201 , variable resistor  802 , and the ground gradually goes away. Resistance value Y is much larger than the resistance value of resistor  104  (resistance value Y&gt;&gt;resistance value of resistor  104 ). 
         [0071]    As described above, the current flowing through coil  201  flows to the ground via variable resistor  802  for a while after time t 20 , and thus a rapid decrease in the voltage of coil  201  can be prevented. Accordingly, the voltage of coil  201  does not fall below relay open voltage Vr after time t 20  inclusive as illustrated in  FIG. 9 . As a result, relay switch  103  is not turned OFF after time t 20  inclusive. 
         [0072]    In a case where the resistance value of variable resistor  802  reaches YΩ, the current flowing through coil  201  flows to the ground via resistor  104  and transistor  803 . Thus, the voltage of coil  201  is maintained at voltage V 21 . 
         [0073]    &lt;Effects of Embodiment 3&gt; 
         [0074]    In this embodiment, the current flowing through coil  201  of relay switch  103  is drawn by using variable resistor  802 . Accordingly, not only can the effect of Embodiment 1 described above be achieved but the configuration can also be simplified. 
         [0075]    &lt;Variation Common to Each Embodiment&gt; 
         [0076]    In Embodiments 1 to 3 described above, the drawing amount is gradually reduced after a predetermined time passes from the start of supply of the electric power to the electronic device. However, the drawing amount may be gradually reduced in a case where a temperature that is detected by a temperature sensor becomes equal to or lower than a predetermined temperature. In this case, the relay switch can be surely turned ON in a high-temperature environment when the relay drive apparatus is used in a high-temperature environment, and power-saving can be enabled in a relatively low temperature environment. 
         [0077]    In Embodiments 1 to 3 described above, the relay drive apparatus is disposed in a vehicle-mounted charger, but can also be disposed in any apparatus other than the vehicle-mounted charger. 
         [0078]    The disclosure of Japanese Patent Application No. 2012-210962, filed on Sep. 25, 2012, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0079]    The relay drive apparatus according to the present invention is suitable for controlling supply of electric power to an electronic device. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100  Relay drive apparatus 
           101  Control section 
           102 ,  106  Transistor 
           103  Relay switch 
           104 ,  401  Resistor 
           105  Time constant circuit 
           201  Coil 
           202  Switch 
           301 ,  302  Terminal 
           402  Capacitor