WO2005104245A1

WO2005104245A1 - Led driver circuit

Info

Publication number: WO2005104245A1
Application number: PCT/JP2004/009019
Authority: WO
Inventors: Ryouichi Miyajima; Takeshi Kobayashi
Original assignee: Tokyoto
Priority date: 2004-04-22
Filing date: 2004-06-25
Publication date: 2005-11-03
Also published as: JP2005311090A

Abstract

[PROBLEMS] To provide an LED driver circuit that is small-sized but capable of driving an LED to exhibit a higher brightness with its heating suppressed. [MEANS FOR SOLVING PROBLEMS] In an LED driver circuit (1), an LED (5) is connected between the plus output side of an AC power supply rectifier circuit (3) and an FET (7), and a detection resistor (R2) for detecting a drive current is connected between the FET and the minus output side of the AC power supply rectifier circuit (3). An FET control circuit (11) applies a control voltage to the gate terminal (7g) to turn on the FET, while causing, in response to a drive current detection of the detection resistor, the control voltage to drop below a threshold voltage of the FET, thereby causing the FET to discharge. This discharging maintains the on-state of the FET, meanwhile the drive current continues to flow, whereby the higher brightness of the LED can be realized.

Description

Specification

LED drive circuit

Technical field

The present invention relates to a light-emitting diode drive circuit for driving a high-output, high-current light-emitting diode of, for example, 1 W or more with a commercial AC power supply.

Background art

[0002] Light-emitting diodes (hereinafter simply referred to as "LEDs") suitable for lighting devices such as street lighting, spotlights, and guide lights are mainly driven by a commercial AC power supply. There are two methods. The first method is to convert AC into DC and drive the LED with the converted DC. However, according to the first method, the power supply becomes large because a power transformer, a large-capacity capacitor, and the like are required to convert AC into DC. Therefore, it is difficult to reduce the size of a lighting device using LEDs. Further, since the conversion causes a loss, the power consumption of the entire lighting device also increases. The second method is a method in which the LED 105 is driven by a rectified current rectified by the rectifier circuit 103, as shown in FIG. The LED has a current limiting resistor 107 connected in series to prevent damage. According to the second method, there is a problem that the amount of heat generated by the current limiting resistor increases because it is necessary to use the current flowing constantly. Thus, as a third method, the applicant of the present application uses a rectifier circuit for rectifying AC and a transistor that functions as a switching element, and generates a drive current in one half wave at the output of the rectifier circuit. An LED drive circuit that turns on and off has been proposed (see Patent Document 1). According to the third method, the base voltage of the transistor is reduced in response to detecting the drive current of the LED flowing when the transistor is turned on, and the transistor is turned off by the drop. By turning it off, there is no need to constantly supply a drive current, and the amount of generated heat is reduced.

Patent Document 1: Japanese Patent Publication No. 3122870

Disclosure of the invention

Problems the invention is trying to solve [0003] According to the above-described third method, it is possible to provide an LED drive circuit that is relatively small and has an advantage of generating relatively little heat. However, in recent years, high-output and high-current LEDs of 1 W or more have been supplied in order to meet the demand for higher brightness. Accordingly, for example, a current of 300 mA may flow through the LED. If a current of 300 mA or more is passed in the third method, the heat generation of the transistor cannot be ignored due to the on-resistance. The more the current is increased in order to achieve higher luminance, the greater the amount of generated heat. For this reason, there has been a demand for an improvement in the third method for flowing a large current while suppressing heat generation. The problem to be solved by the present invention is to improve the above-mentioned third method without impairing the advantages of the third method. An object of the present invention is to provide an LED drive circuit capable of driving a high brightness while suppressing heat generation of the LED.

Means for solving the problem

[0004] In order to solve the above-described problems, the present invention has the following configuration. It should be noted that the definition of terms used in the description of the invention claimed in any one of the claims shall apply to the invention claimed in the other claims as far as its nature allows.

[0005] (Characteristics of the invention described in claim 1)

The LED driving circuit according to the invention described in claim 1 (hereinafter, appropriately referred to as “the driving circuit of claim 1”) is a circuit for driving one LED. A circuit for driving a plurality of LEDs will be described later. Specifically, an AC power supply rectifier circuit having a power supply connection terminal on the input side, one LED with an anode terminal connected to the positive output side of the AC power supply rectification circuit, and an LED connected to the power source terminal of the LED. A FET for turning on or off the drive current of the LED or a current detection resistor placed between the FET and the minus output side of the AC power supply rectifier circuit to detect the drive current passed through the FET. And a FET control circuit for controlling the FET connected to the gate terminal of the FET via a gate resistor. Then, the FET control circuit applies a control voltage for applying a gate voltage exceeding a threshold voltage to the gate terminal as the rectified voltage applied from the plus output side of the AC power supply rectification circuit rises, to the gate resistor. To turn on the FET and drive the current detection resistor beyond the specified value. In response to the detection of the current, the control voltage is reduced to a voltage lower than the threshold voltage and the discharge of the gate terminal is accelerated to delay off the FET. That is, both the anode terminal of the LED and the FET control circuit are connected to the positive output side of the AC power supply rectifier circuit, and the power source terminal of the LED is connected to FET.

[0006] According to the drive circuit of claim 1, the FET control circuit applies a control voltage to the gate resistor due to the rise of the rectified voltage, and the FET is turned on when the gate voltage exceeds the threshold voltage. I do. When the LED is turned on, a drive current flows through the LED to which the rectified voltage is applied, and the LED lights up. The drive current is detected by the current detection resistor, and the FET control circuit that receives this detection drops the control voltage. Due to this drop, the potential of the gate resistance on the FET control circuit side becomes lower than the potential on the gate terminal side. As a result, the charged electric charge is discharged from the gate terminal via the gate resistor, and the gate voltage decreases with the discharge. When the gate voltage drops below the threshold voltage, the FET turns off, which turns off the LED. In other words, the drive current flows even until the gate voltage reaches the threshold voltage due to charge discharge (until the FET is turned off), so that the LED can be turned on with high brightness. In this way, the detection of the drive current by the current detection resistor triggers the FET to be turned off, so that the latter operates with a delay from the former. This delay operation realizes high brightness even at a low voltage and a large current, that is, even when the applied voltage is low. Furthermore, since the on-resistance value of the FET is generally smaller than the on-resistance value of the transistor, the former generates less heat than the latter even when the same current flows. In addition, in order to light the LED with direct current, a power transformer, a large-capacity capacitor, and the like are required, but the drive circuit of claim 1 does not require such a thing. The drive circuit can be reduced in size because it is not needed.

[0007] (Characteristics of the invention described in claim 2)

The LED driving circuit according to the invention described in claim 2 (hereinafter, appropriately referred to as “driving circuit of claim 2”) is a circuit for driving an LED group formed by connecting a plurality of LEDs in series. Specifically, an AC power supply rectifier circuit having a power supply connection terminal on the input side and a plurality of LEDs connected to the anode terminal on the positive output side of the AC power supply rectifier circuit are connected in series. An LED group, a FET connected to the power source terminal of the LED group for turning on and off the drive current of the LED group, and a FET and the AC power supply for detecting the drive current passing through the FET. A current detection resistor arranged between the rectifier circuit and the negative output side, and a FET control circuit for controlling the FET connected to the gate terminal of the FET via a gate resistor are included. is there. Then, the FET control circuit applies a control voltage for applying a gate voltage exceeding a threshold voltage to the gate terminal as the rectified voltage applied from the plus output side of the AC power supply rectification circuit rises, to the gate resistor. To turn on the FET, and when the current detection resistor detects the drive current exceeding the predetermined value, the control voltage is reduced to a voltage lower than the threshold voltage, and the voltage is reduced from the gate terminal. By driving off the FET by promoting electric charge discharge, the driving current can be increased almost in proportion to the increase in the number of LEDs constituting the LED group. That is, both the anode terminal of the LED group and the FET control circuit are connected to the positive output side of the AC power supply rectifier circuit, and the power source terminal of the LED group is connected to the FET.

According to the drive circuit of the second aspect, the FET control circuit applies the control voltage to the gate resistor due to the rise of the rectified voltage, and thereby, the FET is turned on when the gate voltage exceeds the threshold voltage. When turned on, a drive current flows through the LED group to which the rectified voltage is applied, and the LED group is turned on. The drive current is detected by the current detection resistor, and the FET control circuit that receives this detection drops the control voltage. Due to this drop, the potential of the gate resistance on the FET control circuit side becomes lower than the potential on the gate terminal side. As a result, the charged charge is discharged from the gate terminal via the gate resistor, and the gate voltage decreases with the discharge. When the gate voltage falls below the threshold voltage, the FET turns off and the LEDs turn off. In other words, the drive current flows until the gate voltage reaches the threshold voltage (until the FET turns off) due to charge discharge, and this drive current increases almost in proportion to the increase in the number of LEDs. The LED group can be turned on with high brightness. In other words, for example, when comparing the drive current when two LEDs are connected in series and the drive current when three LEDs are connected in series, the drive current when three LEDs are connected is greater than when two LEDs are connected. The current increases. Above As described above, the detection of the drive current by the current detection resistor triggers the FET to be turned off, so that the latter operates with a delay from the former. This delay operation realizes high luminance even at a low voltage and a large current, that is, even when the applied voltage is low. In addition, since the on-resistance value of the FET is generally smaller than the on-resistance value of the transistor, the former generates less heat than the latter even if the same current is applied. In order to light the LED with direct current, a power transformer and a large-capacity capacitor are required. The drive circuit can be reduced in size because it is not needed (the feature of the invention described in claim 3).

The LED driving circuit according to the invention described in claim 3 (hereinafter referred to as “the driving circuit of claim 3”) is used to drive one LED or a group of LEDs connected in series or series / parallel. Circuit. Specifically, an AC power supply rectification circuit having a power supply connection terminal on the input side, a single LED, or an LED group connected in series or in series / parallel, an anode terminal of the LED or the LED group, and The FET connected between the positive output side of the AC power supply rectifier circuit and the FET for turning on / off the drive current of the LED or the LED group, and the drive current that has passed through the LED or the LED group (passed through the FET To detect the drive current), a gate resistor is connected to the current detection resistor placed between the power source terminal of the LED or LED group and the minus output side of the AC power supply rectifier circuit, and the gate terminal of the FET. And an FET control circuit for controlling the FET connected through the FET. Then, the FET control circuit applies a control voltage for applying a gate voltage exceeding a threshold voltage to the gate terminal as the rectified voltage applied from the plus output side of the AC power supply rectifier circuit increases. The FET is turned on by applying the voltage to the gate resistor, and the control voltage is lowered to a voltage lower than the threshold voltage in response to the detection of the drive current exceeding the predetermined value by the current detection resistor, and the gate is turned off. The FET is configured to delay off by prompting charge discharge from the terminal. That is, the anode terminal of the LED or LED group is connected to the positive output side of the AC power supply rectifier circuit through the FET, and the power source terminal of the LED or LED group is connected to the AC power supply rectifier through the current detection resistor. Connected to the negative output side of the circuit. Positive output of AC power supply rectifier circuit On the side, the FET control circuit is connected together with the FET.

[0010] According to the drive circuit of claim 3, the FET control circuit applies the control voltage to the gate resistor due to the rise of the rectified voltage, and the FET is turned on when the gate voltage exceeds the threshold voltage. I do. When the LED is turned on, a drive current flows through the LED due to the rectified voltage applied through the FET, thereby turning on the LED or the LED group. The drive current is detected by the current detection resistor, and the FET control circuit that receives this detection drops the control voltage. Due to this drop, the potential of the gate resistance on the FET control circuit side becomes lower than the potential on the gate terminal side. As a result, the charged electric charge is discharged from the gate terminal via the gate resistor, and the gate voltage decreases with the discharge. When the gate voltage falls below the threshold voltage, the FET turns off, causing the LED or LED group to turn off. In other words, the drive current flows even until the gate voltage reaches the threshold voltage by charge discharge (until the FET is turned off), so that the LED or the LED group can be lit with high luminance. Thus, the detection of the drive current by the current detection resistor triggers the FET to be turned off, so that the latter operates with a delay from the former. This delay operation realizes high brightness even at low voltage and large current, that is, even when the applied voltage is low. Furthermore, since the on-resistance value of the FET is generally smaller than the on-resistance value of the transistor, the former generates less heat than the latter even at the same current. In addition, a power supply transformer and a large-capacity capacitor are required to light the LED or the LED group with direct current. The drive circuit according to claim 3 does not need such a thing. The drive circuit can be reduced in size because it is not needed.

[0011] (Characteristics of the invention described in claim 4)

The LED driving circuit according to the invention described in claim 4 (hereinafter referred to as “the driving circuit of claim 4” as appropriate) is used to drive one LED or a group of LEDs connected in series or series / parallel. Circuit. Specifically, an AC power supply rectification circuit with a power supply connection terminal on the input side, and one LED with an anode terminal connected to the positive output side of the AC power supply rectification circuit, or a series or series-parallel connection To turn on and off the drive current of the LED or LED group connected to the LED or the power source terminal of the LED group, and to detect the drive current passing through the FET The FET and the AC power It is configured to include a current detection resistor arranged between the negative output side of the power supply rectifier circuit and a FET control circuit for controlling the FET connected to the gate terminal of the FET via a gate resistor. I have. The FET control circuit applies a gate voltage exceeding a threshold voltage to the gate terminal as the rectified voltage applied from the positive output side of the AC power supply rectifier circuit via the LED or the group of LEDs increases. The control voltage is applied to the gate resistor to turn on the FET, and the control voltage drops to a voltage lower than the threshold voltage when the current detection resistor detects the drive current exceeding the predetermined value. Then, the FET is delayed off by promoting electric charge discharge from the gate terminal. That is, the anode terminal of the LED or LED group is connected to the positive output side of the AC power supply rectifier circuit, and the cathode terminal of the LED or LED group is connected to the FET control circuit.

According to the drive circuit of claim 4, the FET control circuit applies the control voltage to the gate resistor due to the rise of the rectified voltage applied via the LED or the LED group, whereby the gate voltage becomes the threshold voltage. FET turns on when exceeds. When the LED is turned on, a drive current flows through the LED or the LED group to which the rectified voltage is applied, thereby turning on the LED or the LED group. The drive current is detected by the current detection resistor, and the FET control circuit that receives this detection drops the control voltage. Due to this drop, the potential of the gate resistance on the FET control circuit side becomes lower than the potential on the gate terminal side. As a result, the charged charge is discharged from the gate terminal via the gate resistor, and the gate voltage decreases with the discharge. When the gate voltage falls below the threshold voltage, FET is turned off, which turns off the LED or LEDs (although in practice the LED or LEDs may be turned off even if the FET is off). A small drive current flows through the FET control circuit through the In other words, the drive current flows even until the gate voltage reaches the threshold voltage (until the FET is turned off) due to charge discharge, so that the LED or LED group can be lit with high luminance. As described above, since the detection of the drive current by the current detection resistor triggers the FET to be turned off, the latter operates with a delay from the former. This delay operation realizes high luminance even at a low voltage and a large current, that is, at a low applied voltage. In addition, the on-resistance of the FET is generally smaller than the on-resistance of the transistor. Therefore, even if the same current flows, the former generates less heat than the latter. Further, in order to light the LED or the LED group with direct current, a power transformer and a large-capacity capacitor are required, but the drive circuit of claim 4 does not need such a thing. The drive circuit can be reduced in size because it is not required.

(Characteristics of the invention described in claim 5)

The LED driving circuit according to the invention described in claim 5 (hereinafter referred to as “the driving circuit of claim 5” as appropriate) is used to drive one LED or a group of LEDs connected in series or series / parallel. Circuit. Specifically, an AC power supply rectification circuit with a power supply connection terminal on the input side and a power source terminal connected to the minus output side of the AC power supply rectification circuit, one LED, or a series or series-parallel connection LED group connected to the positive output side of the AC power supply rectifier circuit, or an FET for turning on and off the drive current of the LED group, and for detecting the drive current passing through the FET In addition, a current detection resistor arranged between the FET and the anode of the LED or LED group, and a FET control for controlling the FET connected to the gate terminal of the FET via a gate resistor And a circuit. The FET control circuit applies a control voltage to the gate resistor to apply a gate voltage exceeding a threshold voltage to the gate terminal as the rectified voltage applied from the positive output side of the AC power supply rectifier circuit increases. In response to the fact that the current detection resistor detects a drive current exceeding a predetermined value, the control voltage is reduced to a voltage lower than the threshold voltage to discharge the charge from the gate terminal. The delay is turned off by prompting the FET. The difference between the drive circuit of claim 5 and the drive circuit of claim 4 is that the latter LED or LED group is arranged on the positive output side of the AC power supply rectifier circuit, while the former LED or LED group is Is a point arranged on the minus side of the AC power supply rectifier circuit.

[0014] According to the drive circuit of claim 5, the FET control circuit applies a control voltage to the gate resistor due to an increase in the rectified voltage applied from the positive output side of the AC power supply rectifier circuit. The FET turns on when the voltage exceeds the threshold voltage. When the LED is turned on, a drive current flows to the LED or the LED group to which the rectified voltage is applied, and the LED or the LED group is turned on. The drive current is detected by the current detection resistor. When the FET control circuit receives this detection, it lowers the control voltage. Due to this drop, the potential of the gate resistor on the FET control circuit side becomes lower than the potential on the gate terminal side. As a result, the charged electric charge is discharged from the gate terminal via the gate resistor, and the gate voltage decreases with the discharge. When the gate voltage falls below the threshold voltage, the FET is turned off, thereby turning off the LED or LEDs (although in practice, even if the FET is off, the AC power supply rectifier circuit A small drive current flows from the plus output side to the FET control circuit. In other words, the driving current flows even before the gate voltage reaches the threshold voltage due to charge discharge (until the FET is turned off), so that the LED or the LED group can be lit with high luminance. As described above, since the detection of the drive current by the current detection resistor triggers the FET to be turned off, the latter operates later than the former. This delay operation realizes high luminance even at a low voltage and a large current, that is, at a low applied voltage. Furthermore, since the on-resistance value of the FET is generally smaller than the on-resistance value of the transistor, the former generates less heat than the latter even when the same current is applied. Further, in order to light the LED or the LED group with direct current, a power transformer, a large-capacity capacitor, and the like are required, but the drive circuit of claim 5 does not require such a thing. The drive circuit can be reduced in size because it is not needed.

(Characteristics of the invention described in claim 6)

In the LED driving circuit according to the invention described in claim 6 (hereinafter referred to as “the driving circuit of claim 6” as appropriate), in addition to the basic configuration of the driving circuit of any of claims 1 to 5, the gate resistance Has a bypass path connected in parallel, the bypass path includes a diode directed forward to the FET, and a bypass resistor connected in series to the diode, and the value of the bypass resistance is It is set smaller than the value of the gate resistance.

According to the drive circuit of claim 6, in addition to the basic operation and effect of the drive circuit of any one of claims 1 to 5, the value of the bypass resistor depends on the value of the gate resistance depending on the difference between the two resistance values. The gate current is at least half of the FET gate current, or if the difference between the two resistances is large, most of the gate current during charge charging flows through the bypass resistor. Since the discharge direction is opposite to that of the diode, the electric charge is discharged only through the gate resistance, and the discharge through the bypass resistance is impossible. Since the value of the bypass resistor is smaller than the value of the gate resistor, The charging of the FET via the former takes less time than the discharging of the FET via the latter. By shortening the charging time, the FET can be turned on at a low output voltage, and the heat generated by the FET can be reduced accordingly.

(Characteristics of the invention described in claim 7)

The LED drive circuit according to the invention of claim 7 (hereinafter, appropriately referred to as “the drive circuit of claim 7”) has a basic configuration of the drive circuit of claim 6, and the gate resistance is provided with the FET. It is preferable that a diode in the reverse direction is connected in series.

According to the drive circuit of claim 7, in addition to the basic operation and effect of the drive circuit of claim 6, the gate current at the time of charge charging flows only through the bypass resistor, and the charge discharge is good This is done only through the resistor. Therefore, the charge charging to the FET and the charge discharging from the FET are independent of each other, and as a result, the gate resistance and the bypass resistance can be easily designed.

The invention's effect

According to the LED drive circuit according to the present invention, it is possible to drive the LED with high luminance while suppressing heat generation while being small.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of an LED drive circuit (hereinafter, appropriately referred to as “drive circuit”) according to the first embodiment. FIG. 2 is a diagram illustrating waveforms of a rectified voltage and a drive current of the drive circuit according to the first embodiment. FIG. 3 is a circuit diagram of a drive circuit according to the second embodiment. FIG. 4 is a diagram illustrating a waveform of a drive current of the drive circuit according to the second embodiment. FIG. 5 is a circuit diagram of a drive circuit according to the third embodiment. 6 and 7 are circuit diagrams of a drive circuit according to the fourth embodiment. FIG. 8 is a circuit diagram of a drive circuit according to the fifth embodiment. FIG. 9 is a circuit diagram of another drive circuit according to the fifth embodiment.

(First Embodiment)

This will be described with reference to FIGS. The drive circuit 1 includes a rectifier circuit (AC power supply rectifier circuit) 3, an LED (light emitting element) 5, an FET (field effect transistor) 7, a current detection resistor R2, and a FET control circuit 11. Rectifier circuit 3 is connected to AC power supply E on the input side. AC connection terminals (power supply connection terminals) 3a, 3a, and rectification output terminals 3b (+), 3b (—) for extracting rectified voltage (rectified current) on the output side. AC power source E is generally a commercial power source (for example, 100V-220V, 50Hz-60Hz). However, an AC power source other than the commercial power source can be used. In this embodiment, a power source using a single-phase AC of 100V50HZ as a power source may be a three-phase AC source or the like. The rectifier circuit 3 is configured as a full-wave bridge type, but may be configured as a rectifier circuit such as a half-wave rectifier type.

As the LED 5 in the first embodiment, a large-current high-output LED having a forward voltage of 3.42 V and a forward current of 350 mA was used. LEDs with ratings other than the above can also be used. The color of the LED 5 is white because the drive circuit 1 is mainly used for lighting. It is not necessary to use a color other than white, depending on the taste or application. The driving circuit 1 drives only one LED5. Driving a plurality of LEDs will be described later. The LED 5 has an anode terminal 5a and a force source terminal 5k. The former is connected to the rectification output terminal 3b (+), and the latter is connected to the drain terminal 7d of the FET 7. Although the heat generated by the drive circuit 1 is relatively small, it is needless to say that a radiator plate or the like for supporting the use environment such as the ambient temperature of the drive circuit 1 can be added to the LED 5 as necessary. .

[0023] For FET7, the power that a P-channel FET can also be used Here, an N-channel MOS type FET is used. The FET 7 has a source terminal 7s and a gate terminal 7g serving as a control electrode, in addition to the drain terminal 7d described above. The source terminal 7s is connected to one end of the current detection resistor R2 via the connection point S1, and the other end of the current detection resistor R2 is connected to the rectification output terminal 3b (-). Further, the gate terminal 7g is connected to the FET control circuit 11 (emitter terminal 13e of the transistor 13) via the gate resistor R4, and the FET 7 controls the driving current of the LED 5 in accordance with the signal applied to the gate terminal 7g. It is configured to work as a switching element that turns on and off. A field effect transistor suitable for the FET 7 is, for example, 2SK 2914 force S. This 2SK2914f has a standard on-resistance of 0.42 Ω for standard S and 0.5 Ω at the maximum.

The FET control circuit 11 includes a PNP transistor 13, an NPN transistor 15, a resistor R3 And a resistor R5. The resistor R3 is connected between the rectified output terminal 3b (+) of the rectifier circuit 3 and the emitter terminal 13e of the transistor 13, and the resistor R5 is connected to the emitter terminal 13e of the transistor 13 and the base terminal of the transistor 13. 13b. The base terminal 13b of the transistor 13 is connected to the collector terminal 15c of the transistor 15. The collector terminal 13c of the transistor 13 is connected to the base terminal 15b of the transistor 15. The emitter terminal 15e of the transistor 15 is connected to one rectification output terminal 3b (-). The base terminal 15b of the transistor 15 is connected to the connection point S1 via the resistor R1. The emitter terminal 13e of the transistor 13 is connected to the gate terminal 7g of the FET 7 via the gate resistor R4 as described above. Hereinafter, the connection point between the gate resistors R4 and R3 is referred to as a connection point S2. The connection point S2 coincides with the emitter terminal 13e.

(Operation of Drive Circuit)

This will be described with reference to FIGS. The alternating current supplied from the AC power supply E to the rectifier circuit 3 via the power supply connection terminals 3a, 3a is full-wave rectified by the rectifier circuit 3. The waveform of the output voltage e between the rectification output terminals 3b (+) and 3b (—) of the rectifier circuit 3 is a waveform in which half cycles of a sine wave are arranged as shown in FIG. In FIG. 2, the output voltage e is applied to both the anode terminal 5 a of the LED 5 and the FET control circuit 11. The FET control circuit 11 to which the output voltage e is applied applies the control voltage to the gate resistor R4. That is, the output voltage e is applied to the gate terminal 7g of the FET 7 via the resistor R3 of the FET control circuit 11 and the gate resistor R4 for applying the control voltage. Here, when the output voltage e is zero, the gate current does not flow, but as the output voltage e increases, the gate current flows and charges the gate region of the FET7, and the control voltage further rises to lower the threshold voltage of the FET7. Turn on FET7 when the hold voltage Vth is exceeded. The potential of the gate terminal 7g in the ON state is maintained at a potential higher than the threshold voltage Vth due to charge. When FET7 is turned on, a circuit is formed that returns to rectifier circuit 3 via rectifier circuit 3, rectifier output terminal 3b (10) on the positive side, LED5, FET7, current detection resistor R2, and rectifier output terminal 3b (—) As a result, the drive current i flows through the LED 5 to which the output voltage e is applied, and the LED 5 is turned on.

[0026] The drive current i that has passed through the LED 5 is the force flowing through the current detection resistor R2. At this time, the potential of the connection point S1 between the FET 7 and the current detection resistor R2 and the rectified output terminal 3b (-) of the current detection resistor R2 Since a potential difference occurs between the potential and the potential due to the voltage drop, the potential of the connection point S1 of the current detection resistor R2 is higher than the potential of the rectified output terminal 3b (−) of the current detection resistor R2. The generation of a potential difference at the connection point S1 serves as a trigger, and a base current flows through the resistor R1 to the base terminal 15b of the transistor 15 to turn on the transistor 15. When the transistor 15 is turned on, a base current flows to the base terminal 13b of the transistor 13 via the resistors R3 and R5, and the transistor 13 is turned on. When the transistor 13 is turned on, the potential at the connection point S2 decreases. Here, since the resistor R3 is set so that the lowered potential becomes lower than the threshold voltage Vth, the potential at the connection point S2 becomes lower than the threshold voltage Vth due to the lowering of the potential. That is, the potential of the gate terminal 7g becomes higher than the potential of the connection point S2 across the gate resistor R4. Charge discharge occurs due to the potential difference between both ends of the gate resistor R4, and charges in the gate region gradually flow into the connection point S2 via the gate resistor R4. Along with this discharge, the gate voltage drops. Until the gate voltage drops and reaches a voltage equal to the threshold voltage Vth, the ON state of FET7 continues. When the voltage drops below the threshold voltage Vth, the FET7 turns off.

That is, the FET control circuit 11 in the first embodiment turns on the LED 5 by driving the drive current i when the FET 7 is turned on, and turns off the FET 7 when the drive current i is detected by the current detection resistor R2. The power to turn off the LED 5 is not turned off almost at the same time as the detection of the drive current i, but rather is delayed by charge discharge. If a transistor is used instead of an FET, the transistor can charge less than the FET, so when the gate voltage drops below the threshold voltage, the transistor turns off and the drive current is interrupted. (Indicated by i 'in Figure 2). On the other hand, in the case of FET, the gate region is charged, and the charge is discharged, thereby delaying the turning off of the FET. Due to this delay, the FET causes an extra drive current to flow than the transistor. That is, the brightness of the LED is increased. In addition, the amount of heat generated can be reduced significantly as compared with the case where the drive current always flows by turning on and off the FET7. In addition, since the on-resistance of the FET is lower than that of the transistor, even if the same drive current is applied, the heat generated by the FET can be suppressed by the lower on-resistance. (Second Embodiment)

This will be described with reference to FIGS. The drive circuit 21 according to the second embodiment is different from the drive circuit 1 according to the first embodiment in that the LED 5 having only the latter is connected to the plurality of LEDs 5, which are connected in series. LED group 5 consisting of Therefore, the following description focuses on the differences between the drive circuit 21 and the drive circuit 1, and the same reference numerals as those used in FIG. 1 can be used in FIG. 3 for common parts. Descriptions thereof will be omitted as much as possible. The waveform of the driving current shown in FIG. 4A is a waveform when one LED is used, and is almost the same as the waveform of the driving current shown in FIG. FIG. 4 (a) is a diagram for comparison with a case where a plurality of LEDs are connected. The waveform of the drive current shown in FIG. 4 (b) is a waveform for two LEDs, and the waveform of the drive current shown in FIG. 4 (c) is a waveform for three LEDs. The waveform of the drive current shown in Fig. 4 is obtained when the current detection resistor R2 is set to 2 Ω.One scale on the vertical axis is 250 mA, and one scale on the horizontal axis is 2 mS. Is shown.

The drive circuit 21 shown in FIG. 3 has an LED group 5 composed of three LEDs connected in series. The number of LEDs 5 does not prevent two or four or more LEDs 5 depending on the use of the drive circuit 21 and the like. In order to light up the n LEDs connected in series, a voltage equal to n times the forward voltage of each LED is required. Therefore, if three LEDs 5 are connected in series, the forward voltage of each LED 5 ( At least a voltage equal to three times the LED voltage) is required. A single LED5 requires a forward voltage for one LED, and two LEDs require a forward voltage equal to two forward voltages. As described above, the forward voltage of LED5 is 3.42V, so if it is one LED it is 3.42V, if it is two it is 6.84 (3.42 X 2) V, if it is three it is 10.26 ( 3. At least a voltage of 42 x 3) V is required.

[0030] In Fig. 4, LED5 has a stronger waveform with two LED5's (Fig. 4 (b)) than a single waveform (Fig. 4 (a)). The LED5 has three waveforms (Fig. 4 (c)). The single-peak waveform has a higher height. That is, it can be seen that the current amount increases almost in proportion to the increase rate as the number of LEDs 5 increases. This indicates that according to the drive circuit 21, the brightness of each LED 5 when a plurality of LEDs 5 are connected in series is higher than the brightness when a single LED 5 is connected. By connecting multiple LEDs 5, each LED 5 Assuming that the brightness is significantly lower than the brightness when only one LED 5 is turned on, a device using many LEDs is not suitable. The drive circuit 21 can be suitably used for a device having a large number of LEDs, for example, an illuminator for the reasons described above. The LED group 5 in the second embodiment is formed by connecting a plurality of LEDs 5 in series.However, one or more LEDs 5 are connected in parallel with some or all of the LEDs 5 connected in series. That is, it can be composed of a plurality of LEDs arranged in series and parallel.

(Third Embodiment)

This will be described with reference to FIG. The drive circuit 31 according to the third embodiment differs from the drive circuit 1 according to the first embodiment in the connection position of the LED 5. For this reason, the following description focuses on the differences between the driving circuit 31 and the driving circuit 1, and the parts common to both are denoted by the same reference numerals as those used in FIG. 1 in FIG. The explanation is omitted as much as possible.

The LED 5 of the drive circuit 1 according to the first embodiment is connected to the rectified output terminal 3 b (+) and the drain terminal 7 d of the FET 7. And the current detection resistor R2. Specifically, the anode terminal 5a of the LED 5 is connected to the source terminal 7s, the power source terminal 5k is connected to the FET7 side terminal of the current detection resistor R2, and the rectification output terminal 3b (+) Is connected to one end of the resistor R3 of the FET control circuit 11. The operation and effect of the drive circuit 31 are basically different from the operation and effect of the drive circuit 1.The difference between the case where the LED5 is located upstream of the FET7 and the case where the LED5 is located downstream is also seen from the direction of the drive current i. There is only. Needless to say, a plurality of LEDs connected in series or in series / parallel can also be connected in the drive circuit 31. Note that, even when a plurality of LEDs are connected in series or in series / parallel in the drive circuit 31, the brightness of each LED 5 is lower than the brightness of a single LED 5 as in the drive circuit 21 according to the above-described second embodiment. The increase is almost constant.

(Fourth Embodiment)

This will be described with reference to FIG. The drive circuit 41 according to the fourth embodiment differs from the drive circuit 1 according to the first embodiment in the connection position of the LED 5. For this reason, the following description focuses on the differences between the drive circuit 41 and the drive circuit 1 and focuses on the parts common to both. In FIG. 6, the same reference numerals as those used in FIG. 1 are used, and the description thereof is omitted as much as possible.

The LED 5 in the drive circuit 41 is connected to the rectified output terminal 3b (+) and one end of the resistor R3 of the FET control circuit 11. Specifically, the anode terminal 5a of the LED 5 is connected to the rectified output terminal 3b (+), and the force source terminal 5k is connected to one end of the resistor R3. The output terminal e is applied to the drain terminal 7d and the FET control circuit 11 via the LED5 to the drain terminal 7d and the FET control circuit 11 to the force source terminal 5k. ing. The operation and effect of the drive circuit 41 are basically different from the operation and effect of the drive circuit 1 except that the voltage applied to the FET control circuit 11 is reduced by the LED 5. Also in the drive circuit 41, a plurality of LEDs connected in series or in series / parallel can be connected. Note that even when a plurality of LEDs are connected in series or in series / parallel in the drive circuit 41, the brightness of each LED 5 is greater than the brightness of a single LED 5 as in the drive circuit 21 according to the above-described second embodiment. What you do is almost constant.

The LED 5 of the driving circuit 41 shown in FIG. 6 is a power connected between the rectification output terminal 3b (+) and one end of the resistor R3 of the FET control circuit 11 as described above. It can also be placed on the terminal 3b (1) side. That is, as shown in Fig. 7, the rectification output terminal 3b (-) is connected to the power source terminal 5k of ED5, and the anode terminal 5a of LED5 is connected to the source terminal 7s of FET7 via the current detection resistor R2. . The rectified output terminal 3b (+) is directly connected to the drain terminal 7d of FET7 and one end of the resistor R3. There is no difference between the drive circuit 41 and the drive circuit 4 # in the configuration other than the arrangement of the LED5. The same applies to the operation and effect of the drive circuit and the fact that a plurality of LEDs can be connected in series or in series / parallel.

(Fifth Embodiment)

This will be described with reference to FIGS. The driving circuit 51 according to the fifth embodiment is structurally different from the driving circuit 1 according to the first embodiment in the connection method between the FET 7 and the FET control circuit 11. For this reason, the following description focuses on the differences between the driving circuit 51 and the driving circuit 1, and the parts common to both are denoted by the same reference numerals as those used in FIG. 1 in FIGS. 8 and 9. Description thereof will be omitted as much as possible.

[0037] That is, between the gate terminal 7g of the FET 7 and the FET control circuit 11 (that is, the connection point S2). Is connected to a gate resistor R4 ', and a bypass path 23 is connected in parallel with the gate resistor. The bypass path 23 is composed of a diode D1 in the forward direction toward the FET 7 and a bypass resistor R6 connected in series to the diode D1. The value of the bypass resistor R6 is set smaller than the value of the gate resistor R4 '. For example, if the no-pass resistance R6 is 300ΚΩ, the gate resistance R4 'is about 1ΜΩ. The value of the bypass resistor R6 is set to be smaller than the value of the good resistor R4 'so that the gate current mainly flows through the bypass resistor R6, and the electric charge from the gate terminal 7g discharges only the gate resistor R4'. This is to make it flow. In other words, since the diode D1 is in the forward direction toward the FET7, the gate current is the force S flowing through both the bypass resistor R6 and the gate resistor R4 ', and the resistance of the former is smaller than the resistance of the latter (diode D1). The internal resistance is negligible), and the gate current mainly flows through the bypass resistor R6. On the other hand, the direction of the charge discharge is opposite to the direction of the diode D1, so that the charge discharge flows exclusively through the gate resistor R4 'without flowing through the bypass path 23. Since the value of the bypass resistor R6 is smaller than the value of the gate resistor R4 ', by appropriately setting the value of the resistor R3, the charge of the FET 7 can be performed in a shorter time than the charge discharge. Reducing the charging time turns on the FET at a lower output voltage, which reduces the heat generated by the FET. The same effect can be obtained even if the relative position between the diode D1 and the bypass resistor R6 is reversed from that shown in FIG. 8 and the bypass resistor R6 is set closer to the FET7 than the diode D1.

As shown in FIG. 9, a diode D2 in the reverse direction (forward direction of charge discharge) can be connected to the FET 7 in series with the gate resistor. By providing the diode D2, the gate current is prevented from flowing through the gate resistor R4 '. Therefore, the charging of the FET 7 and the discharging of the FET 7 are independent of each other, and as a result, the gate resistor R4 ′ and the bypass resistor R6 can be easily designed. Furthermore, the above-described bypass path 23 and also D2 may employ the drive circuits 1, 21, 31, 41, and 41 according to the first to fourth embodiments.

Brief Description of Drawings

FIG. 1 is a circuit diagram of a drive circuit according to a first embodiment.

FIG. 2 is a diagram showing waveforms of a rectified voltage and a drive current of the drive circuit according to the first embodiment. Garden 3] is a circuit diagram of a drive circuit according to a second embodiment.

FIG. 4 is a diagram showing a waveform of a drive current of a drive circuit according to a second embodiment. FIG. 5 is a circuit diagram of a drive circuit according to a third embodiment.

Garden 6] is a circuit diagram of a drive circuit according to a fourth embodiment.

FIG. 7 is a circuit diagram of a drive circuit according to a fourth embodiment.

Garden 8] is a circuit diagram of a drive circuit according to a fifth embodiment.

FIG. 9 is a circuit diagram of another drive circuit according to the fifth embodiment.

Garden 10] is a circuit diagram of a conventional drive circuit.

Explanation of symbols

1, 21, 31, 51 LED drive circuit (drive circuit)

3 Rectifier circuit

3a Power connection terminal

3b Rectification output terminal

5 LED (LED group)

7 FET

11 FET control circuit

13, 15

23 Bypass road

Dl, D2 diode

Rl, R3, R5 resistance

R2 current detection resistor

R4 Gate resistance

R6 Bypass resistor

SI, S2 connection point

Claims

The scope of the claims

[1] an AC power supply rectifier circuit having a power supply connection terminal on an input side,

One LED with an anode terminal connected to the positive output side of the AC power supply rectifier circuit, and a FET connected to the power source terminal of the LED for turning on and off the driving current of the LED and

A current detection resistor disposed between the FET and the negative output side of the AC power supply rectification circuit to detect a drive current passing through the FET;

A FET control circuit for controlling the FET connected to the gate terminal of the FET via a gate resistor,

The FET control circuit applies a control voltage to the gate resistor to apply a gate voltage exceeding a threshold voltage to the gate terminal as the rectification voltage applied from the plus output side of the AC power supply rectifier circuit increases. In response to the fact that the current detection resistor has detected a drive current exceeding a predetermined value, the control voltage is reduced to a voltage lower than the threshold voltage, and the voltage from the gate terminal is reduced. It is configured to delay off the FET by prompting charge discharge.

An LED driving circuit, characterized by:

[2] an AC power supply rectifier circuit having a power supply connection terminal on an input side,

An LED group in which a plurality of LEDs having anode terminals connected to the positive output side of the AC power supply rectifier circuit are connected in series,

An FET connected to the power source terminal of the LED group for turning on and off the drive current of the LED group;

The FET control circuit applies a control voltage to the gate resistor to apply a gate voltage exceeding a threshold voltage to the gate terminal as the rectification voltage applied from the plus output side of the AC power supply rectifier circuit increases. To turn on the FET, and In response to the detection of the drive current exceeding the predetermined value by the current detection resistor, the control voltage is reduced to a voltage lower than the threshold voltage to promote discharge of the gate terminal, thereby delaying the FET. By turning it off,

The drive current can be increased almost in proportion to the increase in the number of LEDs that make up the LED group.

An LED driving circuit, characterized by:

[3] an AC power supply rectifier circuit having a power supply connection terminal on an input side,

One LED or a group of LEDs connected in series or series / parallel,

A FET connected between the anode terminal of the LED or the LED group and the positive output side of the AC power supply rectifier circuit for turning on / off the driving current of the LED or the LED group; and

A current detection resistor disposed between a power source terminal of the LED or the LED group and a negative output side of the AC power supply rectifier circuit to detect a drive current passing through the LED or the LED group;

An LED driving circuit, characterized by:

[4] an AC power supply rectifier circuit having a power supply connection terminal on an input side,

A single LED or a series of LEDs connected in series or series / parallel with the anode terminal connected to the positive output side of the AC power supply rectifier circuit,

An FET connected to the power source terminal of the LED or the LED group for turning on and off the driving current of the LED or the LED group; and A current detection resistor disposed between the FET and the negative output side of the AC power supply rectification circuit to detect a drive current passing through the FET;

The FET control circuit is configured to apply a gate voltage exceeding a threshold voltage to the gate terminal as the rectified voltage applied from the positive output side of the AC power supply rectifier circuit via the LED or the LED group increases. The control voltage is applied to the gate resistor to turn on the FET, and the control voltage is reduced to a voltage lower than the threshold voltage in response to the detection of the drive current exceeding the predetermined value by the current detection resistor. It is configured to turn off the FET by lowering it and promoting discharge of the charge from the gate terminal.

An LED drive circuit characterized by the following.

An AC power supply rectifier circuit having a power supply connection terminal on an input side,

A single LED or a series of LEDs connected in series or series / parallel, with a power source terminal connected to the negative output side of the AC power supply rectifier circuit,

An FET connected to the positive output side of the AC power supply rectifier circuit for turning on and off the driving current of the LED or the LED group;

A current detection resistor disposed between the FET and the LED or the anode terminal of the LED group to detect a drive current passing through the FET;

The FET control circuit applies a control voltage to the gate resistor to apply a gate voltage exceeding a threshold voltage to the gate terminal as the rectification voltage applied from the plus output side of the AC power supply rectifier circuit increases. In response to the fact that the current detection resistor has detected a drive current exceeding a predetermined value, the control voltage is reduced to a voltage lower than the threshold voltage, and the voltage from the gate terminal is reduced. The FET is configured to delay off by prompting charge discharge.

An LED driving circuit, characterized by: [6] A bypass path is connected in parallel to the gate resistor,

The bypass path includes a diode in a forward direction toward the FET, and a bypass resistor connected in series to the diode;

6. The LED drive circuit according to claim 1, wherein a value of the bypass resistance is set smaller than a value of the gate resistance.

7. The LED drive circuit according to claim 6, wherein a diode in a direction opposite to the FET is connected in series to the gate resistor.