TWI419606B - A control circuit of a light emitting diode and apparatus thereof - Google Patents

Description

Light-emitting diode control circuit and device thereof

The invention relates to a control circuit, in particular to a control circuit for controlling a light-emitting diode.

Referring to FIG. 1 , a light emitting diode device 900 using an alternating current power source includes a light emitting diode (group) 910 and a current limiting resistor 920 . Moreover, the resistance of the general current limiting resistor 920 will be a fixed value and will not change with temperature, as shown in FIG.

Generally, the LED 910 is operated at an operating temperature T _w higher than room temperature (25 ° C). However, when the LED 910 is operated for a long time, the internal resistance of the LED 910 may be slightly deteriorated due to aging. The variation of the voltage across the LED 910 will change to a certain extent, causing the current flowing through the LED 910 to drift and the brightness of the LED 910 to be unstable and affecting its service life. .

Accordingly, it is an object of the present invention to provide a control circuit capable of maintaining the stability of light emission when the light-emitting diode is turned on and when its internal resistance is changed, and a light-emitting diode device which can stably emit light even after long-term use.

Therefore, the control circuit of the light-emitting diode of the present invention is connected in series with a light-emitting diode to form a series circuit, and the temperature of the light-emitting diode rises from an initial temperature to an operating temperature when the light-emitting diode operates, the control circuit The method comprises: a first resistance unit and a second resistance unit.

When the temperature of the first resistance unit is greater than a critical temperature, the resistance value is proportional to the temperature change, and the critical temperature is between the initial temperature and the operating temperature; and when the second resistance unit is greater than the critical temperature, Its resistance is inversely proportional to temperature changes. In addition, in the control circuit, the first resistance unit and the second resistance unit are connected in series with each other, and when the temperature of the control circuit is greater than the critical temperature, the absolute value of the resistance change rate of the first resistance unit is greater than the resistance value of the second resistance unit. The absolute value of the rate of change is such that when the light-emitting diode operates at the operating temperature and its internal resistance changes, the current flowing through the light-emitting diode changes correspondingly to change the operating temperature, thereby causing the first resistance unit and the second The integrated resistance of the resistor unit changes due to changes in operating temperature to maintain a constant current flow through the LED.

Preferably, the integrated resistance at the critical temperature after the first resistor unit and the second resistor unit are connected in series are substantially the same as the integrated resistance at the initial temperature.

Preferably, the first resistance unit has a rate of change of resistance of at least 10 degrees when the temperature thereof is greater than the critical temperature is at least 2 times greater than the rate of change of the resistance of the second resistance unit for each additional 10 degrees when the temperature thereof is greater than the critical temperature.

Preferably, the first resistance unit and the second resistance unit are connected in series and the integrated resistance change rate is increased by at least 5% for every 10 degrees when the temperature is greater than the critical temperature.

Preferably, when the temperature is between the initial temperature and the critical temperature, the absolute value of the resistance change rate of the first resistance unit is close to the absolute value of the resistance change rate of the second resistance unit, so that the first resistance unit and After the second resistance unit is connected in series, the integrated resistance change rate between the initial temperature and the critical temperature is lower than a preset value. Further, the preset value is 5%.

Preferably, the first temperature unit has a first resistor and a second resistor connected in series, each of which is a thermistor, the temperature coefficient of the first resistor is a positive value, and the temperature coefficient of the second resistor is a negative value. And the absolute value of the temperature coefficient of the first resistor is greater than or equal to the absolute value of the temperature coefficient of the second resistor; the second temperature unit has a third resistor and a fourth resistor connected in series with each other, which are respectively the thermistor, and the third The temperature coefficient of the resistor is a positive value, the temperature coefficient of the fourth resistor is a negative value, and the absolute value of the temperature coefficient of the third resistor is less than or equal to the absolute value of the temperature coefficient of the fourth resistor.

Therefore, the LED device of the present invention is suitable for receiving an AC power source, and the LED device comprises: at least one LED and a control circuit as described above.

The invention has the advantages of maintaining the light-emitting stability of the light-emitting diode when the light-emitting diode is turned on and the internal resistance thereof, and for predicting the operating characteristics of the light-emitting diode at the operating temperature at room temperature.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention.

3 is a first preferred embodiment of a light-emitting diode device 100 of the present invention, the light-emitting diode device 100 includes at least one light-emitting diode 1 and a control circuit for controlling the light-emitting diode 1 to emit light. 2. When the temperature of the light-emitting diode 1 rises from a starting temperature (room temperature) to a critical temperature by the control of the control circuit 2, and when the internal resistance of the light-emitting diode 1 is changed due to long-time operation, , its brightness can have better stability.

In this embodiment, the control circuit 2 receives an alternating current (AC) power source 3 and includes a first resistor unit 4 and a second resistor unit 5, and the alternating current power source 3, the first resistor unit 4, and the light emitting diode 1 And the second resistance unit 5 forms a series circuit. As shown in FIG. 4, a characteristic curve L for representing the resistance value of the control circuit 2 (i.e., the integrated resistance value after the series connection of the first resistance unit 4 and the second resistance unit 5) and the temperature change is defined, and the characteristic curve L is defined. It can be divided into a first curve segment L ₁ and a second curve segment L ₂ by a critical temperature T _t .

The first resistor unit 4 has a first resistor R ₁ and a second resistor R ₂ connected in series with the first resistor R ₁ , and as shown in FIG. 4 , a resistor and temperature are defined to represent the first resistor unit 4 . characteristic curve relationship between L _+, L ₊ of the characteristic critical temperature T _t is likewise divided into a first segment and a second segment L _a L _b. The first resistor R ₁ and the second resistor R ₂ are both thermistors, and the temperature coefficient of the first resistor R ₁ is a positive value, and the temperature coefficient of the second resistor R ₂ is a negative value. In order to make the resistance of the first first resistance unit 4 proportional to the temperature change, the absolute value of the temperature coefficient of the first resistor R ₁ must be greater than or equal to the absolute value of the temperature coefficient of the second resistor R ₂ , in this embodiment. The temperature coefficient of the first resistor R ₁ is 1300, and the temperature coefficient of the second resistor R ₂ is -1000, but not limited thereto.

The second resistor unit 5 has a third resistor R ₃ and a fourth resistor R ₄ connected in series with the third resistor R ₃ , and as shown in FIG. 4 , a resistor and temperature are defined to represent the second resistor unit 5 . The characteristic curve L _{− is} changed, and the characteristic curve L ₋ is divided into a third line segment L _c and a fourth line segment L _d by the critical temperature T _t . The third resistor R ₃ and the fourth resistor R ₄ are both thermistors, and the temperature coefficient of the third resistor R ₃ is a positive value, and the temperature coefficient of the fourth resistor R ₄ is a negative value. Similarly, the absolute value of the temperature coefficient of the third resistor R ₃ must be less than or equal to the absolute value of the temperature coefficient of the fourth resistor R ₄ , so that the resistance of the second resistor unit 5 is inversely proportional to the temperature change, so in this implementation In the example, the temperature coefficient of the third resistor R ₃ is 500, and the temperature coefficient of the fourth resistor R ₄ is -2000, but not limited thereto.

The above numerical examples are only one example. In other possible embodiments, the temperature coefficients of all the resistors in the first resistor unit may be positive values, and the temperature coefficients of all resistors in the second resistor unit may be negative values. . As long as the first resistance unit and the second resistance unit can conform to the defined relationship described below, they are all within the scope of the invention.

Specifically, since the first resistance unit 4 and the second resistance unit 5 are connected in series with each other, the characteristic curve L of the control circuit 2 is obtained by adding the characteristic curve L ₊ and the characteristic curve L ₋ , wherein the first line segment L _{a is added} to the third line segment L _{c to} form a first curved line segment L ₁ , and the second line segment L _{b is} added to the fourth line segment L _{d to} form a second curved portion L ₂ . In the present embodiment, the resistance of the second resistor unit 5 at the starting temperature (room temperature) is greater than or equal to half of the resistance of the first resistor unit 4 at the starting temperature.

Since the light-emitting diode 1 is turned on by the power supply of the power source 3, the temperature of the light-emitting diode 1 rises from an initial temperature (usually room temperature 25 ° C) to an operating temperature T _w , in order to be convenient at room temperature. The operating characteristics of the LED 1 at the operating temperature T _w are tested. The control circuit 2 of the present embodiment is connected in series with the first resistor unit 4 and the second resistor unit 5 to make the characteristic curves L ₊ and L of the two. _- adding so that the resistance of the control circuit 2 at the starting temperature (room temperature) and the critical temperature T _t is nearly the same (ie, the integrated resistance at the initial temperature after the first resistor unit 4 and the second resistor unit 5 are connected in series) The integrated resistance value at the critical temperature T _t is substantially the same after the first resistor unit 4 and the second resistor unit 5 are connected in series, and the critical temperature T _t needs to be between the starting temperature and the operating temperature T _w , such as Figure 4 shows.

Further, when the temperature of the light-emitting diode 1 rises from the initial temperature to the operating temperature _Tw , the resistance of the light-emitting diode 1 is maintained stable, so that the voltage across the voltage remains stable. Therefore, in order to maintain a constant value (ie, maintain stable) of the current flowing through the light-emitting diode 1, the light-emitting diode 1 maintains a certain brightness during the time when the temperature rises, and the control circuit 2 is in the light-emitting diode 1 The resistance value during the period from the rise of the initial temperature to the critical temperature T _t must be able to vary without changing with temperature. Therefore, in this embodiment, as shown in FIG. 4, when the temperature of the control circuit 2 is less than its critical temperature T _t , the absolute value of the resistance change rate of the first resistance unit 4 is close to the resistance of the second resistance unit 5 . The absolute value of the rate of change, such that the resistance of the first resistor unit 4 and the resistance of the second resistor unit 5 can compensate each other such that the amplitude of the first curve segment L ₁ of the control circuit 2 can be less than a predetermined value, That is, the integrated resistance change rate between the initial temperature and the critical temperature T _t after the first resistance unit 4 and the second resistance unit 5 are connected in series may be lower than a preset value. In this embodiment, the preset value is 5%, but it can be adjusted according to the characteristics of different LEDs 1 and different specifications.

When the light-emitting diode 1 is operated for a long time at the operating temperature T _w , the internal resistance of the light-emitting diode 1 is increased due to the aging of the light-emitting diode 1 , so that the instantaneous current flowing through the light-emitting diode 1 is caused by The internal resistance of the light-emitting diode 1 rises and decreases slightly, and the total voltage supplied by the AC power source 3 does not change, causing the temperature of the control circuit 2 to decrease as the current decreases.

Therefore, in order to maintain the current flowing through the light-emitting diode 1 and the control circuit 2 at a constant value (ie, remain stable), as shown by the characteristic curve L of FIG. 4, the control circuit 2 is greater than the critical temperature T _t at the light-emitting diode 1 The resistance value of the time will need to be proportional to the temperature change, so that the resistance value of the control circuit 2 can be lowered (or rising and rising) due to the temperature drop of the control circuit 2, so as to achieve the purpose of current feedback, so that the light emitting diode device The total resistance value of 100 (ie, the sum of the internal resistance of the light-emitting diode 1 and the resistance of the control circuit 2) remains unchanged, so that the current flowing through the light-emitting diode 1 can be maintained at a constant value, so that the light can be made The diode 1 is maintained at the same brightness, increasing the service life of the light-emitting diode 1. In addition, when the voltage of the external AC power source 3 is floating, the fluctuation of the operating power causes the temperature of the control circuit 2 to float, and the effect of the current feedback to stabilize the brightness can be achieved.

In other words, in the present embodiment, when the temperature of the control circuit 2 is greater than the threshold temperature T _t , the absolute value of the resistance change rate of the first resistance unit 4 will be greater than the absolute value of the resistance change rate of the second resistance unit 5, The integrated resistance value after the first resistance unit 4 and the second resistance unit 5 are connected in series may be positively changed, that is, the tangent slope of any point in the second curved section L ₂ is a positive value. In the present embodiment, the resistance change rate of the first resistance unit 4 for every 10 degrees increase when the temperature is greater than the critical temperature T _t is the resistance value of the second resistance unit 5 for each 10 degree increase when the temperature is greater than the critical temperature T _t . More than 2 times the rate of change.

It is worth mentioning that the operating temperature T _{w of the} light-emitting diode 1 needs to be greater than the critical temperature T _{t of the} control circuit 2, so that the operating point of the light-emitting diode 1 can still fall on the characteristic curve when the internal resistance of the light-emitting diode 1 changes. The second curved section L ₂ of L is such that the resistance of the control circuit 2 can be correspondingly varied to achieve the purpose of stabilizing the current.

Thus, the critical temperature T _t based control circuit of embodiment 2 of the present embodiment designed for the resistance R _t is less than the resistance R _w 2 when the operation control circuit of the temperature T _w, the control circuit 2 and the difference of the critical temperature T _t 5% of the resistance value R _t , that is, R _w =R _t +0.05R _t , that is, the resistance R _{w of the} control circuit 2 at the operating temperature T _w is lower than that of the control circuit 2 at the critical temperature T _t The value R _{t has} a range of 5% variation. In this embodiment, the rising range of the second curved segment L ₂ is such that the temperature change rate of the control circuit 2 is at least greater than 5% for each 10° C increase in temperature, that is, the first resistance unit 4 and the second resistance unit 5 are connected in series. The integrated resistance change rate for each additional 10 degrees at a temperature greater than the critical temperature T _t is at least greater than 5%. Therefore, if the operating temperature _{Tw of} the light-emitting diode 1 is 80 ° C, the critical temperature T _t of the light-emitting diode 1 is 70 °C. Of course, the range of resistance R _{w of the} control circuit 2 at the operating temperature T _w (preferably between 5 and 8%), and the increase of the second curve segment L ₂ can be varied according to different needs and The characteristics of the light-emitting diode 1 are changed, and are not limited to the embodiment.

Referring to FIG. 5, a second preferred embodiment of the LED device 100 of the present invention is substantially the same as the first preferred embodiment, except that the first resistor unit 4 has only the first resistor R. ₁ . The second resistor unit 5 has only the third resistor R ₃ , and the first resistor R ₁ and the third resistor R ₃ are the thermistors respectively, and the temperature coefficient of the first resistor R ₁ is a positive value, and the third resistor R The temperature coefficient of ₃ is a negative value, and the absolute value of the temperature coefficient of the first resistor R ₁ is greater than or equal to the absolute value of the temperature coefficient of the third resistor R ₃ .

Referring to FIG. 6, in the present embodiment, the temperature coefficient of the first resistor R ₁ in the control circuit 2 is set to 1500, and the temperature-resistance characteristic curve is shown by L ₆₁ in FIG. 6, and the third resistor R _{3 is} shown. The temperature coefficient is set to -4000, and the temperature-resistance characteristic curve is shown by L ₆₂ of FIG. 6, and the integrated characteristic curve of the first resistance unit 4 and the second resistance unit 5 is L ₆₃ of FIG. Show. Therefore, it can be seen that only one resistor is used in the first resistor unit 4 and the second resistor unit 5 of the embodiment, and the resistance of the control circuit 2 at the starting temperature (about 30 degrees) is substantially equal to the critical temperature T. a resistance value of _t (about 70 degrees), and the resistance value of the entire control circuit 2 when the temperature is greater than the critical temperature T _t (ie, the integrated resistance of the first resistor unit 4 and the second resistor unit 5 in series) may be proportional to the temperature (ie, the tangent slope at any point is positive).

In addition, in other embodiments, the first resistor R ₁ and the third resistor R _{3 of} other temperature coefficients may also be used (eg, the temperature coefficient of the first resistor R ₁ is 400; and the temperature coefficient of the third resistor R ₃ is - 500) and the total resistance at about 50 degrees is approximately the same as the total resistance at room temperature (about 25 degrees).

Therefore, the characteristics, the number, and the connection relationship between the resistors in the first resistor unit 4 and the second resistor unit 5 are not limited to the above embodiments, as long as the resistance of the overall control circuit 2 at the start temperature is The resistance of the critical temperature is substantially the same, and the tangential slope of any point is positive when the temperature is greater than the critical temperature T _t , for example, in the case of having a plurality of resistors, the first resistor R in the first resistor unit 4 ₁ and the second resistor R ₂ may also be positive temperature coefficient thermistors, and the third resistor R ₃ and the fourth resistor R _{4 in the} second resistor unit 5 may both be negative temperature coefficient thermistors.

In summary, the light-emitting diode device 100 of the present invention can change the resistance value of the control circuit 2 according to different operating temperatures, so that the light-emitting diode 1 rises from room temperature to a critical temperature, and the light-emitting diode 1 When the internal resistance changes due to long-term use, the light-emitting diode 1 can be adjusted correspondingly by the resistance of the control circuit 2 to maintain a certain brightness to increase the service life of the light-emitting diode. Moreover, the integrated resistance of the control circuit 2 at the starting temperature (room temperature) and the critical temperature T _t is substantially the same, which will facilitate the designer to predict the characteristics of the operating diode T at the operating temperature T _w at room temperature.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

100. . . Light-emitting diode device

1. . . Light-emitting diode

2. . . Control circuit

3. . . AC power

4. . . First resistance unit

5. . . Second resistance unit

1 is a circuit diagram illustrating a conventional light emitting diode and its control circuit;

2 is a waveform diagram illustrating the relationship between the resistance of a conventional control circuit and temperature changes;

Figure 3 is a circuit diagram showing a first preferred embodiment of the light-emitting diode device of the present invention;

4 is a waveform diagram illustrating a characteristic curve of resistance values and temperature changes of the control circuit, the first resistor unit, and the second resistor unit of the first embodiment;

Figure 5 is a circuit diagram showing a second preferred embodiment of the light-emitting diode device of the present invention; and

Fig. 6 is a waveform diagram showing characteristic curves of resistance and temperature changes of the control circuit, the first resistor unit and the second resistor unit of the second embodiment.

100. . . Light-emitting diode device

1. . . Light-emitting diode

2. . . Control circuit

3. . . AC power

4. . . First resistance unit

5. . . Second resistance unit

Claims (10)

A control circuit for a light-emitting diode is connected in series with a light-emitting diode to form a series circuit. When the light-emitting diode is operated, its temperature rises from an initial temperature to an operating temperature, and the control circuit comprises: a first resistance unit, the first resistance unit having a resistance value proportional to a temperature change when the temperature thereof is greater than a critical temperature, and the critical temperature is between the initial temperature and the operating temperature; and a second a resistance unit, wherein the resistance of the second resistor unit is inversely proportional to a temperature change when the temperature is greater than the threshold temperature, wherein the first resistor unit and the second resistor unit are connected in series; wherein, when the temperature of the control circuit is greater than the The critical value of the resistance change rate of the first resistance unit is greater than the absolute value of the resistance change rate of the second resistance unit, so that the light-emitting diode operates at the operating temperature and the internal resistance changes. When the current flowing through the light emitting diode changes correspondingly, the operating temperature is changed, so that the integrated resistance of the first resistor unit and the second resistor unit is determined according to the operating temperature. Of changes to the light-emitting diode current will flow through the stable. The control circuit of the light-emitting diode according to claim 1, wherein the integrated resistance of the first resistor unit and the second resistor unit in series at the critical temperature and the initial temperature thereof The integrated resistance is essentially the same. The control circuit of the light-emitting diode according to claim 1, wherein the first resistance unit has a resistance change rate of at least 10 degrees greater than the second resistance unit when the temperature thereof is greater than the critical temperature. The temperature is greater than twice the rate of change of the resistance per 10 degrees of the critical temperature. According to the control circuit of the light-emitting diode of claim 1, wherein the first resistance unit and the second resistance unit are connected in series, and the integrated resistance change rate is increased by 10 degrees when the temperature is greater than the critical temperature. At least greater than 5%. According to the control circuit of the light-emitting diode of claim 1, wherein the absolute value of the resistance change rate of the first resistance unit is close to the second between the initial temperature and the critical temperature. The absolute value of the resistance change rate of the resistance unit is such that the integrated resistance change rate between the initial temperature and the critical temperature after the first resistance unit and the second resistance unit are connected in series is lower than a predetermined value. The control circuit of the light-emitting diode according to claim 1, wherein the resistance of the second resistor unit at the initial temperature is greater than or equal to the first resistor unit at the initial temperature. Half of the resistance. The control circuit of the light-emitting diode according to any one of claims 1 to 6, wherein the first resistor unit has a first resistor and a second resistor connected in series with the first resistor, The first resistor and the second resistor are respectively the thermistor, the temperature coefficient of the first resistor is a positive value, the temperature coefficient of the second resistor is a negative value, and the absolute value of the temperature coefficient of the first resistor is greater than or equal to the The absolute value of the temperature coefficient of the second resistor. The control circuit of the light-emitting diode according to any one of claims 1 to 6, wherein the second resistor unit has a third resistor and a fourth resistor connected in series with the third resistor. The third resistor and the fourth resistor are respectively a thermistor, the temperature coefficient of the third resistor is a positive value, the temperature coefficient of the fourth resistor is a negative value, and the absolute value of the temperature coefficient of the third resistor is less than or equal to the The absolute value of the temperature coefficient of the fourth resistor. The control circuit of the light-emitting diode according to any one of claims 1 to 6, wherein the first resistor unit has a first resistor, and the second resistor unit has a third resistor, the first resistor The first resistor and the third resistor are respectively a thermistor, the temperature coefficient of the first resistor is a positive value, the temperature coefficient of the third resistor is a negative value, and the absolute value of the temperature coefficient of the first resistor is greater than or equal to the first The absolute value of the temperature coefficient of the three resistors. A light emitting diode device for receiving an alternating current power source, the light emitting diode device comprising: at least one light emitting diode, when the light emitting diode works, the temperature thereof rises from an initial temperature to an operating temperature And a control circuit, forming a series circuit with the LED and the AC power source, the control circuit comprising a first resistor unit, the resistance and temperature of the first resistor unit when the temperature is greater than a critical temperature The change is proportional, and the critical temperature is between the initial temperature and the operating temperature, and a second resistance unit whose resistance is inversely proportional to the temperature change when the temperature thereof is greater than the critical temperature. The first resistance unit and the second resistance unit are connected in series with each other, and when the temperature of the control circuit is greater than the critical temperature, the absolute value of the resistance change rate of the first resistance unit is greater than the resistance value of the second resistance unit. The absolute value of the rate, such that when the light-emitting diode operates at the operating temperature and its internal resistance changes, the current flowing through the light-emitting diode changes correspondingly to change the operation. Degrees, thereby enabling integration of the first resistor unit and second resistance of the resistance unit due to temperature change should operate, to the light-emitting diode current will flow through the stable.