JP7043550B2 - Warm color dimming controller for LEDs - Google Patents

Description

This application claims the interests of US Provisional Patent Application No. 62 / 328,523 filed April 27, 2016 and European Provisional Patent Application No. 16173125.2 filed June 6, 2016. It is a thing, and its contents are incorporated here as if it were completely described.

The present invention relates to general lighting using light emitting diodes (LEDs), and in particular, a technique for gradually warming the LED light (having a lower CCT) as the LED light is dimmed by a dimmer. Regarding.

Incandescent bulbs have aesthetically pleasing lighting characteristics. For example, an incandescent bulb gradually turns red (warms) as the user dims the light by controlling the dimmer to reduce the average current through the bulb. Although many advances have been made in LED technology, further advances are desired to help achieve the quality of light typically provided by incandescent bulbs.

A control circuit for a light emitting diode (LED) lighting system is provided to achieve a dim-to-warm effect between the minimum brightness-maximum dimming level and the maximum brightness-minimum dimming level. The light. The control circuit is coupled to an LED controller, a clamp circuit coupled to a set of warm correlated color temperature (“CCT”) LEDs, a switch coupled to a set of cool CCT LEDs, and the clamp circuit and the switch. Includes a feedback circuit. The LED controller detects the magnitude of the adjustable input current and controls the clamp circuit based on the input current to clamp the current through the set of worm CCT LEDs to the clamp current level and the switch. To switch on the set of cool CCT LEDs in response that the input current is greater than the first threshold level and in response that the input current is lower than the first threshold level. It is configured to switch off the set of cool CCT LEDs. The feedback circuit is configured to divert current from the set of warm CCT LEDs to the set of cool CCT LEDs in response that the input current exceeds the second threshold level.

Both exemplify a string of warm LEDs and a string of cool LEDs that emit white light, and a warm-colored dimming circuit that controls the current to each string as the input voltage changes from the minimum current to the maximum current. Is illustrated. It is an example of the relative current supplied to the worm LED (Iw) and the current supplied to the cool LED (Ic) over the entire range of the input current. Various functional units in the warming dimming circuit of FIG. 2 are illustrated. It is a circuit diagram of a warm color dimming circuit and a warm LED and a cool LED. It is a graph which shows the ideal CCT of a halogen bulb, and also shows the simulated total CCT of a lamp when the light is dimmed from the maximum to the minimum. In FIGS. 6A-6B, a tapped linear driver that receives an analog dimming signal provides input current to the four warming dimming circuits, each of which has the same CCT at the same dimming level. Illustrates an embodiment of the invention that is used and designed to produce. FIG. 6 is a functional diagram (from a data sheet) of a suitable prior art tapped linear regulator that can be used in the system of FIG.

Elements that are the same or similar have the same reference numeral.

In one embodiment, two series strings of LEDs are used in the lamp. The first string comprises a plurality of the same cool LEDs, such as GaN-based LEDs having a tuned fluorophore that yields a CCT of 4000K. The second string includes a plurality of the same warm LEDs, for example using the same GaN-based LED dies as the cool LEDs, but with a tuned fluorophore that results in a CCT of 2200K. In other embodiments, the number of strings and the CCT may vary. Both CCTs are considered white light.

One end of the two strings is powered, for example a rectified trunk voltage, and the other end of the two strings is connected to different terminals of a warm-to-warm circuit.

An adjustable analog (non-PWM) current is supplied to the input of the warming dimming circuit, the input current level of which can be adjusted by the user controlling a suitable dimmer.

Between the minimum input current and the first input current level, the cool LED string is switched off and all input current flows through the worm LED string. Therefore, this dimming exclusively controls the brightness of the worm LED down to the first input current level. Up to the first input current level, the CCT output of the lamp is a constant warm color temperature.

When the input current is adjusted above the first input current level but below the second input current level, the switch is closed while the current passing through the worm LED string remains clamped to a constant current. , A part of the input current flows through the cool LED string. Therefore, within this range of input current, this dimming exclusively controls the brightness of the cool LED while the brightness of the worm LED remains constant. The CCT output of the lamp is a variable mix of these two CCTs, with the CCT increasing as the input current approaches the second input current level.

When the input current is adjusted above the second input current level to the maximum current, the cool LED remains controlled by the increasing input current and the current to the worm LED is to zero at the maximum input current. It is gradually reduced. Therefore, the CCT output of the lamp approaches the CCT of the cool LED as the input current level approaches its maximum value.

Using this technique, a full range of CCTs up to 4000K-2200K is obtained and both sets of LEDs output white light, so there is a more natural combination of light from different LEDs that produces varying CCTs. do. Since the operation is linear (without PWM or high frequency switching), no EMI is generated and no filter is required. Due to its linear behavior, very small linear regulators, including tapped linear regulators, can be used to generate the input current.

In one embodiment, a tapped linear driver is used as the driver for the warm color dimming circuit. A tapped linear regulator receives voltage from a full-wave diode bridge that rectifies the AC trunk voltage and supplies current to different segments of the two LED strings one after the other as the DC voltage changes at twice the AC frequency. This results in a very small and efficient control system.

FIG. 1 illustrates one embodiment. The power source 10 can be a rectified trunk voltage, battery, regulator, or other source. The series string of the white light cool LED 12 has its anode end coupled to the power supply 10, and the white light warm LED 14 series string also has its anode end coupled to the power supply 10. Depending on the desired maximum light output of the lamp, there may be multiple strings of each type of LED, and those of each type of LED so that those strings of each type of LED are controlled identically. Strings can be connected in parallel.

The cool LED may be a conventional, commercially available, blue light emitting GaN-based LED die in which a suitable fluorophore, such as a YAG phosphor, is deposited on the die. Other phosphors may be used. Such a cool LED 12 will typically have a CCT in the range 3000-6000K. In this example, this CCT is 4000K.

The warm LED 14 is a conventional, commercially available, blue light in which, for example, a YAG fluorescent substance plus a warmer fluorescent substance that emits amber or red light is deposited on a die. It can be a GaN-based LED die that emits light. Other phosphors may be used. Such a worm LED 14 will typically have a CCT in the range of 1900-2700K. In this example, this CCT is 2200K.

Warm LED dies and cool LED dies can be of the same type, so they have the same forward voltage drop. In one embodiment, the same number of LEDs are within each of these strings, and therefore these strings have the same forward voltage drop.

The relative brightness (luminous flux) of the cool LED 12 and the warm LED 14 is determined by the warm color dimming circuit 16. The warm color dimming circuit 16 may be a three-terminal circuit that outputs separate drive currents to the worm LED 14 (Iw) and the cool LED 12 (Ic). The input to the warming dimming circuit 16 is an adjustable analog current (input current Iin) from an external current source 18 that sets the overall dimming of the lamp. A low input current Iin results in a low overall brightness of the lamp with a relatively low CCT, and a high input current Iin results in a high overall brightness of the lamp with a relatively high CCT.

FIG. 2 illustrates a current Iw through the worm LED 14 (directly corresponding to the brightness of the worm LED 14) and a current Ic1 or Ic2 (directly corresponding to the brightness of the cool LED 12) through the cool LED 12 over the entire range of the input current Iin. is doing. The current Ic1 represents the current when the cool LED 12 is completely off between the minimum input current Iin (min) and the intermediate input current Iin1, and the current Ic2 represents the cool LED 12 between the Iin (min) and Iin1. Is somewhat on and therefore represents the current when the CCT changes are continuous over the Iin range. The warm color dimming circuit 16 can be designed to achieve the current curve of Ic1 or Ic2.

The minimum input current Iin (min) corresponds to the maximum dimming level (lightest and warmest) and the maximum input current Iin (max) corresponds to the minimum dimming level (brightest and coolest). ..

The following description assumes that the warm color dimming circuit 16 outputs the current Ic1. Between Iin (min) and Iin1, the warm color dimming circuit 16 outputs only the current Iw and drives the worm LED 14 with a current proportional to the adjustable input current Iin, hence the CCT of the lamp. The output is 2200K. Between Iin1 and Iin2, the warm color dimming circuit 16 clamps Iw so that the brightness of the worm LED 14 is relatively constant, during which time Ic1 increases in proportion to the input current Iin. Therefore, between Iin1 and Iin2, the overall (perceived) CCT output of the lamp becomes colder. Between Iin2 and Iin (max), Iw is ramped down, during which time Ic1 still rises in proportion to the input current Iin. The overall CCT of this lamp at various dimming levels is generally consistent with the varying CCT of halogen lamps or incandescent bulbs.

FIG. 3 illustrates the entire system and shows a warming dimming circuit 16, a string of warm LEDs 14, a string of cool LEDs 12, and an adjustable current source for dimming control 18 that outputs Iin.

For Iins less than Iin1, the control circuit 22 (comparator) keeps the switch 24 off so that no current flows through the cool LED 12 and all input currents Iin flow through the worm LED 14.

When Iin exceeds Iin1, the control circuit 22 turns on the switch 24 so that the current Ic through the cool LED 12 is generally proportional to Iin. The control circuit 22 also controls the clamp circuit 26 to clamp the current Iw to a fixed level so that the brightness of the worm LED 14 does not change between Iin1 and Iin2 (FIG. 2).

When the input current exceeds Iin2, the feedback circuit 28 will be forward biased, gradually bypassing some current to the left leg of the circuit, which will progressively reduce the current Iw through the worm LED 14. The clamp 26 is controlled so as to cause the current.

The currents Iw and Ic obtained in FIG. 3 coincide with the currents Iw and Ic1 in FIG.

FIG. 4 is a schematic circuit diagram of the system of FIG. The circuit of FIG. 4 can be formed as a four-terminal packaged IC, two of which are connected to the cathode ends of a series string of warm LEDs and a series string of cool LEDs. The terminal 3 is a vdd local terminal (labeled in FIG. 4) and the fourth terminal is coupled to ground. An adjustable dimming current is coupled to the anodes of the two series strings.

The controllable Zener diodes U1 and U2 can be a TLV431 adjustable shunt regulator by Diodes, the data sheet of which is incorporated herein. This suitable adjustable shunt regulator has a cathode-anode rating of 18V at a reference voltage (threshold voltage) of 1.25V. The shunt does not necessarily require a Zener diode, but the Zener diode symbol represents the function of the shunt regulator. Other controllable shunt regulator circuits may be used. The input control voltage to the diodes U1 and U2 controls the clamp voltage. The diode U1 is virtually non-conducting between the input currents Iin (min) and Iin1 (FIG. 2), and the pull-up resistor R5 pulls the gate of the MOSFET M1 to a high level to turn on the MOSFET M1. As a result, all input currents Iin flow through the MOSFET M1 and the worm LED 14.

The diode U1, the resistors R1, R5, R8, and the MOSFET M1 form a current regulator (clamp circuit 26), and the gate voltage of the MOSFET M1 determines Iw. The control terminal of the Zener diode U1 is coupled to the upper node of the resistor R1. In a particular circuit example, when the input current Iin raises the current Iw to the point where the voltage at the upper node of resistor R1 reaches 1.25 volts, the Zener diode U1 conducts and the gate voltage is increased in FIG. Clamp the clamped current Iw to the level required to conduct. The reference voltage is set to TL431 (represented by the Zener diode U1) so that the control voltage of 1.25V conducts the Zener diode U1 enough to maintain a voltage of 1.25V to the upper node of the resistor R1. Set. Before the control voltage reaches 1.25 volts, the Zener diode U1 is off. Clamping by the Zener diode U1 starts at Iin1 in FIG. Therefore, the current Iw flowing through the MOSFET M1 between Iin1 and Iin2 is clamped to 1.25V / R1. Therefore, the value of R1 determines the position of Iin1. Although a specific value of 1.25 volts has been described for the control voltage, any technically feasible control voltage may be used.

Resistors R6, R7, and a second adjustable Zener diode U2 (another TL431) act as a comparator to monitor the gate voltage of MOSFET M1. Before the current Iw passing through the resistor R1 reaches the clamp current, the Zener diode U1 draws the minimum current. The resistor R5 is connected to a constant fixed voltage set by the Zener diode D1 (and filtered by the capacitor C1) and pulls the gate of the MOSFET M1 high. Here, the gate voltage is equal to the voltage set by the Zener diode D1 multiplied by (R6 + R7) / (R5 + R6 + R7). When the current through the MOSFET M1 reaches the regulator's clamping current (in Iin1), the Zener diode U1 (TL431) conducts and pulls the gate voltage to the required level, clamping the current through the MOSFET M1. This reduces the voltage in the resistor divider formed by resistors R6 and R7, and the voltage divider reduces the control voltage to the controllable Zener diode U2 (TL431) below its threshold voltage. This allows the Zener diode U2 to act as an open circuit. By doing so, the resistor R4 raises the gate voltage of the MOSFET M2 (switch 24 in FIG. 3) high, which causes the MOSFET M2 to turn on at the input current Iin1. Since the change in the gate voltage before and after the current passing through the resistor R1 reaches the clamp current is relatively large, this circuit is not so affected by the spread of the internal reference threshold voltage of the TL431 adjustable shunt regulator. More specifically, when attempting to design the fixed turn-on threshold of the MOSFET M2 to match the internal reference voltage of the TL431 adjustable shunt regulator, discrepancies can occur due to the spread of that reference voltage. In the technique provided herein, the turn-on threshold of M2 does not attempt to follow the absolute value of the internal reference voltage of the TL431 adjustable shunt regulator and is therefore less susceptible to its spread.

Capacitor C2 and resistance R10 form a compensatory network that maintains closed-loop stability.

Next, the operation with the input current Iin2 will be described. The resistor R3 and the Schottky diode D2 form the feedback circuit 28 of FIG. As soon as the source voltage of the MOSFET M2 becomes higher than the source voltage of the MOSFET M1 by the forward voltage of the Schottky diode D2, a part of the current will be bypassed through the resistors R3 and R1. The current through the resistor R1 now consists of both the resistor R3 and the MOSFET M1. This is the knee (line) point in Iin2 of FIG. 2 and is the start of roll-off (decrease) of the current Iw of the MOSFET M1. This additional current through the resistor R1 further reduces the gate voltage of the MOSFET M1 to the Zener diode U1 to maintain the voltage at the upper node of the resistor R1 at 1.25 volts. The larger resistor R2 moves Iin2 to the left on the x-axis. The slope of the roll-off is determined by the resistor R3. The higher the value of the resistance R3, the smaller the slope. Zener diodes U1 and U2, as well as resistors R6, R7, R4, and R2, serve the function of control circuit 22 (also referred to as "LED controller"). More specifically, as described above, the control circuit 22 controls the switch 24 (MOSFET M2) to enable or disable the flow of current through the cool LED 12, and the clamp circuit 26 (Zener diode U1). , Current regulator including resistors R1, R5, R8, and MOSFET M1) to clamp the current through the worm LED 14. Although the control circuit 22 and the clamp circuit 26 have been described as including the specific components of the circuit shown in FIG. 4, the boundary between the control circuit 22 and the clamp circuit 26 is completely defined at least in some respects. Is not drawn. For example, the resistors R6 and R7 are described as being part of the control circuit 22, and the resistors R5 are described as being part of the clamp circuit 26, but these resistors work together to describe the control circuit 22 and the clamp. It serves both functions of the circuit 26. Those skilled in the art will recognize that the various elements shown in FIG. 4 can be variously grouped to correspond to the elements of FIG.

The resistor R9, the diode D1 and the capacitor C1 form a voltage buffer. This ensures that the gate voltages of both MOSFETs are within their limits and that the results of the resistor dividers (R5, R6, R7) are predictable.

If it is not desirable to completely turn off the cool LED 12 with an input current of less than Iin1, the MOSFET M2 should be rolled off between Iin (min) and Iin1 as indicated by the line Ic2 in FIG. Can be controlled. This can be done by connecting a resistor between the nodes vcs2 and vs2 as a leak path in parallel with the MOSFET M2.

FIG. 5 shows how the resulting lamp CCT output 34 is comparable to the ideal CCT of a halogen bulb while dimming between 100% and about 10% (minimum dimming). Is shown.

The system of the present invention does not require a high frequency filter and can be manufactured very small and inexpensively. It can be used with any type of dimming circuit that regulates the analog input current.

FIG. 6A shows the use of the warm color dimming circuit 16 with the tapped linear LED driver 40. Linear LED drivers with taps that operate from AC trunk voltage are well known and commercially available. The driver 40 may be the MAP9010 AC LED driver 40 by MagnaChip, or any other suitable driver.

The driver 40 receives the rectified AC signal from the full-wave diode bridge 42. The AC signal may have a trunk voltage of 44. A fuse 45 (represented by a resistance symbol) protects the circuit from overcurrent, a capacitor 46 smoothes the transient current, and a transient current suppressor 48 limits the spike. The driver 40 detects an increase and decrease in the level of the incoming DC signal, and applies a current to the four outputs IOUT0-IOUT3 one after another as shown in FIG. 6B. Only one current is output to any of the four output terminals at a time, and at low DC voltage levels just above the forward voltage of the series LEDs in the first group, only IOUT0 outputs the current in the first group. Activates the LED of. Near the maximum DC voltage level, which exceeds the forward voltage of the entire string of LEDs, only IOUT3 outputs current to activate the entire string. The diode 49 ensures that all current only flows into the driver 40. The analog drive current is controlled by a control signal 50, for example, from a user-controlled dimmer.

The first group LEDs on the left are most on because they are on when the DC voltage is higher than the forward voltage of the first group LEDs, and the fourth group LEDs on the right are on. It is the least on because it is turned on only when the DC voltage is near the highest level. The current gradually increases from IOUT0 to IOUT3 to suppress perceptible flicker as the number of activated LEDs constantly changes with DC level changes. Only one cool LED 12 and one warm LED 14 are shown in each group, but there may be more LEDs in each group.

As a result of the currents IOUT0-IOUT3 being different at the same dimming level, the combination of the current Ic to the cool LED 12 and the current Iw to the worm LED 14 is adjusted for each of the warming dimming circuits 16A-16D. As a result, the CCTs of the LEDs of each group match at all dimming levels, and the CCTs of the lamps are prevented from fluctuating from cycle to cycle. Matching the CCT at each dimming level is done by adjusting the values of the resistors R1, R2, R3 (FIG. 4). For example, in a warming dimming circuit 16A that receives the IOUT0 current (lowest) at a particular dimming level where the cool and warm LEDs are on at the same time, the warming dimming circuit 16A receives the IOUT3 current (highest). The currents Ic and Iw having the same ratio as those of the warming dimming circuit 16D are applied to the cool LED and the worm LED. One of ordinary skill in the art can readily select the values of R1, R2, and R3 to maintain equal CCT for each of the warming dimming circuits 16A-16D at any dimming level.

FIG. 7 shows the functional units in the MAP9010 driver reproduced from the datasheet. The MOSFET 60 is controlled so that the outputs IOUT0-IOUT3 supply the desired currents one after another as the rectified DC voltage changes during the AC cycle. An analog dimming signal is given to the terminal RDIM to control the current at the outputs IOUT0-IOUT3. This behavior is further described in the datasheet, which is incorporated herein by reference.

The warming dimming circuit 16 described above may be a simple 3-terminal IC that can be used with conventional LED drivers that provide variable current for dimming. The warm color dimming circuit 16 does not require a high frequency filtering component (eg, a large capacitor or inductor) and is therefore easily mounted on the printed circuit board along with the LEDs. No microprocessor is needed.

Although specific embodiments of the present invention have been illustrated and described, modifications and modifications can be made without departing from the invention in a broader manner, as will be apparent to those skilled in the art, and therefore, attached. Claims should include, within their scope, all modifications and modifications that fall within the true spirit and scope of the invention.

Claims (20)

With a diode bridge configured to provide a rectified alternating current (AC) signal,
With the driver
Have,
The driver
Upon receiving the rectified AC signal,
The first current signal is applied to the first warming dimming circuit at the first time point without applying to the second time point, and the second time point is not applied to the first time point. In addition, the second current signal is applied to the second warming dimming circuit, and the first warming dimming circuit and the second warming dimming circuit are the first warming dimming circuit at the same dimming level . The light emitting diode (LED) driven by the warming dimming circuit and the second warming dimming circuit is configured to provide an output that provides the same correlated color temperature (CCT).
Is configured as
circuit. The circuit according to claim 1, wherein the diode bridge is a full-wave diode bridge. The circuit according to claim 1, wherein the driver is a linear driver with a tap. The circuit according to claim 1 or 2, wherein the diode bridge is configured to provide the rectified AC signal from a trunk voltage signal supplied to the diode bridge. Claim 1 or 2 further comprising a first group of LEDs configured to be activated based on at least one of the outputs from the first warming dimming circuit and the second warming dimming circuit. Circuit described in. 5. The circuit of claim 5, further comprising a second group of LEDs configured to be activated based on the second warming dimming circuit. The circuit according to claim 1 or 2, further comprising a fuse, which is configured to protect the circuit from overcurrent. The circuit according to claim 1 or 2, further comprising a capacitor configured to smooth the transient current. The circuit according to claim 1 or 2, wherein the driver is configured to detect at least one of an increase in the rectified AC signal and a decrease in the rectified AC signal. The driver further generates the first current signal and the second current signal based on detecting at least one of an increase in the rectified AC signal and a decrease in the rectified AC signal. 9. The circuit of claim 9. The circuit according to claim 1, wherein the rectified AC signal is determined based on a control signal. Each of the first warming dimming circuit and the second warming dimming circuit drives an LED of the first array providing the first CCT and an LED of the second array providing the second CCT. The circuit according to claim 1 or 2, wherein the circuit is configured to be the same. The same first number of the LEDs in the first array and the LEDs in the second array is driven by the first warming dimming circuit, and among the LEDs in the first array and the LEDs in the second array. 12. The circuit of claim 12, wherein the same second number is driven by the second warming dimming circuit. Among the LEDs of the first array and the LEDs of the second array, the number of LEDs driven by the first warming dimming circuit is higher than that of the LEDs driven by the second warming dimming circuit. The second warming dimming circuit is less than the rectified AC signal used by the first warming dimming circuit to drive the LEDs in the first array and the LEDs in the second array. The circuit according to claim 12, wherein the LED of the first array and the LED of the second array are driven by a highly rectified AC signal. It ’s a way to make the circuit work.
Provides a rectified alternating current (AC) signal via a diode bridge,
The driver receives the rectified AC signal and receives it.
The driver applies the first current signal to the first warming dimming circuit at the first time point without applying it to the second time point and without applying it to the first time point. At the second time point, the second current signal is applied to the second warming dimming circuit, and the first warming dimming circuit and the second warming dimming circuit are at the same dimming level. A light emitting diode (LED) driven by the first warming dimming circuit and the second warming dimming circuit is configured to provide an output that provides the same correlated color temperature (CCT).
How to have that. 15. The method of claim 15, further comprising providing the rectified AC signal from a trunk voltage signal supplied to the diode bridge. Based on at least one of the outputs from the first warming dimming circuit and the second warming dimming circuit, the first group of LEDs are activated.
Based on the second warming dimming circuit, the second group of LEDs are activated.
The method of claim 15, further comprising. Detecting at least one of the rise in the rectified AC signal and the decline in the rectified AC signal,
The driver is used to generate the first current signal and the second current signal based on detecting at least one of an increase in the rectified AC signal and a decrease in the rectified AC signal. Generate,
The method of claim 15, further comprising. The first warm color dimming circuit and the second warm color dimming circuit are used to drive the LEDs of the first array providing the first CCT and the LEDs of the second array providing the second CCT. do,
Have more
The same first number of the LEDs in the first array and the LEDs in the second array is driven by the first warming dimming circuit, and among the LEDs in the first array and the LEDs in the second array. The same second number is driven by the second warming dimming circuit.
The method according to claim 15. The first warm color dimming circuit and the second warm color dimming circuit are used to drive the LEDs of the first array providing the first CCT and the LEDs of the second array providing the second CCT. do,
Have more
Among the LEDs of the first array and the LEDs of the second array, the number of LEDs driven by the first warming dimming circuit is higher than that of the LEDs driven by the second warming dimming circuit. The second warming dimming circuit is less than the rectified AC signal used by the first warming dimming circuit to drive the LEDs in the first array and the LEDs in the second array. Also configured to drive the LEDs in the first array and the LEDs in the second array with a highly rectified AC signal.
The method according to claim 15.

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