Abstract: An opening and closing member control apparatus includes: an open-command receiving portion for receiving a first open command of a first open and close command inputting member and a second open command of a second open and close command inputting member, which performs a second open command input and a second close command input by a unique operation thereof, a close-command receiving portion for receiving a first close command of the first open and close command inputting member and a second close command of the second open and close command inputting member, and a controlling portion for performing an opening operation and a closing operation of an opening and closing member based on a condition of the opening and closing member, in response to the unique operation of the second open and close command inputting member.

Abstract: A motorized barrier operator that moves a barrier between limit positions, includes a motor for moving the barrier between set limit positions. When the barrier is in a stopped, partially open position the operator implements at least a hybrid control sequence that employs either a four-phase logic or an open-only logic depending upon the status of a mode indicator. In the preferred embodiment the mode indicator is a time light that is activated upon receipt of a user command.

Abstract: Latch control methods and systems are disclosed, including a latch that receives power from a motor associated with a latch. A sensor can be provided for monitoring the current consumption of the motor. A microcontroller can control the latch and/or the motor, based on the current consumption data received from the sensor concerning the current consumption of the motor. Monitoring of the current waveform of the motor therefore provides speed and direction feedback data for control of the latch. Additionally, a microprocessor can process instructions for controlling the interaction of the motor, the latch, the sensor and/or the microcontroller. Such a current monitoring control system is made possible by variation in current consumption of the motor during rotation as a result of commutation, which can be interrogated by measuring the voltage drop across the motor or a shunt resistor, or through the use of other current sensors, such as, for example, a Hall-effect type current sensor.

Abstract: A power closure system with anti-pinch having a closure, a motor operatively connected to the closure, a sensor operatively producing signals indicative of motor speed, an anti-pinch activator coupled to the sensor and the motor, the anti-pinch activator including a predetermined trigger value; a measured value; a stored value; a comparator for comparing the measured value with the stored value and initiating a pinch response when the difference between the measured value and the stored value is greater than the trigger value; and a predetermined modifying calculation for changing the stored value when the measured value indicates a motor speed less than the motor speed indicated by the stored value.

Abstract: A garage door drive includes a housing and at least one light unit. According to the invention, at least one mounting point for the mechanical and electrical connection of the attachably and detachably constructed at least one light unit is arranged on the housing.

Abstract: The invention relates to a method of managing the operation of a seat (10) fitted with an actuator (24) including means (42, 44) for monitoring at least one variable characteristic of the force produced by the actuator (24), means (41) for measuring the position of the actuator, and means (36) for controlling the actuator, the method comprising the steps consisting in: measuring the or each characteristic variable; evaluating the or each characteristic variable on the basis of a predetermined evaluation criterion; and while the actuator is in operation, implementing an appropriate action on the seat as a function of the result of said evaluation. Said evaluation comprises a step of measuring the position of the actuator. Said evaluation criterion for the or each measured characteristic variable as used for said evaluation depends on the position of the actuator.

Abstract: A motor and a rotary potentiometer, or other position sensor, running on the motor shaft are mounted in a first enclosure with an output shaft for driving a power switch open or closed. A part of the system outside the first enclosure makes use of a motor position signal from the rotary potentiometer that is processed by a microcontroller that a worker can interact with at a switch panel to set and adjust motor travel limits without needing access into the motor enclosure. The first enclosure and its components can be used for various applications, including those for either underground or pad-mounted switches, which for the latter case can have the first enclosure inside a second enclosure on a pad, and the second enclosure also contains other power and control elements of the system. A portable unit with the switch panel for travel limits can be provided.

Abstract: A force reversal value for an installed barrier is identified. The force reversal value is compared to a predetermined threshold. When the comparing indicates that the force reversal value exceeds the predetermined threshold, the operation of the moveable barrier operator is halted. A secondary safety device can then be installed and, responsive to the installing, the operator can be reenabled.

Abstract: A control for an electric motor in a vehicle. The control ascertains whether an obstacle is interfering with rotation of the motor. The control establishes a baseline speed, representing normal free running speed of the motor. This baseline speed will be different, in different operating environments. Then the control determines whether measured motor speed drops below the baseline speed by a predetermined amount. If so, then the motor is shut down, or reversed.

Abstract: A drive controller (10?) of the present invention comprises control means (28, 29, 32 to 38) configured to perform control to cause a driven element to move by a driver (M) and a collision detecting means (20?) configured to detect a collision of the driven element. The collision detecting means detects the collision of the driven element based on an estimated speed deviation which is an estimated deviation from an actual speed of the driven element or an estimated acceleration deviation which is an estimated deviation from an actual acceleration of the driven element.

Abstract: An MCU determines whether a backlash over a predetermined value exists in a driving system including a motor and a window driving mechanism. Then, when it is determined that the backlash over the predetermined value exists in the driving system, the MCU sets the time passed from the detection of the peak of the number of rotations of the motor to a predetermined additional time as a termination time of a start cancellation period. When it is determined that the backlash over the predetermined value does not exist in the driving system, the MCU sets, as the termination time of the start cancellation period, the time when the rate of change of the number of revolutions of the motor reaches a predetermined value or the time when the rate of change of a motor input ratio reaches a predetermined value.

Abstract: An electrical system for controlling at least one gate or door or similar element of the type moved by means of at least one corresponding electric motor includes an electric network (NTWRK) consisting of two electric wires adapted to allow the distribution of direct-current power supply and digital information, a central control unit (UC) having two terminals (T1,T2) adapted to be connected respectively but indifferently to the two wires of the network (NTWRK) in order to transmit direct-current power supply and to transmit and receive digital information, a certain number of peripheral units (UP), each having two terminals (T1,T2) adapted to be connected respectively but indifferently to the two wires of the network (NTWRK) in order to receive direct-current power supply and to receive and/or transmit digital information.

Abstract: A method for determining the frequency of current ripples contained in the armature current signal of a commutated direct current (DC) motor includes determining frequency spectral results of the current signal and of a motor electric operating parameter. The frequency spectral results are subtracted from one another to determine the frequency spectral result of the current ripples contained in the current signal. The current ripple frequency is determined from the frequency spectral result of the current ripples contained in the current signal. The operating parameter may be the armature voltage signal, or the armature current signal at a different motor operating state than the motor operating state of the current signal used in the step of determining the current signal frequency spectral result. The rotational speed of a motor shaft is determined based on the current ripple frequency. The shaft rotational position is determined based on the rotational shaft speed.

Abstract: An operator and related method for adjusting an internal force setting for a motorized garage door operator is disclosed. The operator checks for the presence of a secondary entrapment safety feature and automatically increases a force threshold setting from a first value to a second value if the secondary entrapment safety feature is detected. If the safety feature is not detected or it is later disconnected, then the operator automatically sets the force threshold to a more sensitive value.

Abstract: A window lifter system and method coordinates closing of multiple windows by detecting when more than one window pane is approaching a fully closed position and moving one window pane to only an approximately closed position while the other window pane is moved to the fully closed position. By staggering the closure of window panes to the fully closed positions, the system and method provides the illusion that all of the window panes are being closed at the same time while avoiding voltage drops in the vehicle power supply caused by excessively high blocking currents generated when multiple window panes are moved to the fully closed position.

Abstract: An automotive power pivot door is powered by an electric motor through an electromagnetic clutch. A control device of the door has a control unit configured to carry out a routine which comprises de-energizing an electric motor and disengaging the clutch when the door is lifted up to a full-open position; detecting a moved distance by which the door moves down from the full-open position within a first predetermined time (t1) from the time on which the clutch is disengaged; engaging the clutch when the detected moved distance is equal to or greater than a first predetermined distance (L1); disengaging the clutch again when a second predetermined time (t2) passes from the time on which the clutch is engaged; repeating the process for engaging and disengaging the clutch while following the routine; and judging that the holder fails to operate when the frequency of the engaged condition of the clutch indicates a predetermined frequency.

Abstract: In an automotive power window system, a controller detects positions of a window glass that moves through driving operation of a motor during the closing operation of a window. The controller reduces a rotation speed of the motor when the window glass reaches a speed altering position. It calculates the amount of reduction in the rotation speed produced by the rotation speed reducing operation. Then, it corrects a rotation speed obtained during the closing operation by compensating for the amount of reduction. It determines whether an obstruction for the closing operation is present based on the corrected rotation speed. If the obstruction is detected, it controls the motor for releasing the obstruction.

Abstract: A method and system for controlling vehicle door position having reduced power supply current requirements reduces the cost and weight of a vehicle and further reduces power consumption. The vehicle door control system includes an inverter for converting a DC power source to an AC voltage for driving the motor. The inverter is preceded by a boost converter that maintains a constant voltage at the inverter input, and a capacitor is provided between the converter and inverter for energy storage. Kinetic energy is returned from the door and mechanical portions of the motor through the inverter and stored on the capacitor, reducing the power required from the power source. Operation of the inverter and converter are controlled by timers and detection mechanisms that cease operation of the inverter and converter when the door is held in a fully closed or open position for a predetermined interval.

Abstract: A method for controlling a vehicle power seat motor including the steps of generating at least one control signal using a controller, and adjusting the speed of the motor in response to the at least one control signal such that speed of the motor is maintained to a predetermined curve. Maintaining the speed of the motor to the predetermined curve reduces at least one of mechanical wear, erratic motion, and noise of a respective seat mechanism.

Abstract: As a vertical motion motor (M2) comprised of a brushless motor is driven to rotate in response to a control signal from a main controller (10), a pulse signal generated with the shape corresponding to the number of rotations of the vertical motion motor (M2) is counted by a pulse signal count unit of the main controller (10). Feedback control is exercised over the number of rotations of the vertical motion motor (M2) in accordance with a count value (the number of counts) of the pulse signal, so that mirror surface orientation of a door mirror (2) can be accurately adjusted to tilt downward to a predetermined set angle, and to tilt upward back to a home position angle. A mirror angle control apparatus (1) is provided with high durability and reliability, which can exercise accurate control for a long period of time.

Abstract: An anti-pitch assembly is used in combination with a closure device of a motor vehicle. The closure device includes a closure panel, i.e., a windowpane or door, and a motor for moving the closure panel between an open position and a closed position. In the closed position, the closure panel covers an aperture, i.e., a window or door opening, of the motor vehicle. The anti-pinch assembly includes a position sensor that is disposed adjacent the motor or the closure device. The position sensor generates a position signal indicative of the position of the closure panel. A capacitive sensor measures the capacitance of a field extending through the aperture. The capacitive sensor generates a signal therefrom. A controller is electrically connected to the position and capacitive sensors.

Abstract: A control unit for a moveable barrier, such as a garage door, includes a microcontroller connected to a motor speed detector, motor current sensor or a sensor for determining forces exerted on or by the barrier. A user interface includes user actuatable switches for setting a first maximum force value to be exerted on or by the barrier when moving in one direction and the microcontroller automatically sets the value of a second maximum force to be exerted on or by the barrier when moving in the opposite direction. The second force value may be based on the force value set by the user or the second force value may be a preset value. Both force limits may be automatically set as a function of a maximum force exerted on said barrier during movement thereof, during a force learning operation.

Abstract: A control apparatus for a roof glass specifies the selection position of the selection switch when an output voltage from the selection switch is determined to be included in any of the allowable ranges predetermined respectively for the selection positions of the selection switch. The selection position of the selection switch is settled when the specified selection position has not changed even when a predetermined time passes after specifying of the selection position of the selection switch. When those selection positions which have been settled at a time of making the current decision and at a time of making a previous decision satisfy predetermined conditions, the roof glass is allowed to operate to a position corresponding to the selection position of the selection switch settled at a time of making a current decision.

Abstract: The present invention is to provide a power regulated window having a window glass to be closed intentionally when some foreign body is pinched by the window glass for security reasons. When a close signal is output to a semiconductor switching element from window regulator switches, the window glass is closed. When some foreign body such as arm or fingers is pinched by the window glass, a load current of a motor becomes abnormal and the motor rotates reversely to open the window glass in order not to damage the foreign body. Besides this protective function, when the foreign body is pinched by the window glass and a prohibit signal to invalidate the reverse rotation is output, a reversing controller is stopped and the window glass is closed continuously by a bypass switching element.

Abstract: A movable barrier operator having a motor controller (10) and motor (11) that control selective movement of a movable barrier (12) also has an obstacle detector (14) that utilizes an automatically determined excess force threshold value to permit reliable detection of an obstacle under a wide variety of operational circumstances, including changing physical circumstances, aging components, temperature variations, and motor runtime. In a preferred embodiment, a characteristic force value for the system is frequently updated as a function of actual measured force requirements (and further compensated, pursuant to various embodiments, with respect to other conditions such as temperature and motor runtime). This characteristic force value is then utilized to determine the excess force threshold value.

Abstract: A method for controlling a wiper motor of a wiper device for a motor vehicle windshield. A control unit implements the inventive method and a wiper device for a motor vehicle windshield. The control unit controls an electric motor which powers a wiper blade on a windshield sweeping between two end-of-travel zones. In each end-of-travel zone, there is a software end-of-travel stop which is moved by a predetermined value after each passage on the software stop, the latter always remaining in its test zone, thereby providing self-adaptation of the sweeping limits in time. The invention also enables the detection of the presence of obstacles on the wiper blade path.

Abstract: A drive apparatus for an opening/closing body for a vehicle includes a drive unit including a rotational drive apparatus, a reduction gear mechanism linked with a rotational shaft of the rotational drive apparatus, and an output member linked with the rotational shaft through the reduction gear mechanism and linked with the opening/closing body through a connection member, a first pulse signal generator provided at the drive unit and generating a first pulse signal on the basis of a rotation of the rotational shaft, a second pulse signal generator provided at the drive unit and generating a second pulse signal on the basis of a rotation of either one of the reduction gear mechanism and the output member, and a control means for calculating an opening/closing position of the opening/closing body on the basis of the first pulse signal emitted by the first pulse signal generator utilizing the second pulse signal emitted by the second pulse signal generator as a base point and controlling the rotational drive app

Abstract: A device for sensing an obstacle in said opening range of an automotive closure element movable between an open position and and closed position, more particularly an electrically powered door window (20) or sunroof is provided with a weatherseal (30) sealing the window pane (20). The weatherseal (30) is made of an elastomeric material and secured to a frame (12) of the motor vehicle (10). The device comprises in addition a sensor for sensing an obstacle in the opening range of the closure element (20), the sensor comprising at least one electrical conductor (40) generating an electrical field (F) in the opening range of the closure element (20). The device achieves by simple ways and means an engineered orientation of the electrical field such that any interference by the closure element (20) to the capacitive change in the electrical field (F) is precluded by reason of conductive means (50) comprising a conductive surface (51) made of an electrically conductive material.

Abstract: The detection of a pulse signal in an initialization pattern is ensured regardless of the position where a DC motor is stopped. A CPU detects the pulse signal generated by the pulse generator and an angle of rotation of a rotating shaft, and controls an angle of rotation of a rotating shaft based on the detected angle of rotation. The pulse generator generates the pulse signal in the initialization pattern, which indicates the position of origin of the angle of rotation, in accordance with the rotation of the DC motor. If a determination means determines that it is impossible to detect the pulse signal in the initialization pattern when the DC motor is rotated in a first direction, the CPU rotates the DC motor in a second direction.

Abstract: A power window driving apparatus includes a reference current generator generating a reference current. The reference current generator includes a first current generator generating a first current, a first comparison signal, and a second comparison signal, a reference voltage generator generating a reference voltage signal, and a second current generator generating a second current. The power window driving apparatus includes a comparator which includes the first comparison signal with the reference voltage signal, a driving controller which stops or reverses the driving motor when a drastic increase is occur in the motor current based on a result of a comparison by the comparator, and a current increaser which increases an amount of the second current when the motor current is drastically decreased from a steady state, so that an increase in the first current is suppressed when the motor current is shifted from the drastically decrease to an increase.

Abstract: The present invention comprises a clutch assembly having a housing, rotational arm and torque spring, in combination with a position sensor, such that excessive movement or obstruction within the path of the display assembly during deployment, as predefined by the system designer, results in stowage of a deployed on-board entertainment system display assembly.

Abstract: A method for adjusting a plurality of vehicle cockpit devices via a two-part process that utilizes device position constraints to determine candidate arrangements and then, ultimately, recommended arrangements of the vehicle cockpit devices to determine a desired setting of the various devices. The position constraints are determined using positioning data obtained from an occupant. An exploratory search routine is used to determine the candidate arrangements with the cockpit devices being moved to each candidate arrangement so that the occupant can be queried concerning the desirability of each such arrangement. The occupant's responses are then stored for later retrieval. Thereafter, a plurality of recommended arrangements of the cockpit devices are determined using a meta-heuristic pattern search along with a neural network search accelerator that permits screening of each recommended arrangement.

Abstract: A control unit stores a count value, which is used to detect an operational position of a roof glass, in a RAM. The control unit determines whether the count value is properly stored in the RAM when a voltage of a power supply falls below a predetermined voltage and thereafter returns to the predetermined voltage. Even in a case where the control unit determines that the count value is properly stored in the RAM, the control unit determines there is a possibility of having a deviation between an actual operational position of the roof glass and the count value. Thereafter, the control unit resets a reference point of the roof glass.

Abstract: A control device and method of used includes receiving a signal from a first sensor and receiving a signal from a second sensor after receiving the signal from the first sensor. In response to the received signals, the electronic device executes the function.

Abstract: Embodiments of the present invention provide methods and apparatus for controlling seats and for monitoring behavior of power-actuated seats. Certain embodiments permit seat occupancy data, e.g., whether the seat is occupied or a weight-dependent characteristic of the occupant of the seat, to be collected by moving a part of the seat with an actuator. This seat occupancy data may then be used to control other aspects of the seat operation, e.g., set an operational limit of the actuator or reduce auxiliary power to other systems associated with the seat if the seat is unoccupied. For example, part of the seat may be moved with a first actuator, including detecting a control parameter at which the part of the seat begins moving. This control parameter may be correlated to an actuator limit.

Abstract: An electric drive motor drives a door to move in an open/close direction. A pulse encoder outputs a series of pulses. Each pulse has a pulse duration sized to correspond to a rotation speed of the motor. The number of the pulses corresponds to the number of revolution of the motor. A door jamming detecting device for detecting a jamming of the door is configured to carry out calculating a total duration time (Tn) of a given number (n) of the series pulses outputted from the pulse encoder; detecting a given condition wherein the total duration time (Tn) is greater than a threshold value (Ts); and making a judgment of the door jamming when the given condition is kept for a given time (Tm).

Abstract: This invention discloses an electronic control system for an Industrial Motor Operator that uses standard steady state logic to improve reliability in rough service wet and dirty environments. It includes means of providing electronic snow limit to close limit sensing removing the need for two switches and radically improving its accuracy. A low voltage switch reverses the high voltage motor wires and at the same time reverses the open limit, close limit, and snow limit sensors mechanical positions. It discloses a system using lamps to indicate that the power wiring is connecting to three-phase motors in the correct sequence or that single-phase motors have their windings correctly phased.

Abstract: A movable barrier operator can use (11) a first technique to prevent an excess application of force during controlled movement of a movable barrier (43) and at least a second technique (12) to similarly prevent an excess application of force during such movement. Both techniques can then be utilized to determine (13) when an application of excess force may nevertheless occur and not be reasonably avoided. In one embodiment, two techniques (21 and 22) can be used to detect force as applied during movement of the movable barrier and such information can be used to determine (23) whether applied force is being reliably indicated. In another embodiment, travel limit information (51), travel information (52) and travel history information (53) are utilized to assess whether normal operation of the movable barrier operator should be over-ridden (54) due to a possibly expression of undue force.

Abstract: A motor vehicle door lock with an electromechanical central locking system drive (1) and a mechanical central locking system element (2) driven by it, the central locking system drive (1) having an electric drive motor (3) and a motor control (5) with a motor state sensor (6). The central locking system element (2) can be moved by the central locking system drive (1) at least into a locked position and the motor control (5) is designed such that it triggers the electric drive motor (3) for driving the central locking system element (2) into the locked position after receiving an actuation signal from an actuation unit, such as a closing cylinder, a locking button, a remote control receiving unit or a handle (inside door handle, outside door handle).

Abstract: A device for sensing an obstacle in the opening range of a movable closure element of a motor vehicle, more particularly an electrically powered window pane or sunroof is defined. The device is provided with at least one sensor electrode generating an electrical field in the opening range of the closure element. It is furthermore provided with a control unit for detecting a change in the capacitance of the electrical field caused by the presence of an obstacle in the opening range of the closure element, the control unit providing a control signal for a drive powering the closure element. The sensor electrode is connected to the control unit either directly or via a shielded conductor. The control unit is arranged on an electronic controller of the drive and compensates the influence of the shielded conductor on the electrical field.

Abstract: A control for an electric motor in a vehicle. The control ascertains whether an obstacle is interfering with rotation of the motor. The control establishes a baseline speed, representing normal free running speed of the motor. This baseline speed will be different, in different operating environments. Then the control determines whether measured motor speed drops below the baseline speed by a predetermined amount. If so, then the motor is shut down, or reversed.

Abstract: A door actuation system conducts or assists movement of sliding vehicle doors by connecting the door to a bi-directional motor via one or more helical cables that engage with gearing on the bi-directional motor. Rotation of the motor in either direction pushes or pulls the helical cables, causing the door to move toward the open or closed position. The motor can be stopped when the door reaches selected positions other than the open or closed position, holding the door in a partially open position.

Abstract: In the driving operation of a sensorless three-phase motor to be used in a rotation at a comparatively low speed (approximately 2000 RPM or less) and to be bipolar driven, the number of rotations and a rotating position are accurately detected from an induced voltage and a reverse rotation brake is applied in an accurate phase, and furthermore, a short brake is applied at a set rotation number signal or less also in braking. Consequently, it is possible to prevent phase switching from being carried out in an erroneous timing and to prevent a rotation in a reverse direction by an inertia.

Abstract: A power window apparatus that inhibits leakage current when submerged in water. The power window apparatus includes an operation switch. A microcomputer controls a motor. A connector has a down terminal and an up terminal connecting the operation switch and the microcomputer, and a ground terminal used to connect the operation switch and the ground. When operated, the operation switch connects the down terminal or the up terminal to the ground terminal and generates a low-level input signal in the down terminal or in the up terminal. The microcomputer drives the motor in response to the low-level input signal. An inhibition mechanism arranged in the connector inhibits, when water enters into the connector, a leakage current from flowing between a connecting terminal and a ground terminal.

Abstract: A field effect transistor is provided between the ground and an H bridge circuit for rotating a motor in forward and reverse directions in a manner that the drain of the transistor is grounded and the gate thereof is coupled to a DC power source such as a battery serving as a bias source which supplies electric power to the H bridge circuit. Thus, when the DC power source such as a battery is reversely connected, the field effect transistor normally in an on state is turned off. A controller monitors the source voltage of the field effect transistor, and when the controller detects an excess current, the controller outputs a control signal to the high-side driver to prevent the supply of electric power to the motor.

Abstract: A controller PWM control an opening and closing motor (16) of an opening and closing means, increases a duty ratio of the PWM control according to a given increasing rate just after starting the opening and closing motor (16), reducing the duty ratio to a given value by detecting a start of the open close body, and keeping the given value of the duty ratio for a given period.

Abstract: An apparatus and method positions a powered examination chair at a constant, desired speed. The desired speed is achieved irrespective of patient weight and/or direction of chair travel. A power signal supplied to an actuating motor is apportioned according to a load incident on the chair. The determined load accounts for patient weight, as well as to gravitational and mechanical forces.

Abstract: A detector, that prevents erroneous detection of a foreign object caught in a window glass when the engine of a vehicle is being operated and when the engine is stopped using a relatively simple control method. The detector includes a pulse sensor for detecting rotational speed of a motor. A microcomputer calculates a cycle difference sum based on the rotational speed of the motor. The microcomputer compares the cycle difference sum with a obstruction determination threshold to determine whether a foreign object has been caught. The microcomputer detects whether the engine is stopped. When detecting that the engine is stopped, the microcomputer changes the obstruction determination threshold so that the probability of the microcomputer determining that a foreign object has been caught is lower than that when the engine is being operated.

Abstract: An antipinch circuit prevents the motor driven closure of an automotive window if a soft obstacle is compressed between the window and the top of the door frame, and the window is opened in response to the sensing of the obstacle. The circuit measures the motor torque (by measuring motor current) and the motor shaft speed (by measuring motor back EMF). The torque and motor speed are compared to “signatures” of these values in the case of the window closing normally against the top of the door frame, or against an obstacle, and either stopping or reversing the motor rotation accordingly.

Abstract: In an electric motor-driven power steering apparatus which comprises a bridge circuit for connecting a power source between input terminals and also connecting an electric motor between output terminals and energizes the electric motor by this bridge circuit and operates electric motor power to a steering system, the bridge circuit includes a predetermined number of arms constructed by connecting circuits for connecting switching elements in parallel with diodes in series so that the diodes mutually become reverse polarity.