High efficiency DC-DC converter using pulse skipping modulation with programmable burst duration
View Patent ↗A DC-DC converter and method of improving the efficiency of a DC-DC converter at low load current levels using pulse skipping modulation (PSM) with controllable burst duration NT clk , where T clk is the clock cycle interval. As the average load current increases, the time between bursts decreases so that average inductor current matches the load current. The burst duration is kept around NT clk by controlling the duty cycle of the output switches. The higher the load current, the higher is the duty cycle of the output switches. No current sensing is needed. The optimum burst duration for best efficiency curve is a function of the load capacitor.
1. A direct current to direct current (DC-DC) converter comprising:
a pair of switches;
a load capacitor operatively connected to said pair of switches;
a pulse width modulator adapted to generate pulse signals for driving said pair of switches;
an analog comparator with hysteresis adapted to control an output voltage level within a specified range, wherein as said output voltage level rises above a high threshold level, an analog comparator output becomes low and starts skipping clock pulses, wherein as said output voltage level drops below a low threshold level, said analog comparator output becomes high and a clock signal is passed to said pair of switches to charge said load capacitor, and wherein said analog comparator is further adapted to compare said output voltage level with either said low threshold level or said high threshold level;
a first counter;
a first register operatively connected to said first counter, wherein when said analog comparator output becomes low said first counter stops and stores its last value Non in said first register;
a first digital comparator operatively connected to said first register; and
an up-down counter operatively connected to said first digital comparator and said pulse width modulator,
wherein during turn-on of said pair of switches, a load current at a load resistor is supplied by said pair of switches, and said load capacitor charges,
wherein a turn-on time is a time when said output voltage level discharges from said low threshold level to said high threshold level through said load capacitor,
wherein said turn-on time is measured by said first counter and said first register,
wherein said first counter starts counting when said analog comparator output becomes high, which occurs when said output voltage level reaches said low threshold level and said pair of switches turn on, and
wherein when said output voltage level reaches said high threshold level, said analog comparator output becomes low and said first counter stops counting and stores its last value, which represents the measured turn-on time, in said first register.
2. The DC-DC converter of claim 1 , wherein said high threshold level minus said low threshold level defines a hysteresis width of said analog comparator.
3. The DC-DC converter of claim 1 , wherein a voltage coming out of said pair of switches has a duty cycle controlled by said pulse width modulator.
4. The DC-DC converter of claim 1 , wherein the Non value is compared with a desired value Non_ref using said first digital comparator.
5. The DC-DC converter of claim 4 , wherein if Non<Non_ref, said up-down counter counts down to decrease a duty cycle of said pulse waves.
6. The DC-DC converter of claim 4 , wherein if Non>Non_ref, said up-down counter counts up to increase the duty cycle of said pulse waves.
7. The DC-DC converter of claim 4 , wherein a turn-on duration of said pair of switches represented by said Non value converges to said Non_ref at steady state.
8. The DC-DC converter of claim 1 , wherein once said output voltage level exceeds said high threshold level, said analog comparator output becomes low and said pair of switches turn off.
9. The DC-DC converter of claim 1 , wherein when said output voltage level is lower than said low threshold level, said analog comparator output is high and said pulse signals are passed through said pair of switches.
10. The DC-DC converter of claim 1 , further comprising:
a second counter; and
a second register operatively connected to said second counter,
wherein when said output voltage level reaches said low threshold level, said second counter stops counting and stores its value Noff in said second register, and
wherein said value Noff is a measure of said load current.
11. A method of controlling voltage in a direct current to direct current (DC-DC) converter, said method comprising:
electrically connecting a pair of switches to a load capacitor;
generating pulse signals with a pulse width modulator for driving said pair of switches;
controlling an output voltage level within a specified range using an analog comparator with hysteresis, wherein as said output voltage level rises above a high threshold level, an analog comparator output becomes low and starts skipping clock pulses, wherein as said output voltage level drops below a low threshold level, said analog comparator output becomes high and a clock signal is passed to said pair of switches to charge said load capacitor, and wherein said analog comparator is further adapted to compare said output voltage level with either said low threshold level or said high threshold level;
sending a clock signal to a first counter, wherein when said analog comparator output becomes low said first counter stops and stores its last value Non in a first register, wherein said first register is operatively connected to a first digital comparator, wherein said first digital comparator is operatively connected to an up-down counter, wherein said up-down counter is operatively connected to said pulse width modulator;
turning on said pair of switches such that a load current at a load resistor is supplied by said pair of switches, causing said load capacitor to charge; and
measuring a turn-on time using said first counter and said first register, wherein said turn-on-time is a time when said output voltage level discharges from said low threshold level to said high threshold level through said load capacitor,
wherein said first counter starts counting when said analog comparator output becomes high, which occurs when said output voltage level reaches said low threshold level and said pair of switches turn on, and
wherein when said output voltage level reaches said high threshold level, said analog comparator output becomes low and said first counter stops counting and stores its last value, which represents the measured turn-on time, in said first register.
12. The method of claim 11 , wherein said high threshold level minus said low threshold level defines a hysteresis width of said analog comparator.
13. The method of claim 11 , wherein a voltage coming out of said pair of switches has a duty cycle controlled by said pulse width modulator.
14. The method of claim 11 , wherein the Non value is compared with a desired value Non_ref using said first digital comparator.
15. The method of claim 14 , wherein if Non<Non_ref, said up-down counter counts down to decrease a duty cycle of said pulse waves, and wherein if Non>Non_ref, said up-down counter counts up to increase the duty cycle of said pulse waves.
16. The method of claim 14 , wherein a turn-on duration of said pair of switches represented by said Non value converges to said Non_ref at steady state.
17. The method of claim 11 , wherein once said output voltage level exceeds said high threshold level, said analog comparator output becomes low and said pair of switches turn off.
18. The method of claim 11 , wherein when said output voltage level is lower than said low threshold level, said analog comparator output is high and said pulse signals are passed through said pair of switches.
19. The method of claim 11 , further comprising operatively connecting a second register to a second counter, wherein when said output voltage level reaches said low threshold level, said second counter stops counting and stores its value Noff in said second register, and wherein said value Noff is a measure of said load current.
20. A direct current to direct current (DC-DC) converter comprising:
a pair of switches;
a load capacitor operatively connected to said pair of switches;
a pulse width modulator adapted to generate pulse signals for driving said pair of switches;
an analog comparator with hysteresis adapted to control an output voltage level within a specified range, wherein as said output voltage level rises above a high threshold level, an analog comparator output becomes low and starts skipping clock pulses, wherein as said output voltage level drops below a low threshold level, said analog comparator output becomes high and a clock signal is passed to said pair of switches to charge said load capacitor, and wherein said analog comparator is further adapted to compare said output voltage level with either said low threshold level or said high threshold level;
a first counter;
a first register operatively connected to said first counter, wherein when said analog comparator output becomes low said first counter stops and stores its last value Non in said first register;
a first digital comparator operatively connected to said first register;
an up-down counter operatively connected to said first digital comparator and said pulse width modulator;
a second counter; and
a second register operatively connected to said second counter,
wherein when said output voltage level reaches said low threshold level, said second counter stops counting and stores its value Noff in said second register,
wherein said value Noff is a measure of said load current and controls the size of said pair of switches,
wherein for low load current levels, said value of said Noff is high and said size of said pair of switches is decreased to reduce capacitive power losses, and
wherein for high load current levels, said value of said Noff is low and said size of said pair of switches is increased to reduce resistive power losses.