CN100474995C - Operation equipment for LED - Google Patents

Abstract

The present invention provides a circuit having an electronic switch for the LED operating current, characterized in that the device has a pull-down device in parallel with the electronic switch, the resistance of the pull-down device is dimensioned so that the ratio of the operating current with the switch closed to the operating current with the switch open is described by a reduction factor of at least 10. Thus the electromagnetic interference of the circuit device is reduced.

Description

The operational outfit of light-emitting diode

Technical field

The present invention relates to a kind of be used to move light-emitting diode with the operating current that flows through an electronic switch basically circuit arrangement.Relate in particular to a kind of electronics operational outfit that is used to move light-emitting diode herein, this operational outfit contains the device that is useful on adjusting light-emitting diode operating current effective value, and wherein, this device has the working method of pulse.

Background technology

In order to move light-emitting diode, hereinafter to be referred as LED, following circuit arrangement has obtained popularization: give the electronic commutator that supply voltage is provided power supply such as the power supply of public electric wire net or storage battery.LED connects lead through two usually and is connected with supply voltage.On a supply voltage, can move one or more LED.A plurality of LED connect usually, and form so-called shunt.Can a plurality of shunt in parallel, wherein, laterally connection also is possible between shunt.If a plurality of LED are connected on the supply voltage, they then are aggregated into the so-called led module that also may contain the electric current limiting resistance mostly.Therefore voltage-regulation in electronic commutator realized connect the desirable operating current of LED.The circuit arrangement of being referred to is not only applicable to move LED.It also is possible moving so-called organic light emitting devices (OLED) with this.

Usually exist and to regulate LED operating current effective value, just stay out of the hope of electronic commutator.This realized connect the light modulation of LED, dissimilar or different number LED are connected to the possibility on and the same supply voltage.By being inserted, electronic switch connects the adjusting possibility that realizes LED operating current effective value in the lead.Inserting which connection lead of electronic switch, is arbitrarily in principle.The described adjusting possibility of LED operating current effective value has been described in the German patent application with application number 10136658.2 (Scilla).Electronic switch can be implemented as MOSFET cheaply.Interrupt the operating current of LED by the unlatching of switch.Open and the closed pulsed mode that realizes the LED operation by the periodicity of electronic switch.The ratio of the duration of the closure state of switch with the duration of opening determines a duty factor.Can regulate the desirable effective value of light-emitting diode operating current by suitable duty factor.The maximum that when connecting electronic switch, occurs by the given LED operating current of supply voltage.

Electronic switch and the control circuit that is subordinated to this can be aggregated into a unit in the housing with electronic commutator.But also electronic switch and control circuit can be constituted the independent light modulation unit in the separate housing.If the adjusting possibility of LED operating current effective value is welcome, this light modulation unit then can be connected between electronic commutator and the LED.

Being used for opening pulse frequency with closed electronic switch is usually located at human eye and can distinguishes mutually on the frequency of each light pulse.In fact 100Hz is applied until the frequency of a plurality of KHz.The connection lead that does not insert electronic switch forms a utmost point of output voltage.The utmost point relative with supply voltage of electronic switch forms another utmost point of output voltage.Output voltage is flowed to LED or led module.It has the rectangular curve that its fundamental frequency equals above-mentioned pulse frequency.Especially this can be directed at the incompatibility or the radio interference of electromagnetism under long connection conductive wire scenario.For stop this situation with in order to observe relevant standard (such as CISPR 15), usually need the high cost of filtering and shielding form.

Summary of the invention

Task of the present invention provides a kind of circuit arrangement, and this circuit arrangement is realized the pulsed mode of LED, but produces less electromagnetism incompatibility or radio interference with respect to prior art.

Start described circuit arrangement from article, solve this task by the following technical programs.

According to the circuit arrangement that is used to move light-emitting diode of the present invention with the operating current that flows through an electronic switch basically, it is characterized in that, be parallel to described electronic switch and connected a pull device, the resistance of this pull device has so value of design, makes that taking to be worth at least 10 reduction coefficient by one is described in operating current under the closed electronic switch situation to the ratio of the operating current under unlocking electronic switch situation.

How strong the interference that is produced by the circuit arrangement referred to has, and at first depends on the amplitude of the alternating current component of above-mentioned output voltage.Output voltage is made up of DC component and alternating current component.The amplitude of the alternating current component of output voltage is designated hereinafter simply as amplitude of output voltage.The maximum of output voltage appears under the closed electronic switch situation, and comes given by the value of supply voltage.Amplitude of output voltage is half of difference of output voltage maximum and minimum value by definition.Under existing maximum situation, just minimum value determines amplitude of output voltage, and therefore determines the intensity of electromagnetic interference.The minimum value of output voltage is more little, and electromagnetic interference is then strong more.

Basically determine the minimum value of output voltages in the prior art by two parameters: the load impedance under the electronic switch situation that disconnects and the open-circuit impedance of electronic switch.Impedance during at very little operating current is formed together by the impedance that connects lead and LED at the load impedance under the electronic switch situation that disconnects.The open-circuit impedance of electronic switch is interpreted as the impedance of electronic switch under opening.In open-circuit impedance, can consider to lead to the lead impedance of electronic switch, but generally be inessential.Two parameters, promptly load impedance under the electronic switch situation that disconnects and open-circuit impedance stand for example by component parameters difference, the temperature of LED, the strong variations that wears out and select to be determined, the feasible value of inaccurately having determined minimum value.But effectively total, the absolute value that the absolute value of open-circuit impedance surpasses load impedance reaches a plurality of orders of magnitude.Can suppose that also the real part of relevant impedance has determined the characteristic of these impedances basically.At the output voltage under the electronic switch situation of opening therefore approx on the value of dropping to 0.Therefore draw, amplitude of output voltage is substantially equal to half of supply voltage in the prior art.

Be parallel to electronic switch by the present invention and connect a pull device.Should so select the resistance value of pull device, make and in the parallel circuits of forming by pull device and open-circuit impedance, can ignore open-circuit impedance, so that the variation of open-circuit impedance is to not influence of output voltage.Can regulate the minimum value of output voltage by pull device of the present invention.Described minimum value obviously departs from 0 by the present invention, and therefore much bigger than of the prior art.Therefore reduced amplitude of output voltage with respect to prior art, this be directed at electromagnetic interference by reduction of the present invention.

The resistance value of pull device must not be so little by the present invention, to such an extent as to it is on the order of magnitude of the resistance of electronic switch under closure state.In the case the effect of electronic switch and thereby the effect of pulse operation can be restricted.By the unlocking electronic switch operating current of LED is reduced.By the operating current under the closed electronic switch situation one of the ratio explanation of opening the operating current under the electronic switch situation is reduced coefficient.When the value that reduces coefficient is 10 at least, then do not produce the restriction of pulse operation by the present invention.Become greater than 1000 if reduce coefficient, then no longer produce the electromagnetism incompatibility, effectively reduce by the present invention.

Pull down resistor be pull device by the minimum realization of expense of the present invention.If but the value that reduces coefficient should remain unchanged, even when the operational factor resembling load impedance or supply voltage changes, then must realize pull device by adjustable pull down resistor by the present invention.This can utilize one or more semi-conductive as the operation of voltage-controlled resistance, such as the form of FET realizes.The resistance that can not continuously change for example also it is contemplated that with convertible resistance cascade form.Control adjustable pull down resistor by adjusting device.This adjusting device is gathered current reduction coefficient, and the adjustable pull down resistor of following adjusting, makes to observe given reduction coefficient.With the operating current of LED or flow through electronic switch and the electric current of scalable pull down resistor flows to adjusting device, to be used to gather current reduction coefficient.Owing to stipulated the reduction coefficient by operating current, so the collecting work electric current just is enough to obtain the reduction coefficient uniquely.Because operating current is to flow through the electric current of electronic switch and flow through the electric current sum of scalable pull down resistor basically, also is enough to obtain the reduction coefficient so gather these two electric currents.Under the electronic switch situation of closure, can approx the electric current setting by electronic switch be equaled operating current.In order to make about reducing the judgement of coefficient, also can the analyzing and processing amplitude of output voltage.For the constant situation of supply voltage, the voltage of analyzing and processing on electronic switch is enough.

Eliminated output voltage amplitude by pull device of the present invention, the above-mentioned variation that is determined by the electronic switch open-circuit impedance.What remain is the variation that is caused by load impedance.Can be by being connected on the output voltage by the present invention, and therefore be parallel to LED and the drawing upwardly device that connects is eliminated these variations.Existing under the situation of drawing upwardly device, the above-mentioned parameter design rule of pull device also is suitable for.

Realize drawing upwardly device by the present invention cheaply by pull-up resistor.The value of pull-up resistor must for opening and the value that absolute value drew of load impedance during closed electronic switch between.The operating current that flows through LED under the electronic switch situation of closure is high, and load impedance thereby be low.The value of advantageously selecting pull-up resistor so that electronic commutator offers LED with energy basically, and does not offer pull-up resistor greater than this low load impedance.The operating current that flows through LED under the electronic switch situation of opening is low, and by the nonlinear characteristic decision ground of LED, load impedance thereby be high.The value of pull-up resistor must be lower than this high load impedance, so that do not influence amplitude of output voltage by the variation of high capacity impedance of the present invention.

Needn't forcibly both realize pull-up resistor, realize pull down resistor again by a single resistance.Certainly also be possible by the parallel circuits of a plurality of resistance or the realization of series circuit.Be parallel to described resistance and can connect reactance, for example be used to reduce the edge steepness of output voltage.

Description of drawings

Below should the present invention be described in detail with reference to the accompanying drawings in detail by embodiment.Showed:

Fig. 1 is the frame circuit diagram that is used to move the circuit arrangement of the present invention of LED,

Fig. 2 is the time graph of the output voltage of the circuit arrangement that is used to move LED by prior art,

Fig. 3 is the time graph of output voltage that is used to move the circuit arrangement of the present invention of LED,

Fig. 4 has adjustable adjusting pull down resistor, is used to move the frame circuit diagram of the circuit arrangement of the present invention of LED.

Following, resistance passes through alphabetical J by alphabetical S, voltage by alphabetical V and tie point by letter r, switch, follows a numeral respectively and represents.

Embodiment

The frame circuit diagram of the circuit arrangement of the present invention that is used to move LED has been shown in the accompanying drawing 1.Electronic commutator 1 is at tie point J1, and J2 is last to offer light-adjusting module 2 with supply voltage V1.Light-adjusting module 2 is at tie point J3, and J4 is last to offer LED 3 with output voltage V 2.By leading to the connection of tie point J2 from tie point J1 in the light-adjusting module 2, form and lead to first of LED 3 from electronic commutator 1 and connect a section of lead.Lead to second of LED 3 from electronic commutator 1 and connect a section of lead, guide tie point J4 into through the electronic switch S1 the light-adjusting module from tie point J22.Control circuit 4 following control electronic switch S1 make and move LED 3 with the working method of pulse.Be parallel to electronic switch S1 by the present invention and connected pull down resistor R2.The function of R2 and parameter designing rule can be taken from and set forth chapters and sections of the present invention.This is equally applicable to be connected in light-adjusting module 2 between J3 and the J4, pull-up resistor of the present invention.

Accompanying drawing 2 is showed the curve (not having R1 and R2) of 2 couples of time t of output voltage V that is used to move the circuit arrangement of LED by prior art.Described curve is rectangle basically.When electronic switch S1 is closed, always suppose the maximum of V2, when S1 opens, always suppose the minimum value of V2.The maximum of V2 is equivalent to the supply voltage V1 that electronic commutator 1 is provided basically.The minimum value of V2 is similar to 0.Therefore for the amplitude of V2 by the prior art value of drawing basically

$\frac{V1}{2}$

Accompanying drawing 3 is showed the curve (having R1 and R2) of 2 couples of time t of output voltage V of the circuit arrangement of the present invention that is used to move LED.In accompanying drawing 2, described curve is rectangle basically.When electronic switch S1 is closed, always suppose the maximum of V2, when S1 opens, always suppose the minimum value of V2.The maximum of V2 is equivalent to the supply voltage V1 that electronic commutator 1 is provided basically.Described minimum value is V3, wherein, is suitable for basically under situation about noting the above-mentioned explanation of the parameter designing of R1 and R2:

$V3=V1\frac{R1}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="C03100797E00091.png,C03100797E00101.png"\; state="\{\{state\}\}">R</figure-callout>}1+\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="C03100797E00091.png,C03100797E00101.png"\; state="\{\{state\}\}">R</figure-callout>}2}$

Thereby draw value of the present invention basically for the amplitude of V2 and be

$\frac{V1}{2}\frac{R2}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="C03100797E00091.png,C03100797E00101.png"\; state="\{\{state\}\}">R</figure-callout>}1+\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="C03100797E00091.png,C03100797E00101.png"\; state="\{\{state\}\}">R</figure-callout>}2}$

Especially for the R1 situation more much bigger, produced the reducing greatly with respect to prior art of V2 amplitude by the present invention than R2.

Illustrated in the accompanying drawing 4 and had adjustable adjusting pull down resistor, be used to move the frame circuit diagram of the circuit arrangement of the present invention of LED.In accompanying drawing 4, pull down resistor R2 is embodied as adjustable resistance with respect to accompanying drawing 1 by adjusting device 5 controls.Adjusting device 5 following adjusting pull down resistor R2 make and observe the given reduction value that leaves in the adjusting device 5.Give the measured value of adjusting device 5 LED conveying operating currents by measurement mechanism 6.The amplitude of the alternating current component of LED operating current is a yardstick of current reduction value.Therefore can in adjusting device 5, obtain current reduction value.

Claims (8)

1. be used to move the circuit arrangement of light-emitting diode with the operating current that flows through an electronic switch basically, it is characterized in that, be parallel to described electronic switch and connected a pull device, the resistance of this pull device has so value of design, makes that taking to be worth at least 10 reduction coefficient by one is described in operating current under the closed electronic switch situation to the ratio of the operating current under unlocking electronic switch situation.

2. by the circuit arrangement that is used to move light-emitting diode of claim 1, it is characterized in that, be parallel to described light-emitting diode and connected a drawing upwardly device.

3. by the circuit arrangement that is used to move light-emitting diode of claim 1, it is characterized in that, realize described pull device by a pull down resistor.

4. by the circuit arrangement that is used to move light-emitting diode of claim 1, it is characterized in that, realize described pull device by an adjustable pull down resistor, wherein, an adjusting device is so regulated the value of described pull down resistor, makes to observe a given reduction coefficient.

5. by the circuit arrangement that is used to move light-emitting diode of claim 4, it is characterized in that, realize described adjustable pull down resistor by at least one semiconductor element.

6. by the circuit arrangement that is used to move light-emitting diode of claim 4, it is characterized in that, realize described adjustable pull down resistor by a plurality of convertible resistance.

7. by the circuit arrangement that is used to move light-emitting diode of claim 2, it is characterized in that, realize described drawing upwardly device by a pull-up resistor.

8. by the circuit arrangement that is used to move light-emitting diode of claim 1, it is characterized in that, realize described electronic switch by a MOSFET.

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