Power supply switching circuit

Abstract

The utility model discloses a power supply switching circuit, which comprises a resistor R1, a resistor R2, an MOS tube Q1, an MOS tube Q2 and an MOS tube Q3, the grid electrode of the Q2 is respectively connected with the first end of the resistor R1, the grid electrode of the Q1, the drain electrode of the Q3 and a first power supply, the source electrode of the Q2 is connected with the first end of the resistor R2 and the source electrode of the Q3 and is used as a power supply output end, the second end of the resistor R2 is connected with the grid electrode of the Q3 and the drain electrode of the Q1, the drain electrode of the Q2 is connected with a second power supply, and the first power supply is connected with the second power supply. And the source electrode of the Q1 and the second end of the resistor R1 are grounded. When power supply switching is carried out, due to the fact that the MOS tubes are adopted, diodes do not exist, and therefore the problems of power supply loss, heating, voltage drop of output voltage and the like do not exist. And when the first power supply is disconnected, the second power supply is automatically switched to realize the switching of the main power supply and the standby power supply.

Description

Technical Field

[0001] The utility model relates to the technical field of power management, and specifically, to a power supply switching circuit. Background Art

[0002] In many electrical devices, such as vehicle networking terminals, the power supply can be selected as the second power supply or the first power supply inside the electrical device. In the prior art, the circuits for switching between the second power supply and the first power supply can be roughly divided into two types: one is a diode-type main and standby power supply switching circuit, as shown in Figure 1 However, since the voltage drop of the diode is between 0.7 - 1.0V, when the current is large, the loss of the diode is also large, the heat generation is relatively serious, and the efficiency is low; the other is a single MOS transistor-type main and standby power supply switching circuit, as shown in Figure 2 It uses 1 PMOS transistor and 1 diode to realize the switching of the main and standby power supplies. Due to the voltage drop of 0.7 - 1.0 of the diode, the biggest drawback of this circuit is that the output voltage is 0.7 - 1.0V lower than the input voltage. Summary of the Utility Model

[0003] The purpose of the utility model is to provide a power supply switching circuit, which is used to solve the problems that the main and standby power supply switching circuit in the prior art has losses, heat generation, or the output voltage is lower than the input voltage due to the use of a diode.

[0004] The utility model solves the above problems through the following technical solutions:

[0005] A power supply switching circuit includes a resistor R1, a resistor R2, a MOS transistor Q1, a MOS transistor Q2, and a MOS transistor Q3. Among them, the gate of the MOS transistor Q2 is respectively connected to the first end of the resistor R1, the gate of the MOS transistor Q1, the drain of the MOS transistor Q3, and the first power supply. The source of the MOS transistor Q2 is connected to the first end of the resistor R2 and the source of the MOS transistor Q3 and serves as the power output terminal. The second end of the resistor R2 is connected to the gate of the MOS transistor Q3 and the drain of the MOS transistor Q1. The drain of the MOS transistor Q2 is connected to the second power supply. The source of the MOS transistor Q1 and the second end of the resistor R1 are grounded.

[0006] Working Principle:

[0007] When the first power supply is powered on, the G (gate) of MOS transistor Q1 is at the first power supply voltage, and the S (source) of MOS transistor Q1 is at 0V. MOS transistor Q1 is an NMOS. As long as the gate-source voltage (Vgs) of MOS transistor Q1 is greater than its turn-on voltage, MOS transistor Q1 conducts. After MOS transistor Q1 conducts, it pulls down the G of MOS transistor Q3, that is, the G of MOS transistor Q3 is close to 0V. Since the voltage drop of the body diode of MOS transistor Q3 is very small, the S of MOS transistor Q3 is approximately equal to the first power supply voltage. MOS transistor Q3 is a PMOS. As long as the gate-source voltage (Vgs) of MOS transistor Q3 is less than its turn-on voltage, MOS transistor Q3 conducts. At this time, the voltage between the gate and source of MOS transistor Q2 is the conduction voltage drop of MOS transistor Q3, and this voltage is generally dozens of millivolts (mV). MOS transistor Q2 is a PMOS. As long as the gate-source voltage (Vgs) of MOS transistor Q2 is not less than the turn-on voltage of MOS transistor Q2, MOS transistor Q2 turns off, and the second power supply is disconnected. At this time, the output voltage is powered by the first power supply, that is, output voltage = first power supply voltage. The circuit is completely powered by the first power supply.

[0008] When the first power supply is disconnected, the G of MOS transistor Q1 is pulled down to 0V by R1, and MOS transistor Q1 is cut off because the voltages of its gate and source are approximately equal. The G of MOS transistor Q2 is pulled down to 0V by resistor R1. The source of MOS transistor Q2 is approximately equal to 3.3V due to the effect of the body diode. Since MOS transistor Q2 is a PMOS, as long as the Vgs of MOS transistor Q2 is less than the turn-on voltage of MOS transistor Q2, MOS transistor Q2 conducts. The G of MOS transistor Q3 is pulled up to the second power supply by R2. Since MOS transistor Q3 is a PMOS, when Vgs is not less than its turn-on voltage, that is, Q3 is cut off. For the entire circuit, MOS transistor Q1 and MOS transistor Q3 are cut off, and the output voltage is powered by the second power supply, that is, output voltage = second power supply voltage. The circuit is completely powered by the second power supply.

[0009] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0010] When the present invention performs power supply switching, since MOS transistors are used and there are no diodes, there are no problems such as power loss, heating, and voltage drop in the output voltage. And when the first power supply is disconnected, it automatically switches to the second power supply to achieve the switching of the main and backup power supplies. Description of the Drawings

[0011] Figure 1 is the schematic diagram of the diode-type power supply switching circuit in the prior art;

[0012] Figure 2 is the schematic diagram of the single-MOS transistor power supply switching circuit in the prior art;

[0013] Figure 3This is the circuit schematic diagram of the present utility model. Specific embodiments

[0014] The present utility model will be further described in detail below in conjunction with embodiments, but the embodiments of the present utility model are not limited thereto.

[0015] Embodiment:

[0016] Combined with the attached Figure 3 As shown, a power supply switching circuit includes a resistor R1, a resistor R2, a MOS transistor Q1, a MOS transistor Q2, and a MOS transistor Q3. Among them, the gate of the MOS transistor Q2 is respectively connected to the first end of the resistor R1, the gate of the MOS transistor Q1, the drain of the MOS transistor Q3, and a first power supply. The source of the MOS transistor Q2 is connected to the first end of the resistor R2 and the source of the MOS transistor Q3 and serves as a power output terminal. The second end of the resistor R2 is connected to the gate of the MOS transistor Q3 and the drain of the MOS transistor Q1. The drain of the MOS transistor Q2 is connected to a second power supply. The source of the MOS transistor Q1 and the second end of the resistor R1 are grounded.

[0017] Working principle:

[0018] When the first power supply Vbat supplies power, the G (gate) of the MOS transistor Q1 is Vbat, and the S of the MOS transistor Q1 is 0V. The MOS transistor Q1 uses an NMOS. As long as the Vgs of the MOS transistor Q1 is greater than its turn-on voltage, the MOS transistor Q1 conducts. After the MOS transistor Q1 conducts, it pulls down the G of the MOS transistor Q3, that is, the G of the MOS transistor Q3 is close to 0V. Since the voltage drop of the MOS transistor body diode is very small, the S of the MOS transistor Q3 is approximately equal to Vbat. The MOS transistor Q3 uses a PMOS. As long as the Vgs of the MOS transistor Q3 is less than its turn-on voltage, the MOS transistor Q3 conducts. At this time, the voltage between the gate and the source of the MOS transistor Q2 is the conduction voltage drop of the MOS transistor Q3, and this voltage is generally several tens of millivolts (mV). The MOS transistor Q2 uses a PMOS. As long as the Vgs of the MOS transistor Q2 is not less than the turn-on voltage of the MOS transistor Q2, the MOS transistor Q2 turns off, and the second power supply VCC is disconnected. At this time, the output voltage Vout is supplied by the first power supply Vbat, that is, Vout = Vbat. The circuit is completely powered by Vbat.

[0019] When Vbat is disconnected, the G pole of MOS transistor Q1 is pulled down to 0V by R1. MOS transistor Q1 is cut off because the voltages of its gate and source are approximately equal. The G pole of MOS transistor Q2 is pulled down to 0V by resistor R1. The source of MOS transistor Q2 is approximately equal to 3.3V due to the effect of the body diode. Since MOS transistor Q2 is a PMOS, as long as the Vgs of MOS transistor Q2 is less than the turn-on voltage of MOS transistor Q2, MOS transistor Q2 conducts. The G pole of MOS transistor Q3 is pulled up to VCC by R2. Since MOS transistor Q3 is a PMOS, when Vgs is not less than its turn-on voltage, Q3 is cut off. In the whole circuit, MOS transistors Q1 and Q3 are cut off, and Vout is powered by VCC, that is, Vout = VCC. The circuit is completely powered by VCC.

[0020] In this solution, the output voltage is equal to the input voltage, and there is no voltage drop. Since no diode element is used, the voltage drop loss and heat loss caused by the use of diodes in the prior art are solved.

[0021] Although the present invention has been described herein with reference to its illustrative embodiments, the above embodiments are only the preferred embodiments of the present invention. The embodiments of the present invention are not limited by the above embodiments. It should be understood that those skilled in the art can design many other modifications and embodiments, and these modifications and embodiments will fall within the scope and spirit of the principles disclosed in this application.

Claims

1. A power supply switching circuit, characterized in that, It includes resistor R1, resistor R2, MOS transistor Q1, MOS transistor Q2, and MOS transistor Q3. Among them, the gate of the MOS transistor Q2 is respectively connected to the first end of the resistor R1, the gate of the MOS transistor Q1, the drain of the MOS transistor Q3, and the first power supply. The source of the MOS transistor Q2 is connected to the first end of the resistor R2 and the source of the MOS transistor Q3 and serves as the power output terminal. The second end of the resistor R2 is connected to the gate of the MOS transistor Q3 and the drain of the MOS transistor Q1. The drain of the MOS transistor Q2 is connected to the second power supply. The source of the MOS transistor Q1 and the second end of the resistor R1 are grounded.

2. The power supply switching circuit according to claim 1, wherein The MOS transistor Q1 is an NMOS transistor.

3. A power supply switching circuit according to claim 1, wherein The MOS transistor Q2 is a PMOS transistor.

4. The power supply switching circuit according to claim 1, wherein The MOS transistor Q3 is a PMOS transistor.

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