JP2007330007A - Power unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the safety of a power unit using a level shift circuit. <P>SOLUTION: A charge pump circuit 10 generates output voltage Vout, based on input voltage Vin from outside. A control circuit 20 generates control signals S1-S4 for controlling the generation of output voltage Vout by the charge pump 10. The level shift circuit 30 supplies the charge pump circuit 10 with at least a part (S1 and S2) of the control signals S1-S4 outputted from the control circuit 20 after shifting their levels, by use of the output voltage Vout. A voltage fixing circuit 40 forcively fixes the control signals S1' and S2' with their levels shifted by the level shift circuit 30 into specified low level when they satisfy specified conditions. When they satisfy the specified conditions, the signal levels of the control signals S1' and S2' become instable. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power supply device.

  Small information terminals such as mobile phones and PDAs (Personal Digital Assistance) in recent years require a voltage higher than the output voltage of the battery, such as an LED (Light Emitting Diode) used for a liquid crystal backlight. Device exists. For example, in these small information terminals, a Li-ion battery is often used, and its output voltage is usually about 3.5 V, and is about 4.2 V even when fully charged, but the LED has a battery voltage as its driving voltage. Requires a higher voltage. Thus, when a voltage higher than the battery voltage is required, it is necessary to boost the battery voltage using a booster circuit such as a switching regulator or a charge pump system and drive a load circuit such as an LED. Getting voltage. Patent Document 1 describes related technology.

JP-A-9-163247

  In general, the charge pump circuit includes a flying capacitor, an output capacitor, and a plurality of switches that connect these capacitors. The charge pump circuit boosts and outputs the input battery voltage (input voltage) by charging and discharging the flying capacitor and the output capacitor by turning on and off the plurality of switches. On / off of each switch is controlled by a control signal generated by a control circuit that operates based on a clock signal.

  Here, a case where a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor, hereinafter simply referred to as a PMOS transistor) is used as a part of the switch is considered. When the source voltage of the PMOS transistor operates near the output voltage of the charge pump circuit, in order to turn off the transistor, it is necessary to raise the control signal applied to the gate to the vicinity of the output voltage of the charge pump circuit. For this purpose, a level shift circuit for shifting the level of the control signal using the output voltage of the charge pump circuit is provided.

  The present inventor has come to recognize the following problems in such a situation. When the output voltage of the charge pump circuit rises to some extent and operates in a steady state, the voltage level of the control signal supplied to the gate of the PMOS transistor via the level shift circuit is stable, and there is no problem. However, the output voltage of the level shift circuit, that is, the voltage level of the control signal supplied to the gate of the PMOS transistor is indefinite before the output voltage of the charge pump circuit rises sufficiently, such as immediately after the start of the charge pump circuit. There is a case. If the voltage level of the control signal becomes indefinite, the degree of switch on (off) changes, which causes a problem that the operation of the charge pump circuit becomes unstable.

  The present invention has been made in view of these problems, and a comprehensive object thereof is to improve the stability of a power supply device using a level shift circuit.

  One embodiment of the present invention relates to a power supply device that outputs a predetermined output voltage. The power supply device includes a voltage generation circuit that generates an output voltage based on an external input voltage, a control circuit that generates a control signal for controlling the voltage generation circuit, and at least a control signal output from the control circuit. A level shift circuit that partially shifts the output voltage to supply the voltage generation circuit and a control signal that is level-shifted by the level shift circuit is forced to a predetermined voltage level when a predetermined condition is satisfied. And a voltage fixing circuit for fixing.

  According to this aspect, since the level of the control signal level-shifted by the level shift circuit can be fixed as necessary, the operation of the voltage generation circuit can be stabilized.

The time when the predetermined condition is satisfied may be when the signal level of the control signal becomes indefinite.
According to this aspect, the signal level of the control signal level-shifted by the level shift circuit can be prevented from becoming unstable, and the operation of the voltage generation circuit can be stabilized.

The voltage fixing circuit may monitor the output voltage and fix the voltage of the control signal at a predetermined voltage level when the output voltage is lower than a predetermined threshold voltage.
The voltage level of the control signal output from the level shift circuit may become unstable when the output voltage is low. Thus, the circuit operation can be stabilized by fixing the voltage level according to the output voltage.

The voltage fixing circuit may perform time management of the power supply device, and may fix the voltage of the control signal to a predetermined voltage level until a predetermined time elapses after the power supply device is activated.
The voltage level of the control signal output from the level shift circuit may become unstable immediately after the power supply device is activated. Therefore, the circuit operation can be stabilized by fixing the voltage level in accordance with the elapsed time from the startup.

  In one aspect, the voltage generation circuit is connected to the flying capacitor charged by the input voltage, the output capacitor to which the charge stored in the flying capacitor is transferred, the flying capacitor and the output capacitor, and is controlled to be turned on and off by the control signal. A charge pump circuit including a plurality of switches. The level shift circuit may level shift a control signal to be supplied to at least one of the plurality of switches.

The control circuit controls the control signal so that a switch provided on the path from the terminal to which the input voltage is applied to the terminal to which the output voltage is output is fixedly turned on when the boosting rate of the charge pump circuit is 1 time. May be generated. The level shift circuit shifts the level of a control signal to be supplied to a switch provided on the path and supplies the control signal to the switch. The voltage fixing circuit turns on the switch provided on the path when a predetermined condition is satisfied. As such, it may be fixed at a predetermined voltage level.
In this case, when a predetermined condition is satisfied, the switch on the path is fixed in the ON state, so that the output capacitor can be fixed in a state of being directly charged with the input voltage.

  The switch provided on the path is a P-channel MOS transistor, and the voltage fixing circuit may fix the control signal to be supplied to the switch provided on the path to a low level when a predetermined condition is satisfied. Good.

  At least the control circuit, the level shift circuit, and the voltage fixing circuit may be integrated on a single semiconductor substrate. “Integrated integration” includes the case where all of the circuit components are formed on a semiconductor substrate and the case where the main components of the circuit are integrated. A resistor, a capacitor, or the like may be provided outside the semiconductor substrate.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  According to the present invention, the stability of a power supply device using a level shift circuit can be improved.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. Further, the embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

  FIG. 1 is a circuit diagram showing a configuration of a power supply apparatus 100 according to an embodiment of the present invention. The power supply device 100 is mounted on an electronic device such as a battery-driven mobile phone terminal, a PDA, or a music playback device. The battery voltage Vbat output from the battery is set as the input voltage Vin, and the input voltage Vin is set at a predetermined boosting rate. The voltage is boosted and a drive voltage (hereinafter also referred to as output voltage Vout) is supplied to a load (not shown).

  The power supply apparatus 100 includes an input terminal 102 and an output terminal 104. The power supply apparatus 100 boosts the input voltage Vin applied to the input terminal 102 and outputs the boosted voltage from the output terminal 104 as the drive voltage Vout.

  The power supply apparatus 100 includes a charge pump circuit 10, a control circuit 20, a level shift circuit 30, and a voltage fixing circuit 40.

  The charge pump circuit 10 is a voltage generation circuit that generates an output voltage Vout based on an external input voltage Vin. The charge pump circuit 10 includes a flying capacitor Cf, an output capacitor Co, and a plurality of switches M1 to M4.

  The plurality of switches M1 to M4 (hereinafter referred to as the first switch to the fourth switch) are MOS transistors, and the first switch M1 to the third switch M3 are P-channel MOS transistors, and the fourth switch M4. Is composed of an N-channel MOS transistor. The source of the first switch M1 is connected to the input terminal 102, and the drain is connected to the first terminal 12 of the flying capacitor Cf. The drain of the second switch M2 is connected to the first terminal 12 of the flying capacitor Cf, and the source is connected to the output terminal 104. The source of the third switch M3 is connected to the input terminal 102, and the drain is connected to the second terminal 14 of the flying capacitor Cf. The fourth switch M4 has a drain connected to the second terminal 14 of the flying capacitor Cf and a source grounded.

  The control circuit 20 generates a control signal for controlling the generation of the output voltage Vout by the charge pump circuit 10. Specifically, the control circuit 20 generates control signals S1 to S4 for controlling on / off of the first switch M1 to the fourth switch M4. The control signals S1 and S2 are output to the gates of the first switch M1 and the second switch M2 via the level shift circuit 30 and the voltage fixing circuit 40. The control signals S3 and S4 are output to the gates of the third switch M3 and the fourth switch M4.

The step-up rate of the charge pump circuit 10 is switched between 1 and 2 according to a generation pattern of a control signal described later.
When the step-up rate is double, the control circuit 20 turns on the first switch M1 and the fourth switch M4, charges the flying capacitor Cf with the input voltage Vin, the second switch M2, and the third switch M3. And the control signals S1 to S4 are generated so as to alternately repeat the second state in which the charge stored in the flying capacitor Cf is transferred to the output capacitor Co. As a result, an output voltage Vout obtained by doubling the input voltage Vin is generated.

  When the step-up ratio is 1, the control circuit 20 includes a first switch M1 and a second switch provided on a path from the input terminal 102 to which the input voltage Vin is applied to the output terminal 104 to which the output voltage Vout is output. Control signals S1 and S2 are generated so that M2 is fixedly turned on. When the first switch M1 and the second switch M2 are turned on, the input terminal 102 and the output terminal 104 are connected via the two switches, and an output voltage Vout substantially equal to the input voltage Vin is generated.

  Here, attention is focused on the first switch M1 and the second switch M2. When the step-up rate is double, a voltage comparable to the output voltage Vout is applied to the drains or sources of the first switch M1 and the second switch M2. Therefore, in order to control the on / off of the first switch M1 and the second switch M2, it is necessary to supply a logic signal having 0V as a low level and Vout as a high level as a gate voltage. On the other hand, the signal levels of the control signals S1 to S4 generated by the control circuit 20 that operates based on the input voltage Vin are logic signals in which 0V is low and Vin is high. Therefore, the level shift circuit 30 is provided in the power supply device 100 according to the present embodiment.

  The level shift circuit 30 receives control signals S 1 and S 2 to be supplied to the first switch M 1 and the second switch M 2, shifts the level using the output voltage Vout of the charge pump circuit 10, and supplies it to the charge pump circuit 10. . The signal levels of the control signals S1 ′ and S2 ′ level-shifted by the level shift circuit 30 are logic signals with 0V being low level and Vout being high level, and the first switch M1 and the second switch M2 are reliably controlled on and off. Is done.

  Voltage fixing circuit 40 is provided in power supply device 100 according to the present embodiment. The voltage fixing circuit 40 monitors the state of the power supply device 100, and forcibly fixes the control signals S1 and S2 level-shifted by the level shift circuit 30 to a predetermined voltage level when a predetermined condition is satisfied.

  Depending on the state of the power supply apparatus 100, a situation may occur in which the signal levels of the control signals S1 'and S2' output from the level shift circuit 30 are indefinite. The indefinite signal level means a state in which the control signals S1 'and S2' that should originally take a voltage value of 0V or Vout have a voltage value at an intermediate level. When the signal levels of the control signals S1 ′ and S2 ′ become indefinite, the ON / OFF of the first switch M1 and the second switch M2 is not determined, so that the output voltage Vout is not stable or an inrush current is generated in a circuit path. May flow. Therefore, the voltage fixing circuit 40 fixes the signal levels of the control signals S1 'and S2' when there is a possibility that the signal levels of the control signals S1 'and S2' become unstable. When the control signals S1 'and S2' are stable, the voltage fixing circuit 40 does not act on the control signals S1 'and S2'.

  The power supply device 100 according to the present embodiment sets the step-up rate of the charge pump circuit 10 to 1 immediately after startup, and charges the output capacitor Co with the input voltage Vin via the first switch M1 and the second switch M2. To do. Such a power supply device 100 becomes unstable for the following reasons. That is, in order to turn on the first switch M1 and the second switch M2 at the time of startup, the logic levels of the control signals S1 'and S2' must be fixed at a low level. However, if the output voltage Vout supplied to the level shift circuit 30 does not rise to a certain extent, the ON / OFF state of the transistors in the level shift circuit 30 becomes indefinite, and the normal level shift operation is not performed, and the control signal S1 ', S2' becomes indefinite.

  Therefore, in an embodiment, the voltage fixing circuit 40 monitors the output voltage Vout, and when the output voltage Vout is lower than the predetermined threshold voltage Vth, the control signal S1 ′, S2 ′ is sent to the first switch M1, The second switch M2 is fixed to a logic level (that is, low level) at which the second switch M2 is turned on. FIG. 2 is a circuit diagram showing a configuration of the voltage fixing circuit 40. The voltage fixing circuit 40 includes a comparator 42, an inverter 44, a transistor M5, and a resistor R1. The comparator 42 compares the output voltage Vout with the threshold voltage Vth, and outputs a comparison signal Vcmp that is at a high level when Vout> Vth and at a low level when Vout <Vth. The comparison signal Vcmp is inverted by the inverter 44 and input to the gate of the transistor M5 whose source is grounded. A resistor R1 is connected between the drain of the transistor M5 and the signal path of the control signal S1 '(S2').

  According to the voltage fixing circuit 40, when Vout <Vth, the transistor M5 is turned on and the control signal S1 '(S2') is fixed at a low level. When Vout> Vth, the transistor M5 is turned off, and the control signal S1 '(S2') is supplied to the first switch M1 (second switch M2) as it is.

  The operation of the power supply apparatus 100 configured as described above will be described. 3A to 3C are signal waveform diagrams showing the operating state of the power supply apparatus 100 of FIG. 4A shows the level of the control signal S1 ′ (S2 ′) output from the level shift circuit 30, FIG. 4B shows the output voltage Vout, and FIG. The flowing current Ic is shown.

  In order to clarify the effect of the power supply apparatus 100 according to the present embodiment, in FIGS. 3A to 3C, waveforms when the voltage level is not fixed by the voltage fixing circuit 40 are indicated by broken lines. Note that the vertical and horizontal axes in FIGS. 3A to 3C are enlarged or reduced as appropriate for easy understanding, and the waveforms shown are also simplified for easy understanding. Has been.

  First, the case where the voltage level is not fixed by the voltage fixing circuit 40 will be described. When the activation of the power supply apparatus 100 starts at time t0, the step-up rate is set to 1 and the control signals S1 and S2 are generated at a low level so that the first switch M1 and the second switch M2 are turned on. In the state where the output voltage Vout immediately after the start is low, the level shift circuit 30 does not operate stably, and the control signals S1 ′ and S2 ′ that should be fixed to the low level (0V) increase as the output voltage Vout increases. To do. When the voltage levels of the control signals S1 'and S2' change, the ON level of the first switch M1 and the second switch M2 changes, and the operation state of the circuit becomes unstable.

When the output voltage Vout rises to a region where the level shift circuit 30 operates stably at time t1, the control signals S1 ′ and S2 ′ drop to the low level (0 V). As a result, the first switch M1 and the second switch M2 that have been gently turned on until then are completely turned on.
When the first switch M1 and the second switch M2 are completely turned on at time t1, as shown in FIG. 3B, the output voltage Vout rapidly increases. A sudden increase in the output voltage Vout may adversely affect the load circuit. Further, as shown in FIG. 5C, the charging current Ic flowing from the input terminal 102 increases rapidly at time t1. Such a sudden rise in the charging current Ic may affect the reliability of the circuit as an inrush current.

Next, the operation when the voltage level is fixed by the voltage fixing circuit 40 in the power supply device 100 according to the embodiment will be described.
Activation is started at time t0. At this time, since the output voltage Vout is lower than the threshold voltage Vth, the signal levels of the control signals S1 ′ and S2 ′ are fixed at a low level (0 V). The threshold voltage Vth is higher than the output voltage Vout necessary for stabilizing the signal levels of the control signals S1 ′ and S2 ′ output from the level shift circuit 30, that is, indicated by a broken line in FIG. It is desirable to set the output voltage Vout higher than the voltage value at time t1. By setting the threshold voltage Vth in this way, when Vout> Vth, even if the level fixing by the voltage fixing circuit 40 is released, the control signals S1 ′ and S2 ′ output from the level shift circuit 30 itself It is guaranteed that the voltage level is stabilized.

  After time t0, both the first switch M1 and the second switch M2 are turned on. At this time, since the gate voltage is fixed, the degree of ON of the first switch M1 and the second switch M2 is kept almost constant, and the output capacitor Co is gradually charged. As a result, no peak is observed in the charging current Ic, and the output voltage Vout also increases gently.

  As described above, according to the power supply apparatus 100 according to the present embodiment, the output voltage Vout is gently reduced by fixing the logic levels of the control signals S1 ′ and S2 ′ using the voltage fixing circuit 40 as necessary. The circuit operation can be stabilized. Furthermore, the occurrence of inrush current can be suppressed.

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  In the embodiment, the voltage fixing circuit 40 determines whether or not the voltage levels of the control signals S1 'and S2' are fixed by comparing the output voltage Vout and the threshold voltage Vth. However, the present invention is not limited to this. For example, in one embodiment, the voltage fixing circuit performs time management of the power supply apparatus, and outputs the control signals S1 ′ and S2 ′ to a predetermined voltage from when the power supply apparatus is activated until a predetermined time elapses. It may be fixed at a level (low level).

  In the embodiment, the case where the charge pump circuit is used as the voltage generation circuit has been described. However, the present invention is not limited to this and is applied to an insulating or non-insulating switching regulator circuit, a DC / AC converter, or the like. It is also possible. That is, in order to turn on / off a switching element provided in a switching regulator circuit or a DC / AC converter, there is a circuit that performs a level shift using the output voltage. Even in such a circuit, it is possible to improve the stability of the circuit by providing a voltage fixing circuit in the path from the level shift circuit to the switching element and fixing the voltage level of the signal when a predetermined condition is satisfied. .

  In the present embodiment, the transistor to be used is an FET, but another type of transistor such as a bipolar transistor may be used. You can decide by.

  In the present embodiment, all the elements constituting power supply apparatus 100 may be integrated, or a part thereof may be composed of discrete components. Which part is integrated may be determined by cost, occupied area, or the like.

It is a circuit diagram which shows the structure of the power supply device which concerns on embodiment. It is a circuit diagram which shows the structure of a voltage fixing circuit. FIGS. 3A to 3C are signal waveform diagrams showing the operating state of the power supply device of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Charge pump circuit, 20 Control circuit, 30 Level shift circuit, 40 Voltage fixing circuit, Cf Flying capacitor, Co output capacitor, M1 1st switch, M2 2nd switch, M3 3rd switch, M4 4th switch, 100 Power supply device , 102 input terminals, 104 output terminals.

Claims (8)

A power supply device that outputs a predetermined output voltage,
A voltage generation circuit for generating the output voltage based on an external input voltage;
A control circuit for generating a control signal for controlling the voltage generation circuit;
A level shift circuit for level-shifting at least a part of the control signal output from the control circuit using the output voltage and supplying the level shift circuit;
A voltage fixing circuit for forcibly fixing the control signal level-shifted by the level shift circuit to a predetermined voltage level when a predetermined condition is satisfied;
A power supply apparatus comprising:   The power supply apparatus according to claim 1, wherein the predetermined condition is satisfied when a signal level of the control signal becomes indefinite.   The voltage fixing circuit monitors the output voltage and fixes the control signal at the predetermined voltage level when the output voltage is lower than a predetermined threshold voltage. Power supply.   The voltage fixing circuit performs time management of the power supply apparatus, and fixes the control signal to the predetermined voltage level from the start of the power supply apparatus until a predetermined time elapses. Item 2. The power supply device according to Item 1. The voltage generation circuit includes:
A flying capacitor charged by the input voltage;
An output capacitor to which the charge stored in the flying capacitor is transferred;
A plurality of switches connected to the flying capacitor and the output capacitor and controlled to be turned on and off by the control signal;
A charge pump circuit comprising:
The power supply apparatus according to claim 1, wherein the level shift circuit shifts a level of a control signal to be supplied to at least one of the plurality of switches. In the control circuit, when the step-up rate of the charge pump circuit is 1, a switch provided on a path from a terminal to which the input voltage is applied to a terminal to which the output voltage is output is fixedly turned on. Generating the control signal as
The level shift circuit level-shifts a control signal to be supplied to the switch provided on the path and supplies the control signal to the switch.
6. The power supply device according to claim 5, wherein the voltage fixing circuit fixes the predetermined voltage level so that the switch provided on the path is turned on when the predetermined condition is satisfied.   The switch provided on the path is a P-channel MOS transistor, and the voltage fixing circuit outputs a control signal to be supplied to the switch provided on the path when the predetermined condition is satisfied. The power supply device according to claim 6, wherein the power supply device is fixed to a level.   4. The power supply device according to claim 1, wherein at least the control circuit, the level shift circuit, and the voltage fixing circuit are integrated on a single semiconductor substrate. 5.

Images