JP3205826U - LED drive circuit - Google Patents

Abstract

Provided is an LED driving circuit suitable for use as a school teaching material capable of arbitrarily adjusting light of an LED light source, having excellent power efficiency with little power loss and heat generation, and capable of protecting an LED from overcurrent. . A total of a voltage of a light emitting source 6 including an LED or a plurality of LEDs and an input DC power supply 1 when a current having a predetermined limit current value in the normal forward voltage-forward current characteristics of the LED flows. DC voltage conversion circuit 4 that converts the voltage to a predetermined DC voltage value that is equal to or less than the forward voltage value, and converts the DC voltage output of the DC voltage conversion circuit into a PWM voltage pulse whose ON / OFF time ratio can be arbitrarily varied in a predetermined cycle. And a pulse voltage generation circuit 5 for applying this pulse voltage to the light source, and a current for detecting the current of the light source and limiting the current value when the current value reaches a predetermined limit current value of the LED. The limiting circuit 8 is provided. [Selection] Figure 1

Description

  The present invention relates to an LED driving circuit suitable for use in a school lighting fixture, and more particularly, as a lighting fixture teaching material using an LED as a light source, assembling, lighting up or dimming the light source. In particular, the present invention relates to an LED drive circuit that can be used for learning of electricity and light.

  LED lighting is used not only for school teaching materials but also for various applications. Examples of LED driving circuits include those disclosed in Patent Document 1 and Patent Document 2.

Japanese Patent No. 4506593 Japanese Patent Laying-Open No. 2015-88412

The LED drive circuit described in Patent Document 1 boosts the voltage of an input DC power supply to a DC voltage value suitable for driving a plurality of LEDs connected in series with each other by a voltage booster circuit, and drives the plurality of LEDs. Further, the current flowing through the LED is made constant by a constant current circuit to stabilize the light emission luminance of the LED and protect the LED from overcurrent.
However, since the thing of this patent document 1 does not have the adjustment function of LED brightness | luminance, and the brightness | luminance cannot be adjusted arbitrarily, it is learning for giving the knowledge about light control to a student as an object for school teaching materials. There is a problem that it is not suitable for teaching materials and is insufficient and inappropriate.
Furthermore, the output voltage of the booster circuit that drives the LED is normally set larger than the forward voltage of the LED in order to make the current flowing through the LED constant by the constant current circuit, and the difference voltage becomes a voltage drop in the constant current circuit. In addition, there is a problem that power loss and accompanying heat generation are large.

The LED drive circuit described in Patent Document 2 can adjust the luminance of the LED by driving the LED with an on / off pulse voltage having a predetermined period and adjusting the on / off time ratio.
However, in this Patent Document 2, a current limiting resistor is connected in series with an LED to limit the current for LED overcurrent protection. Since a DC power source such as a commercial AC adapter is used, the voltage is higher than the LED forward voltage VF and has a large voltage difference. For this reason, the voltage difference from the forward voltage VF of this LED becomes a voltage drop by the current limiting resistor, and there is a problem that a large power loss and a large heat generation accompanying it occur.

  In view of the above problems, the object of the present invention is to provide a school teaching material capable of arbitrarily adjusting the light source of the LED light source, having excellent power efficiency with very little power loss and heat generation, and capable of protecting the LED from overcurrent. It is to provide an LED driving circuit suitable for use.

  The LED driving circuit according to claim 1 of the present invention is a light source including one or a plurality of LEDs, and a voltage of an input DC power source is a current having a predetermined limit current value on a normal forward voltage-forward current characteristic of the LED. DC voltage conversion circuit that converts the voltage to a predetermined DC voltage value that is less than or equal to the forward voltage value when the current flows, and PWM that can vary the on / off time ratio of the DC voltage output of this DC voltage conversion circuit in a predetermined cycle A pulse voltage generating circuit that converts the voltage into a voltage pulse and applies the pulse voltage to the light emitting source, and detects the current of the light emitting source. When the current value reaches a predetermined limit current value of the LED, the current value reaches the limit current value. It is characterized by comprising a current limiting circuit for limiting.

  According to a second aspect of the present invention, there is provided an LED driving circuit according to the first aspect, wherein the light source is formed by connecting a plurality of LEDs in series, and the output voltage of the DC voltage conversion circuit is a normal forward voltage-forward voltage of the plurality of LEDs connected in series. It is set to a predetermined DC voltage value equal to or less than the total forward voltage value when a current of a predetermined limit current value on the directional current characteristic flows.

  According to a third aspect of the present invention, there is provided the LED driving circuit according to the first aspect, wherein the direct current voltage conversion circuit turns on and off the feeding current of the inductor fed from the input power source at a high frequency, and the diode is driven by the boosted voltage of the inductor induced at the time of turning off And a booster circuit for detecting the charging voltage of the capacitor and controlling the on / off state so that the voltage becomes the predetermined voltage to generate the predetermined output voltage.

  According to a fourth aspect of the present invention, in the LED driving circuit according to the first aspect, the pulse voltage generation circuit can arbitrarily adjust the on / off time ratio of the PWM voltage pulse by an artificial operation.

  The LED drive circuit according to claim 5 is the LED drive circuit according to claim 1, wherein the input DC power supply is an AC adapter for charging a smartphone or the like, and has a terminal for receiving the DC voltage output of the adapter.

  According to a sixth aspect of the present invention, in the LED driving circuit according to the first aspect, the light emission source is used for irradiation of the growing plant.

  According to the LED driving circuit of claim 1 of the present invention, the voltage of the input DC power supply is the forward voltage value when a current of a predetermined limit current value on the normal forward voltage-forward current characteristic of the LED flows. By providing a DC voltage conversion circuit that converts the voltage so as to have the following predetermined DC voltage value, the LED can be provided with a DC voltage that can basically limit the current within a range that does not exceed the limit current. As a result, power loss and heat generation in the current limiting circuit portion are extremely small, and power efficiency can be improved.

  In addition, by providing a pulse voltage generation circuit that converts the DC voltage output of the DC voltage conversion circuit into a PWM voltage pulse whose ON / OFF time ratio can be arbitrarily varied in a predetermined cycle, and applies the pulse voltage to the LED light source. The brightness of the LED light source can be arbitrarily adjusted by arbitrarily adjusting the average current of the LED light source.

  In addition, since a current limiting circuit is provided for detecting the current of the LED light source and limiting the current value when the current value reaches a predetermined limit current value of the LED, the forward voltage of the LED − If the voltage exceeds the predetermined forward voltage of the LED and an overcurrent flows due to variations in current characteristics or voltage fluctuations of the voltage pulse, the LED is limited to a current value within the allowable limit range of the LED. It can be protected from overcurrent.

  Therefore, the LED drive circuit suitable for use as a school teaching material that can arbitrarily control the LED light source, has excellent power efficiency with very little power loss and heat generation, and can also protect against overcurrent destruction of the LED is provided. can do.

  According to the LED drive circuit of claim 2, even when the light source is formed by connecting a plurality of LEDs in series, the output voltage of the DC voltage conversion circuit is equal to the normal forward voltage-forward voltage of the plurality of LEDs connected in series. By setting to a predetermined DC voltage value equal to or less than the total forward voltage value when a current of a predetermined limit current value on the directional current characteristic flows, the same function and effect as in the first aspect can be obtained.

  According to the LED drive circuit of claim 3, the DC voltage conversion circuit turns on and off the feeding current of the inductor fed from the input power source at a high frequency, and charges the capacitor with the voltage of the inductor induced at the time of turning off. A stable predetermined output voltage is generated by the booster circuit that detects the charging voltage of the capacitor and controls the on / off state to generate the predetermined output voltage so that it becomes the predetermined voltage. Therefore, it is possible to stabilize the voltage applied to the LED to a voltage that does not exceed a predetermined forward voltage of the LED, and to further reduce power loss in the current limiting circuit portion.

  According to the LED driving circuit of claim 4, the pulse voltage generation circuit can arbitrarily adjust the on / off time ratio of the PWM voltage pulse by human operation, so that the student can freely use it when used for school teaching materials. The brightness of the LED can be adjusted, and the relationship between the current of the LED and the brightness can be learned.

  According to the LED drive circuit of claim 5, the input DC power supply uses an AC adapter for charging a smartphone and the like, and has many users because it has a terminal for receiving the DC voltage output of the adapter. This can be easily used as a power source from an AC adapter for charging a smartphone.

  According to the LED drive circuit of claim 6, since the light emission source is used for irradiation of the growing plant, the heat generation due to the power loss of the light emitting source is small as described above. Overheating due to unnecessary heat generation is not given, and adverse effects due to heating on the growth of the plant for growth can be prevented.

Electric circuit diagram of LED drive circuit of Embodiment 1 of the present invention

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a first embodiment of the present invention. In FIG. 1, the basic configuration of this embodiment is that the voltage of the input DC power source 1 is the normal forward voltage-forward direction of the LEDs 61 and 62 of the light source 6. DC voltage conversion circuit 4 for performing voltage conversion so that a predetermined DC voltage value is equal to or less than a total forward voltage value when a current of a predetermined limit current value in current characteristics flows, and a DC voltage output of this DC voltage conversion circuit Is converted into a PWM voltage pulse whose ON / OFF time ratio can be arbitrarily varied in a predetermined cycle, and the pulse voltage generation circuit 5 for applying this pulse voltage to the light emitting source 6 and the current of the light emitting source 6 are detected, and this current value is When a predetermined limit current value of the LEDs 61 and 62 is reached, the current limit circuit 8 is configured to limit to the limit current value.

The detailed configuration of each circuit will be described.
The DC power supply 1 uses the output of a DC voltage (for example, four dry batteries in series 6V, a smartphone charging adapter 5V) of a dry battery or a smartphone charging AC adapter, and supplies power from the outside via the connector 2. In addition, when supplying the DC voltage output of the AC adapter for smartphone charging, a dedicated USB terminal connected in parallel is provided separately from the connector 2 in the figure, and the lead wire for the DC voltage output of the AC adapter for smartphone charging is provided. It can be connected to the terminal.
In the figure, reference numeral 3 denotes a power switch, which arbitrarily turns on / off the power supply from the external DC power supply 1.

  The DC voltage conversion circuit 4 turns on and off the power supply current of the power source noise elimination capacitor 401 and the inductor 402 fed from the DC power source 1 at a high frequency (several KHZ to several MHZ), and induces the inductor 402 when the current is turned off. The capacitor 404 is charged by the boosted voltage via the diode 403, and the charging voltage of the capacitor 404 is detected via the voltage dividing resistors 405 and 406. This is a predetermined voltage (the above-mentioned total forward voltage suitable for driving two LEDs). It has a boost control circuit element 407 that controls the on / off time ratio so that the voltage is slightly lower (eg, 6.2 V), and is configured by a boost circuit that generates a predetermined output voltage from the capacitor 404.

  The pulse voltage generation circuit 5 divides the DC output voltage of the voltage conversion circuit 4 to generate a comparison voltage, and a resistance 503, an operational amplifier 504, a resistance 505, and a resistance 503 connected to each other as shown in FIG. The comparator 506 includes a capacitor 506, and in response to the output levels H and L of the operational amplifier 504, the resistor 503 is alternately connected in parallel to the resistors 501 and 502 of the voltage dividing circuit, thereby comparing the comparison level with two comparison levels. L1 and L2 are alternately switched to L1 (output H is L1 and output L is L2). In the operational amplifier 504, the two comparison voltage levels L1 and L2 to be switched and the resistor 505 are switched during the output H of the operational amplifier 504. Capacitor that is gradually charged through the resistor 505 and gradually discharged through the resistor 505 during the period of the output L of the operational amplifier 504. By comparison with the 06 voltage, it generates a triangular wave voltage VC of a predetermined frequency from the capacitor 506. This frequency is set to a frequency that does not cause flickering of the LED light emission by human vision.

  Further, the pulse voltage generation circuit 5 is connected in series between resistors 507 and 508 connected in series with each other, and is artificially operated to adjust the voltage dividing resistance value. The variable resistor 509 is adjustable from the adjustable resistor 509. An operational amplifier 516 that compares the adjusted comparison voltage VO with the triangular wave output voltage VC of the capacitor 506 and generates a PWM on / off pulse output having an adjustable on / off time ratio at a predetermined frequency, and is driven on / off via resistors 510 and 511 by this on / off pulse output. Transistors 512 and 513, their collector resistors 514, and a current detection resistor 515 for detecting the current of the drive transistor 513.

  The light emitting source 6 has two LEDs 61 and 62 connected in series to each other, is connected to the transistor 513 through the connector 7, and is fed and driven with the boosted voltage corresponding to the on / off of the transistor 513. The The number of LEDs is not limited to two, but may be a single number or a plurality of predetermined numbers of three or more. Furthermore, it is possible to configure a single LED connected in parallel, or two or more LEDs connected in series, but the number of LEDs connected in parallel needs to be the same. .

  The current limiting circuit 8 divides the voltage made constant by the resistor 801 and the constant voltage diode 802 and provides the operational amplifier 805 with a limited current comparison voltage level L3 that is compared with the detected current of the current detecting resistor 515. 803 and 804, and a transistor 807 driven by a resistor 806 by the output of the operational amplifier 805 and controlling the base current of the transistors 512 and 513.

Next, functions and operations of the embodiment of the LED driving circuit configured as described above will be described.
When the power switch 3 is turned on, power supply to the inductor 4 from the input DC power supply 1 (for example, voltage 6V or 5V) is interrupted at a high frequency by the boost control circuit element 407, and the voltage boost induced in the inductor 4 when the power supply is turned off. The capacitor 404 is charged via the diode 403 by the voltage. The charging voltage of the capacitor 404 is applied to the boost control circuit element 407 via the resistors 405 and 406, and the voltage of the capacitor 404 becomes the predetermined value (for example, 6.2 V) set in the boost control circuit element 407. In this way, the high-frequency on / off state is controlled to control the voltage of the capacitor 404 to the predetermined value.

  The boosted voltage of the capacitor 404 becomes a driving voltage for the light emitting source 6, and the predetermined voltage value set in this embodiment takes into account variations in characteristics between the LED elements in the case of this embodiment, and each of the two LEDs 61 and 62. Normal forward voltage VF-forward current IF characteristics of a predetermined limit current value on the forward current IF characteristic, a value in the vicinity of the total value of forward voltage values VF (Max) when a current of a predetermined limit current value flows (for example, 6. 2V).

  This boosted DC voltage having a predetermined value is converted into a pulse voltage having a predetermined frequency in the pulse voltage generation circuit 5 to drive the light emitting source 6. This operation will be described below. The DC output voltage of the voltage conversion circuit 4 is divided to generate a comparison voltage. When the output level of the operational amplifier 504 is H, the resistor 503 is connected in parallel with the resistor 501 of the voltage divider circuit, and when the output level L of the operational amplifier 504 is Switches the comparison level alternately between two comparison levels L1 and L2 (output H is L1 and output L is L2) by connecting the resistor 503 in parallel with the resistor 502 of the voltage dividing circuit. Given.

  The capacitor 506 is gradually charged through the resistor 505 during the period of the output H of the operational amplifier 504. When the charged voltage reaches the comparison voltage level L1, the operational amplifier 504 becomes the output L, and the comparison level is also set to the level L2. The capacitor 506 is gradually discharged through the resistor 505. When this voltage decreases to the comparison level L2, the operational amplifier 504 is inverted to the output H, and the capacitor 506 is again charged. A triangular wave voltage VC having a predetermined frequency is generated from the capacitor 506 by such inversion and repetition of charging / discharging of the capacitor 506.

  The triangular wave voltage VC having a predetermined frequency is supplied to an operational amplifier 516 at a subsequent stage. This operational amplifier 516 is connected in series between resistors 507 and 508 and is artificially operated to adjust a voltage dividing resistance value from a variable resistor 509. The adjustable comparison voltage VO and the triangular wave voltage VC are compared, and a PWM on / off pulse output whose on / off time ratio of a predetermined frequency is adjustable is generated. The transistors 512 and 513 are driven to turn on and off by the on / off pulse output via the resistors 510 and 511, and the LEDs 61 and 62 of the light source 6 are turned on and off in response thereto. During the on period, the DC voltage conversion circuit 4 is turned on. The boosted voltage is applied and no voltage is applied during the OFF period.

  Here, as described above, this applied voltage is a predetermined forward voltage VF-forward current IF characteristic of each of the two LEDs 61 and 62 in consideration of variation in characteristics between the LED elements. The driving transistor 513 is set to a value in the vicinity thereof (for example, 6.2 V) that is equal to or less than the total value of the forward voltage value VF (Max) value when the current of the limit current value flows. Even during the on-period, there is no need to limit the current, and the transistor becomes completely conductive, and the voltage drop becomes the minimum value. During the on-off drive, there is almost no voltage drop due to the transistor 513 and the heat generation associated therewith, resulting in excellent power efficiency. .

  By the way, even if the set value of the applied voltage is set low considering the variation between the elements of the LED, an LED in which the current flows exceeding the limit current value due to the variation between the elements is rarely used. If the applied voltage rises and fluctuates temporarily for some reason or if the current exceeds the limit current value in the LEDs 61 and 62, this current is detected from the current detection output of the detection resistor 515. , The operational amplifier 805 detects that the set level L3 corresponding to the limit current values of the LEDs 61 and 62 is exceeded, and the driving transistors 512 and 513 are controlled in the off direction via the transistor 807 to control the currents of the LEDs 61 and 62. Is limited to the current limit. For this reason, the LEDs 61 and 62 are protected from overcurrent even if a situation occurs in which a current exceeding the limit value flows.

  In such a case, a voltage drop occurs in the driving transistor 513 and some power loss occurs. However, such a case is rare, and usually in most cases, the driving transistor 513 is used. There is no power loss due to voltage drop due to current limitation.

  Further, the ON / OFF pulse voltage output of the pulse voltage generation circuit 5 can be adjusted by the variable resistor 509 that can be manually manipulated to adjust the voltage dividing resistance value. The average current value is determined by the on / off time ratio, and the brightness of the LED can be adjusted. When used in school materials, students can freely adjust the brightness of the LED and have knowledge of the relationship between brightness and current. Can learn and be suitable as a school teaching material.

  The LED drive circuit of the present invention is not limited to school teaching materials, but if used for irradiation for growing a growing plant, heat generation due to power loss is small, so overheating due to unnecessary heat generation from the heating source to the growing plant is avoided. It is not given and the bad influence by the heating with respect to the growth of the plant for cultivation can be prevented.

Industrial application fields

  This device can be used for various applications that require lighting or lighting.

1 Input DC power supply 2, 7 Connector 3 Power switch 4 DC voltage conversion circuit 5 Pulse voltage generation circuit 6 Light source 61, 62 LED
8 Current limit circuit

Claims (6)

A light source comprising one or more LEDs,
The voltage of the input DC power supply is converted so that it becomes a predetermined DC voltage value that is less than or equal to the forward voltage value when a current of a predetermined limit current value in the normal forward voltage-forward current characteristics of the LED flows. DC voltage conversion circuit,
The DC voltage output of this DC voltage conversion circuit is converted into a PWM voltage pulse whose ON / OFF time ratio can be arbitrarily varied in a predetermined cycle, and the pulse voltage generation circuit for applying this pulse voltage to the light emitting source, and the current of the light emitting source An LED driving circuit having a current limiting circuit that detects and limits the current value when the current value reaches a predetermined current limit value of the LED   The light-emitting source is composed of a plurality of LEDs connected in series, and the output voltage of the DC voltage conversion circuit is a current having a predetermined limit current value in the normal forward voltage-forward current characteristics of the plurality of LEDs connected in series. 2. The LED driving circuit according to claim 1, wherein the LED driving circuit is set to a predetermined voltage value equal to or lower than a total forward voltage value at the time of   The DC voltage converter circuit turns on and off the feeding current of the inductor fed from the input power supply at a high frequency, charges the capacitor via the diode with the inductor voltage induced at the time of turning off, and further detects the charging voltage of the capacitor. 2. The LED drive circuit according to claim 1, wherein the LED drive circuit is constituted by a booster circuit that controls the on / off state to generate the predetermined output voltage so that the predetermined voltage is the predetermined voltage.   2. The PWM drive circuit according to claim 1, wherein the pulse voltage generation circuit can arbitrarily adjust the on / off time ratio of the PWM voltage pulse by an artificial operation.   2. The LED drive circuit according to claim 1, wherein the input DC power supply uses an AC adapter for charging a smartphone and has a terminal for receiving a DC voltage output of the adapter.   2. The LED driving circuit according to claim 1, wherein the light emission source is used for irradiation of a plant for cultivation.

Images