Organic light emitting diode power converter
View Patent ↗A power converter circuit converts an AC line signal to a DC signal for powering an organic light emitting diode. The circuit uses only capacitive elements to limit current to the LED. Inductive and resistive elements are not included in the circuit to limit current. The absence of inductive components eliminates electromagnetic interference generated by the circuit and avoids circuit components magnetically coupling to one another. The circuit includes complementary MOSFET switches that alternately conduct to convert the AC line voltage into a DC current for powering the LED.
1. A power converter circuit for supplying power to a light emitting diode comprising:
a voltage source;
a first switch connected to the voltage source;
a second switch connected to the voltage source, the second switch being in parallel to the first switch with respect to the voltage source;
a first capacitor for storing charge during a conductive state of the first switch;
a second capacitor for storing charge during a conductive state of the second switch; and,
at least one light emitting diode that illuminates upon receiving forward current from at least one of the first and second switches;
wherein the first and second capacitors limit the current provided to the light emitting diode.
2. The power converter circuit as set forth in claim 1 , further including:
an energy storage capacitor that stores charge from at least the first capacitor.
3. The power converter circuit as set forth in claim 1 , further including:
a current sensing resistor in a series relationship with the light emitting diode to sense and regulate the current through the light emitting diode.
4. The power converter circuit as set forth in claim 1 , further including:
a control circuit that controls the conductive state of the second switch.
5. The power converter circuit as set forth in claim 4 , further including:
a voltage comparator that senses a source-drain voltage of the first switch and controls the conductive state of the first switch based on the conductive state of the second switch.
6. The power converter as set forth in claim 5 , wherein the voltage comparator and the control circuit are micropower logic circuits.
7. The power converter as set forth in claim 1 , wherein the value of the first and second capacitors, C, is based on the relationship:
C
=
1
2
π
fX
c
where X c is the impedance of the first and second capacitors in Ohms needed to adequately limit the current to the light emitting diode and ƒ is the frequency of the line signal in Hertz.
8. The power converter as set forth in claim 7 , wherein the impedance of the first and second capacitors X c is found by the relationship:
X
c
=
2
V
in
π
I
0
where V in is the RMS voltage of the voltage source and I 0 is the desired current through the light emitting diode.
9. The power converter as set forth in claim 8 , wherein the value of the first and second capacitors is approximately 14.73 μF.
10. The power converter as set forth in claim 1 , wherein the light emitting diode is an organic light emitting diode.
11. An AC to DC converter for limiting current to a light emitting diode consisting of only non-inductive components, the components comprising:
a voltage source;
a first switch connected to the voltage source;
a second switch connected to the voltage source, the second switch being in parallel to the first switch with respect to the voltage source;
a first capacitor for storing charge during a conductive state of the first switch;
a second capacitor for storing charge during a conductive state of the second switch;
at least one light emitting diode that illuminates upon receiving forward current from at least one of the first and second switches;
a control circuit that controls the conductive state of the second switch; and
a voltage comparator that senses a source-drain voltage of the first switch and controls the conductive state of the first switch based on the conductive state of the second switch.
12. The AC to DC converter as set forth in claim 11 , wherein the light emitting diode is an organic light emitting diode.
13. The AC to DC converter as set forth in claim 11 , further including an energy storage capacitor that stores charge from at least the first capacitor.
14. The AC to DC converter as set forth in claim 11 , further including a current sensing resistor in a series relationship with the light emitting diode to sense and regulate the current through the light emitting diode.
15. The AC to DC converter as set forth in claim 11 , wherein the voltage comparator and the control circuit are micropower logic circuits.
16. A method of limiting current to a light emitting diode using only non-inductive components comprising:
placing first and second switches in a parallel relationship with respect to a voltage source for providing current to a light emitting diode;
connecting a first current limiting capacitor between the first switch and the voltage source;
connecting a second current limiting capacitor between the second switch and the voltage source; and,
sensing the current across the light emitting diode with a current sensing resistor; and,
controlling a period of conductivity of the first switch, which is complementary to the period of conductivity of the second switch, with a micropower logic voltage comparator.
17. The method as set forth in claim 16 , further including:
controlling a period of conductivity of the second switch with a micropower logic control circuit.
18. The method as set forth in claim 16 , further including:
charging a storage capacitor with the first and second current limiting capacitors;
discharging the storage capacitor to at least partially power the light emitting diode.
19. The method as set forth in claim 16 , wherein the light emitting diode is an organic light emitting diode.
20. A method of limiting current to a light emitting diode using only non-inductive components comprising:
placing first and second switches in a parallel relationship with respect to a voltage source for providing current to a light emitting diode;
connecting a first current limiting capacitor between the first switch and the voltage source;
connecting a second current limiting capacitor between the second switch and the voltage source;
sensing the current across the light emitting diode with a current sensing resistor;
charging a storage capacitor with the first and second current limiting capacitors; and
discharging the storage capacitor to at least partially power the light emitting diode.
21. The method as set forth in claim 20 , further including controlling a period of conductivity of the second switch with a micropower logic control circuit.
22. The method as set forth in claim 20 , wherein the light emitting diode is an organic light emitting diode.