Abstract:
A voltage regulator includes a source port configured to be coupled to a power source and a load port configured to be coupled to a load. The voltage regulator also includes a constant current source circuit in electrical communication with the source port and the load port configured to regulate current flowing between the source port and the load port. Current flows in both a positive direction and a negative direction between the source port and the load port, and the constant current source circuit regulates the current that flows in the positive direction and the current that flows in the negative direction.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    This application relates to voltage regulators. Specifically, this application relates to a voltage regulator that regulates an AC voltage. 
         [0003]    2. Description of the Related Art 
         [0004]    Voltage regulators are electrical circuits utilized to regulate unregulated voltage sources. For example, a DC-to-DC (direct current-to-direct current) voltage regulator circuit may be utilized to convert a loosely regulated voltage produced by an automobile alternator into a tightly regulated voltage for operating accessories, such as MP3 players, mobile phones, and the like. An AC-to-DC (alternating current-to-direct current) voltage regulator may be utilized to convert the loosely regulated AC line voltage found in a home to a regulated DC voltage for an appliance, such as a laptop computer. An AC-to-AC regulator may be utilized to convert the loosely regulated AC line voltage found in a home to a regulated AC voltage suitable for powering, for example, a desktop computer. 
         [0005]    A typical AC-to-AC voltage regulator operates by first converting the loosely regulated AC line voltage into a DC voltage. The DC voltage may be regulated. The DC voltage is then converted back into an AC voltage via, for example, an inverter circuit. One problem, however, with such a voltage regulator is that a relatively high number of components are required. The high number of components makes it difficult to fit such a circuit into a confined space, such as an electrical junction box. 
       SUMMARY 
       [0006]    In one aspect, a voltage regulator includes a source port configured to be coupled to a power source and a load port configured to be coupled to a load. The voltage regulator also includes a constant current source circuit in electrical communication with the source port and the load port configured to regulate current flowing between the source port and the load port. Current flows in both a positive direction and a negative direction between the source port and the load port. The constant current source circuit regulates the current that flows in the positive direction and the current that flows in the negative direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The accompanying drawings are included to provide a further understanding of the claims and are incorporated in and constitute a part of this specification. 
           [0008]      FIG. 1  is a block diagram of an exemplary embodiment of a voltage regulator; 
           [0009]      FIG. 2  is a schematic diagram of an exemplary voltage regulator; 
           [0010]      FIGS. 3A and 3B  illustrate voltage waveforms of the input voltage and output voltage of the exemplary voltage regulator of  FIG. 1 ; and 
           [0011]      FIGS. 4A and 4B  illustrate current waveforms flowing through a load coupled to the voltage regulator and current waveforms flowing through an exemplary constant current source circuit of the exemplary voltage regulator of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The embodiments below describe an exemplary voltage regulator configured to generate a substantially constant peak-to-peak voltage and RMS (root-mean-square) voltage from a power source that exhibits significant variations in output voltage. 
         [0013]      FIG. 1  is a schematic of an exemplary voltage regulator block diagram  100 . Shown are a voltage regulator  105 , a load  110 , and a power source  120 . The power source  120  corresponds to a source of AC (alternative current) voltage. In one embodiment, the power source  120  represents the line voltage provided by a power utility company. For example, line voltage may be anywhere between 150 Volts p-p (peak-to-peak) to 360 Volts p-p and may be generally sinusoidal in nature. The power source  120  may be loosely regulated. That is, the voltage provided by a given power utility company may vary, for example, due to loading variation on the power line. 
         [0014]    The load  110  is a device that requires a regulated source of power. More specifically, the load  110  represents the impedance measured across input power terminals of the device. The impedance of the load  110  may be substantially resistive, although the load  110  may have indicative and/or reactive components. In one implementation, the load  110  represents the impedance of a timer mechanism (not shown), such as a timer for actuating a sprinkler system or to turn on equipment. The timer may be configured to operate from a fixed AC line voltage, such as the 120 Volt RMS standard line voltage utilized in the United States. 
         [0015]    The voltage regulator  105  includes a source port  125  for coupling to the power source  120  and an output port  130  for coupling to the load  110 . The voltage regulator  105  is configured to convert voltage provided by the power source  120  into a voltage suitable for operating the load  110 . For example, the voltage regulator  105  may convert power line voltages provided in different countries, such as 120 Vrms and 240 Vrms, into a regulated voltage suitable for operating the load  110 . The voltage that operates the load  110  may be substantially constant. As such, the voltage regulator  105  also operates to regulate power line voltage variations that may occur, for example, due to loading variations on the power line. The voltage regulator  105  includes a constant current source circuit  115  configured to regulate current flowing through the load  110 , which in turn regulates voltage across power terminals of the load  110 . 
         [0016]      FIG. 2  is a schematic  200  that includes an exemplary voltage regulator circuit  205  that may represent circuitry within the voltage regulator  105 , described above. The voltage regulator circuit  205  includes a bridge-rectifier subcircuit  210 , and a constant-current-source subcircuit  265 . The voltage regulator circuit  205  also includes an AC-to-DC converter circuit that includes a diode  225  and capacitor  255  that cooperate to convert AC voltage provided by the power source  120  to a DC voltage across the capacitor at nodes Va  275  and GND  270  for operating the constant-current-source sub circuit  265 . 
         [0017]    The constant-current-source sub circuit  265  implements an emitter follower circuit that includes transistor Q 1   240 , resistor R 7   220 , resistor R 8   235 , resistor R 9   245 , resistor R 10   230 , and zener diode D 12   250 . The first and the second ends of resistor R 8   235  are coupled to node Va  275  and to the cathode of zener diode D 12   250 , respectively. The anode of zener diode D 12   250  is coupled to node GND  270 . The cathode of zener diode D 12   250  is also coupled to the base of transistor Q 1   240 . The emitter of transistor Q 1  is coupled to a first end of resistor R 9   245 . The second end of resistor R 9   245  is coupled to node GND  270 . 
         [0018]    In operation, resistor R 8   235  and zener diode D 12   250  cooperate to produce a substantially constant reference voltage at the base of transistor Q 1   240 . When the voltage at the collector of transistor Q 1   240  exceeds the reference voltage, current will begin to increase across resistor R 9   245  until the voltage across resistor R 9   245  substantially equals the reference voltage at the base of transistor Q 1   240 . From this point on, the voltage across resistor R 9   245  will remain substantially constant, resulting in a substantially constant current flowing through resistor R 9   245 . By virtue of the gain of the transistor, most of this current is sourced from the collector of transistor Q 1   240 . In other words, the current flowing into the collector of transistor Q 1   240  will be substantially the same as the current flowing out of the emitter of transistor Q 1   240  and through resistor R 9   245 . 
         [0019]    The amount of current flowing into the collector of transistor Q 1   240  is dependent on the zener voltage of zener diode D 12   250  and the resistance of resistor R 9   245 . In one implementation, the resistance of resistor R 8   235  is 27 KOhms, the zener voltage of zener diode D 12   250  is about 5.6 Volts, and the resistance of resistor R 9   245  is 410 ohms. In this configuration, the current flowing into the collector of transistor Q 1   240  is approximately 12 mA when transistor Q 1   240  is in a linear mode of operation. 
         [0020]    The current flowing into the collector of transistor Q 1   240  is equal to the sum of the current flowing through resistor R 10   230  and the current flowing through resistor R 7   220 . The current flowing through resistor R 7   220  is equal to the magnitude of the current flowing through the load  110 . The rectifier circuit  210  is configured to rectify AC current flowing though the load  110  and to communicate the rectified AC current to resistor R 7   220 . The value of resistor R 10   230  may be matched to the impedance of the load  110 . In one implementation, the impedance of the load  110  and resistance of resistor R 10   230  are about 27 KOhms. 
         [0021]    The exemplary component values describe above cooperate to advantageously produce a substantially constant peak-to-peak voltage of 160 Vp-p across the load  110  in the presence of significant variations in the peak-to-peak voltage provided by the power source  120 . For example, the voltage across the load  110  may remain constant for power source  120  voltages between 160 Vp-p and 431 Vp-p, and even greater. The voltage across the load  110  may be adjusted by varying the component values. For example, the voltage across the load  110  may be increased by decreasing the resistance of resistor R 9   245  and/or by selecting a zener diode D 12   250  with a higher zener voltage. Conversely, the voltage across the load  110  may be decreased by increasing the resistance of resistor R 9   245  and/or by selecting a zener diode D 12   250  with a lower zener voltage. In one implementation, the respective values are chosen so that the voltage across the load  110  equals the lowest expected voltage produced by the power source  120 . 
         [0022]      FIGS. 3A and 3B  illustrate voltage waveforms of the exemplary voltage regulator of  FIG. 2 . Shown is a power source voltage waveform  310  that represents the voltage output from the power source  120  ( FIG. 2 ). Also shown is a load voltage waveform  305  that represents the voltage across the load  110  ( FIG. 2 ). As shown in  FIG. 3A , when the peak-to-peak power source voltage  310  is approximately 160 Vp-p, the load voltage  305  is also about 160 Vp-p, or about the same as the power source voltage  310 , and the respective voltage waveforms are nearly identical. 
         [0023]    In  FIG. 3B , the peak-to-peak power source voltage  310  is increased to approximately 300 Vp-p. As shown, the load voltage  305  remains substantially constant at about 160 Vp-p. As shown in both  FIGS. 3A and 3B , the load voltage  305  remains sinusoidal in nature throughout variations in the power source voltage  310 . Therefore, the RMS (root-mean-square) value of the load voltage  305  is also substantially constant over variations in the power source voltage  310 . The peak-to peak and RMS values of the load voltage  305  remain substantially constant for even greater power source voltages  310 , such as 431 Vp-p. Regulation of even higher power source voltages  310  may be is possible provided components capable of withstanding the higher voltages are selected. 
         [0024]      FIGS. 4A and 4B  illustrate current waveforms of current flowing through the load  110  ( FIG. 2 ), resistor R 10   230  ( FIG. 2 ), and collector of transistor Q 1   240  ( FIG. 2 ). The currents shown in  FIGS. 4A and 4B  coincide with the voltages shown in  FIGS. 3A and 3B , respectively. 
         [0025]    Referring to  FIG. 4A , when the peak-to-peak voltage of the power source  110  is approximately equal to the desired voltage across the load  110 , the current  405  flowing through resistor R 10   230  is substantially constant. The current  410  flowing through the collector of transistor Q 1   240  substantially equals the magnitude of the current flowing through the load  110 . In this mode of operation, transistor Q 1   240  may not be operating in a linear region. 
         [0026]    Referring to  FIG. 4B , as the peak-to-peak voltage of the power source  120  increases beyond the desired load  110  voltage, transistor Q 1   240  enters a linear mode of operation. In this mode of operation, the current  410  flowing through the collector of transistor Q 1   240  is substantially constant. As the magnitude of the current  415  flowing through the load  110  increases, the current  405  flowing through resistor R 10   230  decreases by a corresponding amount, such that the sum of the two currents  405  and  415  equals the current  410  flowing through the collector of transistor Q 1   240 . 
         [0027]    As described above, the exemplary voltage regulator circuit is able to maintain a substantially constant peak-to-peak voltage and RMS voltage across the load resistor in the presence of significant variations in the voltage provided by the power source. Moreover, the number of components is relatively low, enabling the voltage regulator circuit to fit within small confined spaces. 
         [0028]    While the voltage regulator has been described with reference to certain component configurations and component values, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the claims. For example, the values of the various components may be adjusted to increase or decrease the voltage provided across the load. Additionally, different types of components may be utilized. For example, a constant current source circuit that utilizes a JFET, MOSFET, or other transistor as the active component may be utilized. The voltage reference provided to the base of the transistor may be generated differently. 
         [0029]    Moreover, although reference is made to various components being coupled to one another, it is to be understood that the components do not necessarily have to be directly coupled. For example, fuses and the like may be inserted between components without affecting the operation of the exemplary circuits. Capacitors and inductors may be inserted between components of the exemplary circuits to condition various voltages and currents of the circuit. 
         [0030]    Many other modifications may be made to adapt a particular situation or material to the teachings without departing from its scope. Therefore, it is intended that the voltage regulator defined by the claims not be limited to the particular embodiment disclosed, but rather any circuit that falls within the scope of the claims.