JP2008282119A - Power source circuit and electronic equipment using power source circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow normal voltage detection even for the sharp transition of a main power source. <P>SOLUTION: This power source circuit includes a first active element and a second active element serially connected between a main power source line and an internal power source line; a third active element connected between a sub-power source line and an internal power source line; a voltage detection circuit connected to the mail power source line for outputting a voltage detection signal to be switched when the main power source is changed from an OFF state to a specific voltage or more, and to be switched when the main power source is changed from an ON state to a specific voltage or less; a holding time generation circuit connected to the main power source line for outputting a holding release signal a predetermined time after the main power source is changed to an ON state; a selection circuit for bringing the first active element into a conductive state, and for bringing the third active element into a non-conductive state when the voltage detection signal is switched, and the holding release signal is output, and for bringing the first active element into a non-conductive state, and for bringing the third active element into the conductive state when the voltage detection signal is switched; and a constant voltage generation circuit for outputting a constant voltage bringing the second active element into the conductive state. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a power supply circuit that performs power supply switching between a main power supply and a sub power supply, and an electronic apparatus using the power supply circuit.

  A real time clock (RTC) incorporated in an electronic device needs to always measure time even when the power of the product in which the electronic device is incorporated is turned off. For this reason, two power sources are generally required for the RTC power source. One is a main power supply that supplies operating power to the RTC when the power of the incorporated product is ON. The other is a sub power supply that supplies an operating power independent from the main power in preparation for when the main power is turned off. The sub power supply is generally supplied with power from a secondary battery. Therefore, the RTC is provided with a power supply switching circuit that detects the state of the main power supply and the sub power supply and selects one of them as an internal operation power supply.

  For example, Patent Document 1 describes a power supply switching circuit that switches between a main power supply and a secondary battery using a diode.

  The operation of the power supply switching circuit is usually a voltage detection circuit for detecting the ON / OFF state of the main power supply, and a power supply that switches either the main power supply or the sub power supply to the internal operation power supply according to the output value of the voltage detection circuit The switching circuit and a charging circuit for charging a secondary battery connected to the sub power source when the main power source is ON are configured.

  Of particular note is that the voltage detection circuit detects the transition from ON to OFF of the main power supply and the transition from OFF to ON so that the power supply switching circuit operates normally. The power supply necessary for its own operation needs to be an internal operation power supply to which a voltage is constantly supplied. As a result, the voltage detection circuit can always perform a voltage detection operation.

Japanese Patent Laid-Open No. 4-163652 (FIG. 3)

  However, when the main power supply changes suddenly from ON to OFF, the voltage detection circuit detects the voltage drop of the main power supply, and the internal operation power supply is delayed due to the time delay until the power supply switching circuit switches the internal operation power supply to the sub power supply. Causes a voltage drop instantaneously, which causes destruction of time data inside the RTC. In the worst case, the internal operation power supply also becomes the ground potential without switching the power supply. Furthermore, when the main power supply changes from OFF to ON, the internal operation power supply also changes abruptly, so that the voltage detection circuit may not be able to detect normal voltage for a certain period.

  The present invention has been made in view of such circumstances, and a power supply circuit that can normally detect a voltage even when the main power supply changes suddenly and can switch between a main power supply and a sub power supply, and An object of the present invention is to provide an electronic device using a power supply circuit.

  In order to solve the above problems, in the power supply circuit of the present invention, a main power supply line to which a main power supply is applied, a subpower supply line to which a subpower supply is applied, an internal power supply line to which an internal power supply is output, and the main power supply line A first active element and a second active element connected in series between a power supply line and the internal power supply line, and a third active element connected between the sub power supply line and the internal power supply line And a power supply switching circuit including the power supply circuit, connected to the main power supply line, and switched from a first potential to a second potential when the main power supply becomes a specified voltage or more from an OFF state, A voltage detection circuit that outputs a voltage detection signal that switches from the second potential to the first potential when the main power source becomes the specified voltage or less from the ON state; and the main power source line is connected to the main power source. A hold release signal is issued after a predetermined time from the ON state. A holding time generation circuit that is activated, and when the voltage detection signal is switched from the first potential to the second potential and the hold release signal is output, the first active element is turned on and the third active element is turned on. When the voltage detection signal is switched from the second potential to the first potential, the first active element is turned off and the third active element is turned on. And a constant voltage generation circuit that operates with the internal power supply and outputs a constant voltage that makes the second active element conductive to the gate terminal of the second active element. To do.

  According to this configuration, the period during which the voltage detection circuit becomes unstable at the rise of the main power supply can be held by the hold time generation circuit, so that the voltage of the main power supply can be normally detected and switching between the main power supply and the sub power supply can be performed. It can be carried out. Furthermore, since the constant voltage generation circuit and the second active element can prevent the internal power supply from dropping below the sub power supply when the main power supply suddenly falls, it is normal for a sudden transition of the main power supply. The voltage can be detected, and the main power supply and the sub power supply can be switched.

  In order to solve the above problems, in the power supply circuit of the present invention, a main power supply line to which a main power supply is applied, a subpower supply line to which a subpower supply is applied, an internal power supply line to which an internal power supply is output, A first active element and a second active element connected in series between the main power supply line and the internal power supply line, and a third active element connected between the sub power supply line and the internal power supply line. A power supply switching circuit including an active element, operates with the sub power supply, is connected to the main power supply line, and switches from the first potential to the second potential when the main power supply becomes a specified voltage or higher from the OFF state. A voltage detection circuit that outputs a voltage detection signal that switches from the second potential to the first potential when the main power source becomes the specified voltage or less from the ON state; and the voltage detection signal is changed from the first potential to the first potential. At the time of switching to the second potential, the first active When the child is turned on and the third active element is turned off, and the voltage detection signal is switched from the second potential to the first potential, the first active element is turned off and the first active element is turned off. And a constant voltage generation circuit that operates with the sub-power supply and outputs a constant voltage that makes the second active element conductive to the gate terminal of the second active element. It is a summary to include.

  According to this configuration, when the main power supply suddenly falls, the constant voltage generation circuit and the second active element can prevent the internal power supply from dropping below the sub power supply. However, the voltage can be detected normally and the main power supply and the sub power supply can be switched.

  In order to solve the above problems, in the power supply circuit of the present invention, a main power supply line to which a main power supply is applied, a subpower supply line to which a subpower supply is applied, an internal power supply line to which an internal power supply is output, A first active element and a second active element connected in series between the main power supply line and the internal power supply line, and a third active element connected between the sub power supply line and the internal power supply line. A power supply switching circuit including an active element, operates with the sub power supply, is connected to the main power supply line, and switches from the first potential to the second potential when the main power supply becomes a specified voltage or higher from the OFF state. A voltage detection circuit that outputs a voltage detection signal that switches from the second potential to the first potential when the main power source becomes the specified voltage or less from the ON state; and the main power source line; Hold release signal after a predetermined time since the A holding time generation circuit for outputting the first active element in a conductive state and the first active element when the voltage detection signal is switched from the first potential to the second potential and the holding release signal is output. When the voltage detection signal is switched from the second potential to the first potential, the first active element is turned off and the third active element is turned on. And a constant voltage generation circuit that operates with the sub-power supply and outputs a constant voltage that makes the second active element conductive to the gate terminal of the second active element. And

  According to this configuration, the period during which the voltage detection circuit becomes unstable at the rise of the main power supply can be held by the hold time generation circuit, so that the voltage of the main power supply can be normally detected and switching between the main power supply and the sub power supply can be performed. It can be carried out. Furthermore, since the constant voltage generation circuit and the second active element can prevent the internal power supply from dropping below the sub power supply when the main power supply suddenly falls, it is normal for a sudden transition of the main power supply. The voltage can be detected, and the main power supply and the sub power supply can be switched.

  In order to solve the above problems, the electronic device of the present invention is characterized by including the above-described power supply circuit. Therefore, an electronic device such as a timepiece or a mobile phone equipped with a timekeeping device that requires constant power supply. Use with equipment is considered.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings.

(First embodiment)
<Configuration of power supply circuit>
First, the configuration of the power supply circuit according to the first embodiment will be described with reference to FIG. FIG. 1 is a circuit diagram showing a configuration of a power supply circuit according to the first embodiment of the present invention.

  As shown in FIG. 1, the power supply circuit 1 includes a power supply switching circuit 100, a voltage detection circuit 200, a hold time generation circuit 300, a selection circuit 400, and a constant voltage generation circuit 500. A main power supply MVDD is supplied to the main power supply line NMV. A sub power supply SVDD is supplied to the sub power supply line NSV. In the present embodiment, description will be made with the main power supply MVDD = 3.3V and the sub power supply SVDD = 1.8V.

  The power supply switching circuit 100 includes a Pch transistor TR1 as a first active element and a Pch transistor TR2 as a second active element connected in series between a main power supply line NMV and an internal power supply line NOV, and a sub power supply line. The Pch transistor pair TR3 is a third active element composed of two Pch transistors TR31 and TR32 connected between the NSV and the internal power supply line NOV. The power supply switching circuit 100 switches between the main power supply MVDD and the sub power supply SVDD, and supplies the internal power supply OVDD to the internal power supply line NOV. A capacitor C1 is connected to the internal power supply line NOV.

  The source terminal of the Pch transistor TR1 is connected to the drain terminal of the Pch transistor TR2, the drain terminal of the Pch transistor TR1 is connected to the main power supply line NMV, and the source terminal of the Pch transistor TR2 is connected to the internal power supply line NOV. Yes. By connecting in this way, it is possible to prevent the current of the internal power supply line NOV from flowing back to the main power supply line NMV.

  Further, the drain terminal of the Pch transistor TR31 is connected to the drain terminal of the Pch transistor TR32, the source terminal of the Pch transistor TR31 is connected to the sub power supply line NSV, and the source terminal of the Pch transistor TR32 is connected to the internal power supply line NOV. Has been. By connecting in this way, it is possible to prevent the current of the internal power supply line NOV from flowing back to the sub power supply line NSV.

  The voltage detection circuit 200 operates with the power supply voltage = the internal power supply OVDD, and when the main power supply MVDD becomes the specified voltage or higher from the OFF state (that is, VSS), the internal power supply OVDD that is the second potential from the VSS that is the first potential. The voltage detection signal Vsen which switches from the internal power supply OVDD to VSS is output when the main power supply MVDD becomes the specified voltage or less from the ON state (ie, 3.3 V). In the present embodiment, description will be made with the specified voltage = 1.2V.

  The hold time generation circuit 300 outputs the hold release signal Vhld until the main power supply MVDD rises from the OFF state to the ON state, and sets the hold release signal Vhld to the ON state (3) after the main power supply MVDD is turned ON. .3V) to OFF state (VSS).

  The selection circuit 400 operates with the power supply voltage = the internal power supply OVDD, and includes two level shifters LS1 and LS2, two inverters IN1 and IN2, and a two-input NAND circuit NA1. The level shifter LS1 receives the voltage detection signal Vsen and outputs it to one input terminal of the NAND circuit NA1. The level shifter LS2 receives the hold release signal Vhld and outputs it to the other input terminal of the NAND circuit NA1 via the inverter IN1. The output terminal of the NAND circuit NA1 outputs the selection signal Vcon to the gate terminal of the Pch transistor TR1, and further outputs the inverted selection signal VconX to the gate terminals of the Pch transistors TR31 and TR32 via the inverter IN2.

  The constant voltage generation circuit 500 operates with power supply voltage = internal power supply OVDD, and outputs a constant voltage VREG1 to the gate terminal of the Pch transistor TR2. In the present embodiment, description will be made with the constant voltage VREG1 = 1.2V and the threshold voltage Vth of the Pch transistor TR2 = 0.6V.

<Operation of power supply circuit>
Next, the operation of the power supply circuit will be described with reference to FIG. FIG. 2 is a timing chart showing the operation of the power supply circuit.

  It is assumed that the sub power supply SVDD = 1.8 V has been applied before the time t0 when the main power supply MVDD is in the OFF state. Prior to time t0, the voltage detection signal Vsen = VSS, the hold release signal Vhld = VSS, the selection signal Vcon = 1.8 V, the inverted selection signal VconX = VSS, the Pch transistor pair TR3 is in a conductive state, and the Pch transistor TR1 is non Since it is in a conductive state, the internal power supply OVDD is 1.8V. Since the voltage of the source terminal of the Pch transistor TR2 is the internal power supply OVDD = 1.8V, the voltage of the gate terminal (constant voltage VREG1 = 1.2V) + the threshold voltage Vth (0.6V) ≧ the voltage of the source terminal (1.8V) ) And become non-conductive.

  The main power supply MVDD rises from VSS to 3.3 V from time t0 to time t2. The hold release signal Vhld also rises from VSS to 3.3 V from time t0 to time t2 according to the main power supply MVDD.

  At time t1, the main power supply MVDD reaches the specified voltage = 1.2V, so that the voltage detection signal Vsen is switched from VSS to the internal power supply OVDD = 1.8V.

  At a time t3 after a predetermined time has elapsed since the main power supply MVDD reached 3.3V at the time t2, the hold release signal Vhld is switched from 3.3V to VSS. At this time, since the potentials of the two input terminals of the NAND circuit NA1 become H level, the selection signal Vcon is switched to VSS, the inverted selection signal VconX is first switched to 1.8V, and the Pch transistor pair TR3 is in a non-conductive state, Pch Since the transistors TR1 and TR2 are turned on, the internal power supply OVDD is switched to 3.3V. Since the internal power supply OVDD is switched to 3.3V, the voltage detection signal Vsen and the inverted selection signal VconX are also switched to 3.3V.

  The main power supply MVDD falls from 3.3 V to VSS from time t4 to time t7. The internal power supply OVDD also falls from the time t4 according to the main power supply MVDD, but at the time t5, the internal power supply OVDD becomes 1.8 V, and the Pch transistor TR2 is turned off. Since the Pch transistor pair TR3 is also non-conductive, the potential of 1.8V is held in the capacitor C1, and the internal power supply OVDD is held at 1.8V. In response to the change of the internal power supply OVDD, the voltage detection signal Vsen and the inverted selection signal VconX are also changed.

  At time t6, the main power supply MVDD reaches the specified voltage = 1.2V, so that the voltage detection signal Vsen is switched from the internal power supply OVDD = 1.8V to VSS. At this time, the selection signal Vcon is switched from VSS to the internal power supply OVDD = 1.8V, and the inversion selection signal VconX is switched from the internal power supply OVDD = 1.8V to VSS. Since the Pch transistor pair TR3 is conductive and the Pch transistors TR1 and TR2 are nonconductive, the internal power supply OVDD maintains 1.8V.

  According to the present embodiment described above, the following effects can be obtained.

  In the present embodiment, the period (time t1 to t3) in which the voltage detection circuit 200 becomes unstable at the rise of the main power supply MVDD can be held by the hold release signal Vhld output from the hold time generation circuit 300, so that it is normal. The voltage of the main power supply MVDD can be detected, and the main power supply MVDD and the sub power supply SVDD can be switched. Furthermore, when the main power supply MVDD suddenly falls, the constant voltage generation circuit 500 and the Pch transistor TR2 can prevent the internal power supply OVDD from dropping below the sub power supply SVDD. However, the voltage can be detected normally and the main power supply MVDD and the sub power supply SVDD can be switched.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to such embodiment at all, In the range which does not deviate from the meaning of this invention, it can be implemented with various forms. Hereinafter, a modification will be described.

  (Modification 1) Modification 1 of the power supply circuit according to the present invention will be described. In the first embodiment, the voltage detection circuit 200 and the constant voltage generation circuit 500 operate with the internal power supply OVDD and have the hold time generation circuit 300. However, as shown in FIG. The voltage detection circuit 200 and the constant voltage generation circuit 500 may be operated by the sub power source SVDD. FIG. 4 is a timing chart showing the operation of the power supply circuit 1 of FIG.

  (Modification 2) Modification 2 of the power supply circuit according to the present invention will be described. In the first modification, the voltage detection circuit 200 and the constant voltage generation circuit 500 are operated by the sub power source SVDD, and the hold time generation circuit 300 is not included. However, as shown in FIG. May be included. FIG. 6 is a timing chart showing the operation of the power supply circuit 1 of FIG.

1 is a circuit diagram showing a configuration of a power supply circuit according to a first embodiment of the present invention. The timing diagram which shows operation | movement of a power supply circuit. The circuit diagram which shows the structure of the power supply circuit which concerns on the modification 1 of this invention. FIG. 9 is a timing diagram illustrating an operation of a power supply circuit according to Modification 1; The circuit diagram which shows the structure of the power supply circuit which concerns on the modification 2 of this invention. FIG. 9 is a timing chart showing an operation of a power supply circuit according to Modification 2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Power supply circuit, 100 ... Power supply switching circuit, 200 ... Voltage detection circuit, 300 ... Holding time generation circuit, 400 ... Selection circuit, 500 ... Constant voltage generation circuit

Claims (4)

A main power line to which the main power is applied;
A sub power line to which the sub power is applied;
An internal power line from which the internal power is output;
A first active element and a second active element connected in series between the main power supply line and the internal power supply line, and a third active element connected between the sub power supply line and the internal power supply line. A power switching circuit including an active element;
It operates with the internal power supply, is connected to the main power supply line, and switches from the first potential to the second potential when the main power supply becomes equal to or higher than the specified voltage from the OFF state, and the main power supply switches from the ON state to the specified voltage. A voltage detection circuit that outputs a voltage detection signal that switches from the second potential to the first potential when:
A holding time generation circuit that is connected to the main power supply line and outputs a holding release signal after a predetermined time from when the main power supply is in the ON state;
When the voltage detection signal is switched from the first potential to the second potential and the hold release signal is output, the first active element is turned on and the third active element is turned off. A selection circuit that brings the first active element into a non-conducting state and the third active element into a conducting state when the voltage detection signal is switched from the second potential to the first potential;
A constant voltage generating circuit that operates with the internal power supply and outputs a constant voltage for bringing the second active element into a conductive state to a gate terminal of the second active element;
including,
A power supply circuit characterized by that. A main power line to which the main power is applied;
A sub power line to which the sub power is applied;
An internal power line from which the internal power is output;
A first active element and a second active element connected in series between the main power supply line and the internal power supply line, and a third active element connected between the sub power supply line and the internal power supply line. A power switching circuit including an active element;
It operates with the sub power supply, is connected to the main power supply line, and switches from the first potential to the second potential when the main power supply becomes equal to or higher than the specified voltage from the OFF state. A voltage detection circuit that outputs a voltage detection signal that switches from the second potential to the first potential when:
When the voltage detection signal is switched from the first potential to the second potential, the first active element is turned on and the third active element is turned off, and the voltage detection signal is changed to the second potential. A selection circuit that switches the first active element to a non-conducting state and the third active element to a conducting state at the time of switching from a potential to the first potential;
A constant voltage generating circuit that operates with the sub-power supply and outputs a constant voltage for bringing the second active element into a conductive state to a gate terminal of the second active element;
including,
A power supply circuit characterized by that. A main power line to which the main power is applied;
A sub power line to which the sub power is applied;
An internal power line from which the internal power is output;
A first active element and a second active element connected in series between the main power supply line and the internal power supply line, and a third active element connected between the sub power supply line and the internal power supply line. A power switching circuit including an active element;
It operates with the sub power supply, is connected to the main power supply line, and switches from the first potential to the second potential when the main power supply becomes equal to or higher than the specified voltage from the OFF state. A voltage detection circuit that outputs a voltage detection signal that switches from the second potential to the first potential when:
A holding time generation circuit that is connected to the main power supply line and outputs a holding release signal after a predetermined time from when the main power supply is in the ON state;
When the voltage detection signal is switched from the first potential to the second potential and the hold release signal is output, the first active element is turned on and the third active element is turned off. A selection circuit that brings the first active element into a non-conducting state and the third active element into a conducting state when the voltage detection signal is switched from the second potential to the first potential;
A constant voltage generating circuit that operates with the sub-power supply and outputs a constant voltage for bringing the second active element into a conductive state to a gate terminal of the second active element;
including,
A power supply circuit characterized by that.   An electronic apparatus comprising the power supply circuit according to claim 1.

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