Patent Publication Number: US-10312843-B2

Title: System including light emitting semiconductors for dissipating power

Description:
FIELD 
     The disclosed system and method relates to a system for dissipating power and, more particularly, to a circuit for dissipating power that includes a semiconductor that emits light. 
     BACKGROUND 
     There are two main types of linear actuators, namely fluid power actuators that operate on differential pressure and electromechanical actuators driven by an electric motor. Electromechanical actuators may be back-driven or self-locking. If an electromechanical actuator is self-locking, then the actuator may not be back-driven by exerting a force on the output. Many aerospace vehicles employ back-driven actuators. The actuators are typically back-driven when a stream of air exerts a force that causes a spoiler that is presently deployed to retract. 
     The electrical power created by back-driving is conventionally dissipated by elements such as resistors and diodes. In one example, a direct current (DC) motor is back-driven by an H-bridge circuit. An H-bridge circuit is a type of electronic circuit that enables a voltage to be applied across the DC motor in either direction. In the example as described, diodes are used to dissipate the electrical power and to protect other electrical components included in the H-bridge circuit. Specifically, the H-bridge circuit includes transistors that switch rapidly based on a pulse-width modulation (PWM) scheme. The PWM scheme controls either speed or torque of the DC motor. When the transistors are switched off and the supply current to the DC motor is suddenly interrupted, a voltage spike is created since the DC motor is an inductive load. The voltage spike may be referred to as flyback, and the diodes in the H-bridge are used to protect the transistors from the flyback created by the pulsing of the DC motor. The diodes generate heat when dissipating electrical power. Furthermore, the heat created by the diodes rises in response to the pulse rate of the PWM scheme increasing. Moreover, the heat created by the diodes needs to be disposed. 
     It may be challenging to dispose of the heat generated by the diodes. In fact, heat generation in aerospace application is especially problematic because the components of the vehicle are required to operate within specific temperature ranges during all mission phases. The challenges faced with heat dissipation in an aerospace vehicle may be further compounded since aerospace vehicles also encounter relatively high aerodynamic forces during operation. This results in more work that needs to be performed by an actuator in order to move a surface. Moreover, the actuators are also usually required to operate at very high rates such as, for example, over 100,000 Hertz. Finally, since aerospace vehicles travel at high speeds through space, the air surrounding the space vehicle is already at an elevated temperature. Thus, it may not be possible to release most of the heat generated by the diodes. 
     SUMMARY 
     The disclosed system provides an approach for dissipating power by a semiconductor that emits light in response to an inductive load generating a voltage spike that causes a voltage drop across the semiconductor to be at least equal to a forward voltage. The light emitting semiconductor generates less heat when compared to other devices such as resistors or diodes. 
     In one example, a circuit is disclosed. The circuit includes an inductive load, at least one electrical component in communication with the inductive load, and a semiconductor. The semiconductor is configured to emit light in response to a voltage drop across the semiconductor being at least equal to a forward voltage. The semiconductor is placed in parallel with the electrical component and emits the light in response to the inductive load generating a voltage spike during operation that causes the voltage drop across the semiconductor to be at least equal to the forward voltage. 
     In another example, a circuit is disclosed. The circuit includes an inductive load and a flyback semiconductor in parallel with the inductive load. The flyback semiconductor is configured to emit light in response to a voltage drop across the flyback semiconductor being at least equal to a forward voltage. The flyback semiconductor emits the light in response to the inductive load generating a voltage spike during operation that causes the voltage drop across the flyback semiconductor to be at least equal to the forward voltage. 
     In yet another example, a method for dissipating power is disclosed. The method includes driving an inductive load of a circuit, wherein the circuit includes at least one electrical component in communication with the inductive load. The method also includes generating a voltage spike during operation of the inductive load that causes a voltage drop across a semiconductor to be at least equal to a forward voltage. The semiconductor is placed in parallel with the at least one electrical component. Finally, the method includes emitting light by the semiconductor in response to the voltage drop across the semiconductor being at least equal to the forward voltage. 
     Other objects and advantages of the disclosed method and system will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exemplary schematic diagram of the disclosed circuit for an actuator, where the disclosed circuit is an H-bridge that includes a plurality of light emitting diodes (LEDs) for protecting the transistors; and 
         FIG. 2  is an exemplary schematic diagram of the inductive load as either a relay or a solenoid valve. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is an exemplary schematic block diagram of an actuator  10  including the disclosed circuit  20  for powering an inductive load  12 . In the exemplary embodiment as shown, the inductive load  12  is a back-driven direct current (DC) motor  12 , and the circuit  20  is an H-bridge circuit  20 . As explained in greater detail below, the H-bridge circuit  20  includes at least one electrical component in communication with the DC motor  12 . The at least one electrical component is a plurality of transistors Q 1 -Q 4 . The H-bridge circuit  20  also includes a semiconductor configured to emit light in response to a voltage drop across the semiconductor being at least equal to a forward voltage. In the embodiment as shown, the semiconductor is a light emitting diode (LED), and is illustrated as a plurality of LEDs D 1 -D 4 . 
     The LEDs D 1 -D 4  are each placed in parallel with a corresponding one of the transistors Q 1 -Q 4 . Specifically, LED D 1  is in parallel with transistor Q 1 , LED D 2  is in parallel with transistor Q 2 , LED D 3  is in parallel with transistor Q 3 , and LED D 4  is in parallel with transistor Q 4 . The LEDs D 1 -D 4  are configured to emit light in response to the DC motor  12  generating a voltage spike during operation. The voltage spike causes the voltage drop across each LED D 1 -D 4  to be at least equal to the forward voltage. The H-bridge circuit  20  also includes a first pushbutton PB 1 , a second pushbutton PB 2 , a resistor R 1 , a resistor R 2 , a resistor R 3 , a resistor R 4 , a resistor R 5 , and a resistor R 6 . 
     As explained below, the LEDs D 1 -D 4  are used as flyback diodes or snubber diodes to protect the transistors Q 1 -Q 4  from excess voltage or voltage spikes that sometimes occur during operation of the DC motor  12 . Specifically, the LEDs D 1 -D 4  dissipate a portion of the excess voltage by emitting light, while the remaining power is dissipated as heat. Although LEDs are illustrated, the circuit  20  is not limited to the embodiment as shown in  FIG. 1 . Instead, in another embodiment the circuit  20  includes any semiconductor configured to emit light when forward-biased such as laser diodes or photocells. In particular, in one embodiment the circuit  20  includes single-junction photocells for dissipating a portion of the excess voltage by emitting light. 
     The transistors Q 1 -Q 4  control a polarity of a supply current to the DC motor  12 . In the example as shown in  FIG. 1 , the transistors Q 1 -Q 4  are illustrated as bipolar junction transistors (BJTs), however other types of transistors may be used as well such as, for example, metal-oxide-semiconductor field-effect transistors (MOSFETs). Each transistor Q 1 -Q 4  includes a base B, an emitter E, and a collector C. The resistors R 1 -R 4  are each provided to limit the current that enters the base B of a corresponding one of the transistors Q 1 -Q 4 . Specifically, the resistor R 1  corresponds to transistor Q 1 , the resistor R 2  corresponds to transistor Q 2 , the resistor R 3  corresponds to transistor Q 3 , and the resistor R 4  corresponds to transistor R 4 . The resistor R 5  is a pull-down resistor connected between ground GND and the pushbutton PB 1 . The resistor R 6  is a pull-down resistor connected between the ground GND and the pushbutton PB 2 . 
     In one embodiment, when transistors Q 1  and Q 4  are activated or closed and the transistors Q 2  and Q 3  are opened, then a rotor (not shown) of the DC motor  12  turns in a clockwise direction. Current flows from left to right in the DC motor  12 , or in other words, positive voltage across terminals  30 ,  32 . When transistors Q 2  and Q 3  are activated and the transistors Q 1  and Q 4  are opened, then the rotor of the DC motor  12  turns in a counterclockwise direction and current flows from right to left in the DC motor  12 . If the terminals  30 ,  32  of the DC motor  12  are open, then the DC motor  12  freewheels. If the terminals  30 ,  32  are short circuited, then the DC motor  12  brakes. 
     The LEDs D 1 -D 4  are used to substantially eliminate flyback, which is the sudden voltage spike seen across an inductive load such as the DC motor  12  when a supply current (not illustrated) is suddenly reduced or interrupted. The LEDs D 1 -D 4  also protect against an overdriven or back-driven condition of the DC motor  12 . In one embodiment, a torque or speed of the DC motor  12  is controlled based on pulse-width modulation (PWM), which causes the transistors Q 1 -Q 4  to switch rapidly. 
     An over-driven motor condition occurs when an external torque is exerted upon a shaft of a motor. The external torque causes the motor to increase in speed, thereby increasing the electromotive force (EMF) across the terminals of the motor. The EMF increases and eventually becomes greater than a supply voltage, which reverse-biases the transistors included in the drive circuit of the motor. However, as explained below, the LED D 1  becomes conductive once a voltage drop across the LED D 1  is at a forward voltage, which diverts the current away from the emitter E of the transistor Q 1 . Similarly, the LED D 4  also begins to conduct once the voltage drop across the LED D 4  is at the forward voltage. Therefore, the LED D 4  also diverts current away from the emitter E of the transistor Q 4 . 
     Continuing to refer to  FIG. 1 , once the pushbutton PB 1  is depressed the transistor Q 1  turns on and voltage on a positive side  30  of the DC motor  12  goes high. The DC motor  12  turns clockwise, and increases in speed. As the speed of the DC motor  12  increases, the voltage at the negative side  34  of the DC motor rises until the current to the DC motor  12  is about zero. Then, the external torque is exerted upon the motor shaft, causing the DC motor  12  to increase even more in speed. 
     In response to the voltage at the positive terminal  30  of the DC motor  12  increasing to a value greater than the supply voltage and the forward bias voltage of the LED D 1 , the LED D 1  begins to conduct and current flows through the LED D 1 . The current then flows through the pushbutton PB 1  and the resistor R 5 . Similarly, the LED D 4  also begins to conduct current as well, since the voltage at the terminal  32  of the DC motor  12  is lower than the voltage at ground. Both the LEDs D 1  and D 4  conduct current and release energy in the form of photons, therefore creating light. Thus, a portion of the LEDs (D 1  and D 4 ) are activated in response to an overdriven condition of the DC motor  12  to divert current away from the transistors (Q 1  and Q 4 ) that correspond to the activated LEDs. 
     A back-driven motor condition occurs when an external torque is exerted upon a shaft of a motor in a direction that is opposite to the rotation of the shaft. The external torque causes the EMF to decrease and become negative in value. The faster the motor spins in the opposite direction, the more current is drawn which may damage the transistors. However, if the voltage at the terminal  30  of the DC motor  12  becomes lower than ground, minus the forward voltage of the LED D 3 , then the LED D 3  begins to conduct, which diverts the current away from the emitter E of the transistor Q 3 . Similarly, the LED D 2  also begins to conduct because the voltage at the terminal  32  of the DC motor  12  rises above the supply voltage. Therefore, the LED D 2  also diverts current away from the emitter E of the transistor Q 2 . Thus, a portion of the LEDs (D 2  and D 3 ) are activated in response to a back-driven condition of the DC motor  12  to divert current away from the transistors (Q 2  and Q 3 ) that correspond to the activated LEDs. 
     Continuing to refer to  FIG. 1 , once the pushbutton PB 1  is depressed the transistor Q 1  turns on and voltage on a positive side  30  of the DC motor  12  goes high. The DC motor  12  turns clockwise, and increases in speed. As the speed of the DC motor  12  increases, the voltage at the negative side  34  of the DC motor rises until the current to the DC motor  12  is about zero. Then, the external torque is exerted upon the motor shaft, causing the DC motor  12  to increase even more in speed. 
     In response to the voltage at the positive terminal  30  of the DC motor  12  increasing to a value greater than the supply voltage and the forward bias voltage of the LED D 1 , the LED D 1  begins to conduct and current flows through the LED D 1 . The current then flows through the pushbutton PB 1  and the resistor R 5 . Similarly, the LED D 4  also begins to conduct current as well, since the voltage at the terminal  32  of the DC motor  12  is lower than the voltage at ground. Both the LEDs D 1  and D 4  conduct current and release energy in the form of photons, therefore creating light. 
     The forward voltage of an LED is between 1.8 and 3.3 volts, and varies based on the color of the LED. For example, the forward voltage of a red LED is about 1.8 volts. The forward voltage rises as the light frequency increases. Thus, the forward voltage of a blue LED ranges from about 3 to 3.3 volts. However, the forward voltage of the LEDs is kept as low as possible, since the lower the forward voltage, the less power that is dissipated. Furthermore, in applications having flyback current, a lower voltage drop across the LED results in a larger voltage across the inductive elements of the load. Thus, the flyback current drops to zero more quickly, and means that the load is more responsive. 
     In contrast to conventional electronic components used to dissipate power such as resistors and diodes, the LEDs D 1 -D 4  do not dissipate power only as heat. Instead, a portion of the power in the LEDs D 1 -D 4  are dissipated as light. In one embodiment, the light created by the LEDs D 1 -D 4  consumes about 30% of the power dissipated. Therefore, the LEDs D 1 -D 4  dissipate only about 70% of the heat that a conventional diode would create in the same application. However, the light created by a red LED consumes about 39% of the power dissipated. Furthermore, the light emitted by a laser diode consumes about 50% of the power dissipated. Therefore, in some types of heat sensitive applications a laser diode or a red LED are utilized. 
     In some embodiments, the LEDs D 1 -D 4  are not placed in an enclosure with the circuit  20 . Instead, the LEDs D 1 -D 4  may be mounted behind a window (not illustrated) so that the emitted light is released into the environment. In another embodiment, the LEDs D 1 -D 4  are mounted upon an external surface of a vehicle, such as a space vehicle (not illustrated). Thus, any light produced by the LEDs D 1 -D 4  is released into the environment, and any heat is transferred to the external skin of the space vehicle. 
     Although  FIG. 1  illustrates an H-bridge powering a back-driven DC motor, the disclosure is not limited to the embodiment as shown in  FIG. 1 . For example,  FIG. 2  illustrates the circuit  20  including two inductive loads, namely a normally open (NO) relay  42 , which is configured to control a solenoid valve  40 . The solenoid valve  40  is illustrated in an open position. The relay  42  controls the solenoid valve  40 . Specifically, the relay  42  actuates the solenoid valve  40  between the open position and a closed position. The solenoid valve  40  includes a coil  44 , an armature  46 , and a valve body  50 . The valve body  50  of the solenoid valve  40  defines an inlet  52 , an outlet  54 , and a passageway  56  that extends between the inlet  52  and the outlet  54 . The passageway  56  allows for a fluid such as water to enter the solenoid valve  40  through the inlet  52 . When the solenoid valve  40  is opened, the fluid is allowed to exit the solenoid valve  40  through the outlet  54 . The armature  46  of the solenoid valve  40  is normally in the closed position, where an end  61  of the armature  46  is seated against a surface  58  defined by the passageway  56  of the valve body  50 . When seated, the armature  46  blocks the flow of fluid through the passageway  56  of the valve body  50 . 
     Continuing to refer to  FIG. 2 , the coil  44  of the solenoid valve  40  is in communication with a power supply  60 . In the exemplary embodiment as shown, the power supply  60  is a  12  Volt power supply. The relay  42  is in communication with the power supply  60 , a power source  64 , and a transistor  68 . In the embodiment as shown, the relay  42  is a single pole single throw normally open relay including a relay coil  62  and a switch  48 . However, the relay  42  is not limited to the specific embodiment as shown in  FIG. 2 . The transistor  68  includes an emitter E, a base B, and a collector C, where the base B of the transistor  68  is in communication with a digital output pin  66  of a digital controller (not illustrated). Although the transistor  68  is shown as a BJT, other types of transistors may be used as well. The digital output pin  66  transmits a control signal to switch the relay  42  into a closed position. 
     In response to energizing the relay coil  62  of the relay  42 , the switch  48  of the relay  42  is closed. Thus, current may flow from the 12V supply through the coil  44  of the solenoid valve  40 . When the solenoid coil  44  is energized, the solenoid valve  40  opens, and allows for fluid to flow through the passageway  56  of the valve body  50 . 
     A flyback semiconductor  70  is placed in parallel with the solenoid valve  40 . Similar to the embodiment as shown in  FIG. 1 , an LED is illustrated, however other types of light emitting semiconductors such as single-junction photocells and laser diodes may be used as well. The flyback semiconductor  70  substantially eliminates the flyback created by the solenoid valve  40 . The flyback semiconductor  70  also protects various electrical components of the circuit  20  from a back-driven condition of the solenoid valve  40 . A back-driven condition occurs when current flows through the coil  44  of the solenoid valve  40 , but a greater opposite external force is exerted upon the armature  46 . That is, the coil  44  is energized to open the solenoid valve  40 , but a greater force is exerted upon the armature  46  to keep the solenoid valve  40  closed. A second flyback semiconductor  72 , which is illustrated as an LED, is also placed in parallel with the relay  42  to substantially eliminate flyback as well. 
     Finally, an antiparallel semiconductor  74  is provided. The antiparallel semiconductor  74  is placed within the circuit  20  with respect to the flyback semiconductor  70 . The antiparallel semiconductor  74  is configured to protect against an over-driven condition of the solenoid valve  40 . An over-driven condition occurs when current flows through the coil  44  of the solenoid valve  40 , but a greater external force that is exerted in the same direction is also exerted upon the armature  46 . 
     Referring generally to the figures, the disclosed system provides one or more light emitting semiconductor components for dissipating power, which generate less heat than a conventional diode would create in the same application. In the event the disclosure is employed in an aerospace application, technical effects and benefits may include actuators that are capable of retracting at full speed, reduced weight when compared to fast-charged batteries, and smaller heat sinks when compared to a resistor-only system. Specifically, the heat sinks may be up to 30 to 35 percent smaller when compared to resistor-only systems. Therefore, the disclosure provides enhanced actuator performance and decreased weight, which may be especially important in applications such as aerospace vehicles. 
     While the forms of apparatus and methods herein described constitute preferred examples of this invention, it is to be understood that the invention is not limited to these precise forms of apparatus and methods, and the changes may be made therein without departing from the scope of the invention.