CN102076138A - Electric supply input LED (Light Emitting Diode) constant current driver - Google Patents

Abstract

The invention relates to an electric supply input LED (Light Emitting Diode) constant current driver. The LED constant current driver comprises a power supply converter and a current controller; the current controller comprises a current detector, an oscillator, an error amplifier, an integrator, a comparator, a latch, a switch driver, a switch, a diode, an inductor and a band-gap reference voltage source; and the integrator integrates a difference signal output by the error amplifier and outputs a sawtooth voltage signal. A new current control method, i.e. an I2 control method, is designed on the basis of an improved Buck driving circuit, and the width of a pulse signal is regulated by utilizing a difference integral of a detection signal and a reference signal, so that the average value of voltages Vcs during connection of a single-period switch in a steady state is equal to a reference voltage Vref, and the steady state error of average currents is eliminated, therefore, the average currents are precise. The electric supply input LED constant current driver has a better adjusting function and a more obvious control function as comparison with a common current control circuit.

Description

A Mains Input LED Constant Current Driver

technical field

The invention belongs to the field of commercial power lighting of LEDs, and in particular relates to a constant current driver for commercial power input lighting LEDs.

Background technique

Due to many advantages such as long life, high photoelectric conversion efficiency, energy saving and environmental protection, and short response time, LED has become the focus of attention in the field of lighting, and has developed extremely rapidly in recent years. While LED lighting applications are becoming more and more widespread, LED drive circuits are also facing greater challenges, such as having to be able to handle increasing currents. Because a small voltage fluctuation will cause a large change in the LED current, in order to prevent the LED from being damaged, a special driving circuit is required to control the current of each LED in the LED array to keep constant. In addition, because LED lighting requires dimming or more complex control properties, multiple control strategies must be provided for this.

The traditional constant voltage driving method, as shown in Figure 1, has the disadvantages of insufficient voltage regulation accuracy and poor current stabilization capability. Since the LED is a current-sensitive device, a small voltage change of the regulated power supply will cause a large change in the LED current during normal operation. As the LED current changes, the brightness of the LED will be bright and inconsistent. At the same time, due to the damage of a certain LED in the LED group, the overall current will increase, which will easily lead to damage to the entire LED group and shorten the life. Therefore, this driving circuit needs to be improved urgently. .

In order to overcome the disadvantages of the constant voltage driving method, the constant current driving method is widely used now. As shown in Figure 2, the current control strategy commonly used by constant current drivers: detect the current in the LED and use it as a feedback signal, the error amplifier A11 will output the current feedback voltage Vcs and the bandgap reference voltage source The difference of the reference voltage Vref output by U13 is amplified, and the difference amplified signal is sent to the pulse width (PWM) modulator U11, and the PWM modulator U11 generates a corresponding pulse width modulation signal according to the amplitude of the difference signal, and the switch driver U12 The on-off of the switch Q11 is controlled according to the pulse width modulation signal, so that the inductor L11 is charged and discharged, so as to keep the average current flowing through the LED constant. However, this strategy has poor tracking ability, and it is easy to cause the current in the LED to oscillate around the target value, and the stability ability is poor.

Contents of the invention

In order to solve the above problems, the present invention is proposed, and the purpose of the present invention is to provide a new LED constant current driver with simple circuit structure, good stability, low cost, high precision of steady current and high conversion efficiency.

In order to achieve the above object, the present invention adopts the following technical solutions: a commercial power input LED constant current driver includes: a power converter, which converts the input commercial power into direct current through full-bridge rectification and filtering; a current controller, through the control switch The on-off time of the inductance is charged and discharged to keep the current flowing through the LED circuit constant.

According to one aspect of the present invention, the power converter includes: a rectifier bridge, which converts the input AC voltage into a DC voltage; two parallel electrolytic capacitors, which filter the DC voltage, filter out the AC component in the DC voltage, and maintain the output voltage of stability.

The current controller includes: a current detector, an oscillator, an error amplifier, an integrator, a comparator, a latch, a switch driver, a switch, a diode, an inductor, and a bandgap reference voltage source; Integrate the value signal and output a sawtooth wave voltage signal;

The connection relationship of each part of the current controller is: one end of the current detector is connected to the source of the switch, and the other end is grounded; the gate of the switch is connected to the output end of the switch driver, and the drain of the switch is connected to the anode of the diode and the first end of the inductor , the cathode of the diode is connected to the anode of the load LED group, the second terminal of the inductor is connected to the cathode of the load LED group, the non-inverting input terminal of the error amplifier is connected to the reference voltage, the inverting input terminal is connected to the output feedback voltage of the current detector, and the output terminal is connected to the integral The input of the integrator, the output of the integrator is connected to the inverting input of the comparator, the same input of the comparator is connected to the output feedback voltage of the current detector, the reset terminal of the latch is connected to the output of the comparator, and the set terminal is connected to the oscillation The clock signal generated by the device, the non-inverting output terminal is connected to the switch driver.

The beneficial effects of the present invention are: according to the LED constant current driver proposed by the above technical scheme, based on the improved Buck drive circuit, a new current control method-I ² control method is designed, and the difference integral between the detection signal and the reference signal is used To adjust the width of the pulse signal, so that the average value of the voltage Vcs during the turn-on period of the single cycle switch is equal to the reference voltage Vref in the steady state, eliminating the steady-state error of the average current, so as to accurately average the current. It has better regulation performance than ordinary current control circuit, and the effect of control is more obvious.

Description of drawings

Fig. 1 shows the structure of the traditional constant voltage drive mode;

Figure 2 shows the structure of the control structure commonly used in current LED constant current drivers;

Fig. 3 shows a schematic diagram of the main structure of the LED constant current driver proposed by the present invention.

Detailed ways

The present invention will be described in further detail below according to the drawings and embodiments. An exemplary embodiment of the present invention will be described in detail below.

A commercial power input LED constant current driver includes: a power converter, which converts the input commercial power into direct current through full-bridge rectification and filtering; a current controller, which controls the on-off time of the switch to charge and discharge the inductor to Keep the current flowing through the LED circuit constant.

According to one aspect of the present invention, the power converter includes: a rectifier bridge, which converts the input AC voltage into a DC voltage; two parallel filter capacitors, which filter the DC voltage, filter out the AC component in the DC voltage, and maintain the output voltage of stability.

The LED constant current driver drives the load LED group 30, and the load LED group 30 is used as a high-power lighting lamp, an LCD backlight, an indicator light, and the interior and exterior lighting of a car.

As shown in FIG. 3 , the LED constant current driver includes a power converter 20 and a current controller 10 .

The power converter 20 includes: a rectifier bridge D22, and electrolytic capacitors C21 and C22. The rectifier bridge D22 performs full-wave rectification on the input AC power to convert it into DC power; the capacitors C21 and C22 connected in parallel filter the DC power to filter out the AC components in the DC power.

The current controller 10 makes the current Io flowing in the load LED group 30 reach a predetermined current value. Here, the predetermined value represents the current to be applied to the load LED group 30 .

The current controller 10 includes a current detector F21, an oscillator T21, an error amplifier A21, an integrator J21, a comparator A22, a latch U21, a switch driver U22, a switch Q21, a diode D21, an inductor L21, and a bandgap reference voltage source U23 .

The current detector F21 detects the current Io flowing in the load LED group 30 . The current detector F21 can be realized by a resistor with a predetermined resistance, wherein one end of the current detector F21 is connected to the source of the switch Q21, and the other end of the current detector F21 is grounded. In this embodiment, the current Io flowing in the load LED group 30 can be calculated according to the voltage generated by the current Io flowing through the current detector F21 and the resistance of the current detector F21. Of course, any other suitable current detector can be used as the current detector of design choice without departing from the scope and spirit of the present invention.

The gate of the switch Q21 is connected to the output end of the switch driver U22, and the drain of the switch Q21 is connected to the anode of the diode D21 and the first end of the inductor L21. The cathode of the diode D21 is connected to the anode of the load LED group 30 . The second terminal of the inductor L21 is connected to the cathode of the load LED group 30 . Preferably, the switch Q21 is realized by an N-channel metal oxide semiconductor field effect transistor (NMOSFET).

The magnitude of the voltage on the gate of the switch Q21 determines the on-off state of the switch Q21. When the switch Q21 is turned on, the current flows through the inductor L21, and the inductor current i _L increases; when the switch tube Q21 is turned off, the inductor current continues to flow through the diode D21, and the inductor current i _L decreases. LED20 is connected in series with inductor L21, so the current flowing through LED20 is i _L .

The non-inverting input terminal of the error amplifier A21 is connected to the reference voltage Vref, the inverting input terminal is connected to the output feedback voltage Vcs of the current detector F21, and the output terminal is connected to the input of the integrator J21. The output of the integrator J21 is connected to the inverting input of the comparator A22. The non-inverting input terminal of the comparator A22 is connected to the output feedback voltage Vcs of the current detector F21. When the switch Q21 is turned on, the feedback voltage Vcs rises approximately linearly, and the error amplifier A21 calculates and amplifies the difference between the feedback voltage Vcs and the reference voltage Vref, and sends the amplified difference signal to the integrator J21. The integrator J21 integrates the difference signal to generate a sawtooth wave voltage signal, and outputs the signal to the inverting input terminal of the comparator A22. The comparator A22 compares the sawtooth wave voltage signal with the feedback Vcs, and outputs a pulse width modulation signal with an adjustable duty cycle.

The reset terminal R of the latch U21 is connected to the output of the comparator A22, the set terminal S is connected to the clock signal generated by the oscillator T21, and the non-inverting output terminal Q is connected to the switch driver U22. When the output of the comparator A22 is high level, the Q terminal outputs a logic 0, the switch driver U22 outputs a low voltage signal, and the switch S is turned off. When the output of the comparator A22 is low level, the output logic of the Q terminal is determined by the clock signal. When the clock is high level, the Q terminal outputs logic 1, the switch driver U22 outputs a high voltage signal, and the switch S is turned on; The terminal output is to maintain the previous state. In this way, the current controller 10 of this embodiment can control the on-off time of the switch Q21 by detecting the current Io flowing in the load LED group 30 until the current Io reaches a predetermined target value.

The LED constant current driver of the embodiment of the present invention has constant current output and adjustable current, from tens of milliamps to 1 ampere, and is suitable for the application of multiple high-power LEDs in series; the circuit structure is simple, the peripheral components are few, and the production cost is low. Low conversion efficiency can be greater than 90%; suitable for 1W-3W high-power LED lighting, large-screen LCD backlighting, LED signal lights, warning lights, emergency lights, miner's lamps and lights of various luminous colors, lighting in public places Lamps, automotive interior and exterior lighting and signal indicators.

The foregoing describes one embodiment of the present invention, changes may be made in these embodiments without departing from the principle and spirit of the invention as defined by the claims and their equivalents.

Claims (2)

1. a civil power is imported the LED constant-flow driver, comprising:

Power supply changeover device becomes direct current to the civil power of input through full-bridge rectification, filtering;

Current controller, discharges and recharges inductance, the current constant in the led circuit that keeps flowing through at the conducting turn-off time by control switch;

Wherein, power supply changeover device is made up of the electrochemical capacitor of rectifier bridge, two parallel connections; Current controller comprises: current detector, oscillator, error amplifier, comparator, latch, switch driver, switch, diode, inductance, bandgap voltage reference;

It is characterized in that: in current controller, also comprise: integrator, the difference signal that error amplifier is exported carries out integration, output sawtooth voltage signal;

Current controller each several part annexation is: an end of current detector (F21) is connected other end ground connection with the source electrode of switch (Q21); The grid of switch (Q21) connects the output of switch driver (U22), the drain electrode of switch (Q21) connects the anode of diode (D21) and first end of inductance (L21), the negative electrode of diode (D21) connects the anode of load LED group, the negative electrode of the second termination load LED group of inductance (L21), the in-phase input end of error amplifier (A21) connects reference voltage, inverting input connects the output feedback voltage of current detector (F21), the input of output termination integrator (J21), the output of integrator (J21) connects the reverse input end of comparator (A22), the output feedback voltage of the current detector of input termination in the same way (F21) of comparator (A22), the reset terminal (R) of latch (U21) connects the output of comparator (A22), set end (S) connects the clock signal that oscillator (T21) produces, and in-phase output end (Q) connects switch driver (U22).

2. a kind of civil power input LED constant-flow driver as claimed in claim 1, it is characterized in that: the switch in the current controller (Q21) selects for use N road ditch metal oxide semiconductor field effect tube to realize.

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