KR101155046B1 - Circuit for controlling Constant Power in LED Converter Power Control and realizing Function thereof - Google Patents

Abstract

PURPOSE: A constant current control circuit of an LED converter and a function implementing method thereof are provided to prevent an overload of the LED converter by controlling power applied to a transformer while supplying power. CONSTITUTION: A resonant condenser(240) resonates a primary voltage. An overpower detection circuit measures the change of a resonant frequency and a resonant voltage of the resonant condenser. A power control circuit(218) generates a frequency control signal according to a control signal of an overpower detection circuit. An FET(Field Effect Transistor) driving circuit(214) increases an oscillation frequency according to a frequency control signal. The FET driving circuit reduces power supplied to a load.

Description

Implementation of constant current control circuit and function of LED converter {Circuit for controlling Constant Power in LED Converter Power Control and realizing Function about}

The present invention relates to an LED converter, and more particularly to a constant current control circuit of the LED converter.

Light emitting diodes (hereinafter referred to as "LED lamps") are semiconductor devices, so they have a long life, a fast lighting speed, and low power consumption. In addition, it is strong in impact and advantageous in miniaturization and thinning. Recently, with the rise of energy saving and environmental problems, LED lamps are gradually replacing the existing fluorescent and general lighting in industrial sites such as homes, various stores, factories.

One of the unique characteristics of LED lamps is that the operating voltage changes with the temperature of the LED.

Figure 1a is a conceptual diagram showing the unique characteristics of the LED lamp.

As shown in FIG. 1A, assuming that an infinitely large container is filled with a certain amount of water and the pipe is connected to the outside, and the pipe can move up and down, the height of the water is the voltage supplied to the LED lamp, and the pipe Is the operating voltage inherent to the LED lamp, and the water flowing through the pipe can be regarded as the current. If the height of the pipe is higher than the water level, no water flows through the pipe, but if the height of the pipe is lower than the water level, the water will flow out, and the lower the height of the pipe, the more water will flow out.

Due to the voltage fluctuation characteristics of the LED, the higher the temperature, the lower the operating voltage of the LED lamp. Then, the current flowing through the LED lamp is increased.

The LED lamp has a current that can be allowed by itself, and this is called the rated current of the LED lamp. If it exceeds its rating, the LED lamp is damaged due to overheating.

Therefore, the circuit can be stably operated only by inserting a circuit for adjusting the rated current into the substrate on which the LED is arranged or by supplying only a constant current to a converter device that supplies power to the LED lamp.

Therefore, the constant current function is required for the LED converter.

Conventional techniques for making constant current converters are complex and costly, so constant current converters are on the market at high cost.

In general, the fluorescent lamp is driven by the AC voltage (AC), while the LED lamp is driven by the DC voltage (DC). Accordingly, in order to use an LED lamp as a light source, a power supply device for converting an AC voltage into a DC voltage and generating a DC voltage DC having a desired level is required. Since such a power supply device is usually a hermetic structure, it is necessary to solve the heat and power overload problems, and to solve or improve the power overload problem, a current resonant converter having high efficiency characteristics should be applied.

The LLC resonant converter is being used in the industry because it has a great advantage not only in reducing the price of the product but also in miniaturizing the product through the idea of using the parasitic component present in the transformer as the LLC component.

Figure 1b is a view showing the output current control of the conventional current resonant converter.

As shown in FIG. 1B, the conventional current resonant converter 100 detects a current by using a current sensing resistor and a current sensing circuit 160 on the secondary side (DC output), and detects the current, which is a photocoupler 170. The current control is performed by transferring the control circuit 110 to the primary side IGBT (Insulated Gate Bipolar Transistor) or FET (Field Effect Transistor). The photocoupler 170 insulates the primary side and the secondary side and keeps the output voltage constant.

As shown in FIG. 1C, when the power consumption of the load (eg, 250 W) is greater than the output (eg, 200 W) of the converter, the overload detection circuit 150 of the converter operates the FET driver circuit 114. The converter 100 is stopped to protect the converter 100, and as a result, the power supply applied to the load 130 (for example, the LED lamp) is cut off, so that the user is recognized as a defective phenomenon of the LED lamp power supply. 1C is an exemplary diagram illustrating a case where the power consumption of the load is greater than the output of the converter.

In the conventional LLC resonant converter, the constant current control according to the load variation of the secondary side (DC output stage) uses a complicated and expensive method as shown in FIG. 1B.

In addition, when the power consumption of the load (for example 250W) is more than a certain range, the power supply to the LED lamp is cut off, so that the user is recognized that there is a defect (defect) in the LED lamp device or power supply device Has

An object of the present invention is to provide a constant current control apparatus and method for recognizing an overload situation of an LED converter and controlling the power applied to a transformer by utilizing a primary side current control circuit.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the present invention will be realized and attained by the structure particularly pointed out in the claims, as well as the following description and the annexed drawings.

According to the present invention, the overcurrent detection circuit 250 detects a change in the switching frequency as well as the resonant voltage of the resonant capacitor 240 to accurately recognize the overload situation of the LED converter, and cuts off the power supply applied to the LED lamp. Instead, by controlling the power applied to the transformer 220 while maintaining the power supply to solve the overload situation of the LED converter, improved reliability for the LED lamp device.

In addition, it is possible to implement a compact LED converter circuit at a low cost and simple circuit configuration while performing both constant voltage and constant current.

Figure 1a is a conceptual diagram showing the unique characteristics of the LED lamp.
Figure 1b is a view showing the output current control of the conventional current resonant converter.
Figure 1c is an exemplary view showing a case where the power consumption of the load is larger than the output of the converter.
2 is a block diagram of an LED converter according to the present invention.
3 is a circuit diagram of a current resonant converter.
4 is a graph showing a frequency change and a resonance capacitor voltage change.
Fig. 5 is a circuit diagram showing a resonance part equivalent circuit of a current resonant converter.
6 is a correlation graph of resonant frequency and load power.
Figure 7a is a graph showing the AC transfer characteristics of the capacitor according to the present invention.
Figure 7b is a graph showing the AC transfer characteristics of the conventional capacitor.
8 is a flowchart showing the operation of the LED converter according to the present invention.

In order to achieve the above object, the constant current control circuit of the LED converter according to the present invention, the transformer for converting the input AC power to a direct current and the resonance, and the resonance of the primary side voltage in conjunction with the inductors of the transformer An overpower detection circuit for determining whether the LED converter is in an overloaded state by measuring a capacitor, a change in the resonance voltage and the resonance frequency of the resonant capacitor, and controlling the overpower detection circuit in the case where the LED converter is in an overloaded state. And a power control circuit for generating a frequency adjustment signal in accordance with the signal, and a FET driving circuit for lowering the power provided to the load by increasing the oscillation frequency in accordance with the frequency adjustment signal.

In order to achieve the above object, the constant current control method of the LED converter according to the present invention relates to the constant current control of the current resonance type converter,

When the resonant capacitor 240 resonates with the inductors of the transformer 220 to resonate the primary side voltage, a process of obtaining a load power by detecting a change in the resonant voltage and the resonant frequency of the resonant capacitor, and an overpower detection circuit 250 In step), it is determined whether the load power is higher than the rated power of the LED converter, and when the load power is higher than the rated power of the LED converter, transferring a control signal according to the power control circuit 218, and the power control circuit 218 ), Generating a frequency adjustment signal according to the control signal of the overpower detection circuit; and, in the FET driving circuit 214, increasing the oscillation frequency according to the frequency adjustment signal to lower the power provided to the load. It is done by

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

2 is a block diagram of an LED converter according to the present invention.

LED converter 200 according to the present invention is a current resonant converter, as shown in Figure 2, largely, the control circuit 210, transformer 220, load 230, resonant capacitor 240, over-power It comprises a detection circuit 250.

The control circuit 210 includes a FET driving circuit 214 and a power control circuit 218.

The FET driving circuit 214 receives a commercial AC power and first rectifies and generates a square wave of a high frequency of 18 KHz or higher to induce resonance of the transformer 220 and the resonant capacitor 240.

The control circuit 210 receives an external commercial AC power, performs a switching process using a field effect transistor (FET), and controls power by controlling the magnitude of the resonance of the transformer 220 and the resonant capacitor 240.

The junction transistor BJT is a transistor that turns on / off the collector-emitter by the base current IB, and the MOSFET is a transistor that turns on / off the drain-source by the voltage between the gate and the source. That is, the junction transistor BJT is driven by current, and the MOSFET is driven by voltage. Junction transistors BJT are used for small capacities, and MOSFETs are used for large capacities. However, in the current-driven circuit and the voltage-driven circuit, the current-driven circuit is more complicated and the response speed is slightly slower.

The power control circuit 218 refers to the signal transmitted from the overpower detection circuit 250 to increase the switching frequency when the load power is higher than the rated power of the LED converter, and to increase the switching frequency when the load power is lower than the reference value. Lower the power to control the LED converter.

The transformer 220 receives the square wave pulse voltage generated by the switching elements Q1 and Q2 of the input side switching unit (not shown) and performs LC resonance in conjunction with the resonance capacitor 240. In this case, the transformer 220 is connected to the resonance capacitor. It plays a role to transfer the generated resonance voltage to the secondary side (DC output side). That is, by adjusting the oscillation frequency by a predetermined modulation method (eg, pulse width modulation), the inductance (eg, Lm, Ls) inside the transformer 200 and the resonance characteristics of the resonance capacitor 240 are used. The power supplied to the secondary side is regulated.The transformer 220 converts the AC power of the primary side into DC and applies it to the load (eg, LED lamp) stage.

The resonant capacitor 230 resonates with the primary side voltage in conjunction with inductors (eg, Lm and Ls) inside the transformer 200.

The overpower detection circuit 250 detects the output power by detecting the resonant voltage and frequency periodically (or continuously), and determines whether the output power is higher than the reference value (for example, the rated power of the LED converter) by the LED converter. If higher than the rated power of (overload situation), the control signal is transmitted to the power control circuit 218.

According to the control signal, the power control circuit 218 generates a frequency adjustment signal for lowering the power of the LED converter.

In addition, according to the frequency adjustment signal of the power control circuit 218, the FET driving circuit 214 lowers the power provided to the load 230 by increasing the oscillation frequency. The present invention performs a constant current operation to lower the power to maintain the current flowing in the load 230 while reducing the voltage. If the load power is lower than the rated power of the LED converter, the FET driving circuit 214 operates to lower the oscillation frequency to increase the power provided to the load 230 to maintain the current applied to the load at all times.

In the related art, the overpower detection circuit 150 simply monitors the magnitude of the resonance voltage, so that the amount of power consumed at the load side 230 cannot be accurately determined, and thus, the circuit of the present method has a simple and low cost advantage. It did not apply to the circuit. Therefore, a complex method of separately detecting the power detection circuit 160 on the secondary side (DC output terminal) and sending it back to the primary side was used.

3 is a circuit diagram of a current resonant converter, and FIG. 8 is a flowchart showing the operation of the LED converter according to the present invention.

2 to 3 and 8, the operation of the LED converter according to the present invention will be described.

As the power consumption of the load 230 increases, the series inductance Ls of the transformer 220 decreases, and thus the resonance voltage detected by the resonance capacitor 240 increases as shown in FIG. 4. . 4 is a graph showing a change in frequency and a change in the resonance capacitor voltage.

In addition, the overload detection circuit 250 monitoring the resonance capacitor 240 detects a change in the resonance voltage and frequency detected by the resonance capacitor 240 and lowers the power of the LED converter ( Example: overload situation). In operation S120 to S130, a control signal indicating an overload situation is transmitted to the power control circuit 218 as shown in FIG. (S140)

As shown in FIG. 5, the transformer 220 generally has two inductances, a magnetizing inductor (Lm) and a series inductor (Ls).

The magnetic inductance Lm is present in the transformer 220 and is an unchanging inductance L value determined by the amount of magnetic that is inherently formed. (Measure the value by measuring the primary inductance after the secondary side short.

The series inductance Ls is an inductance L value that varies depending on the secondary load situation (varies by the amount of magnetic flux that induces and disappears the secondary side current). The primary inductance L value is measured after the secondary side open, and the value obtained by subtracting the magnetic inductance Lm from the measured value is the series inductance Ls value. 5 is a circuit diagram showing a resonant partial equivalent circuit of a current resonant converter.

In Fig. 5, the magnetic inductance Lm does not change, but the series inductance Ls changes in value depending on the load situation on the secondary side. If the current on the secondary side is large, the series inductance Ls decreases and increases when the current on the secondary side is small. That is, since the inductance L value of the transformer 220 changes, the resonance frequency also changes.

Thereafter, the power control circuit 218 receiving the control signal generates a frequency adjustment signal for adjusting the power of the LED converter. (S150)

In addition, according to the frequency control signal of the power control circuit 218, the FET driving circuit 214 lowers the power provided to the load 230 by increasing the oscillation frequency. (S160) In the present invention, the power of the load is set. When the power is exceeded, the power is lowered to perform the constant current operation to maintain the current flowing in the load 230 and reduce the voltage.

6 is a correlation graph of resonant frequency and load power.

As shown in FIG. 6, a frequency capable of delivering maximum energy in LC resonance is referred to as a 'resonance frequency' and is lowered or raised based on a resonance frequency, and a power value transmitted through the transformer 220 (hereinafter, 'DC power'). Increase or decrease).

In the present invention, the maximum power comes out at the resonant frequency and is controlled in the direction of increasing the frequency in order to lower the power. The present invention sets the lowest frequency of the control circuit 210 in accordance with the resonant frequency and lowers the power provided to the load 230 as the frequency is increased, so that when the control circuit 210 applies the maximum frequency, Set the power to output. Therefore, when the power provided to the load 230 increases, the control circuit 210 increases the switching frequency to reduce the load power, and when the load power is low, the control circuit 210 lowers the switching frequency to raise the power to the load 230. It will control the power value provided.

Figure 7a is a graph showing the AC transfer characteristics of the capacitor according to the present invention.

As shown in Fig. 7A, the higher the frequency, the better the AC transfer characteristic.

The current control circuit 218 according to the present invention is designed by appropriately utilizing the phenomenon that the resonance voltage is lowered and the AC transfer characteristic is increased when the resonance frequency is increased.

That is, the resonance characteristics are determined, and a circuit for controlling power is made by using a C-R filter (not shown) suitable for a feedback process. The C-R filter is provided in the overpower detection circuit 250, and design capacity is important.

The reason why the design capacity of the C-R filter is important is that the transmission characteristics must be designed accordingly according to the resonance characteristics of the configured transporter 220 and the resonant capacitor 240.

When the resonance frequency is formed on the lower side due to the load condition, that is, when the load is large and the series inductance Ls is large, the FET driving circuit 214 is controlled to compensate for this by controlling the FET driving circuit so that the power is small even when the same resonance voltage is increased. shall.

To this end, the C-R filter transmits a small feedback signal by lowering the transfer characteristic to the power control circuit 218 so as to recognize the same resonance voltage as small.

As a result, the power control circuit 218 maintains power by operating in a direction in which the resonance voltage increases.

On the other hand, when the resonance frequency is formed at the higher side due to the load situation, that is, when the load is small and the series inductance Ls is small, the FET driving circuit 214 is controlled so that the resonance voltage can be reduced even when the same resonance voltage is large. This must be compensated.

To this end, the C-R filter transmits a large feedback signal by increasing a transfer characteristic to the power control circuit 218 to recognize the same resonance voltage as a large one.

As a result, the power control circuit 218 maintains power by operating in a direction in which the resonance voltage decreases.

In FIG. 7A, the relationship between the change in series inductance Ls, the change in resonant frequency, and the change in power can be seen that the smaller the series inductance Ls, the faster the resonance frequency and the larger the magnitude.

In the present invention, in order to control the characteristic that the power increases when the resonant frequency increases, the power is controlled by varying a parameter for transmitting the resonant voltage to the power control circuit 218 according to the resonant frequency.

Fig. 7B is a graph showing the AC transfer characteristics of the conventional capacitor, which is related to the case where the change in the AC transfer characteristics is not large.

As shown in Fig. 7B, when the AC transfer characteristic is almost similar in the frequency band actually used, the overpower detection point is determined only by the magnitude of the resonance voltage.

In this case, even if the resonant voltage is the same, the power is still increased when the frequency is fast, so when using the circuit of this characteristic, the power is still increased even if the frequency is increased to control power. Therefore, generally, it is used only for the purpose of determining that it is an overpower situation and stopping operation | movement.

Above, the LED converter according to the present invention includes a constant power control circuit for maintaining the total power by inducing a voltage drop when the load increases for output load variation. Then, the power applied to the transformer 220 is controlled to adjust the FET driving circuit 214 to overload, thereby limiting the operation of the power 220 or more. The present invention provides a single circuit with a constant current function for load protection, which is intended to be provided in the constant current control method of the conventional load current detection method, and an overload protection function that enables output voltage blocking and reoperation in case of a sudden load change such as a short circuit. It is designed to meet the requirements of circuit simplification and low cost and high function.

Although the present invention has been described with reference to the embodiment (s) shown in the drawings, this is merely exemplary, and various modifications can be made therefrom by those skilled in the art, and the embodiments described above ( It will be appreciated that all or some of these may be optionally combined. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

100, 200: LED converter 110, 210: control circuit
114, 214: FET drive circuit 130, 230: load
150, 250: overpower detection circuit 160: current detection circuit
170: photo coupler 218: power detection circuit
220: transformer 240: resonant capacitor

Claims (5)

A transformer 220 for converting the input AC power into DC and outputting the DC power;
A resonant capacitor 240 for resonating the primary voltage in conjunction with the inductors of the transformer;
An over power detection circuit (250) for determining whether the LED converter is in an overload condition by measuring changes in the resonance voltage and the resonance frequency of the resonance capacitor;
A power control circuit 218 for generating a frequency adjustment signal according to a control signal of the overpower detection circuit when the LED converter is overloaded;
And a FET driving circuit (214) for lowering the power provided to the load by increasing the oscillation frequency according to the frequency adjustment signal. The method of claim 1, wherein the over-power detection circuit 250
The load power is obtained by detecting the resonance voltage and the frequency.
And determining whether the load power is higher than the set power of the LED converter, and when the load power is higher than the set power of the LED converter, transferring a control signal according to the power control circuit. The method of claim 2, wherein the FET driving circuit 214 is
When the load power is lower than the set power of the LED converter, the oscillation frequency is lowered to increase the power provided to the load, if the load power is higher than the set power of the LED converter LED converter, characterized in that to lower the power by raising the oscillation frequency Constant current control circuit. The method of claim 1, wherein the LED converter
Constant current control circuit of the LED converter, characterized in that the current resonant converter. In the constant current control of the current resonance type LED converter,
When the resonant capacitor 240 resonates with the inductor of the transformer 220 to resonate the primary voltage, detecting load voltage by detecting changes in the resonant voltage and the resonant frequency of the resonant capacitor;
In the overpower detection circuit 250, determining whether the load power is higher than the set power of the LED converter, and if the load power is higher than the set power of the LED converter, transmitting a control signal according to the power control circuit 218;
Generating, by the power control circuit (218), a frequency adjustment signal in accordance with a control signal of the overpower detection circuit;
In the FET drive circuit (214), the step of increasing the oscillation frequency in accordance with the frequency adjustment signal comprising the step of lowering the power provided to the load.

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