High efficiency voltage regulator with auto power-save mode

1. A DC-to-DC converter, comprising:

an amplifier that compares a feedback voltage to a reference voltage and outputs an error signal;

a comparator that compares the error signal to a ramp signal and outputs a comparison signal;

means for controlling the DC-to-DC converter to operate in a power-save mode in response to a digital control signal being in a light load condition; and

a controller that receives the comparison signal and outputs the digital control signal, wherein the digital control signal is used to control the means such that the DC-to-DC converter supplies a regulated voltage onto a load.

2. The DC-to-DC converter of claim 1 , further comprising:

a control signal monitoring circuit that monitors the digital control signal, wherein the control signal monitoring circuit detects the digital control signal being in the light load condition and in response thereto outputs a first enabling signal that is received by the comparator and by the means.

3. The DC-to-DC converter of claim 2 , wherein the control signal monitoring circuit detects the digital control signal being in a heavy load condition, and wherein the means for controlling causes the DC-to-DC converter to operate in a normal mode in response to the digital control signal being in the heavy load condition.

4. The DC-to-DC converter of claim 3 , wherein the DC-to-DC converter consumes less power in the power-save mode than in the normal operation mode.

5. The DC-to-DC converter of claim 3 , wherein the comparator has a substantially smaller power consumption in the power-save mode than in the normal operation mode.

6. The DC-to-DC converter of claim 3 , wherein the means comprises a switch and a current amplifier, and wherein the current amplifier has a substantially smaller power consumption in the power save mode than in the normal operation mode.

7. The DC-to-DC converter of claim 2 , wherein the control signal monitoring circuit detects the digital control signal being in a heavy load condition and in response thereto outputs a second enabling signal that is received by the comparator and by the means.

8. The DC-to-DC converter of claim 2 , wherein the control signal monitoring circuit comprises:

a timer that monitors the digital control signal and outputs a digital value when the digital control signal remains unchanged for a predetermined time period; and

a sequential logic element that outputs the first enabling signal in response to the digital value.

9. The DC-to-DC converter of claim 8 , wherein the sequential logic element outputs the second enabling signal when the digital control signal changes from a digital low to a digital high.

10. The DC-to-DC converter of claim 8 , wherein the sequential logic element is taken from the group consisting of: a flip-flop circuit, and an SR latch circuit.

11. A method, comprising:

(a) monitoring a digital control signal generated by a controller of a DC-to-DC converter, wherein the DC-to-DC converter supplies a regulated voltage onto a load;

(b) detecting that the DC-to-DC converter is operating in a light load condition based on characteristics of the digital control signal; and

(c) operating the DC-to-DC converter in a power-save mode in response to the detecting in (b).

12. The method of claim 11 , wherein the light load condition is detected in (b) by determining that the digital control signal remains unchanged for a predetermined time period.

13. The method of claim 11 , further comprising:

(d) detecting that the DC-to-DC converter is operating in a heavy load condition based on the characteristics of the digital control signal; and

(e) operating the DC-to-DC converter in a normal mode in response to the detecting in (b).

14. The method of claim 13 , wherein the heavy load condition is detected in (d) by determining that the digital control signal changes from a digital low to a digital high.

15. The method of claim 13 , wherein the DC-to-DC converter consumes less power in the power-save mode than in the normal operation mode.

16. A DC-to-DC converter comprising:

a power switch unit that receives a digital control signal, wherein the digital control signal controls the power switch unit such that the DC-to-DC converter a regulated voltage onto a load; and

means for monitoring the digital control signal, wherein the means detects a light load condition based on characteristics of the digital control signal and in response thereto causes the DC-to-DC converter to operate in a power-save mode.

17. The DC-to-DC converter of claim 16 , wherein the light load condition is detected by determining that the digital control signal remains unchanged for a predetermined time period.

18. The DC-to-DC converter of claim 16 , wherein the means also detects a heavy load condition based on the characteristics of the digital control signal and in response thereto causes the DC-to-DC converter to operate in a normal operation mode.

19. The DC-to-DC converter of claim 18 , wherein the heavy load condition is detected by determining that the digital control signal changes from a digital low to a digital high.

20. The DC-to-DC converter of claim 18 , wherein the DC-to-DC converter consumes less power in the power-save mode than in the normal operation mode.

21. The DC-to-DC converter of claim 1 , wherein the DC-to-DC converter is part of a portable audio player.

22. The method of claim 11 , wherein the characteristics of the digital control signal include a pattern of the digital control signal.

23. The DC-to-DC converter of claim 16 , wherein the means detects the light load condition without directly sensing a current supplied to the load.