TWI604757B - Line voltage compensation system for LED constant current control - Google Patents

Description

Line voltage compensation system for LED constant current control

Certain embodiments of the invention relate to integrated circuits. More specifically, some embodiments of the present invention provide a line voltage compensation system for LED constant current control.

As a new energy-saving and environmentally friendly light source, LED is widely used in various fields due to its high brightness, low power consumption and long life. Since the luminance of the LED is proportional to the current flowing in the range close to the rated current and is independent of the voltage across it, the LED is expected to supply power by the constant current source during operation.

Figure 1 shows a conventional LED linear constant current control system 100. The system is widely used in the field of LED lighting due to its simple structure and low system cost. The primary control unit of system 100 (shown in phantom) includes sense resistor 101, power adjustment transistor 102, and error amplifier 103. The positive input terminal of the error amplifier inputs a reference voltage V _ref , and the negative input terminal is connected to the sense resistor 101 ; the output of the error amplifier is connected to the gate of the power adjustment transistor 102 .

As shown in FIG. 1, system 100 receives an alternating current (AC) input voltage 110 when powered up. The voltage 110 is comprised by a rectifier 120 (eg, a full wave rectifier bridge), which in turn generates a rectified output current for operation of the power conversion system 100. One end of the capacitor 104 is connected to the output of the rectifier 120, and one end is grounded. The rectified output current produces a _bulk voltage V _bulk on capacitor 104.

After the power amplifier of the control unit is powered on, the gate voltage is controlled to make the power regulating tube 102 in an on state. When the V _bulk voltage is higher than the minimum breakdown voltage of the LED, the current flows through the LED and flows into the sensing resistor 101 via the power adjustment tube 102, wherein the voltage of 101 corresponds to the inflow current of the LED. The error amplifier adjusts the voltage _Vsense of the sensed resistor 101 and the reference voltage _{Vref of the} other input to adjust the gate voltage of the power regulating transistor 102, thereby achieving constant current control of the LED. The output LED current I _{led is} shown in Equation 1: Wherein R ₁ represents the resistance of the resistor 101, and V _ref represents a reference voltage.

In some applications such as high PF (Power Factor) or TRIAC dimming, since the capacitance of the capacitor 104 is small, the V _bulk enters the anode of the LED with the waveform rectified by the AC signal. This results in the LED being unable to conduct due to insufficient breakdown voltage in the city electrical frequency cycle (for example, 0.02 s) where the V _bulk voltage is low, so that no current flows through the LED. So in this application scenario, the output LED current I _{led is} shown in Equation 2: Where T represents the power frequency period and _Ton represents the on time of the LED in the power frequency period.

The problem brought by this is that, according to (Equation 2), when the voltage of the mains grid fluctuates, the on-time _Ton of the LED in the electrical cycle of the L city also changes, resulting in a change in the output current _{Iled of the LED} . The input line voltage regulation of the system is poor. The voltage regulation rate characterizes the relative change in output current due to changes in the input voltage when all other influence quantities (eg, temperature, etc.) remain constant, expressed as a percentage. The smaller the voltage regulation rate, the better the system performance. Excessive voltage regulation will lead to unstable system operation.

Therefore, there is a great need for improved line voltage compensation techniques for LED constant current control.

Certain embodiments of the invention relate to integrated circuits. More specifically, some embodiments of the present invention provide systems and methods for overvoltage protection. By way of example only, some embodiments of the invention are applied to an LED lighting system. However, it should be understood that the invention has broader Scope of application.

According to an embodiment, a line voltage compensation system for LED constant current control is provided, the system includes: an error amplifier, a positive input terminal input reference voltage of the error amplifier, a negative input terminal connected to the compensation resistor; and a power adjustment tube The source of the power adjustment tube is connected to the first sensing resistor, the gate is connected to the output end of the error amplifier, and the drain is connected to the cathode of the external LED; wherein the first sensing resistor has one end and the compensation resistor and the error The negative input terminals of the amplifier are connected in series, one end is grounded, the second sensing resistor is connected between the negative input terminal of the error amplifier and the cathode of the LED, and one end of the compensation resistor is connected to the negative input end of the error amplifier, and one end is connected. A sense resistor.

In accordance with another embodiment, an LED luminaire comprising a line voltage compensation system for LED constant current control as described in an embodiment of the present disclosure is provided.

According to an embodiment, one or more benefits may be obtained. These and other additional objects, features and advantages of the present invention will become apparent from the Detailed Description and appended claims.

101‧‧‧Sensor Resistors

407‧‧‧voltage source

507‧‧ ‧ diode

607‧‧‧Regulators

V _ref ‧‧‧reference voltage

V _bulk ‧‧‧ body voltage

I _led ‧‧‧LED current

100, 200, 300, 400, 500, 600‧‧‧ systems

102, 205, 305, 405, 505, 605‧‧‧ power adjustment tubes

103, 204, 304, 404, 504, 604‧‧‧ error amplifier

104, 206, 306, 406, 506, 606‧‧ ‧ capacitors

110, 210, 310, 410, 510, 610, V _sense ‧ ‧ voltage

120, 220, 320, 420, 520, 620‧‧ ‧ rectifier

201, 301, 401, 501, 601‧‧‧ first sensing resistor

202, 302, 402, 502, 602‧‧‧ second sensing resistor

203, 303, 403, 503, 603‧‧‧ compensation resistors

230, 330, 430, 530, 630‧‧‧ LED

Figure 1 shows a conventional LED linear constant current control system.

2 is a schematic diagram of a line voltage compensation circuit of an LED linear constant current system, in accordance with an embodiment of the present disclosure.

3 is a schematic diagram of a line voltage compensation circuit of an LED linear constant current system in accordance with a preferred embodiment of the present disclosure.

Figure 4 is a schematic diagram of an improved line voltage compensation circuit for an LED linear constant current system in accordance with the embodiment of Figure 3.

Figure 5 is a schematic diagram of an improved line voltage compensation circuit for an LED linear constant current system in accordance with the embodiment of Figure 3.

Figure 6 is a schematic diagram of an improved line voltage compensation circuit for an LED linear constant current system in accordance with the embodiment of Figure 3.

Features and exemplary embodiments of various aspects of the invention are described in detail below. In the following detailed description, numerous specific details are set forth However, it will be apparent to those skilled in the art that the present invention may be practiced without some of the details. The following description of the embodiments is merely provided to provide a better understanding of the invention. The present invention is in no way limited to any specific configurations and algorithms presented below, but without departing from the spirit and scope of the invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessary obscuring the invention.

Certain embodiments of the invention relate to integrated circuits. More specifically, some embodiments of the present invention provide a line voltage compensation system for LED constant current control. By way of example only, some embodiments of the invention are applied to LED lighting. However, it will be appreciated that the invention has a broader scope of applicability.

The invention provides a line voltage compensation system for LED constant current control, which can realize low-cost LED linear constant current system line voltage compensation function through the setting of the system peripheral sensing resistor and the compensation resistor. Preferably, the control method of the present invention can be applied to the field of LED illumination in a linear constant current control mode with high PF or TRAIC dimming.

2 is a schematic diagram of a line voltage compensation circuit of an LED linear constant current system, in accordance with an embodiment of the present disclosure. As shown in FIG. 2, the control system 200 for controlling the LEDs 230 may include a first sensing resistor 201, a second sensing resistor 202, a compensation resistor 203, an error amplifier 204, and a power adjustment tube 205.

As shown in FIG. 2, system 200 receives an alternating current (AC) input voltage 210 when powered up. The voltage 210 is comprised by a rectifier 220 (eg, a full wave rectifier bridge), which in turn generates a rectified output current for operation of the power conversion system 200. One end of the capacitor 206 is connected to the output of the rectifier 220, and one end is grounded. The rectified output current produces a _bulk voltage V _bulk on capacitor 206.

The forward input of the error amplifier 204 inputs a reference voltage V _ref , the negative input is grounded via a series connected compensation resistor 203 , a first sense resistor 201 , and is connected to the rectifier 220 via a second sense resistor 202 The output of the error amplifier 204 is connected to the gate of the power adjustment transistor 205. The source of the power adjustment tube 205 is connected to the first sense resistor 201, the gate is connected to the output of the error amplifier 205, and the drain is connected to the cathode of the LED 230. One end of the first sensing resistor 201 is connected in series with the negative input terminal of the compensation resistor 203 and the error amplifier 204, and one end is grounded. A second sense resistor 202 is coupled between the negative input of the error amplifier 204 and the output of the rectifier 220. One end of the compensation resistor 203 is connected to the negative input terminal of the error amplifier 204, and one end is connected to the first sensing resistor 201.

In the example of FIG. 2, the power adjustment tube 205 is an insulated gate bipolar transistor (IGBT). In another example, power conditioning tube 205 is a bipolar junction transistor. In another example, power conditioning transistor 205 is a field effect transistor (eg, a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET)). In various examples, control system 200 can include more or fewer components, wherein the value of reference voltage _Vref can be set as desired by those skilled in the art.

The second sensing resistor 202 has a resistance value R2. R2 is a line voltage sensing resistor, and the current I _R2 flowing through the second sensing resistor 202 is as shown in Equation 3: Wherein, V _bulk represents that the mains is rectified by the rectifier 220 to generate a voltage on the capacitor 206 (which characterizes the input voltage of the system), R ₂ represents the resistance of the second sense resistor 202, and V _ref represents the reference voltage. The current I _R2 flowing through the second sense resistor 202 corresponds to a change in the input voltage V _bulk .

Assuming that the compensation resistor 203 has a resistance value R3 to adjust the compensation amount of the line voltage, the output LED current I _{led is} as shown in Equation 4 or Equation 5:

Or Equation 5 Wherein, R ₁ represents the resistance of the first sensing resistor 201, and R ₃ represents the resistance of the compensation resistor 203.

In the system of Fig. 2, the V _bulk connected to the second sense resistor 202 is a mains rectified voltage having a maximum voltage of up to several hundred volts. Therefore, the system sometimes has to use a relatively high-priced high withstand voltage resistor, or a combination of a plurality of resistors connected in series as the second sense resistor 202.

3 is a schematic diagram of a line voltage compensation circuit of an LED linear constant current system in accordance with a preferred embodiment of the present disclosure. As shown in FIG. 3, the control system 300 for controlling the LEDs 330 may include: a first sensing resistor 301, a second sensing resistor 302, a compensation resistor 303, an error amplifier 304, and a power adjustment tube 305. .

As shown in FIG. 3, system 300 receives an alternating current (AC) input voltage 310 when powered up. Voltage 310 is comprised by a rectifier 320 (eg, a full wave rectifier bridge), which in turn generates a rectified output current for operation of power conversion system 300. One end of the capacitor 306 is connected to the output of the rectifier 320, and one end is grounded. The rectified output current produces a _bulk voltage V _bulk on capacitor 306.

The positive input terminal of the error amplifier 304 inputs a reference voltage V _ref , the negative input terminal is connected to the compensation resistor 303 and the first sensing resistor 301 , and the output of the error amplifier is connected to the gate of the power adjustment tube 305 . The source of the power adjustment tube 303 is connected to the first sense resistor 301, the gate is connected to the output of the error amplifier 304, and the drain is connected to the cathode of the LED 330. One end of the first sensing resistor 301 is connected in series with the negative input terminal of the compensation resistor 303 and the error amplifier 304, and one end is grounded. A second sense resistor 302 is coupled between the negative input of the error amplifier 304 and the cathode of the LED 330. One end of the compensation resistor 303 is connected to the negative input terminal of the error amplifier 304, and one end is connected to the first sensing resistor 301.

In the example of FIG. 3, the power adjustment tube 305 is an insulated gate bipolar junction transistor (IGBT). In another example, power conditioning tube 305 is a bipolar junction transistor. In another example, power conditioning tube 305 is a field effect transistor (eg, a metal oxide semiconductor field effect transistor (MOSFET)). In various examples, control system 300 can include more or fewer components, wherein the value of reference voltage _Vref can be set as desired by those skilled in the art.

As shown in FIG. 3, the second sense resistor 302 connected to the cathode of the LED 330 has a resistance value R2, and R2 represents a line voltage sense resistor. The current I _R2 flowing through the second sensing resistor 302 is as shown in Equation 6: Wherein, V _bulk represents that the commercial power is rectified by the rectifier 320 to generate a voltage on the capacitor 306 (which characterizes the input voltage of the system), R ₂ represents the resistance of the second sensing resistor 302, and V _led represents the forward voltage of the LED 330. Drop, and V _ref represents the reference voltage.

Similarly, assuming that the compensation resistor 303 has a resistance value R3 to adjust the compensation amount of the line voltage, the output LED 330 current I _{led is} as shown in Equation 7 or Equation 8: Or Equation 8, Wherein R ₁ represents the resistance of the first sensing resistor 301.

Since the maximum voltage at the cathode of the LED is only about several tens of volts, and the current flowing through the second sensing resistor 302 also corresponds to the change in the input voltage V _bulk , the second sensing resistor 302 in the system of FIG. 3 can The line voltage compensation function is realized by selecting a common withstand voltage resistor with a lower cost. Alternatively, the second sense resistor 302 can be a single resistor.

In yet another embodiment, further compensation optimization for the architecture of Figure 3 is illustrated in accordance with FIG. In the system 400 of FIG. 4, the second sense resistor 402 is connected in series between the negative input of the error amplifier 404 and the cathode of the LED 430 via a voltage source 407; The negative electrode of the voltage source 407 is connected to the second sensing resistor 402, and the positive electrode is connected to the cathode of the LED 430. Other components and connection methods are similar to those of FIG. 3 and will not be described herein.

The current through the second sensing resistor 402 corresponds to a change in the input voltage V _bulk , as shown in equation (9),

Wherein, V _bulk represents that the commercial power is rectified by the rectifier 420 to generate a voltage on the capacitor 406 (which characterizes the input voltage of the system), R ₂ represents the resistance of the second sensing resistor 402, and V _led is the forward voltage drop of the LED conduction. V0 is the voltage of the voltage source 407.

Similarly, assuming that the compensation resistor 403 has a resistance value R3 to adjust the compensation amount of the line voltage, the output LED 430 current I _{led is} as shown in Equation 10 or Equation 11:

Or Equation 8, Wherein R ₁ represents the resistance of the first sensing resistor 301.

Since the second sensing resistor 402 is connected to the cathode of the LED through the voltage source 407, and the maximum voltage of the node is several tens of volts, the performance requirement of the resistor is low, and the line voltage compensation can be realized by using a low-cost ordinary withstand voltage resistor. Features.

In yet another embodiment, further compensation optimization for the architecture of Figure 3 is illustrated in accordance with FIG. In the system 500 of FIG. 5, the second sensing resistor 502 is connected in series between the negative input terminal of the error amplifier 504 and the cathode of the LED 530 through the diode 507; wherein the negative electrode of the diode 507 is The second sensing resistor 502 is connected, and the positive electrode is connected to the cathode of the LED 530. Other components and connection methods are similar to those of FIG. 3 and will not be described herein. The unidirectional conduction characteristic of the diode 507 is used to stabilize the voltage, and the second sensing resistor 502 is further protected, thereby reducing the performance requirements of the resistor.

In still another embodiment, the structure of the third figure is shown according to FIG. One step compensation optimization. In the system 600 of FIG. 6, the second sense resistor 602 is connected in series between the negative input terminal of the error amplifier 604 and the cathode of the LED 630 via the voltage stabilizing diode 607; wherein the voltage stabilizing diode 607 The positive electrode is connected to the second sensing resistor 502, and the negative electrode is connected to the cathode of the LED 630. Other components and connection methods are similar to those of FIG. 3 and will not be described herein. The reverse breakdown characteristic of the voltage stabilizing diode 607 is used to stabilize the voltage, and the second sensing resistor 602 is further protected, thereby reducing the performance requirements of the resistor.

The invention provides a line voltage compensation system for LED constant current control System, low-cost LED lines can be realized through the system's peripheral sensing resistors and compensation resistors. Linear constant current system line voltage compensation function. Preferably, the control method of the present invention can be applied to take high PF Or TRAIC dimming linear constant current control in the field of LED lighting.

For example, using one or more software components, one or more hardware components, and/or one or more combinations of software and hardware components, some or all of the various embodiments of the present invention are each separately and/or It is implemented in a manner that is combined with at least another component. In another example, some or all of the elements of various embodiments of the invention are each implemented individually and/or in combination with at least another element, such as one or more analog circuits and/or one or more digits. In one or more circuits such as circuits. In another example, various embodiments and/or examples of the invention may be combined.

Although specific embodiments of the invention have been described, it will be understood by those skilled in the art Therefore, it is to be understood that the invention is not to be limited

300‧‧‧ system

301‧‧‧First sensing resistor

302‧‧‧Second sensing resistor

303‧‧‧Compensation resistor

304‧‧‧Error amplifier

305‧‧‧Power adjustment tube

306‧‧‧ capacitor

310‧‧‧ voltage

320‧‧‧Rectifier

330‧‧‧LED

V _ref ‧‧‧reference voltage

V _bulk ‧‧‧ body voltage

Claims (15)

A line voltage compensation system for LED constant current control, the system comprising: an error amplifier, a positive input terminal of the error amplifier inputting a reference voltage, a negative input terminal connected to the compensation resistor; a power adjustment tube, The source of the power adjustment tube is connected to the first sensing resistor, the gate is connected to the output end of the error amplifier, and the drain is connected to the cathode of the external LED; wherein the first sensing resistor has one end and a compensation resistor And a negative input terminal of the error amplifier connected in series, one end is grounded, a second sensing resistor is connected between the negative input terminal of the error amplifier and a cathode of the LED, and the compensation resistor is connected at one end to the a negative input terminal of the error amplifier, one end of which is connected to the first sensing resistor; wherein a voltage source is further connected in series between the second sensing resistor and the LED, a negative pole of the voltage source and the first The two sense resistors are connected and the positive pole is connected to the cathode of the LED. The system of claim 1, wherein the current IR2 flowing through the first sensing resistor is determined as follows: Where Vbulk represents the input voltage of the system, R2 represents the resistance of the second sense resistor, Vled represents the forward voltage drop of the LED conduction, and Vref represents the reference voltage. The system of claim 1, wherein the power adjustment tube is an insulated gate bipolar junction transistor IGBT. The system of claim 1, wherein the reference voltage is variable. The system of claim 1, wherein the first sensing resistor is a single resistor. A line voltage compensation system for LED constant current control, the system comprising: An error amplifier, a positive input terminal of the error amplifier inputs a reference voltage, a negative input terminal is connected to the compensation resistor; a power adjustment tube, a source of the power adjustment tube is connected to the first sensing resistor, and the gate is The output of the error amplifier is connected, and the drain is connected to the cathode of the external LED; wherein, one end of the first sensing resistor is connected in series with the compensation resistor and the negative input end of the error amplifier, one end is grounded, and the second sense a resistance resistor is connected between the negative input terminal of the error amplifier and a cathode of the LED, the compensation resistor is connected at one end to a negative input terminal of the error amplifier, and one end is connected to the first sensing resistor A diode is further connected in series between the second sensing resistor and the LED, a cathode of the diode is connected to the second sensing resistor, and a cathode is connected to a cathode of the LED. The system of claim 6, wherein the current IR2 flowing through the first sensing resistor is determined as follows: Where Vbulk represents the input voltage of the system, R2 represents the resistance of the second sense resistor, Vled represents the forward voltage drop of the LED conduction, and Vref represents the reference voltage. The system of claim 6, wherein the power adjustment tube is an insulated gate bipolar junction transistor IGBT. The system of claim 6 wherein the reference voltage is variable. The system of claim 6 wherein the first sensing resistor is a single resistor. A line voltage compensation system for LED constant current control, the system comprising: an error amplifier, a positive input terminal of the error amplifier inputting a reference voltage, a negative input terminal connected to the compensation resistor; a power adjustment tube, The source of the power adjustment tube is connected to the first sensing resistor, and the gate is The output of the error amplifier is connected, and the drain is connected to the cathode of the external LED; wherein, one end of the first sensing resistor is connected in series with the compensation resistor and the negative input end of the error amplifier, one end is grounded, and the second sense a resistance resistor is connected between the negative input terminal of the error amplifier and a cathode of the LED, the compensation resistor is connected at one end to a negative input terminal of the error amplifier, and one end is connected to the first sensing resistor a voltage stabilizing diode is further connected in series between the second sensing resistor and the LED, a positive pole of the voltage stabilizing diode is connected to the second sensing resistor, and a negative pole and the LED Cathode connection. The system of claim 11, wherein the current IR2 flowing through the first sensing resistor is determined as follows: Where Vbulk represents the input voltage of the system, R2 represents the resistance of the second sense resistor, Vled represents the forward voltage drop of the LED conduction, and Vref represents the reference voltage. The system of claim 11, wherein the power adjustment tube is an insulated gate bipolar junction transistor IGBT. The system of claim 11, wherein the reference voltage is variable. The system of claim 11, wherein the first sensing resistor is a single resistor.