Patent Description:
Light-emitting diode (LED) light sources (such as, for example, LED light engines) are often used in place of or as replacements for conventional incandescent, fluorescent, or halogen lamps, and the like. LED light sources may comprise a plurality of light-emitting diodes mounted on a single structure in a suitable housing. LED light sources are typically more efficient and provide longer operational service as compared to incandescent, fluorescent, and halogen lamps. In order to illuminate properly, an LED driver is typically coupled between an alternating-current (AC) source and the LED light source for regulating the power supplied to the LED light source. The LED driver may regulate either the voltage provided to the LED light source to a particular value, the current supplied to the LED light source to a specific peak current value, or both the current and the voltage. Examples of LED drivers are described in greater detail in commonly-assigned <CIT>, and <CIT>, both entitled LOAD CONTROL DEVICE FOR A LIGHT-EMITTING DIODE LIGHT SOURCE.

<CIT> and <CIT> each disclose a load control device, which can be supplied from an AC input voltage or a DC input voltage, comprising a power converter, a load regulation circuit, a rectifier circuit configured to rectify the input voltage to generate a rectified voltage when the input voltage is an AC voltage, to pass through the input voltage when the input voltage is a DC voltage, and a control circuit.

<CIT> discloses a load control device comprising a power converter, a load regulation circuit, a rectifier circuit and a control circuit configured to disable the power converter during dimming.

<CIT> discloses a load control device comprising a power converter, a load regulation circuit, a rectifier circuit comprising one or more controllable switching circuits which are rendered non-conductive when the input voltage is an AC voltage and rendered conductive when the input voltage is a DC voltage.

<CIT> discloses a load control device comprising a power converter, a load regulation circuit, a rectifier circuit and a control circuit configured to control the power converter to adjust the magnitude of the bus voltage towards a target bus voltage.

As the electrical infrastructure changes to accommodate renewable energy sources (e.g., wind power, photovoltaic solar power, full cells, etc.), it is likely that there will be a movement towards DC power distribution as this is the native version of generation for many of these technologies. For example, photovoltaic solar arrays generate DC power and often this is directly stored in batteries. From there, power may be provided directly from the batteries, or it may be inverted to alternating current for use by appliances. With this anticipated move to a DC power bank, it would be desirable to provide power directly as DC power rather than convert it to AC power. Many AC electrical loads actually use DC power to perform their functions, and traditionally require rectification, and often, active power factor correction (PFC), to make the AC power useful to the electrical load. However, the rectification and active power factor correction operations introduce an efficiency loss.

As described herein, a load control device for controlling power delivered from a power source to an electrical load may comprise a power converter configured to generate a bus voltage across a bus capacitor; a load regulation circuit configured to receive the bus voltage and to control the power delivered to the electrical load; and a control circuit configured to control the load regulation circuit to control the power delivered to the electrical load. The control circuit may be configured to operate in an AC mode when an input voltage is an AC voltage, and in a DC mode when the input voltage is a DC voltage. The control circuit may be configured to disable the power converter in the DC mode, for example, when the power required by the load is less than a threshold amount. In addition, the control circuit may be configured to control the power converter circuit to adjust the magnitude of the bus voltage towards a target bus voltage, and adjust the target bus voltage as a function of the power required by the load, when the power required by the load is greater than the threshold amount in the DC mode. Additionally, or alternatively, the control circuit may be configured to reduce the target bus voltage in the DC mode.

The load control device may comprise a controllable switching circuit electrically coupled in series with the bus capacitor. The control circuit may be configured to render the controllable switching circuit conductive in the AC mode and non-conductive in the DC mode. The control circuit may include a rectifier circuit that includes input terminals and a DC detect circuit. The rectifier circuit may also include a plurality (e.g., two) controllable switching circuits. The DC detect circuit may be electrically coupled between the input terminals of the rectifier circuit. The DC detect circuit may be configured to render the controllable switching circuits of the rectifier circuit conductive when the voltage across the DC detect circuit is a DC voltage (e.g., and render them non-conductive when the voltage across the DC detect circuit is AC voltage). The load control device may also include a ripple detect circuit (e.g., AC ripple detect circuit) that is configured to receive a rectified voltage and generate a ripple detect signal that indicates whether AC ripple is present in the rectified voltage. The ripple detect circuit may provide the ripple detect signal to the control circuit, and the control circuit may be configured to determine whether the input voltage is AC voltage or DC voltage based on the ripple detect signal.

The rectifier circuit may be configured to rectify the input voltage to generate a rectified voltage when the input voltage is an AC voltage, and to pass through the input voltage when the input voltage is a DC voltage. The rectifier circuit may comprise: (<NUM>) first and second input terminals (e.g., AC input terminals); (<NUM>) first and second output terminals (e.g., DC output terminals); (<NUM>) a first diode configured to conduct current from the first input terminal to the first output terminal; (<NUM>) a second diode configured to conduct current from the second output terminal to the second input terminal; (<NUM>) a third diode configured to conduct current from the second input terminal to the first output terminal; (<NUM>) a fourth diode configured to conduct current from the second output terminal to the first input terminal; (<NUM>) a first controllable switching circuit (e.g., a MOSFET) coupled in parallel with the first diode; and (<NUM>) a second controllable switching circuit (e.g., a MOSFET) coupled in parallel with the second diode. The first and second switching circuits may be rendered non-conductive when a voltage across the input terminals is an AC voltage and rendered conductive when the voltage across the input terminals is a DC voltage. The rectifier circuit may also comprise a DC detect circuit that may be electrically coupled between the input terminals and may be configured to render the first and second controllable switching circuits conductive when the voltage across the DC detect circuit is a DC voltage.

<FIG> is a simplified block diagram of a load control device, e.g., a light-emitting diode (LED) driver <NUM>, for controlling the amount of power delivered to an electrical load, such as an LED light source <NUM> (e.g., an LED light engine), and thus the intensity of the electrical load. The LED light source <NUM> is shown as a plurality of LEDs connected in series, but may comprise a single LED, or a plurality of LEDs connected in parallel, or a suitable combination thereof, depending on the particular lighting system. The LED light source <NUM> may comprise one or more organic light-emitting diodes (OLEDs). The LED driver <NUM> may comprise a first input terminal <NUM> (e.g., a hot terminal) and a second input terminal <NUM> (e.g., a neutral terminal) that are adapted to be coupled to a power source (not shown), such as, e.g., an alternating-current (AC) power source, or a direct-current (DC) power source. The first and second input terminals <NUM>, <NUM> may be configured to receive an input voltage VIN, e.g., an AC mains input voltage, or a DC input voltage.

The LED driver <NUM> may comprise a radio-frequency (RFI) filter circuit <NUM>, a rectifier circuit <NUM>, a boost converter <NUM>, a load regulation circuit <NUM>, a control circuit <NUM>, a current sense circuit <NUM>, a memory <NUM>, a communication circuit <NUM>, and/or a power supply <NUM>. The RFI filter circuit <NUM> may minimize the noise provided on the AC mains. The rectifier circuit <NUM> may be a dynamic rectifier circuit configured to change its operation in response to whether an AC voltage or a DC voltage is present at the input terminals <NUM>, <NUM> (as will be described in greater detail below with reference to <FIG> and <FIG>). The rectifier circuit <NUM> may be configured to rectify the input voltage VIN to generate a rectified voltage VRECT when the input terminals are connected to an AC power source and an AC voltage is present at the input terminals <NUM>, <NUM>. The rectifier circuit <NUM> may be configured to pass through the input voltage VIN (e.g., not rectify the input voltage VIN) when the input terminals are connected to a DC power source and a DC voltage is present at the input terminals <NUM>, <NUM>.

The boost converter <NUM> may receive the rectified voltage VRECT and generate a boosted direct-current (DC) bus voltage VBUS across a bus capacitor CBUS (such as, e.g., an electrolytic capacitor). The boost converter <NUM> may comprise any suitable power converter circuit for generating an appropriate bus voltage, such as, for example, a flyback converter, a single-ended primary-inductor converter (SEPIC), a Ćuk converter, or other suitable power converter circuit. The boost converter <NUM> may operate as a power factor correction (PFC) circuit to adjust the power factor of the LED driver <NUM> towards a power factor of one. The LED driver <NUM> may comprise an input capacitor CIN (such as, e.g., a film capacitor) coupled across the input of the boost converter <NUM>. Examples of LED drivers having boost converters are described in greater detail in commonly-assigned <CIT>, and U. S Patent No. <CIT>, both entitled LOAD CONTROL DEVICE FOR A LIGHT-EMITTING DIODE LIGHT SOURCE.

The load regulation circuit <NUM> may receive the bus voltage VBUS and control the amount of power delivered to the LED light source <NUM>, for example, to control the intensity of the LED light source <NUM> between a low-end (i.e., minimum) intensity LLE (e.g., approximately <NUM>-<NUM>%) and a high-end (i.e., maximum) intensity LHE (e.g., approximately <NUM>%). An example of the load regulation circuit <NUM> may be an isolated, half-bridge forward converter. An example of the load control device (e.g., LED driver <NUM>) comprising a forward converter is described in greater detail in commonly-assigned <CIT>, entitled LOAD CONTROL DEVICE FOR A LIGHT-EMITTING DIODE LIGHT SOURCE. The load regulation circuit <NUM> may comprise, for example, a buck converter, a linear regulator, or any suitable LED drive circuit for adjusting the intensity of the LED light source <NUM>.

The control circuit <NUM> may be configured to control the operation of the boost converter <NUM> and/or the load regulation circuit <NUM>. The control circuit <NUM> may comprise, for example, a digital controller or any other suitable processing device, such as, for example, a microcontroller, a programmable logic device (PLD), a microprocessor, an application specific integrated circuit (ASIC), or a field-programmable gate array (FPGA). The control circuit <NUM> may generate a bus voltage control signal VBUS-CNTL, which may be provided to the boost converter <NUM> for adjusting the magnitude of the bus voltage VBUS towards a target bus voltage VBUS-TARGET. The control circuit <NUM> may receive a bus voltage feedback control signal VBUS-FB from the boost converter <NUM>, which may indicate the magnitude of the bus voltage VBUS.

The control circuit <NUM> may generate drive control signals VDR1, VDR2. The drive control signals VDR1, VDR2 may be provided to the load regulation circuit <NUM> for adjusting the magnitude of a load voltage VLOAD generated across the LED light source <NUM>, and/or the magnitude of a load current ILOAD conducted through the LED light source <NUM>, for example, to control the intensity of the LED light source <NUM> to a target intensity LTRGT. The control circuit <NUM> may adjust an operating frequency fOP and/or a duty cycle DCINV (e.g., an on-time TON as a percentage of the period T) of the drive control signals VDR1, VDR2 to adjust the magnitude of the load voltage VLOAD and/or the load current ILOAD. The control circuit <NUM> may receive a load voltage feedback signal VV-LOAD generated by the load regulation circuit <NUM>. The load voltage feedback signal VV-LOAD may indicate the magnitude of the load voltage VLOAD.

The current sense circuit <NUM> may receive a sense voltage VSENSE generated by the load regulation circuit <NUM>. The sense voltage VSENSE may indicate the magnitude of the load current ILOAD. The current sense circuit <NUM> may receive a signal-chopper control signal VCHOP from the control circuit <NUM>. The current sense circuit <NUM> may generate a load current feedback signal VI-LOAD, which may be a DC voltage indicating the average magnitude IAVE of the load current ILOAD. The control circuit <NUM> may receive the load current feedback signal VI-LOAD from the current sense circuit <NUM> and control the drive control signals VDR1, VDR2 accordingly. For example, the control circuit <NUM> may control the drive control signals VDR1, VDR2 to adjust a magnitude of the load current ILOAD to a target load current ITRGT to thus control the intensity of the LED light source <NUM> to the target intensity LTRGT (e.g., using a control loop). The control circuit <NUM> may be configured to determine a load power PLOAD presently being consumed by the LED light source <NUM> using the load voltage feedback signal VV-LOAD and the load current feedback signal VI-LOAD. The load current ILOAD may be the current that is conducted through the LED light source <NUM>. The target load current ITRGT may be the desired current that the control circuit <NUM> would ideally cause to be conducted through the LED light source <NUM> (e.g., based at least on the load current feedback signal VI-LOAD).

The control circuit <NUM> may be coupled to the memory <NUM>. The memory <NUM> may store operational characteristics of the LED driver <NUM> (such as, e.g., the target intensity LTRGT, the low-end intensity LLE, the high-end intensity LHE, etc.). The communication circuit <NUM> may be coupled to, for example, a wired communication link, or a wireless communication link, such as a radio-frequency (RF) communication link or an infrared (IR) communication link. The control circuit <NUM> may be configured to update the target intensity LTRGT of the LED light source <NUM> and/or the operational characteristics stored in the memory <NUM> in response to digital messages received via the communication circuit <NUM>. The LED driver <NUM> may be operable to receive a phase-control signal from a dimmer switch for determining the target intensity LTRGT for the LED light source <NUM>. The power supply <NUM> may receive the rectified voltage VRECT and generate a direct-current (DC) supply voltage Vcc for powering the circuitry of the LED driver <NUM>.

The LED driver <NUM> may also comprise a ripple detect circuit <NUM>, which may receive the rectified voltage VRECT and may generate a ripple detect signal VRIP-DET that may indicate whether AC ripple is present in the rectified voltage VRECT (i.e., whether an AC voltage is coupled to the input terminals <NUM>, <NUM>). The control circuit <NUM> may receive the ripple detect signal VRIP-DET, and may operate in an AC mode if an AC voltage is coupled to the input terminals <NUM>, <NUM>, or a DC mode if a DC voltage is coupled to the input terminals. The ripple detect circuit <NUM> may also be coupled to receive the input voltage VIN and/or the bus voltage VBUS. The LED driver <NUM> may also comprise a controllable switching circuit <NUM> (e.g., including a MOSFET) electrically coupled in series with the bus capacitor CBUS for disconnecting the bus capacitor, as will be described in greater detail below.

When operating in the AC mode, the control circuit <NUM> may enable the operation of the boost converter <NUM> to generate the bus voltage VBUS across the bus capacitor CBUS. The control circuit <NUM> may render the controllable switching circuit <NUM> conductive and may control the magnitude of the bus voltage VBUS to a maximum magnitude VBUS-MAX (e.g., approximately <NUM> volts). The control circuit <NUM> may also operate the boost converter <NUM> as a PFC circuit during the AC mode to adjust the power factor of the LED driver <NUM> towards a power factor of one.

When operating in the DC mode, the control circuit <NUM> may be configured to disable the operation of the boost converter <NUM> to reduce power loss in the LED driver <NUM>, for example, due to the power loss in the boost converter when enabled. When disabled, the boost converter <NUM> may pass through the DC voltage from the input terminals <NUM>, <NUM>, and the bus voltage VBUS may have a minimum magnitude VBUS-MIN (e.g., approximately <NUM> volts). When operating in the DC mode, the control circuit <NUM> may be configured to enable the boost converter <NUM> during a startup routine of the LED driver <NUM>, and disable the boost converter during normal operation.

The control circuit <NUM> may render the controllable switching circuit <NUM> non-conductive to disconnect the bus capacitor CBUS in the DC mode because the bus capacitor CBUS may not be required when a DC voltage is present at the input terminals <NUM>, <NUM>. The LED driver <NUM> may also comprise a capacitor CFILM (e.g., a film capacitor) coupled across the input of the load regulation circuit <NUM> for supplying high-frequency current that may be required to circulate through the load regulation circuit. Because the bus capacitor CBUS may comprise one or more electrolytic capacitors, disconnecting the bus capacitor CBUS may increase the lifetime of the LED driver <NUM>. In addition, disconnecting the bus capacitor CBUS may reduce an inrush current conducted by the LED driver <NUM> when power is first applied to the input terminals <NUM>, <NUM>.

The control circuit <NUM> may also enable the operation of the boost converter <NUM> in the DC mode when the power PLOAD required by LED light source <NUM> exceeds a threshold amount PTH (e.g., approximately <NUM>%). In addition, the control circuit <NUM> may also be configured to control the target bus voltage VBUS-TARGET as a function of the power PLOAD required by LED light source <NUM>, for example, as shown in <FIG>. The control circuit <NUM> may be configured to adjust the target bus voltage VBUS-TARGET linearly between the minimum magnitude VBUS-MIN and the maximum magnitude VBUS-MAX when the power PLOAD required by LED light source <NUM> is above the threshold amount PTH. The control circuit <NUM> may be configured to control the target bus voltage VBUS-TARGET using open loop control, for example, by using a lookup table to determine the target bus voltage VBUS-TARGET in response to the target intensity LTRGT and/or target load current ITRGT. The control circuit <NUM> may also be configured to control the target bus voltage VBUS-TARGET using closed loop control, for example, by using the load voltage feedback signal VV-LOAD and the load current feedback signal VI-LOAD to determine the power PLOAD required by LED light source <NUM>. The control circuit <NUM> may be configured to learn the target intensity LTRGT and/or the target load current ITRGT at which the power PLOAD required by LED light source <NUM> exceeds the threshold amount PTH (e.g., during a startup routine).

The control circuit <NUM> may be configured to temporarily increase the magnitude of the bus voltage VBUS during transient events (e.g., when increasing and/or decreasing the target intensity LTRGT and/or the target load current ITRGT).

Rather than disabling the boost converter <NUM> in the DC mode, the control circuit <NUM> may also scale back the operation of the boost converter (e.g., reduce the target bus voltage VBUS -TARGET) so as to reduce losses in the boost converter.

<FIG> is an example diagram of an AC ripple detect circuit <NUM> for an LED driver. The AC ripple detect circuit <NUM> may be an example of the AC ripple detect circuit <NUM> of the LED driver <NUM> shown in <FIG>. The AC ripple detect circuit <NUM> may include resistors R310, R312, capacitor C314, and diodes D316, D318. The AC ripple detect circuit <NUM> may receive the rectified voltage VRECT and may generate the ripple detect signal VRIP-DET. The control circuit <NUM> may receive the ripple detect signal VRIP-DET and may determine whether AC voltage or DC voltage is connected to the input terminals (e.g., the input terminals <NUM>, <NUM>). For example, the control circuit <NUM> may receive the ripple detect signal VRIP-DET and determine whether AC ripple is present in the rectified voltage VRECT.

If AC voltage is present at the input terminals <NUM>, <NUM>, a full-wave rectified voltage may be present at the resistor R310. The full-wave rectified voltage may be twice the normal line frequency. The full-wave rectified voltage may be divided via the resistors R310, R312, and the divided voltage may charge the capacitor C314 and be fed through the diode D318 to generate the ripple detect signal VRIP-DET. If DC voltage is present at the input terminals <NUM>, <NUM>, the voltage present at the resistor R310 will not be characterized by a significant AC frequency component. As such, the capacitor C314 will not charge, resulting in the ripple detect signal VRIP-DET having a lower value (e.g., <NUM> volts) than instances where AC voltage is present at the input terminals <NUM>, <NUM>. Accordingly, the control circuit <NUM> may receive the ripple detect signal VRIP-DET, and may operate in an AC mode if an AC voltage is coupled to the input terminals <NUM>, <NUM>, or a DC mode if a DC voltage is coupled to the input terminals. The ripple detect circuit <NUM> may also be coupled to receive the input voltage VIN and/or the bus voltage VBUS.

<FIG> is a simplified schematic diagram of an isolated, half-bridge forward converter <NUM> and a current sense circuit <NUM> of an LED driver (e.g., the LED driver <NUM> shown in <FIG>). The forward converter <NUM> may be an example of the load regulation circuit <NUM> of the LED driver <NUM> shown in <FIG>. The current sense circuit <NUM> may be an example of the current sense circuit <NUM> of the LED driver <NUM> shown in <FIG>.

The forward converter <NUM> may comprise a half-bridge inverter circuit having two field effect transistors (FETs) Q410, Q412 for generating a high-frequency inverter voltage VINV from the bus voltage VBUS. The FETs Q410, Q412 may be rendered conductive and non-conductive in response to the drive control signals VDR1, VDR2. The drive control signals VDR1, VDR2 may be received from the control circuit <NUM>. The drive control signals VDR1, VDR2 may be coupled to the gates of the respective FETs Q410, Q412 via a gate drive circuit <NUM> (e.g., which may comprise part number L6382DTR, manufactured by ST Microelectronics). The control circuit <NUM> may generate the inverter voltage VINV at a constant operating frequency fOP (e.g., approximately <NUM>-<NUM>) and thus a constant operating period TOP. However, the operating frequency fOP may be adjusted under certain operating conditions. For example, the operating frequency fOP may be decreased near the high-end intensity LHE. The control circuit <NUM> may be configured to adjust a duty cycle DCINV of the inverter voltage VINV to control the intensity of an LED light source <NUM> towards the target intensity LTRGT. The control circuit <NUM> may adjust the duty cycle DCINV of the inverter voltage VINV to adjust the magnitude (e.g., the average magnitude IAVE) of the load current ILOAD towards the target load current ITRGT. The magnitude of the load current ILOAD may vary between a maximum rated current IMAX and a minimum rated current IMIN.

The inverter voltage VINV may be coupled to the primary winding of a transformer <NUM> through a DC-blocking capacitor C416 (e.g., which may have a capacitance of approximately <NUM>µF), such that a primary voltage VPRI is generated across the primary winding. The transformer <NUM> may be characterized by a turns ratio nTURNS (i.e., N<NUM>/N<NUM>), which may be approximately <NUM>:<NUM>. A sense voltage VSENSE may be generated across a sense resistor R422, which may be coupled in series with the primary winding of the transformer <NUM>. The secondary winding of the transformer <NUM> may generate a secondary voltage that may be coupled to the input terminals of a full-wave diode rectifier bridge <NUM> for rectifying the secondary voltage generated across the secondary winding. The positive output terminal of the rectifier bridge <NUM> may be coupled to the LED light source <NUM> through an output energy-storage inductor L426 (e.g., which may have an inductance of approximately <NUM> mH), such that the load voltage VLOAD may be generated across an output capacitor C428 (e.g., which may have a capacitance of approximately <NUM>µF).

The current sense circuit <NUM> may comprise an averaging circuit for producing the load current feedback signal VI-LOAD. The averaging circuit may comprise a low-pass filter comprising a capacitor C430 (e.g., which may have a capacitance of approximately <NUM> uF) and a resistor R432 (e.g., which may have a resistance of approximately <NUM> kΩ). The low-pass filter may receive the sense voltage VSENSE via a resistor R434 (e.g., which may have a resistance of approximately <NUM> kΩ). The current sense circuit <NUM> may comprise a transistor Q436 (e.g., a FET as shown in <FIG>) coupled between the junction of the resistors R432, R434 and circuit common. The gate of the transistor Q436 may be coupled to circuit common through a resistor R438 (e.g., which may have a resistance of approximately <NUM> kΩ). The gate of the transistor Q436 may receive the signal-chopper control signal VCHOP from the control circuit <NUM>. An example of the current sense circuit <NUM> may be described in greater detail in commonly-assigned No. <CIT>, entitled FORWARD CONVERTER HAVING A PRIMARY-SIDE CURRENT SENSE CIRCUIT.

<FIG> is a simplified schematic diagram of an example rectifier circuit <NUM> (e.g., the rectifier circuit <NUM> of the LED driver <NUM> shown in <FIG>). The rectifier circuit <NUM> may comprise first and second input terminals <NUM>, <NUM> (e.g., AC input terminals) and first and second output terminals <NUM>, <NUM> (e.g., DC output terminals). The rectifier circuit <NUM> may comprise a full-wave rectifier including four diodes <NUM>, <NUM>, <NUM>, <NUM>. The first diode <NUM> may be electrically coupled between the first input terminal <NUM> and the first output terminal <NUM>, and may be configured to conduct current from the first input terminal <NUM> to the first output terminal <NUM>. The second diode <NUM> may be electrically coupled between the second input terminal <NUM> and the second output terminal <NUM>, and may be configured to conduct current from the second output terminal <NUM> to the second input terminal <NUM>. The third diode <NUM> may be electrically coupled between the second input terminal <NUM> and the first output terminal <NUM>, and may be configured to conduct current from the second input terminal <NUM> to the first output terminal <NUM>. The fourth diode <NUM> may be electrically coupled between the first input terminal <NUM> and the second output terminal <NUM>, and may be configured to conduct current from the second output terminal <NUM> to the first input terminal <NUM>.

The rectifier circuit <NUM> may comprise a first controllable switching circuit <NUM> (e.g., a MOSFET) having main terminals electrically coupled in parallel with the first diode <NUM>, and a second controllable switching circuit <NUM> (e.g., a MOSFET) having main terminals electrically coupled in parallel with the second diode <NUM>. The first and second diodes <NUM>, <NUM> may be body diodes of the first and second controllable switching circuits <NUM>, <NUM>, respectively, or may be implemented as separate parts. The rectifier circuit <NUM> may be configured to operate in an AC mode when a voltage (e.g., an input voltage) across the input terminals <NUM>, <NUM> is an AC voltage, and in a DC mode when the voltage across the input terminals is a DC voltage. The first and second switching circuits <NUM>, <NUM> may be rendered non-conductive in the AC mode (e.g., when the voltage across the input terminals is an AC voltage), and rendered conductive in the DC mode (e.g., when the voltage across the input terminals is a DC voltage).

The rectifier circuit <NUM> may further comprise a rectifier control circuit, such as a DC detect circuit <NUM>, coupled between the input terminals <NUM>, <NUM> to receive the voltage across the input terminals. The DC detect circuit <NUM> may be configured to generate gate drive voltages VG1, VG2 that may be coupled to gate terminals of the MOSFETs of the first and second controllable switching circuits <NUM>, <NUM>, respectively, for rendering the first and second controllable switching circuits conductive and non-conductive.

<FIG> illustrates example waveforms of the rectifier circuit <NUM> when the rectifier circuit is operating in the AC mode and in the DC mode. The DC detect circuit <NUM> may be configured to control the magnitudes of the first and second gate drive voltages VG1, VG2 towards a circuit common (e.g., approximately zero volts) to render the first and second controllable switching circuits <NUM>, <NUM> non-conductive in the AC mode when the input voltage (e.g., the voltage across the input terminals <NUM>, <NUM>) is an AC voltage. The DC detect circuit <NUM> may be configured to control the magnitudes of the first and second gate drive voltages VG1, VG2 towards a supply voltage Vcc (e.g., as generated by the power supply <NUM> of the LED driver <NUM> in <FIG>) to render the first and second controllable switching circuits <NUM>, <NUM> conductive in the DC mode when the input voltage (e.g., the voltage across the terminals <NUM>, <NUM>) is a DC voltage.

<FIG> is an example diagram of a DC detect circuit <NUM> for an LED driver. The DC detect circuit <NUM> may be an example of the DC detect circuit <NUM> of <FIG>. As such, the DC detect circuit <NUM> may be part of a rectifier circuit, such as the rectifier circuit <NUM> shown in <FIG>. The DC detect circuit <NUM> may include two input terminals, such as the first and second input terminals <NUM>, <NUM> (e.g., AC input terminals) of the rectifier circuit <NUM>. Further, the DC detect circuit may be connected to two output terminals through an AC/DC rectifier circuit, such as the first and second output terminals <NUM>, <NUM> (e.g., DC output terminals) of the rectifier circuit <NUM>. Accordingly, the DC detect circuit <NUM> may be configured to generate gate drive voltages for controlling controllable switching circuits, such as the gate drive voltages VG1, VG2 that are coupled to gate terminals of the MOSFETs of the first and second controllable switching circuits <NUM>, <NUM>, respectively, for rendering the first and second controllable switching circuits conductive and non-conductive. In this regard, the DC detect circuit may operate whether it is coupled to an AC voltage or to a DC voltage via the input terminals <NUM>, <NUM>.

The DC detect circuit <NUM> may include capacitors C702, C720, and C722, resistors R704, R714, R718, R726, and R730, Zener diodes Z706, Z708, and Z716, a diode D724, a MOSFET <NUM>, and an NPN transistor <NUM>. The DC detect circuit <NUM> may include a power supply, or use a power supply of the LED drive, such as the power supply <NUM>, for example.

When an AC voltage is coupled to the input terminals <NUM>, <NUM>, the combination of the capacitor C702 and resistor R704 will cause there to be a net zero DC voltage across the capacitor C702. As a result, the MOSFET <NUM> will be non-conductive and in diode mode across diode <NUM>. Further, when an AC voltage is coupled to the input terminals <NUM>, <NUM>, the combination of the capacitor C722 and resistor R726 will cause there to be a net zero DC voltage across the capacitor C722. For example, the NPN transistor <NUM> may see pulsing currents at its gate, rendering the NPN transistor <NUM> conductive and causing the capacitor C720 to discharge. The discharge of the capacitor C720 may cause the MOSFET <NUM> to be rendered non-conductive and in diode mode across the diode <NUM>. Accordingly, when an AC voltage is coupled to the input terminals <NUM>, <NUM>, the DC detect circuit will not drive either of the MOSFETs <NUM>, <NUM> to be conductive such that the diodes <NUM>, <NUM>, <NUM>, <NUM> act as a full-wave rectifier.

When a DC voltage is coupled to the input terminals <NUM>, <NUM>, the Zener diodes Z706, Z708 will clamp the input DC voltage and cause the capacitor C702 to charge. When the capacitor C702 is charged, the MOSFET <NUM> will turn on, which will drive the first gate drive voltage VG1 towards a supply voltage Vcc (e.g., as generated by the power supply <NUM> of the LED driver <NUM> in <FIG>) and render the MOSFET <NUM> conductive. Further, when a DC voltage is coupled to the input terminals <NUM>, <NUM>, the capacitor C722 will charge and there will not be pulsing currents flowing through R726 (e.g., as is seen when AC voltage is coupled to the input terminals). As a result, the NPN transistor <NUM> will be rendered non-conductive, which will drive the second gate drive voltage VG2 towards the supply voltage Vcc and render the MOSFET <NUM> conductive. When the MOSFETs <NUM>, <NUM> are conductive, the voltage losses across the diodes <NUM>, <NUM> are eliminated.

<FIG> is a simplified flowchart of an example control procedure <NUM> that may be executed by a control circuit of a load control device (e.g., the control circuit <NUM> of the LED driver <NUM>). For example, the control procedure <NUM> may be executed periodically to control the LED driver to operate in an AC mode or a DC mode in response to ripple detected on an input voltage of the LED driver. At <NUM>, the control circuit may determine whether the ripple detect signal VRIP-DET indicates that AC voltage or DC voltage is coupled to the input terminals (e.g., the input terminals <NUM>, <NUM>). If the control circuit determines that AC voltage is coupled to the input terminals at <NUM>, then the control circuit may operate in AC mode at <NUM>. For example, the control circuit may ensure that the bus capacitor is connected at <NUM>. For instance, the control circuit may connect the bus capacitor by closing a switch (e.g., the controllable switching circuit <NUM>) at <NUM>. The control circuit may also enable the boost converter at <NUM>, and set the target bus voltage to VBUS-MAX at <NUM>.

If the control circuit determines that DC voltage is coupled to the input terminals at <NUM>, then the control circuit may operate in DC mode at <NUM>. For example, the control circuit may ensure that the bus capacitor is disconnected at <NUM>. For instance, the control circuit may disconnect the bus capacitor by opening the switch (e.g., the controllable switching circuit <NUM>) at <NUM>. At <NUM>, the control circuit may determine whether the power PLOAD required by the electrical load exceeds a threshold amount PTH (e.g., approximately <NUM>%). If the control circuit determines that the power PLOAD required by the electrical load does not exceed the threshold amount PTH at <NUM>, then the control circuit may disable the boost converter at <NUM>. For example, the control circuit may disable the boost converter to reduce power loss in the LED driver, for example, due to the power loss in the boost converter when enabled. When disabled, the boost converter may pass through the DC voltage from the input terminals, and the bus voltage VBUS may have a minimum magnitude VBUS-MIN (e.g., approximately <NUM> volts). In some instances, when operating in the DC mode, the control circuit may be configured to enable the boost converter during a startup routine (not shown) of the LED driver, and disable the boost converter during normal operation.

If the control circuit determines that the power PLOAD required by the electrical load does exceed the threshold amount PTH at <NUM>, then the control circuit may enable the boost converter at <NUM>. At <NUM>, the control circuit may set the target bus voltage according to the power required. For example, the control circuit may be configured to control the target bus voltage VBUS-TARGET as a function of the power PLOAD required by LED light source <NUM>. The control circuit may be configured to adjust the target bus voltage VBUS-TARGET linearly between the minimum magnitude VBUS-MIN and the maximum magnitude VBUS-MAX when the power PLOAD required by LED light source is above the threshold amount PTH. The control circuit may be configured to control the target bus voltage VBUS-TARGET using open loop control, for example, by using a lookup table to determine the target bus voltage VBUS-TARGET in response to the target intensity LTRGT and/or target load current ITRGT. The control circuit may be configured to control the target bus voltage VBUS-TARGET using closed loop control, for example, by using the load voltage feedback signal VV-LOAD and the load current feedback signal VI-LOAD to determine the power PLOAD required by LED light source. The control circuit may be configured to learn the target intensity LTRGT and/or the target load current ITRGT at which the power PLOAD required by LED light source exceeds the threshold amount PTH (e.g., during a startup routine).

Claim 1:
A load control device (<NUM>) for controlling power delivered from a power source to an electrical load (<NUM>), the load control device (<NUM>) configured to receive an input voltage from the power source, the load control device (<NUM>) comprising:
a power converter (<NUM>) configured to generate a bus voltage;
a load regulation circuit (<NUM>) configured to receive the bus voltage and to control the power delivered to the electrical load (<NUM>);
a rectifier circuit (<NUM>, <NUM>) configured to receive the input voltage from the power source, the rectifier circuit configured to rectify the input voltage to generate a rectified voltage when the input voltage is an AC voltage, the rectifier circuit (<NUM>, <NUM>) configured to pass through the input voltage when the input voltage is a DC voltage,
a control circuit (<NUM>) configured to control the load regulation circuit (<NUM>) to control the power delivered to the electrical load (<NUM>), the control circuit (<NUM>) configured to operate in an AC mode when the input voltage is an AC voltage or in a DC mode when the input voltage is a DC voltage;
characterized in that
the rectifier circuit (<NUM>, <NUM>) comprises first and second controllable switching circuits (<NUM>, <NUM>), the first and second controllable switching circuits (<NUM>, <NUM>) arranged to be rendered non-conductive when the input voltage is an AC voltage and arranged to be rendered conductive when the input voltage is a DC voltage; and
wherein the control circuit (<NUM>), when operating in the DC mode during normal operation, is further configured to disable the power converter (<NUM>) when a power required by the electrical load (<NUM>) is less than or equal to a pre-determined threshold amount.