Method and apparatus for high efficiency ac/dc conversion of low voltage input

Abstract

Embodiments of the subject invention relate to a method and apparatus for providing a low-power AC/DC converter designed to operate with very low input voltage amplitudes. Specific embodiments can operate with input voltages less than or equal to 1 V, less than or equal to 200 mV, and as low as 20 mV, respectively. Embodiments of the subject low-power AC/DC converter can be utilized in magnetic induction energy harvester systems. With reference to a specific embodiment, a maximum efficiency of 92% was achieved for a 1 V input, and efficiencies exceeding 70% were achieved for a 200 mV input. A specific embodiment functioned properly when connected to a magnetic energy harvester device operating below 200 mV input.

1 . An AC/DC converter, comprising:
 a first active diode, wherein the first active diode comprises a first comparator and a first switch;   a second active diode, wherein the second active diode comprises a second comparator and a second switch;   a first energy storage element; and   a second energy storage element;   wherein the converter is configured to connect to an input AC voltage source such that the first active diode is in series between the input AC voltage source and the first energy storage element and the second active diode is in series between the input AC voltage and the second energy storage element, such that when the voltage of the input AC voltage source is below a voltage of the first energy storage element, the first active diode turns on and current flows from the first energy storage element to the input AC voltage source, and when the voltage of the input AC voltage source is higher than the voltage of the second energy storage element, current flows from the input AC voltage source to the second energy storage element,   wherein the first comparator comprises a first positive input port, a first negative input port, at least one first bias port, and a first output port;   wherein the first switch comprises a first transistor;   wherein the second comparator comprises a second positive input port, a second negative input port, at least one second bias port, and a second output port;   wherein the second switch comprises a second transistor;   wherein the first switch is selected from the group consisting of: an electromechanical switch, a bipolar junction transistor, an analog switch, a junction gate field-effect transistor, and a MOS transistor.   
     
     
         2 . The converter according to  claim 1 , wherein the converter operates with an input AC power source of less than or equal to 20 mV. 
     
     
         3 . The converter according to  claim 1 , wherein the first switch is the a bipolar junction transistor. 
     
     
         4 . The converter according to  claim 2 , wherein the first switch is a first transistor, wherein the second switch is a second transistor. 
     
     
         5 . The converter according to  claim 4 , wherein the first and second transistors are bipolar junction transistors (BJT). 
     
     
         6 . The converter according to  claim 4 , wherein the first and second transistors are junction gate field-effect transistor (JFET). 
     
     
         7 . The converter according to  claim 1 , further comprising a first resistor in series with the first active diode between the input AC power source and the first energy storage element. 
     
     
         8 . The converter according to  claim 1 , further comprising a first low pass filter in parallel with the first energy storage element. 
     
     
         9 . The converter according to  claim 1 , further comprising a shunt capacitor connected across output terminals of the input AC power source. 
     
     
         10 . The converter according to  claim 1 , further comprising a linear or switching regulator connected to the output of the converter. 
     
     
         11 . The converter according to  claim 1 , wherein the converter operates with an input AC power source of less than or equal to 1 V. 
     
     
         12 . The converter according to  claim 1 , wherein the converter operates with an input AC power source of less than or equal to 200 mV. 
     
     
         13 . The converter according to  claim 1 , wherein the converter has an efficiency greater than 70%. 
     
     
         14 . A magnetic induction energy harvester system, comprising:
 a magnetic energy harvester, wherein the magnetic energy harvester outputs a harvester output AC voltage; and   an AC/DC converter, wherein the AC/DC converter comprises:
 a first active diode; 
 a second active diode; 
 a first energy storage element; and 
 a second energy storage element; 
   wherein the converter is configured to connect to the harvester output AC voltage such that the first active diode is in series between harvester output AC voltage and the first energy storage element and the second active diode is in series between the harvester output AC voltage and the second energy storage element, such that when a voltage of the harvester output AC voltage is below a voltage of the first energy storage element, the first active diode turns on and current flows from the first energy storage element to the harvester output AC voltage, and when the voltage of the harvester output AC voltage is higher than a voltage of the second energy storage element, current flows from the harvester output AC voltage to the second energy storage element.   
     
     
         15 . The system according to  claim 14 , wherein the first active diode and the second active diode are powered by one or more of the following: the first energy storage element, the second energy storage element, and the harvester output AC voltage. 
     
     
         16 . The system according to  claim 14 , further comprising a first resistor in series with the first active diode between the input AC power source and the first energy storage element. 
     
     
         17 . The system according to  claim 14 , further comprising a first low pass filter in parallel with the first energy storage element. 
     
     
         18 . The system according to  claim 14 , further comprising a shunt capacitor connected across output terminals of the input AC power source. 
     
     
         19 . The system according to  claim 14 , further comprising a linear or switching regulator connected to the output of the converter. 
     
     
         20 . The system according to  claim 14 , further comprising a ladder circuit connected to the output of the converter.