KR102769115B1 - Apparatus of driving a light source - Google Patents

Abstract

The light source driving device includes a light source and a control unit that controls the light emission of the light source.
The control unit includes a switch having a collector connected to a light source, a voltage regulator disposed between a base of the switch and a node, and a first resistor disposed between the node and an emitter of the switch.

Description

{Apparatus of driving a light source}

The embodiment relates to a light source driving device.

Light-emitting diodes (LEDs) are widely used as light sources. These light-emitting diodes are emerging as promising markets in the automotive and lighting industries. Since light-emitting diodes are semi-permanent and can have high brightness and high output, they have been actively developed as light sources for vehicles in recent years.

In order to drive a vehicle light source, a light source driving device is required. Conventional light source driving devices are provided with a control switch to block the operation of the light source when a current exceeding a critical current flows through the light source so as to prevent excessive current from flowing through the light source. The driving current flowing through the light source depends on the base-emitter voltage of the control switch, and the base-emitter voltage of the control switch changes depending on the temperature. Normally, the temperature deviation for the driving current required in the industry is within 10%, but in conventional light source driving devices, a temperature deviation of +12% occurs when the temperature increases from room temperature (25°C), and a temperature deviation of -17% occurs when the temperature decreases from room temperature (25°C).

In this way, if the temperature deviation is outside the temperature deviation commonly used in the industry, there is a problem that the driving current flowing to the light source fluctuates greatly, so that even though the light source is normally emitting light, it is recognized as an overcurrent and the light source emission is blocked by the control of the corresponding control switch, resulting in a malfunction. This causes a serious decrease in the reliability of the product.

The present invention aims to solve the above-mentioned and other problems.

Another object of the invention is to provide a light source driving device of a novel structure.

Another object of the embodiment is to provide a light source driving device capable of minimizing temperature deviation of driving current.

Another object of the embodiment is to provide a light source driving device that can simplify the structure and reduce the cost.

Another object of the embodiment is to provide a light source driving device capable of stable light emission.

According to one aspect of the embodiment to achieve the above or other purposes, a light source driving device includes: a light source; and a control unit that controls light emission of the light source. The control unit may include: a switch including a collector connected to the light source; a constant voltage element disposed between a base of the switch and a node; and a first resistor disposed between the node and an emitter of the switch.

The above light source can be emitted by turning on the switch.

The above-mentioned voltage regulator may include at least one diode.

When an input voltage from a power source is applied to the node, the switch can be turned on by the threshold voltage of the diode.

When the above switch is turned on, the driving current flowing to the light source can be calculated by the following mathematical formula.

[Mathematical formula]

I _LED =(V _f -V _EB )/R ₁

I _LED is the driving current flowing through the light source, V _f is the threshold voltage of the voltage regulator, V _EB is the emitter-base voltage of the switch, and R ₁ is the resistance value of the first resistor.

The threshold voltage of the diode and the emitter-base voltage of the switch can change with temperature.

The temperature-dependent variation of the emitter-base voltage of the above switch can be compensated for by the temperature-dependent variation of the threshold voltage of the above diode.

It may include a second resistor placed between the base and ground of the switch.

The effect of the light source driving device according to the embodiment is described as follows.

According to at least one of the embodiments, there is an advantage in that a driving current having a minimum temperature deviation is generated by compensating for the temperature deviation of the diode with the temperature deviation of the switch, thereby enabling stable light emission of the light source.

According to at least one of the embodiments, there is an advantage in that stable light emission is possible by controlling the light emission of a light source using a diode that is less sensitive to temperature, thereby minimizing fluctuations in driving current due to temperature deviation.

According to at least one of the embodiments, there is an advantage in that the configuration is simple and cost-saving because a separate switch for blocking the occurrence of overcurrent is not required by allowing a maximum rated constant current to flow to the light source.

According to at least one of the embodiments, by controlling the light emission of the light source using a diode, there is an advantage in that the light source emits light with a constant current of the maximum rating, thereby enabling maximum brightness and uniform light emission.

Further scope of applicability of the embodiments will become apparent from the detailed description below. However, since various changes and modifications within the spirit and scope of the embodiments will become apparent to those skilled in the art, it should be understood that the detailed description and specific embodiments, such as the preferred embodiments, are given by way of example only.

Figure 1 illustrates a circuit diagram of a light source driving device according to an embodiment.
Figure 2 shows the relationship between the collector current of the switch and the voltage between the base and emitter.
Figure 3 shows the relationship between the forward current and forward voltage of a diode.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. However, the technical idea of the present invention is not limited to some of the embodiments described, but can be implemented in various different forms, and within the scope of the technical idea of the present invention, one or more of the components between the embodiments can be selectively combined or substituted and used. In addition, terms (including technical and scientific terms) used in the embodiments of the present invention can be interpreted as meanings that can be generally understood by those skilled in the art to which the present invention belongs, unless explicitly and specifically defined and described, and terms that are commonly used, such as terms defined in a dictionary, can be interpreted in consideration of the contextual meaning of the related technology. In addition, terms used in the embodiments of the present invention are used to describe the embodiments and are not intended to limit the present invention. In this specification, singular forms may also include plural forms unless specifically stated in the phrase, and when described as “at least one (or more than one) of B and (and) C,” it may include one or more of all combinations that can be combined with A, B, and C. In addition, when describing components of embodiments of the present invention, terms such as first, second, A, B, (a), (b), etc. may be used. These terms are only intended to distinguish the components from other components, and are not limited by the nature, order, or sequence of the components. In addition, when a component is described as being "connected," "coupled," or "connected" to another component, it may include not only cases where the component is directly connected, coupled, or connected to the other component, but also cases where the component is "connected," "coupled," or "connected" by another component between the component and the other component. In addition, when it is described as being formed or arranged "above or below" each component, "above" or "below" includes not only cases where two components are in direct contact with each other, but also cases where one or more other components are formed or arranged between the two components. In addition, when expressed as "above" or "below," it may include the meaning of not only the upward direction but also the downward direction based on one component.

Figure 1 illustrates a circuit diagram of a light source driving device according to an embodiment.

Referring to FIG. 1, a light source driving device according to an embodiment may include a light source (20).

The light source (20) is connected between the power source (10) and ground (GND) and can emit light by the input voltage of the power source (10). The power source (10) can supply an input voltage having a range of, for example, 8 V to 16 V. The power source (10) can be supplied from a battery mounted on a vehicle or can be supplied from a DC-DC converter. The DC-DC converter can convert the voltage of the battery into a desired voltage.

For example, the light source (20) may be a lamp of a vehicle. Lamps of a vehicle may include, for example, a brake lamp, a tail lamp, a backup lamp, or a turn signal lamp.

The input voltage of the power supply (10) can be supplied by the operation control of the corresponding lamp of the vehicle. For example, the input voltage can be generated from the power supply (10) under the control of the control device (not shown) only when a driver's command or operation is input and supplied to the light source (20), or the input voltage generated in advance can be supplied to the light source (20). For example, when the driver steps on the brake pedal, the input voltage generated by the power supply (10) in response to the driver's action can be supplied to the light source (20).

If a driver's command or operation is not input, the input voltage may not be generated from the power source (10) or the supply of the input voltage to the light source (20) may be cut off. For example, if the driver releases the brake pedal, the input voltage may not be generated by the power source (10) or the supply of the input voltage may be cut off in response to the driver's action.

The embodiment is characterized in that the light source (20) emits light only when an input voltage is supplied from the power source (10), and the detailed structure and function for achieving this will be described in detail later.

The light source (20) may include a single light emitting element.

Although not shown, the light source (20) may include, for example, a plurality of strings connected in parallel to the power source (10). Instead of strings, they may also be referred to as an array or block.

For example, the first string may include a plurality of light-emitting elements. The light-emitting elements may include, but are not limited to, semiconductor light-emitting elements such as light-emitting diodes (LEDs), light-emitting element packages or light-emitting devices in which the semiconductor light-emitting elements are employed. The light-emitting elements may be connected in series with each other. For example, the second string may include a plurality of light-emitting elements. The plurality of light-emitting elements may be connected in series with each other. As another example, the plurality of light-emitting elements included in each string may be connected in parallel with each other. The number of light-emitting elements included in each string, the method of connecting the light-emitting elements, and the like may vary depending on the specifications or characteristics of various vehicle lamps.

The light source (20) may include a capacitor connected in parallel to each string.

The light source driving device according to the embodiment may include a control unit (30).

The control unit (30) is connected to the power source (10) and can control the light emission of the light source (20).

Specifically, the control unit (30) may include a switch (Q), a constant voltage element (32), and a first resistor (34).

The constant voltage element (32) may include at least one diode. Two or more diodes may be connected in series with each other. When two or more diodes are connected in series, the threshold voltage of the constant voltage element (32) may be the sum of the threshold voltages of each of the two or more diodes.

Since the description below is limited to having two or more diodes, the threshold voltage (V _f ) means the sum of the threshold voltages of each of the two or more diodes.

The switch (Q) may include a base (B) connected to a diode (32), a collector (C) connected to a light source (20), and an emitter (E) connected to a first resistor (34). The diode (32) may be connected between a node (n) and the base (B) of the switch (Q). The first resistor (34) allows current to flow to the light source (20) and may be connected between the node (n) and the emitter (E) of the switch (Q).

The driving current (I _LED ) flowing to the light source (20) can be generated only when an input voltage is applied from the power source (10). For example, when the input voltage is not applied from the power source (10), the driving current (I _LED ) does not flow to the light source (20), so the light source (20) cannot emit light. For example, when the input voltage is applied from the power source (10), the driving current (I _LED ) flows to the light source (20) based on the threshold voltage (V _f ) of the diode (32), so that the light source (20) can emit light.

The driving current (I _LED ) flowing to the light source (20) can be expressed as in the following mathematical expression 1.

[Mathematical formula 1]

I _LED =(V _f -V _EB )/R ₁

I _LED is the driving current (I _LED ) flowing in the light source (20), V _f is the threshold voltage of the diode (32), V _EB is the voltage between the emitter and base of the switch (Q), and R ₁ may be the resistance value of the first resistor (34).

From mathematical expression 1, the driving current (I _LED ) flowing in the light source (20) can be related to the resistance value of the first resistor (34), the threshold voltage (V _f ) of the diode (32), and the emitter-base voltage (V _EB ) of the switch (Q).

The resistance value of the first resistor (34), the threshold voltage (V _f ) of the diode (32), and the emitter-base voltage (V _EB ) of the switch (Q) can be fixed values.

In the embodiment, the driving current (I _LED ) flowing to the light source (20) may be fixed to, for example, 15 mA. This driving current (I _LED ) may not fluctuate as a constant current. That is, the driving current (I _LED ) flowing to the light source (20) may be a constant current of the maximum rating. The constant current of the maximum rating may mean a constant current having the maximum size that can flow to the light source (20).

That is, when an input voltage is applied from the power supply (10), a driving current (I _LED ) of a maximum rated constant current flows through the light source (20), and the light source (20) can emit light with a brightness corresponding to the maximum rated constant current. If an input voltage is not applied from the power supply (10), a driving current (I _LED ) does not flow through the light source (20), and thus light is not emitted from the light source (20). In other words, in the embodiment, the driving current (I _LED ) flowing through the light source (20) can be one of 0 and 15 mA (maximum rated constant current) depending on whether the input voltage of the power supply (10) is applied.

Meanwhile, the threshold voltage (V _f ) of the diode (32) and the emitter-base voltage (V _EB ) of the switch (Q) may vary depending on the temperature.

Figure 2 shows the relationship between the collector current of the switch and the voltage between the emitter and the base, and Figure 3 shows the relationship between the forward current and the forward voltage of the diode.

As illustrated in FIG. 2, as the temperature increases, the magnitude of the emitter-base voltage (V _EB ) of the switch (Q) may decrease. As illustrated in FIG. 3, as the temperature increases, the threshold voltage (V _f ) of the diode (32) may decrease. In FIG. 3, the vertical axis represents the forward voltage, and when this forward voltage becomes greater than the threshold voltage (V _f ) of the diode (32), the diode (32) may be turned on, and a threshold voltage may be generated in the diode.

To easily understand this, the temperature change characteristics of the switch (Q) and the temperature change characteristics of the threshold voltage (V _f ) can be expressed as shown in Table 1 below.

-40℃ 25℃ 85℃ Threshold voltage (V _f ) of diode (32) 1.67V 1.56V 1.4V Emitter-base voltage (V _EB ) of the switch (Q) 0.84V 0.78V 0.65V

As shown in Table 1, both the magnitude of the emitter-base voltage (V _EB ) of the switch (Q) and the threshold voltage (V _f ) of the diode (32) can decrease as the temperature increases. When the temperature change characteristics described in FIGS. 2, 3, and Table 1 are substituted into Equation 1, the driving current (I _LED ) flowing in the light source (20) in Equation 1 can be determined by the difference (V _f -V _EB ) between the emitter-base voltage (V _EB ) of the switch (Q) and the threshold voltage of the diode (32). Referring to Table 1, the magnitude of the emitter-base voltage (V _EB ) of the switch (Q) and the difference (V _f -V _EB ) between the threshold voltages of the diode (32) at room temperature (25°C) can be 1.56 V - 0.78 V = 0.78 V. When the ambient temperature increases from room temperature (25°C) to 85°C, the difference between the magnitude of the emitter-base voltage (V _EB ) of the switch (Q) and the threshold voltage of the diode (32) (V _f V _EB ) may be 1.4 V - 0.65 V = 0.75 V. Accordingly, the deviation between the magnitude of the emitter-base voltage (V _EB ) of the switch (Q) and the difference between the threshold voltage of the diode (32) (V _f -V _EB ) at room temperature and at 85°C may be 4%.

Referring to mathematical expression 1, the driving current (I _LED ) flowing in the light source (20) is determined by the difference (V _f -V _EB ) between the magnitude of the voltage (V _EB ) between the emitter and base of the switch (Q) and the threshold voltage of the diode (32) when the resistance value of the first resistor (34) is fixed, so the deviation for the driving current (I _LED ) flowing in the light source (20) at room temperature and 85°C can also be 4%.

As described above, in the embodiment, for example, the driving current (I _LED ) flowing to the light source (20) has a constant current, for example, 15 mA. The deviation for the temperature change characteristic for this constant current can be expressed as shown in Table 2 below.

-40℃ 25℃ 85℃ Deviation electric current 15.96mA 15mA 14.4mA -5.7% to +5.8%

As shown in Table 2, the temperature deviation for the driving current (I _LED ) flowing to the light source (20) can be -5.7% to +5.8%. Typically, the temperature deviation for the driving current (I _LED ) required in the industry is within 10%. Therefore, in the embodiment, the temperature deviation for the driving current (I _LED ) is smaller than the deviation required in the industry, so that the reliability of the product can be secured.

In an embodiment, the control unit (30) may include a second resistor (36).

The second resistor (36) can be connected between the base (B) of the switch (Q) and ground (GND). The second resistor (36) is an optional component and can be omitted. The second resistor (36) can allow current to flow stably to the base (B) of the switch (Q).

The above detailed description should not be construed as restrictive in all respects but should be considered as illustrative. The scope of the embodiments should be determined by a reasonable interpretation of the appended claims, and all changes within the equivalency range of the embodiments are intended to be included within the scope of the embodiments.

10: Power
20: Light source
30: Control Unit
32: Constant voltage element
34: 1st resistor
36: Second resistor
Q: Switch
B: Base
E: Emitter
C: Collector
I _LED : Driving current
V _f : threshold voltage of the diode
V _EB : Emitter-base voltage
n: node
GND: Ground

Claims (8)

light source; and
Including a control unit that controls the light emission of the above light source,
The above control unit,
A switch including a collector connected to the light source;
A constant voltage element placed between the base and node of the above switch; and
A first resistor is disposed between the node and the emitter of the switch,
When the input voltage from the power source is applied to the node, the switch is turned on by the threshold voltage of the constant voltage element,
A light source driving device in which the driving current flowing to the light source when the above switch is turned on is calculated by the following mathematical formula.
[Mathematical formula]
I _LED =(V _f -V _EB )/R ₁
I _LED is the driving current flowing in the light source, V _f is the threshold voltage of the constant voltage element, V _EB is the emitter-base voltage of the switch, and R ₁ is the resistance value of the first resistor, and the threshold voltage of the constant voltage element and the emitter-base voltage of the switch each decrease as the temperature increases. In the first paragraph,
The above light source is a light source driving device that emits light by turning on the above switch. In the first paragraph,
The above-mentioned voltage regulator comprises two or more diodes,
A light source driving device in which the threshold voltage of the above-mentioned constant voltage element is the sum of the threshold voltages of each of the two or more diodes. In the first paragraph,
The variation of the emitter-base voltage of the above switch due to an increase in temperature is compensated by the variation of the threshold voltage of the above constant-voltage element due to an increase in temperature,
A light source driving device in which the variation in the emitter-base voltage of the above switch due to a decrease in temperature is compensated for by the variation in the threshold voltage of the above constant-voltage element due to a decrease in temperature. In the first paragraph,
A light source driving device including a second resistor placed between the base and ground of the above switch. delete delete delete

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