Button cell power-saving circuit for real-time clock circuit

Abstract

The utility model discloses a button cell power-saving circuit used for a real-time clock circuit. The button cell power-saving circuit comprises a power supply, a diode, an RTC chip, a power field effect transistor and a button cell. The power supply is used for providing power supply voltage for the RTC power supply loop; the anode of the diode is connected to the power supply, and the cathode is connected to the power input end of the RTC chip; the drain electrode of the power field effect transistor is connected to the power input end of the RTC chip, the source electrode is connected to the positive electrode of the button cell, and the grid electrode is connected to a power supply so as to control the conduction state of the power field effect transistor; when the power supply supplies power normally, the RTC chip obtains voltage from the power supply through the diode, at the moment, the power field effect transistor is not conducted, and the button battery does not output current; when the external power supply loses power, the voltage of the power supply is reduced to 0, the power field effect transistor is conducted, and the button cell supplies power to the RTC chip. The power consumption can be reduced, and the service life of the button cell is prolonged.

Description

Technical Field

[0001] The utility model relates to the technical field of button battery circuits, in particular to a button battery power saving circuit used in a real-time clock circuit. Background Art

[0002] In the prior art, button batteries are widely used as backup power sources in devices such as real-time clock circuits (RTCs). However, conventional button battery control circuits usually use at least two Schottky diodes, which not only have the problem of high power consumption, but also part of the power is consumed by the Schottky diodes, and the full power of the button battery cannot be provided to the real-time clock circuit. Utility Model Content

[0003] The utility model aims to provide a button battery power saving circuit for a real-time clock circuit, which can reduce power consumption and extend the service life of the button battery.

[0004] In order to solve the above technical problems, the utility model provides a button battery power saving circuit for a real-time clock circuit, comprising a power supply, a diode, an RTC chip, a power field effect transistor and a button battery;

[0005] The power supply is used to provide a power supply voltage for the RTC power supply circuit;

[0006] The positive electrode of the diode is connected to the power supply, and the negative electrode is connected to the power input terminal of the RTC chip;

[0007] The drain of the power field effect transistor is connected to the power input terminal of the RTC chip, the source is connected to the positive electrode of the button battery, and the gate is connected to the power supply to control the conduction state of the power field effect transistor;

[0008] When the power supply is supplying power normally, the RTC chip obtains voltage from the power supply through the diode, at which time the power field effect transistor is not turned on and the button battery does not output current; when the external power supply loses power, the voltage of the power supply drops to 0, the power field effect transistor is turned on, and the button battery supplies power to the RTC chip.

[0009] Furthermore, the power supply includes a direct current power supply with a voltage range of 3.0 to 3.6V.

[0010] Furthermore, the diode includes a Schottky diode.

[0011] Furthermore, the power field effect transistor includes a P-channel MOSFET.

[0012] Furthermore, the invention also includes: when the external power supply fails, the gate voltage range of the P-channel MOSFET is between -3.0V and -1.0V.

[0013] Furthermore, the on-resistance range of the P-channel MOSFET is between 16 and 24 mΩ.

[0014] Furthermore, the current range of the RTC chip is between 0.5 and 1.2 μA.

[0015] Through the above technical solution, the utility model has the following beneficial effects:

[0016] Through the setting of power supply, diode, RTC chip, power field effect transistor and button battery; and the power supply is used to provide normal power supply voltage for RTC power supply circuit; the positive pole of the diode is connected to the power supply, and the negative pole is connected to the power input terminal of the RTC chip, which is used to provide stable voltage for the RTC chip under normal power supply; the drain of the power field effect transistor is connected to the power input terminal of the RTC chip, the source is connected to the positive pole of the button battery, and the gate is connected to the power supply to control the conduction state of the power field effect transistor; when the power supply is normally supplied, the RTC chip obtains voltage from the power supply through the diode, at which time the power field effect transistor is not turned on, and the button battery does not output current; when the external power supply is lost, the voltage of the power supply drops to 0, the power field effect transistor is turned on, and the button battery starts to supply power to the RTC chip. This circuit uses the power field effect transistor as the button battery control circuit, and the voltage drop is only 16μV, while the traditional Schottky diode has a voltage drop of 0.3V. Therefore, this circuit uses the power field effect transistor as the button battery control circuit, which not only reduces the loss of the control circuit, but also saves the power of the button battery. Therefore, this circuit can reduce power consumption and extend the service life of the button battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the overall structure of a button battery power saving circuit for a real-time clock circuit in one embodiment of the utility model;

[0018] Figure 2 This is a schematic diagram of the structure of a traditional button battery control circuit.

[0019] In the figure, 1. power supply; 2. diode; 3. RTC chip; 4. power field effect transistor; 5. button battery. DETAILED DESCRIPTION

[0020] A button cell power saving circuit for a real-time clock circuit of the present invention will be described in more detail below in conjunction with the accompanying drawings, wherein preferred embodiments of the present invention are shown, and it should be understood that those skilled in the art may modify the present invention described herein while still achieving the advantageous effects of the present invention. Therefore, the following description should be understood as being widely known to those skilled in the art, and not as a limitation to the present invention.

[0021] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the accompanying drawings are in very simplified form and in non-precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0022] like Figure 1 As shown, an embodiment of the utility model proposes a button battery power saving circuit for a real-time clock circuit, including a power supply 1, a diode 2, an RTC chip 3 (Real Time Clock chip, i.e., real-time clock chip), a power field effect transistor 4 and a button battery 5.

[0023] Specifically, the power supply 1 is used to provide a power supply voltage for the RTC power supply circuit; the positive electrode of the diode 2 is connected to the power supply 1, and the negative electrode is connected to the power supply 1 input terminal of the RTC chip 3, and is used to provide a stable voltage for the RTC chip 3 under normal power supply conditions; the drain of the power field effect transistor 4 is connected to the power supply 1 input terminal of the RTC chip 3, the source is connected to the positive electrode of the button battery 5, and the gate is connected to the power supply 1 to control the conduction state of the power field effect transistor 4.

[0024] Among them, the RTC chip can adopt the following types of chips, such as DS3231, DS1302, NXP semiconductor RTC chip and BL5372, etc. The RTC chip can be selected according to actual conditions.

[0025] In a specific example, when the power supply 1 is supplying power normally, the RTC chip 3 obtains voltage from the power supply 1 through the diode 2, at which time the power field effect transistor 4 is not turned on, and the button battery 5 does not output current; when the external power supply fails, the voltage of the power supply 1 drops to 0, the power field effect transistor 4 is turned on, and the button battery 5 supplies power to the RTC chip 3 to ensure uninterrupted power supply to the RTC chip 3.

[0026] The power supply 1 includes a DC power supply with a voltage range of 3.0 to 3.6 V. For example, the voltage of the power supply 1 can be 3.0 V, 3.3 V, and 3.6 V. It is known to those skilled in the art that the voltage of the DC power supply can be selected according to actual conditions.

[0027] Preferably, the diode 2 comprises a Schottky diode. The Schottky diode has a lower forward voltage drop, which means that when the diode 2 is turned on, the voltage consumed by the Schottky diode is lower, thereby reducing the power consumption of the circuit. It is known to those skilled in the art that the diode 2 can also use other diodes 2 while achieving the same effect.

[0028] Preferably, the power field effect transistor 4 comprises a P-channel MOSFET. The P-channel MOSFET has a lower on-resistance in the on state, which means that the loss is smaller when it is turned on, thereby improving the efficiency of the circuit. In addition, the P-channel MOSFET has a fast switching characteristic, can respond quickly to the control signal, and realize fast switching.

[0029] Furthermore, the present embodiment also includes: when the external power supply fails, the gate voltage range of the P-channel MOSFET is between -3.0 and -1.0V. For example, it can be -3.0V, -2.5V, -2.0V and -1.0V. The on-resistance range of the P-channel MOSFET is between 16 and 24mΩ. For example, it can be 16mΩ, 20mΩ, 22mΩ and 24mΩ. The current range of the RTC chip 3 is between 0.5 and 1.2μA. For example, it can be 0.5μA, 0.8μA and 1.2μA.

[0030] In this embodiment, specifically, one part is the RTC power supply circuit under normal power supply conditions, which is composed of a 3.3V power supply 1, a Schottky diode and an RTC chip 3, etc.; the other part is the RTC power supply circuit under power failure conditions, which is composed of a button battery 5, a P-channel MOSFET and an RTC chip 3, etc.

[0031] In this embodiment, the rated voltage of the button battery 5 is 3V, the voltage of the power supply 1 is 3.3V under normal circumstances, and when the power is off, the voltage of the 3.3V power supply 1 drops to 0V, the minimum supply voltage of the RTC chip 3 is 1.8V, and the supply current is 0.8μA.

[0032] When the 3.3V power supply 1 is powered normally, the 3.3V power supply 1 passes through the Schottky diode to supply power to the RTC chip 3. The power supply voltage of the RTC chip 3 is about 3V, and the voltage drop of the entire power supply circuit is the conduction voltage drop of the Schottky diode, which is about 0.3V. When the 3.3V power supply 1 is powered normally, the gate voltage of the P-channel MOSFET is 0.3V (lower than its conduction threshold), the P-channel MOSFET is not turned on, and the output current of the button battery 5 is 0.

[0033] In the case of power failure, the voltage of 3.3V power supply 1 becomes 0V, the gate voltage of P-channel MOSFET is -3.0V, P-channel MOSFET is turned on, button battery 5 provides power supply 1 for RTC chip 3, the on-resistance of P-channel MOSFET is 20mΩ, the current of RTC chip 3 is 0.8μA, and the voltage drop of the whole power supply circuit is about 16μV. In the case of power failure, the reverse voltage of 3V is across the Schottky diode, and the Schottky diode is not turned on.

[0034] Therefore, by using the P-channel MOSFET as the button battery 5 control loop, the voltage drop is only 16μV, while the traditional Schottky diode voltage drop is 0.3V (such as Figure 2 As shown in FIG. 1 , the use of a P-channel MOSFET as the button battery 5 control loop greatly reduces the loss of the control loop and saves the power of the button battery 5 .

[0035] In summary, the button battery power saving circuit for a real-time clock circuit proposed by the utility model has the following advantages:

[0036] Through the setting of power supply, diode, RTC chip, power field effect transistor and button battery; and the power supply is used to provide normal power supply voltage for RTC power supply circuit; the positive pole of the diode is connected to the power supply, and the negative pole is connected to the power input terminal of the RTC chip, which is used to provide stable voltage for the RTC chip under normal power supply; the drain of the power field effect transistor is connected to the power input terminal of the RTC chip, the source is connected to the positive pole of the button battery, and the gate receives a control signal to control the conduction state of the power field effect transistor; when the power supply is normally supplied, the RTC chip obtains voltage from the power supply through the diode, at which time the power field effect transistor is not turned on, and the button battery does not output current; when the external power supply is lost, the voltage of the power supply drops to 0, the power field effect transistor is turned on, and the button battery starts to supply power to the RTC chip. This circuit uses the power field effect transistor as the button battery control circuit, and the voltage drop is only 16μV, while the traditional Schottky diode has a voltage drop of 0.3V. Therefore, this circuit uses the power field effect transistor as the button battery control circuit, which not only reduces the loss of the control circuit, but also saves the power of the button battery. Therefore, this circuit can reduce power consumption and extend the service life of the button battery.

[0037] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A button battery power saving circuit for a real-time clock circuit, characterized in that: Including power supply, diode, RTC chip, power field effect transistor and button battery; The power supply is used to provide a power supply voltage for the RTC power supply circuit; The positive electrode of the diode is connected to the power supply, and the negative electrode is connected to the power input terminal of the RTC chip; The drain of the power field effect transistor is connected to the power input terminal of the RTC chip, the source is connected to the positive electrode of the button battery, and the gate is connected to the power supply to control the conduction state of the power field effect transistor; When the power supply is supplying power normally, the RTC chip obtains voltage from the power supply through the diode, at which time the power field effect transistor is not turned on and the button battery does not output current; when the external power supply loses power, the voltage of the power supply drops to 0, the power field effect transistor is turned on, and the button battery supplies power to the RTC chip.

2. The button battery power saving circuit for a real-time clock circuit as claimed in claim 1, characterized in that: The power supply includes a direct current power supply with a voltage range of 3.0 to 3.6V.

3. The button battery power saving circuit for a real-time clock circuit as claimed in claim 1, characterized in that: The diode comprises a Schottky diode.

4. The button battery power saving circuit for a real-time clock circuit as claimed in claim 1, characterized in that: The power field effect transistor includes a P-channel MOSFET.

5. The button battery power saving circuit for a real-time clock circuit as claimed in claim 4, characterized in that: Also includes: When the external power supply is lost, the gate voltage of the P-channel MOSFET ranges from -3.0 to -1.0V.

6. The button battery power saving circuit for a real-time clock circuit as claimed in claim 5, characterized in that: The on-resistance of the P-channel MOSFET is in the range of 16-24 mΩ.

7. The button cell power saving circuit for a real-time clock circuit as claimed in claim 6, characterized in that: The current range of the RTC chip is between 0.5 and 1.2 μA.

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