Sensor-less operation and detection of CCM and DCM operation modes in synchronous switching power converters
Generally, described herein are embodiments of control schemes for sensor-less operation and detection of CCM and DCM in a switching power converter. In one aspect, embodiments of a controller are described that utilize dual control loops and do not require sensing the inductor current or any current in the converter which eliminates or reduces the challenges and problems associated with current sensing. Advantages of embodiments of methods described herein become more significant when used in ultra high switching frequency converters since embodiments of the controller result in eliminating the need for high-speed low-noise current sensing circuitries, when used in on-chip integrated power converters where sensing accuracy may be a more significant issue compared to on-board power converters, and in power converters with paralleled modules since embodiments of the controller eliminate sensing circuitries in each of the modules.
1. A method of sensor-less operation and detection of continuous conduction mode (CCM) and discontinuous conduction mode (DCM) in a switching power converter comprising:
determining a duty-cycle (D) of a control switch (S u ) of a switching power convertor;
determining a duty-cycle width ratio (D 1 ) of a synchronous rectifier switch (S 1 ) of the switching power convertor; and
controlling the switching power convertor such that duty-cycle width ratio (D 1 ) duty-cycle width ratio (D 1 ) is a function of the minimization of duty-cycle (D) such that an optimum duty-cycle width ratio (D 1 ) can be detected for CCM and DCM operation of the switching power convertor which allows detection by a sensor-less CCM-DCM (SLCD) power controller of a zero crossing time instant of a current through an inductor of the switching power convertor without sensing the current through the inductor, wherein controlling the power convertor such that duty-cycle width ratio (D 1 ) is a function of the minimization of duty-cycle (D) such that an optimum duty-cycle width ratio (D 1 ) can be detected for CCM and DCM operation of the switching power convertor comprises controlling the switching power convertor such that D 1 =D/D CCM ·(1−D CCM )=D/V o −V in ·(1−V o /V in ), where D CCM is a value of duty-cycle (D) in CCM, V o is an output voltage value of the power convertor, and V in is an input voltage of the power convertor.
2. The method of claim 1 , wherein the minimization of duty-cycle (D) comprises an iterative function with duty-cycle width ratio (D 1 ) being incremented or decremented based on a difference in sign between changes in duty-cycle (D) and duty cycle width ratio (D 1 ) such that a value of duty-cycle (D) moves toward its minimum possible value for a specific power stage.
3. The method of claim 2 , wherein the specific power stage is a buck converter power stage.
4. The method of claim 2 , wherein the iterative function is delayed by a number of switching cycles in order to make sure any disturbance caused by adjusting duty-cycle width ratio (D 1 ) is settled.
5. The method of claim 4 , wherein the number of switching cycles is four.
6. The method of claim 1 , wherein the switching power convertor has a switching frequency (f s ).
7. The method of claim 6 , wherein the switching frequency (f s ) can be varied by the control module as a function of the duty-cycle (D) such that
f
s
=
f
s
-
CCM
D
CCM
·
D
=
f
s
-
CCM
V
o
/
V
i
n
·
D
,
where f s-CCM is a CCM switching frequency, which is a maximum operation switching frequency of the power convertor, V o is an output voltage value of the power convertor, and V in is an input voltage of the power convertor.
8. A sensor-less continuous conduction mode (CCM) and discontinuous conduction mode (DCM) (SLCD) power controller comprised of:
a power converter comprised of:
a control switch (S u ), wherein S u has a duty-cycle (D);
a synchronous rectifier switch (S 1 ), wherein S 1 has a duty-cycle width ratio (D 1 ); and
an inductor; and
a control module, wherein the control module controls the power convertor such that duty-cycle width ratio (D 1 ) is a function of the minimization of duty-cycle (D) such that an optimum duty-cycle width ratio (D 1 ) can be detected for CCM and DCM operation of the power convertor which allows detection by the SLCD power controller of a zero crossing time instant of a current through the inductor without sensing the current through the inductor, wherein the minimization of duty-cycle (D) by the control module comprises an iterative function with duty-cycle width ratio (D 1 ) being incremented or decremented based on a difference in sign between changes in duty-cycle (D) and duty cycle width ratio (D 1 ) such that duty-cycle (D) moves toward its minimum possible value for a specific power stage, and wherein the iterative function is delayed by a number of switching cycles in order to make sure any disturbance caused by adjusting duty-cycle width ratio (D 1 ) is settled and the control module controls the power convertor such that D 1 =D/D CCM ·(1−D CCM ) =D/V o −V in ·(1−V o /V in ), where D CCM is a CCM value of duty-cycle (D) in CCM, V o is an output voltage value of the power convertor, and V in is an input voltage of the power convertor.
9. The SLCD power controller of claim 8 , wherein the specific power stage is a buck converter power stage.
10. The SLCD power controller of claim 8 , wherein the number of switching cycles is four.
11. The SLCD power controller of claim 8 , wherein the power convertor has a switching frequency (f s ).
12. The SLCD power controller of claim 11 , wherein the switching frequency ifs) can be varied by the control module as a function of the duty-cycle (D) such that
f
s
=
f
s
-
CCM
D
CCM
·
D
=
f
s
-
CCM
V
o
/
V
i
n
·
D
,
where f s-CCM is a CCM switching frequency, which is a maximum operation switching frequency of the power convertor, V o is an output voltage value of the power convertor, and V in is an input voltage of the power convertor.