TWI497010B - LED lamps THD improvement circuit - Google Patents

Description

THD improvement circuit for LED lamps

The invention belongs to the technical field of Light Emitting Diode (LED) power supply devices, in particular to a THD (Total Harmonic Distortion) improvement circuit for an LED lamp, which is external to the external through a simple circuit architecture. The change of the voltage source is compensated to make the LED power reach a stable state while limiting the effect of THD within the specification.

Since LEDs have been used in the lighting market due to their low power consumption and high efficiency, how to control the lighting brightness, work efficiency or service life of LED lamps has become the goal of various manufacturers. At present, LED lamps mostly use a constant current architecture control circuit, which is connected to an N-type Metal Oxide Semiconductor Field Effect Transistor (N-MOSFET) and a current resistor. The current resistance defines the drive current flowing through the LED. The current resistor receives the driving current and forms a feedback voltage at one of the two operational amplifiers, and the operational amplifier compares the voltage drop value with a reference voltage value, and then passes through the operational amplifier, the N-MOSFET, and The negative feedback circuit formed by the current resistors has a voltage drop across the current resistor fixed to be equal to the reference voltage value to maintain the driving current in a constant state, and at the same time, it is convenient to limit the THD to a limited range. Products are sold in various markets.

In general, lighting fixtures are designed according to different harmonic standards depending on the country and region of sale. For example, lighting fixtures sold in the EU or European Free Trade Zone refer to EN61347 and EN61000-3-2 current. Harmonic quality standards, when the input power is greater than 25W, refer to Class C requirements, and less than 25W meet Class D requirements. At present, although EN61347 does not regulate THD, Taiwan's national standard CNS15233 requires THID to be less than 33%. The US Energy Star standard ANSI_C82-77-2002 requires THD to be less than 32% and some special products to be 20%. However, when the voltage value of the external power supply of the LED lamp changes, the driving current and THD will change accordingly, and the larger the output power, the more difficult the THD is to be controlled and cannot be stably maintained in the specification, resulting in unstable product quality. Cut into some markets and limit the economic value of the industry. At this time, if the safety component is stabilized, the THD will increase the cost of the lamps and will not benefit the economic benefits.

In view of this, how to stabilize the LED while using the simplest circuit architecture to limit the THD to a range and comply with the standards of EN61000-3-2, CNS15233 or ANSI_C82-77-2002 without additional safety components. The improvement of the working quality of the luminaire by the illuminating power is the subject of the invention.

In view of the problems of the prior art, it is an object of the present invention to provide a THD improvement circuit for an LED lamp to improve product adaptability and economic value by using a circuit with a simple structure to limit THD within a limited range.

According to the purpose of the present invention, the THD improving circuit of the LED lamp is used for improving the lighting stability of the LED lamp. The LED lamp is provided with at least one light emitting diode, a regulator, a current resistor and a first comparator. The illuminator is coupled to the illuminating diode, the current resistor and the first comparator, and the illuminating diode receives an input voltage to form a driving current, so that the current resistor receives the driving current and forms at both ends After the voltage is fed back to the first comparator, the first comparator controls the regulator to adjust the driving current, wherein the THD improving circuit of the LED lamp has a detecting unit and a second comparator. a first switch and a second switch, the detecting unit is electrically connected to the negative input end of the light emitting diode and the second comparator, and the positive input end of the second comparator receives a reference voltage value, and the output The first switch and the second switch are coupled to the positive input end of the first comparator, and the other end of the second switch receives the reference voltage The detection unit detects The input voltage outputs a detected voltage value to the second comparator to compare the reference voltage value. When the detected pressure value is less than the reference pressure value, the second comparator turns on the first switch and ends the second Switching, outputting the detected voltage value to the first comparator, so that the current value of the driving current depends on the actual voltage of the input voltage a value change; when the detected pressure value is greater than the reference pressure value, the second comparator turns off the first switch to turn on the second switch, and outputs the reference voltage value to the first comparator to fix the driving current Dividing the reference voltage by the current value of the current resistor amounts to a fixed LED current and limits the THD's effectiveness within the specification.

Moreover, when the light emitting diode is a series of complex array strings and a voltage node is formed between each of the strings, the THD improving circuit of the LED lamp further has at least one segmented conductive device that receives the input. The voltage is converted to form an output current, and the voltage switches are coupled to the voltage nodes through the plurality of switching switches to detect the voltage values of the voltage nodes, and the switching voltages are controlled after the switches are controlled. In the open/close state, the output current is output to the corresponding set of strings, and the effect of illuminating the light-emitting diodes in a segmental manner is achieved.

In summary, the present invention utilizes an external resistor to detect the external power supply variation and then uses the transistor to switch the operational reference value when the lamp is operated, so as to replace the traditional complicated regulation mode to achieve high and low voltage compensation and stabilize the total harmonic value of the circuit. To improve the lighting quality and product life of the LED lamp, and to simplify the circuit structure and reduce the process difficulty and production cost.

1‧‧‧LED lamps

10‧‧‧Rectifier circuit

11‧‧‧Control circuit

110‧‧‧Control chip

1100‧‧‧First comparator

111‧‧‧Regulator

112‧‧‧current resistance

12‧‧‧THD improvement circuit

120‧‧‧Detection unit

1200‧‧‧First resistance

1201‧‧‧second resistance

121‧‧‧Second comparator

122‧‧‧First switch

123‧‧‧Second switch

124‧‧‧Backgate

125‧‧‧Compensation resistance

126‧‧‧ drive

127‧‧‧ Segmented Conductor

14‧‧‧Lighting diode

Figure 1 is a block diagram of a preferred embodiment of the present invention.

Figure 2 is a circuit diagram showing an embodiment of a preferred embodiment of the present invention.

Figure 3 is a waveform diagram of an embodiment of the preferred embodiment of the present invention.

Figure 4 is a circuit diagram showing a second embodiment of the preferred embodiment of the present invention.

Figure 5 is a schematic circuit diagram of a third embodiment of the preferred embodiment of the present invention.

Figure 6 is a waveform diagram of a third embodiment of the preferred embodiment of the present invention.

In order for your review board to have a clear understanding of the contents of the present invention, please refer to the following description for matching drawings.

Please refer to FIG. 1 and FIG. 2 for a block diagram of a preferred embodiment of the present invention and a circuit diagram of an embodiment. As shown in the figure, the LED lamp 1 is provided with a rectifying circuit 10, a control circuit 11, a THD improving circuit 12 and at least one light emitting diode 14. The control circuit 11 is provided with at least one of the first comparators 1100. The control chip 110, a regulator 111 and a current resistor 112, the THD improving circuit 12 has a detecting unit 120, a second comparator 121, a first switch 122, a second switch 123 and a reverse gate 124. In order to stabilize the illumination intensity projected by the LED lamp 1 and to limit the total THD value to be maintained within the standard specifications. The rectifier circuit 10 can be coupled to an external power source (not shown), the control circuit 11 and the LED diode 14 for rectifying the AC voltage of the external power source to form the driving control circuit 11 and the bridge rectifier. The light-emitting diode 14 operates at an input voltage (V _in ), and the light-emitting diode 14 uses the input voltage to perform electro-optic energy conversion to emit light while forming a driving current (I _LED ). The regulator 111 is an N-MOSFET, the drain is coupled to the LED 14 , the source is coupled to the current resistor 112 and the negative input of the first comparator 1100 , and the gate is coupled to the first comparator The output of the 1100 provides a stable linear dimming performance to form a negative feedback circuit architecture. At the same time, it is known from the physical characteristics of the operational amplifier that when the positive input terminal of the first comparator 1100 receives a reference voltage value (V _ref When the negative input is also locked to the same voltage value.

The detecting unit 120 has a first resistor 1200 and a second resistor 1201, and the first switch 122 and the second switch 123 are N-MOSFETs. The first resistor 1200 is coupled to the LED 14 at one end, and coupled to the second resistor 1201, the negative input terminal of the second comparator 121, and the drain of the first switch 122, and the first switch The gate of the second comparator 121 is coupled to the output of the first comparator 1100 and the source of the second switch 123. The gate of the second switch 123 receives the reference voltage, and the gate is coupled to the output of the reverse gate 124 to be coupled to the output of the second comparator 121 through the reverse gate 124.

Moreover, the detecting unit 120 divides the input voltage by the second resistor 1201 to form a stable detected voltage value (V _sen ), so that the second comparator 121 compares the reference voltage value. When the detected voltage is less than the reference voltage, the second comparator 121 outputs a high-voltage signal to turn on the first switch 122. At the same time, the high-voltage signal is inverted by the reverse gate 124 and then turned into a low-voltage standard. The second switch 123 is turned off by the signal, so that the first switch 122 directly outputs the detected detection voltage value received by the 汲 terminal to the first comparator 1100. In this way, the current value of the driving current will change according to the actual voltage value of the input voltage, thereby realizing the dimming effect. On the other hand, when the detected voltage is greater than the reference voltage, the second comparator 121 turns off the first switch 122 and turns on the second switch 123, so that the second switch 123 outputs the reference that the 汲 terminal receives. The voltage is applied to the first comparator 1100. According to the above operational amplifier principle, the driving current will be a constant current value divided by the current resistance 112 to achieve a fixed LED current and limit the THD efficiency within the specification, as shown in FIG.

Furthermore, in order to avoid the high-low voltage variation of the input voltage during dimming, the electro-optical energy conversion performance of the LED 14 is affected, or the physical characteristics of the LED 14 are prevented from contaminating the input voltage, and a high-low voltage difference occurs. The problem is that the THD improving circuit 12 is provided with a compensation resistor 125, one end of which is coupled to the first resistor 1200 and the second resistor 1201 to form a first node (N ₁ ), and another One end of the regulator 111, the current resistor 112 and the negative input of the first comparator 1100 are coupled to form a second node (N ₂ ). When the input voltage is increased to increase the first node voltage value to be greater than the second node voltage value, the compensation resistor 125 forms a compensation current (I _com ) from the first node to the second node direction, and vice versa. When the input voltage is lowered, the compensation current flowing from the second node to the first node is formed. Due to the operating characteristic of the negative feedback circuit, the voltage value of the second node is fixed to the reference voltage value such that the current resistance 112 has a constant voltage drop value, and the resistance of the current resistor 112 does not change. The current value (I _cur ) flowing through the current resistor 112 is fixed. Moreover, the driving current sums the compensation current as the current flowing through the current resistor 112, and I _LED +I _COM =I _cur , so when the compensation current flows to the current resistor 112, the driving current can be reduced. The effect, and vice versa, increases the drive current. In other words, the compensation current is formed by the voltage difference between the first node and the second node to compensate the driving current to further stabilize the luminous power of the LED 14 at a constant value.

Incidentally, when the LEDs 14 are in a plurality of parallel use modes, the LEDs 14 can be coupled to the regulator 111 via a driver 126 for adjustment by an internal current mirror of the driver 126. After the driving current is amplified by the series, the driving current is controlled to be output to the corresponding LED 14 to partially or sequentially illuminate the LEDs 14. In order to reduce the THD of the linear driving circuit of the LED lamp 1 and increase the power factor (PF), the driving current needs to be increased or decreased according to the AC voltage waveform of the external power source, so in addition to the above, the THD is improved. The circuit 12 is further coupled to the segment resistor 127 as shown in FIG. 5, and is coupled to the first resistor 1200 through the VS1 pin and coupled to the second resistor 1201 through the VS2 pin, and directly or through the ISET pin. The driver 126 is coupled to the drain of the regulator 111 to directly output the driving current or to pass through the current mirror to amplify and output. When the LEDs 14 are in a series of complex arrays as shown in FIG. 5, for example, the LEDs 14 are divided into first to fourth strings from top to bottom. When three voltage nodes (V ₁ , V ₂ , V ₃ ) are formed between the first and second, second and third, third and fourth strings, the segmented conductive device 127 is respectively transmitted through the OUT0~3 pins. And coupled to each of the corresponding voltage nodes. The segmentation switch 127 obtains a voltage signal by the first resistor 1200 and the second resistor 1201, and then internally generates a plurality of pilot communication numbers to respectively output the corresponding OUT0~3 pins to turn on the corresponding illumination. The diode strings are arranged such that the strings are sequentially turned on in accordance with the change in the voltage of the external power source, so that the THD value is ensured by increasing the time during which the drive current changes with the AC voltage. In this way, the two LEDs generated by the detecting unit 120 can control the LED strings to achieve time-sharing, and the more the number of segments, the better.

As shown in FIG. 6 , the actual measurement signal waveform, I _{LED_1} is the output current waveform of the LED lamp 1 with the single-stage string of the LEDs 14 and the THD improvement circuit 12 and the compensation resistor 125 are not provided. I _{LED_2} is a four- _segment string of the LEDs 14 and the current waveform of the THD improving circuit 12 and the compensation resistor 125 is not provided; I _{LED_3} is a four- _segment string of the LEDs 14. The THD improving circuit 12 is provided without the current waveform of the compensating resistor 125; the I _{LED_4} is the four- _phase string of the LEDs 14 and the THD improving circuit 12 and the compensating resistor 125 are provided. The current waveform shows that the on-period of I _{LED_1} is short and the current waveform does not change with the voltage waveform and has poor THD and PF values. The conduction period of I _{LED_2} increases, but the current waveform does not change with the voltage waveform, which makes the THD and PF values improve, but it is still not ideal. The conduction period of I _{LED_3} increases and the current waveform changes with the voltage waveform, which greatly improves the THD and PF values. The conduction period of I _{LED_4} increases and the current waveform changes with the voltage waveform. When the voltage of the external power source is higher, the current drop in the conduction period is larger, so that the LED lamp 1 achieves input power not due to the input voltage. Increased functionality that produces dramatic changes. Thus, the present invention can effectively limit the THD value and enhance the economic value of the product.

The above description is only illustrative of preferred embodiments and not limiting. Any equivalent modifications or alterations to the spirit and scope of the invention are intended to be included in the scope of the appended claims.

1‧‧‧LED lamps

10‧‧‧Rectifier circuit

11‧‧‧Control circuit

110‧‧‧Control chip

1100‧‧‧First comparator

111‧‧‧Regulator

112‧‧‧current resistance

12‧‧‧THD improvement circuit

120‧‧‧Detection unit

121‧‧‧Second comparator

122‧‧‧First switch

123‧‧‧Second switch

14‧‧‧Lighting diode

Claims (9)

A THD improvement circuit for an LED lamp is provided for improving the illumination stability of the LED lamp. The LED lamp is provided with at least one light emitting diode, a regulator, a current resistor and a first comparator, and the regulator is coupled The light-emitting diode, the current resistor and the first comparator, and the light-emitting diode receives an input voltage to form a driving current, and the current resistor receives the driving current to form a voltage value at both ends and feedback After the first comparator is controlled, the first comparator controls the regulator to adjust the driving current, wherein the THD improving circuit of the LED lamp has a detecting unit, a second comparator, and a first switch. And a second switch, the detecting unit is connected to the negative input end of the light emitting diode and the second comparator, and the positive input end of the second comparator receives a reference voltage value, and the output end is coupled to the first a switch and a trigger end of the second switch; the first switch and the second switch are coupled to the positive input end of the first comparator, and the other end of the second switch receives the reference voltage; the detecting unit Detecting the input voltage And outputting a detection pressure value to the second comparator to compare the reference voltage value, when the detection pressure value is less than the reference pressure value, the second comparator turns on the first switch and turns off the second switch, and outputs the instant The detection voltage value is applied to the first comparator, so that the current value of the driving current changes according to the actual voltage value of the input voltage; when the detection pressure value is greater than the reference voltage value, the second comparator is turned off. The first switch turns on the second switch, outputs the reference voltage value to the first comparator, and fixes the driving current to the reference voltage value divided by the current value of the current resistor to fix the LED current and limit the THD to The effectiveness of the specification. The THD improving circuit of the LED lamp of claim 1, wherein the detecting unit has a first resistor and a second resistor, the first resistor is coupled to the LED and coupled to the other end. The second resistor, the negative input end of the second comparator, and the first switch end, and the second resistor divides the input voltage to form a stable detected pressure value. The THD improving circuit of the LED lamp of claim 2, wherein the first open relationship is an N-type MOSFET, the drain is coupled to the first resistor and the second resistor, the gate The output of the second comparator is coupled to the output of the first comparator Into the end. The THD improvement circuit of the LED lamp of claim 3 is further provided with a reverse gate, the input end of which is coupled to the output end of the second comparator, and the output end of which is coupled to the second switch. The THD improving circuit of the LED lamp of claim 4, wherein the second open relationship is an N-type MOSFET, the source of which is coupled to the positive input terminal of the first comparator, the gate The output of the reverse gate is coupled, and the drain receives the reference voltage. The THD improvement circuit of the LED lamp of the fifth aspect of the invention is further provided with a compensation resistor, the compensation resistor is coupled to the first resistor and the second resistor to form a first node, and the other end is coupled to the The regulator, the current resistor and the negative input end of the first comparator form a second node, and the compensation resistor forms a compensation current by the voltage difference between the first node and the second node to compensate the driving current The light-emitting power of the light-emitting diode is stabilized at a constant value. The THD improving circuit of the LED lamp of claim 6, wherein when the input voltage is increased, the first node pressure value is increased and greater than the second node voltage value, so that the compensation resistor is formed by the first The compensation current flows from a node to the second node, and when the input voltage decreases, the compensation resistor forms the compensation current flowing from the second node toward the first node. The THD improvement circuit of the LED lamp of claim 1, wherein when the light emitting diodes are in a plurality of parallel use modes, the light emitting diode systems are coupled to the regulator through a driver to The driving current is adjusted by the driver to adjust the number of stages, and the driving current is controlled to be output to the corresponding light emitting diode. The THD improvement circuit of the LED lamp of claim 1, wherein the LED lamp is formed when the LEDs are in a series of complex arrays and a voltage node is formed between the strings. The THD improving circuit further has at least one segmented conductive device, which is coupled to the input voltage and converted to form an output current, and coupled to the voltage nodes through a plurality of internal switching switches to detect the voltage of each voltage node. After the value is compared with one of the built-in switching voltage values, the opening and closing states of the switching switches are controlled to output the output current to the corresponding group of strings, thereby realizing the effect of the segmental actuation of the light-emitting diodes.