Patent Publication Number: US-7592793-B2

Title: Voltage regulator providing power from AC power source

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a power converter. More particularly, the present invention relates to a voltage regulator. 
     2. Description of Related Art 
       FIG. 1  shows a traditional voltage regulator for supplying a regulated voltage V Z  from a line voltage V AC . A rectifier circuit  10  including a plurality of rectifiers is coupled to the line voltage V AC  and provides the rectification to generate an input voltage V IN . A capacitor  11  is connected from the input voltage V IN  to a capacitor  15  to produce the regulated voltage V Z . A zener diode  16  is connected to the capacitor  15  for the regulation. A resistor  12  is used for the discharge of the capacitor  11 . This traditional voltage regulator has been widely used in home appliances, such as coffee maker, cooling fan and remote controller, etc. However, the drawback of this traditional voltage regulator is high power consumption, particularly for light load and no load situations. Both the resistor  12  and the zener diode  16  cause significant power losses. Therefore, reducing the power loss is required. The object of present invention is to provide a high efficiency voltage regulator for generating a regulated voltage from an AC power source. 
     SUMMARY OF THE INVENTION 
     The present invention provides a voltage regulator includes a switch coupled to receive a voltage source for producing a supply voltage at the output terminal of the voltage regulator. An input detection circuit is coupled to the voltage source to generate a control signal in response to the voltage level of the voltage source. The control signal is utilized to turn off the switch when the voltage level of the voltage source is higher than a threshold voltage. An output detection circuit is coupled to the supply voltage to generate a first enable signal and a second enable signal in response to the voltage level of the supply voltage. The first enable signal is coupled to switch off the switch once the voltage level of the supply voltage is higher than an output-over-voltage threshold. The switch can only be turned on when the voltage level of the voltage source is lower than the threshold voltage and the voltage level of the supply voltage is lower than a hysteresis threshold. The second enable signal is utilized to disable a regulator when the supply voltage is lower than an output-under-voltage threshold. The regulator is coupled to the supply voltage to generate a regulated output voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
         FIG. 1  shows a circuit diagram of a traditional voltage regulator. 
         FIG. 2  shows a circuit diagram of a preferred embodiment of a voltage regulator according to the present invention. 
         FIG. 3  shows a circuit diagram of a preferred embodiment of a supply circuit of the voltage regulator according to the present invention. 
         FIG. 4  shows a circuit diagram of a preferred embodiment of an output detection circuit of the supply circuit according to the present invention. 
         FIG. 5  shows a circuit diagram of another preferred embodiment of the voltage regulator according to the present invention. 
         FIG. 6  shows the input voltage waveform of the voltage regulator shown in  FIG. 5  according to the present invention. 
         FIG. 7  shows a circuit diagram of a preferred embodiment of the supply circuit of the voltage regulator shown in  FIG. 5  according to the present invention. 
         FIG. 8  shows a circuit diagram of a preferred embodiment of the output detection circuit of the supply circuit shown in  FIG. 7  according to the present invention. 
         FIG. 9  shows a circuit diagram of a preferred embodiment of a regulator of the supply circuit according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  shows a circuit diagram of a preferred embodiment of a voltage regulator according to the present invention. The rectifier circuit  10  includes a plurality of rectifiers. The rectifier circuit  10  is coupled to receive the line voltage V AC  to produce the input voltage V IN  coupled to an input terminal IN of a supply circuit  20 . The line voltage V AC  is an AC power source. The input voltage V IN  is a voltage source and is rectified by the rectifier circuit  10 . The supply circuit  20  generates a supply voltage V C  at a first output terminal SW. Furthermore, the supply circuit  20  will generate a regulated output voltage V O  at the second output terminal OUT. A ground terminal GND of the supply circuit  20  is coupled to the ground. A capacitor  50  is connected to the first output terminal SW for holding energy. Furthermore a capacitor  55  is connected to the second output terminal OUT. The voltage regulator is also called a voltage regulation circuit or a power supply circuit. 
       FIG. 3  is a circuit diagram of a preferred embodiment of the supply circuit  20  of the voltage regulator. The supply circuit  20  comprises a switch  60  coupled to the input terminal IN to receive the input voltage V IN  for providing the supply voltage V C  at the first output terminal SW. An output detection circuit  100  is coupled to the first output terminal SW to detect the supply voltage V C  for generating a first enable signal S OV  at a first enable terminal OV of the output detection circuit  100  in response to the voltage level of the supply voltage V C . The first enable signal S OV  is coupled to switch off the switch  60  when the voltage level of the supply voltage V C  is higher than an output-over-voltage threshold. Besides, the output detection circuit  100  generates a second enable signal S EN  at a second enable terminal EN of the output detection circuit  100  in response to the voltage level of the supply voltage V C . The second enable signal S EN  is connected to a regulator  300  to turn off the regulator  300  when the voltage level of the supply voltage V C  is lower than an output-under-voltage threshold. The regulator  300  is coupled to the supply voltage V C  at the first output terminal SW to generate the regulated output voltage V O . The regulated output voltage V O  is coupled to the second output terminal OUT. 
       FIG. 4  shows a circuit diagram of a preferred embodiment of the output detection circuit  100 . Zener diodes  110  and  112  are connected in serial. The zener diode  112  is further connected to the first output terminal SW to detect the supply voltage V C . The zener diode  110  is connected to a resistor  115 . The resistor  115  is further coupled to a transistor  120 . The resistor  115  is used to turn on the transistor  120  when the voltage level of the supply voltage V C  is higher than the voltage of zener diodes  110  and  112 . A transistor  125  is parallel connected with the zener diode  112  to short circuit the zener diode  112  when the transistor  120  is turned on, which achieve a hysteresis for detecting the over voltage of the supply voltage V C . The zener voltage of the zener diodes  110  and  112  determines the output-over-voltage threshold. The zener voltage of the zener diode  112  determines a hysteresis threshold for the hysteresis. The first enable signal S OV  will switch on the switch  60  when the voltage level of the supply voltage V C  is lower than the hysteresis threshold. 
     A transistor  140  is coupled to the transistor  120  and the first output terminal SW. The transistor  140  is turned on in response to the turn-on of the transistor  120 . A resistor  116  is coupled to the first output terminal SW, the transistors  125  and  140 . The resistor  116  provides a bias to transistors  125  and  140 . A resistor  117  is connected to the transistor  140  and an inverter  129  to control the inverter  129  when the transistor  120  is turned on. The inverter  129  is coupled to the transistor  140 . The inverter  129  is further connected to the switch  60  and generates the first enable signal S OV  to turn off the switch  60  once the voltage level of the supply voltage V C  is higher than the output-over-voltage threshold. 
     A zener diode  150  is also connected to the first output terminal SW to detect the supply voltage V C . A resistor  155  is connected to the zener diode  150  and a transistor  165  to turn on the transistor  165  once the voltage level of the supply voltage V C  is higher than the output-under-voltage threshold. The zener voltage of the zener diode  150  determines the output-under-voltage threshold. A resistor  156  is coupled to the first output terminal SW and a transistor  170 . The transistor  170  is further coupled to the first output terminal SW and the transistor  165 . The transistor  170  generates the second enable signal S EN  when the voltage level of the supply voltage V C  is lower than the output-under-voltage threshold. The voltage level of the output-over-voltage threshold is higher than the hysteresis threshold. The voltage level of the hysteresis threshold is higher than the output-under-voltage threshold. 
       FIG. 5  shows a circuit diagram of another preferred embodiment of the voltage regulator, in which the control of a supply circuit  30  is synchronized with the line voltage V AC . The input of the supply circuit  30  can only be turned on when the input voltage V IN  is lower than an input threshold voltage, which reduces the switching loss of the switch  60  and improves the efficiency of the voltage regulator.  FIG. 6  shows the waveform of the input voltage V IN , in which the input voltage V IN  is delivered to the first output terminal SW when the input voltage V IN  is lower than a threshold voltage V T . The threshold voltage V T  is correlated to the input threshold voltage. The supply circuit  30  includes a detection terminal DET coupled to the input voltage V IN  through a voltage divider  40 . The voltage divider  40  comprises resistors  41  and  42 . The resistors  41  and  42  are coupled in series. 
       FIG. 7  shows a preferred embodiment of the supply circuit  30  of the voltage regulator shown in  FIG. 5 . The supply circuit  30  comprises the switch  60  coupled to the input terminal IN to receive the voltage source V IN  for providing the supply voltage V C  at the first output terminal SW. The input voltage V IN  is the voltage source. A positive input terminal of an input detection circuit  75  is coupled to the detection terminal DET to detect the input voltage V IN  via the voltage divider  40  and generate a control signal in response to the voltage level of the input voltage V IN . The control signal is coupled to an input terminal CNT of an output detection circuit  200  to turn off the switch  60  when the voltage level of the input voltage V IN  is higher than the threshold voltage V T . The input detection circuit  75  includes the threshold voltage V T  that is correlated to the input threshold voltage. The threshold voltage V T  is coupled a negative input terminal of the input detection circuit  75 . 
     The output detection circuit  200  is coupled to the first output terminal SW to detect the supply voltage V C  and generate the first enable signal S OV  at the first enable terminal OV in response to the voltage level of the supply voltage V C . The first enable signal S OV  is coupled to the switch  60  to switch off the switch  60  when the voltage level of the supply voltage V C  is higher than the output-over-voltage threshold. Besides, the output detection circuit  200  generates the second enable signal S EN  at the second enable terminal EN in response to the voltage level of the supply voltage V C . The second enable signal S EN  is connected to the regulator  300  to turn off the regulator  300  when the voltage level of the supply voltage V C  is lower than the output-under-voltage threshold. The regulator  300  is coupled to the second output terminal OUT. 
     The circuit schematic of the output detection circuit  200  is shown in  FIG. 8 . Zener diodes  210  and  212  are connected in serial. The zener diode  212  is further connected to the first output terminal SW to detect the supply voltage V C . The zener diode  210  is connected to a resistor  215 . The resistor  215  is further coupled to a transistor  220 . The resistor  215  is used to turn on the transistor  220  when the voltage of the supply voltage V C  is higher than the voltage of zener diodes  210  and  212 . A transistor  225  is parallel connected with the zener diode  212  to short circuit the zener diode  212  when the transistor  220  is turned on, which achieve the hysteresis for detecting the over voltage of the supply voltage V C . The zener voltage of the zener diodes  210  and  212  determines the output-over-voltage threshold. The zener voltage of the zener diode  212  determines the hysteresis threshold for the hysteresis. The first enable signal S OV  will switch on the switch  60  when the voltage level of the supply voltage V C  is lower than the hysteresis threshold. 
     A transistor  240  is coupled to the transistor  220  and the first output terminal SW. The transistor  240  is turned on in response to the turn-on of the transistor  220 . A resistor  216  is coupled to the first output terminal SW, the transistors  225  and  240 . The resistor  216  provides a bias to transistors  225  and  240 . A resistor  217  is connected to the transistor  240  and an input terminal of an NOR gate  229  to control the NOR gate  229  when the transistor  220  is turned on. Another input terminal of the NOR gate  229  is connected to the input terminal CNT of the output detection circuit  200  to receive the control signal. An output terminal of the NOR gate  229  is connected to the switch  60  and generates the first enable signal S OV  to turn off the switch  60  once the voltage level of the supply voltage V C  is higher than the output-over-voltage threshold or the voltage level of the input voltage V IN  is higher than the threshold voltage V T . 
     A zener diode  250  is also connected to the first output terminal SW to detect the supply voltage V C . A resistor  255  is connected to the zener diode  250  and a transistor  265  to turn on the transistor  265  once the voltage level of the supply voltage V C  is higher than the output-under-voltage threshold. The zener voltage of the zener diode  250  determines the output-under-voltage threshold. A resistor  256  is coupled to the first output terminal SW and a transistor  270 . The transistor  270  is further coupled to the first output terminal SW and the transistor  265 . The transistor  270  generates the second enable signal S EN  when the voltage level of the supply voltage V C  is lower than the output-under-voltage threshold. The voltage level of the output-over-voltage threshold is higher than the hysteresis threshold. The voltage level of the hysteresis threshold is higher then the output-under-voltage threshold. 
       FIG. 9  shows a circuit diagram of the regulator  300  that includes an operational amplifier  310 , a pass element  320  and resistors  351 ,  352 . The operational amplifier  310  includes a reference voltage V REF  coupled to a negative input terminal of the operational amplifier  310 . The resistor  352  is coupled to a positive input terminal of the operational amplifier  310 . The second enable signal S EN  is coupled to the operational amplifier  310  to provide a power source to operate the operational amplifier  310 . The pass element  320  is coupled to the operational amplifier  310 , the first output terminal SW and the second output terminal OUT. The operational amplifier  310  and the pass element  320  are disabled once the second enable signal S EN  is disabled. The resistor  351  is coupled to the positive input terminal of the operational amplifier  310  and the pass element  320 . The pass element  320  can be a transistor. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.