CN201628106U - A LED light-emitting unit with a precise current-stabilizing circuit - Google Patents

Abstract

The utility model discloses an LED light-emitting unit with a precision current stabilizing circuit, which comprises an LED light-emitting unit circuit and the precision current stabilizing circuit which are in series connection. The precision current stabilizing circuit consists of a transistor (Q), a voltage stabilizing tube (D), a first resistor (R1) and a second resistor (R2); a transmitting electrode of the transistor (Q) is in series connection with the first resistor (R1); and the voltage stabilizing tube (D) is in series connection with the second resistor (R2). The LED light-emitting unit with the precision current stabilizing circuit has the advantages of fine current stabilizing characteristic enabling a whole backlight source to be even and uniform in brightness, fine visual effect and long service life, thereby leading users to reduce maintenance cost and greatly improving advertising display effect.

Description

A LED light-emitting unit with a precise current-stabilizing circuit

Technical field:

The utility model relates to a light-emitting unit, in particular to an LED light-emitting unit connected to a precise current-stabilizing circuit.

Background technique:

LED is a new type of light-emitting device, which can emit light efficiently only by DC low-voltage power supply, and is currently a highly recommended green light source. But the LED is a current-driven device, and the change of the supply current will affect the brightness and color of the light. In addition, the volt-ampere characteristic of the LED has a negative temperature coefficient (-2mv/℃), and the temperature rise will increase the LED current, but the brightness will not increase. Shortened lifespan.

The following four types of application technology solutions are available, focusing on current limiting, steady current and temperature compensation respectively.

(1) Power supply with constant current source

Since LEDs operate on a low-voltage DC power supply, there are always a large number of LEDs working in groups at the same time in actual use, so at least a constant current power supply that can supply more than 1 ampere is required. From a technical point of view, if the current of the constant current source is required to be stable Degree ≤ 1% is already a high requirement. However, the 1% current stability means that the maximum supply current may vary by 10mA, while the working current of the LED is generally 20-30mA, so this constant current source has no effect on the steady flow of the LED, and has no practical value.

(2) Use a thermistor to compensate for LED current changes caused by temperature changes

Because the PN junction of the LED has a negative temperature effect, when the temperature changes, it will affect the brightness and color temperature of the LED, so it is conceived to use a thermistor with a linear positive temperature coefficient (LPTC) to operate in series with the LED, so that the temperature coefficient of the mutual compensation composition is very small resistive load, which reduces current changes caused by temperature changes. But the actual use is limited, because most of thermistor products are NTC (negative temperature coefficient) products, and PTC products are relatively few. Electrons cross the boundary into adjacent regions, thereby creating a "high resistance". Moreover, when the temperature exceeds a certain value, the resistance and the temperature increase almost increase in a stepwise manner (called the Curie temperature effect), and it is difficult to obtain a linear positive temperature coefficient (LPTC) product. Therefore, LPTC thermistors have few specifications and high prices, making it difficult to apply them in practice.

(3), using a voltage stabilizer plus a current limiting resistor

In practical applications, the most common method is to use a regulated source to supply power to several LEDs in series and add current-limiting resistors. When the selected LED operating current is I _o , the supply voltage is V _o , and the voltage drop across the LED is V when the LED is working. _f , if n LEDs are used in series to operate under V _o voltage, the required blocking resistance is R, then the formula is:

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Example: The power supply voltage is 12V, 3 LEDs are used in series, the V _f of each LED is 3.2V, and the operating current is 20mA, then

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 12</span>}\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; 3.2</span>}\mathrm{<span\; class="notranslate">\; V</span>}}{\mathrm{<span\; class="notranslate">\; 20</span>}\mathrm{<span\; class="notranslate">\; mA</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 120</span>}\mathrm{<span\; class="notranslate">\; \&Omega;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

This method is simple and can limit the operating current of the LED under certain conditions. However, the influence caused by the change of the power supply voltage cannot be solved. For example, the stability of the regulated power supply is ≤3%, that is, the maximum voltage change may be 0.36 volts, and the volt-ampere characteristic of the LED is

$\mathrm{<span\; class="notranslate">\; If</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}\mathrm{<span\; class="notranslate">\; e</span>}{\mathrm{<span\; class="notranslate">\; q</span>}}^{\mathrm{<span\; class="notranslate">\; vf</span>}}}{\mathrm{<span\; class="notranslate">\; Kt</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula, _If(0) is the reverse saturation current (that is, the initial current); q is the electronic charge; k is the Boltzmann coefficient; T is the absolute temperature. It can be seen from formula (3) that I _f and vf have an exponential relationship, so the change of I _f caused by 0.36 volts, and the corresponding changes in LED brightness and color temperature cannot be ignored.

(4), use LC and many components to form a constant current source circuit

The original intention is to use a more complex constant current source to solve the stability of the LED working current and the current increase due to temperature rise. However, the complex constant current source circuit increases the unreliability of the system, which offsets the advantages of reliability and long service life of the LED. In addition, the price of the system also affects the promotion and use of LEDs.

Utility model content:

The purpose of the utility model is to make up for the shortcomings of the prior art LED constant current circuit such as complicated connection, low stability and high price, and provide a simple and reliable LED light-emitting unit with a precise constant current circuit.

In order to achieve the above object, the technical scheme of the utility model is as follows:

An LED light-emitting unit with a precise current-stabilizing circuit, which includes an LED light-emitting unit circuit, and also includes a precise current-stabilizing circuit,

The LED light-emitting unit circuit is connected in series with a precise current-stabilizing circuit;

The precise current stabilizing circuit is composed of a transistor Q, a voltage stabilizing tube D, a first resistor R1 and a second resistor R2;

The emitter of the transistor Q is connected in series with the first resistor R1;

The regulator tube D is connected in series with the second resistor R2;

The other end of the first resistor R1 is connected to the positive pole of the regulator tube D;

One end of the second resistor R2 is connected to the collector of the transistor Q;

The base of the transistor Q is connected between the second resistor R2 and the regulator D;

The current-limiting resistor of the LED light-emitting unit circuit is connected to the second resistor R2, and the diode terminal of the light-emitting LED is connected to the collector of the transistor Q.

The utility model is an LED light-emitting unit with a precise current-stabilizing circuit, which has good current-stabilizing characteristics, makes the brightness of the entire backlight source uniform, and has a good visual effect, and there is no such thing as a backlight source usually composed of a current-blocking resistor and an LED. Unevenness, local light spots or a small display area is slightly dim, and the service life is long, so that users can reduce maintenance costs and greatly improve the advertising display effect.

Description of drawings:

The utility model will be further described below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is a schematic diagram of the utility model

Fig. 2 is the precision steady current circuit diagram in the utility model

Fig. 3 is the circuit diagram of the utility model LED light-emitting unit

Fig. 4 is a structural dimension diagram of the LED light-emitting unit of the present invention

Fig. 5 is a structural dimension diagram of the LED light-emitting unit of the present invention

Detailed ways:

In order to make the technical means, creative features, goals and effects achieved by the utility model easy to understand, the utility model will be further elaborated below in conjunction with specific illustrations.

Referring to Figure 1-3:

An LED light-emitting unit with a precise current-stabilizing circuit, which includes an LED light-emitting unit circuit, and also includes a precise current-stabilizing circuit, which is necessary for LED current-stabilizing circuits. Current (tens of milliamps) range, the current used by LED is generally 20-30mA, the precise current-stabilizing circuit composed of low-power transistors and low-power regulator tubes uses few components, but it has high reliability and low price. Low.

The LED light-emitting unit circuit is connected in series with the precise current-stabilizing circuit; the precise current-stabilizing circuit is composed of a transistor Q, a voltage-stabilizing tube D, a first resistor R1 and a second resistor R2; the emitter of the transistor Q is connected in series with the first resistor R1; The voltage tube D is connected in series with the second resistor R2; the other end of the first resistor R1 is connected to the positive pole of the regulator tube D; one end of the second resistor R2 is connected to the collector of the transistor Q; the base of the transistor Q is connected to the second Between the second resistor R2 and the regulator tube D; the current-limiting resistor of the LED light-emitting unit circuit is connected to the second resistor R2, and the diode terminal of the light-emitting LED is connected to the collector of the transistor Q.

The light-emitting unit also includes an LED light-emitting unit circuit, and the LED light-emitting unit circuit includes a current-limiting resistor and three LED light-emitting diodes; the LED light-emitting diode is connected in series with the current-limiting resistor; the LED light-emitting unit circuit is connected in series with a precise current-stabilizing circuit; the LED light-emitting unit circuit The current-limiting resistor is electrically connected to the voltage input terminal of the precise current-stabilizing circuit, and the diode terminal of the light-emitting LED is connected to the transistor on the precise current-stabilizing circuit. Figures 4 and 5 are structural dimension diagrams of the LED light-emitting unit of the present invention. The length of the installation panel is 38mm, the width is 8mm, and the height is 1.6mm. The fixing block of the LED light-emitting unit is arranged on the installation panel, and its height is 1.9mm. , a width of 3.2mm. The measured circuit stability of the LED light-emitting unit is ≤0.5% within the temperature range of 0°～70°C. When the power supply voltage is 15V±10% (13.5V～16.5V), the measured working current of the LED is always stable in the range of 20mA≤0.1mA Within, that is, the current change ≤ 0.5%. Using the same light-emitting unit measured above, disconnect the current-stabilizing circuit (that is, only 3 LEDs are connected in series and add a current-limiting resistor). Under the 12V power supply, the working current of the LED light-emitting unit is 23mA; and when the power supply voltage changes by ±2% ( That is, when the working current changes from 21mA to 25mA when it is 11.78V～12.24V, that is, the working current has a change of ±8.7%. Such a change range is enough to make the LED brightness change significantly.

When installation is required, multiple light-emitting units can be soldered to a long circuit board connected in parallel to form a rigid light bar with a fixed length (such as 0.5 meters long). Each light-emitting unit is poured into the plastic case with glue, and after solidification and hardening, it becomes a small light-emitting module. The modules can be connected by wires to form a flexible light strip, which is convenient for users to flexibly arrange and use. Since the additional series current stabilizing circuit requires a working voltage of about 2 volts, the required working voltage of the LED light-emitting unit with a precision stabilizing circuit should not be less than 14 volts, and 15 volts can be selected as the power supply voltage according to the DC voltage series standard.

The utility model is an LED light-emitting unit with a precise current-stabilizing circuit, which has good current-stabilizing characteristics, makes the brightness of the entire backlight source uniform, and has a good visual effect, and there is no such thing as a backlight source usually composed of a current-blocking resistor and an LED. Unevenness, local light spots or a small display area is slightly dim, and the service life is long, so that users can reduce maintenance costs and greatly improve the advertising display effect.

The basic principles and main features of the present utility model and the advantages of the present utility model have been shown and described above. Those skilled in the art should understand that the utility model is not limited by the above-mentioned embodiments. The above-mentioned embodiments and descriptions only illustrate the principle of the utility model. Without departing from the spirit and scope of the utility model, the utility model The new model also has various changes and improvements, and these changes and improvements all fall within the scope of the claimed utility model. The scope of protection required by the utility model is defined by the appended claims and their equivalents.

Claims (2)

1. LED luminescence unit with accurate current stabilization circuit, it comprises LED luminescence unit circuit, it is characterized in that, and it also comprises accurate current stabilization circuit, and described LED luminescence unit circuit is connected in series with accurate current stabilization circuit; Described accurate current stabilization circuit is made up of transistor (Q), voltage-stabiliser tube (D), first resistance (R1) and second resistance (R2), and the emitter stage of described transistor (Q) is connected in series with first resistance (R1); Described voltage-stabiliser tube (D) is connected in series with second resistance (R2); The end in addition of described first resistance (R1) links to each other with the positive pole of voltage-stabiliser tube (D); One end of described second resistance (R2) is connected with the colelctor electrode of transistor (Q); The base stage of described transistor (Q) is connected between second resistance (R2) and the voltage-stabiliser tube (D).

2. a kind of LED luminescence unit with accurate current stabilization circuit according to claim 1 is characterized in that the current-limiting resistance of described LED luminescence unit circuit is connected with second resistance (R2), and emitting led diode end links to each other with the colelctor electrode of transistor (Q).

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