TWI635776B - Controller for switching regulator, switching regulator and led lighting system - Google Patents

Abstract

A controller for a switching regulator of an LED lighting system having a current monitor, a voltage divider, an integrating circuit, and a comparator circuit. A current monitor is used to sense the LED current through the current sense resistor of the switching regulator and generate a sense current. The voltage divider is configured to receive the sensing current to generate first to third partial pressures, wherein the first partial pressure is greater than the second partial pressure, and the second partial pressure is greater than the third partial pressure. The integrating circuit is for comparing the second divided voltage with the reference voltage and correspondingly generating an integrated voltage across the RC circuit. The comparator circuit is for comparing the integrated voltage with the first divided voltage and the third divided voltage, and generates a driving signal.

Description

Controller, switching regulator and LED lighting system for switching regulators

The present invention relates to a switching regulator for a light source, and more particularly to a controller for a switching regulator, a switching regulator, and an LED illumination system.

The LED lighting system includes a switching regulator and an LED, wherein the switching regulator has a controller therein. The switching regulator is controlled by its controller to supply current to the LEDs. The controller includes an element that calculates an actual amount of charge delivered to the LED system based on an effective time period of the current and the LED current time period, wherein the LED current time period is a duty cycle modulated at a rate greater than 50 Hz and utilized to utilize the actual amount of charge To modify and provide the desired target amount of charge to be transmitted during the future effective time period of the LED current time period.

The LED system also has multiple components to calculate the effective time period of the LED current time period and the actual amount of charge delivered to the LED system, and the LED system also has a number of other components to be used for the effective time period of the LED current time period. The actual amount of charge is compared to the expected amount of charge, and the difference between the actual amount of charge and the desired amount of charge is compensated for in the future effective time period. In order to accurately control the desired amount of charge, the average LED current should be properly controlled and the light intensity of the LEDs be effectively controlled.

Unfortunately, some conventional switching regulators used in LED systems have logic gates and gate drivers (or pre-drivers), so delay problems occur that make it impossible to easily control the average LED current. In addition, the ratio of the inductance of the inductor used in the switching regulator to the input voltage and output voltage (ie, regulator output) of the LED lighting system may also affect the control of the average LED current.

Please refer to Figure 1, which is a block diagram of a conventional LED lighting system. The conventional LED system includes a switching regulator and an LED 12, wherein the switching regulator is a buck regulator, and includes a controller 10, a first current sensing resistor 11, a second current sensing resistor 13, and Zener Polar body 14 and inductor L. The controller 10 is connected to the first current sensing resistor 11, the LED 12, the second current sensing resistor 13, the Zener diode 14, and the inductor L. One end of the first current sensing resistor 11 is for receiving the input voltage Vin, and the other end of the first current sensing resistor 11 is connected to one end of the inductor L. The anode of the Zener diode 14 is connected to the other end of the inductor L, and the cathode 14 of the Zener diode is connected to one end of the second current sensing resistor 13. The anode and cathode of the LED 12 are connected to the other end of the second current sensing resistor 13 and the ground voltage GND, respectively.

The controller includes an error signal generating circuit 101, a fast current monitor 102, a hysteresis controller 103, a resistor 104, a hysteresis comparator 105, a gate driver 106, and an NMOS switch transistor 107. The fast current monitor 102 is connected in parallel with the first current sensing resistor 11 to sense the voltage across the first current sensing resistor 11 and correspondingly generate a first sensing current. The error signal generating circuit 101 is connected in parallel with the second current sensing resistor 13 to sense the voltage across the second current sensing resistor 13 and generate a corresponding error signal, wherein the error signal indicates the desired regulator output and the actual stability. The error between the output of the press.

The hysteresis controller 103 is connected to the negative input terminal and the output terminal of the hysteresis comparator 105, and the positive input terminal of the hysteresis comparator 105 and the hysteresis controller 103 receive the reference voltage Vref such that the hysteresis controller 103 and the hysteresis comparator 105 are formed for control. A hysteresis comparison circuit of the on/off state of the NMOS switch transistor 107. The negative input of hysteresis comparator 105 also receives the voltage across resistor 104, where resistor 104 The two ends of the hysteresis controller 103 are respectively connected to the negative input terminal of the hysteresis comparator 105 and the ground voltage GND, and the voltage between the two ends of the resistor 104 is based on the error signal, the first sensing current and the hysteresis control outputted by the hysteresis controller 103. Formed by a signal. The gate driver 106 is operative to receive the output signal of the hysteresis comparator 105 to generate a drive signal to the gate terminal of the NMOS switch transistor 107. The drain terminal and the source terminal of the NMOS switch transistor 107 are connected to the other end of the inductor L and the ground voltage GND, respectively.

The error signal generating circuit 101 includes an integrator 1011, a precision current monitor 1012, a subtraction unit 1013, and a demand current source 1014. The precision current monitor 1012 is connected in parallel with the second current sensing resistor 13 for sensing the voltage across the second current sensing resistor 13 to generate a second sensing current accordingly. A subtraction unit 1013 is coupled to the integrator 1011 and the demand current source 1014 for subtracting the demand current from the second sense current to produce a subtraction current to the integrator 1011. The demand current source 1014 is for receiving the reference voltage Vref to generate the demand current accordingly. Integrator 1011 is also coupled to the negative input of hysteresis comparator 105 and is used to integrate the subtraction current to produce an error signal. The error signal is the integral of the difference between the demand current and the second sense current, which means that the error signal represents the error between the desired regulator output and the actual regulator output.

Note that although the conventional switching regulator and its controller 10 can solve the above problems affecting the average LED current, two current monitors (ie, the fast monitor 102 and the precision current monitor 1012) are required, thus increasing the circuit hard Body cost, especially the cost of the precision current monitor 1012. Switching regulators with simpler circuits and their controllers are still in demand.

An exemplary embodiment of the present invention provides a controller for a switching regulator of an LED lighting system having a current monitor, a voltage divider, an integrating circuit, and a comparator circuit, wherein the voltage divider A current monitor is connected, an integrating circuit is connected to the voltage divider, and a comparator circuit is connected to the integrating circuit and the voltage divider. A current monitor is used to sense the LED current through the current sense resistor of the switching regulator and generate a sense current. The voltage divider is configured to receive the sensing current to generate first to third partial pressures, wherein the first partial pressure is greater than the second partial pressure, and the second partial pressure is greater than the third partial pressure. The integrating circuit is for comparing the second divided voltage with the reference voltage and correspondingly generating an integrated voltage across the RC circuit. The comparator circuit is for comparing the integrated voltage with the first divided voltage and the third divided voltage, and generates a driving signal. .

Exemplary embodiments of the present invention also provide a switching regulator including the aforementioned controller.

Exemplary embodiments of the present invention also provide an LED illumination system including the aforementioned switching regulator.

In summary, the controller of the switching regulator provided for the LED lighting system can solve the problem of the actual average LED current deviating from the desired average LED current.

The objects, features, and concepts of the present invention will be more fully understood and understood by the appended claims. However, the following detailed description and drawings are merely for the purpose of illustration

10‧‧‧ Controller

101‧‧‧Error signal generation circuit

1011‧‧‧ integrator

1012‧‧‧Precise current monitor

1013‧‧‧Subtraction unit

1014‧‧‧Required current source

102‧‧‧ fast current monitor

103‧‧‧hysteresis controller

104‧‧‧resistance

105‧‧‧hysteresis comparator

106‧‧‧gate driver

107‧‧‧ NMOS switch transistor

11‧‧‧First current sense resistor

12, LD1‧‧‧LED

13‧‧‧Second current sensing resistor

14‧‧‧Zina diode

20‧‧‧LED Lighting System

21‧‧‧ Current monitor

22‧‧‧Divider

23‧‧‧Integral Circuit

24‧‧‧ Comparator Circuit

25‧‧‧Logical Circuit

26‧‧‧Zina diode

A1~A4‧‧‧Area

Avg_Current‧‧‧ Expected current value

C1‧‧‧ capacitor

CMP1‧‧‧ comparator

CUV1‧‧‧Ideal LED current curve

CUV2, CUV3‧‧‧ non-ideal LED current curve

Delay1‧‧‧ conduction delay

Delay2‧‧‧ cutoff delay

GND‧‧‧ Grounding voltage

K‧‧ ratio

L, L1‧‧‧ inductance

M1‧‧‧NMOS transistor

M2‧‧‧ NMOS switch transistor

OP1, OP2‧‧‧Operational Amplifier

R1~R5‧‧‧ resistance

Rs‧‧‧ current sense resistor

Vin‧‧‧Input voltage

Vref‧‧‧reference voltage

Vs‧‧‧ voltage across the current sense resistor Rs

Average voltage of Vs_avg‧‧‧Vs

Vx‧‧‧ voltage regulator output

The drawings are provided to enable a person of ordinary skill in the art to have a further understanding of the invention, and are incorporated in and constitute a part of the specification. The drawings illustrate exemplary embodiments of the invention and, together,

Figure 1 is a block diagram of a conventional LED lighting system.

2 is a schematic diagram of a controller for a switching regulator in an LED lighting system in accordance with an exemplary embodiment of the present invention.

Figure 3 is a waveform diagram of the actual LED current of the controller provided with the exemplary embodiment of the present invention and the non-ideal LED current without the aforementioned controller.

Reference will now be made in detail to the exemplary embodiments embodiments embodiments Wherever possible, the same reference numerals are in the

An exemplary embodiment of the present invention provides a controller for a switching regulator in an LED lighting system (note that the switching regulator can be a buck regulator). The controller has a current monitor, a voltage divider, an integrating circuit, and a comparator circuit. The current monitor is connected in parallel with the current sense resistor, wherein the current sense resistor is used to sense the LED current through the LED. The voltage divider is connected to the current monitor and is used to receive the sense current output of the current monitor. The voltage divider is configured to generate a first partial pressure, a second partial pressure, and a third partial pressure according to the sensing current, wherein the first partial pressure is greater than the second partial pressure, and the second partial pressure is greater than the third partial pressure.

An integrator circuit is coupled to the voltage divider and comparator circuit and is operative to compare the second partial voltage and the reference voltage to produce an integrated voltage across the RC integrating circuit having series connected resistors and capacitors. A comparator circuit is coupled to the voltage divider and compares the integrated voltage to the first divided voltage and the third divided voltage to generate a drive signal to control the NMOS switching transistor to regulate the LED current.

By using an integrating circuit, the non-ideal effect on the desired average LED current can be reduced. Specifically, the delay of the logic circuit, the inductance value of the inductor, and the ratio of the input voltage of the LED illumination system to the output voltage (ie, the regulator output) (ie, the presence of non-ideal effects) can be compensated for The actual average LED current is approximated to the desired average current. Furthermore, by using an integrating circuit, the forward voltage of the LED has no effect on the actual average LED current.

Referring to FIG. 2, FIG. 2 is a schematic diagram of a controller for a switching regulator in an LED lighting system according to an exemplary embodiment of the present invention. The LED illumination system 20 of Figure 2 includes a switching regulator and an LED LD1, wherein the switching regulator is coupled to the LED LD1 and is used to regulate the LED current through the LED LD1.

The switching regulator includes a controller, a current sensing resistor Rs, an inductor L1, and a Zener diode 26. The controller includes a current monitor 21, a voltage divider 22, an integration circuit 23, a comparator circuit 24, a logic circuit 25, and an NMOS switch transistor M2. The controller is used to control the switching regulator to regulate the LED current so that the actual average LED current is expected.

The input voltage Vin is applied to one end of the current sensing resistor Rs. The anode of the LED LD1 is connected to the other end of the current sensing resistor Rs, and the cathode of the LED LD1 is connected to one end of the inductor L1. The anode and cathode of the Zener diode 26 are connected to the other end of the inductor L1 and the one end of the current sense resistor Rs, respectively. The other end of the inductor L1 is used to generate the regulator output Vx.

The current sensing resistor Rs is connected in parallel to the current monitor 21, that is, both ends of the current sensing resistor Rs are connected to the input terminal of the current monitor 21. The voltage divider 22 is connected to the output of the current monitor 21. The two input terminals of the integrator circuit 23 are respectively connected to the inner terminals of the voltage divider 22 and apply a reference voltage K*Vs_avg, where K is a constant, and Vs_avg is the average voltage value of the voltage Vs across the current sense resistor Rs. The three inputs of comparator circuit 24 are coupled to the input of voltage divider 22, the other internal of voltage divider 22, and the output of integrator circuit 23, respectively.

The input terminal and the output terminal of the logic circuit 25 are respectively connected to the output terminal of the comparator circuit 24 and the gate terminal of the NMOS switch transistor M2, and the 汲 terminal and the source terminal of the NMOS switch crystal M2 are respectively connected to the other end of the inductor L1 and the ground voltage. GND.

The current monitor 21 is for receiving the voltage Vs across the current sensing resistor Rs, so the LED current passing through the current detecting resistor Rs can be sensed by the current monitor 21. As such, the current monitor 21 can sense the current based on the LED current output. The current monitor 21 can be realized by the resistor R1, the operational amplifier OP1, and the NMOS transistor M1, but the present invention is not limited thereto.

One end of the resistor R1 is connected to the one end of the current sensing resistor Rs, and the positive input terminal and the negative input terminal of the operational amplifier OP1 are respectively connected to the other end of the current sensing resistor Rs and the other end of the resistor R1. The output of the operational amplifier OP1 is connected to the gate terminal of the NMOS transistor M1, and the NMOS terminal and the source terminal of the NMOS transistor M1 are connected to the other end of the resistor R1 and an input terminal of the voltage divider 22, respectively.

The negative feedback loop is present in the current monitor 21 by the connection of the elements of the current monitor 21 described above, so the sense current is actually approximately Vs/R1. The voltage divider 22 is configured to receive the sensing current and generate first to third partial voltages at the input end and the two internal ends, wherein the first partial pressure is greater than the second partial pressure, and the second partial pressure is greater than the third partial voltage .

The voltage divider 22 can be implemented by resistors R2, R3, and R4 connected in series, and the present invention is not limited thereto. In fact, the first partial pressure is approximately (Vs/R1)*(R2+R3+R4), and the second partial pressure is actually approximately (Vs/R1)*(R3+R4), and the third partial pressure is actually approximately Yes (Vs/R1)*R4. When resistors R2, R3 and R4 are suitably designed, the first to third partial voltages are approximately 1.1 K * Vs, K * Vs, and 0.9 K * Vs, respectively, where K is the ratio of (R3 + R4) / R1.

The integrating circuit 23 compares the second divided voltage (i.e., K*Vs) with the reference voltage K*Vs_avg, and generates an integrated voltage based on the comparison result. Specifically, when the second divided voltage is larger than the reference voltage, a positive voltage is applied to the RC circuit of the integrating circuit 23, so that the integrated voltage across the RC circuit increases; when the second divided voltage is not greater than the reference voltage, negative The voltage is applied to the RC circuit of the integrator circuit 23 such that the integrated voltage across the RC circuit is lowered.

The integrating circuit 23 can be realized by an operational amplifier OP2, a resistor R5, and a capacitor C1. Resistor R5 and capacitor C1 are connected in series to form an RC circuit. The positive input of op amp OP2 is connected to the partial voltage The internal terminal of the device 22 receives the second divided voltage, the negative input of the operational amplifier OP2 applies the reference voltage K*Vs_avg, and the output of the operational amplifier OP2 is connected to the positive input of the comparator circuit 24. One end of the resistor R5 is connected to the output terminal of the operational amplifier OP2, and both ends of the capacitor C1 are respectively connected to the other end of the resistor R5 and the ground voltage GND.

The comparator circuit 24 compares the integrated voltage with the first and third divided voltages to output a drive signal. The comparator circuit 24 can be implemented by a comparator CMP1 having two negative inputs and one positive input, and the invention is not limited thereto. The two negative inputs of the comparator CMP1 are connected to the input of the voltage divider 22 and the other internal terminal thereof, respectively, and the positive input of the comparator CMP1 is connected to the output of the integrating circuit 23. The output of comparator CMP1 is coupled to the input of logic circuit 25.

A logic circuit 25 having a plurality of logic gates is operative to receive the drive signal and accordingly generate a switching signal at its output to control the on/off state of the NMOS switch transistor M2. When the integrated voltage is less than the third divided voltage, the NMOS switch crystal M2 is turned off, and the LED current is increased. When the integrated voltage is greater than the first divided voltage, the NMOS switching transistor M2 is turned on, and the LED current is lowered.

Referring to FIG. 3, FIG. 3 is a waveform diagram of actual LED current of the controller provided by the exemplary embodiment of the present invention and non-ideal LED current without using the foregoing controller. The current curve CUV2 of the non-ideal LED shows that the on and off delays delay1 and delay2 of the NMOS switch transistor M2 affect the average LED current. Note here that the on-delay delay1 and the off-delay delay2 are different from each other, and the regions A1 and A2 shown in FIG. 3 are different from each other such that the actual average LED current cannot be the desired current value Avg_Current.

Further considering the ratio of the input voltage of the LED illumination system and the output voltage (ie, the regulator output Vx), the non-ideal LED current can be represented by the non-ideal LED current curve CUV3, wherein when the NMOS switch transistor M2 is turned off, it is not ideal. The slope of the LED current curve CUV3 is (Vin-Vout) / L, and when the NMOS switching transistor M2 is turned on, the slope of the non-ideal LED current curve CUV3 is Vout / L. It should be noted that since the above multiple effects are different from each other, the areas A3 and A4 shown in Fig. 3 Will be identical to each other, so the actual average LED current is not the desired current value Avg_Current. However, by using an integrating circuit, the non-ideal effect on the desired average LED current can be reduced, and the actual LED current curve can be similar to the ideal LED current curve CUV1.

Thus, in an exemplary embodiment of the invention, the provided controller for a switching regulator for an LED lighting system can address the problem of the actual average LED current deviating from the desired average LED current. The delay, input voltage, regulator output, and even the forward voltage of the LED do not affect the actual average LED current.

The above description is only exemplary embodiments of the invention and is not intended to limit the scope of the invention. Accordingly, various equivalents, modifications, and alterations of the present invention are intended to be included within the scope of the present invention.

Claims (10)

A controller for a switching regulator of an LED lighting system, comprising: a current monitor for sensing an LED current through a current sensing resistor of the switching regulator and generating a sensing a current divider connected to the current monitor for receiving the sense current to generate a first to third partial pressure, wherein the first partial pressure is greater than the second partial pressure, the second partial pressure Greater than the third partial pressure; an integrating circuit coupled to the voltage divider for comparing the second divided voltage with a reference voltage and correspondingly generating an integrated voltage across an RC circuit thereof; A comparator circuit is coupled to the integrating circuit and the voltage divider for comparing the integrated voltage with the first divided voltage and the third divided voltage and generating a drive signal. The controller of claim 1, wherein the current monitor comprises: a first resistor connected at one end to an input voltage and one end of the current sensing resistor; a first operational amplifier having a positive input Connected to the other end of the current sensing resistor, a negative input terminal is connected to the other end of the first resistor; and an NMOS transistor has a drain terminal connected to the other end of the first resistor, and a source terminal thereof Connected to the voltage divider, a gate terminal thereof is coupled to an output of the first operational amplifier. The controller of claim 1, wherein the voltage divider comprises a second to fourth resistor connected in series. The controller of claim 1, wherein the integrating circuit comprises the RC circuit and a second operational amplifier, wherein a positive input terminal of the second operational amplifier is configured to receive the second partial voltage, the second operation A negative input of the amplifier is for receiving the reference voltage, and an output of the second operational amplifier is coupled to the RC circuit. The controller of claim 1, wherein the comparator circuit includes a comparator having a positive input terminal and two negative input terminals, wherein the positive input terminal of the comparator is configured to receive the integrated voltage, and the The two negative inputs of the comparator are for receiving the first partial pressure and the third partial pressure. The controller of claim 4, further comprising: a logic circuit connected to the comparator circuit for receiving the driving signal and correspondingly generating a switching signal; and an NMOS switching transistor having a gate The terminal is connected to the inductor of the switching regulator, and the LED of the LED lighting system is connected between the current sensing resistor and the inductor. The controller of claim 6, wherein the integrated voltage is increased when the second divided voltage is greater than the reference voltage; and the integrated voltage is decreased when the second divided voltage is not greater than the reference voltage; When the voltage is greater than the first partial voltage, the NMOS switch transistor is turned on, and the LED current is decreased; when the integrated voltage is less than the third divided voltage, the NMOS switch transistor is turned off, and the LED current is increased. A switching regulator for an LED lighting system, comprising: the controller according to any one of claims 1 to 5; the current sensing resistor has one end for receiving the input voltage and the other end An anode coupled to the LED of the LED illumination system; an inductor having one end coupled to a cathode of the LED; and wherein the controller is coupled to the current sense resistor and the other end of the inductor. The switching regulator of claim 8 further includes: a Zener diode having an anode and a cathode connected to the other end of the inductor and the current sensing resistor, respectively. An LED lighting system comprising: an LED; and a switching regulator comprising: the controller according to any one of claims 1 to 5; the current sensing resistor having one end for receiving the input voltage The other end is connected to an anode of the LED of the LED illumination system; an inductor having one end connected to a cathode of the LED; and a Zener diode having an anode and a cathode respectively connected to the inductor One end and the current sense resistor; wherein the controller is coupled to the current sense resistor and the other end of the inductor.