Average current and frequency control
Apparatuses, systems and methods for regulating the output currents of a power supply at a target output current include a buck converter module operably connected to a power source and a load. A first switch couples the power source to the buck converter module during a first period of a given operating cycle, while the buck converter module stores and provides electrical power to the load. During a second period, the buck converter may discharge the electrical power stored during the first period. A current sensor senses the currents during at least one of the first period and the second period and, over the operating cycle, the switching is adjusted so the average output current equals the target output current. Adjustments to the first and second period durations result in maximum and a minimum currents symmetrically disposed about the average current provided to the load during the operating cycle.
1. A power regulating device comprising:
a buck converter module configured, during an OFF period (t OFF ) of a current operating cycle (n), to provide an output current that decreases to a load until a minimum current threshold is reached, the OFF period (t OFF ) including a recover period (t D ) followed by a second period during which the output current corresponds to a decreasing ramp function.
2. The power regulating device of claim 1 , further comprising:
a driver module, coupled to the buck converter module, configured to:
sense an output voltage of the buck converter module;
determine the output current based on the output voltage; and
end the OFF period (t OFF ) when the output current reaches the minimum current threshold.
3. The power regulating device of claim 2 , wherein the output voltage during the OFF period (t OFF ) corresponds to a decreasing ramp function.
4. The power regulating device of claim 2 , wherein the driver module further comprises:
a period compare module which compares, over two or more operating cycles, an actual switching period to a target switching period; and
flushes out permutations in the output current.
5. The power regulating device of claim 2 , wherein, during an ON period (t ON ) of the current operating cycle (n), the driver module increases the output current to the load until a maximum current threshold is reached.
6. The power regulating device of claim 5 , wherein the driver module adjusts the maximum current threshold so that an operating frequency (F(n)) for the current operating cycle (n) is defined by:
F ( n )=1/( t (ON(n)) +t (OFF(n)) ).
7. The power regulating device of claim 6 , wherein the operating frequency (F(n)) satisfies an electro-magnetic compatibility (EMC) requirement.
8. The power regulating device of claim 1 ,
wherein the buck converter module comprises an inductor having an inductance (L); and
wherein an operating frequency (F(n)) for the current operating cycle (n) corresponds to a ratio of an output voltage to the inductance (L).
9. The power regulating device of claim 4 ,
wherein the load further comprises at least one light-emitting-diode (LED) unit; and
wherein an LED pixel driver module, coupled to the LED unit, rapidly changes the output current demanded by the load.
10. A power regulating device, comprising:
a buck converter module configured, during an OFF period (t OFF ) of a current operating cycle (n), to provide an output current that decreases to a load until a minimum current threshold is reached,
the buck converter module having an operating frequency (F(n)) over two or more operating cycles equal to a target switching period.
11. A system comprising:
a light emitting diode (LED) unit;
a power converter, coupled to the LED unit, providing an output voltage and an output current to the LED unit; and
a driver module, coupled to the power converter, which:
monitors the output voltage;
determines, based on the output voltage, the output current; and
during an OFF period (t OFF ) of a current operating cycle (n) of the LED unit:
decreases the output current until a minimum current threshold is reached; and
terminates the OFF period (t OFF ) when the output current reaches the minimum current threshold, the OFF period (t OFF ) including a recover period (t D ) followed by a second period during which the output current corresponds to a decreasing ramp function.
12. The system of claim 11 , wherein the driver module further comprises:
a current sensor comprising a sensing resistor coupled to an operational amplifier.
13. The system of claim 11 ,
wherein, during an ON period (t ON ) of the current operating cycle (n), the driver module increases the output current until a maximum current threshold is reached; and
wherein the maximum current threshold corresponds to an operating frequency (F(n)) defined by:
F ( n )=1/( t (ON(n)) +t (OFF(n)) ).
14. The system of claim 13 , wherein the operating frequency (F(n)) satisfies an electro-magnetic compatibility (EMC) requirement.
15. The system of claim 14 , wherein the power converter further comprises:
a buck converter module comprising an inductor having an inductance (L); and
wherein an operating frequency (F(n)) is defined by a ratio of the output voltage to the inductance (L).
16. The system of claim 12 , wherein the current sensor senses the output current during an ON period (t ON ) and the OFF period (t OFF ).
17. A method for providing adaptive on-time control of a light emitting diode (LED) unit, comprising:
monitoring an output voltage provided to a light emitting diode (LED) unit, the LED unit including, during a given operating cycle (n), an ON time (t ON ) and an OFF time (t OFF ), the OFF time (t OFF ) including a recover period (t D ) followed by a second period during which an output current corresponds to a decreasing ramp function;
determining, based on the output voltage, an output current provided to the LED unit;
increasing, during the ON time (t ON ), the output current until a maximum current threshold is reached.
18. The method of claim 17 ,
wherein a buck converter module, having an inductor with an inductance (L), provides the output voltage and the output current to the LED unit; and
wherein an operating frequency (F(n)) is defined by a ratio of the output voltage to the inductance (L).
19. The method of claim 17 , further comprising:
decreasing, during the OFF time (t OFF ), the output current until a minimum current threshold is reached, the maximum current threshold being selected based on an operating frequency (fin)) defined by:
F ( n )=1/( t (ON(n)) +t (OFF(n)) ).