CN102843816A - High-power LED (light emitting diode) power circuit - Google Patents

Abstract

The invention provides a high-power LED (light emitting diode) power circuit which comprises an AC-DC (alternating current-direct current) module and a DC-DC module, wherein the DC-DC module adopts a specific LED driving chip. The high-power LED power circuit is takes an LED as a lighting source, so that the circuit is higher in power conversion efficiency, stable in performance parameter, and accurate in current output. In the aspect of a solar street lamp, under the condition that the output voltage of a solar photovoltaic battery is 24V, the circuit is more proper for application.

Description

The great power LED power circuit

Background technology

The present invention provides a kind of great power LED power circuit.

Technical field

Since the nineties in 20th century; Along with the semi-conductive rise of the third generation that with GaN is representative; Succeeding in developing of blue green light and white light emitting diode; Use as new and effective semiconductor illuminating light source, has remarkable advantages such as long, energy-conservation, environmental protection of life-span based on the superhigh brightness LED (LED) of the third generation semi-conducting material manufacturing of GaN, will become another qualitative leap continue incandescent lamp, fluorescent lamp after on the human illumination history.At present, the luminous efficiency of great power LED has generally reached more than the 110lm/W, and the scholarly forecast laboratory level can reach 180lm/W within the year, is applied to illuminations such as urban road and automobile external and fully maybe.Can expect that the high-brightness LED light fixture product of energy-conservation, safety, fashion, environmental protection will form a very potential market.

Though great power LED has advantages such as high efficiency, life-span length and energy-conserving and environment-protective, its electricity discreteness is bigger, is prone to be acted upon by temperature changes.The light output of LED is directly relevant with the LED electric current, thus, LED answers the variation of factors such as control compensation input voltage and ambient temperature in using, otherwise the light output of LED will change with the variation of factors such as input voltage and ambient temperature.If the LED electric current is out of control, then the LED long-term work will influence its reliability and life-span under big electric current, even cause LED to lose efficacy.Therefore LED requires drive circuit to have perfect protective circuit, as low pressure latch, overvoltage protection, overtemperature protection, overcurrent protection etc., and drive circuit requires to have advantages such as high power conversion efficiency, high integration and high reliability.According to above factor, the present invention is based on the drive circuit that the MAX16832C chip for driving has designed a great power LED, characteristics such as that this circuit has is simple in structure, stable performance.

LED is a kind of current driving apparatus, and its constant current source driving circuit is exactly a voltage/current converter, and this converter can both provide constant electric current for LED under situation such as load size and ambient temperature variation.In buck converter, utilize the switch motion of power MOSFET to control input voltage usually, the voltage of the LED load of inductance and series connection thereof is regulated.When the MOSFET conducting, the inductance stored energy; When MOSFET turn-offed, the energy storage of inductance was that LED provides electric current.When MOSFET turn-offs, be connected on the path that the diode at LED and inductance two ends provides electric current to return.

Summary of the invention

The shortcoming that the present invention overcomes prior art provides a kind of great power LED power circuit, and it is said that its technical scheme that adopts is asked for an interview the back.

A kind of great power LED power circuit comprises the AC-DC module, the DC-DC module, and wherein, wherein the DC-DC module adopts special-purpose LED chip for driving.

Wherein, special-purpose LED chip for driving is selected the U.S. letter voltage-dropping type chip MAX16832C of company for use.

It is said that embodiment of the present invention is asked for an interview the back literary composition.

Description of drawings

Fig. 1 is voltage-dropping type led drive circuit figure;

Fig. 2 is the block diagram of drive scheme;

Fig. 3 is the MAX16832C pinouts;

Fig. 4 is based on the drive circuit schematic diagram of MAX16832C.

Embodiment

Provide preferred embodiment of the present invention below, these embodiment and unrestricted content of the present invention.

Embodiment 1

The sketch of step-down led drive circuit is as shown in Figure 1.In off-line and low voltage application, have a great attraction with the drive circuit of buck converter, because buck converter can produce the LED electric current of constant current very efficiently as LED.Under the bigger situation of input voltage and LED voltage fluctuation, adopt the buck converter of peak current control only to need simple FEEDBACK CONTROL design, just can make the LED current fluctuation less.In addition, the appropriate design buck converter can make its efficient surpass 90%, so be a kind of very attractive solution that drives high-brightness LED based on the drive circuit of buck converter.The design is applied to indoor and outdoor illumination.Indoor and outdoor illumination supply power voltage specification has two kinds of 220V (being applicable to domestic and European), 110V (being applicable to the Japan and the U.S.) in the world, is higher than the work pressure drop of LED far away, so the optional voltage-dropping type of drive scheme is represented by Fig. 2.

The AC-DC module realizes the transformation of alternating voltage to direct voltage, and this module is generally realized by Switching Power Supply.The DC-DC module realizes the transformation of direct voltage to direct current, offers the constant electric current of LED.This module is the design's a emphasis.The DC-DC module is realized by special-purpose LED chip for driving.The present invention selects is the voltage-dropping type chip MAX16832C of U.S. letter company.This chip has following advantage: input voltage can reach 65V, and output current can reach 1A, output current precision 3%, and switching frequency can reach 2*10 ⁶/ s, overheated turn-off protection, the low-voltage turn-off function, resistance LED constant current able to programme can relatively be suitable for LED and drive through numeral, simulation light modulation, can realize purpose of energy saving again.The MAX16832C chip adopts and strengthens heat radiating type 8 pin SO encapsulation, and pin arrangements is as shown in Figure 3.

Each pin of MAX16832C chip is described below: the CS pin is the current detecting input, between IN pin and CS pin, connects a resistance LED electric current is set; The IN pin is positive voltage input, through one 1 μ F or bigger capacitive bypass to GND; The GND pin is ground; The PGND pin is a Power Groud; The LX pin is a switching node; The DIM pin drags down DIM close current adjuster for the input of logic level brightness regulation; Draw high DIM and then enable current regulator; The TEMP1 pin is that Zigzag type heat management and linear luminance are regulated input, if use Zigzag type heat management or analoging brightness to regulate, then uses one 0.01 μ F capacitive bypass to GND.

Led drive circuit parameter request based on the MAX16832C chip is following: the representative value of input voltage is 24V, and output current is 350mA, and output voltage is 3～20V, and circuit efficiency is more than 90%, and operating temperature range is-40～125 ℃.

Drive circuit by the MAX16832C chip is formed is as shown in Figure 4.Operation principle: after adding a DC input voitage, have the voltage of a 200mV between chip CS pin and the IN pin, the Rsense between them just can confirm the output current value size; The LX pin of chip is the drain electrode of a high-power NMOS of chip internal, has only when voltage is high level on the grid of NMOS pipe the NMOS conducting; A circuit-formed loop Vin; Rsense, LED, L1.This loop is that power supply is directly supplied power to LED, and this process is given inductance L 1 accumulation of energy.When the grid voltage of NMOS pipe was low level, the loop that form this moment was L1, D1, Rsense, LED.The DIM pin can be through an external square wave in order to regulate LED brightness; The external thermistor of TEMP1 pin can be realized the overheated turn-off function of external circuit; The low pressure that has chip self latchs, the function of overvoltage protection, and when input voltage is lower than 65V or is higher than 65V, chip quits work; Overcurrent protection function is realized by the feedback of the voltage difference between chip CS pin and the IN pin; When the electric current that flows through Rsense bigger than normal; Then the voltage between CS pin and the IN pin increases; Feed back to the drive circuit of NMOS by the chip internal feedback circuit, regulate the ON time of NMOS, the electric current that flows through on the Rsense will be got back to normal condition.C1 and C2 are input filter capacitor, be used to leach and the previous stage circuit between the interference signal of line, guarantee the chip steady operation.Ceramic capacitor-type is a best choice, because it has high ripple current rating value, long, good advantages such as temperature performance of life-span; Rsense is a current sampling resistor, can regulate the size of output current through selecting different values, and the requirement of resistance is that power error is more little good more; L1 is an inductance, and energy-storage travelling wave tube is used for level and smooth output current; D1 is a Schottky diode, in circuit, plays the afterflow effect; R2 is a potentiometer, can realize simulating dimming function; R4 is a resistance, is connected to DIM pin and voltage input pin Vin, draws high the DIM pin level all the time, does not realize the digital dimming function.

Switching mode voltage conversion circuit during circuit, stable for circuit performance, must set a suitable operating frequency.When confirming switching frequency, consider power supply conversion efficiency, circuit volume and circuit cost Several Factors.When switching frequency hanged down, efficient was than higher, but circuit volume that need be bigger and higher design cost; And higher switching frequency can reduce power supply conversion efficiency, also can dwindle the volume and the cost of circuit simultaneously.Less than 100V, power is less than the drive circuit of 30W at output voltage, the consideration of should compromising of switching loss and component size, and taking all factors into consideration switching frequency fSW should be between 100～200kHz, and selecting switching frequency here is 150kHz.

Rsense is a current viewing resistor, and promptly sampling resistor through being added in the constant voltage at its two ends, produces a constant-current supply, is the operating current of LED; Also can change the resistance size of sampling resistor, realize resistance LED constant current able to programme.When selector, to select the resistance of 1% precision, low temperature drift, to guarantee the output current precision.The relation of output average current and current sampling resistor can be expressed as

$R_{\mathrm{sense}}=\frac{1}{2}\frac{(V_{\mathrm{SNSHI}}+V_{\mathrm{SNSLO}})}{I_{\mathrm{LED}}}---\left(1\right)$

In the formula: VSNSHI is for detecting the upper limit of voltage threshold; VSNSLO is for detecting the lower limit of voltage threshold.The parameter request of design of drive circuit is ILED=350mA, can find in the electrical characteristic table in the technical manual of MAX16832C chip: VSNSHI=230mV, and VSNSLO=170mV, substitution formula (1) is calculated can get Rsense ≈ 0.57 Ω.

Because the output of switching device is to change more violent signal in time, can not directly drive load, need to add an energy-storage travelling wave tube thereafter, through charge and discharge, smoothly export signal to energy-storage travelling wave tube.Usually select inductance as energy-storage travelling wave tube.Select the inductance of larger capacity, switching frequency can be lower, and output signal ripple is also smaller, at this moment can reduce even save output ripple electric capacity, but the volume of circuit and cost will increase; Less inductance can reduce the volume and the cost of circuit, but this be with bigger output ripple electric capacity, to increase output ripple electric capacity and reduce power supply conversion efficiency be cost.Inductance value is determined by formula (2)

$L=\frac{(V_{\mathrm{in}}-n{V}_{\mathrm{LED}})\×n{V}_{\mathrm{LED}}\×R_{\mathrm{sense}}}{V_{\mathrm{in}}\×\mathrm{\ΔV}\×f_{\mathrm{SW}}}---\left(2\right)$

Can find in the electrical characteristic table in the technical manual of MAX16832C chip: V=(VSNSHI-VSNSLO)=60mV.Vin=24V, Rsense ≈ 0.57 Ω, nVLED=20V, fSW=150kHz, substitution formula (2) calculates L=211.1 μ H, so get nominal value L=220H.

In the time of the conducting of chip internal metal-oxide-semiconductor, electric current is through Vin, Rsense, LED, L1, again through chip to ground.LED lights in this course, and accomplishes the charging work to inductance.But when metal-oxide-semiconductor turn-offed, above-mentioned loop was turned off, and LED extinguishes, and had also stored certain energy on the inductance and can't discharge.For LED is worked on, need in circuit, add a Schottky diode, make electric current through L1, D1, R1, LED forms another loop.Energy on the inductance discharges to LED through Schottky diode, and it is normally luminous to keep LED.Selecting Schottky diode, is that reverse recovery time is fast because its forward conduction voltage drop is very low, and it is little to leak electricity, and can reduce the loss of energy on Schottky diode like this.The crest voltage of D1 equals maximum input voltage, adopts 50% safety allowance.Because of VDIODE=1.5*30V=45V, IDIODE=350mA is 75V so choose rated voltage, and rated current is the Schottky diode of 0.5A.

Test process is to carry out for 25 times in indoor temperature, and the key instrument of using in the test has digital DC stabilized voltage power supply, digital multimeter and digital signal generator.Present embodiment uses this drive circuit to drive the large power white light LED of 1～7 operating current as 350mA respectively, and input voltage is 24V, and design meets the requirements basically, and circuit can operate as normal.The result who obtains is as shown in table 1.

Table 1

Can find out that from table 1 along with the increase of LED number, (η) is increasingly high for the conversion efficiency of drive circuit, and the output current maintenance is constant; When LED number reached 7, output current increased, but the integrated circuit conversion efficiency descends.Main cause is: when load is 1 LED, and current constant, so the switching frequency of chip is bigger, the entire circuit power loss is bigger like this; Along with the increase of LED number, switching frequency then reduces, and the power loss of entire circuit just reduces like this; When load is 6 LED; This moment, output voltage was about 20V, and the kHz/s of unit probably is initial setting frequency 150kHz, and at this time the conversion efficiency of circuit is the highest; And when load is 7 LED, the value of setting when output voltage surpasses circuit design, though output current becomes greatly, whole drive circuit works is undesired, conversion efficiency also reduces.

The present invention uses LED as lighting source, and circuit can be realized higher power supply conversion efficiency, and performance parameter is stable, precise current output.Aspect solar street light, be that circuit application is proper under the situation of 24V when the solar cell output voltage.

Claims (2)

1. a great power LED power circuit comprises the AC-DC module, the DC-DC module, and wherein, wherein the DC-DC module adopts special-purpose LED chip for driving.

2. great power LED power circuit as claimed in claim 1 is characterized in that, wherein, special-purpose LED chip for driving is selected the U.S. letter voltage-dropping type chip MAX16832C of company for use.

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