Patent Description:
<CIT> and <CIT> both disclose an LED module with a single stage AC input flyback converter but do not disclose a resistor connected to a cathode of an LED array or a differential amplifier coupled to a variable dimming voltage.

<CIT> and <CIT> disclose an LED module with a single stage AC input converter, which is not a boost converter, but do not disclose a differential amplifier coupled to a variable dimming voltage and to a voltage across a resistor connected to a cathode of an LED array.

<CIT> discloses an LED module with a two stage AC input converter and a differential amplifier coupled to a variable dimming voltage to a voltage across a resistor connected to a cathode of an LED array but does not disclose a single stage AC input boost converter or a controller having an error amplifier coupled to an output voltage of the differential amplifier.

<CIT> discloses an LED module with a single stage DC input boost converter for driving an LED array and a differential amplifier coupled to a variable dimming voltage but does not disclose a single stage AC input boost converter or a differential amplifier is coupled to the voltage across a resistor connected to a cathode of an LED array said voltage being regulated to the variable dimming voltage.

<CIT> discloses an LED module with a single stage AC input SEPIC converter with a signal amplifier for amplifying a current sense voltage which is lower than an on-chip fixed reference voltage but does not disclose a differential amplifier coupled to a variable dimming voltage.

Embodiments include systems, methods, and apparatuses for driving and dimming one or more light emitting diodes (LEDs). In an embodiment, the LED module comprises a resistor connected to a cathode end of one or more LEDs and a ground. A voltage across the resistor is proportional to a current through the one or more LEDs. The claimed LED module includes a differential amplifier. A first input of the differential amplifier is coupled to the voltage across the resistor and a second input of the differential amplifier is coupled to a variable dimming voltage controlled by a user. The claimed LED module includes a controller for regulating an output voltage supplied to an anode end of the one or more LEDs. The controller includes an error amplifier having a first input coupled to a fixed internal reference voltage and a second input coupled to an output voltage of the differential amplifier. The claimed LED module includes a switching transistor coupled to the controller.

The controller turns the switching transistor on and off based on an output of the differential amplifier to vary the output voltage and the current through the one or more LEDs to adjust the brightness of the one or more LEDs.

In the following description, numerous specific details are set forth, such as particular structures, components, materials, dimensions, processing steps, and techniques, in order to provide a thorough understanding of the present embodiments. However, it will be appreciated by one of ordinary skill of the art that the embodiments may be practiced without these specific details. In other instances, well-known structures or processing steps have not been described in detail in order to avoid obscuring the embodiments. It will be understood that when an element as a layer, region, or substrate is referred to as being "on" or "over" another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" or "directly" over another element, there are no intervening elements present. It will also be understood that when an element is referred to as being "beneath," "below," or "under" another element, it can be directly beneath or under the other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly beneath" or "directly under" another element, there are no intervening elements present.

In the interest of not obscuring the presentation of embodiments in the following detailed description, some processing steps or operations that are known in the art may have been combined together for presentation and for illustration purposes and in some instances may have not been described in detail. In other instances, some processing steps or operations that are known in the art may not be described at all. It should be understood that the following description is rather focused on the distinctive features or elements of various embodiments described herein.

In some light emitting diode (LED) lighting applications, it may be desirable to have a dimming capability, where the user is able to control the brightness of the LEDs. Conventional LED drivers may include a dimming function, but these drivers may not be appropriate for a particular application and/or may not have certain desired features.

For example, an LED module that uses a rectified AC mains voltage as the power source may be connected to about <NUM> LEDs in series, which may result in a voltage drop of over <NUM> V. A boost converter may be used to step up the rectified voltage to over <NUM> V in conjunction with a self-oscillating switching circuit (i.e., no oscillator used). Accordingly, a general purpose (non-LED) off-the-shelf boost converter controller IC using self-oscillation may be the preferred choice of controller to use in the boost converter for economic reasons. However, because an internal reference voltage reference applied to an internal error amplifier may be a fixed reference voltage, a general purpose boost converter controller IC may not have a dimming capability. Accordingly, it may be desirable to design a LED driver using a conventional controller that also has a dimming function. This object is achieved by the claimed LED module and the claimed method of operating an LED module.

Referring now to <FIG>, a circuit diagram of a prior art <NUM>-stage AC input LED driver is shown. A boost converter <NUM> is used as a power factor correction (PFC) in a <NUM>-stage switching mode power supply (SMPS) to achieve a high quality input current to drive one or more (e.g., <NUM>) LEDs 102A-102N in a LED array <NUM>. Each of the one or more LEDs 102A-102N may be a blue-emitting GaN-based LED and may drop about <NUM> volts. Therefore, the boost converter <NUM> may boost a rectified AC mains voltage to, for example, <NUM> V. A phosphor may convert the blue LED light to white light for general illumination. The boost converter <NUM> may also maintain a stable output voltage irrespective of variation of input voltage and output load.

The AC mains voltage may be applied, via a fuse <NUM>, to an EMI filter <NUM>. A full diode bridge of a mains bridge rectifier <NUM> may rectify the AC voltage and an input capacitor <NUM> may at least partially filter the rectified AC voltage. A controller <NUM> may turn on a switching transistor <NUM> and a right end of an inductor <NUM> may be pulled to ground for charging the inductor <NUM>. The controller <NUM> may be a conventional transition-mode PFC controller. The controller <NUM> may be an integrated circuit (IC) configured to control PFC pre-regulators by using a transition mode technique.

The controller <NUM> may be used for a boost mode, a buck mode, or a buck-boost mode converter.

At a particular time in the switching cycle to generate a target current through the one or more LEDs 102A-102N, the switching transistor <NUM> may be turned off. This may result in the voltage at the right end of the inductor <NUM> rising to forward bias a diode <NUM>. This may recharge an output capacitor <NUM>, which may smooth the waveform and essentially supply a DC voltage to an output at a regulated current to an output SMPS stage <NUM>.

The switching transistor <NUM> may switch on and off at a relatively high frequency, such as approximately <NUM> to approximately <NUM>. The switching transistor <NUM> may couple a right end of an inductor <NUM> to either a ground or a positive voltage at the high frequency to generate the boosted output voltage. The switching transistor <NUM> may be a metal-oxide-semiconductor field-effect transistor (MOSFET) or a bipolar transistor that carries a steep slope voltage waveform, which may be a square wave voltage, at the switching frequency.

It should be noted that the term "square wave," as used herein, does not require the waveform to have rectangular pulses. Neither does it require the waveform to have a duty cycle of <NUM>% (i.e., having equal durations of high and low levels). In some applications, non-instantaneous switching and parasitic effects may result in non-rectangular waveforms. Accordingly, the term "square wave" means a switched voltage that swings between a high level and low level as a result of a switching transistor being turned on and off at times to achieve a target output voltage or current.

Accordingly, the high frequency square wave voltage may be generated with a relatively high voltage (e.g., up to <NUM> V), and a relatively large average current (e.g., up to <NUM> Amp). The output capacitor <NUM> may be used to somewhat filter the ripple to supply a regulated DC current. In one example, the square wave voltage may rapidly transition between ground and about <NUM> V. A drain node <NUM> of the switching transistor <NUM> may carry the square wave voltage. Any high frequency ripple in the current supplied may be acceptable since any high frequency ripple may not be perceived, as long as the peak current stays within the current rating of the one or more LEDs 102A-102N. A separate diode-coupled path containing a diode <NUM> may exist between the mains bridge rectifier <NUM> and the output capacitor <NUM>. The separate diode-coupled path may provide for a fast partial charge up upon start-up.

The output SMPS stage <NUM> may include at least a switching transistor <NUM>, a magnetic component <NUM> and a capacitor <NUM>. The output SMPS state <NUM> may convert the output voltage of the boost converter <NUM> into a current to drive the LED array <NUM>.

As shown in <FIG>, voltage feedback in the <NUM>-stage AC input LED driver may be a negative feedback system. A divided resistor, made up of a first resistor R1 and a second resistor R2 may be connected as a feedback signal to sense the boost converter output voltage at node A. The booster converter output voltage may be compared to a fixed reference voltage VRefOut in the controller <NUM>. By controlling the gate voltage of the switching transistor <NUM>, the voltage input into the controller <NUM> may be regulated to be essentially same as VRefOut. This may result in A-node voltage that is regulated to the required level.

The <NUM>-stage AC input LED driver may have good performance characteristics, but it may suffer from disadvantages of relatively high cost, low efficiency, large form factor, and increased design complexity.

Referring now to <FIG>, a block diagram illustrating a controller <NUM> is shown. The controller <NUM> may be a conventional PFC controller built on an integrated circuit (IC) and may be used as the controller <NUM> as shown in <FIG>. The controller <NUM> may include one or more pins connecting it to the LED module.

An inverting input (INV) pin <NUM> may invert an input of an error amplifier <NUM>. Information on an output voltage of a PFC pre-regulator may be fed into the INV pin <NUM> through a resistor divider.

A compensation (COMP) pin <NUM> is connected to an output of the error amplifier <NUM>. A compensation network (not shown) may be placed between this pin and the INV pin <NUM> to achieve stability of a voltage control loop and ensure a high power factor and low total harmonic distortion (THD).

A multiplier (MULT) pin <NUM> may be a main input to a multiplier <NUM>. The MULT pin <NUM> may be connected to the mains voltage via a resistor divider (not shown) and may provide a sinusoidal reference to a current loop.

A current sense (CS) pin <NUM> may be an input to a pulse width modulator (PWM) comparator <NUM>. Current flowing through the switching transistor <NUM> may be sensed through a resistor. The resulting voltage may be applied to this pin and compared with an internal sinusoidal-shaped reference, which may be generated by the multiplier <NUM>. This may be used to determine the turn-off of an external power transistor.

A zero crossing detector (ZCD) pin <NUM> may boost a demagnetizing sensing input of the inductor <NUM> for transition-mode operation. A negative-going edge may trigger the turn-on of the external power transistor.

A ground (GND) pin <NUM> may act as a current return for the signal part of the controller <NUM> and a gate driver.

A gate driver (GD) pin <NUM> may be a gate driver output. A totem pole output stage may be able to drive the external power transistor with a peak current of approximately <NUM> mA source and <NUM> mA sink. The high-level voltage of this the GD pin <NUM> may be capped at approximately <NUM> V to avoid excessive gate voltages in case it is supplied with a high supply voltage (Vcc).

A Vcc pin <NUM> may be the supply voltage of the signal part of the controller <NUM> and the gate driver. The supply voltage upper limit may be extended to <NUM> V min. to provide additional headroom for supply voltage changes.

The GD pin <NUM> may be connected to the gate of the external power transistor, which may be the switching transistor <NUM> as shown in <FIG>. The external power transistor may be connected to a suitable output circuit for generating a regulated voltage or current. The current through the external power transistor (and an inductor) may be sensed and a current feedback signal may be applied to the CS pin <NUM>.

A divided output voltage may be fed back into the error amplifier <NUM> via the INV pin <NUM>. The divided output voltage may be the R2 voltage as described above with reference to <FIG>. A non-inverting input of the error amplifier <NUM> may be coupled to an internal reference voltage Vref, which may be fixed at <NUM> volts. The multiplier <NUM> may be used to modulate the output of the error amplifier <NUM>, which may be compensated by an external capacitor connected to the COMP pin <NUM>, by a sinusoidal rectified AC mains voltage (e.g., <NUM>). The sinusoidal rectified AC mains voltage may be used as the input voltage for the PFC stage <NUM> as shown in <FIG>. The PWM comparator <NUM> may compare the current signal at the high switching frequency, such as <NUM>, to the output of the multiplier <NUM> to reset (i.e., turn off) the external power transistor during each switching cycle to achieve regulation.

The voltage and current feedback loops may cause the two inputs into the error amplifier <NUM> to match. The external power transistor may be turned back on when a zero current detector <NUM> detects that the current through the inductor <NUM> in <FIG> is approximately zero to reduce switching losses.

As with other conventional controllers, the error amplifier <NUM> is internal to the IC and the internal reference voltage is fixed. Accordingly, the controller <NUM> may not be able to drive series-connected LEDs using a dimming controller, since the error amplifier <NUM> compares the divided output voltage to a fixed <NUM> volt reference. An LED driver that uses this control but has a dimming function may be desirable.

Embodiments of the invention are explained in the following with the aid of <FIG>.

Referring now to <FIG>, a circuit diagram of a single stage AC input boost converter to directly drive and dim LEDs is shown. The single stage circuit uses a boost converter as both the PFC stage and output stage to drive the LED array. The LED array is directly connected to the boost output. Unlike the <NUM>-stage AC input LED driver shown in <FIG>, no additional output SMPS stage (as shown as output SMPS stage <NUM>) is needed. As described below, the average output voltage control of the boost converter is changed to average output current control to control the LED current for dimming purposes.

A single stage boost converter <NUM> is used as the PFC and the output stage to achieve a high quality input current to drive one or more (e.g., <NUM>) LEDs 302A-302N in series in a LED array <NUM>. Each of the one or more LEDs 302A-302N may be a blue-emitting GaN-based LED and may drop about <NUM> volts. Therefore, the boost converter <NUM> may boost a rectified AC mains voltage to at least <NUM> V to drive the one or more LEDs 302A-302N. A phosphor may convert the blue LED light to white light for general illumination. The boost converter <NUM> may also maintain a stable output voltage irrespective of variation of input voltage and output load.

The AC mains voltage is applied, via a fuse <NUM>, to an EMI filter <NUM>. A full diode bridge of a mains bridge rectifier <NUM> rectifies the AC voltage and an input capacitor <NUM> at least partially filters the rectified AC voltage. A first controller <NUM> and a second controller <NUM> may operate together to turn on a switching transistor <NUM> and a right end of an inductor <NUM> is pulled to ground for charging the inductor <NUM>. The first controller <NUM> is similar to the controller <NUM> described above with reference to <FIG>.

At a particular time in the switching cycle to generate a target current through the one or more LEDs 302A-302N, the switching transistor <NUM> is turned off. This results in the voltage at the right end of the inductor <NUM> rising to forward bias a diode <NUM>. This recharges an output capacitor <NUM>, which smooths the waveform and essentially supply a DC voltage at a regulated current to the one or more LEDs 302A-302N.

The switching transistor <NUM> may switch on and off at a relatively high frequency, such as approximately <NUM> to approximately <NUM>. The switching transistor <NUM> couples a right end of an inductor <NUM> to either a ground or a positive voltage at the high frequency to generate the boosted or output voltage. The switching transistor <NUM> may be a metal-oxide-semiconductor field-effect transistor (MOSFET) or a bipolar transistor that carries a steep slope voltage waveform, which may be a square wave voltage, at the switching frequency.

There is a separate diode-coupled path containing a diode <NUM> between the mains bridge rectifier <NUM> and the output capacitor <NUM>. The separate diode-coupled path provides for a fast partial charge up upon start-up. Upon start-up, the output capacitor <NUM> voltage may be less than the rectified mains voltage. The forward biasing of the diode <NUM> quickly charges the output capacitor <NUM> to the rectified mains voltage. Thereafter, the voltage across the output capacitor <NUM> is increased to the regulated level and the diode <NUM> becomes reverse biased.

Voltage feedback in the single stage boost converter <NUM> is based on an output current of the LED array <NUM>. As shown in <FIG>, the divided resistor made up of R1 and R2 has been changed to a resistor R3, which is connected to the LED array <NUM> and senses the LED array current. The R3 voltage is used as feedback signal of the second controller <NUM>. The R3 voltage is compared to a variable reference voltage VRefDim. The VRefDim may vary with a dimming command, which may be input through any conventional means, such as a dial, knob, or digital input. The higher the value of VRefDim, the higher the current required from the boost converter <NUM>.

The second controller <NUM> outputs an error signal as an input to the first controller <NUM>. The error signal represents the difference between the R3 voltage and the VRefDim. The first controller <NUM> uses the error signal as a feedback signal to be compared to VRefOut, which is a fixed reference voltage. By controlling the gate voltage of the switching transistor <NUM>, the R3 voltage is regulated to be essentially the same as VRefDim. This regulates the LED current to a required level. As VRefDim varies with a dimming command, the LED current will change, and the LED array <NUM> is dimmed as required.

Because of the high output voltage of the boost converter <NUM>, the LED array <NUM> may have a high total forward voltage. This may help improve circuit efficiency due to lower current and circuit losses. Depending on the application requirements, high-voltage (multi-junction) LEDs may be used in the LED array <NUM> to reduce the number of LEDs needed to achieve the high total forward voltage. The single stage AC input boost converter may be used in different configurations to directly drive and dim LEDs.

Referring now to <FIG>, a circuit diagram of a single stage AC input boost converter <NUM> that uses a universal <NUM>-<NUM> V AC input voltage to directly drive and dim one or more LEDs 402A-402N is shown.

A single stage boost converter <NUM> is used as the PFC and the output stage to achieve a high quality input current as well as to drive one or more (e.g., <NUM>) LEDs 402A-402N. The one or more LEDs 402A-402N may be single junction LEDs connected in series. Alternatively, the one or more LEDs 402A-402N may be multi-junction LEDs connected in series.

Each of the one or more LEDs 402A-402N may be a blue-emitting GaN-based LED. Each single junction LED may drop about <NUM> volts, thus <NUM> LEDs in series may drop <NUM> V. Therefore, the boost converter <NUM> may boost a rectified AC mains voltage to approximately <NUM> V to drive the one or more LEDs 402A-402N. A phosphor may convert the blue LED light to white light for general illumination. The boost converter <NUM> may also maintain a stable output voltage irrespective of variation of input voltage and output load.

The AC mains voltage may be applied, via a fuse <NUM>, to an EMI filter <NUM>. A full diode bridge of a mains bridge rectifier <NUM> rectifies the AC voltage and an input capacitor <NUM> at least partially filters the rectified AC voltage. A controller <NUM> turn on a switching transistor <NUM> and a right end of an inductor <NUM> is pulled to ground for charging the inductor <NUM>. The controller <NUM> is similar to the controller <NUM> described above with reference to <FIG>.

At a particular time in the switching cycle to generate a target current through the one or more LEDs 402A-402N, the switching transistor <NUM> may be turned off. This results in the voltage at the right end of the inductor <NUM> rising to forward bias a diode <NUM>. This charges an output capacitor <NUM>, which smooths the waveform and essentially supplies a DC voltage at a regulated current to the one or more LEDs 402A-402N.

The switching transistor <NUM> may switch on and off at a relatively high frequency, such as approximately <NUM> to approximately <NUM>. The switching transistor <NUM> couples a right end of an inductor <NUM> to either a ground or a positive voltage at the high frequency to generate the boosted or decreased output voltage. The switching transistor <NUM> may be a metal-oxide-semiconductor field-effect transistor (MOSFET) or a bipolar transistor that carries a steep slope voltage waveform, which may be a square wave voltage, at the switching frequency.

There is a separate diode-coupled path containing a diode <NUM> between the mains bridge rectifier <NUM> and the output capacitor <NUM>. The separate diode-coupled path provides for a fast partial charge up upon start-up. Upon start-up, the output capacitor <NUM> voltage may be less than the rectified mains voltage. The forward biasing of the diode <NUM> quickly charges the output capacitor <NUM> to the rectified mains voltage. Thereafter, the voltage across the output capacitor <NUM> increases to the regulated level and the diode <NUM> becomes reverse biased.

Voltage feedback in the single stage boost converter <NUM> is based on an output current of the LED array <NUM>. An operational amplifier U1 is used to amplify a difference between R3 voltage representing the current through the one or more LEDs 402A-402N and a VRefDim representing a dimming command or level. The output of the operational amplifier U1 is scaled down via a resistor divider R5/R6 and then connected as the feedback signal of the controller <NUM>. A capacitor C1 is used as frequency compensation for the operational amplifier U1.

Referring now to <FIG>, a circuit diagram of a single stage AC input boost converter <NUM> configured with the controller <NUM> and a first dimming circuit <NUM> is shown. The circuit diagram illustrates aspects of a typical application circuit that produces a driving current based on an input of a wide-range mains voltage. It should be noted that well-known structures, including one or more resistors, diodes, and capacitors, and processing steps have not been described in detail in order to avoid obscuring the embodiments described herein.

The single stage AC input boost converter <NUM> directly drive and dim a series string of LEDs 32A-32N. The series string of LEDs 32A-32N may be <NUM> LEDs in series, each dropping around <NUM> volts. The single stage AC input boost converter <NUM> may generate, for example, <NUM> V. Multi-junction LEDs may instead be used. As shown in <FIG>, the controller <NUM> may be an IC having an on-chip error amplifier and an internal fixed voltage reference coupled to an input of the error amplifier. The controller <NUM> is not typically used for supplying a dimmable control for LEDs.

Voltage feedback in the single stage AC input boost converter <NUM> may be provided by a differential amplifier <NUM> and a dimming controller <NUM>. The series string of LEDs 32A-32N may be driven by the regulated current output of the single stage AC input boost converter <NUM>.

There is a separate diode-coupled path containing a diode <NUM> between a rectified AC mains voltage, provided by a full diode bridge <NUM>, and an output capacitor <NUM>. The separate diode-coupled path provides for a fast partial charge up upon start-up. Upon start-up, the output capacitor <NUM> voltage may be less than the rectified mains voltage. The forward biasing of the diode <NUM> quickly charges the output capacitor <NUM> to the rectified mains voltage.

Thereafter, the voltage across the output capacitor <NUM> increases to the regulated level and the diode <NUM> becomes reverse biased.

An input power supply may be an AC mains voltage <NUM>. A fuse <NUM> may couple the AC mains voltage <NUM> to the full diode bridge <NUM> to rectify the voltage. The rectified AC voltage is smoothed by an input capacitor <NUM>.

A DC voltage Vcc is supplied to a package pin, such as a DIP-<NUM> or SO-<NUM> terminal at terminal <NUM> of the controller <NUM> for powering the chip. The controller <NUM> may include a voltage regulator to power the internal circuitry.

After leaving the full diode bridge <NUM>, the rectified voltage is applied to a primary winding <NUM> (i.e., inductor) of a transformer. The voltage passing through a secondary winding <NUM> of the transformer is detected for a zero current crossing in the primary winding <NUM>. This indicates that the primary winding <NUM> has depleted its stored energy. The detected voltage signal is applied to a zero crossing detector (ZCD) pin <NUM> of the controller.

The controller <NUM> turns on a power switching transistor <NUM> when the zero crossing current is detected. The turning on of the switching transistor <NUM> couples the right end of the primary winding <NUM> to a ground in order to recharge the primary winding <NUM>. The switching transistor <NUM> is turned off when a voltage signal proportional to the instantaneous switching transistor <NUM> current, applied to the current sense (CS) pin <NUM> of the controller <NUM>, crosses a threshold set by the output of a multiplier <NUM> internal to the controller <NUM>. This turn-on and turn-off cycle repeats. The duty cycle (i.e., on time/cycle time) may be what is required to keep an input of an error amplifier <NUM>, which may be internal to the controller <NUM>, at <NUM> V.

When the switching transistor <NUM> turns off, the right end of the primary winding <NUM> rises to forward bias a diode <NUM> to charge the output capacitor <NUM> to supply a DC output voltage to the load. The switching frequency of the switching transistor <NUM> is determined by the self-oscillation. The switching frequency may be over <NUM>.

Instead of a resistor divider (shown in <FIG>) connected across the DC voltage output of the output capacitor <NUM>, where the selection of the resistors generates exactly <NUM> volts at the target output voltage, feedback voltage may be obtained from the output of the differential amplifier <NUM>. The feedback voltage may be applied to the INV pin <NUM> of the controller. From the INV pin <NUM>, the feedback voltage may be sent to the inverting input port of the error amplifier <NUM>.

An anode end of the series string of LEDs 32A-32N is connected to the top terminal of the output capacitor <NUM>. A low value sense resistor <NUM> is connected between the cathode end of the series string of LEDs 32A-32N and a ground. The voltage across the low value sense resistor <NUM> is proportional to the current through the series string of LEDs 32A-32N, which is related to the brightness level. The top node of the low value sense resistor <NUM> is coupled to a non-inverting input of the differential amplifier <NUM>, which amplifies the voltage difference between the voltage from the low value sense resistor <NUM> and a reference dimming voltage at its inputs. The differential amplifier <NUM> may also be connected as an operational amplifier (not shown).

The inverting input of the differential amplifier <NUM> is connected to a variable voltage source dim controller <NUM>, which outputs a dimming voltage Vdim. The level of Vdim is controlled by a user controlled input of the dimming controller <NUM>.

In order to achieve a steady state regulation of the current supplied to the series string of LEDs 32A-32N, the output of the differential amplifier <NUM> may be <NUM> volts. This ensures that the inputs into the error amplifier <NUM> match. Due to the high gain of the differential amplifier <NUM>, the Vdim signal and the voltage across the low value sense resistor <NUM> may be approximately matched when a target current is generated and supplied to the series string of LEDs 32A-32N. In this way, the level of Vdim, supplied by the dim controller <NUM> controls the brightness of the series string of LEDs 32A-32N while using the conventional controller <NUM> in the single stage AC input boost converter <NUM>.

Referring now to <FIG>, a circuit diagram of a single stage AC input boost converter <NUM> configured with the controller <NUM> and a second dimming circuit <NUM> is shown. The circuit diagram illustrates aspects of a typical application circuit that produces a driving current based on an input of a wide-range mains voltage. It should be noted that well-known structures, including one or more resistors, diodes, and capacitors, and processing steps have not been described in detail in order to avoid obscuring the embodiments described herein.

The single stage AC input boost converter <NUM> directly drives and dims the series string of LEDs 32A-32N. The single stage AC input boost converter <NUM> is similar to the single stage AC input boost converter described above with reference to <FIG>. However, the second dimming circuit <NUM> includes a resistor divider, including resistor <NUM> and resistor <NUM>, to match the voltage range of the output of the differential amplifier <NUM> and the INV pin <NUM> of the controller <NUM>. A resistor <NUM> and a capacitor <NUM> provide frequency compensation for a more stable operation of the negative feedback system to avoid oscillation.

Referring now to <FIG>, a circuit diagram illustrating a generic converter circuit <NUM> with a dimming function is shown. The generic converter circuit <NUM> includes an IC <NUM> with an error amplifier <NUM> and a fixed voltage reference source generating Vref, which is augmented with a dimming capability. The generic converter circuit <NUM> includes the second dimming circuit <NUM>. An on-chip controller <NUM> controls the duty cycle of a switching transistor <NUM> to achieve a regulated current through the series string of LEDs 32A-32N. The controller <NUM> is similar to the controller <NUM> described above with reference to <FIG>. The controller <NUM> uses at least the feedback from a differential amplifier <NUM> and an error amplifier <NUM> to keep the inputs into the error amplifier <NUM> equal (e.g., <NUM> volts). The controller <NUM> may use self-oscillation or an on-chip oscillator to control the switching frequency of a switching transistor. An output circuit <NUM> may contain a conventional inductor/capacitor/diode circuit commonly used in a boost configuration. It should be noted that other configurations may be used.

Although an input port of the differential amplifier <NUM> is shown directly coupled to the current sense resistor <NUM>, there may be other components that create a proportional signal applied to the amplifier <NUM>. The switching transistor may be internal or external to the IC <NUM>.

Claim 1:
An LED module comprising:
a resistor (R3, <NUM>) connected to a cathode end of an LED array (<NUM>, <NUM>) of the LED module, the LED array comprising one or more LEDs (<NUM>, <NUM>, <NUM>) and connected to ground, wherein a voltage across the resistor (R3, <NUM>) is proportional to a current through the one or more LEDs (<NUM>, <NUM>, <NUM>); and
a single stage AC input boost converter (<NUM>, <NUM>, <NUM>, <NUM>) comprising:
a differential amplifier (U1, <NUM>, <NUM>), wherein a first input of the differential amplifier (U1, <NUM>, <NUM>) is coupled to the voltage across the resistor (R3, <NUM>) and a second input of the differential amplifier (U1, <NUM>, <NUM>) is coupled to a variable dimming voltage (VRefDim, Vdim) controlled by a user;
a controller (<NUM>, <NUM>, <NUM>) for regulating an output voltage supplied to an anode end of the LED array (<NUM>, <NUM>) , wherein the controller (<NUM>, <NUM>, <NUM>) comprises an error amplifier having a first input coupled to a fixed internal reference voltage (VRefOut) and a second input coupled to an output of the differential amplifier (U1, <NUM>, <NUM>); and
a switching transistor (<NUM>, <NUM>, <NUM>) coupled to the controller (<NUM>, <NUM>, <NUM>, <NUM>), wherein the controller (<NUM>, <NUM>, <NUM>) turns the switching transistor (<NUM>, <NUM>, <NUM>) on and off based on the output of the differential amplifier (U1, <NUM>, <NUM>) to vary the output voltage of the single stage AC input boost converter (<NUM>, <NUM>, <NUM>, <NUM>) and the current through the one or more LEDs of the LED array (<NUM>, <NUM>) such that the voltage across the resistor (R3, <NUM>) is regulated to the variable dimming voltage (VRefDim, Vdim).