The subject matter of this disclosure relates generally to current regulators.
Light emitting diode (LED) lighting systems are used in a variety of applications, including but not limited to instrument lighting, automotive headlamps, advertising, video displays and the like. In such applications, LED lighting systems can provide several advantages over incandescent lighting systems such as lower energy consumption, longer lifetime, smaller size and faster switching.
In an embodiment, a circuit comprises: a current regulator configured to selectively couple a first voltage supply to an energy storage device coupled to a load to regulate current through the load; and a voltage regulator configured to selectively couple a charge storage device to the load and to regulate a second voltage supply provided by the charge storage device.
In an embodiment, a method comprises: regulating, by a current regulator, current through a load, the load coupled to an energy storage device that is selectively coupled by the current regulator to a first voltage supply; charging a charge storage device with load current; and regulating, by a voltage regulator, a second voltage supply provided by the charge storage device, the charge storage device selectively coupled by the voltage regulator to the load.
In an embodiment, a lighting system comprises: a light emitting diode (LED); a storage capacitor; an inductor coupled in series with the LED; a current regulator configured to selectively couple a first voltage supply to the inductor to regulate current through the LED; and a voltage regulator configured to selectively couple the storage capacitor to the LED and to regulate a second voltage supply provided by the storage capacitor.
In accordance with an example scenario, a light emitting diode (LED) system includes a current regulator that uses a first voltage supply (e.g., 40V) to drive a current through an LED string and a second voltage supply (e.g., 3.3V to 5V) to control the LED system. The second voltage supply may be provided by a second voltage regulator or by a circuit extension of the first voltage supply. However, there may be financial costs associated with implementing these circuit arrangements in the power supply for the LED system.
In an embodiment, charge storage device 110 is coupled to load 104 and begins to charge from load current when the second voltage supply V2 is lower than the first target voltage. Charge storage device 110 is decoupled from load 104 when the second voltage supply V2 is higher than the first target voltage. Although charge storage device 110 can be designed to impede discharge when decoupled from the load current, charge storage device 110 will nonetheless slowly discharge until the second voltage supply V2 is lower than the first target voltage, at which time switch 112 will again couple charge storage device 110 to load 104 to start charging from the load current. Accordingly, the regulated second voltage supply V2 is generated by charge storage device 110. The charge storage device 110 is charged using load current provided by the first voltage supply V1.
Current regulator 102 selectively couples load 104 to the first voltage supply V1 using switch 106. Current regulator 102 is configured to regulate current through load 104 to a second target voltage. Energy storage device 103 (e.g., an inductor) provides current to load 104 when the first voltage supply V1 is decoupled from load 104.
Comparator 202 compares a voltage generated by LED string current (V_IREF) with a reference voltage (V_REF_IREF), and generates an output that controls or toggles (e.g., opens or closes) switch 216A to thereby couple or decouple high voltage supply (V_HV) from LED string 206. Inductor 204 is coupled in series with LED string 206 and can include one or more coils. LED string 206 can include one or more LEDs or other light emitting elements. Diode 207 is coupled in series with LED string 206 and storage capacitor 208, and can be, for example, a Schottky diode. Diode 207 is configured to decouple a low voltage supply (V_3V) across storage capacitor 208 from switch 216B, to prevent a discharge of storage capacitor 208 when switch 216B is closed. Storage capacitor 208 is configured to store charge when switch 216A is opened and to generate V_3V. Diode 210 is coupled to inductor 204 and configured to supply inductor 204 with current when V_HV is decoupled by switch 216A. In some embodiments, diode 210 is a free-wheeling diode configured to eliminate “fly back” (e.g., a sudden voltage spike) across inductor 204 when V_HV is decoupled by switch 216A.
Resistor 212 (R_IREF) is coupled in series with storage capacitor 208 and switch 216B and is used to transform the LED string current into a voltage (V_IREF). In some implementations, resistor 212 can be a resistive network or a variable resistor. Comparator 202 compares V_IREF with a reference voltage VREF_IREF and generates an output that controls switch 216A. Switch 216A is coupled to the output of comparator 202 and couples or decouples V_HV to LED string 206. Switch 216B controls the charge and discharge of storage capacitor 208.
Although the example circuit 200 is configured for an LED lighting application, circuit 100, and variations thereof, can also be used to achieve current regulation for other applications, such as those that could benefit from a low cost secondary voltage supply.
In an embodiment, a startup circuit or a dedicated startup voltage capacitor is coupled to circuit 200 to provide a startup voltage during a startup phase. When the startup voltage is sufficient to operate comparators 202, 214, and to drive switches 216A and 216B, switch 216A changes to CLOSE state. Switch 216B starts in OPEN state. This configuration of switches 216A, 216B causes a current to flow through inductor 204 and LED string 206. Because switch 216B is in OPEN state, storage capacitor 208 is charged by LED string current. Comparator 214 compares voltage V_3V with voltage reference V_REF_3V3, and if V_3V is higher than V_REF_V3V, switch 216B is changed to CLOSE state and the LED string current flows directly via switch 216B to resistor 212. Diode 207 prevents discharging of storage capacitor 208 through switch 216B when switch 216B is in CLOSE state.
In an embodiment, current regulation through LED string 206 is controlled by resistor 212, comparator 202, switch 216A, diode 210 and inductor 204 to maintain steady current flow through LED string 206. Resistor 212 transforms the LED string current into voltage V_IREF. V_IREF is compared with comparator 202 against voltage reference V_REF_IREF. If the current through LED string 206 is below V_REF_IREF, switch 216A changes to CLOSE state. If the current is above V_REF_IREF, switch 216A changes to OPEN state. When switch 216A is in OPEN state, V_HV is decoupled and diode 210 supplies inductor 204 with current. Inductor 204 drives the decreasing current through LED string 206 until the current is below V_REF_IREF, at which time switch 216A will change to CLOSE state again, coupling V_VH to inductor 204 and LED string 206.
In circuit 200, comparator 202 is regulating the current flow through LED string 206 to a target current and comparator 214 is regulating the voltage over storage capacitor 208 to a target voltage. Circuit 200 therefore is advantageous in that a single voltage supply V_HV can be used to drive current through a load (e.g., LED string 206) and to generate a secondary voltage supply that can be used to power at least a portion of circuit 200, thus reducing the overall cost of the power supply.
Referring to
Referring to
In an embodiment, process 400 can begin by charging a storage capacitor (402) of a circuit, such as a current regulator for a LED lighting application. If (404), the voltage across the storage capacitor is greater than a target voltage, the charging is stopped (406). Otherwise, the charging continues. For example, a switch controlled by a comparator output can shunt the storage capacitor when the voltage across the storage capacitor exceeds a target voltage as determined by the comparator output. While shunted, the capacitor will start to discharge over time and when the voltage across the capacitor drops below the target voltage, the switch is opened to allow current from the voltage supply to start charging the storage capacitor again. This regulated voltage across the storage capacitor can be used as a second voltage supply (e.g., a low voltage supply) to power components of the circuit, such as the comparator. In an embodiment, a diode coupled to the storage capacitor is used to prevent the storage capacitor from discharging through the switch, as described in reference to
In an embodiment, process 500 can begin by coupling a voltage supply to an inductor (502). For example, in an LED lighting application a high voltage supply can be used to supply LED string current through the inductor.
Process 500 can continue by transforming the load current into a voltage (504). For example, a resistor can be coupled in series with the load to transform the current into a voltage that changes with changes in the load current.
Process 500 can continue by determining if (506) the voltage exceeds a target voltage, and then decoupling the voltage supply from the inductor (508). For example, when the voltage exceeds the target voltage, a switch can be controlled by a comparator output to decouple the voltage supply, thus enabling the inductor to drive current to the load. In an embodiment, a free-wheeling diode can be coupled in series with the inductor to eliminate voltage spikes due to decoupling of the voltage supply, as described in reference to
Process 500 can continue by transforming the load current to a voltage (510), and if (512) the voltage drops below the target voltage, coupling the voltage supply to the inductor (502). Referring to
As shown in
While this document contains many specific implementation details, these should not be construed as limitations on the scope of what may be claimed but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a sub combination or variation of a sub combination.