JP5290649B2 - Power supply circuit and battery built-in equipment - Google Patents

Description

  The present invention relates to a power supply circuit and a battery built-in device, and more particularly to a power supply circuit that switches a plurality of power supplies and a battery built-in device including such a power supply circuit.

  In general, portable electronic devices such as a video camera and a mobile phone can be driven by an internal battery and can also be driven by an external power source. In this case, a power supply circuit that switches between a built-in battery and an external power supply and supplies a voltage to the load is used.

  Patent Document 1 listed below describes a power supply circuit that automatically switches between a DC power supply and a built-in battery and supplies power to a load circuit. In this power supply circuit, the source of the first P-channel MOSFET and the source of the second P-channel MOSFET are connected to the output terminal to which the load circuit is connected, and the drain of the first MOSFET is connected to the external DC power supply. The drain of the second MOSFET is connected to the built-in battery.

  The two MOSFETs are controlled on / off by a differential switching circuit. The differential switching circuit turns on the second MOSFET and turns off the first MOSFET when the voltage of the built-in battery is higher than the voltage of the external DC power supply. Thereby, electricity is supplied to the load circuit from the built-in battery via the second MOSFET. Conversely, when the voltage of the built-in battery is lower than the voltage of the external DC power supply, the differential switching circuit turns on the first MOSFET and turns off the second MOSFET. As a result, the load circuit is energized from the external DC power source via the first MOSFET.

  Thus, in the power supply circuit, when the voltage of the external DC power supply matches the voltage of the built-in battery, the power supply is switched, and the higher of the two voltages is used.

JP-A-6-70487

  However, since the power supply switching by the power supply circuit is executed only based on which power supply voltage is higher, the voltage of the built-in battery can be higher even if the voltage of the external DC power supply is at a level that can drive the load circuit. In this case, the built-in battery is used.

  An object of the present invention is to provide a power supply circuit capable of reducing the use of a specific power supply among a plurality of power supplies and a battery built-in device capable of reducing the use of a built-in battery.

  A power supply circuit according to the present invention is a power supply circuit that outputs a voltage to a load connection terminal by switching between a first power supply connected to a first power supply connection terminal and a second power supply connected to a second power supply connection terminal. A first output unit connected to the first power source connection terminal and outputting a first output voltage using a supply voltage from the first power source; and connected to the second power source connection terminal from the second power source. A second output unit that outputs a second output voltage using a supply voltage, and an output unit that outputs a higher one of the first output voltage and the second output voltage to the load connection terminal; The first output voltage is connected to the output unit, the first power supply connection terminal, and the second power supply connection terminal, based on the supply voltage from the first power supply and the supply voltage from the second power supply. A control unit for controlling the second output voltage, the control unit When the supply voltage difference, which is the voltage difference between the supply voltage from the second power supply and the supply voltage from the first power supply, is smaller than a preset positive power supply switching voltage difference, the first output voltage The first output voltage and the second output voltage are controlled to be higher, and when the supply voltage difference is larger than the power supply switching voltage difference, the second output voltage is higher. And controlling the first output voltage and the second output voltage.

  Here, when the supply voltage difference is larger than the power supply switching voltage difference, the control unit reduces the voltage difference between the first output voltage and the second output voltage as the supply voltage difference is smaller. Is preferred.

  The controller preferably makes the value of the first output voltage equal to the value of the second output voltage when the supply voltage difference is equal to the power supply switching voltage difference.

  The first output unit has a first input terminal connected to the control unit, and converts the supply voltage from the first power source to a constant voltage value equal to a voltage applied to the first input terminal. The second output unit includes a second input terminal connected to the control unit, and supplies a second supply voltage from the second power source to the second constant voltage circuit that outputs the first output voltage. The control unit includes a second constant voltage circuit that makes a constant voltage value equal to the voltage applied to the input terminal and outputs the second output voltage, and the control unit includes the voltage of the first input terminal and the second input terminal. It is preferable to control the first output voltage and the second output voltage by controlling the voltage of the first output voltage.

  In addition, the control unit reduces a predetermined voltage determined in advance from a supply voltage of the first power source and applies the first voltage reducing unit to the first input terminal of the first output unit, and the second power source. A second voltage reduction unit that reduces a voltage equal to or higher than the predetermined voltage from the supply voltage and applies the second voltage to the second input terminal of the second output unit, wherein the supply voltage difference is greater than the power supply switching voltage difference If larger, the voltage difference between the voltage at the second input terminal and the voltage at the first input terminal is reduced by increasing the voltage reduction amount at the second voltage reduction unit as the supply voltage difference is smaller. Is preferred.

  The second voltage reduction unit includes a resistor connected between the second power supply connection terminal and the second input terminal of the second output unit, and a current setting unit that sets an amount of current flowing through the resistor. A push-pull that complementarily controls a first current having a current amount corresponding to a supply voltage from the first power supply and a second current having a current amount corresponding to a supply voltage from the second power supply. It is preferable that the circuit includes a current setting unit that includes a circuit and supplies a current having the same amount of current as the first current to the resistor.

  The battery built-in device according to the present invention is a battery built-in device operable by switching between an internal battery connected to the internal battery connection terminal and an external power supply connected to the external power supply connection terminal, the external power supply connection A first output unit that is connected to a terminal and outputs a first output voltage using a supply voltage from the external power supply; and a second output that is connected to the built-in battery connection terminal and uses a supply voltage from the built-in battery A second output unit that outputs a voltage, an output unit that outputs a higher one of the first output voltage and the second output voltage, the output unit, the external power connection terminal, and the built-in battery connection A control unit connected to a terminal and controlling the first output voltage and the second output voltage based on a supply voltage from the external power source and a supply voltage from the built-in battery, and the control unit Supply from the external power supply When the supply voltage difference, which is the voltage difference of the supply voltage from the built-in battery with respect to the pressure, is smaller than a preset positive power supply switching voltage difference, the first output voltage is higher. The first output voltage and the second output voltage are controlled, and when the supply voltage difference is larger than the power supply switching voltage difference, the first output voltage and the second output voltage are higher. The second output voltage is controlled.

  According to the above configuration, even when the supply voltage from the second power supply (or the internal battery) is higher than the supply voltage from the first power supply (or external power supply), the supply voltage difference is the power supply switching voltage difference. If smaller than the first output voltage, the first output voltage is output. For this reason, the use of the second power supply can be reduced compared to the configuration in which the power supply is switched when the supply voltage from the first power supply matches the supply voltage from the second power supply. Therefore, the second power source can be preserved, and performance degradation, a decrease in service life, etc. can be suppressed for the second power source.

  FIG. 1 is a block diagram illustrating a power supply circuit 10 according to an embodiment of the invention. In FIG. 1, the power sources 1 and 2 and the load 3 connected to the power circuit 10 are also shown for the sake of explanation. The power supply circuit 10 includes one of a voltage VDD1 supplied from the first power supply 1 through the first power supply connection terminal 11 and a voltage VDD2 supplied from the second power supply 2 through the second power supply connection terminal 12. This circuit outputs the output voltage Vo to the load connection terminal 13, that is, to the load 3 connected to the load connection terminal 13. For this reason, the power supply circuit 10 may be called a power supply switching circuit. Here, a case where the voltages VDD1, VDD2, and Vo are DC voltages is illustrated. For the sake of simplicity of explanation, symbols for various voltages are also used for the voltage values. The supply voltage VDD1 from the first power supply 1 is also referred to as the first supply voltage VDD1, and the supply voltage VDD2 from the second power supply 2 is also referred to as the second supply voltage VDD2.

  Various power sources can be applied as the power sources 1 and 2, respectively. For example, a primary battery that can only be discharged, a secondary battery that can be charged as well as discharged (so-called storage battery), and a direct current converted and output from a commercial AC voltage For example, a power source (so-called AC-DC converter), a power source (so-called DC-DC converter) that boosts or steps down a DC voltage to a predetermined voltage value and outputs the converted voltage can be used. The power sources 1 and 2 may be the same type of power source (for example, secondary batteries) or different types of power sources (for example, a secondary battery and an AC-DC converter).

  One or both of the power supplies 1 and 2 may be housed in the same device together with the power supply circuit 10. For example, in the device 50 illustrated in the block diagram of FIG. 2, the internal battery 52 is provided inside the device as the second power source 2 (see FIG. 1) together with the power supply circuit 10. In addition, the battery built-in device 50 is configured to be connected to an external power supply 51 as the first power supply 1 (see FIG. 1) at the power supply connection terminal 11. The built-in battery 52 is composed of, for example, a primary battery or a secondary battery, and the external power source is composed of, for example, an AC-DC converter. Further, the built-in battery 52 may be provided so as to be removable outside the casing of the device 50, or may be fixed inside the casing.

  Examples of the battery built-in device 50 include a mobile phone, a portable music player, and a portable computer. However, the device 50 is not limited to a portable device, and various types of devices including, for example, a built-in battery 52 as a backup power source. It may be a device.

  1 and 2, the load 3 is a circuit that operates when the voltage Vo is supplied from the power supply circuit 10, for example, and includes various arithmetic circuits, control circuits, and drive circuits. The load 3 may be another power supply circuit that generates various voltages using the output voltage Vo from the power supply circuit 10. Further, the load 3 may be a component accompanied by a mechanical operation such as a motor.

  Note that for simplicity of explanation, the term “terminal” is used, but the terminal can be arbitrarily defined for a conductive portion on the circuit, and its specific configuration and shape are not limited. That is, the terminal may be, for example, a connector part or a metal fitting, a lead part of an element, or a part of wiring. Further, the expression “connection” means an electrical connection unless otherwise specified.

  As shown in the block diagram of FIG. 1, the power supply circuit 10 includes an output unit 20 and a control unit 30 that controls the output unit 20.

  The output unit 20 includes a first output unit 110 and a second output unit 210. The first output unit 110 is connected to the first power supply connection terminal 11 and generates and outputs the first output voltage Vo1 using the voltage VDD1 supplied from the first power supply 1 via the terminal 11. The second output unit 210 is connected to the second power supply connection terminal 12 and generates and outputs the second output voltage Vo2 using the voltage VDD2 supplied from the second power supply 2 via the terminal 12. The output unit 20 selectively outputs the higher voltage of the first output voltage Vo1 and the second output voltage Vo2 to the load connection terminal 13.

  The control unit 30 is connected to the first output unit 110 and the second output unit 210 and is connected to the first power supply connection terminal 11 and the second power supply connection terminal 12, and is supplied from the first power supply 1. Based on the magnitude relationship between the voltage value VDD1 and the supply voltage value VDD2 from the second power supply 2, the output voltage value Vo1 from the first output unit 110 and the output voltage value Vo2 from the second output unit 210 are controlled.

  Here, FIGS. 3 and 4 are characteristic diagrams illustrating the operation of the power supply circuit 10. In order to avoid complication of the drawing, the graph is divided into the upper and lower stages of FIG. 3 and FIG. 3 and 4 exemplify the case where the second supply voltage VDD2 is constant. The first supply voltage VDD1 is taken on the horizontal axis of each graph, and the voltages VDD1, VDD2, Vo1, Vo2, Vo, ΔVDD are taken. The relationship of each voltage value of (= VDD2-VDD1) is illustrated.

  Here, the voltage ΔVDD is a voltage difference between the first supply voltage VDD1 and the second supply voltage VDD2, and a voltage difference of the second supply voltage VDD2 with respect to the first supply voltage VDD1, that is, the first supply voltage VDD1 is used as a reference potential. In this case, the potential of the second supply voltage is used. In this case, the supply voltage difference ΔVDD can take any of a positive value, 0 (zero), and a negative value.

  As shown in FIGS. 3 and 4, in the power supply circuit 10, when the supply voltage difference ΔVDD is smaller than a preset positive value ΔVt, the output voltage Vo1 of the first output unit 110 is the second output unit. The output voltages Vo1 and Vo2 are controlled so as to be higher than the output voltage Vo2 of 210. As a result, the power supply circuit 10 outputs the voltage Vo1 generated by using the first supply voltage VDD1 as the output voltage Vo.

  On the other hand, when the supply voltage difference ΔVDD is larger than the positive value ΔVt, the output voltages Vo1 and Vo2 are controlled so that the second output voltage Vo2 is higher than the first output voltage Vo1. As a result, the power supply circuit 10 outputs the voltage Vo2 generated by using the second supply voltage VDD2 as the output voltage Vo.

  When the supply voltage difference ΔVDD is equal to the positive value ΔVt, either of the output voltages Vo1 and Vo2 may be used as the output voltage Vo.

  The positive value ΔVt serving as a reference value when the first output voltage Vo1 and the second output voltage Vo2 are switched is referred to as a power supply switching voltage difference ΔVt.

  Here, for comparison with the power supply circuit 10, when the first supply voltage VDD1 and the second supply voltage VDD2 coincide with each other, in other words, when ΔVDD = 0, the characteristic diagram of the configuration in which the power supplies 1 and 2 are switched. Is shown in FIG. In FIG. 11, the characteristic lines of the voltages VDD1 and VDD2 are the same as those in FIGS.

  As can be seen from a comparison between FIG. 4 and FIG. 11, according to the power supply circuit 10, even when the second supply voltage VDD2 is higher than the first supply voltage VDD1, the supply voltage difference ΔVDD is the power supply switching voltage. When the difference is smaller than ΔVt, the first output voltage Vo1 is output. Therefore, the use of the second power supply 2 (use of the built-in battery 52 in the example of FIG. 2) can be reduced as compared with the configuration in which the power supply is switched when the supply voltage values VDD1 and VDD2 match. Therefore, the second power source 2 can be preserved, and performance degradation, a decrease in service life, etc. can be suppressed for the second power source 2. For example, when the battery built-in device 50 of FIG. 2 is connected to the external power supply 51 and the supply voltage VDD1 of the external power supply 51 and the supply voltage VDD2 of the built-in battery 52 are substantially equal, it is preferable to use the external power supply 51. Since 52 can be preserved, it turns out to be preferable.

  Further, as shown in FIGS. 3 and 4, in the power supply circuit 10, under the control of the control unit 30, when ΔVDD> ΔVt, the smaller the supply voltage difference ΔVDD, the smaller the voltage difference between the output voltages Vo1 and Vo2. Controlled. 3 illustrates a case where the second output voltage value Vo2 is brought close to the first output voltage value Vo1 in comparison with FIG. 11, but conversely, the first output voltage value Vo1 is changed to the second output voltage value Vo2. It is also possible to perform control so that the voltage values approach each other, and it is also possible to control so as to reduce the voltage difference by changing both voltage values Vo1 and Vo2. Further, as shown in FIGS. 3 and 4, when ΔVDD = ΔVt, the output voltage values Vo1 and Vo2 are controlled to be equal. In this case, the value of ΔVDD when Vo1 = Vo2 corresponds to ΔVt.

  On the other hand, as in the operation example of the power supply circuit 10 shown in FIG. 5, the output voltages Vo1 and Vo2 simply follow the changes in the supply voltages VDD1 and VDD2, and the output voltages Vo1 and Vo2 are set with ΔVDD = ΔVt as a boundary. Even in the case of switching, it is possible to preserve the second power supply 2 in the same manner as described above.

  Comparing the operation example of FIG. 5 with the operation examples of FIGS. 3 and 4, there is a difference in the voltage difference between the output voltages Vo1 and Vo2 at ΔVDD = ΔVt. That is, in the operation examples of FIGS. 3 and 4, the voltage difference between the output voltages Vo1 and Vo2 at the time of power supply switching is smaller than that in the operation example of FIG. For this reason, it is possible to reduce or prevent a rush current from flowing through the load 3 via the load connection terminal 13, and to prevent a malfunction of the load 3.

  In view of this point, even when ΔVDD> ΔVt and the second output voltage Vo2 changes between the operation example of FIG. 5 and the operation examples of FIG. 3 and FIG. It is possible to prevent current. On the other hand, when the output voltages Vo1 and Vo2 are switched as in the operation examples of FIGS. 3 and 4, the voltage values Vo1 and Vo2 are made equal (continuous), thereby preventing the effect of preventing the rush current. Can be. Further, the voltage values Vo1 and Vo2 are continuously switched when ΔVDD = ΔVt, so that the voltage values Vo1 and Vo2 are switched smoothly, and the output voltage value Vo near ΔVDD = ΔVt can be stabilized.

  In the above, the case where the second supply voltage VDD2 is constant is illustrated, but FIG. 6 illustrates the case where the first supply voltage VDD1 is constant. In FIG. 6, the horizontal axis of each graph takes the second supply voltage VDD2, and shows the relationship between the voltage values of voltages VDD1, VDD2, Vo, and ΔVDD. In the case of the operation example of FIG. 6, the same explanation as above applies, and the second power source 2 can be preserved. Moreover, although both the supply voltages VDD1 and VDD2 may fluctuate, the operation of the power supply circuit 10 in such a case can be easily understood from the above description.

  7 to 10 show examples of the circuit configuration of the power supply circuit 10. Such an exemplary circuit will be described below, but other circuit configurations may be applied as long as the various functions of the units 20 and 30 can be realized.

  In the example of FIG. 7, the first output unit 110 is configured by a constant voltage circuit including a first input terminal 112, an operational amplifier 114, and a driver transistor 116. In FIG. 7, the driver transistor 116 is illustrated as a P-channel MOSFET. The driver transistor 116 has a parasitic diode 118 between the source terminal and the drain terminal.

  Regarding the driver transistor 116, the input side terminal (here, the drain terminal) is connected to the first power supply connection terminal 11, and the output side terminal (here, the source terminal) from which the first output voltage Vo1 is output is the load connection terminal 13. The control terminal to which a voltage for controlling the conduction state between the input side terminal and the output side terminal is applied is connected to the output terminal of the operational amplifier 114.

  Regarding the operational amplifier 114, the reference voltage input terminal (here, the inverting input terminal) is connected to the first input terminal 112, and the feedback input terminal (here, the non-inverting input terminal) is the output side terminal of the driver transistor 116, in other words. Connected to the load connection terminal 13.

  According to such a configuration, the first output unit 110 converts the first supply voltage VDD1 to a voltage equal to the voltage Vc1 applied to the first input terminal 112, and outputs the constant voltage as the first output voltage Vo1. be able to.

  Similarly, in the example of FIG. 7, the second output unit 210 is configured by a constant voltage circuit including a second input terminal 212, an operational amplifier 214, and a driver transistor 216. In FIG. 7, the driver transistor 216 is illustrated as a P-channel MOSFET. Note that the driver transistor 216 includes a parasitic diode 218 between the source terminal and the drain terminal.

  Regarding the driver transistor 216, the input side terminal (here, the drain terminal) is connected to the second power supply connection terminal 12, and the output side terminal (here, the source terminal) from which the second output voltage Vo2 is output is the load connection terminal 13. The control terminal to which a voltage for controlling the conduction state between the input side terminal and the output side terminal is applied is connected to the output terminal of the operational amplifier 214.

  Regarding the operational amplifier 214, the reference voltage input terminal (here, the inverting input terminal) is connected to the second input terminal 212, and the feedback input terminal (here, the non-inverting input terminal) is the output side terminal of the driver transistor 216, in other words. Connected to the load connection terminal 13.

  According to such a configuration, the second output unit 210 makes the second supply voltage VDD2 constant to a voltage equal to the voltage Vc2 applied to the second input terminal 212, and outputs the constant voltage as the second output voltage Vo2. be able to.

  In the example of FIG. 7, the output terminals of the driver transistors 116 and 216 are directly connected to each other. In this case, the driver transistor 116 is turned off when the feedback voltage Vo is higher than the reference voltage Vc1, and the driver transistor 216 is turned off when the feedback voltage Vo is higher than the reference voltage Vc2. By setting the driver transistors 116 and 216 and the operational amplifiers 114 and 214, the higher one of the output voltages Vo1 and Vo2 can be output as the output voltage Vo. With this configuration, the voltages Vo1 and Vo2, in other words, the power sources 1 and 2 can be switched without using an additional switching element.

  Although FIG. 7 illustrates the configuration in which the feedback input terminals of the driver transistors 116 and 216 are respectively connected to the load connection terminal 13, both feedback input terminals are connected to each other and connected to the load connection terminal 13 through one common wiring. May be.

  In addition, the output units 110 and 210 may be configured by constant voltage circuits having other configurations. For example, N-channel MOSFETs are used for the driver transistors 116 and 216 and input terminals of the operational amplifiers 114 and 214 are connected. It is also possible to reverse the above. Further, for example, the voltage Vo1 or the voltage Vo2 can be selectively output by a configuration in which the input terminals 112 and 212 are connected to the control terminals of the driver transistors 116 and 216 without using the operational amplifiers 114 and 214. However, it is more preferable that the output units 110 and 210 be negative feedback circuits as described above, so that a constant voltage can be obtained as the output voltage Vo and the stable voltage Vo can be supplied to the load 3.

  As described above, the output voltage values Vo1 and Vo2 are controlled by the applied voltage values Vc1 and Vc2 applied to the input terminals 112 and 212 of the output units 110 and 210, respectively. As shown in FIG. 7, the input terminals 112 and 212 of the output units 110 and 210 are connected to the control unit 30, and the voltage of the input terminals 112 and 212 is controlled by the control unit 30. Below, the structural example of the control part 30 is demonstrated.

  In the example of FIG. 7, the control unit 30 reduces the supply voltage VDD1 from the first power supply 1 and applies it to the input terminal 112 of the first output unit 110, and the second power supply 2 And a second voltage reduction unit 250 that reduces the supply voltage VDD2 and applies it to the input terminal 212 of the second output unit 210.

  In the example of FIG. 7, the first voltage reduction unit 150 includes a resistor 152, a diode 154, and a constant current source 156. One end of the resistor 152 is connected to the first power connection terminal 11, the other end of the resistor 152 is connected to the anode of the diode 154, and the cathode of the diode 154 is connected to the constant current source 156. Source 156 is grounded. The other end of the resistor 152, in other words, the anode of the diode 154 is connected to the input terminal 112 of the first output unit 110.

  According to such a configuration, since the constant current I1 from the constant current source 156 flows to the resistor 152, the voltage Vc1 obtained by reducing the first supply voltage VDD1 by the voltage drop at the resistor 152 is the input terminal of the first output unit 110. 112 (see FIGS. 3 to 6). The resistance value of the resistor 152 and the current value of the constant current I1 are set in advance to a predetermined value, and thus the voltage drop amount by the resistor 152 becomes a preset constant value. Since the current I1 flowing through the resistor 152 is set by the constant current source 156, the constant current source 156 can be referred to as the current setting unit 162 of the first voltage reduction unit 150.

  The constant current source 156 can be configured by, for example, the circuit illustrated in FIG. Such exemplary constant current source 156 includes a transistor 170, a resistor 172, and an operational amplifier 174. The transistor 170 is illustrated as an NPN bipolar transistor in FIG. 8, the collector terminal is connected to the cathode of the diode 154, and the emitter terminal is grounded via the resistor 172. The base terminal of the transistor 170 is connected to the output terminal of the operational amplifier 174. In the operational amplifier 174, the inverting input terminal is connected to the emitter terminal of the transistor 170, and the non-inverting input terminal is connected to the resistors 402 and 404.

  The resistors 402 and 404 are connected in series between the power supply potential VDD and the ground potential, and a voltage obtained by dividing the voltage VDD by the resistors 402 and 404 is applied to the non-inverting input terminal of the operational amplifier 174. Note that an adjustment terminal 406 is connected to a connection point between the resistors 402 and 404. By connecting a resistance (not shown) to the adjustment terminal 406, the voltage dividing ratio of the power supply voltage VDD can be adjusted. For example, a constant voltage generated by using the output voltage Vo of the power supply circuit 10 can be used as the power supply potential VDD.

  In the example of FIG. 7, the second voltage reduction unit 250 includes a resistor 252, diodes 254 and 258, and constant current sources 256 and 260. One end of the resistor 252 is connected to the second power supply connection terminal 12, the other end of the resistor 252 is connected to the anode of the diode 254, and the cathode of the diode 254 is connected to the constant current source 256. Source 256 is grounded. The other end of the resistor 252, in other words, the anode of the diode 254 is connected to the anode of the diode 258, the cathode of the diode 258 is connected to the constant current source 260, and the constant current source 260 is grounded. ing. The other end of the resistor 252, in other words, the anodes of the diodes 254 and 258 are connected to the input terminal 212 of the second output unit 210.

  According to such a configuration, since the current (I2 + I3) obtained by adding the constant current I2 from the constant current source 256 and the constant current I3 from the constant current source 260 flows to the resistor 252, the second supply voltage VDD2 is a voltage drop across the resistor 252. The voltage Vc2 reduced by the amount is applied to the input terminal 212 of the second output unit 210 (see FIGS. 3 to 6).

  The resistance value of the resistor 252 and the current value of the constant current I2 are set to predetermined values in advance. On the other hand, the constant current source 260 is connected to the power supply connection terminals 11 and 12 and has a function of setting the current value of the current I3 according to the voltage values of the supply voltages VDD1 and VDD2 (details will be described later). ). Therefore, by setting the voltage drop amount due to the current I2 in the resistor 252 and the voltage drop amount due to the current I1 in the resistor 152 to be the same, the total voltage drop amount in the resistor 252 (the voltage due to the current obtained by adding the currents I2 and I3) The amount of drop) can be set equal to or greater than the amount of voltage drop across the resistor 152.

  Since the current flowing through the resistor 252 is set by the constant current sources 256 and 260, the constant current sources 256 and 260 can be referred to as the current setting unit 262 of the second voltage reduction unit 250.

  The constant current source 256 can be configured by, for example, the circuit illustrated in FIG. Such exemplary constant current source 256 includes a transistor 270, a resistor 272, and an operational amplifier 274. The transistor 270 is illustrated as an NPN bipolar transistor in FIG. 9, the collector terminal is connected to the cathode of the diode 254, and the emitter terminal is grounded via the resistor 272. The base terminal of the transistor 270 is connected to the output terminal of the operational amplifier 274. In the operational amplifier 274, the inverting input terminal is connected to the emitter terminal of the transistor 270, and the non-inverting input terminal is connected to the resistors 402 and 404.

  The constant current source 260 can be configured by, for example, the circuit illustrated in FIG. Such an example constant current source 260 includes an operational amplifier 302, transistors 304, 308, 310, 312, 322, 324, 342, 344, 352, 354, 356, 358 and resistors 306, 326, 328, 330, 346. , 348. In FIG. 10, transistors 304, 312, 322, 324, 342, 344, 356, and 358 are illustrated as NPN bipolar transistors, and transistors 308, 310, 352, and 354 are illustrated as PNP bipolar transistors.

  The non-inverting input terminal of the operational amplifier 302 is connected to the resistors 412 and 414. The resistors 412 and 414 are connected in series between the power supply potential VDD and the ground potential, and a voltage obtained by dividing the voltage VDD by the resistors 412 and 414 is applied to the non-inverting input terminal of the operational amplifier 302. The inverting input terminal of the operational amplifier 302 is grounded via a resistor 306 and is connected to the emitter terminal of the transistor 304. The base terminal of the transistor 304 is connected to the output terminal of the operational amplifier 302. For this reason, the operational amplifier 302, the transistor 304, and the resistor 306 constitute a constant current circuit. The output current of the constant current circuit is set by the voltage applied to the non-inverting input terminal of the operational amplifier 302, that is, the voltage dividing ratio of the power supply potential VDD by the resistors 412 and 414. Note that an adjustment terminal 416 is connected to a connection point between the resistors 412 and 414. By connecting a resistor (not shown) to the adjustment terminal 416, the voltage dividing ratio of the power supply voltage VDD can be adjusted.

  The collector terminal of the transistor 308 is connected to the collector terminal of the transistor 304. The emitter terminals of the transistors 308 and 310 are both connected to the first power supply connection terminal 11, and the base terminals of the transistors 308 and 310 are connected to each other and to the collector terminal of the transistor 308. Therefore, the transistors 308 and 310 constitute a current mirror circuit.

  The collector terminal of the transistor 312 is connected to the collector terminal of the transistor 310. The base terminal of the transistor 312 is connected to the base terminals of the transistors 322 and 342, and is connected to the collector terminal of the transistor 312. The emitter terminals of the transistors 312, 322, and 342 are grounded. Therefore, the transistors 312, 322, and 342 constitute a current mirror circuit. The collector terminal of the transistor 322 is connected to one end of the resistor 330, and the collector terminal of the transistor 342 is connected to the other end of the resistor 330.

  The emitter terminal of the transistor 324 is connected to the one end of the resistor 330. The base terminal of the transistor 324 is connected to the first power supply connection terminal 11 via a resistor 326 and grounded via a resistor 328. The collector terminal of the transistor 324 is connected to the collector terminal of the transistor 352. The emitter terminal of the transistor 344 is connected to the other end of the resistor 330. The base terminal of the transistor 344 is connected to the second power supply connection terminal 12 via a resistor 346 and grounded via a resistor 348. The collector terminal of the transistor 344 is connected to the second power supply connection terminal 12.

  The emitter terminals of the transistors 352 and 354 are both connected to the first power supply connection terminal 11, and the base terminals of the transistors 352 and 354 are connected to each other and to the collector terminal of the transistor 352. Thus, the transistors 352 and 354 form a current mirror circuit. The collector terminal of the transistor 354 is connected to the collector terminal of the transistor 356.

  The base terminal of the transistor 356 is connected to the base terminal of the transistor 358 and to the collector terminal of the transistor 356. The emitter terminals of the transistors 356 and 358 are grounded. Thus, the transistors 356 and 358 constitute a current mirror circuit. The collector terminal of the transistor 358 is connected to the cathode of the diode 258.

  According to such a configuration, since the voltage obtained by dividing the first supply voltage VDD1 by the resistors 326 and 328 is input to the base terminal of the transistor 324, the transistor 324 has a current amount corresponding to the voltage value of the first supply voltage VDD1. A current (first current) Ia having Similarly, since the voltage obtained by dividing the second supply voltage VDD2 by the resistors 346 and 348 is input to the base terminal of the transistor 344, the transistor 344 has a current amount corresponding to the voltage value of the second supply voltage VDD2. (Second current) Ib is output.

  Here, the transistors 324 and 344 are connected to the resistor 330 and the transistors 322 and 342, and the transistors 322 and 342 have a current amount equal to the constant current generated by the operational amplifier 302 and the transistor 304. Current flows. For this reason, the total current of the currents Ia and Ib is held at a preset constant value. In other words, the currents Ia and Ib are controlled complementarily. That is, the push-pull circuit 320 includes the resistors 326, 328, 346, 348, 330 and the transistors 324, 344, 322, 342.

  Further, according to the above configuration, a current having the same amount as the current Ia is taken out through the transistors 352, 354, 356, and 358 and flows to the resistor 252 as the current I3.

  Therefore, as the first supply voltage VDD1 increases or as the second supply voltage VDD2 decreases, the current Ia, that is, the current I3 increases, and the voltage drop at the resistor 252 increases. As a result, the voltage Vc2 is smaller than when only the current I2 flows through the resistor 252 (see FIGS. 3, 4, and 6). Since the total current of the currents Ia and Ib is regulated to a constant value as described above, the voltage Vc2 converges to a voltage value corresponding to the constant current value (see FIGS. 3, 4, and 6).

  Conversely, as the first supply voltage VDD1 decreases or as the second supply voltage VDD2 increases, the current Ia, that is, the current I3 decreases, and the voltage drop across the resistor 252 is dominated by the component due to the current I2 ( (See FIGS. 3, 4, and 6). As a result, for example, when the resistance values of the resistors 252 and 152 are equal and the set current amounts of the currents I2 and I1 are equal, the voltage drop amount at the resistor 252 and the voltage drop amount at the resistor 152 are the same (FIG. 3). FIG. 4 and FIG. 6).

  According to the power supply circuit 10 having the above configuration, the operation examples of FIGS. 3 and 4 can be realized.

  The voltage value of the voltage Vc2 when the voltage Vc2 starts to decrease due to the increase in the current I3 can be set in advance, for example, by selecting the resistance values of the resistors 326 and 346, and the supply voltage difference ΔVDD is greater than the power supply switching voltage difference ΔVt. It is set within a large voltage range. Thus, when the supply voltage difference ΔVDD is larger than the power supply switching voltage difference ΔVt, the voltage reduction amount in the second voltage reduction unit 250 increases as the supply voltage difference ΔVDD decreases. As a result, control is performed to bring the applied voltage value Vc2 applied to the second input terminal 212 closer to the applied voltage value Vc1 applied to the first input terminal 112, that is, control to bring the second output voltage value Vo2 closer to the first output voltage value Vo1. Can do.

  Further, according to the above configuration, when the output voltages Vo1 and Vo2 are switched, both the voltages Vo1 and Vo2 become equal, so that the output voltage Vo can be switched smoothly (continuously), and in the vicinity of ΔVDD = ΔVt. The output voltage value Vo can be stabilized. Here, the voltage values Vo1 and Vo2 (in other words, the control voltage values Vc1 and Vc2) when Vo1 = Vo2 can be controlled by the amount of current flowing through the transistors 322 and 342. That is, when the output current amount of the constant current circuit by the operational amplifier 302 and the transistor 304 is adjusted, for example, by selecting the resistance values of the resistors 412 and 414 or adding a resistor to the adjustment terminal 416, Vo1 = Vo2. It is possible to set the voltage value Vo2 (= Vc2).

  Further, since the control unit 30 of the above example generates the control voltages Vc1 and Vc2 by reducing the supply voltages VDD1 and VDD2 and controlling the voltage reduction amount, the configuration of the control unit 30 is simple. That's it.

  Although the case where the power supply circuit 10 switches between the two power supplies 1 and 2 has been exemplified above, it is possible to configure a power supply circuit that switches between three or more power supplies by applying the power supply circuit 10, and such a power supply circuit. The circuit includes the above-described configuration of the power supply circuit 10.

1 is a block diagram illustrating a power supply circuit according to an embodiment of the present invention. 1 is a block diagram illustrating a battery built-in device according to an embodiment of the invention. FIG. 10 is a characteristic diagram illustrating the operation of the power supply circuit according to the embodiment of the invention. FIG. 10 is a characteristic diagram illustrating the operation of the power supply circuit according to the embodiment of the invention. FIG. 10 is a characteristic diagram illustrating the operation of the power supply circuit according to the embodiment of the invention. FIG. 10 is a characteristic diagram illustrating the operation of the power supply circuit according to the embodiment of the invention. 1 is a circuit diagram illustrating a power supply circuit according to an embodiment of the invention. 1 is a circuit diagram illustrating a power supply circuit according to an embodiment of the invention. 1 is a circuit diagram illustrating a power supply circuit according to an embodiment of the invention. 1 is a circuit diagram illustrating a power supply circuit according to an embodiment of the invention. It is a characteristic view for a comparison.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 1st power supply, 2nd power supply 10, 10 power supply circuit, 11 1st power supply connection terminal, 12 2nd power supply connection terminal, 13 Load connection terminal, 20 Output part, 30 Control part, 50 Battery built-in type apparatus, 51 External power supply (First power supply), 52 built-in battery (second power supply), 110 first output section, 112 first input terminal, 150 first voltage reduction section, 152,252 resistance, 162,262 current setting section, 210 second output Unit, 212 second input terminal, 250 second voltage reduction unit, 320 push-pull circuit, I1, I2, I3 current, Ia first current, Ib second current, VDD1 supply voltage from the first power supply, VDD2 second power supply Supply voltage, Vc1 applied voltage to the first input terminal, Vc2 applied voltage to the second input terminal, Vo1 first output voltage, Vo2 second output voltage, Vo output voltage, ΔVDD Supply voltage difference, ΔVt Power supply switching voltage difference.

Claims (7)

A power supply circuit that switches between a first power supply connected to the first power supply connection terminal and a second power supply connected to the second power supply connection terminal and outputs a voltage to the load connection terminal;
A first output unit connected to the first power supply connection terminal for outputting a first output voltage using a supply voltage from the first power supply; and a supply from the second power supply connected to the second power supply connection terminal A second output unit that outputs a second output voltage using a voltage, an output unit that outputs the higher one of the first output voltage and the second output voltage to the load connection terminal;
The first output voltage is connected to the output unit, the first power supply connection terminal, and the second power supply connection terminal, based on the supply voltage from the first power supply and the supply voltage from the second power supply. A control unit for controlling the second output voltage;
With
The controller is
When the supply voltage difference, which is the voltage difference between the supply voltage from the second power supply and the supply voltage from the first power supply, is smaller than a preset positive power supply switching voltage difference, the first output voltage Controlling the first output voltage and the second output voltage so that the higher one is higher,
When the supply voltage difference is larger than the power supply switching voltage difference, the first output voltage and the second output voltage are controlled such that the second output voltage is higher. circuit. The power supply circuit according to claim 1,
The control unit reduces the voltage difference between the first output voltage and the second output voltage as the supply voltage difference is smaller when the supply voltage difference is larger than the power supply switching voltage difference. Power supply circuit. The power supply circuit according to claim 2,
The control unit is configured to make the value of the first output voltage equal to the value of the second output voltage when the supply voltage difference is equal to the power supply switching voltage difference. The power supply circuit according to any one of claims 1 to 3,
The first output unit has a first input terminal connected to the control unit, the supply voltage from the first power supply is made constant to the same voltage value as the voltage applied to the first input terminal, and the first output unit It consists of a first constant voltage circuit that outputs as one output voltage,
The second output unit has a second input terminal connected to the control unit, and converts the supply voltage from the second power source into a constant voltage value equal to a voltage applied to the second input terminal, thereby generating the second input terminal. It consists of a second constant voltage circuit that outputs as two output voltages,
The control unit controls the first output voltage and the second output voltage by controlling the voltage of the first input terminal and the voltage of the second input terminal. The power supply circuit according to claim 4,
The controller is
A first voltage reduction unit for reducing a predetermined voltage from a supply voltage of the first power source and applying the voltage to the first input terminal of the first output unit;
A second voltage reduction unit for reducing a voltage equal to or higher than the predetermined voltage from a supply voltage of the second power source and applying the voltage to the second input terminal of the second output unit;
Including
When the supply voltage difference is larger than the power supply switching voltage difference, the voltage reduction amount in the second voltage reduction unit is increased as the supply voltage difference is smaller, thereby increasing the voltage at the second input terminal and the first input voltage difference. A power supply circuit characterized by reducing a voltage difference from a voltage of an input terminal. The power supply circuit according to claim 5,
The second voltage reduction unit includes:
A resistor connected between the second power connection terminal and the second input terminal of the second output unit;
A current setting unit for setting a current amount flowing in the resistor, the first current having a current amount corresponding to a supply voltage from the first power source and a current amount corresponding to a supply voltage from the second power source; A current setting unit including a push-pull circuit for controlling the second current in a complementary manner, and causing a current of the same amount as the first current to flow through the resistor;
A power supply circuit comprising: A battery built-in device that can operate by switching between an internal battery connected to the internal battery connection terminal and an external power supply connected to the external power connection terminal,
A first output unit connected to the external power supply connection terminal for outputting a first output voltage using a supply voltage from the external power supply; and a supply voltage from the internal battery connected to the internal battery connection terminal. A second output unit that outputs a second output voltage, and an output unit that outputs a higher one of the first output voltage and the second output voltage;
The first output voltage and the second output voltage are connected to the output unit, the external power supply connection terminal, and the internal battery connection terminal, and are based on a supply voltage from the external power supply and a supply voltage from the internal battery. A control unit for controlling
With
The controller is
When the supply voltage difference, which is the voltage difference of the supply voltage from the internal battery with respect to the supply voltage from the external power supply, is smaller than a preset positive power supply switching voltage difference, the first output voltage is more Controlling the first output voltage and the second output voltage to be higher;
When the supply voltage difference is larger than the power supply switching voltage difference, the battery controls the first output voltage and the second output voltage so that the second output voltage is higher. Built-in equipment.

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