JPH0352010A - Power source switching circuit - Google Patents

Abstract

PURPOSE:To switch two power sources irrelevantly to whether their output voltages are large or small by switching the biases of the substrates of analog switches by using the other power sources and adding transistors(TR) to be driven by level shifting circuits in series with an analog switch. CONSTITUTION:The transistors 5 and 6 are added in series between two power source terminals and the TRs of the switch so as to securely turn off the TRs 1 - 4 of the switch even if the large-small relation between the output voltages of the two power sources -V1 and -V2 changes, and the TRs are driven by the level shifting circuits 7 and 9. Further, MOS TRs 5 and 6 are provided between the 1st and 2nd power source terminals and substrate so as to switch the potentials of the substrate of the MOS TRs 1 - 4 constituting the switch, and their gates are connected to the 2nd and 1st power source terminals in a cross state. Consequently, the two power sources can be switched without reference to whether their output voltages are large or small.

Description

[Detailed description of the invention]

[Industrial Application Field J] The present invention relates to a power supply switching circuit installed in a semiconductor integrated circuit (hereinafter referred to as an IC), which switches between two different power supplies to supply power to circuits inside the IC.

[Summary of the Invention 1] The present invention enables two different analog switch substrate biases to be switched using different power supplies, and a transistor driven by a level shift circuit to be added in series to the analog switch. This prevents through-current from flowing even if the magnitude relationship between the power supplies and the other power supply changes while one of the power supplies is turned on by a control signal. [Prior Art] For example, in ICs for watches, a power supply switching circuit as shown in Fig. 2 has traditionally been used to prevent a temporary drop in power supply voltage when driving a buzzer or lamp. This power supply switching circuit has a drain connected to a negative power supply voltage -Vl, a source and a substrate connected to a negative power supply voltage -VSS, and a gate connected to an inverter 8 that inverts a control signal inputted from a control input signal terminal 10. It consists of an N-channel MOS transistor 2, which is connected to a power source, and an N-channel MOS transistor 3, whose drain is connected to a power supply voltage VSS, whose source and substrate are connected to a power source voltage V2, and whose gate is connected to a control terminal 10. The configuration is such that either one of the negative power supply voltage -Vt and the negative power supply voltage -V2 is output as the negative power supply voltage -vSS. A watch IC usually has two power supply systems, 1.5V and 3V, and with the IC board connected to GND, -1.5V is connected to the negative power supply -Vl, and -3V is connected to the negative power supply -V2. By applying a control signal, the IC can be temporarily turned off when driving a buzzer or lamp.
The internal power supply is switched from l5V to -3V.

[Problem to be solved by the invention]

In the conventional circuit explained based on FIG. 2, when the negative power supply voltage -v2 becomes higher than the negative power supply voltage -Vl, the diode between the substrate and drain of the transistor is forward biased, and the current flows. For this reason. The transistor will not function properly as a switching element. Therefore, in this circuit, the magnitude relationship of the power supply voltage to be switched must be constant, and it had the disadvantage that it could not be used as a general power supply changeover switch. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved power switching circuit capable of overcoming the above-mentioned problems in the prior art. [A Thousand Steps to Solve the Problem] In order to achieve the above object, in the present invention, two power supply terminals are connected so that the transistor of the switch can be turned off reliably even if the magnitude relationship between the output voltages of the two power supplies changes. A transistor was added in series between the switch and the switch transistor, and the structure was configured to be driven by a level shift circuit. Further, in order to switch the potential of the substrate of the MOS transistor serving as a switch, MOS transistors are provided between the first and second power supply terminals and the above substrate, and each gate is connected to the second and first power supply terminal. Connected like a sash.

[Operation} When the control input terminal is connected to the GND level, the negative voltage -VSS is equal to the negative voltage -V2. I
Since the inside of C is driven by this negative voltage -V2, the negative voltage -V
It will be between 2. When the negative voltage -V2 becomes a higher potential (lower in terms of voltage) than the negative voltage -Vl, the amplitude of the control signal becomes smaller than the negative voltage -Vl, so the amplitude is changed to the reference voltage GND by level shift. and the negative voltage -Vl, and turn off the series transistor on the negative power supply -vl side. Furthermore, due to the transistors connected in a sash-like configuration, the potential of the substrate does not rise above the potential equal to the lower of the negative voltage 1Vt and the negative voltage 1V2 plus the forward voltage of the diode. Further, the potential of the substrate is a negative voltage −V
It does not fall below the lower of the lower value of l and the negative voltage -V2, and the value obtained by subtracting M{a of the MOS transistor from the higher value. [Example] The present invention will be explained in detail below with reference to the drawings. FIG. 1 shows an embodiment of the present invention using an N-channel MOS transistor. In Figure 1. MOS transistor 3 and MOS transistor 4 are driven by a control signal, and are turned ON between negative voltage -VSS and negative voltage -V2.
/OFF L is here. MOSl-Landisk l and M
The OS transistors 2 are each driven by a signal having a phase opposite to the control signal, and are turned ON/OFF between a negative voltage -VSS and a negative voltage -Vl. MOS transistor l
The output signal of the inverting level shift circuit 7 connected to the power supply Vt is input to the gate of the . MOS transistor 2
The output signal of the inverter 8 connected to the power supply -VSS is input to the gate of the inverter 8. The gate of the MOS transistor 4 is connected to the output of a non-inverting level shift circuit connected to a negative voltage -V2. Further, a normal rotation type level shift circuit, an inversion type level shift circuit, an inverter,
A control signal input terminal 10 is connected to the MOS transistor 3. On the other hand, the MOS transistors 1, 2, 3, and 4 have a common substrate, and are connected to the power source -Vl and the power source -V2 via MOS transistors 5 and 6, respectively. M
The OSl-transistors 5 and 6 are driven by the power supply -v2 and the power supply -Vl, respectively. In a power supply switching circuit having such a configuration, when the control input terminal 10 is at the GND level, a negative voltage -
vSS becomes a level equal to the negative voltage -v2. When the negative voltage -V2 is a lower potential than the negative voltage -Vl, the potential of the substrate does not become higher than -V2 by more than the forward voltage of the diode. This is because when the voltage increases, charge flows from the board toward the power supply V2. Further, when the potential of the substrate decreases to a potential lower than -Vl by more than the threshold value of the MOSI transistor, the transistor 6 becomes conductive and charge flows between the substrate and the power source -v2. At this time, if the potential of the substrate is higher than -V2, positive feedback is applied and the transistor 6 is turned on even further. For this purpose, the board is fixed at -■2. Moreover, at this time, if the potential of the substrate is lower than -v2, the potential of the substrate is pulled up in the -v2 direction, and the MOS transistor 6 is turned off.
F. In any case, the potential of the substrate remains within a certain range. MOS transistors 5 and 6 are connected to two power supplies -v1
Since it is symmetrical with respect to -v2, it is clear that this characteristic is maintained regardless of the magnitude relationship between negative voltage -vl and negative voltage -V2.Next, from negative voltage -Vl, Consider the case where the potential of negative voltage -V2 becomes high. As for the substrate, it is maintained within a constant potential as described above. by the way. Since -vSS is supplied as a power source inside the IC, the amplitude of the control signal and the inverter output is between the reference voltage GND and the negative voltage -v2. On the other hand, the inverting level shift circuit 7
The amplitude of the output of is between the reference voltage GND and the negative voltage -Vl, so even if it is assumed that the negative voltage -Vl becomes sufficiently lower than the negative voltage -v2, the MOS transistor l will definitely turn off. ．． Even when the potential of the control signal input terminal is -vSS, the circuit operation will be shown by the same explanation due to the symmetry of the circuit of the present invention, so the explanation will be omitted here. Note that in the above embodiment, N
An embodiment using channel MOSI transistors has been described. The present invention is not limited to the above embodiments, but can be applied to circuits using P-channel MOS transistors and other field effect transistors, and similar effects can be obtained. ．．

【Effect of the invention】

According to the present invention, as described above, it is possible to switch between two power supplies with different power supply voltages regardless of the magnitude of their output voltages, so by using it in a battery backup system, etc., it is possible to switch between two power supplies with different power supply voltages. This is extremely effective as it eliminates the need for circuitry.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the power supply switching circuit of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the power supply switching circuit of the present invention. FIG. 3 is a circuit diagram showing a power source switching circuit. 1 to 6 ・ 7 ・ ・ 8 ・ ・ ・ Transistor ・ Inverting type level shift circuit ・ Inverter 9 ・ Non-inverting type level shift circuit 10 ・ Control signal input terminal or higher

Claims (1)

[Claims] Provided on a common electrically connected board,
first, second, third, and fourth MOS transistors connected in series; a first power supply terminal connected to the source of the first MOS transistor; and a first power terminal connected to the source of the fourth MOS transistor. a second power supply terminal provided on the common substrate; a fifth MOS transistor provided on the common substrate and having a drain connected to the first power supply terminal and a source connected to the substrate; a sixth MOS transistor having a drain connected to the second power supply terminal and a source connected to the substrate; and an inverted type MOS transistor connected to the first power supply terminal and inputting its output to the gate of the first MOS transistor. a level shift circuit, a third power supply terminal connected to a common drain of the second and third MOS transistors, and a third power supply terminal connected to the third power supply terminal and inputting an output to the gate of the second MOS transistor; an inverter connected to the second power supply terminal and inputting an output to the gate of the fourth MOS transistor; a gate of the third MOS transistor and the inverting level shifter; , and a control signal input terminal that is a common connection point with each input terminal of the normal rotation type level shifter.