Abstract:
A power window switch circuit, even if soaked, prevents windows from opening or closing unintentionally. A DOWN switch ( 128 ) and an UP switch ( 129 ) each include a first fixed contact (DN 1 , UP 1 ) connected with a power supply, a second fixed contact (DN 2 , UP 2 ) grounded, and movable contacts ( 131, 132, 133, 134 ) for selectively connects either the first or second fixed contact with the first terminal of corresponding relay coils ( 21, 23 ). A transistor (TR 4 ) responsive to a soak signal is connected between the ground and the second fixed contacts (DN 2 , UP 2 ) of the UP and DOWN switches. The second terminals of the first and second relay coils are grounded through their respective transistors. When a soak is detected, a soak detector ( 15 ) supplies a soak signal to the transistors.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a power window switch circuit, and more particularly, it relates to a power window switch circuit having a drive motor, a relay, a switch and the like for raising and lowering a window glass. 
     BRIEF SUMMARY OF THE INVENTION 
     In general, a vehicle has a power window apparatus for opening and closing a window glass of a side door and the like, and the power window apparatus includes an UP switch (raising switch) and a DOWN switch (lowering switch) manually operated for raising and lowering the window glass. 
     FIG. 1 schematically shows an electric circuit of a power window switch circuit  10  in a conventional power window apparatus. The power window switch circuit  10  includes a DOWN switch  28 , an UP switch  29 , an automatic switch  30 , a control circuit  12 , a drive circuit  20 , and a drive motor M which is preferably a DC motor for raising and lowering a window glass. The drive circuit  20  includes a first relay  22 , a second relay  24 , and transistors TR 1  to TR 3 . The DOWN switch  28  and the UP switch  29  are used, for example, as a tumbler two-stepped click type switch. The DOWN switch  28  has a first knob (hereinafter referred to as “the DOWN side knob”), and a second knob (hereinafter referred to as “the UP side knob”). When the DOWN side knob is pressed by one step, a movable contact  31  of the DOWN switch  28  is connected to a fixed contact DN. When the UP side knob is pressed by one step, a movable contact  32  of the UP switch  29  is connected to a fixed contact UP. When the DOWN side knob is pressed by two steps, the DOWN switch  28  and the automatic switch  30  are both turned on. Moreover, when the UP side knob is pressed by two steps, the UP switch  29  and the automatic switch  30  are both turned on. In the automatic operation, after the knob is pressed by two steps, the DOWN switch  28  or the UP switch  29  is turned off but the automatic switch  30  is maintained in ON state for a predetermined period of time. 
     When the automatic switch  30  and the DOWN switch  28  are turned on, the control circuit  12  continues to supply a high (H) level relay drive signal to the base of the transistor TR 3  even after the DOWN switch  28  is turned off, until the window glass reaches a completely open position, and supplies an ON signal to the base of the transistor TR 1 , thereby turning on the transistors TR 1  and TR 3 . This supplies excitation current to the relay coil  21  of the first relay  22 . When the relay coil  21  is excited, the movable contact  25   c  of the relay contact  25  is switched from a ground side fixed contact  25   a  to a power supply side fixed contact  25   b , and the drive motor M is supplied with the drive current and rotated in normal direction. The drive motor M drives a wire-type or arm-type regulator (not shown) so as to lower the window glass. When the window glass reaches the completely open position, a completely open position limit switch (not depicted) begins to operate. In response to this switch operation, the control circuit  12  stops drive of the drive motor M by the relay drive signal and maintains the window glass at the completely open position. 
     When the automatic switch  30  and the UP switch  29  are turned on, the control circuit  12  continues to supply a high (H) level relay drive signal to the base of the transistor TR 2  even after the UP switch  29  is turned off, until the window glass reaches a completely closed position, and supplies an ON signal to the base of the transistor TR 1 , thereby turning on the transistors TR 1  and TR 2 . This supplies excitation current to the relay coil  23  of the second relay  24 . When the relay coil  23  is excited, the movable contact  26   c  of the relay contact  26  is switched from a ground side fixed contact  26   a  to a power supply side fixed contact  26   b , and the drive motor M is rotated in reverse direction. The drive motor M drives the regulator (not shown) so as to raise the window glass. When the window glass reaches the completely closed position, a completely closed position limit switch (not shown) begins to operate. In response to this switch operation, the control circuit  12  stops drive of the drive motor M by the relay drive signal and maintains the window glass at the completely closed position. 
     When the DOWN side knob is operated to turn on the DOWN switch  28 , the control circuit  12  supplies a high (H) level relay drive signal to the base of the transistor TR 3  and supplies the ON signal to the base of the transistor TR 1 , thereby turning on the transistors TR 1  and TR 3 . Accordingly, while the DOWN switch  28  is in ON state, excitation current is supplied to the relay coil  21  and drive motor M is rotated in the normal direction, thereby lowering the window glass. 
     When the UP side knob is operated to turn on the UP switch  29 , the control circuit  12  supplies the high (H) level relay drive signal to the base of the transistor TR 2  and supplies the ON signal to the base of the transistor TR 1 , thereby turning on the transistors TR 1  and TR 2 . Accordingly, while the UP switch  29  is in ON state, excitation current is supplied to the relay coil  23  and drive motor M is rotated in the reverse direction, thereby raising the window glass. 
     When the first relay  22 , the second relay  24 , and the control circuit  12  are soaked by an electrolyte liquid such as rain, leak resistance R 11  to R 15  may be caused as shown by dotted lines in FIG.  1 . 
     For example, even if the DOWN switch  28  is turned off and the control circuit  12  does not supply the ON signal and the H level relay drive signal to the transistors TR 1  and TR 3 , respectively, the transistors TR 1  and TR 3  are turned on by the leak resistance R 11  and R 13 . This excites the relay coil  21 , and the movable contact  25   c  is connected to the power supply side fixed contact  25   b , which rotates the drive motor M in the normal direction and unintentionally lowers the window glass. 
     Moreover, even if the UP switch  29  is turned off and the control circuit  12  does not supply the ON signal and the H level relay drive signal to the transistors TR 1  and TR 2 , respectively, the transistors TR 1  and TR 2  are turned on by the leak resistance R 11  and R 12 . This excites the relay coil  23 , and the movable contact  26   c  is connected to the power supply side fixed contact  26   b , which rotates the drive motor M in the reverse direction and unintentionally raises the window glass. 
     Furthermore, even if the transistor TR 3  is in OFF state, generation of leak resistance R 11  and R 15  may excite the relay coil  21 , which in turn rotates the drive motor M in the normal direction to lower the window glass unintentionally. Furthermore, even if the transistor TR 2  is in OFF state, generation of leak resistance R 11  and R 14  may excite the relay coil  23 , which in turn rotates the drive motor M in the reverse direction to raise the window glass unintentionally. 
     When the leak resistance R 11  to R 13  are generated, the transistors TR 1  to TR 3  are turned on, the relay coils  21  and  23  are excited, and the movable contacts  25   c  and  26   c  are connected to the power supply side fixed contacts  25   b  and  26   b , respectively. In this case, identical voltage is applied to both the terminals of the drive motor M. Accordingly, even if the DOWN side knob or the UP side knob is operated, the drive motor M is not driven and the window glass is not raised or lowered. 
     When the leak resistance R 11 , R 14 , and R 15  are generated, the transistor TR 1  is turned on by the leak resistance R 11 , the relay coils  21  and  23  are excited, and identical voltage is applied to both the terminals of the drive motor M. Accordingly, even if the DOWN side knob or the UP side knob is operated in this state, the drive motor M is not driven and the window glass is not raised or lowered. 
     As has been described above, depending on the position where leak resistance is generated, four possible states should be considered: (a) only the UP side relay coil  23  is excited; (b) only the DOWN side relay coil  21  is excited; (c) both of the relay coils  21  and  23  are excited; (d) neither the relay coils  21  nor  23  is excited. Accordingly, when the power window switch circuit  10  is soaked, it cannot be decided whether the window glass is raised or lowered. As a result, movement of the power window switch circuit  10  which is operated by a person in the vehicle cannot be properly achieved. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It is therefore an object of the present invention to provide a power window switch circuit which can prevent theunintentional raising or lowering of a window glass when the power window switch circuit is soaked. 
     According to a first embodiment of the present invention, there is provided a power window switch circuit which includes a first relay coil having two terminals; a down switch connected to the first relay coil for lowering a window glass; a second relay coil having two terminals; and an up switch connected to the second relay coil for raising a window glass. Each of the down switch and the up switch includes a first fixed contact connected to a power supply; a second fixed contact connected to the ground; and a movable contact selectively connecting one of the first and the second fixed contact to a first terminal of the corresponding relay coil. A first switching element responsive to a soak detection signal is connected between the second fixed contacts of the down switch and the up switch and the ground. The first switching element is also connected between second terminals of the first and second relay coils and the ground. The power window switch circuit further includes a soak detection circuit for supplying the soak detection signal to the first switching element when detecting the soak. 
     According to a second embodiment of the present invention, there is provided a power window switch circuit which includes a first relay coil having two terminals; a down switch connected to the first relay coil for lowering a window glass, a second relay coil having two terminals; and an up switch connected to the second relay coil for raising the window glass. The down switch includes a first fixed contact connected to a power supply; a second fixed contact connected to a first terminal of the first relay coil; and first and second movable contacts corresponding to the first and second fixed contacts. The up switch includes a third fixed contact connected to a power supply; a fourth fixed contact connected to a first terminal of the second relay coil; and third and fourth movable contacts corresponding to the third and fourth fixed contacts. A first switching element is connected between the first movable contact of the down switch and a first terminal of the first relay coil. A second switching element is connected between the third movable contact of the up switch and a first terminal of the second relay coil. A third switching element is connected between the second and fourth movable contacts of the down switch and the up switch and the ground. The third element turns on one of the first and second switching elements when turned on in response to a soak detection signal. The power window switch circuit further includes a soak detection circuit for supplying the soak detection signal to the third switching element when detecting the soak. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic electric circuit diagram of a conventional power window switch circuit. 
     FIG. 2 is a schematic electric circuit diagram of a power window switch circuit according to a first embodiment of the present invention. 
     FIG. 3 is a schematic electric circuit diagram of a power window switch circuit according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2 schematically shows an electric circuit of a power window switch circuit  100  in an automobile power window apparatus according to a first embodiment of the present invention. It should be noted that like components as in FIG. 1 are denoted by identical reference symbols. The power window apparatus is provided at a side door of the driver seat side. The power window switch  100  includes a control circuit  12 , a drive circuit  120 , a DOWN switch  128 , an UP switch  129 , an automatic switch  30 , and a drive motor M. The drive circuit  120  includes a first relay  22 , a second relay  24 , transistors TR 1  to TR 3  and diodes D 1  to D 4 . 
     Between a plus (+) terminal (shown by “+IG” in FIG. 2) and a minus (−) terminal (shown by the symbol for the ground in FIG. 2) of a battery power supply, the transistor TR 1 , the diode D 4 , the relay coil  21  of the first relay  22 , and the transistor TR 3  are connected in series. Between an anode of the diode D 4  and the ground, the diode D 3 , a relay coil  23  of the second relay  24 , and the transistor TR 2  are connected in series. A resistor R 1  is connected between the plus terminal of the power supply and the transistor TR 1 . A base of the transistor TR 1  is connected via the resistor R 2  to the control circuit  12 . The transistors TR 2  and TR 3  have bases connected to the control circuit  12 . 
     The DOWN switch  128  is a dipole single setting switch including: a first fixed contact DN 1  connected to the plus terminal of the power supply; a first movable contact  131  and a second movable contact  133  connected to each other via the diode D 2 ; and a second fixed contact DN 2 . The DOWN switch  128  constitutes a false transfer contact. When the DOWN switch  128  is turned off, the second movable contact  133  is connected to the second fixed contact DN 2  and the first movable contact  131  is not connected to the first fixed contact DN 1 . That is, the first movable contact  131  functions as a constantly open contact with respect to the first fixed contact DN 1 , while the second movable contact  133  functions as a constantly closed contact with respect to the second fixed contact DN 2 . The first movable contact  131  is connected via a resistor R 5  to the control circuit  12 , while the second movable contact  133  is connected to the plus terminal of the relay coil  21 . The second fixed contact DN 2  is connected to the anode of the diode D 8 . 
     The UP switch  129  is a dipole single setting switch including: a first fixed contact UPI connected to the plus terminal of the power supply; a first movable contact  132  and a second movable contact  134  connected to each other via the diode D 1 ; and a second fixed contact UP 2 . The UP switch  129  constitutes a false transfer contact. When the UP switch  129  is turned off, the second movable contact  134  is connected to the second fixed contact UP 2  and the first movable contact  132  is not connected to the first fixed contact UP 1 . That is, the first movable contact  132  functions as a constantly open contact with respect to the first fixed contact UP 1 , while the second movable contact  134  functions as a constantly closed contact with respect to the second fixed contact UP 2 . The first movable contact  132  is connected via a resistor R 4  to the control circuit  12 , while the second movable contact  134  is connected to the plus terminal of the relay coil  23 . The second fixed contact UP 2  is connected to the anode of the diode D 8 . 
     The automatic switch  30  has a fixed contact connected to the plus terminal of the power supply and a movable contact connected via a resistor R 3  to the control circuit  12 . 
     The first relay  22  has a relay contact  25  including a movable contact  25   c  connected to the first terminal of the drive motor M, a power supply side fixed contact  25   b  connected to the plus terminal of the power supply, and a ground side fixed contact  25   a  connected to the ground. When the relay coil  21  is in a deexcited state, the movable contact  25   c  is connected to the ground side fixed contact  25   a  and when the relay coil  21  is excited, the movable contact  25   c  is connected to the power supply side fixed contact  25   b.    
     The second relay  24  has a relay contact  26  including a movable contact  26   c  connected to the second terminal of the drive motor M, a power supply side fixed contact  26   b  connected to the plus terminal of the power supply, and a ground side fixed contact  26   a  connected to the ground. When the relay coil  23  is in the deexcited state, the movable contact  26   c  is connected to the ground side fixed contact  26   a  and when the relay coil  23  is excited, the movable contact  26   c  is connected to the power supply side fixed contact  26   b.    
     The drive circuit  120  further includes a leak detection circuit  15  as a soak detection circuit, transistors TR 4  and TR 5 , diodes D 5  to D 8 , and resistors R 6  to R 9 . Each of the diodes D 1  to D 8  functions as a diode for preventing back flow. 
     The leak detection circuit  15  has an electrode  16  connected to the plus terminal of the power supply and an electrode  17  connected via the base resistor R 8  to the base of the transistor TR 4 . The electrodes  16  and  17  are arranged at a predetermined distance from each other. When leak is caused between the electrodes  16  and  17  of the leak detection circuit  15 , leak resistance is generated between the electrodes  16  and  17  to turn on the leak detection circuit  15 . When no leak is present between the electrodes  16  and  17 , the leak detection circuit  15  is turned off. It is preferable that the leak detection circuit  15  be located at a position identical to or in the vicinity of the control circuit  12 . 
     The resistor  9  is connected between the base of the transistor TR 4  and the ground. The transistor TR 4  has an emitter grounded and a collector connected to respective cathodes of the diodes D 5  to D 8 . The diode D 5  has an anode connected to the minus terminal of the relay coil  23 , the diode D 6  has an anode connected to the minus terminal of the relay coil  21 , and the diode D 7  has an anode connected via the resistor R 7  to the base of the transistor TR 5 . The resistor R 6  is connected between the plus terminal of the power supply and the base of the transistor TR 5 . The transistor TR 5  has an emitter connected to the plus terminal of the power supply and a collector connected to the base of the transistor TR 1 . 
     In the first embodiment, the relay coil  21  constitutes the first relay coil and the relay coil  23  constitutes the second relay coil. The first movable contact  131  and the second movable contact  133  constitute a movable contact portion. The first movable contact  132  and the second movable contact  134  constitute a movable contact portion. The DOWN switch  128  and the diode D 2  constitute a DOWN switch circuit. The UP switch  129  and the diode D 1  constitute an UP switch circuit. The transistor TR 1  constitutes a second switching element, the transistor TR 4  constitutes a first switching element, and the transistor TR 5  constitutes invalidation means. The plus terminal of the power supply constitutes a power supply side terminal and the anode of the diode D 8  constitutes a ground side terminal. 
     Next, explanation will be given on the function of the power window switch circuit  100 . 
     Firstly, explanation will be given on operation of the power window switch circuit  100  when not soaked by an electrolyte liquid such as rain and when the DOWN switch  128  and the UP switch  129  are both in an OFF state, i.e., in a non-operation state. In this case, the second movable contacts  133  and  134  are connected to the second fixed contacts DN 2  and UP 2 , respectively, and the first movable contacts  131  and  132  are not connected to the first fixed contacts DN 1  and UP 1 . Furthermore, the transistors TR 1  to TR 3  are in an OFF state. Consequently, no power supply voltage is supplied from the plus terminal of the power supply to the plus terminals and minus terminals of the relay coils  21  and  23 . Therefore, the relay coils  21  and  23  are not excited. Consequently, the drive motor M is not driven and the window glass is not lowered or raised. 
     Next, when the DOWN side knob is operated in this state, the second movable contact  133  is disconnected from the second fixed contact DN 2  and with a slight delay, the first movable contact  131  is connected to the first fixed contact DN 1  to turn on the DOWN switch  128 . In response to the ON operation of the DOWN switch  128 , the control circuit  12  turns on the transistors TR 1  and TR 3 . Thus, the relay coil  21  is excited and the drive motor M is rotated in the normal direction to lower the window glass. 
     Next, when the UP side knob is operated in this state, the second movable contact  134  is disconnected from the second fixed contact UP 2  and with a slight delay, the first movable contact  132  is connected to the first fixed contact UP 1  to turn on the UP switch  129 . In response to the ON operation of the UP switch  129 , the control circuit  12  turns on the transistors TR 1  and TR 2 . Thus, the relay coil  23  is excited and the drive motor M is rotated in the reverse direction to raise the window glass. 
     Next, explanation will be given on operation of the power window switch circuit  100  which is soaked by an electrolyte liquid such as rain and when the DOWN switch  128  and the UP switch  129  are both in the OFF state, i.e., in the non-operation state. In this case, the soak causes leak between the electrodes  16  and  17  of the leak detection circuit  15 , and the leak detection circuit  15  is turned on. Then, the transistors TR 4  and TR 5  are turned on. In response to the ON operation of the transistor TR 5 , the transistor TR 1  is turned off. That is, operation of the transistor TR 1  becomes inactive. The ON operation of the transistor TR 4  lowers voltage of the minus terminal of the relay coil  21  via the diode D 6  to the ground voltage, and voltage of the minus terminal of the relay coil  23  is lowered via the diode D 5  to the ground voltage. Furthermore, voltage of the plus terminal of the relay coil  21  is lowered to the ground voltage via the second movable contact  133 , the second fixed contact DN 2 , and the diode D 8 , and voltage of the plus terminal of the relay coil  23  is lowered to the ground voltage via the second movable contact  134 , the second fixed contact UP 2 , and the diode D 8 . Then, terminals of the relay coils  21  and  23  are both set to the ground voltage and accordingly, the movable contacts  25   c  and  26   c  are maintained in a connected state to the ground side fixed contacts  25   a  and  26   a . Consequently, both the terminals of the drive motor M are set to the ground voltage and the drive motor does not operate. 
     Thus, even if leak resistance is generated in the power window switch circuit  100 , voltage of both the terminals of the relay coils  21  and  23  are set to the ground voltage by the ON operation of the transistor TR 4  and accordingly, the relay coils  21  and  23  are not excited and the drive motor M is not operated. This prevents unintentional lowering or raising of the window glass. 
     Next, in this state, when the DOWN switch  128  is turned on, the power supply voltage is supplied from the plus terminal of the power supply via the diode D 2  to the plus terminal of the relay coil  21  and the relay coil  21  is excited. Here, the transistor TR 1  is turned off by the ON operation of the transistor TR 5  and the UP switch  129  is also in an OFF state. Accordingly, the power supply voltage is not supplied to the plus terminal of the relay coil  23  and the relay coil  23  is kept in the deexcited state. As a result, only the relay coil  21  is excited and the movable contact  25   c  of the relay contact  25  is switched to the power supply side fixed contact  25   b . The drive motor M is rotated in the normal direction and the window glass is lowered. 
     Next, when the UP switch  129  is turned on, the power supply voltage is supplied from the plus terminal of the power supply via the diode D 1  to the plus terminal of the relay coil  23  and the relay coil  23  is excited. Here, the transistor TR 1  is turned off by the ON operation of the transistor TR 5  and the DOWN switch  128  is also in the OFF state. Accordingly, the power supply voltage is not supplied to the plus terminal of the relay coil  21  and the relay coil  21  is kept in the deexcited state. As a result, only the relay coil  23  is excited and the movable contact  26   c  of the relay contact  26  is switched to the power supply side fixed contact  26   b . The drive motor M is rotated in the reverse direction and the window glass is raised. 
     The power window switch circuit  100  of the first embodiment has advantages as follows. 
     (1) Even if the power window switch circuit  100  is soaked, it is possible to definitely lower or raise the window glass according to the ON operation of the DOWN switch  128  or the UP switch  129 . 
     (2) When the power window switch circuit  100  is soaked and the DOWN switch  128  or the UP switch  129  is in the OFF state, unintentional lowering or raising of the window glass can be prevented. 
     (3) In the ON operation of the DOWN switch  128  or the UP switch  129 , the second movable contact  133  or  134  is disconnected from the second fixed contact DN 2  or UP 2  and after this, the first movable contact  131  or  132  is connected to the first fixed contact DN 1  or UP 1 . Accordingly, it is possible to prevent dead short (in the first embodiment, short-circuit between the plus terminal of the power supply and the anode of the diode D 8 ) when the OFF operation of the second movable contact is performed simultaneously with the ON operation of the first movable contact or when the ON operation of the first movable contact is performed prior to the OFF operation of the second movable contact. 
     (4) When the power window switch circuit  10  is soaked and the DOWN switch  128  and the UP switch  129  are in the OFF state, the transistor TR 1  is in the OFF state because of the ON operation of the transistors TR 4  and TR 5 . Accordingly, even if an ON signal is supplied from the control circuit  12  to the transistor TR 1 , the transistor TR 1  is not turned on and excitation current is not supplied to the relay coils  21  and  23 . As a result, it is possible to prevent unintentional lowering or raising of the window glass. 
     (5) When the first movable contact  131  or  132  of the DOWN switch  128  or the UP switch  129  is connected to the first fixed contact DN 1  or UP 1 , the diode D 1  or D 2  enables prevention of the current flow from the second movable contact  133  or  134  to the first movable contact  131  or  132 . Accordingly, the power supply voltage is definitely supplied from the plus terminal of the power supply via the diode D 1  or D 2  to the plus terminal of the relay coil  21  or  23 . Thus, the relay coil  21  or  23  accurately functions. 
     It should be noted that the first embodiment may be modified as follows. 
     In the aforementioned case, the transistors TR 1  and TR 5  are PNP transistors, but it is also possible to use NPN transistors. In this case, the transistor TR 1  has a collector connected to the plus terminal of the power supply and an emitter connected to the anode of the diode D 3 , while the transistor TR 5  has a collector connected to the plus terminal of the power supply and an emitter connected to the base of the transistor TR 1 . 
     The transistors TR 2  to TR 4  which are NPN transistors in the aforementioned case may be replaced by PNP transistors. In this case, the transistor TR 2  has an emitter connected to the minus terminal of the relay coil  23  and a collector grounded. Moreover, the transistor TR 3  has an emitter connected to the minus terminal of the relay coil  21  and a collector grounded. Furthermore, the transistor TR 4  has an emitter connected to the cathode of the diodes D 5  to D 8  and a collector grounded. 
     The transistors TR 2  and TR 3  used in the first embodiment may be replaced by a transistor array having two transistor elements. In this case, it is possible to reduce the size of the power window apparatus. 
     The first and second relays  22  and  24  used in the first embodiment may be replaced by two relays contained in a single package. In this case, it is possible to reduce the size of the power window apparatus. 
     FIG. 3 schematically shows a power window switch circuit  200  according to a second embodiment of the present invention. The power window switch circuit  200  has a drive circuit  120  including a first relay  22  and a second relay  24 , transistors TR 1  to TR 3 , TR 24  to TR 26 , diodes D 21  to D 28 , and resistors R 1  to R 3 , R 21  to R 26 . Each of the diodes D 21  to D 28  functions to prevent back flow. 
     Between the plus terminal and the minus terminal of the battery power supply, the transistor TR 1 , the diode D 21 , the relay coil  21  for lowering the window glass, and the transistor TR 3  are connected in series. Between the cathode of the diode D 21  and the ground, the relay coil  23  for raising the window glass, and the transistor TR 2  are connected in series. Between the plus terminal of the power supply and the base of the transistor TR 1 , the resistor R 1  is connected. The transistor TR 1  has a base connected via the resistor R 2  to the control circuit  12 . The transistors TR 2  and TR 3  have bases connected to the control circuit  12 . 
     The DOWN switch  128  has a first movable contact  131  connected via the resistor  5  to the control circuit  12 , a second movable contact  133  connected to the anode of the diode D 25 , and a second fixed contact DN 2  connected to the minus terminal of the relay coil  23 . 
     The UP switch  129  has a first movable contact  132  connected via the resistor  4  to the control circuit  12 , a second movable contact  134  connected to the anode of the diode D 25 , and a second fixed contact UP 2  connected to the minus terminal of the relay coil  21 . 
     The leak detection circuit  15  has an electrode  17  connected via the base resistor R 25  to a base of the transistor TR 26 . The resistor R 24  is connected between the base of the transistor TR 26  and the ground. The transistor TR 26  has an emitter grounded and a collector connected to cathodes of the diodes D 24  to D 28 . The diode D 24  has an anode connected to a power line of the control circuit  12 , and the resistor R 26  is connected between the plus terminal of the power supply and the power line. 
     The diode D 26  has an anode connected via the resistor R 21  to the base of the transistor TR 1  and the diode D 27  has an anode connected via the resistor R 22  to the base of the transistor TR 24 . The diode D 28  has an anode connected via the resistor R 23  to the base of the transistor TR 25 . 
     The transistor TR 24  has an emitter connected to the first movable contact  131  of the DOWN switch  128  and a collector connected via the diode D 22  to the minus terminal of the relay coil  23 . The transistor TR 25  has an emitter connected to the first movable contact  132  of the UP switch  129  and a collector connected via the diode D 23  to the minus terminal of the relay coil  21 . 
     In the second embodiment, the relay coil  23  constitutes a first relay coil while the relay coil  21  constitutes a second relay coil. The transistor TR 24  constitutes a first switching element; the transistor TR 25  constitutes a second switching element; the transistor TR 26  constitutes a third switching element; and the transistor TR 1  constitutes a fourth switching element. 
     Next, explanation will be given on operation of the power window switch circuit  200 . 
     When the power window switch circuit  200  is not soaked by an electrolyte liquid such as rain and when the DOWN switch  128  and the UP switch  129  are both in the OFF state, no power supply voltage is supplied to the relay coils  21  and  23 . Moreover, since the transistor TR 1  is in the OFF state, the power supply voltage is not supplied to the plus terminals, either. Accordingly, the relay coils  21  and  23  are not excited. Consequently, the drive motor M is not driven and the window glass is not lowered or raised. 
     Next, when the DOWN switch  128  is turned on in this state, a first relay coil excitation signal is supplied via the first movable contact  131  to the control circuit  12 , which in turn turns on the transistors TR 1  and TR 3 , exciting the relay coil  21 . As a result, the drive motor M is rotated in the normal direction to lower the window glass. 
     Next, when the UP switch  129  is turned on, a second relay coil excitation signal is supplied via the first movable contact  132  to the control circuit  12 , which in turn turns on the transistors TR 1  and TR 3 , exciting the relay coil  23 . As a result, the drive motor M is rotated in the reverse direction to raise the window glass. 
     Next, when the power window switch circuit  200  is soaked by an electrolyte liquid such as rain and the DOWN switch  128  and the UP switch  129  are both in the OFF state, the leak detection circuit  15  is turned on and the transistors TR 26  is turned on. In response to this ON operation of the transistor TR 26 , the transistor TR 1  is turned on and the transistors TR 24  and TR 25  are set to a state in which they can be turned on. In response to the ON operation of the transistor TR 1 , the power supply voltage is supplied via the diode D 21  to the plus terminals of the relay coils  21  and  23 . Moreover, in response to the ON operation of the transistor TR 26 , the minus terminals of the relay coils  21  and  23  are connected via the diode D 25  to the ground. This excites the relay coils  21  and  23  and the relay contacts  25  and  26  are simultaneously turned on. Then, the power supply voltage is supplied to both the terminals of the drive motor M and the drive motor does not operate. 
     In response to the ON operation of the transistor TR 26 , the transistors TR 24  and TR 25  are set to a state where they can be turned on. However, since the switches  128  and  129  are off, the power supply voltage is not supplied to the emitters of the transistors TR 24  and TR 25 . As a result, the transistors TR 24  and TR 25  are not turned on and no current flows between the emitter and the collector. 
     Thus, even if leak resistance is generated in the power window switch circuit  200 , the power supply voltage is supplied to the respective plus terminals and the minus terminals are grounded, exciting the relay coils  21  and  23 . Accordingly, the drive motor M does not operate. This prevents unintentional lowering or raising of the window glass. 
     Moreover, the power line (power supply circuit to the control circuit  12 ) of the control circuit  12  is connected via the diode D 24  to the collector of the transistor TR 26 . Accordingly, the power line is set to a ground voltage by the ON operation of the transistor TR 26 . For this reason, when the power window switch circuit  200  is soaked, a predetermined power voltage required for the circuit operation is not supplied to the control circuit. Thus, an output signal from the control circuit  12  prevents malfunction of the drive circuit  220  (such as excitation of the relay coils  21  and  23  by the ON operation of the transistors TR 1  to TR 3 ). 
     Next, in this state, when the DOWN switch  128  is turned on, the power supply voltage is supplied from the plus terminal of the power supply via the fixed contact DN 1  and the first movable contact  131  to the emitter of the transistor TR 24 . Then, the transistor TR 24  is turned on and the power supply voltage is supplied via the diode D 22  to the minus terminal of the relay coil  23 . Both the terminals of the relay coil  23  are set to an identical potential and the relay coil  23  is set to the deexcited state. As a result, only the relay coil  21  is maintained in the excited state and the drive motor M is rotated in the normal direction to lower the window glass. 
     Next, when the UP switch  129  is turned on, the power supply voltage is supplied from the plus terminal of the power supply via the fixed contact UP 1  and the first movable contact  132  to the emitter of the transistor TR 25 . Then, the transistor TR 25  is turned on and the power supply voltage is supplied via the diode D 23  to the minus terminal of the relay coil  21 . Both the terminals of the relay coil  21  are set to an identical potential and the relay coil  21  is set to the deexcited state. As a result, only the relay coil  23  is maintained in the excited state and the drive motor M is rotated in the reverse direction to raise the window glass. 
     The power window switch circuit  200  of the second embodiment has advantages as follows. 
     (1) Even if the power window switch circuit  200  is soaked, it is possible to certainly lower or raise the window glass according to the ON operation of the DOWN switch  128  or the UP switch  129 . 
     (2) When the power window switch circuit  200  is soaked and the DOWN switch  128  or the UP switch  129  is in the OFF state, unintentional lowering or raising of the window glass can be prevented. 
     (3) When the power window switch circuit  200  is soaked and the leak detection circuit  15  and the transistor TR 26  are turned on, the power line of the control circuit  12  is grounded. Thus, it is possible to prevent output of a signal causing malfunction from the control circuit  12  to the drive circuit  220 . 
     (4) If the DOWN switch  128  is turned on when the power window switch circuit  200  is soaked, electric current flows between the emitter and the collector of the transistor TR 24  and excitation current is not supplied to the relay coil  23 . Thus, only the relay coil  21  is excited to lower the window glass. That is, even if the power window switch circuit  200  is soaked, it is possible to assure lowering of the window glass. 
     (5) If the UP switch  129  is turned on when the power window switch circuit  200  is soaked, electric current flows between the emitter and the collector of the transistor TR 25  and excitation current is not supplied to the relay coil  21 . Thus, only the relay coil  23  is excited to raise the window glass. That is, even if the power window switch circuit  200  is soaked, it is possible to assure accurate rising of the window glass. 
     (6) When the DOWN switch  128  or the UP switch  129  is turned on, the first movable contact  131  or  132  is connected to the first fixed contact DN 1  or UP 1  after the second movable contact  133  or  134  is disconnected from the second fixed contact DN 2  or UP 2 . Thus, it is possible to prevent short-circuit between the plus terminal of the power supply and the anode terminal of the diode D 25 . 
     It should be noted that the second embodiment may be modified as follows. 
     The transistors TR 1 , TR 24 , and TR 25  used in the second embodiment are PNP transistors, but it is also possible to use NPN transistors. In this case, the transistor TR 1  has a collector connected to the plus terminal of the power supply and an emitter connected to the anode of the diode D 21 . The transistor TR 24  has a collector connected to the first movable contact  131  of the DOWN switch  128  and an emitter connected to the anode of the diode D 22 . Furthermore, the transistor TR 25  has a collector connected to the first movable contact  132  of the UP switch  129  and an emitter connected to the anode of the diode  23 . 
     The transistors TR 2 , TR 3 , and TR 26  which are NPN transistors in this embodiment may be replaced by PNP transistors. In this case, the transistor TR 2  has an emitter connected to the minus terminal of the relay coil  23  and a collector grounded. The transistor TR 3  has an emitter connected to the minus terminal of the relay coil  21  and a collector grounded. Furthermore, the transistor TR 26  has an emitter connected to the cathode of the diodes D 24  to D 28  and a collector grounded. 
     In the second embodiment, the transistors TR 24  and TR 25  were used, which may be replaced by a transistor array having two transistor elements. In this case, it is possible to reduce the size of the power window apparatus.