CN204206554U - A kind of Dimmable LED power supply - Google Patents

Abstract

The utility model discloses a kind of Dimmable LED power supply, comprise circuit for power conversion, light adjusting circuit, accessory power supply and controller MCU, described circuit for power conversion is made up of two-stage circuit, be respectively Active Power Factor Correction APFC circuit and DC/DC Switching Power Supply, external electrical network is successively by Active Power Factor Correction APFC circuit, DC/DC Switching Power Supply exports constant current driven LED, described Active Power Factor Correction APFC circuit is also connected with accessory power supply, described accessory power supply provides electric energy for controller MCU, after described controller MCU receives host computer instruction by RS485 bus, output pwm signal regulates the brightness of output current to LED of DC/DC Switching Power Supply to control by light adjusting circuit, described controller MCU adopts ATmega8 single-chip microcomputer.

Description

A kind of Dimmable LED power supply

Technical field

The utility model relates to LED power, especially relates to a kind of LED power of tunable optical.

Background technology

White light LEDs is applied to illumination, will improve more than 5 times than existing light source life, fully can solve the mercurous environmental issue of fluorescent tube, therefore LED is free of contamination environmental protection light source, and the space and the luminous efficiency of LED chip is still much improved, cost is expected to continuous reduction.LED will promote the well-being of mankind as lighting source of future generation.Due to the voltage-current characteristic of LED, present White-light LED illumination generally uses constant-current supply to drive, and in order to better play a little energy-conservation of LED illumination, in LED power, add dimming function is trend of the times.Mode now for LED light modulation has two kinds, PWM light modulation and simulation light modulation.Pulse width modulation (PWM) light modulation uses switching circuit with sufficiently high frequency operation relative to eye recognition power, uses PWM to arrange the mean value of cycle and duty cycle change light output; Simulation light modulation is the amplitude changing electric power outputting current, and change the light output of LED, both respectively have pluses and minuses.Digital dimming can introduce potential electromagnetic interference frequency, and for reduction can hear noise and radiation, the light modulating frequency General Requirements several ten thousand hertz of high-end illuminator as far as possible, but higher light modulating frequency will significantly reduce the dimming scope of driving.Simulation light modulation faces the challenge of output current precision, each LED driving will be used certain series resistance and be distinguished electric current, electric current distinguishes that voltage is selected by compromise low energy consumption loss and high s/n ratio, and the permissible error in driving, skew and delay result in a relatively-stationary error.Output current to be reduced just must reduce electric current identification voltage in a closed-loop system, the precision of output current will be reduced so conversely.

The utility model, in order to overcome above-mentioned defect, has carried out useful improvement.

Utility model content

The purpose of this utility model is to solve above-mentioned deficiency of the prior art, provides a kind of high precision operating amplifier that adds on the basis of traditional analog light adjusting circuit to improve the Dimmable LED power supply of output current precision.

To achieve these goals, the utility model is by the following technical solutions:

A kind of Dimmable LED power supply, comprise circuit for power conversion, light adjusting circuit, accessory power supply and controller MCU, its special character is: described circuit for power conversion is made up of two-stage circuit, be respectively Active Power Factor Correction APFC circuit and DC/DC Switching Power Supply, external electrical network is successively by Active Power Factor Correction APFC circuit, DC/DC Switching Power Supply exports constant current driven LED, described Active Power Factor Correction APFC circuit is also connected with accessory power supply, described accessory power supply provides electric energy for controller MCU, after described controller MCU receives host computer instruction by RS485 bus, output pwm signal regulates the brightness of output current to LED of DC/DC Switching Power Supply to control by light adjusting circuit, described controller MCU adopts ATmega8 single-chip microcomputer,

Described light adjusting circuit comprises operational amplifier, resistance R1 wherein in light adjusting circuit, resistance R2, resistance R3 forms resistance pressure-dividing network, switching tube Q1 is connected with the in-phase end C1 of operational amplifier by resistance R2, and the dimmer voltage V+ of the in-phase end C1 of operational amplifier is controlled, the electric current of LED is converted to sampling voltage VS by resistance sampling resistance RS and is connected with the end of oppisite phase of operational amplifier, described dimmer voltage V+ and sampling voltage VS through operational amplifier relatively after export, the output of operational amplifier passes through the output current of the FB pin Current Control DC/DC Switching Power Supply of optocoupler modulation power control chip.

The beneficial effects of the utility model: when white LED lamp is applied to Tunnel Lamp, street lighting, electromagnetic compatibility has higher requirements, the basis of traditional light adjusting circuit adding, operational amplifier compares sampling voltage and dimmer voltage, energy fine adjustment output current, the dimming commands received from RS485 bus by single-chip microcomputer can realize multistage light modulation, and the brightness of the precision and LED that improve output current precisely controls.

Accompanying drawing explanation

Fig. 1 is the hardware frame figure of the utility model embodiment;

Fig. 2 is the utility model embodiment analog light-adjusting circuit figure;

Fig. 3 is the utility model embodiment D/A circuit waveform figure.

Embodiment

Below in conjunction with accompanying drawing and embodiment, the utility model is further described.

Embodiment design of integer electro-circuit of the present utility model adds analog light-adjusting circuit in traditional LED constant current power supply, design Intelligent Light-control System, as shown in Figure 1.At the power conversion section of this system, adopt the design of APFC and DC/DC two-stage circuit, simulation adjusting control circuit uses ATmega8 single-chip microcomputer to build, and the brightness of control centre's regulation and control LED lamp, adopts RS485 bus to send dimming commands.

After receiving the dimming commands of RS485 bus, single-chip microcomputer, by exporting corresponding pwm signal, carrys out the output current of by-pass cock power supply.And we adopt operational amplifier fine adjustment output current, need pwm signal to be converted to linearity light adjusting voltage.As shown in Figure 2, pwm signal input is D/A change-over circuit to amplifier in-phase end.

R1, R2, R3 form resistance pressure-dividing network, and Q1, as switching tube, controls its ON time by PWM dim signal, the voltage on the switch control rule C1 of Q1, i.e. the in-phase end voltage of amplifier.The electric current of LED, by sample resistance Rs, is converted to sampling voltage Vs, the end of oppisite phase of input amplifier.Dimmer voltage V+ and sampling voltage Vs through operational amplifier relatively after output logic level, by the FB pin electric current of optocoupler modulation power control chip, thus regulate the output current of DC/DC circuit.

Known sampling voltage: Vs=Rs × ILED from circuit, when power supply exports maximum current, PWM dim signal duty ratio is 100%, after inverter paraphase, Q1 turns off always, voltage now on resistance pressure-dividing network R3 is: V+ (max)=R3 × VCC/ (R1+R2+R3), when PWM dim signal duty ratio reduces to 0, Q1 conducting, C1 discharges, the saturation voltage drop of Q1 is VCES, now: V+ (min)=R3 × VCES/ (R2+R3), V+<Vs, amplifier output low level, regulable control chip reduces output current, until meet Vs ≈ V+, now power supply minimum output current is: ILED=V+ (min)/Rs,

As shown in Figure 3, Q1 turns off, and C1 charges; Q1 conducting, C1 discharges.Within a PWM cycle, the average voltage on electric capacity is: V+=V+ (max) × h, in formula: h is PWM dim signal duty ratio, has according to the short characteristic of the void of operational amplifier: V+ ≈ Vs.It can thus be appreciated that after the resistance of selected R1, R2, R3, electric power outputting current accurately will be controlled by pwm signal duty ratio.

The above execution mode only have expressed a kind of execution mode of the present utility model, but therefore can not be interpreted as the restriction to the utility model scope.It should be pointed out that for the person of ordinary skill of the art, without departing from the concept of the premise utility, can also make some distortion and improvement, these all belong to protection range of the present utility model.

Claims (1)

1. a Dimmable LED power supply, comprise circuit for power conversion, light adjusting circuit, accessory power supply and controller MCU, it is characterized in that: described circuit for power conversion is made up of two-stage circuit, be respectively Active Power Factor Correction APFC circuit and DC/DC Switching Power Supply, external electrical network is successively by Active Power Factor Correction APFC circuit, DC/DC Switching Power Supply exports constant current driven LED, described Active Power Factor Correction APFC circuit is also connected with accessory power supply, described accessory power supply provides electric energy for controller MCU, after described controller MCU receives host computer instruction by RS485 bus, output pwm signal regulates the brightness of output current to LED of DC/DC Switching Power Supply to control by light adjusting circuit, described controller MCU adopts ATmega8 single-chip microcomputer,

Described light adjusting circuit comprises operational amplifier, resistance R1 wherein in light adjusting circuit, resistance R2, resistance R3 forms resistance pressure-dividing network, switching tube Q1 is connected with the in-phase end C1 of operational amplifier by resistance R2, and the dimmer voltage V+ of the in-phase end C1 of operational amplifier is controlled, the electric current of LED is converted to sampling voltage VS by resistance sampling resistance RS and is connected with the end of oppisite phase of operational amplifier, described dimmer voltage V+ and sampling voltage VS through operational amplifier relatively after export, the output of operational amplifier passes through the output current of the FB pin Current Control DC/DC Switching Power Supply of optocoupler modulation power control chip.