CN112235923A - Sleep circuit, control method thereof and lighting device - Google Patents

Abstract

The invention relates to a sleep circuit, which is connected between a power supply and a load, the positive pole of the power supply is connected to the positive pole of the load, and the negative pole of the power supply is connected to the negative pole of the load. The sleep circuit includes a switch unit, a protection unit and a sleep control unit, and the switch unit is connected to Between the negative pole of the power supply and the negative pole of the load; the protection unit is connected to the positive pole of the power supply and the negative pole of the power supply, and is connected to the switch unit, and the protection unit is used to control the switch unit to be turned on or off; the sleep control unit is connected to the protection unit, and the sleep control unit is used for receiving an external control signal; wherein the protection unit controls the switch unit to turn off when the power supply voltage is lower than the preset overdischarge protection voltage; and the protection unit controls the switch unit to turn off when responding to the external control signal. By implementing the present invention, the connection with the external circuit can be disconnected when the power supply voltage is too low or the power supply is not in use, so that the power consumption of the power supply can be slowed down, so as to avoid the low voltage of the power supply as much as possible to ensure the life of the power supply.

Description

Sleep circuit, control method and lighting device

technical field

The present invention relates to the field of integrated circuits, in particular to a sleep circuit, a control method thereof, and a lighting device.

Background technique

Power damage is prone to occur during the use and storage of electronic products. One is that some users are still using the power supply when the power supply has reported low power until the electronic product is turned off. This situation may easily cause the voltage of the power supply to be too low, so that the power supply cannot be charged; , shutdown or standby, the circuit on it is still consuming power, sometimes until the power supply is exhausted, and the user does not charge it, so it is easy to cause the voltage of the power supply to be too low, which makes it impossible to charge.

The current general practice is to set a protection unit in the circuit. When the protection unit detects that the power supply voltage is lower than the preset over-discharge protection voltage, the control power supply is disconnected from the circuit, and the circuit enters a sleep power-off state to reduce the power supply. loss to prevent the power supply voltage from being too low. However, this method can only cut off the connection between the power supply and the circuit when the power supply is lower than the preset over-discharge protection voltage. During the period from when the power supply is low until the protection unit cuts off the connection between the power supply and the circuit, the power supply will be in a long-term state. The low voltage discharge state has a great influence on the life of the power supply and is also easy to damage the power supply. Therefore, it is necessary to design a sleep circuit to cut off the power output when the power supply voltage of the electronic product is too low or not in use, so as to ensure the life of the power supply.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a sleep circuit and a control method thereof and a lighting device for the above-mentioned defects of the prior art, aiming to solve the problem that the existing electronic products cannot be cut off in time when the power supply voltage is too low or not in use. output problem.

The technical solutions adopted by the present invention to solve the technical problems are as follows: in the first aspect, a sleep circuit is provided, which is connected between a power supply and a load, the positive pole of the power supply is connected to the positive pole of the load, and the negative pole of the power supply is connected to the positive pole of the load. The load negative electrode is connected, the sleep circuit includes: a switch unit, a protection unit and a sleep control unit, the switch unit is connected between the power supply negative electrode and the load negative electrode; the protection unit is connected with the power supply positive electrode and the power supply negative electrode , and is connected with the switch unit, and the protection unit is used to control the switch unit to be turned on or off; the sleep control unit is connected with the protection unit, and the sleep control unit is used for receiving external control signals; wherein, The protection unit controls the switch unit to turn off when the power supply voltage is lower than a preset overdischarge protection voltage; and the protection unit controls the switch unit to turn off in response to an external control signal.

Further, the sleep control unit includes: a signal receiving subunit, a triggering subunit and a single-chip microcomputer, the signal receiving subunit is used for receiving external control signals; the triggering subunit is connected to the protection unit and the positive pole of the power supply; the single-chip microcomputer is connected to the Between the protection unit and the signal receiving subunit, the single-chip microcomputer is used to control the triggering subunit to conduct according to an external control signal.

Further, the signal receiving subunit includes an infrared receiving head, a first capacitor, a first resistor and a second resistor, and one end of the first capacitor is connected to the power supply end of the infrared receiving head and is connected to the first resistor. One end of the first resistor is connected to the positive pole of the power supply, the other end of the first capacitor is connected to and grounded to the grounding end of the infrared receiving head, and the control end of the infrared receiving head is connected to the One end of the second resistor is connected, the other end of the second resistor is connected to the single-chip microcomputer, the power supply terminal of the single-chip microcomputer is connected to the positive pole of the power supply, and the ground terminal of the single-chip microcomputer is grounded.

Further, the triggering subunit includes a triode and a third resistor, the collector of the triode is connected to the positive electrode of the power supply, and the emitter of the triode is connected to the protection unit and to one end of the third resistor. The other end of the third resistor is connected to the negative pole of the power supply, and the base of the triode is connected to the sleep control terminal of the single chip microcomputer.

Further, the protection unit includes: a collection subunit and a power supply protection chip, the collection subunit is connected to the positive pole of the power supply, and the collection subunit is used to collect the power supply voltage; the power supply protection chip is connected to the collection subunit and connected with the switch unit, the power protection chip is used to control the switch unit to disconnect when the power supply voltage is lower than the preset over-discharge protection voltage, and to control the switch unit when receiving an external control signal disconnect.

Further, the protection unit further includes a filtering subunit, which is connected to the collecting subunit and is connected to the negative electrode of the power supply.

Further, the switch unit includes a first switch tube, the output end of the first switch tube is connected to the negative pole of the power supply, and the control end of the first switch tube is connected to the discharge control end of the power protection chip , the input end of the first switch tube is connected to the negative electrode of the load.

Further, the first switch tube is a first N-channel MOS tube, the source of the first N-channel MOS tube is connected to the negative electrode of the power supply, and the gate of the first N-channel MOS tube is connected It is connected to the discharge control terminal of the power protection chip, and the drain of the first N-channel MOS transistor is connected to the negative electrode of the load.

A second aspect provides a control method for a sleep circuit, where the sleep circuit is the sleep circuit according to the first aspect, the sleep circuit is configured to execute the control method, and the control method includes: collecting the power supply voltage; compare the power supply voltage with the preset overdischarge voltage; when the power supply voltage is lower than the preset protection voltage, control the switch unit to disconnect; or, when receiving an external control signal, control the The switch unit is turned off.

In a third aspect, a lighting device is provided, comprising: a power supply, a light source, a controller, and the sleep circuit according to the first aspect, wherein the sleep circuit is connected between the power supply and the light source, and the control The controller is used to send the external control signal to control the sleep circuit to enter sleep.

The beneficial effect of the present invention is that, through the provided protection unit, switch unit and sleep control unit, when the protection unit detects that the power supply voltage is lower than the preset over-discharge protection voltage, the protection unit controls the switch unit to disconnect; and the protection unit responds to In response to an external control signal, the switch unit is controlled to disconnect, so that the power supply is disconnected from the switch unit, the sleep control unit, and the load, thereby disconnecting the power supply from the external circuit and load. Therefore, through the above two methods that can cut off the connection between the power supply and the external circuit and the load, the power supply can automatically stop the output in a low voltage state and stop the output through external control in a normal voltage state, so that the power consumption of the power supply is slowed down. In order to avoid the low voltage of the power supply as much as possible to ensure the life of the power supply.

Description of drawings

The specific embodiments of the present invention will be described in further detail below in conjunction with the accompanying drawings and examples. In the accompanying drawings:

Fig. 1 is the structural block diagram of the sleep circuit of the present invention;

Fig. 2 is the structural representation of the sleep circuit of the present invention;

3 is a schematic structural diagram of a signal receiving subunit in the sleep circuit of the present invention;

4 is a schematic structural diagram of a single-chip microcomputer in the sleep circuit of the present invention;

FIG. 5 is a flow chart of the control method of the sleep circuit of the present invention.

Detailed ways

Preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principle of the present invention, and are not intended to limit the protection scope of the present invention. The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

1-2, the present invention provides a sleep circuit 10, which is connected between a power source 20 and a load 30, the positive electrode of the power source 20 is connected to the positive electrode of the load 30, and the negative electrode of the power source 20 is connected to the negative electrode of the load 30. The sleep circuit 10 includes : the switch unit 100, the protection unit 200 and the sleep control unit 300, the switch unit 100 is connected between the negative pole of the power supply 20 and the negative pole of the load 30; the protection unit 200 is connected to the positive pole of the power supply 20 and the negative pole of the power supply 20, and is connected to the switch unit 100 to protect The unit 200 is used to control the switch unit 100 to be turned on or off; the sleep control unit 300 is connected to the protection unit 200, and the sleep control unit 300 is used to receive external control signals; wherein, the protection unit 200 is used when the voltage of the power supply 20 is lower than the preset overdischarge When the voltage is protected, the switch unit 100 is controlled to be turned off; and the protection unit 200 is controlled to be turned off when the protection unit 200 responds to an external control signal.

With the protection unit 200 , the switch unit 100 and the sleep control unit 300 provided, when the protection unit 200 detects that the voltage of the power supply 20 is lower than the preset over-discharge protection voltage, the protection unit 200 controls the switch unit 100 to disconnect, so that the power supply 20 Disconnecting the switch unit 100 , the sleep control unit 300 and the load 30 can greatly reduce the output of the power supply 20 , effectively cut off the output of the power supply 20 in a low voltage state, and ensure the life of the power supply 20 .

Furthermore, after the sleep control unit 300 receives the external control signal, the sleep control unit 300 makes the protection unit 200 control the switch unit 100 to disconnect, so as to disconnect the power supply 20 from the switch unit 100, the sleep control unit 300, and the load. 30 is connected, so that the output of the power supply 20 can be greatly reduced, so as to avoid the situation of low voltage of the power supply 20 as much as possible, so as to ensure the life of the power supply 20 .

Therefore, through the above two methods of cutting off the connection between the power supply 20 and the external circuit and the load 30, the power supply 20 can automatically stop output in a low voltage state or stop output through external control in a normal voltage state, so as to avoid the occurrence of the power supply 20 as much as possible. In the case of lower voltage, to ensure the life of the power supply 20.

Specifically, the preset over-discharge protection voltage is generally 90% of the nominal voltage of the power supply 20 . For example, the nominal voltage of the power supply 20 is 5V. When the protection unit 200 detects that the voltage of the power supply 20 is lower than 4.5V, it sends a shutdown signal to control the switch unit 100 to disconnect, so that the power supply 20 is disconnected from the switch unit 100, Connection of the sleep control unit 300 and the load 30 .

Further, in this embodiment, the external control signal is a signal sent from the controller, for example, it may be a remote control, a mobile phone, a tablet computer, and the like.

In one embodiment, referring to FIGS. 2-4, the sleep control unit 300 includes: a signal receiving subunit 301, a triggering subunit 302 and a single-chip microcomputer 303, the signal receiving subunit 301 is used for receiving external control signals; the triggering subunit 302 is connected to The protection unit 200 and the power supply 20 are connected to the positive pole; the single-chip microcomputer 303 is connected between the protection unit 200 and the signal receiving sub-unit 301, and the single-chip microcomputer 303 is used to control the triggering sub-unit 302 to conduct according to the external control signal. In this embodiment, the signal receiving subunit 301 is used to receive an external control signal, and after receiving the external control signal, it sends a control signal to the single-chip microcomputer 303. After receiving the control signal, the single-chip microcomputer 303 sends a sleep trigger signal, and the triggering subunit 302 receives the control signal. After the dormancy trigger signal, a dormancy signal is sent, and finally the protection unit 200 controls the switch unit 100 to disconnect after receiving the dormancy signal, thereby disconnecting the power supply 20 from the switch unit 100, the signal receiving subunit 301, the triggering subunit 302, The single chip 303 and the load 30 are connected to achieve the purpose of reducing the power consumption of the power supply 20 .

In one embodiment, referring to FIGS. 3-4 , the signal receiving subunit 301 includes an infrared receiving head U1, a first capacitor C1, a first resistor R1 and a second resistor R2, and one end of the first capacitor C1 is connected to the infrared receiving head U1 The power supply end of the first resistor R1 is connected to one end of the first resistor R1, the other end of the first resistor R1 is connected to the positive pole of the power supply 20, and the other end of the first capacitor C1 is connected to the ground end of the infrared receiving head U1 and grounded. The control terminal is connected to one end of the second resistor R2, the other end of the second resistor R2 is connected to the single-chip microcomputer 303, the power supply terminal of the single-chip microcomputer 303 is connected to the positive pole of the power supply 20, and the ground terminal of the single-chip microcomputer 303 is grounded.

In this embodiment, the signal receiving sub-unit 301 is selected as the infrared receiving head U1, the infrared receiving head U1 is cheap in cost and has a mature solution, which can save a certain development cost. Of course, it can be understood that the signal receiving sub-unit 301 can also use a Bluetooth or WiFi module, which can be selected according to actual needs. Further, the function of the single-chip microcomputer 303 is to convert the infrared signal received by the infrared receiving head U1 into an electrical signal that can be recognized by the circuit.

In one embodiment, referring to FIG. 2 , the trigger sub-unit 302 includes a transistor Q and a third resistor R5 , the collector of the transistor Q is connected to the positive electrode of the power supply 20 , the emitter of the transistor Q is connected to the protection unit 200 and is connected to the third One end of the resistor R5 is connected, the other end of the third resistor R5 is connected to the negative electrode of the power supply 20 , and the base electrode of the transistor Q is connected to the sleep control end of the single-chip microcomputer 303 . In this embodiment, the third resistor R5 is used to collect the voltage of the power supply 20 to feed back to the protection chip. The transistor Q is used as a switch. After receiving the sleep trigger signal sent by the single-chip microcomputer 303 , the transistor Q turns itself on or off. The transistor Q has the advantages of fast response and long service life, which can effectively ensure the service life of the sleep circuit 10 . Of course, it can be understood that, after corresponding changes are made to the circuit, the transistor Q can also be replaced with another switch tube, such as a MOS tube. Preferably, in order to prevent the transistor Q from being damaged by excessive current, a fifth resistor R5 is connected between the base of the transistor Q and the sleep control terminal of the single-chip microcomputer 303 to limit the current.

In one embodiment, referring to FIG. 2 , the protection unit 200 includes: a collection subunit and a power supply protection chip U3, the collection subunit is connected to the positive pole of the power supply 20, and the collection subunit is used to collect the voltage of the power supply 20; the power supply protection chip U3 is connected to the collection The subunit is connected to the switch unit 100, and the power protection chip U3 is used to control the switch unit 100 to disconnect when the voltage of the power supply 20 is lower than the preset over-discharge protection voltage, and to control the switch unit 100 to disconnect when an external control signal is received. . In this embodiment, the collection subunit is a fourth resistor R4, one end of the fourth resistor R4 is connected to the positive pole of the power supply 20, the other end is connected to the power supply terminal of the power protection chip U3, and the ground terminal of the power supply protection chip U3 is connected to the power supply The negative pole of 20 is connected, and the current detection terminal of the power protection chip U3 is connected to the emitter of the transistor Q. The fourth resistor R4 is used to collect the voltage of the power supply 20 so that the protection unit 200 can collect the voltage of the power supply 20 . By connecting the current detection terminal of the power protection chip U3 to the emitter of the transistor Q, the power protection chip U3 can receive the potential signal sent by the transistor Q.

In one of the embodiments, referring to FIG. 2 , the protection unit 200 further includes a filtering subunit, which is connected to the collecting subunit and is connected to the negative pole of the power supply 20 . The filtering subunit is a second capacitor C2, one end of which is connected to the other end of the fourth resistor R4, and the other end is connected to the ground end of the power protection chip U3. Through the filtering effect of the second capacitor C2, the power supply 20 can be filtered out. The AC component makes the current received by the power protection chip U3 smoother and prolongs the service life of the power protection chip U3.

In one embodiment, referring to FIG. 2 , the switch unit 100 includes a first switch transistor MOS1 , the output terminal of the first switch transistor MOS1 is connected to the negative pole of the power supply 20 , and the control terminal of the first switch transistor MOS1 is connected to the power supply protection chip U3 . The discharge control end is connected, and the input end of the first switch tube MOS1 is connected to the negative electrode of the load 30 . In this embodiment, the first switch transistor MOS1 is selected as the switch unit 100 , which can be turned on or off by pressurizing or depressurizing it, so as to facilitate the automatic control of the circuit.

In one embodiment, referring to FIG. 2 , the first switch transistor MOS1 is a first N-channel MOS transistor, the source of the first N-channel MOS transistor is connected to the negative electrode of the power supply 20 , the first N-channel MOS transistor is The gate is connected to the discharge control terminal of the power protection chip U3 , and the drain of the first N-channel MOS transistor is connected to the negative electrode of the load 30 . In this embodiment, when the power protection chip U3 detects that the voltage of the power supply 20 is lower than the preset voltage or receives a trigger signal, it sends a shutdown signal, and the shutdown signal turns off the first N-channel MOS transistor, thereby , the switch unit 100 is disconnected, so that the power supply 20 is disconnected from the switch unit 100 , the sleep control unit 300 , and the load 30 . When the power supply 20 is charged, the first N-channel MOS transistor is reconnected under the action of an external voltage, and the sleep circuit 10 resumes normal operation. Of course, it can be understood that in different circuit designs, a P-channel MOS transistor or a triode Q can also be used, and only the connection structure of the circuit can be changed.

Preferably, the switch unit 100 may further include a second N-channel MOS transistor MOS2, the source of the second N-channel MOS transistor MOS2 is connected to the drain of the first N-channel MOS transistor, and the second N-channel MOS transistor MOS2 The gate of the MOSFET is connected to the charging control terminal of the power protection chip U3, and the drain of the second N-channel MOS transistor MOS2 is connected to the other terminal of the third resistor R5. In this embodiment, the function of the second N-channel MOS transistor MOS2 is that when the power supply 20 is charging, the power protection chip U3 detects that the voltage of the power supply 20 exceeds a preset overcharge protection voltage, and the preset overcharge protection voltage is 120% of the nominal voltage of the power supply 20. At this time, the power protection chip U3 controls the second N-channel MOS transistor MOS2 to turn off, so that the power supply 20 is disconnected from the charging power supply 20, so as to achieve the effect of overcharge protection.

Referring to FIG. 5 , the present invention provides a control method of the sleep circuit 10 . The sleep circuit 10 is the sleep circuit 10 as described above, and the sleep circuit 10 is used to execute the control method, and the control method includes:

S01. Collect the voltage of the power supply 20;

S02, compare the voltage of the power supply 20 with the preset overdischarge voltage;

S03. When the voltage of the power supply 20 is lower than the preset protection voltage, the switch unit 100 is controlled to be disconnected; or,

S04. When receiving an external control signal, control the switch unit 100 to turn off.

In this embodiment, when the power protection chip U3 detects that the voltage of the power supply 20 is lower than the preset over-discharge protection voltage, the power protection chip U3 sends a shutdown signal to control the first N-channel MOS transistor to be turned off, so that the power supply 20 is turned off. The connection with the switch unit 100 , the sleep control unit 300 , and the load 30 is disconnected.

Further, when the infrared receiving head U1 receives an external control signal, it sends a control signal, the single-chip 303 sends a sleep trigger signal after receiving the control signal, and the transistor Q is turned on after receiving the sleep trigger signal, thereby sending a sleep signal, The potential of the current detection terminal of the power protection chip U3 is pulled up, so that the power protection chip U3 enters the protection state, thus, the power protection chip U3 sends a shutdown signal to control the first N-channel MOS transistor to be disconnected, so that the power supply 20 is disconnected Connection to the switch unit 100 , the sleep control unit 300 , and the load 30 .

Therefore, on the electronic product installed with the sleep circuit 10 of the present invention, the output of the power supply 20 can be cut off when the voltage of the power supply 20 is too low, so that the power consumption of the power supply 20 can be slowed down; and when the electronic product is not in use, the power supply 20 can be cut off. Output, the power consumption of the power supply 20 is slowed down, so as to avoid the situation that the voltage of the power supply 20 is low as far as possible, the above two ways of disconnecting the power supply 20 from the external circuit can ensure the life of the power supply 20 to ensure the use of electronic products life.

The present invention also provides a lighting device, which includes: a power source 20, a light source, a controller, and the above-mentioned sleep circuit 10, the sleep circuit 10 is connected between the power source 20 and the light source, and the controller is used to send an external control signal to The sleep circuit 10 is controlled to enter sleep mode. By setting the sleep circuit 10 on the lighting device, the connection between the power supply 20 and the external circuit can be cut off when the voltage of the power supply 20 of the lighting device is too low, so that the power consumption of the power supply 20 can be slowed down; The connection between the power supply 20 and the external circuit is cut off, so that the power consumption of the power supply 20 is slowed down, so as to avoid the situation that the voltage of the power supply 20 is low as far as possible, and the above two ways of disconnecting the power supply 20 from the external circuit can ensure the life of the power supply 20 , to ensure the service life of the lighting device.

It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them. For those skilled in the art, the technical solutions recorded in the above embodiments can be modified, or some of the technical features can be modified. Equivalent replacements are made; and all such modifications and replacements shall fall within the protection scope of the appended claims of the present invention.

Claims (10)

1. A sleep circuit connected between a power source and a load, the power source anode being connected to the load anode and the power source cathode being connected to the load cathode, the sleep circuit comprising:

a switching unit connected between the power source negative electrode and the load negative electrode;

the protection unit is connected with the positive electrode of the power supply and the negative electrode of the power supply and is connected with the switch unit, and the protection unit is used for controlling the switch unit to be switched on or switched off;

the dormancy control unit is connected with the protection unit and used for receiving an external control signal;

when the power supply voltage is lower than a preset over-discharge protection voltage, the protection unit controls the switch unit to be switched off; and the protection unit controls the switch unit to be switched off when responding to an external control signal.

2. The sleep circuit according to claim 1, wherein the sleep control unit comprises:

the signal receiving subunit is used for receiving an external control signal;

a trigger subunit connected to the protection unit and the power supply positive electrode;

and the single chip microcomputer is connected between the protection unit and the signal receiving subunit, and is used for controlling the conduction of the trigger subunit according to an external control signal.

3. The sleep circuit according to claim 2, wherein the signal receiving subunit includes an infrared receiving head, a first capacitor, a first resistor, and a second resistor, one end of the first capacitor is connected to a power end of the infrared receiving head and is connected to one end of the first resistor, the other end of the first resistor is connected to the positive electrode of the power supply, the other end of the first capacitor is connected to a ground end of the infrared receiving head and is grounded, a control end of the infrared receiving head is connected to one end of the second resistor, the other end of the second resistor is connected to the single chip, the power end of the single chip is connected to the positive electrode of the power supply, and the ground end of the single chip is grounded.

4. The sleep circuit of claim 3, wherein: the trigger subunit includes triode and third resistance, the collecting electrode of triode with the positive pole of power is connected, the projecting pole of triode with the protection unit is connected and with the one end of third resistance is connected, the other end of third resistance with the negative pole of power is connected, the base of triode with the dormancy control end of singlechip is connected.

5. The sleep circuit according to any of claims 1 to 4, wherein the protection unit comprises:

the acquisition subunit is connected with the positive electrode of the power supply and is used for acquiring the power supply voltage;

the power protection chip is used for controlling the power supply voltage to be lower than the preset over-discharge protection voltage to disconnect the switch unit and to control the switch unit to disconnect when receiving an external control signal.

6. The sleep circuit of claim 5, wherein the protection unit further comprises a filtering subunit connected to the acquisition subunit and to the negative terminal of the power supply.

7. The sleep circuit of claim 6, wherein: the switch unit comprises a first switch tube, the output end of the first switch tube is connected with the negative electrode of the power supply, the control end of the first switch tube is connected with the discharge control end of the power supply protection chip, and the input end of the first switch tube is connected with the negative electrode of the load.

8. The sleep circuit of claim 7, wherein: the first switch tube is a first N-channel MOS tube, a source electrode of the first N-channel MOS tube is connected with a negative electrode of the power supply, a grid electrode of the first N-channel MOS tube is connected with a discharge control end of the power supply protection chip, and a drain electrode of the first N-channel MOS tube is connected with a negative electrode of the load.

9. A control method of a sleep circuit according to any one of claims 1 to 8, wherein the sleep circuit is used for executing the control method, and the control method comprises:

collecting the power supply voltage;

comparing the power supply voltage with a preset over-discharge voltage;

when the power supply voltage is lower than a preset protection voltage, controlling the switch unit to be switched off; or,

and when receiving an external control signal, controlling the switch unit to be switched off.

10. An illumination device, comprising: a power source, a light source, a controller and a sleep circuit as claimed in any one of claims 1 to 8, the sleep circuit being connected between the power source and the light source, the controller being arranged to issue the external control signal to control the sleep circuit to go to sleep.

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