JP6744428B2 - Warm color dimming controller for LED - Google Patents

Description

This application claims the benefit 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. The contents of which are hereby incorporated as if fully set forth.

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

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

A control circuit for a light emitting diode (LED) lighting system is provided to achieve a warm-up dim-to-warm effect between a minimum brightness-maximum dimming level and a maximum brightness-minimum dimming level. It The control circuit includes an LED controller, a clamp circuit coupled to a set of warm correlated color temperature (“CCT”) LEDs, a switch coupled to the set of cool CCT LEDs, and the clamp circuit and the switch. And a feedback circuit. The LED controller senses an adjustable input current magnitude and controls the clamp circuit based on the input current to clamp the current through the set of warm CCT LEDs to a clamp current level and to switch the switch. To turn on the set of cool CCT LEDs in response to the input current being greater than a first threshold level and in response to the input current being less than the first threshold level. 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 to the input current exceeding a second threshold level.

Both exemplify a string of warm LEDs and a string of cool LEDs that emit white light, and further, a warming dimming circuit that controls the current to each string when the input voltage changes from the minimum current to the maximum current. Is illustrated. Figure 3 is an example of the relative current supplied to a warm LED (Iw) and cool LED supplied (Ic) over the full range of input current. 3 illustrates various functional units within the warming dimming circuit of FIG. It is a circuit diagram of a warming dimming circuit and a warm LED and a cool LED. FIG. 3 is a graph showing the ideal CCT of a halogen bulb and the simulated overall CCT of the lamp as the light is dimmed from maximum to minimum. 6A-6B show that the input currents to the four warming dimming circuits are provided by a linear driver with taps receiving analog dimming signals, each of the four warming dimming circuits providing the same CCT at the same dimming level. 1 illustrates one embodiment of the invention used and designed to produce. 7 is a functional diagram (from a data sheet) of a preferred prior art tapped linear regulator that may be used in the system of FIG.

Elements that are the same or similar are given the same reference symbols.

In one embodiment, two series strings of LEDs are used in the lamp. The first string comprises a plurality of the same cool (cold) LEDs, such as, for example, a GaN-based LED with a tuned phosphor that results in a CCT of 4000K. The second string includes multiple identical warm LEDs, such as those that use the same GaN-based LED die as the cool LEDs but with a tuned phosphor that results in a CCT of 2200K. In other embodiments, the number of strings and CCT may be different. Both CCTs are considered white light.

A power source such as a rectified mains voltage is applied to one end of the two strings, and the other ends of the two strings are connected to different terminals of a warming dimming (dim-to-warm) circuit.

An adjustable analog (non-PWM) current is provided at the input of the warming dimming circuit, which input current level can be adjusted by the user by 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 warm LED string. Therefore, this dimming controls the brightness of the warm LED exclusively up to the first input current level. Up to the first input current level, the CCT output of the lamp has a constant warm color temperature.

Above the first input current level but below the second input current level, when the input current is adjusted, the current through the warm LED string remains clamped at a constant current and the switch is closed. , Part of the input current flows through the cool LED string. Therefore, within this range of input current, this dimming controls the brightness of the cool LED exclusively, while the brightness of the warm LED remains constant. The CCT output of the lamp is a changing blend of these two CCTs, with the CCT increasing as the input current approaches the second input current level.

When the input current is adjusted to a maximum current higher than the second input current level, the cool LED remains controlled by the increasing input current and the current to the warm LED goes up to zero at the maximum input current. 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 because both sets of LEDs output white light, there is a more natural combination of light from different LEDs producing varying CCTs. To do. Since the operation is linear (without PWM or high frequency switching), no EMI occurs and no filter is needed. Due to its linear behavior, very small linear regulators, including tapped linear regulators, can be used to produce the input current.

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

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

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

The warm LED 14 is a conventional, commercially available, blue light source that is deposited on a die, such as, for example, a YAG phosphor with a warmer phosphor that emits amber or red light. Can be a GaN-based LED die emitting light. Other phosphors may be used. Such warm LEDs 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 in each of these strings, so these strings have the same forward voltage drop.

The relative brightness (light flux) of the cool LED 12 and the warm LED 14 is determined by the warming dimming circuit 16. The warming dimming circuit 16 may be a three-terminal circuit that outputs separate drive currents to the warm 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 the current Iw through the warm LED 14 (which corresponds directly to the brightness of the warm LED 14) and the current Ic1 or Ic2 through the cool LED 12 (which corresponds directly to the brightness of the cool LED 12) over the entire range of the input current Iin. 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 is between the Iin(min) and Iin1. Is somewhat on, and therefore represents the current when the CCT change is continuous over the Iin range. The warming dimming circuit 16 can be designed to achieve an Ic1 or Ic2 current curve.

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

In the following description, it is assumed that the warming dimming circuit 16 outputs the current Ic1. Between Iin(min) and Iin1, the warming dimming circuit 16 outputs only the current Iw to drive the warm LED 14 with a current proportional to the adjustable input current Iin, and hence the CCT of the lamp. The output is 2200K. Between Iin1 and Iin2, the warming dimming circuit 16 clamps Iw so that the brightness of the warm LED 14 is relatively constant, while Ic1 rises 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, while Ic1 still rises in proportion to the input current Iin. The overall CCT of this lamp at various dimming levels is roughly consistent with the varying CCT of a halogen lamp or incandescent lamp.

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

With Iin less than Iin1, no current flows through the cool LED 12, and the control circuit 22 (comparator) keeps the switch 24 off so that all the input current Iin flows through the warm 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 warm LED 14 does not change between Iin1 and Iin2 (FIG. 2).

When the input current exceeds Iin2, the feedback circuit 28 becomes forward biased and progressively diverts some current to the left leg of the circuit, which progressively reduces the current Iw through the warm LED 14. The clamp 26 is controlled so that

The currents Iw and Ic obtained in FIG. 3 match 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 terminals are connected to the cathode ends of the series string of warm LEDs and the series string of cool LEDs. The third terminal is the 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 TLV431 Adjustable Shunt Regulators by Diodes, the data sheet of which is incorporated herein. The preferred adjustable shunt regulator has a cathode-anode rating of 18V with 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. Between input currents Iin(min) and Iin1 (FIG. 2), diode U1 is effectively non-conducting and pull-up resistor R5 pulls the gate of MOSFET M1 high to turn MOSFET M1 on. As a result, all input current Iin flows through MOSFET M1 and warm 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 Zener diode U1 is coupled to the upper node of resistor R1. In the particular circuit example, when the input current Iin raises the current Iw to the point where the voltage at the upper node of the resistor R1 is 1.25 volts, the Zener diode U1 conducts and the gate voltage is changed to Clamp the clamped current Iw to the level required to conduct. The reference voltage on TL431 (represented by Zener diode U1) has a reference voltage such that the control voltage of 1.25V causes Zener diode U1 to conduct sufficiently to maintain the voltage of 1.25V on the upper node of resistor R1. Is set. Zener diode U1 is off before the control voltage reaches 1.25 volts. The clamping by the Zener diode U1 starts at Iin1 in FIG. Therefore, the current Iw flowing through the MOSFET M1 is clamped at 1.25 V/R1 between Iin1 and Iin2. Therefore, the value of R1 determines the position of Iin1. Although a specific value of 1.25 volts is stated for the control voltage, any technically feasible control voltage may be used.

The resistors R6, R7 and the second adjustable Zener diode U2 (another TL431) act as a comparator for monitoring the gate voltage of the MOSFET M1. Zener diode U1 draws a minimum current before current Iw through resistor R1 reaches the clamp current. Resistor R5 is connected to a fixed voltage set by Zener diode D1 (and filtered by capacitor C1), pulling the gate of MOSFET M1 high. Here, the gate voltage is equal to (R6+R7)/(R5+R6+R7) multiplied by the voltage set by the Zener diode D1. When the current through MOSFET M1 reaches the clamp current (in Iin1) of the regulator, Zener diode U1 (TL431) conducts, pulling the gate voltage to the required level and clamping the current through MOSFET M1. This reduces the voltage in the resistive voltage divider formed by resistors R6 and R7, and the divided voltage reduces the control voltage to the controllable Zener diode U2 (TL431) below its threshold voltage. As a result, the Zener diode U2 acts as an open circuit. By doing so, resistor R4 pulls the gate voltage of MOSFET M2 (switch 24 in FIG. 3) high, which turns on MOSFET M2 with input current Iin1. This circuit is less sensitive to the spread of the internal reference threshold voltage of the TL431 adjustable shunt regulator because the change in gate voltage before and after the current through resistor R1 reaches the clamp current is relatively large. More specifically, when the fixed turn-on threshold of MOSFET M2 is designed to match the internal reference voltage of the TL431 adjustable shunt regulator, a mismatch may occur due to the spread of the reference voltage. In the technique provided here, 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 resistor R10 form a compensation network that maintains closed loop stability.

Next, the operation at the input current Iin2 will be described. Resistor R3 and Schottky diode D2 form feedback circuit 28 of FIG. As soon as the source voltage of MOSFET M2 becomes higher than the source voltage of MOSFET M1 by the forward voltage of Schottky diode D2, some current will be diverted through resistors R3 and R1. The current through resistor R1 now consists of both resistor R3 and MOSFET M1. This is a knee 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 resistor R1 causes zener diode U1 to further reduce the gate voltage of MOSFET M1 to maintain the voltage at the top node of resistor R1 at 1.25 volts. The larger resistance R2 moves Iin2 to the left on the x-axis. The roll-off slope is determined by the resistor R3. The higher the value of the resistor R3, the smaller the inclination. Zener diodes U1 and U2 and resistors R6, R7, R4, and R2 perform the function of control circuit 22 (also referred to as "LED controller"). More specifically, the control circuit 22 controls the switch 24 (MOSFET M2) to enable or disable the flow of current through the cool LED 12, as described above, and the clamp circuit 26 (zener diode U1). , Resistor R1, R5, R8, and MOSFET M1) to clamp the current through warm LED 14. It should be noted that although the control circuit 22 and the clamp circuit 26 have been described as including certain components of the circuit shown in FIG. 4, the boundary between the control circuit 22 and the clamp circuit 26 is completely complete, at least in part. Is not drawn. For example, resistors R6 and R7 are described as being part of control circuit 22 and resistor R5 is described as being part of clamp circuit 26, but these resistors work together to control circuit 22 and clamp. It fulfills both functions of the circuit 26. Those skilled in the art will recognize that the various elements shown in FIG. 4 may be grouped variously 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 divider (R5, R6, R7) are predictable.

If it is not desired to completely turn off the cool LED 12 with an input current less than Iin1, then 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 nodes vcs2 and vs2 as a leak path in parallel with MOSFET M2.

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

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

FIG. 6A illustrates the use of warming dimming circuit 16 with a tapped linear LED driver 40. Tapped linear LED drivers operating from AC mains voltage are well known and commercially available. The driver 40 may be a MAP9010 AC LED driver 40 by MagnaChip, or other suitable driver.

The driver 40 receives the rectified AC signal from the full wave diode bridge 42. The AC signal may be the mains voltage 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 the rising and falling levels of the incoming DC signal and provides current to its four outputs IOUT0-IOUT3 one after the other, as shown in FIG. 6B. Only one current is output at any one of the four output terminals at a time, and at low DC voltage levels just above the forward voltage of the first group of series LEDs, only IOUT0 will output current and the first group will output. To activate the LED. Near the maximum DC voltage level, which is above 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, such as from a user controlled dimmer.

The left group of LEDs is on most when the DC voltage rises above the forward voltage of the first group of LEDs, so it is on most, and the group of LEDs on the right side of group 4 is It is the least on because it is turned on only when the DC voltage is near the highest level. The current is gradually increased from IOUT0 to IOUT3 to suppress perceptible flicker when the number of activated LEDs is constantly changing with DC level changes. Although only one cool LED 12 and one warm LED 14 are shown in each group, there may be more LEDs in each group.

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

FIG. 7 shows functional units in the MAP9010 driver reproduced from the data sheet. MOSFET 60 is controlled to provide the desired currents at outputs IOUT0-IOUT3 one after another as the rectified DC voltage changes during the AC cycle. An analog dimming signal is provided at terminals RDIM to control the current at the outputs IOUT0-IOUT3. This operation is further explained in the data sheet, which is incorporated herein by reference.

The warming dimming circuit 16 described above can be a simple 3-terminal IC that can be used with a conventional LED driver that provides a variable current for dimming. The warming dimming circuit 16 does not require high frequency filtering components (eg, large capacitors or inductors) and is therefore easily implemented on the printed circuit board with the LEDs. No microprocessor required.

While particular embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that variations and modifications can be made without departing from the invention in its broader aspects and are therefore The following claims are to encompass within their scope all such changes and modifications as fall within the true spirit and scope of this invention.

Claims (18)

A control circuit of the light-emitting diodes (LED) lighting system, the control circuit,
A clamp circuit coupled to the set of warm correlated color temperature (“CCT”) LEDs,
A switch combined with a set of cool CCT LEDs,
LED controller,
Based on the input current, and controls the clamp circuit clamps the current through the set of the worm CCT LED to clamp current level,
Controlling the switch to turn on the set of cool CCT LEDs in response to the input current being greater than a first threshold level, the input current being less than the first threshold level. In response, switch off the set of cool CCT LEDs,
An LED controller configured as
A feedback circuit coupled to the clamp circuit and the switch, the feedback circuit coupled to the clamp circuit in response to the input current exceeding a second threshold level higher than the first threshold level. A feedback circuit configured to divert current from the set of cool CCT LEDs to the set of cool CCT LEDs,
A control circuit having a. The control circuit of claim 1, wherein the LED controller is further configured to sense the magnitude of the input current. The clamp circuit has a first transistor, a first Zener diode, a first resistor, and a second resistor,
The first zener diode is a gate of the first transistor so as to clamp the current through the set of warm CCT LEDs through the first resistor and the second resistor at the clamp current level. Configured to control the voltage,
The control circuit according to claim 1. 4. The control circuit of claim 3 , wherein the switch has a second transistor coupled to the set of cool CCT LEDs. The LED controller includes the first Zener diode, the second Zener diode, a third resistor, a fourth resistor, a fifth resistor, and a sixth resistor,
The third resistor, the fourth resistor, and the second Zener diode are configured to render the second transistor conductive in response to conducting the first Zener diode. The control circuit according to claim 4 . The feedback circuit has a Schottky diode and a seventh resistor, and in the Schottky diode and the seventh resistor, the source voltage of the second transistor is higher than the source voltage of the first transistor. Responsive to a high, diverting a current from the second transistor through the seventh resistor to the second resistor to reduce the gate voltage of the first transistor, thereby The control circuit of claim 5 , configured to reduce the current through the set of warm CCT LEDs. The first resistor is coupled to the control terminal of the first zener diode and both the first transistor and the second resistor,
An anode of the first zener diode is coupled to a ground terminal, and a cathode of the first zener diode is coupled to a gate of the first transistor,
The control circuit according to claim 6 . The second zener diode is coupled to the gate of the second transistor and the ground terminal, the control terminal of the second zener diode is coupled to the third resistor and the fourth resistor,
The third resistor is coupled to the gate of the first transistor,
The fourth resistor is coupled to the ground terminal and the third resistor,
The fifth resistor is coupled to a high voltage and the gate of the second transistor,
The sixth resistor is coupled to the source of the second transistor and the ground terminal,
The control circuit according to claim 7 . The Schottky diode is coupled to the source of the second transistor and the seventh resistor,
The seventh resistor is coupled to the source of the first transistor,
The control circuit according to claim 8 . The control circuit of claim 1, wherein the warm CCT LED has a color temperature of approximately 2200 K and the cool CCT LED has a color temperature of approximately 4000 K. A method of controlling an LED lighting system, comprising:
Controlling a clamp circuit based on the input current to clamp the current through the set of warm CCT LEDs to a clamp current level;
Controlling a switch to turn on a set of cool CCT LEDs in response to the input current being greater than a first threshold level and responsive to the input current being less than the first threshold level; Turning off the cool CCT LED set,
By using a feedback circuit coupled to the clamp circuit and the switch, the clamp circuit is responsive to the worm when the input current exceeds a second threshold level that is higher than the first threshold level. and that the set of CCT LED to divert current to the set of the cool CCT LED,
A method having. Clamping the current controls the gate voltage of a first transistor coupled to the set of warm CCT LEDs at the clamp current level via a first resistor and a second resistor. Have,
The first resistor is coupled to the control terminal of the first zener diode and both the first transistor and the second resistor,
An anode of the first zener diode is coupled to a ground terminal, and a cathode of the first zener diode is coupled to a gate of the first transistor,
The method according to claim 11 . 13. The method of claim 12, wherein turning on the set of cool CCT LEDs comprises conducting a second transistor in response to conducting the first zener diode. Bypassing current from the set of warm CCT LEDs to the set of cool CCT LEDs is
Responsive to the source voltage of the second transistor being higher than the source voltage of the first transistor to divert a current from the second transistor to the second resistor through a further resistor. 14. The method of claim 13 , comprising lowering the gate voltage of the first transistor, thereby reducing the current through the set of warm CCT LEDs. A control circuit for a light emitting diode (LED) lighting system, comprising:
A clamp circuit coupled to the set of warm correlated color temperature (“CCT”) LEDs,
A switch combined with a set of cool CCT LEDs,
LED controller ,
The switch disconnects the set of cool CCT LEDs to cause the adjustable input current to flow through the set of warm CCT LEDs when the adjustable input current is below a first current threshold;
If the adjustable input current is adjusted above the first current threshold but remains below the second current threshold, controlling the clamping circuit to set the warm CCT LED set. Clamp the current through it to a constant clamp current level,
If the adjustable input current is adjusted higher than the first current threshold but remains lower than the second current threshold, the switch is closed to cause a portion of the input current to decrease. Allows to flow through a set of cool CCT LEDs,
Gradually increasing the current through the set of warm CCT LEDs when the adjustable input current is higher than the second current threshold and increases past the second current threshold to a maximum current. To zero,
The input current flowing through the set of cool CCT LEDs when the adjustable input current is higher than the second current threshold and increases past the second current threshold to the maximum current. Increasing to the maximum current and increasing the input current through the set of cool CCT LEDs comprises diverting current from the set of warm CCT LEDs to the set of cool CCT LEDs.
An LED controller configured as
A control circuit having a. The control circuit further comprises a feedback circuit coupled to the clamp circuit and the switch, the feedback circuit responsive to the input current exceeding the second current threshold to cause the clamp circuit to: 16. The control circuit of claim 15 , configured to divert current from a set of warm CCT LEDs to the set of cool CCT LEDs. Clamping the current controls the gate voltage of a first transistor coupled to the set of warm CCT LEDs at the clamp current level via a first resistor and a second resistor. Have,
The first resistor is coupled to the control terminal of the first Zener diode and both the first transistor and the second resistor,
An anode of the first zener diode is coupled to a ground terminal, and a cathode of the first zener diode is coupled to a gate of the first transistor,
The control circuit according to claim 15 . Closing the switch to allow a portion of the input current to flow through the set of cool CCT LEDs causes a second transistor to conduct in response to the first zener diode conducting. The control circuit according to claim 17 , further comprising:

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