JP5444012B2 - Charge pump circuit - Google Patents

Description

The present invention relates to a charge pump circuit in which an influence on a load device or a peripheral circuit due to switching noise is suppressed. The present invention also includes a so-called charge pump regulator circuit capable of controlling the target output voltage level.

  FIG. 5 shows a circuit diagram of a general doubler (double) charge pump circuit. The charge pump circuit 90 shown in FIG. 5 is a circuit intended to obtain a voltage twice as large as the input voltage Vin as the output voltage Vo.

  The charge pump circuit 90 includes a fly capacitor Cf and a smoothing output capacitor Co. One electrode of the fly capacitor Cf forms a node Na, and the other electrode forms a node Nb.

  The node Na is applied with the input voltage Vin via the switch SW1, and is connected to one electrode (output end side) of the output capacitor Co via the switch SW4. The other electrode of the output capacitor Co is connected to the ground line. The node Nb is applied with the input voltage Vin via the switch SW3 and is connected to the ground line via the switch SW2. The switches SW <b> 1 to SW <b> 4 are on / off controlled by the control unit 10.

  Under such a configuration, first, as shown in FIG. 5A, the switches SW3 and SW4 are turned off and the switches SW1 and SW2 are turned on. At this time, the input voltage Vin is applied between both electrodes of the fly capacitor Cf, and the voltage Vin is held.

  Next, as shown in FIG. 5B, the switches SW1 and SW2 are turned off, and SW3 and SW4 are turned on. At this time, since the voltage of the node Nb on the low voltage side of the fly capacitor Cf is Vin, the voltage Vin of the node Nb is added to the voltage of Vin held in the fly capacitor Cf, and the voltage of 2 Vin is applied to the node Na. Will occur. Since the switch SW4 is connected, the voltage of the node Na is output as it is as the output voltage Vo. In this way, a voltage twice as large as the input voltage Vin can be obtained as the output voltage Vo.

  FIG. 6 shows a circuit diagram of a charge pump regulator circuit that realizes an arbitrary voltage by a boost charge pump operation. The charge pump circuit 91 shown in FIG. 6 includes a PWM control circuit 21 and an error amplifier 22 as the control unit 10.

  The charge pump circuit 91 monitors the output voltage Vo, amplifies the error signal by the error amplifier 22 that compares the monitor voltage and the fixed reference voltage Vref, and outputs the amplified error signal to the PWM control circuit 21. The PWM control circuit 21 controls the charging duty to the fly capacitor Cf or the discharging duty from the fly capacitor Cf to the output capacitor Co by performing opening / closing control of the switches SW1 to SW4 based on the input error amplification signal. doing. In FIG. 6, (a) shows the connection state of each switch when charging the fly capacitor Cf, and (b) shows the connection state of each switch when discharging to Cf. With this configuration, automatic control is performed so that the output voltage Vo becomes the target fixed reference voltage Vref.

  Both of the configurations of FIGS. 5 and 6 are of the type that conveys the charge stored in the fly capacitor Cf to the output capacitor Co. In these configurations, when the fly capacitor Cf holding the electric charge is connected to the output capacitor Co through the switches SW3 and SW4, spike noise is generated, and the connected load device is destroyed or the peripheral circuit is connected. May cause abnormal characteristics. This is largely due to the influence of parasitic capacitance existing in the circuit.

  Even when the feedback control is configured as shown in FIG. 6, since the cause of the noise is present outside the feedback loop, the effect of automatically attenuating the noise by simply performing the feedback control is effective. I can't get it. In order to obtain such an effect, it is conceivable to include a component (for example, a constant current source) having a noise suppressing effect in the control unit 10. However, according to this method, the load followability of the charge pump booster circuit is impaired. The presence of a feedback control loop delay also affects the generation of noise.

  In order to deal with such a problem, in Patent Document 1 below, when the output voltage becomes higher than the overshoot voltage, a transistor connected between the output terminal and the GND terminal is connected, so that the output terminal The structure which discharges is disclosed. This not only protects the load device, but also shortens the settling time until stabilization.

JP 2009-177906 A

  However, in the case of the method described in Patent Document 1, when the overshoot voltage is generated, the output terminal is discharged toward the GND line through the transistor, so that energy loss inevitably occurs. To do. Further, since the voltage raised after the charge pump is compared with the fixed reference voltage, it is impossible to absorb noise generated at the rising edge of switching.

  In view of the above problems, an object of the present invention is to provide a charge pump circuit capable of both suppressing energy loss and suppressing the influence of switching noise.

In order to achieve the above object, the charge pump circuit of the present invention comprises:
A first electrode connectable to an input voltage source via a first switch; a second electrode connectable to a ground line via a second switch and connectable to the input voltage source via a third switch; A fly capacitor having
A smoothing output capacitor having a first electrode connectable to the first electrode of the fly capacitor via a fourth switch, and a second electrode connected to the ground line;
A snubber capacitor having a first electrode connected to the first electrode of the fly capacitor or connectable via a switch, and a second electrode capable of changing an applied voltage;
And a control unit for changing the voltage applied to the second electrode of the snubber capacitor.

  When configured in this way, when the switching noise generated when the switch is turned on and off is superimposed on the voltage of the node connected to the first electrode of the fly capacitor, even if the noise cannot be sufficiently absorbed by the output capacitor, Can be absorbed with a snubber capacitor. Thereby, it can avoid supplying the voltage containing a high frequency noise with respect to the load device connected to an output terminal.

  In addition, the noise component is absorbed by the snubber capacitor, and the snubber capacitor can be connected to the electrode of the fly capacitor, so the noise-derived charge absorbed by the snubber capacitor is supplied to the fly capacitor charge again. Is possible. Therefore, it is not a configuration in which a voltage including a noise component is directly discharged to the ground line as in the conventional case, and an effect of reducing power consumption can be obtained as compared with the conventional case.

In addition to the features described above, the present invention
The control unit is
A charge operation for turning on the first switch and the second switch and turning off the third switch and the fourth switch;
The first switch and the second switch are turned off, and the discharge operation for turning the third switch and the fourth switch on is controlled while alternately switching,
In the discharging operation, a voltage applied to the second electrode of the snubber capacitor is made lower than that in the charging operation.

  By doing so, since the voltage of the second electrode of the snubber capacitor is reduced during the discharge operation, the voltage of the node connected to the first electrode of the fly capacitor includes a noise component. However, this voltage is likely to be given to the snubber capacitor side preferentially over the external load. Therefore, the effect of preventing the voltage including the noise component from being supplied to the external load can be further enhanced.

  In addition to the above feature, the present invention is characterized in that the control unit performs control to turn on the second switch before the first switch during the charge operation.

  By doing so, since the voltage of the second electrode of the fly capacitor has been lowered in advance, the electric charge held in the snubber capacitor during the charge operation can be easily discharged to the first electrode of the fly capacitor. The regenerative operation of the charge held in the snubber capacitor can be executed with priority over the charge supplied from the input voltage source.

In the present invention, in addition to the above feature, the second electrode of the snubber capacitor can be connected to the input voltage source via a fifth switch, and can be connected to a ground line via a sixth switch.
The controller is
During the charging operation, the fifth switch is turned on, the sixth switch is turned off,
In the discharge operation, the fifth switch is turned off and the sixth switch is turned on.

  By doing so, the second electrode of the snubber capacitor becomes the output voltage of the input voltage source during the charging operation, and the second electrode of the snubber capacitor becomes the ground voltage during the discharging operation. Thereby, the voltage of the 2nd electrode of a snubber capacitor can be reduced at the time of a discharge operation, and the noise component superimposed on the voltage hold | maintained at the 1st electrode of the fly capacitor can be absorbed by a snubber capacitor.

At this time, it is preferable that the control unit performs control to turn on the first switch after turning on the second switch and the fifth switch during the charging operation.

  The effect of turning on the second switch before the first switch is as described above. Further, by turning on the fifth switch before the first switch, the first electrode of the snubber capacitor is connected to the first electrode of the fly capacitor before the input voltage source. Thereby, the electric charge held in the snubber capacitor can be forcibly supplied to the fly capacitor. Therefore, when the first switch is turned on after that, if the voltage held between the two electrodes of the fly capacitor is insufficient compared to the voltage of the input voltage source, only this shortage is derived from the input voltage source. Charge is supplied to the first electrode of the fly capacitor. In other words, the current consumption from the input voltage source only covers the shortage due to the regenerative operation from the snubber capacitor, so the power consumption is higher than when charging the fly capacitor with the current from the input voltage source. The amount can be reduced.

  In the discharging operation, it is preferable to perform control to turn on the fourth switch after turning on the third switch and the sixth switch.

  By doing so, the noise voltage superimposed by turning on the third switch can be once absorbed by the snubber capacitor. Therefore, when the fourth switch is subsequently turned on, only noise generated by turning on the fourth switch needs to be considered. That is, the amount of noise component to be absorbed at the timing when the fourth switch is turned on to obtain the output voltage Vo can be reduced.

The charge pump circuit of the present invention is
The control unit is
A first electrode of the output capacitor and a variable reference voltage source are connected to an input terminal, a second electrode of the snubber capacitor is connected to an output terminal, and an output from the voltage of the first electrode of the output capacitor and the variable reference voltage source An error amplifier that amplifies the difference between the voltages to be applied to the second electrode of the snubber capacitor,
When switching from the charge operation to the discharge operation, another feature is that control is performed to reduce the voltage value output from the variable reference voltage source.

  Even in such a configuration, the voltage of the second electrode of the snubber capacitor can be reduced during the discharge operation, and the noise component superimposed on the voltage held in the first electrode of the fly capacitor is absorbed by the snubber capacitor. be able to.

In addition to the above features, the charge pump circuit of the present invention includes:
The control unit is
A first electrode of the output capacitor and a fixed reference voltage source are connected to the input terminal, a PWM control circuit is connected to the output terminal, and the voltage of the first electrode of the output capacitor and the voltage output from the fixed reference voltage source An error amplifier for feedback control that amplifies the difference and gives it to the PWM control circuit;
Another feature is that the PWM control circuit determines the duty ratio of each switch in accordance with the output voltage of the error amplifier for feedback control.

  With this configuration, a charge pump regulator circuit that achieves both suppression of power consumption and absorption of noise components can be realized.

In addition to the above features, the charge pump circuit of the present invention includes:
A snubber resistor having a first terminal connected to the first electrode of the snubber capacitor and a second terminal connected to the first electrode of the fly capacitor directly or via a switch;
Another feature is that the first electrode of the snubber capacitor is configured to be connectable to the first electrode of the fly capacitor via the snubber resistor.

  The switching noise may have resonance derived from a parasitic inductance component. If a resonance component exists in noise, it takes time to absorb the noise by the snubber capacitor. For this reason, by providing a snubber resistor in series with the snubber capacitor, the resonance of noise can be forcibly attenuated, and the noise absorption by the snubber capacitor can be executed quickly.

At this time, it has a bypass switch formed in parallel with the snubber resistor,
It is preferable that the control unit controls the bypass switch to be turned on during the charging operation, thereby bypassing the snubber resistor and forming a current path via the bypass switch.

  When the charge accumulated in the snubber capacitor is regenerated in the fly capacitor during the charge operation by absorbing noise during the discharge operation, power consumption occurs in the resistor when a current flows through the snubber resistor. For this reason, by connecting the snubber capacitor and the fly capacitor via the bypass switch during the charge operation, the regenerative operation can be performed without passing a current through the snubber resistor, and the power consumption can be reduced.

In addition to the above features, the charge pump circuit of the present invention includes:
The capacitance value of the snubber capacitor and the resistance value of the snubber resistor are each configured to be variable,
A monitor circuit for observing a waveform of a voltage applied to the first electrode of the output capacitor and measuring a ringing frequency;
The control unit may perform a predetermined calculation from the capacitance value of the snubber capacitor and the ringing frequency to determine a resistance value of the snubber resistor.

  By doing so, voltage oscillation can be forcibly attenuated with respect to noise components including resonance derived from parasitic inductance, and high speed noise absorption by the snubber capacitor can be realized.

  According to the configuration of the present invention, the switching noise can be absorbed by the snubber capacitor even when the charge holding allowable amount of the smoothing output capacitor is insufficient. It can be prevented from being supplied to the device. Furthermore, since the electric charge held in the snubber capacitor can be used again to charge the fly capacitor, the power consumption can be reduced as compared with the conventional configuration in which the voltage including the noise component is discharged to the ground line.

Circuit diagram of charge pump circuit of the present invention Another circuit diagram of the charge pump circuit of the present invention Another circuit diagram of the charge pump circuit according to the present invention Voltage change timing diagram of each node of charge pump circuit Circuit diagram of conventional doubler charge pump circuit Circuit diagram of conventional charge pump regulator circuit

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected about the same component as FIGS.

[First Embodiment]
A circuit diagram of a first embodiment of the charge pump circuit of the present invention is shown in FIG. The charge pump circuit 1 shown in FIG. 1 is configured to additionally include switches SW5 and SW6 and a snubber capacitor Cr as compared with the conventional charge pump circuit 90 shown in FIG. In FIG. 1, (a) shows a charge operation, and (b) shows a discharge operation.

  As shown in FIG. 1A, as in the case of FIG. 5A, the switches SW3 and SW4 are turned off and the switches SW1 and SW2 are turned on. As a result, the input voltage Vin is applied across the fly capacitor Cf, and the capacitor is charged. This operation is called “charging operation”.

  Next, as shown in FIG. 1B, as in the case of FIG. 5B, the switches SW1 and SW2 are turned off, and the switches SW3 and SW4 are turned on. As a result, the voltage at the node Nb on the low voltage side of the fly capacitor Cf rises from the GND level to the Vin level. As a result, a voltage of 2 Vin is generated at the node Na on the high voltage side of the fly capacitor Cf. Since the switch SW4 is connected, the voltage at the node Na is output as it is as the output voltage Vo. This operation is called “discharge operation”. The charge operation and discharge operation are exactly the same as those in FIG.

  Next, switching noise that is a problem will be described.

  If there is no charge left in the output capacitor Co, if the ESR (Equivalent Series Resistance) and wiring impedance of this capacitor are low, even if switching noise occurs, it will be absorbed by the output capacitor Co. The noise does not flow out to the load device connected to the output terminal, and the load device is not affected. However, if the charge is sufficiently held in the output capacitor Co, the switching noise cannot be sufficiently absorbed by the output capacitor Co, and the rest flows out from the output terminal toward the load device. As a result, the load device is adversely affected.

  The charge pump circuit 1 of the present invention includes a snubber capacitor Cr in order to cope with this problem. Hereinafter, description will be made on the point that the influence of the switching noise on the load device can be suppressed by providing the snubber capacitor Cr.

  As shown in FIG. 1A, the switch SW5 is turned on and the switch SW6 is turned off during the charging operation. At this time, there is no voltage difference between the two electrodes of the snubber capacitor Cr, and no electric charge is retained. At this time, the voltage of the node Nc is Vin. At this time, it is assumed that almost no charge is accumulated in the output capacitor Co.

  Next, as shown in FIG. 1B, in the discharging operation, the switch SW5 is turned off and the switch SW6 is turned on. As described above, the voltage of the node Na is pushed up to 2 Vin during the discharge operation. Here, when the switch SW6 is connected, the voltage of the node Nc becomes 0V, so that a voltage of 2Vin is applied to the snubber capacitor Cr.

  By the way, when the terminal on the node Nc side of the snubber capacitor Cr decreases from Vin to 0 V during the discharge operation, the voltage at the node Na decreases in accordance with the capacitance ratio of the snubber capacitor Cr. When the switches SW3 and SW4 are turned on at the time, spike noise is instantaneously superimposed on the node Na. Therefore, it is necessary to determine the electrostatic capacitance of the snubber capacitor Cr so that these are canceled out and the voltage of the node Na becomes approximately 2 Vin in the steady state after the discharge operation is performed. If the capacitance of the snubber capacitor Cr is too large, the voltage at the node Na may not reach 2 Vin in a steady state after executing the discharge operation. On the other hand, if it is too small, the effect of canceling the spike noise cannot be obtained. For this reason, an appropriate capacitance of the snubber capacitor Cr is determined in consideration of the magnitude of noise and the total parasitic capacitance of the node Na (particularly, the capacitance of the fly capacitor Cf). As an example, the capacitance of the snubber capacitor Cr can be set to about 1/10 of the capacitance of the fly capacitor Cf.

  The voltage at the node Na is obtained as the output voltage Vo through the switch SW4. At this time, since no charge is accumulated in the output capacitor Co, even if the spike noise component is larger than the voltage reduction effect of the node Na by the snubber capacitor Cr, this noise component is absorbed by the output capacitor Co. The noise component does not flow out from the output terminal.

  Next, the operation returns to the charge operation again. That is, the switches SW3, SW4, and SW6 are turned off, and the switches SW1, SW2, and SW5 are turned on. At this time, the voltage of the node Nc rises from 0V to the input voltage Vin. For this reason, the voltage of the node Na is pushed up from 2Vin. At this time, after transiently being pushed up to about 3 Vin, it is steadily lowered to the input voltage Vin. The pushed voltage of the node Na contributes to the charge accumulation of the fly capacitor Cf. That is, the charge held in the snubber capacitor Cr can be transferred to the fly capacitor Cf.

  Here, especially by turning on SW5 before the switch SW1, the charge from the snubber capacitor Cr is held before the charge derived from the power supply voltage Vin is held in the fly capacitor Cf. Thereby, the electric charge held in the snubber capacitor Cr can be effectively used for charging the fly capacitor Cf, and the power consumption can be reduced as compared with the conventional configuration.

  In the present embodiment, it is preferable that the switches SW2, SW5, and SW1 are turned on in the order of the charge operation, and the switches SW3, SW6, and SW4 are turned on in the order of the discharge operation.

  During the charging operation, the switch SW2 is turned on prior to SW1 and SW5, thereby reducing the voltage at the node Nb so that the charge previously held in the snubber capacitor Cr can be held in the fly capacitor Cf. There is an aim. Thereafter, the switch SW5 is turned on before SW1, thereby supplying the charge held in the snubber capacitor Cr before the input voltage Vin to the fly capacitor Cf. Thereby, the electric charge held in the snubber capacitor Cr can be effectively utilized for charging the fly capacitor Cf. In particular, when the fly capacitor Cf is fully charged by the electric charge applied from the snubber capacitor Cr, no current flows from the input voltage Vin via the switch SW1, and the power consumption can be greatly reduced.

  Next, in the discharge operation, after the switch SW3 is turned on to increase the voltage at the node Na, the switch SW6 is turned on before the switch SW4 is turned on, so that the noise component superimposed on the node Na is removed. Before being output as the output voltage Vo, it can be absorbed by the snubber capacitor Cr.

[Second Embodiment]
A circuit diagram of a second embodiment of the charge pump circuit of the present invention is shown in FIG. The charge pump circuit 1a shown in FIG. 2 includes, as the control unit 10, a monitor circuit 11a that observes the voltage waveform of the output voltage Vo, a monitor circuit 11b that observes the voltage waveform of the node Na, and switches based on the results of both monitor circuits. Is provided with a pre-driver 12 for executing on / off control.

  Furthermore, the charge pump 1a is provided with a snubber resistor R and switches SW7 and SW8. Snubber resistor R has one end connected to one electrode of snubber capacitor Cr and the other end connected to node Na via switch SW7. The switch SW8 is connected in parallel to the snubber resistor R, and has a bypass function that prevents current from flowing through the snubber resistor R when the switch SW8 is turned on.

  The noise component described above in the first embodiment is largely affected by the parasitic capacitance of each transistor. In addition, the noise component may also be affected by parasitic inductance. When affected by the parasitic inductance, a resonance waveform is formed in the switching noise. At this time, it takes time for the switching noise to be stably attenuated by the ESR of the output capacitor Co. In this embodiment, a snubber resistor R is provided as a countermeasure to accelerate the damping operation.

  By the way, as described above in the first embodiment, as one of the features of the present invention, after the electric charge including the noise component is absorbed by the snubber capacitor Cr, this electric charge is used (regenerated) for the charging operation of the fly capacitor Cf. This has the effect of reducing power consumption. However, when the snubber resistor R is configured as shown in FIG. 2, if a current generated during the regenerative operation flows to the snubber resistor R, power consumption occurs here, and the power consumption of the present invention is reduced. The effect is diminished. For this reason, in the configuration of the present embodiment, the switch SW8 for bypassing the snubber resistor R is provided, and the power consumption in the snubber resistor R is avoided by turning on the switch SW8 during the regenerative operation. .

  The same effect can be obtained even if the resistance value of the snubber resistor R is changed by the control by the control unit 10 and control is performed to greatly reduce the resistance value during the regenerative operation. . In this case, the switch SW8 may not be provided. Furthermore, at this time, the snubber resistor R can be replaced by the on-resistance of the switch SW7. In this case, by providing a plurality of switches in parallel as the switch SW7, the resistance value of the snubber resistor R that is equivalently realized by the combined resistance of the on-resistances of the switches can be made variable.

  In the configuration of FIG. 2, it is preferable to turn on the switches SW6 and SW7 after turning on the switch SW3 and then turn on the switch SW4 after the switch SW3 is turned on. In the case of the configuration of the first embodiment, one electrode of the snubber capacitor Cr is always connected to the node Na. Therefore, when the switch SW3 is turned on to increase the voltage at the node Na, a part of the charge is converted into the snubber capacitor Cr. Therefore, the voltage rise at the node Na is moderated accordingly. On the other hand, in the case of the present embodiment, the switch SW7 is turned off when the switch SW3 is turned on, so that no element such as the snubber capacitor Cr or the snubber resistor R is connected to the node Na. You can increase the climb speed.

  Thereafter, when the switches SW6 and SW7 are turned on, electric charges are supplied from the node Na whose voltage has increased to the snubber capacitor Cr, and rapid charging becomes possible.

  Further, as shown in FIG. 2, the charge pump circuit 1a of the present embodiment includes monitor circuits 11a and 11b. The role of this monitor circuit will be described below.

  In the case of this embodiment, it is the structure provided with the snubber resistance R. As described above, additional power consumption can be avoided by preventing current from flowing through the snubber resistor R during the regenerative operation. However, when noise is absorbed by the fly capacitor Cr during the discharge operation, Since a snubber resistor R is provided to attenuate resonance of noise including an inductance component, a current inevitably flows through the snubber resistor R. Therefore, as long as this is the case, additional power consumption is unavoidable compared to the first embodiment.

  By the way, the present invention has a problem in that a voltage including a noise component is supplied as an output voltage Vo to an external load device. Such a problem occurs when the allowable amount of the output capacitor Co is small and a voltage including a noise component cannot be absorbed by the output capacitor Co. In other words, in other words, when the voltage including the noise component can be sufficiently absorbed by the output capacitor Co, it is not necessary to absorb it using the snubber capacitor Cr.

  In this embodiment, based on this fact, when the voltage including the noise component can be sufficiently absorbed by the output capacitor Co, the switch SW7 is not turned on, and only when the output capacitor Co cannot fully absorb the voltage, the switch SW7 is turned on. Absorption by the snubber capacitor Cr. Monitor circuits 11a and 11b are provided to determine whether or not the voltage including the noise component can be sufficiently absorbed by the output capacitor Co.

  In this way, when voltage absorption by the snubber capacitor Cr is not necessarily required, current can be avoided from flowing from the node Na to the snubber resistor R, and an effect of suppressing wasteful power consumption can be obtained.

  The pre-driver 12 recognizes the voltage of the node Na at the time when the switch SW3 is turned on by the output voltage of the monitor circuit 11b. At this time, the output voltage of the monitor circuit 11a is read and the voltage held at both ends of the output capacitor Co is recognized. If it is determined that the noise component currently superimposed on the node Na can be sufficiently absorbed by the output capacitor Co, the switch SW4 is turned on without turning on the switch SW7. On the other hand, when it is determined that the output capacitor Co cannot absorb it, the switches SW6 and SW7 are first turned on to absorb the high voltage noise component of the node Na with the snubber capacitor Cr, and then the switch SW4 is turned on.

  Note that a comparator for comparing the output voltages of the monitor circuits 11a and 11b may be provided in the pre-driver 12, and the above determination may be made according to the comparison result. In this case, when the load condition to which the output voltage Vo is supplied is a strict ripple condition required as the input voltage, the determination (the switch SW7 on / off control) is performed in consideration of the ripple rate. What should I do?

  On the other hand, if the load device does not require a strict ripple condition as the input voltage, the pre-driver 12 performs on / off control of the switch SW7 only by the result of the monitor circuit 11a without including the monitor circuit 11b. You can also. In this case, the pre-driver 12 includes a comparator to which the voltage measured by the monitor circuit 11a and a predetermined reference voltage serving as an index for determining that the switch SW7 needs to be turned on are input. If the measurement result exceeds this reference voltage, control can be performed to turn on the switch SW7.

When the monitor circuit 11a for observing the output voltage Vo is provided as in the present embodiment, the monitor circuit 11b measures the ringing frequency of this voltage waveform in the control unit 10, and the predriver 12 A configuration may be used in which the capacitance of the snubber capacitor Cr and the resistance value of the snubber resistor R are determined based on the frequency. By doing so, resonance can be prevented and noise components can be further suppressed. As an example of a specific method, the ringing frequency is observed while gradually increasing the capacitance of the snubber capacitor Cr from, for example, 0. Then, a parasitic capacitance is derived from the relationship between the ringing frequency reduction rate and the capacitance of the snubber capacitor Cr, and the parasitic inductance is calculated from a so-called resonance condition formula based on this parasitic capacitance. Then, the resonance impedance is calculated from the parasitic capacitance and the parasitic inductance, and the obtained value is used as the resistance value of the snubber resistor R.

  Even when the snubber capacitor Cr is configured to perform noise absorption regardless of the allowable charge amount of the output capacitor Co during the discharge operation, a voltage including a noise component is not supplied to the load device. The object of the present invention can be achieved. For this reason, it is good also as a structure which is not provided with the monitor circuits 11a and 11b in the structure of this embodiment. However, as described above, by providing these monitor circuits, the switch SW7 can be turned off during the discharge operation when there is a sufficient charge capacity of the output capacitor Co. At this time, the power in the snubber circuit R can be turned off. Consumption is suppressed. Therefore, from the viewpoint of reducing power consumption, it is more preferable to include the monitor circuits 11a and 11b.

[Third Embodiment]
A circuit diagram of a third embodiment of the charge pump circuit of the present invention is shown in FIG. FIG. 3 is a configuration in which the output voltage Vo is fed back to the control unit 10 and the on / off control of each switch is performed according to this value, as in FIG. 6, so-called charge that can control the magnitude of the desired output voltage Vo. A pump regulator circuit is configured.

  Specifically, an error amplifier 22a is provided which receives an output voltage Vo and a fixed reference voltage Vref and amplifies and outputs the difference. In addition, an error amplifier 22b is provided which receives the output voltage Vo and the fixed reference voltage Vref and amplifies and outputs the difference. The PWM control circuit 21 determines a switching duty based on the output voltage of the error amplifier 22b, and executes on / off control of each switch.

  As an example of a method for determining the switching duty, the output voltage of the error amplifier 22b is sampled every period of the oscillation signal output from the oscillation circuit included in the PWM control circuit 21. Then, the sawtooth wave or triangular wave synchronized with the frequency of the oscillation signal is compared with the output voltage of the error amplifier 22b, and the switching duty is determined according to this difference.

  By controlling the on / off of each switch by feeding back the output voltage Vo, the output voltage Vo is automatically controlled so as to become a desired fixed reference voltage Vref. This is the same as the conventional charge pump regulator circuit shown in FIG.

  As described above, in the case of the configuration of FIG. 6, the voltage observed as the output voltage Vo is a voltage supplied from the node Na that has already been lifted after the charge pump. For this reason, a voltage that already contains a noise component generated at the rising edge of switching is input to the error amplifier 22b, and the effect of absorbing this noise component cannot be obtained.

  Therefore, in this embodiment, as in the second embodiment, the switch SW7 and the snubber capacitor Cr are provided. The switch SW7 is turned on before the switch SW4 is turned on during the discharge operation, and the noise component is preliminarily generated by the snubber capacitor Cr. Absorb. Then, the voltage of the node Na after absorbing the noise is input to the error amplifier 22b, and feedback control is executed based on this voltage. In this embodiment, the snubber resistance R is provided as in the second embodiment. However, the snubber resistance R is provided for the purpose of preventing a decrease in attenuation rate due to vibration of noise components. Accordingly, when the vibration frequency is sufficiently low, the snubber resistance R may not be provided.

  In the present embodiment, an error amplifier 22a to which the output voltage Vo and the variable reference voltage Vr1 are input is provided. The output voltage of the error amplifier 22a is supplied to the node Nc.

  The control unit 10 sets the voltage value of the variable reference voltage Vr1 to a high level during the charging operation, and sets the voltage value of the variable reference voltage Vr1 to a low level during the discharging operation. By setting the voltage value of the variable reference voltage Vr1 to a low level during the discharge operation, the voltage of the node Nc is set to a low level. Thereby, as in the second embodiment, a sufficient voltage difference is provided between the node Na pushed up during the discharge operation and the node Nc, and the noise component included in the voltage of the node Na can be sufficiently absorbed.

  Switching noise is generated most greatly when the switch SW4 is turned on. For this reason, it is preferable to minimize the voltage value of the variable reference voltage Vr1 in accordance with the ON timing of the switch SW4. Thereby, the noise component generated when the switch SW4 is turned on can also be absorbed by the snubber capacitor Cr.

  FIG. 4 schematically shows change timings of the voltages at the nodes Na, Nb, and Nc. The node Nc decreases at the timing when the voltage value of the variable reference voltage Vr1 is changed to a low level (B in the figure), and immediately after this, the noise component superimposed on the voltage of the node Na is rapidly absorbed by the snubber capacitor Cr. The voltage at the node Na drops (A in the figure). Thereafter, the value of the variable reference voltage Vr1 is increased, and the voltage of the node Nc is increased. This is because the snubber capacitor Cr is only for the purpose of absorbing superimposed noise, and if the snubber capacitor Cr is charged more than necessary, the voltage charged up to the input voltage Vin will decrease, and the target voltage will be reduced. This is because it cannot be obtained. Switching noise is generated immediately after the switch is controlled, and the largest noise is superimposed immediately after the switch SW4 is turned on. Therefore, the variable reference voltage Vr1 is minimized when the switch SW4 is turned on, and immediately after that, the magnitude of Vr1 is gradually increased. This is indicated by the fact that the voltage at the node Nc gradually increases after abruptly decreasing.

  The reason why the value of the variable reference voltage Vr1 is decreased to the minimum value and then gradually increased without increasing at once is that noise is generated at the node Nc due to a sudden increase in voltage, and the influence is increased by the node. This is to prevent it from occurring in Na.

  When the switch SW4 is turned on, the voltage of the node Nc is sufficiently lowered, so that the voltage of the node Na on which the noise component is superimposed is supplied to the external load device as the output voltage Vo through the switch SW4. This contributes to the charging of the snubber capacitor Cr with higher priority. As a result, the voltage at the node Na rapidly decreases, and then the voltage is supplied to the external load device while charging the snubber capacitor Cr and the output capacitor Co. After the noise component is absorbed by the snubber capacitor Cr, the voltage at the node Na gradually decreases, indicating that the output capacitor Co or the snubber capacitor Cr is charged. However, the voltage fluctuation is very small compared to when absorbing noise, and it is not necessary to consider the influence on the load device due to this fluctuation.

  When the output voltage Vo reaches the fixed reference voltage Vref, the switch SW4 is turned off and the charging operation is started. At this time, by using the electric charge held in the snubber capacitor Cr before turning on the switch SW1 for charging the fly capacitor Cf, an effect of reducing power consumption can be obtained as in the first and second embodiments. .

  If the output voltage Vo has not reached the fixed reference voltage Vref in the state after the noise component is removed by the snubber capacitor Cr, the value of the variable reference voltage Vr1 is increased until the output voltage Vo reaches Vref, It is only necessary to shift to the charge operation at the reached stage.

  As described above, according to the configuration of each embodiment of the charge pump circuit (including the charge pump regulator circuit) of the present invention, even if the allowable amount of the output capacitor Co is insufficient, the snubber capacitor Cr Therefore, switching noise can be absorbed, so that a voltage on which the noise component is superimposed can be prevented from being supplied to the load device. In the charge pump regulator circuit, since feedback control is performed based on the output voltage after the noise component is absorbed, a desired output voltage can be obtained without being affected by the noise component.

  In the above embodiment, only for the configuration of FIG. 3 in which the voltage of the node Nc is directly controlled by the output voltage of the error amplifier 22a, the charge pump that controls the switching duty according to the difference between the output voltage Vo and the fixed reference voltage Vref. Although the regulator circuit is used, as a matter of course, the configuration of the first and second embodiments can be a charge pump regulator circuit by including the error amplifier 22b and the PWM control circuit 21.

DESCRIPTION OF SYMBOLS 1, 1a, 1b: Charge pump circuit of this invention 10: Control part 11a, 11b: Monitor circuit 12: Pre-driver 21: PWM control circuit 22, 22a, 22b: Error amplifier 90: Conventional charge pump circuit 91: Conventional Charge pump regulator circuit Cf: fly capacitor Co: output capacitor Cr: snubber capacitor Na, Nb, Nc: node R: snubber resistance SW1, SW2, SW3, SW4, SW5, SW6, SW7, SW8: switch Vin: input voltage Vo: Output voltage Vref: Fixed reference voltage

Claims (12)

A first electrode connectable to an input voltage source via a first switch; a second electrode connectable to a ground line via a second switch and connectable to the input voltage source via a third switch; A fly capacitor having
A smoothing output capacitor having a first electrode connectable to the first electrode of the fly capacitor via a fourth switch, and a second electrode connected to the ground line;
A snubber capacitor having a first electrode connected to the first electrode of the fly capacitor or connectable via a switch, and a second electrode capable of changing an applied voltage;
A charge pump circuit comprising: a control unit that performs on / off control of each switch and voltage change applied to the second electrode of the snubber capacitor. The control unit is
A charge operation for turning on the first switch and the second switch and turning off the third switch and the fourth switch;
The first switch and the second switch are turned off, and the discharge operation for turning the third switch and the fourth switch on is controlled while alternately switching,
2. The charge pump circuit according to claim 1, wherein a voltage applied to the second electrode of the snubber capacitor is lowered during the discharge operation as compared with that during the charge operation.   3. The charge pump circuit according to claim 2, wherein the control unit turns on the second switch before the first switch during the charging operation. A second electrode of the snubber capacitor can be connected to the input voltage source via a fifth switch and can be connected to a ground line via a sixth switch;
The controller is
During the charging operation, the fifth switch is turned on, the sixth switch is turned off,
4. The charge pump circuit according to claim 2, wherein control is performed to turn off the fifth switch and turn on the sixth switch during the discharge operation. 5. 5. The charge pump circuit according to claim 4 , wherein the controller turns on the first switch after turning on the second switch and the fifth switch during the charge operation. 6.   6. The charge according to claim 4, wherein the control unit performs control to turn on the fourth switch after turning on the third switch and the sixth switch during the discharge operation. 7. Pump circuit. The controller is
A first electrode of the output capacitor and a variable reference voltage source are connected to an input terminal, a second electrode of the snubber capacitor is connected to an output terminal, and an output from the voltage of the first electrode of the output capacitor and the variable reference voltage source An error amplifier that amplifies the difference between the voltages to be applied to the second electrode of the snubber capacitor,
4. The charge pump circuit according to claim 2, wherein when switching from the charge operation to the discharge operation, control is performed to reduce a voltage value output from the variable reference voltage source. 5. The controller is
A first electrode of the output capacitor and a fixed reference voltage source are connected to the input terminal, a PWM control circuit is connected to the output terminal, and the voltage of the first electrode of the output capacitor and the voltage output from the fixed reference voltage source An error amplifier for feedback control that amplifies the difference and gives it to the PWM control circuit;
8. The charge pump circuit according to claim 2, wherein the PWM control circuit determines a duty ratio of each switch in accordance with an output voltage of the feedback control error amplifier. 9. A snubber resistor having a first terminal connected to the first electrode of the snubber capacitor and a second terminal connected to the first electrode of the fly capacitor directly or via a switch;
The charge pump according to any one of claims 2 to 8, wherein the first electrode of the snubber capacitor is configured to be connectable to the first electrode of the fly capacitor via the snubber resistor. circuit. A bypass switch formed in parallel with the snubber resistor;
10. The charge pump according to claim 9, wherein the control unit controls the bypass switch to be turned on during the charging operation, thereby bypassing the snubber resistor and forming a current path through the bypass switch. 11. circuit. The capacitance value of the snubber capacitor and the resistance value of the snubber resistor are each configured to be variable,
A monitor circuit for observing a waveform of a voltage applied to the first electrode of the output capacitor and measuring a ringing frequency;
The said control part performs predetermined calculation from the electrostatic capacitance value of the said snubber capacitor, and the said ringing frequency, and determines the resistance value of the said snubber resistance, The any one of Claims 2-10 characterized by the above-mentioned. Charge pump circuit.
  The charge pump circuit according to claim 1, wherein a capacitance of the snubber capacitor is smaller than a capacitance of the fly capacitor.

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