Power supply apparatus and method for AMOLED
View Patent ↗A power supply apparatus and method for an active matrix organic light emitting diode (AMOLED) is disclosed. The power supply apparatus supplies power to the AMOLED while using a switching frequency varied in accordance with a clock signal, and includes a load checker for comparing a load current of the AMOLED with a first reference voltage, and outputs a result of the comparison as a load check signal, and a frequency oscillator for generating the clock signal which has a variable frequency in response to the load check signal. The power supply apparatus is switched in accordance with a clock signal having a frequency modulated based on a load condition of the AMOLED, for example, a load current. Accordingly, it is possible to reduce switching power loss caused by unnecessary power consumption under the condition that a small load current is generated, thereby achieving an enhancement in efficiency.
1. A power supply apparatus for an active matrix organic light emitting diode (AMOLED), the power supply apparatus comprising:
a load checker which compares a load current of the AMOLED with a first reference voltage, and outputs a result of the comparison as a load check signal; and
a frequency oscillator for generating a clock signal, which has a variable frequency, in response to the load check signal,
wherein the frequency oscillator comprises:
a current source which supplies a constant current;
a plurality of capacitors electrically connected in parallel between the constant current and the ground;
a first switch electrically connected between a part of the capacitors and the ground, the first switch being switched in response to the load check signal;
a second switch electrically connected to a remaining part of the capacitors in parallel, the second switch being switched in response to the clock signal; and
a switching unit for outputting the clock signal in accordance with a result of a comparison of voltages respectively charged in the capacitors with second reference voltages.
2. The power supply apparatus of claim 1 , wherein the load checker comprises:
an external resistor having a first end electrically connected to the load current and a second end electrically connected to a ground; and
a first comparator having a negative input terminal electrically connected to the first end of the external resistor and a positive input terminal connected to the first reference voltage.
3. The power supply apparatus of claim 1 , wherein the switching unit comprises:
a second comparator having a negative input terminal electrically connected to a voltage charged in at least one of the capacitors and a negative input terminal electrically connected to a lower-level one of the second reference voltages;
a third comparator having a positive input terminal electrically connected to the voltage charged in the at least one of the capacitors and a negative input terminal connected to a higher-level one of the second reference voltages; and
an SR flip-flop having an S-input terminal electrically connected to an output from the third comparator, an R-input terminal electrically connected to an output from the second comparator, and an output terminal to output the clock signal.
4. The power supply apparatus of claim 1 , wherein the first switch comprises:
an NMOS transistor having a drain and a source which are electrically connected between at least one of the capacitors and the ground; and
a gate electrically connected to the load check signal.
5. The power supply apparatus of claim 1 , wherein the second switch comprises:
an NMOS transistor having a drain and a source which are electrically connected to the current source and the ground, respectively; and
a gate electrically connected to the clock signal.
6. The power supply apparatus of claim 1 , wherein the capacitor part electrically connected to the first switch has a capacitance corresponding to one half of a capacitance of the capacitor part electrically connected to the second switch.
7. The power supply apparatus of claim 2 , wherein the external resistor has a resistance determined in accordance with a condition of the load current.
8. The power supply apparatus of claim 2 , wherein the first reference voltage has a level determined in accordance with a condition of the load current.
9. A power supply apparatus for an active matrix organic light emitting diode (AMOLED), to supply power to the AMOLED while using a switching frequency varied in accordance with a clock signal, the power supply apparatus comprising:
a load checker which compares a load current of the AMOLED with a first reference voltage and outputs a result of the comparison as a load check signal, the load checker comprising an external resistor having one end electrically connected to the load current and another end electrically connected to a ground, and a first comparator having a negative input terminal electrically connected to one end of the external resistor and a positive input terminal electrically connected to the first reference voltage; and
a frequency oscillator which generates the clock signal, which has a variable frequency, in response to the load check signal, the frequency oscillator comprising a current source which supplies a constant current, a plurality of capacitors electrically connected in parallel between the constant current and the ground, a first switch electrically connected between a first part of the capacitors and the ground, the first switch being switched in response to the load check signal, a second switch electrically connected in parallel to a second part of the capacitors, the second switch being switched in response to the clock signal, and a switching unit which outputs the clock signal in accordance with a result of a comparison of voltages respectively charged in the capacitors with second reference voltages.
10. The power supply apparatus of claim 9 , wherein the switching unit comprises:
a second comparator having a negative input terminal electrically connected to a voltage charged in at least one of the capacitors and a negative input terminal electrically connected to a lower-level one of the second reference voltages;
a third comparator having a positive input terminal electrically connected to the voltage charged in the at least one of the capacitors and a negative input terminal connected to a higher-level one of the second reference voltages; and
an SR flip-flop having an S-input terminal electrically connected to an output from the third comparator, an R-input terminal electrically connected to an output from the second comparator, and an output terminal to output the clock signal.
11. The power supply apparatus of claim 9 , wherein the first switch comprises:
an NMOS transistor having a drain and a source which are electrically connected between at least one of the capacitors and the ground; and
a gate electrically connected to the load check signal.
12. The power supply apparatus of claim 9 , wherein the second switch comprises:
an NMOS transistor having a drain and a source which are electrically connected to the current source and the ground, respectively; and
a gate electrically connected to the clock signal.
13. The power supply apparatus of claim 9 , wherein the capacitor part electrically connected to the first switch has a capacitance corresponding to one half of a capacitance of the capacitor part electrically connected to the second switch.
14. The power supply apparatus of claim 9 , wherein the external resistor has a resistance determined in accordance with a condition of the load current.
15. The power supply apparatus of claim 9 , wherein the first reference voltage has a level determined in accordance with a condition of the load current.
16. The power supply apparatus of claim 9 , wherein:
the first switch comprises an NMOS transistor having a drain and a source which are electrically connected between at least one of the capacitors and the ground, and a gate electrically connected to the load check signal; and
the second switch comprises an NMOS transistor having a drain and a source which are electrically connected to the current source and the ground, respectively, and a gate electrically connected to the clock signal.