JP2001028461A - Current drive-type component drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen a circuit in power consumption as a whole, when an LED is turned on. SOLUTION: When switches 1, 1, and 1 are turned on, the source terminals of the corresponding FET(field effect transistor) are shut off from their drain terminals. With this setup, a current IF generated by a constant current source 3 flows passing through the LEDs 2, 2, and 2 to enable them to emit light, respectively. At this point, only the LEDs 2, 2, and 2 are present but a part such as a resistor which wastes an electric power uselessly is not present in a flow path where a current IF flows, so that all the circuit can be lessened in power consumption. When the switches 1, 1, and 1 are turned off, the source terminals and drain terminals of FETs 4, 4, and 4 are connected electrically together. With this setup, the current IF flows through the FETs 4, 4, and 4 bypassing the LEDs 2, 2, and 2, and the LEDs 2, 2, and 2 are turned off.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current-driven component, such as a light emitting diode (hereinafter referred to as an LED), which is driven by supplying a certain current, that is, a constant current. The present invention relates to a driving circuit for driving.

[0002]

2. Description of the Related Art The above LED is used in various electronic devices.
For example, it is widely used for applications such as a so-called pilot lamp for displaying an ON / OFF state of a switch. In order to realize such a pilot lamp-like function, conventionally, for example, a circuit as shown in FIG. 4 is generally configured.

That is, for a predetermined DC voltage V _CC (specifically, between the DC voltage V _CC and the ground potential), the switch 1
0, the LED 11 and the resistor 12 are connected in series. The order of connection is not particularly limited, but the LED 11 is connected so that a voltage is applied in the forward direction. More specifically, the anode (anode) terminal is connected to the DC voltage _VCC side, and the cathode (cathode) is connected. Connect the terminal to the ground potential side. The resistor 12 is for controlling the current supplied to the LED 11, and selects the resistance value so that the current flowing through the LED 11, that is, the forward current _IF becomes a rated value.

According to the configuration of FIG. 4, when the switch 10 is turned on (closed), the switch 10, the LED 11 and the resistor 1 are turned on.
A series circuit consisting of 2 which in the current I _F flows, LED
11 lights up. On the other hand, switch 10 is OFF (open)
When in the state, since the current I _F does not flow, L
The ED 11 is not turned on, that is, is in a light-off state.

[0005]

[SUMMARY OF THE INVENTION However, in the conventional circuit configuration, when the lighting of the LED 11, since current also I _F flows through the resistor 12 connected thereto in series, as it were wasted by the resistor 12 There is a problem that power is consumed. This problem becomes more conspicuous as the lighting time of the LED 11 is longer (for example, when the LED 11 is configured to be constantly turned on), or as the number of the LEDs 11 is increased, particularly as the number of the turned on LEDs 11 is increased. Become.

Accordingly, the present invention is to reduce the power consumption of the entire circuit when driving (operating) the components in a drive circuit for driving a current-driven component represented by the LED 11. Aim.

[0007]

In order to achieve the above object, the present invention provides a current-driven component provided in a main line and driven by supplying a predetermined current, and a current-driven component. A constant current source circuit that generates the predetermined current necessary to drive the main line and circulates the current through the main line, and a bypass line that bypasses a portion of the main line where the current-driven component is provided. And a detour control circuit that allows the predetermined current to flow through the detour path when a detour command is given from the outside.

According to the present invention, a current-driven component is provided in the main line. Then, the constant current source circuit generates a predetermined current required for driving the current-driven component, that is, a rated current of the current-driven component, and causes the current to flow through the main line. Therefore, the current drive type component performs rated drive using the predetermined current supplied from the constant current source circuit via the main line as a drive source.

On the other hand, when a detour command is given from outside,
A detour control circuit circulates the predetermined current via a detour path. As a result, the predetermined current flows around the portion of the main line that is the flow path, where the current-driven component is provided. Therefore, the predetermined current is
The current-driven component is no longer supplied, and the current-driven component is in a non-driven (ie, OFF) state. However, the predetermined current does not mean that the flow of the current itself is interrupted,
Only a part, that is, a part where the current drive type component is provided, continues to flow through the main line via the detour path.

Therefore, a plurality of current-driven components are provided in series on the main line. In this way, a plurality of current driven components can be driven by one constant current source circuit. And
The bypass control circuit is individually provided for each current-driven component or for each of a predetermined number of continuous current-driven components. In this way, the drive and non-drive of each current drive type component
External control can be performed individually or in units of a predetermined number.

As the current-driven component, for example, an LED can be used, that is, the present invention can be applied to an LED driving circuit.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment in which a current drive type component drive circuit according to the present invention is applied to, for example, an LED drive circuit will be described with reference to FIGS.

FIG. 1 is an electric circuit diagram showing an example of the present embodiment. As shown in the figure, the present embodiment includes a plurality of, for example, three switches 1, 1, 1. Then, three LEDs 2, 2, 2 respectively corresponding to these switches 1, 1, 1 are provided, and these LEDs 2, 2,
The ON / OFF state of each switch 1, 1, 1 is displayed by 2, 2, that is, each LED 2, 2, 2 is set to each switch 1,
It is assumed that the pilot lamps function as 1, 1 pilot lamps.

In order to realize this, in the present embodiment, for a predetermined DC voltage V _CC (specifically, between the DC voltage V _CC and the ground potential), the three LEDs 2, 2,.
2 in series. Here, the LEDs 2, 2, and 2 are of the same standard. Then, the LEDs 2, 2, 2 are connected so that a voltage is applied in the forward direction, respectively.
_Are connected to the DC voltage V _CC side, and each cathode terminal is connected to the ground potential side.

Further, a constant current source is provided at a certain position in the series circuit of the LEDs 2, 2, and 2, for example, between the cathode terminal of the LED 2 located at the lowest side (ground potential side) in FIG. Circuit 3 is provided. This constant current source circuit 3
Intended current draw type generally known, generates the same magnitude of current and the rated value of the forward current I _F according to the basis of the DC voltage V _CC, and the LED2,2,2, DC this The current flows from the voltage V _CC to the ground potential. In addition,
Instead of the current draw type constant current source circuit 3, a generally known current source type may be used.
In this case, the current discharging type constant current source circuit is provided between the DC voltage V _CC and the anode terminal of the LED 2 located at the uppermost side in FIG.

Further, three field effect transistors (hereinafter, referred to as FETs) 4, 4, and 4 are provided corresponding to the LEDs 2, 2, and 2, respectively. Here, FETs 4, 4,
For example, a generally known n-channel depletion-type JFET (junction FET) is used as 4. Then, each source terminal (S) of these FETs 4, 4, 4
Are connected to the respective anode terminals of the corresponding LEDs 2, 2, and 2, and the drain terminals (D) of the FETs 4, 4, and 4 are connected to the respective cathode terminals of the LEDs 2, 2, and 2, respectively. Further, each source terminal and each gate terminal (G) of each FET 4, 4, 4 are connected to each other via separate resistors 5, 5, 5, respectively, and each gate terminal is connected to a corresponding switch. 1, 1, and 1 are connected to the ground potential. The resistors 5, 5, 5
When each switch 1, 1, 1 is OFF, each FET 4,
The potentials of the gate terminal and the source terminal are made equal to each other, that is, the potential difference V _GS between them is set to V _GS = 0. Here, as each of the resistors 5, 5, 5, for example, a resistor having a resistance value of 1 MΩ is used.

In the configuration of FIG. 1, for example, it is assumed that all the switches 1, 1, 1 have been turned on. Thereby, each gate terminal of each FET4,4,4 is grounded, and each source terminal is connected to the corresponding LED.
2, 2 and 2 have the same potential as the anode terminals, and the voltage between the gate terminal and the source terminal is V _GS as each FE.
Applied to T4, T4, T4. Then, each FET 4, 4,
The respective channel currents of No. 4 are almost completely cut off, so that the respective source terminals and drain terminals are electrically cut off. At the same time, the anode terminals of the LEDs 2, 2, and 2 are grounded via the resistors 5, 5, and 5, respectively. Considering that the resistors 5, 5 have a very large resistance value, almost no current flows through each of the resistors 5, 5, 5. Therefore, current I _F generated by the constant current source circuit 3 (strictly for most current I _F is), as shown by the dashed-line arrow in the figure, via a respective LED2,2,2 flow (That is, each FET 4, 4, 4 and each resistor 5, 5,.
5), whereby each LED 2, 2, 2
Lights up.

[0018] At that time, the flow path of the current I _F, extra dissipative elements, such as resistors 12 in the prior art described above does not exist. Therefore, the power consumption of the entire circuit when each of the LEDs 2, 2, and 2 is lit can be reduced as compared with the above-described related art. This means that L
As the number of EDs 2, 2, 2 is larger, each LED 2,
Lighting time of 2, 2 (ON state of each switch 1, 1, 1)
The longer the is, the more noticeable.

Next, it is assumed that any one of the switches 1, 1, 1 is turned off. In this case, the potential of the gate terminal and the potential of the source terminal of the FET 4 corresponding to the switch 1 that has been turned off are equal, that is, the potential difference V _GS between them is V _GS =
It becomes 0, and the channel current of the FET 4 is saturated.
Then, the impedance between the source terminal and the drain terminal of the FET 4 decreases, and the two terminals become substantially conductive. Accordingly, the current I _F, as shown by dotted arrows in the drawing, to bypass the LED2 corresponding to the switch 1 is OFF (bypass), between the source and drain terminals of FET4 in the conductive state Flows through. Therefore, the L corresponding to the switch 1 that has been turned off
The current I _F is not supplied to ED2, its LED2 is turned off.

[0020] Incidentally, even if the current I _F is not supplied to the LED2 corresponding to the switch 1 which is the OFF, does not mean that the current I _F itself is interrupted, the current I
_F flows around the LED2. Therefore, even if a certain switch 1 is turned off and the corresponding LED 2 is turned off, there is no effect on the operation of the LEDs 2 and 2 corresponding to the other switches 1 and 1 which are turned on.

When all the switches 1, 1, 1 are turned off, of course, all the LEDs 2, 2, 2 are turned off. However, even in this case, the current I _F is not necessarily the distribution itself is interrupted, it continues to flow through each FET4,4,4 bypassing all LED2,2,2. Therefore, even if all the LEDs 2, 2, and 2 are turned off, although slightly,
Power is consumed by each of the FETs 4, 4, and 4.

As described above, even when all the LEDs 2, 2, and 2 are turned off, the power is consumed, albeit slightly, in view of the fact that the LEDs 2, 2, and 2 are turned off.
It is very effective to apply the present invention to an electronic device including a large number of LEDs 2 and 2 and configured to light LEDs 2, 2, and 2 for a long time. Such electronic devices include, for example, emergency broadcast devices in buildings.

In other words, the emergency broadcast equipment generally has a plurality of switches for switching the valid / invalid state of the broadcasting action to each broadcast target area, and the ON / OFF state of each switch. Multiple LEs
For example, a large number of Ds are provided in the device body. Each LED is normally illuminated when broadcasting to the corresponding broadcast target area is enabled. Since such an emergency broadcasting device is premised on simultaneous broadcasting, the broadcasting action is always valid for all broadcasting target areas, that is, all LEDs are often turned on. Therefore, the present embodiment greatly contributes to reducing the power consumption of the entire device in the broadcasting device in which the LED is constantly lit as described above.

In the present embodiment, the constant current source circuit 3
To drive (turn on) each LED 2, 2, 2
Since generating a current I _F required, for example, the DC voltage V
_CC is even somewhat unstable, it is possible to supply a stable current I _F to each LED2,2,2, it can be driven in a stable manner the LED2,2,2. On the other hand, in the prior art shown in FIG. 4 described above, if the DC voltage V _CC is unstable, for example, it is necessary to provide a stabilized power supply circuit in addition to the configuration shown in FIG. The structure becomes complicated, and the cost of the whole circuit increases.
Thus, when the DC voltage V _CC is unstable, the effectiveness of the present embodiment becomes more remarkable.

In FIG. 1, each LED 2, 2, 2
Distribution channels of the current I _F indicated by the dashed-line arrow in the figure through the can, corresponds to the main line of the claims, each FET
4, 4, and 4, the current I _F indicated by the dotted arrow in FIG.
Corresponds to the detour path described in the claims. Then, each FET 4,4,4 and each resistor 5,5,
5 corresponds to the detour control circuit described in the claims, and turning off each of the switches 1, 1, 1 corresponds to the detour command described in the claims.

In this embodiment, three LEDs
Although the case where two, two, and two are driven has been described, the present invention can be applied to a case where other numbers of LEDs are driven. However, when driving a plurality of LEDs, each LED is connected to the constant current source circuit 3 in series.
At this time, the number of connected LEDs is limited by a voltage drop (forward voltage V _P ) of each LED itself, a voltage drop of the constant current source circuit 3 itself, a DC voltage V _CC , and the like.

Also, one LED 2 is provided for each switch 1, in other words, one LED 2 is provided for each detour control circuit composed of a combination of the FET 4 and the resistor 5. However, the present invention is not limited to this. For example, one switch 1
(Or one detour control circuit), a plurality of continuous LEDs 2, 2,... May be provided. In this way, the lighting and extinguishing of each LED 2, 2,...
It can be operated collectively with two switches 1.

When the switches 1, 1, 1 are turned on, the corresponding LEDs 2, 2, 2 are turned on. On the contrary, the switches 1, 1, 1 are turned on.
Each of the LEDs 2, 2, and 2 may be turned on when 1, 1 is turned off. Also, as described in the present embodiment, each LED 2, 2, 2 is connected to each switch 1, 1,
Not only does it function as a pilot lamp for one,
The present invention can be applied to a case where the LEDs 2, 2, and 2 are driven for other uses. In the present embodiment, each LE
D2, 2, and 2 are of the same standard, but are not limited thereto. Each forward current I of each LED 2, 2, 2
_{As long as} the rated values of _F are substantially equal to each other, different standards, for example, those having different forward voltages _VP and luminescent colors may be used.

Furthermore, the technology according to the present invention may be applied to a circuit that drives not only the LEDs 2, 2, and 2 but also other current-driven components as long as the component is driven using a constant current as a power supply. The present invention is also applicable to a circuit in which the LEDs 2, 2, and 2 and other (different) current-driven components are connected in series. However, even in this case, as the current-driven parts, including LED2,2,2, rated values of the forward current I _F is to use a substantially equal.

The FE corresponding to the detour control circuit
Instead of the combination circuit of T4 and resistor 5, for example, a relay circuit 6 as shown in FIG. 2 may be used.
The relay circuit 6 generally has a contact type and a b type.
It is known that there is a contact type. In any case, the circuit is configured so that the power is not consumed by the relay circuit 6 when the LED 2 is turned on.

Further, a circuit as shown in FIG. 3, for example, may be employed separately from FIG. That is, a switching contact type relay circuit 7 is provided in series with the LED 2, for example, on the anode terminal side of the LED 2. Then, (path indicated by dotted arrows in other words the figure) by the relay circuit 7, whether to distribute the current I _F through the main line (or path indicated by the arrows in the dashed line in the drawing), or, via bypass line It switches whether to distribute by. In this case, as in the case of FIG. 2, the relay circuit 7 is configured not to consume power when the LED 2 is lit.

Of course, instead of the above relay circuits 6 and 7,
For example, the bypass control circuit can be configured by a simple manual switch circuit or a generally known analog switch circuit.

[0033]

As described above, according to the present invention, the current required to drive a current-driven component at a rated speed is generated by a constant current source circuit, and is supplied to the current-driven component via a main line. Supplied. Therefore, unlike the prior art shown in FIG. 4 described above, components for current control such as the resistor 12 and the like,
In other words, there is no need to provide components that consume extra power in the main line other than the current-driven components to be driven.
Therefore, there is an effect that the power consumption of the entire circuit when the current drive type component is driven can be reduced accordingly. This effect becomes more remarkable as the drive time of the current drive type components is longer and the number of current drive type components is larger.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of a drive circuit according to the present invention.

FIG. 2 is an electric circuit diagram partially showing another example of the embodiment;

FIG. 3 is an electric circuit diagram partially showing another example of the embodiment different from FIG. 2;

FIG. 4 is a diagram showing a circuit configuration of a conventional drive circuit.

[Explanation of symbols]

 Reference Signs List 1 switch 2 LED (light emitting diode) 3 constant current source circuit 4 FET (field effect transistor) 5 resistor

Claims (3)

[Claims] 1. A current-driven component provided in a main line and driven by being supplied with a predetermined current; and generating the predetermined current required to drive the current-driven component. A constant current source circuit that circulates through the main line; and a detour path that detours a portion of the main line where the current-driven component is provided. A drive circuit for a current-driven component, comprising: a detour control circuit that allows the predetermined current to flow. 2. A plurality of said current-driven components are provided in series in said main line, and said bypass control circuit is provided for each of said current-driven components or for each of a predetermined number of current-driven components that are continuously arranged. A drive circuit for a current-driven component according to claim 1. 3. The drive circuit for a current driven component according to claim 1, wherein the current driven component is a light emitting diode.