JPH058800U - Power supply switching circuit - Google Patents

Abstract

(57) [Summary] [Object] To provide a power supply switching circuit capable of always ensuring the operation of an integrated circuit device having a backup function such as a RAM. [Configuration] For example, when the switch 10 is turned on,
The voltage comparison circuit 2 compares the voltage V _{DD of the} battery 13 with the voltage V _{BAT of the} battery 14. If the voltage V _{DD of the} battery 13 is higher than the voltage V _{BAT of the} battery 14, the P-channel IG-FET 5 is turned on based on the outputs of the inverter circuits 3 and 4, and the P-channel IG-FET 6 is Turns off. Therefore, the voltage V _DD is supplied as the drive voltage for the RAM circuit block 12. The voltage comparison circuit 2 and the inverter circuits 3 and 4 are driven based on the output voltage of the power output terminal 9. [Effect] Even if the voltage V _{BAT of the} battery 14 is lowered, the normal operation of the integrated circuit device 1 can be guaranteed if the voltage V _{DD of the} battery 13 is a voltage that can guarantee the operation of the integrated circuit device 1. .. By providing the capacitor 11, it is possible to prevent the generation of noise.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a power supply switching circuit for comparing and switching two kinds of power supply voltages, and more particularly to a power supply switching circuit suitable for use in a semiconductor device having a backup function such as RAM.

[0002]

[Prior Art]

 FIG. 3 is a circuit diagram showing an integrated circuit device having a conventional power supply switching circuit. The integrated circuit device 1 has a power supply terminal 7 connected to a battery 13 for normal operation via a switch 10 and a power supply terminal 8 connected to a backup battery 14. The integrated circuit device 1 is configured as shown below. The voltage comparator circuit 2 has its + input terminal connected to the power supply terminal 7, and its − input terminal connected to the power supply terminal 8. The inverter circuit 3 inputs the comparison result of the power supply comparison circuit 2, inverts it, and outputs it. The inverter circuit 4 inputs the output of the inverter circuit 3, inverts it, and outputs it. The P-channel type insulated gate field effect transistor (hereinafter referred to as P-channel type IG-FET) 5 has its gate connected to the output terminal of the inverter circuit 3, its drain connected to the power supply terminal 7, and its source connected to it. It is connected to the power output terminal 9. The P-channel IG-FET 6 has its gate connected to the output terminal of the inverter circuit 4, its drain connected to the power supply terminal 8, and its source connected to the power supply output terminal 9. The drive voltage of the RAM circuit block 12 is supplied from the power supply output terminal 9, and the output of the inverter circuit 4 is supplied as the RAM control signal 16. The drive voltage of the voltage comparison circuit 2 and the inverter circuit 3 is supplied from the power supply terminal 8, and the drive voltage of the inverter circuit 4 is supplied from the power supply terminal 7.

In the integrated circuit device thus configured, when the switch 10 is turned on in the normal operation, the voltage comparison circuit 2 causes the voltage V of the battery 13 to rise._DDAnd the voltage V of the battery 14_{BA T} Are compared and the comparison result is output. In this case, the voltage V of the battery 13_DDIs the voltage V of the battery 14_BAT If it is higher than that, the P-channel type IG-FET 5 is turned on and the P-channel type IG-FET 6 is turned off based on the outputs of the inverter circuits 3 and 4. Therefore, as the drive voltage of the RAM circuit block 12, the voltage V_DDIs supplied. When the switch 10 is turned off, the P-channel type IG-FET 5 is turned off and the P-channel type IG-FET 6 is turned on. Therefore, the voltage V as the drive voltage of the RAM circuit block 12 is reduced._BAT Is supplied. In this way, the power supply of the integrated circuit device can be switched.

[0004]

[Problems to be solved by the device]

However, in the above-described conventional power supply switching circuit, the drive voltage of the voltage comparison circuit 2 and the inverter circuit 3 is supplied from the power supply terminal 8 and the drive voltage of the inverter circuit 4 is supplied from the power supply terminal 7, so that a backup If the voltage V _BAT of the battery 14 for operation drops below the operating voltage of the integrated circuit device 1, the operation of the integrated circuit device 1 cannot be guaranteed even if the voltage V _DD of the battery 13 for normal operation is supplied. There is a problem.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a power supply switching circuit that can always guarantee the operation of the integrated circuit device.

[0006]

[Means for Solving the Problems]

 A power supply switching circuit according to the present invention comprises a voltage comparison circuit for comparing voltages of a first power supply and a second power supply, a first inverter circuit for inputting a comparison result of the voltage comparison circuit, and a first inverter circuit of the first inverter circuit. A second inverter circuit for inputting an output, and a first P-channel type insulation having a gate connected to the output terminal of the first inverter circuit, a drain connected to the first power supply, and a source connected to an output terminal. A gate type field effect transistor, and a second P-channel type insulated gate having a gate connected to the output terminal of the second inverter circuit, a drain connected to the second power source, and a source connected to the output terminal. -Type field effect transistor and a capacitor connected between the output terminal and the ground terminal, and the voltage comparison circuit and the first and second inverter circuits output the output. And drives based on the output voltage of the child.

[0007]

[Action]

 In the present invention, the voltage comparison circuit compares the voltages of the first and second power supplies, and when the voltage of the first power supply is larger than the voltage of the second power supply, the first and second inverters. Based on the output of the circuit, the first P-channel type IG-FET is turned on and the second P-channel type IG-FET is turned off. At this time, the voltage of the first power supply is supplied to the output terminal. On the other hand, when the voltage of the second power supply is higher than the voltage of the first power supply, the first P-channel IG-FET is turned off based on the outputs of the first and second inverter circuits. , The second P-channel IG-FET is turned on. At this time, the voltage of the first power supply is supplied to the output terminal. Therefore, the driving voltage of the voltage comparison circuit and the first and second inverter circuits is supplied with the higher one of the output voltages of the output terminals, that is, the voltages of the first and second power supplies. Therefore, the operation of the integrated circuit device including this voltage comparison circuit can always be guaranteed. For example, when a battery for normal operation is used as the first power source and a battery for backup is used as the second power source, even if the voltage of the battery for backup decreases, the operation of the integrated circuit device Can always be guaranteed.

In the present invention, since the capacitance is connected between the output terminal and the ground terminal, it is possible to prevent the source voltage of the first and second P-channel IG-FETs from changing when the power source is switched. This can be prevented, and thus the circuit operation can be stabilized.

[0009]

【Example】

 Next, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an integrated circuit device having a power supply switching circuit according to a first embodiment of the present invention. The integrated circuit device 1 has its power supply terminal 7 connected to a normal operating battery 13 via a switch 10, and its power supply terminal 8 connected to a backup battery 14. The integrated circuit device 1 is configured as shown below. The + input end of the voltage comparison circuit 2 is connected to the power supply terminal 7, and the − input end thereof is connected to the power supply terminal 8. The inverter circuit 3 inputs the comparison result of the power supply comparison circuit 2, inverts it, and outputs it. The inverter circuit 4 inputs the output of the inverter circuit 3, inverts it, and outputs it. The P-channel IG-FET 5 has its gate connected to the output terminal of the inverter circuit 3, its drain connected to the power supply terminal 7, and its source connected to the power supply output terminal 9. The P-channel type IG-FET 6 has its gate connected to the output terminal of the inverter circuit 4, its drain connected to the power supply terminal 8 and its source connected to the power supply output terminal 9. The drive voltage of the RAM circuit block 12 is supplied from the power supply output terminal 9, and the output of the inverter circuit 4 is supplied as the RAM control signal 16. One end of the capacitor 11 is connected to the power output terminal 9 and the other end is grounded. The drive voltage of the voltage comparison circuit 2 and the inverter circuits 3 and 4 is supplied from the power output terminal 9.

In the integrated circuit device configured as above, when the switch 10 is turned on during the normal operation, the voltage comparison circuit 2 causes the voltage V of the battery 13 to rise._DDAnd the voltage V of the battery 14_{BA T} Are compared and the comparison result is output. In this case, the voltage V of the battery 13_DDIs the voltage V of the battery 14_BAT If it is higher than that, the P-channel type IG-FET 5 is turned on and the P-channel type IG-FET 6 is turned off based on the outputs of the inverter circuits 3 and 4. Therefore, as the drive voltage of the RAM circuit block 12, the voltage V_DDIs supplied. When the switch 10 is turned off, the P-channel type IG-FET 5 is turned off and the P-channel type IG-FET 6 is turned on. Therefore, the voltage V as the drive voltage of the RAM circuit block 12 is reduced._BAT Is supplied. In this way, the power supply of the integrated circuit device can be switched.

According to this embodiment, when the switch 10 is turned on, the drive voltage of the voltage comparison circuit 2 and the inverter circuits 3 and 4 is the voltage of the battery 13 via the P-channel IG-FET 5. Since V _DD is supplied, even if the voltage V _{BAT of the} battery 14 is a voltage that cannot guarantee the operation of the integrated circuit device 1, the voltage V _{DD of the} battery 13 must be a voltage that guarantees the operation of the integrated circuit device 1. Thus, the normal operation of the integrated circuit device 1 can be guaranteed.

In this embodiment, since the source capacitances of the P-channel type IG-FETs 5 and 6 are connected, the source voltage of the P-channel type IG-FETs 5 and 6 fluctuates due to the operating current when the power source is switched. This can be prevented, and the generation of noise can be prevented. As a result, the circuit operation can be stabilized.

FIG. 2 is a circuit diagram showing an integrated circuit device having a power supply switching circuit according to a second embodiment of the present invention. In this embodiment, the power source of the RAM integrated circuit 15 provided outside the integrated circuit device 1 is switched. Therefore, in FIG. 2, the same parts as those in FIG. The description is omitted.

In the present embodiment, a RAM integrated circuit 15 is provided outside the integrated circuit device 1 instead of the RAM circuit block 12 in FIG. 1, and the RAM integrated circuit 15 has a driving voltage of the power supply output terminal 9 And the output of the inverter circuit 4 is supplied as the RAM control signal 16.

In this case, if the voltage V _{DD of the} battery 13 is a voltage that can guarantee the operation of the integrated circuit device 1 and the RAM integrated circuit 15, the switch 10 can operate even if the voltage V _{BAT of the} battery 14 is lowered. It is possible to guarantee normal operation when in the on state.

[0017]

[Effect of the device]

 As described above, according to the present invention, the higher one of the voltages of the first and second power supplies is supplied to the drive voltage of the voltage comparison circuit for controlling switching and the first and second inverter circuits. Therefore, the operation of the integrated circuit device can always be guaranteed.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an integrated circuit device including a power supply switching circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing an integrated circuit device including a power supply switching circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing an integrated circuit device including a conventional power supply switching circuit.

[Explanation of symbols]

1; Integrated circuit device 2; Voltage comparison circuit 3, 4; Inverter circuit 5, 6; P-channel insulated gate field effect transistor 7, 8; Power supply terminal 9; Power supply output terminal 10; Switch 11; Capacitance 12; RAM circuit Blocks 13 and 14; Battery 15; RAM integrated circuit 16; RAM control signal

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location 7832-5B G06F 1/00 335 C

Claims (1)

Claims for utility model registration 1. A voltage comparison circuit for comparing the voltages of the first and second power supplies, a first inverter circuit for inputting the comparison result of the voltage comparison circuit, and the first A second inverter circuit for inputting the output of the first inverter circuit, a first inverter circuit having a gate connected to the output terminal of the first inverter circuit, a drain connected to the first power supply, and a source connected to the output terminal. P-channel type insulated gate field effect transistor, and second P-channel type whose gate is connected to the output terminal of the second inverter circuit, drain is connected to the second power source and source is connected to the output terminal. An insulated gate field effect transistor; and a capacitor connected between the output terminal and the ground terminal, wherein the voltage comparison circuit and the first and second inverter circuits are Power supply switching circuit, characterized in that the drive based on the output voltage of the output terminal.