LED driver control using MCU

Abstract

A system and method for controlling current to an LED array are disclosed. The system includes a microcontroller and an external transistor. The microcontroller has access to relevant voltages in the circuit, including the voltage across a sense resistor, the voltage at the drain of the external transistor, and a high-voltage input. By monitoring these voltages, the microcontroller can control the gate input to the external transistor to control the current in the LED array. Furthermore, the microcontroller includes a means for dimming the LED array, if desired. This configuration allows post-manufacturing changes to the system's operation without requiring any hardware modifications.

Description

[0001] This disclosure describes systems and methods for controlling an LED array using a microcontroller without using a separate LED driver integrated circuit. Background Art

[0002] LED (light emitting diode) bulbs typically use an external driver integrated circuit (IC) to rectify and control the current through the LED array.

[0003] Figure 1 A general block diagram of an LED array control circuit is shown. Typically, an LED array control circuit includes a high-voltage AC rectifier and filter block 1, which provides a high-voltage (HV) signal to the circuit. The input to this HV AC rectifier and filter block 1 is typically line voltage, such as 120 or 240 VAC. The HV AC rectifier and filter block 1 rectifies this input voltage and generates an HV signal. The HV signal is typically a DC signal and serves as an input to an LED driver block 2. The LED driver block 2 typically includes a FET to control the path of current from the LED array to ground. The LED driver block 2 also includes circuitry for controlling the enabling and disabling of the FET. The HV signal is also used to power the LED array block. The LED array block 3 includes an LED array and typically also includes a mechanism for measuring the current flowing through the LED array. For example, a high-side or low-side sense resistor can be used to measure the current through the LED array. An inductor may also be placed in the LED array block 3. A microcontroller unit (MCU) 4 communicates with the LED driver block 2 and can be used to adjust the dimming level of the LED array. This block diagram can be implemented in various ways.

[0004] For example, Figure 2 One such circuit is shown, which includes an external LED driver IC 50 and associated circuitry. In this example, a full-wave rectifier 10 is used to generate a DC voltage, referred to as the HV signal. This DC voltage is provided to the anode of the first LED in the LED array 20. The LEDs in the LED array 20 are typically arranged in series. An inductor 30 is used to keep the current flowing through the LEDs in the LED array 20 more constant. One terminal of the inductor 30 is connected to the cathode of the LED array 20, such as the last LED in the LED array 20, and a second terminal is connected to the LED IC 50. Within the LED driver IC 50, there is a transistor, typically a field effect transistor (FET), where the output from the inductor is connected to the drain of the FET. The source of the FET can be connected to a sense resistor 60, which is provided external to the LED driver IC 50.

[0005] The anode of the diode 70 is connected to the output of the inductor 30. The cathode of the diode 70 is connected to the HV signal. When the FET is disabled, the diode is used to conduct current through the LED array 20.

[0006] Additionally, in some embodiments, the LED driver IC 50 includes a PWM input that allows a separate microcontroller 40 to provide an input that can be used to achieve a desired dimming level.

[0007] In operation, the LED driver IC 50 enables the FET, causing current to flow through the LED array 20, the inductor 30, the FET, and the sense resistor 60. This can be referred to as active mode. The LED driver IC monitors the voltage at the sense resistor 60, and when it reaches a predetermined value (not selectable), it turns off the FET. At this point, the inductor 30 continues to provide current, which is directed through the diode 70 and back into the LED array 20. This can be referred to as loop mode.

[0008] In some embodiments, the FET typically has a predetermined off-time, which can be determined based on a one-shot circuit located within the LED driver IC 50. In other words, once the FET is turned off due to the sense resistor 60 reaching a predetermined voltage, the FET remains off for a predetermined period of time before being enabled again. In some embodiments, the FET can have predetermined minimum and maximum off-times and on-times.

[0009] The PWM input is used to further control the amount of current flowing through the FET. When low, the PWM input turns the FET off. When high, the PWM input allows normal operation of the LED driver IC 50.

[0010] In other embodiments, a sense resistor may be placed on the high side of the FET to measure the current through the LED array 20 even when the FET is disabled.

[0011] Figure 2 A specific embodiment of the LED array control circuit is shown. Of course, the circuit can be implemented in other ways. In all of these embodiments, the LED driver IC 50 is separate from the microcontroller 40, and the only communication between the microcontroller 40 and the LED driver IC 50 is a signal from the microcontroller 40 to the LED driver IC 50 related to the dimming amount.

[0012] This approach has several disadvantages. First, the microcontroller 40 has no visibility into the operation of the LED array 20. In other words, the microcontroller 40 only provides a single output to the LED driver IC 50 and does not receive any input. Therefore, the microcontroller 40 cannot determine when a fault has occurred.

[0013] Furthermore, the microcontroller 40 is only able to perform limited calibration via the PWM input and is dependent on the frequency and DC voltage available to the LED driver IC 50 .

[0014] Finally, this approach requires multiple components; a microcontroller 40 to provide dimming control, and a separate LED driver IC 50 to control the current flowing through the LED array 20, which may require more real estate and increase cost.

[0015] Therefore, it would be beneficial if there were a system and method that reduced circuit complexity while providing greater flexibility. It would also be beneficial if changes to the circuit could be made using firmware updates rather than hardware changes. Summary of the Invention

[0016] A system and method for controlling current to an LED array are disclosed. The system includes a microcontroller and an external transistor. The microcontroller has access to relevant voltages in the circuit, including the voltage across a sense resistor, the voltage at the drain of the external transistor, and a high-voltage input. By monitoring these voltages, the microcontroller can control the gate input to the external transistor to control the current in the LED array. Furthermore, the microcontroller includes a means for dimming the LED array, if desired. In certain embodiments, this configuration allows post-manufacturing changes to the system's operation without requiring any hardware modifications.

[0017] According to one embodiment, a circuit for driving an LED array is disclosed. The circuit includes an LED array in communication with a high voltage (HV) signal; an inductor in series with the LED array; a sense resistor connected to ground; an external transistor including a drain, a source, and a gate, wherein the drain is in communication with the inductor and the source is in communication with the sense resistor such that when the external transistor is enabled, current flows from the HV signal through the LED array, the inductor, the external transistor, and the sense resistor; a diode disposed between the drain and the HV signal; and a microcontroller including: an output signal, referred to as a drive signal, that controls the gate of the external transistor; a first analog input, referred to as a sense signal, that communicates with the source of the external transistor; and a second analog input, referred to as a scaled drain signal, that communicates with a signal representing a voltage at the drain of the external transistor; wherein during a first initialization procedure, the microcontroller determines an amount of time for the sense signal to reach a predetermined voltage after the external transistor is enabled, referred to as an on-time value, and wherein during normal operation, the microcontroller uses the on-time value to control the drive signal. In certain embodiments, a microcontroller includes a timer and an analog comparator, wherein the analog comparator compares a sense signal with a predetermined voltage and generates an output when the sense signal is greater than the predetermined voltage. When the analog comparator output is asserted, the timer value is saved as an on-time value. In some embodiments, the value indicating the predetermined voltage is stored in a writable register and correlates to a desired dimming level. In certain embodiments, during a second initialization procedure, the microcontroller determines the amount of time it takes for the scaled drain signal to fall to a second predetermined voltage after the external transistor is disabled, referred to as the off-time value. During normal operation, the microcontroller uses the off-time value to control the drive signal. In some embodiments, the value indicating the second predetermined voltage is stored in a writable register and correlates to the desired dimming level. In certain embodiments, the microcontroller includes a timer and a second analog comparator, wherein the analog comparator compares the scaled drain signal with a second predetermined voltage and generates an output when the scaled drain signal is less than the second predetermined voltage. When the output of the second analog comparator is asserted, the timer value is saved as the off-time value. In some embodiments, the microcontroller adds the on-time value and the off-time value to calculate the period of the drive signal. In some embodiments, a timer within the microcontroller is used to control the drive signal based on the on-time value and the off-time value. In some embodiments, the circuit includes a scaling circuit that communicates with the drain of the external transistor to generate a scaled version of the voltage at the drain, referred to as a scaled drain signal. In some embodiments, the microcontroller includes a third analog input representing an HV signal, referred to as a scaled HV signal. In certain embodiments, the circuit includes a second scaling circuit that communicates with the HV signal to generate a scaled HV signal.In some embodiments, the microcontroller monitors the scaled HV signal before executing the first initialization procedure. In some embodiments, the controller waits for the scaled HV signal to reach a maximum value before executing the first initialization procedure. In some embodiments, the drive signal is directly connected to the gate of the external transistor.

[0018] According to another embodiment, a circuit for driving an LED array is disclosed. The circuit includes an LED array in communication with a high voltage (HV) signal; an inductor in series with the LED array; a sense resistor connected to ground; an external transistor including a drain, a source, and a gate, wherein the drain is in communication with the inductor and the source is in communication with the sense resistor such that when the external transistor is enabled, current flows from the HV signal through the LED array, the inductor, the external transistor, and the sense resistor; a diode disposed between the drain and the HV signal; and a microcontroller including an output signal, referred to as a drive signal, that controls the gate of the external transistor; and a first analog input, referred to as a sense signal, in communication with the source of the external transistor; wherein, after executing a first initialization procedure, the microcontroller controls the drive signal without monitoring the sense signal. In some embodiments, the microcontroller includes a second analog input that communicates with a signal representing the voltage at the drain of the external transistor, referred to as the scaled drain signal; and, during a second initialization procedure, the microcontroller determines an amount of time for the scaled drain signal to fall to a second predetermined voltage after the external transistor is disabled, referred to as the off-time value, and wherein, during normal operation, the microcontroller uses the off-time value to control the drive signal without monitoring the scaled drain signal.

[0019] According to another embodiment, a microcontroller for controlling an LED array is disclosed. The microcontroller includes: an output signal, referred to as a drive signal, configured to control the gate of an external transistor; a first analog input, referred to as a sense signal, in communication with the source of the external transistor; and a second analog input, referred to as a scaled drain signal, in communication with a signal representing a voltage at the drain of the external transistor; a timer; a writable register; and an analog comparator; wherein, during a first initialization procedure, the analog comparator compares the sense signal to a predetermined voltage, wherein a value indicative of the predetermined voltage is stored in the writable register; and wherein, when the output of the analog comparator is asserted, an amount of time, referred to as an on-time value, after the drive signal is asserted to cause the sense signal to reach the predetermined voltage is saved as the on-time value; and wherein, during normal operation, the microcontroller uses the on-time value to control the drive signal. In some embodiments, the microcontroller includes a second analog comparator and a second writable register, wherein the second analog comparator compares the scaled drain signal to a second predetermined voltage, wherein a value indicating the second predetermined voltage is stored in the second writable register; and wherein, when the output of the second analog comparator is asserted, the amount of time after the drive signal is deasserted for the scaled drain signal to fall to the second predetermined voltage, referred to as the off-time value, is saved as the off-time value; and wherein, during normal operation, the microcontroller uses the on-time value and the off-time value to control the drive signal. In some embodiments, the microcontroller includes a second analog comparator and a second writable register, wherein the second analog comparator compares the scaled drain signal to the second predetermined voltage, wherein a value indicating the second predetermined voltage is stored in the second writable register; and wherein, when the output of the second analog comparator is asserted, the total amount of time after the drive signal is asserted until the scaled drain signal falls to the second predetermined voltage is saved as a period, and wherein, during normal operation, the microcontroller uses the on-time value and the period to control the drive signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] For a better understanding of the present disclosure, reference is made to the accompanying drawings, wherein like elements are represented by like numerals, and wherein:

[0021] Figure 1 is a block diagram showing an LED array control circuit according to the prior art;

[0022] Figure 2 is an embodiment of a circuit for controlling an LED array according to the prior art;

[0023] Figure 3 is a circuit for controlling an LED array according to one embodiment;

[0024] Figure 4shows a timing diagram illustrating a scaled drain signal, a current through an LED array, a sense signal, and a drive signal according to one embodiment;

[0025] Figure 5 shows the internal architecture of a microcontroller according to one embodiment; and

[0026] Figures 6A-6B An initialization procedure that may be executed by a microcontroller is shown according to one embodiment. DETAILED DESCRIPTION

[0027] As described above, there are many limitations to using a separate LED driver IC 50. Therefore, a system and method that incorporates current control of the LED array 20 into a microcontroller would be very beneficial.

[0028] Figure 3 FIG. 1 shows a block diagram according to one embodiment. Figure 2 Components shown have the same function and are provided with the same reference numerals.

[0029] In this embodiment, an external transistor 110 is used. The external transistor can be a field effect transistor (FET). The drain of the external FET 110 is in communication with the second terminal of the inductor 30. For example, the drain can be electrically connected to the second terminal of the inductor. The source of the external FET 110 is in communication with the sense resistor 60. In some embodiments, the source is electrically connected to the sense resistor 60.

[0030] The microcontroller 100 is used to control the current flowing through the LED array 20. To do this, the microcontroller 100 controls the gate of the external FET 110, such as by using a drive signal. The microcontroller 100 also has an analog input, which is the voltage across the sense resistor 60, labeled "SENSE."

[0031] The microcontroller 100 may also have an analog input related to the voltage at the drain of the external FET 110. In some embodiments, this voltage may be much greater than the supply voltage for the microcontroller 100. Therefore, in some embodiments, a first scaling circuit, such as a voltage divider including resistors 120 and 121, may be used to scale the drain voltage to a voltage less than the supply voltage of the microcontroller 100. In other embodiments, any other circuit, such as a transformer or an operational amplifier circuit, may be used to scale the drain voltage. The output from this first scaling circuit may be referred to as a scaled drain. In other embodiments, the first scaling circuit may not be required, so that the drain voltage is connected directly to the microcontroller 100. In both embodiments, the microcontroller 100 receives an analog input representing the voltage at the drain of the external FET 110.

[0032] Similarly, the microcontroller 100 may also have an additional analog input related to the voltage of the HV signal. In some embodiments, a second scaling circuit, such as a second voltage divider including resistors 130 and 131, can be used to scale the high voltage (HV) signal to a voltage less than the supply voltage of the microcontroller 100. In other embodiments, any other circuit, such as a transformer or an operational amplifier circuit, can also be used to scale the high voltage (HV) signal. The output from the second scaling circuit can be referred to as scaling HV. In other embodiments, the second scaling circuit may not be required, so that the high voltage (HV) signal is directly connected to the microcontroller 100. In both embodiments, the microcontroller 100 receives an analog input representing the HV signal.

[0033] Thus, in some embodiments, the microcontroller 100 may have three analog inputs ("sense," "scaled drain," and "scaled high voltage") and provide one digital output (i.e., "drive signal"). In other embodiments, the three analog inputs may include a sense signal, an analog signal representing the drain voltage, and an analog signal representing the high voltage signal. In other embodiments, the three analog inputs may include the sense signal, the drain voltage, and the high voltage signal. Using these signals, the microcontroller 100 can control the external FET 110 and thereby control the current to the LED array 20.

[0034] Figure 4 A timing diagram illustrating the scaled drain signal, the current flowing through the LED array 20, the sense signal, and the drive signal is shown in accordance with one embodiment. Note that the drain voltage follows the same pattern as the scaled drain signal, only with a different amplitude. At time T0, the drive signal is asserted. This causes the scaled drain signal to drop to a voltage close to zero due to its connection to ground through the external FET 110 and the sense resistor 60. Current then begins to flow through the external FET 110 and the sense resistor 60. Due to the inductance and capacitance of the current path, the flow of current gradually increases, as shown by the sense signal and the current flowing through the LED array 20. Therefore, the sense signal can slowly ramp up from zero volts to a higher voltage. At the same time, the current flowing through the LED array 20 also ramps upward.

[0035] At time T1, the drive signal is deasserted, stopping the flow of current through the sense resistor 60, causing the sense signal to go to zero volts. The system then enters loop mode, where the inductor 30 provides current to continue activating the LED array 20. Ideally, the current provided by the inductor 30 is approximately the same as the current through the sense resistor 60 immediately before the external FET 110 is disconnected.

[0036] To provide this current, the voltage across inductor 30 changes almost instantaneously, as shown by the scaled drain signal. As current flows from inductor 30 through diode 70 and through LED array 20, it consumes the energy stored in inductor 30. Over time, as the energy in inductor 30 is depleted, the current flowing through LED array 20 decreases. Once the energy is depleted, the scaled drain signal drops.

[0037] At time T2, the cycle repeats, where the drive signal is again asserted.

[0038] Therefore, based on these signals, the microcontroller 100 can control the LED array 20. In addition, the microcontroller 100 can also control the dimming of the LED array 20 using these signals.

[0039] As described above, conventional LED driver ICs use the voltage across the sense resistor 60 and a fixed off-time to control the LED array 20. In some embodiments, conventional LED driver ICs may have some visibility into how much off-time is required. The present microcontroller 100 can more accurately and precisely control the LED array 20.

[0040] like Figure 4 As shown, there are two key parameters: the duration that the drive signal is asserted (on-time) and the duration that the drive signal is de-asserted (off-time). Both parameters can be used to control the current flowing through the LED array 20 and also control its brightness.

[0041] These parameters can be determined in a variety of ways.

[0042] exist Figure 5 In one embodiment shown in , the microcontroller 100 includes an analog comparator 200 to compare the sensed signal with a programmable voltage 210. The programmable voltage 210 can be stored in a writable register so that it can be modified if necessary. The output of the writable register can be communicated with a digital-to-analog converter (DAC), which converts the value in the writable register into an analog voltage. In other embodiments, the register value can be used to divide the incoming voltage. In certain embodiments, this programmable voltage 210 can be determined based on the amount of dimming desired. For example, when dimming is not desired, a first value can be used, while when a certain level of dimming is desired, a second value less than the first value can be used. In certain embodiments, the output from the analog comparator 200 can be used as an interrupt signal to the logic controller 220. In other embodiments, the output from the analog comparator 200 can be used to directly modify the variable value.

[0043] The logic controller 220 may be an embedded processing unit that executes instructions. These instructions may be stored in the memory 240. In certain embodiments, these instructions may be updated via firmware updates. The logic controller 220 may also include other functions, such as interrupts, a direct memory access (DMA) engine, and other functions. The instructions allow the logic controller 220 to perform the functions described herein.

[0044] Figures 6A-6B Two initialization procedures are shown that can be used to determine the on-time and the off-time.

[0045] like Figure 6A As shown, in one embodiment, the logic controller 220 asserts the drive signal, as shown in block 600. The assertion of the drive signal can be controlled directly by the logic controller 220, or it can be performed by the timer 230. Then, the timer 230 is started, as shown in block 610. When the voltage of the sense signal exceeds the programmable voltage 210, the output from the analog comparator 200 is asserted and an interrupt can be generated. In response, the logic controller 220 can read the current value of the timer 230 and save the value in the memory 240, as shown in block 620. This value can be referred to as the on-time value, and the process can be referred to as the on-time initialization procedure. The on-time value refers to the amount of time the drive signal should be asserted in order for the sense signal to reach the programmable voltage 210.

[0046] In another embodiment, the transfer of the value in timer 230 to memory 240 may be automated upon assertion of the output from analog comparator 200 , such as via a direct memory access (DMA) engine in logic controller 220 .

[0047] The microcontroller 100 may also include a second analog comparator 250 to compare the scaled drain signal to a second programmable voltage 260. This second programmable voltage 260 can be stored in a writable register so that it can be modified if necessary. The output of the writable register can be communicated with a digital-to-analog converter (DAC), which converts the value in the writable register into an analog voltage. This second programmable voltage 260 can be determined based on the desired amount of dimming. In some embodiments, the output from the second analog comparator 250 can be used as an interrupt signal to the logic controller 220.

[0048] In some embodiments, the second analog comparator 250 may be the same physical component as the analog comparator 200 , but configured with different inputs.

[0049] For example, Figure 6BAs shown, in one embodiment, the drive signal is deasserted, as shown in block 650. Then, the timer 230 is started, as shown in block 660. When the voltage of the scaled drain signal drops below the second programmable voltage 260, the output from the second analog comparator 250 is asserted and an interrupt may be generated. In response, the logic controller 220 may read the current value of the timer 230 and save the value in the memory 240, as shown in block 670. This value may be referred to as the off-time value, and this process may be referred to as an off-time initialization procedure.

[0050] In another embodiment, upon assertion of the output from the second analog comparator 250 , the transfer of the value in the timer 230 to the memory 240 may be automated, such as via a direct memory access (DMA) engine in the logic controller 220 .

[0051] In another embodiment, the microcontroller 100 may include one or more analog-to-digital converters (ADCs). In this embodiment, the logic controller 220 may sample the ADCs to monitor for increases in the sense signal or decreases in the scaled drain signal. As described above, the logic controller 220 may use the timer 230 to capture the on-time value and the off-time value. Note that this embodiment also utilizes Figure 6A and 6B The initialization procedure shown in .

[0052] In another embodiment, the timer is not reset after the first initialization procedure. In this embodiment, the timer value at the end of the second initialization procedure is the period of the drive signal. The off-time value can be calculated by subtracting the on-time value from the period. In this embodiment, block 660 can be omitted, and block 670 can be used to save the period of the drive signal to memory 240.

[0053] The on-time value and the off-time value can be used in a variety of ways. In one embodiment, these two values ​​are loaded into one or more timers, which are used to control the drive signal. The on-time value is used to determine the assertion time of the drive signal, while the off-time value can be used to determine the de-assertion time of the drive signal.

[0054] In another embodiment, the on-time value and the off-time value are added together to calculate the period of the drive signal waveform. Alternatively, as described above, the period can be determined directly by the second initialization procedure.

[0055] The timer 230 can then be loaded with the sum so that the timer 230 resets when the sum is reached. The timer 230 can also include a comparator so that the drive signal is asserted as long as the counter value is less than the on-time value. Thus, in this embodiment, the on-time value and the off-time value are used to calculate the frequency (or period) and duty cycle of the drive signal.

[0056] Once the initialization routine is complete, the microcontroller 100 no longer needs to monitor the sense or scaled drain signal. Instead, the microcontroller 100 relies solely on the timer value calculated earlier. This can reduce power consumption because the analog comparators 200, 250 and optionally the logic controller 220 can be placed in a low-power state after the initialization routine has been completed.

[0057] Therefore, in this embodiment, unlike conventional LED driver ICs, the microcontroller 100 does not continuously monitor the sense signal in order to control the external FET 110 .

[0058] This initialization procedure may also be performed whenever the desired dimming level is changed.

[0059] In some embodiments, for example, the initialization procedure may be performed periodically to account for variations in the high voltage signal.

[0060] In certain embodiments, the microcontroller 100 may execute one or both of the initialization routines at predetermined times. For example, the microcontroller 100 may monitor the scaled HV signal and execute one or both of the initialization routines when the scaled HV signal is at or near its maximum value. Specifically, the HV signal waveform may be a fully rectified sine wave, wherein a capacitor is used to maintain the voltage during the lower portion of the sine wave. Therefore, the voltage of the HV signal may vary by more than 50V between its peak value and its minimum value. This change in voltage may affect the duration determined by the two initialization routines. For example, if an initialization routine that determines the on-time value is executed when the HV signal is at its minimum voltage, the on-time value may be greater than if the initialization routine is executed when the HV signal is at its maximum value.

[0061] In other embodiments, one or both of the initialization routines may be performed when the HV signal is at or near its minimum value. In yet another embodiment, one or both of the initialization routines may be performed at or near both the maximum and minimum HV values, and the results may be averaged.

[0062] Therefore, when executing Figures 6A-6B Prior to the process shown, the microcontroller 100 may monitor the scaled HV signal, HURu, by using an analog-to-digital converter (ADC) 270 (see Figure 5 ). To detect a maximum value, the microcontroller 100 may monitor the output of the ADC 270 until the value output from the ADC 270 begins to decrease. Conversely, to detect a minimum value, the microcontroller 100 may monitor the output of the ADC 270 until the value output from the ADC 270 begins to increase. Once the microcontroller 100 detects the desired change, it may begin Figures 6A-6B One or both of the initialization procedures described in .

[0063] Although the above description describes using a timer to control the external FET 110 after completing an initialization procedure, other embodiments are possible.

[0064] For example, in one embodiment, the on-time initialization routine is executed as described above. However, instead of using a timer to determine the off-time, the microcontroller 100 can use the value of the scaled drain signal. In other words, the external FET 110 can be turned on for a predetermined time, as determined by the on-time initialization routine. Once the external FET 110 is turned off, the microcontroller 100 can compare the scaled drain signal to a predetermined value (e.g., as performed in the off-time initialization routine). Once the scaled drain signal falls to the predetermined value, the external FET 110 is turned on, and the on-time value is loaded into the timer 230. In some embodiments, the output of the second analog comparator 250 can directly cause the assertion of the drive signal and the start of the timer 230.

[0065] In another embodiment, the off-time initialization routine is performed as described above. However, instead of using a timer to determine the on-time, the microcontroller 100 can use the value of the sense signal. In other words, the external FET 110 can be turned off for a predetermined time, as determined by the off-time initialization routine. Once the external FET 110 is turned on, the microcontroller 100 can then compare the sense signal with a predetermined value (e.g., as performed in the on-time initialization routine). Once the sense signal increases to the predetermined value, the external FET 110 is turned off, and the off-time value is loaded into the timer 230. In some embodiments, the output of the analog comparator 200 can directly cause the deassertion of the drive signal and the start of the timer 230.

[0066] In yet another embodiment, the microcontroller 100 does not perform the aforementioned initialization procedure. Instead, the microcontroller 100 may monitor the sense signal and the scaled drain signal and assert and de-assert the drive signal based on the voltage on each of these signals. The voltage at which the analog comparator 200 and the second analog comparator 250 are triggered may be a function of the desired dimming level.

[0067] In some embodiments, the voltage to be applied to the gate of the external transistor 110 may be less than or equal to the supply voltage of the microcontroller 100. In this embodiment, the drive signal from the microcontroller 100 is directly connected to the gate of the external transistor 110. In other embodiments, the voltage to be applied to the gate of the external transistor 110 may be greater than the supply voltage of the microcontroller 100.

[0068] In some embodiments, the microcontroller 100 may include a voltage boost circuit so that the drive signal from the microcontroller 100 obtains the voltage required by the gate of the external transistor 110. In other embodiments, an external circuit such as an operational amplifier (opamp) is used to multiply the drive signal by a gain factor to achieve the desired gate voltage. In still other embodiments, the drain signal may be an open-drain signal in which an external resistor is connected between the drive signal and a higher voltage.

[0069] Thus, the drive signal from the microcontroller 100 is connected directly to the gate of the external transistor 110, or to the input of a circuit that modifies the drain signal so that it has a desired voltage range before being connected to the gate. In all embodiments, the drive signal is used to control the gate of the external transistor 110, either directly or indirectly.

[0070] Furthermore, the microcontroller 100 may include a network interface 280 that can communicate with the logic controller 220. The network interface 280 can support any network protocol, such as a wireless network protocol utilizing an antenna 281. The wireless network protocol can be Bluetooth®, ZigBee®, Z-Wave, or any other suitable protocol. In certain embodiments, the microcontroller 100 can receive commands via the network interface 280. These commands can instruct the microcontroller 100 to turn off the LED array 20, turn on the LED array 20, or change the dimming level. In response to a command to change the dimming level, the microcontroller 100 can, for example, change the values ​​of the programmable voltage 210 and the second programmable voltage 260, and then execute the initialization procedure described above. Furthermore, in certain embodiments, upon receiving a command to turn on the LED array 20, the microcontroller 100 can execute the initialization procedure. Furthermore, the microcontroller 100 can also receive firmware updates via the network interface 280, thereby allowing the functionality of the LED array control circuit to be modified after manufacture.

[0071] The present system and method offer numerous advantages. First, by incorporating the functionality of the LED driver IC into microcontroller 100, the overall circuit cost can be reduced. Second, by incorporating the LED driver controller into microcontroller 100, device calibration can be performed. Finally, the use of microcontroller 100 allows the circuit to be modified or updated after it has been shipped to the customer via firmware updates transmitted via network interface 280. In contrast, any modifications to the LED driver IC must be made via hardware changes. For example, additional features can be added to the circuit at a later date, if desired.

[0072] The present disclosure is not limited in scope by the specific embodiments described herein. In fact, in addition to those embodiments described herein, various other embodiments and modifications of the present disclosure will also be apparent to those of ordinary skill in the art based on the foregoing description and accompanying drawings. Therefore, these other embodiments and modifications are intended to fall within the scope of the present disclosure. In addition, although the present disclosure has been described herein for a specific purpose in the context of a specific implementation in a specific environment, it should be appreciated by those of ordinary skill in the art that its usefulness is not limited thereto, and the present disclosure can be beneficially implemented in any number of environments for any number of purposes. Therefore, the claims set forth below should be interpreted in view of the full breadth and spirit of the present disclosure as described herein.

Claims

1. A circuit for driving an LED array, comprising: The LED array communicates with a high voltage (HV) signal; an inductor connected in series with the LED array; a sense resistor connected to ground; an external transistor comprising a drain, a source, and a gate, wherein the drain is in communication with the inductor and the source is in communication with the sense resistor such that when the external transistor is enabled, current flows from the HV signal through the LED array, the inductor, the external transistor, and the sense resistor; a diode, disposed between the drain and the HV signal; as well as Microcontroller, including: an output signal, called a drive signal, which controls the gate of the external transistor; a first analog input, in communication with the source of the external transistor, referred to as a sense signal; and a second analog input in communication with a signal representative of the voltage at the drain of the external transistor, referred to as a scaled drain signal; wherein, during a first initialization procedure, the microcontroller determines an amount of time, referred to as an on-time value, for a sense signal to reach a predetermined voltage after the external transistor is enabled, and wherein, during normal operation, the microcontroller uses the on-time value to control the drive signal.

2. The circuit according to claim 1, wherein The microcontroller includes a timer and an analog comparator, wherein the analog comparator compares the sense signal with the predetermined voltage and generates an output when the sense signal is greater than the predetermined voltage, and wherein when the output of the analog comparator is asserted, the value of the timer is saved as an on-time value.

3. The circuit according to claim 1, wherein A value indicative of the predetermined voltage is stored in a writable register and is associated with a desired dimming level.

4. The circuit according to claim 1, wherein During a second initialization procedure, the microcontroller determines an amount of time for the scaled drain signal to fall to a second predetermined voltage after the external transistor is disabled, referred to as an off-time value, and wherein, during normal operation, the microcontroller uses the off-time value to control the drive signal.

5. The circuit according to claim 4, wherein A value indicative of the second predetermined voltage is stored in a writable register and is associated with a desired dimming level.

6. The circuit according to claim 4, wherein The microcontroller includes a timer and a second analog comparator, wherein the second analog comparator compares the scaled drain signal with the second predetermined voltage and generates an output when the scaled drain signal is less than the second predetermined voltage, and wherein the value of the timer is saved as an off-time value when the output of the second analog comparator is asserted.

7. The circuit according to claim 4, wherein The microcontroller adds the on-time value and the off-time value to calculate the period of the driving signal.

8. The circuit according to claim 4, wherein A timer inside the microcontroller is used to control the driving signal based on the on-time value and the off-time value.

9. The circuit of claim 1 , comprising a scaling circuit in communication with the drain of the external transistor to generate a scaled version of the voltage at the drain, referred to as a scaled drain signal.

10. The circuit of claim 1, wherein The microcontroller comprises a third analog input representing a HV signal, called the scaled HV signal. 11 . The circuit of claim 10 , further comprising a second scaling circuit in communication with the HV signal to generate the scaled HV signal.

12. The circuit according to claim 10, wherein The microcontroller monitors the scaled HV signal before executing a first initialization procedure.

13. The circuit according to claim 12, wherein The controller waits for the scaled HV signal to reach a maximum value before executing the first initialization procedure.

14. The circuit of claim 1, wherein: The drive signal is directly connected to the gate of the external transistor.

15. A circuit for driving an LED array, comprising: The LED array communicates with a high voltage (HV) signal; an inductor connected in series with the LED array; a sense resistor connected to ground; an external transistor comprising a drain, a source, and a gate, wherein the drain is in communication with the inductor and the source is in communication with the sense resistor such that when the external transistor is enabled, current flows from the HV signal through the LED array, the inductor, the external transistor, and the sense resistor; a diode, disposed between the drain and the HV signal; as well as Microcontroller, including: an output signal, referred to as a drive signal, which controls the gate of the external transistor; and a first analog input, in communication with the source of the external transistor, referred to as a sense signal; a second analog input in communication with a signal representative of the voltage at the drain of the external transistor; wherein, after executing the first initialization procedure, the microcontroller controls the driving signal without monitoring the sensing signal; and wherein, during a second initialization procedure, the microcontroller determines an amount of time for the scaled drain signal to fall to a second predetermined voltage after the external transistor is disabled, referred to as an off-time value, and wherein, during normal operation, the microcontroller uses the off-time value to control the drive signal without monitoring the scaled drain signal.

16. A microcontroller for controlling an LED array, comprising: The output signal, called the drive signal, is configured to control the gate of the external transistor; a first analog input, in communication with the source of the external transistor, referred to as a sense signal; as well as a second analog input in communication with a signal representative of the voltage at the drain of the external transistor, referred to as a scaled drain signal; Timer; Writable registers; as well as Analog comparator; wherein, during a first initialization procedure, the analog comparator compares the sense signal to a predetermined voltage, wherein a value indicative of the predetermined voltage is stored in the writable register; and wherein, when the output of the analog comparator is asserted, an amount of time, referred to as an on-time value, after the drive signal is asserted to cause the sense signal to reach the predetermined voltage is saved as the on-time value; And wherein, during normal operation, the microcontroller uses the on-time value to control the drive signal.

17. The microcontroller according to claim 16, further comprising a second analog comparator and a second writable register, wherein The second analog comparator compares the scaled drain signal to a second predetermined voltage, wherein a value indicative of the second predetermined voltage is stored in the second writable register; and wherein, when the output of the second analog comparator is asserted, an amount of time, referred to as an off-time value, for the scaled drain signal to fall to the second predetermined voltage after the drive signal is de-asserted is saved as an off-time value; and wherein, during normal operation, the microcontroller uses the on-time value and the off-time value to control the drive signal.

18. The microcontroller according to claim 16, further comprising a second analog comparator and a second writable register, wherein The second analog comparator compares the scaled drain signal to a second predetermined voltage, wherein a value indicative of the second predetermined voltage is stored in the second writable register; and wherein, when the output of the second analog comparator is asserted, the total amount of time after the drive signal is asserted until the scaled drain signal falls to the second predetermined voltage is saved as a period, and wherein, during normal operation, a microcontroller uses the on-time value and the period to control the drive signal.

Images