JP2012210063A - Voltage conversion circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To convert an input voltage into a positive voltage and a negative voltage having an arbitrary value in a simple configuration.SOLUTION: A voltage conversion circuit 100 comprises transistors Tr1 to Tr 5, a coil L, and a control circuit 10. The control circuit 10 turns on the transistors Tr1 and Tr2 and turns off the transistors Tr3, Tr4, and Tr5 in charge periods in a first period and a second period, turns on the transistors Tr3 and Tr4 and turns off the transistors Tr1, Tr2, and Tr5 in a discharge period in the first period, and turns on the transistors Tr2 and Tr5 and turns off the transistors Tr1, Tr3, and Tr4 in a discharge period in the second period.

Description

  The present invention relates to a technique for generating a positive voltage and a negative voltage.

  2. Description of the Related Art As a voltage conversion circuit that converts a predetermined positive voltage into a larger positive voltage and negative voltage, one using a charge pump is known. Patent Document 1 discloses a charge pump circuit that outputs +2 VDD and −2 VDD using two capacitance elements and seven switching elements when the input voltage is VDD.

JP-A-6-165482

However, in the technique of Patent Document 1, since the seven switching elements are used, the configuration is complicated, and it is necessary to turn them on / off at an appropriate timing. Therefore, a control circuit that controls the seven switching elements However, the configuration becomes complicated. Furthermore, there is a problem that the positive voltage and the negative voltage output from the charge pump circuit must have the same absolute value, and an arbitrary magnitude cannot be specified.
In view of the above circumstances, an object of the present invention is to generate an arbitrary positive voltage and negative voltage from an input voltage while simplifying the configuration.

  Means employed by the present invention to solve the above problems will be described. The voltage conversion circuit of the present invention includes a first terminal to which an input voltage is supplied, a second terminal to which one terminal of the coil is connected, a third terminal to which the other terminal of the coil is connected, and a ground voltage. A fourth terminal for supplying positive voltage, a fifth terminal for outputting positive voltage, a sixth terminal for outputting negative voltage, and a first switching element provided between the first terminal and the second terminal; A second switching element provided between the third terminal and the fourth terminal, a third switching element provided between the second terminal and the fourth terminal, and the third terminal A fourth switching element provided between the fifth terminal, a fifth switching element provided between the second terminal and the sixth terminal, and a first period for generating the positive voltage And the second period for generating the negative voltage. A control circuit that controls the switching element to be turned on or off, and the control circuit turns on the first switching element and the second switching element in the charging period of the first period, and the third switching element, Turning off the fourth switching element and the fifth switching element, and turning on the third switching element and the fourth switching element in a discharging period following the charging period of the first period; The second switching element and the fifth switching element are turned off, and the first switching element and the second switching element are turned on in the charging period of the second period, and the third switching element and the fourth switching element are turned on. And turning off the element and the fifth switching element to charge the second period In a discharge period following the period, the second switching element and the fifth switching element are turned on, and the first switching element, the third switching element, and the fourth switching element are turned off.

  According to the present invention, in the charging period of the first period and the second period, the current flows in the same direction to store power in the coil, and in the discharging period of the first period, the positive voltage is generated by discharging the current from the fifth terminal. On the other hand, during the discharge period of the second period, a negative voltage is output by sucking current from the sixth terminal. Thereby, both a positive voltage and a negative voltage can be output by one coil and five switching elements. Therefore, the configuration is simplified as compared with the conventional technique, and the number of switching elements can be reduced. In addition, the configuration of the control circuit that controls the switching element can be simplified. Furthermore, the absolute value of the positive voltage and the absolute value of the negative voltage are made independent by independently controlling the length of the charging period and discharging period of the first period and the length of the charging period and discharging period of the second period. Can be set.

  As a preferred aspect of the present invention, the control circuit includes the second switching element and the third switching element in a stop period following the discharge period of the first period and a stop period following the discharge period of the first period. The first switching element, the fourth switching element, and the fifth switching element may be turned off by turning on. In this case, since the electric power stored in the coil is set to zero during the stop period, no electric power remains in the coil during the next charging period. For this reason, the magnitude of the positive voltage and the magnitude of the negative voltage can be accurately controlled.

  As a preferred embodiment of the present invention, a first detection unit that detects that the current flowing through the coil has become zero during the discharge period of the first period and outputs a first detection signal; and a discharge of the second period A second detection unit that detects that the current flowing in the coil during the period becomes zero and outputs a second detection signal, and the control circuit is configured to output the first detection signal based on the first detection signal. The discharge period of the period may be ended, and the discharge period of the second period may be ended based on the second detection signal. In this case, the magnitude of the coil current is detected and the discharge period is terminated, so that the power stored in the coil can be output efficiently.

  More specifically, the first detection unit is a first comparator that compares a voltage at one terminal of the second switching element or the third switching element with a voltage at the other terminal, and the second detection element The unit is preferably a second comparator that compares the voltage at one terminal of the second switching element or the third switching element with the voltage at the other terminal.

  As a preferred embodiment of the present invention, a first means for generating a first signal having a pulse width corresponding to the difference between the positive voltage and the target voltage, and a second pulse width corresponding to the difference between the negative voltage and the target voltage. A second means for generating a signal, wherein the control circuit controls the length of the charging period of the first period based on the first signal, and the charging of the second period based on the second signal You may control the length of a period. According to the present invention, since the pulse width of the first signal and the pulse width of the second signal are controlled independently, a positive voltage and a negative voltage of arbitrary magnitude can be output.

1 is a block diagram of a voltage conversion circuit according to an embodiment of the present invention. It is a timing chart of each signal. It is explanatory drawing for demonstrating on / off of the transistor in the charge period of a 1st period and a 2nd period. It is explanatory drawing for demonstrating on / off of the transistor in the discharge period of a 1st period. It is explanatory drawing for demonstrating on / off of the transistor in the stop period of a 1st period and a 2nd period. It is explanatory drawing for demonstrating on / off of the transistor in the discharge period of a 2nd period.

<Embodiment>
FIG. 1 is a block diagram of a voltage conversion circuit 100 according to an embodiment of the present invention. The voltage conversion circuit 100 converts the input voltage VDD supplied between the terminal 1 and the terminal T4, outputs the positive voltage Vp from the terminal T5, and outputs the negative voltage Vn from the terminal T6 (DC). -DC converter). The DC power supply circuit 20 supplies the input voltage VDD between the terminals T1 and T4. Terminal T4 is grounded. A capacitive element 21 provided between the terminal T1 and the terminal T4 smoothes the input voltage VDD. A reference voltage Vref is supplied to the terminal T7, and a clock signal CLK is supplied to the terminal T8. Further, the capacitive element 22 is connected to the terminal T5, and the capacitive element 23 is connected to the terminal T6. The capacitive elements 22 and 23 are used to smooth the positive voltage Vp and the positive voltage Vn.

  The voltage conversion circuit 100 includes P-channel transistors Tr1 and Tr4 that function as switching elements, and N-channel transistors Tr2, Tr3, and Tr5. These are controlled to be turned on / off by control signals S1 to S5 generated by the control circuit 10. The transistor Tr1 is provided between the terminal T1 and the terminal T2, and controls whether or not the input voltage VDD is supplied to one terminal of the coil L. The transistor Tr2 is provided between the terminal T3 and the terminal T4 and controls whether or not the other terminal of the coil L is grounded. The transistor Tr3 is provided between the terminal T2 and the terminal T4 and controls whether one terminal of the coil L is grounded. The transistor Tr4 is provided between the terminal T3 and the terminal T5 and controls whether or not to output the positive voltage Vp. The transistor Tr5 is provided between the terminal T2 and the terminal T6 and controls whether or not to output the negative voltage Vn.

  The comparator 12 (second detection unit) is provided in parallel with the transistor Tr2. When the coil current IL becomes zero, the comparator 12 generates a detection signal X2 that switches from high level to low level and supplies the detection signal X2 to the control circuit 10. The comparator 13 (first detection unit) is provided in parallel with the transistor Tr3. When the coil current IL becomes zero, the comparator 13 generates a detection signal X1 that switches from high level to low level and supplies the detection signal X1 to the control circuit 10.

  The triangular wave generation circuit 11 generates a triangular wave signal Vramp in synchronization with the clock signal CLK. The amplifier 15 generates an error signal Err1 based on the difference between the positive voltage Vp and the reference voltage Vref, and the amplifier 16 generates an error signal Err2 based on the difference between the negative voltage Vn and the reference voltage Vref. The comparator 17 compares the triangular wave signal Vramp and the error signal Err1, generates a PWM signal P1, and outputs the PWM signal P1 to the control circuit 10. The comparator 18 compares the triangular wave signal Vramp and the error signal Err2, generates a PWM signal P2, and outputs it to the control circuit 10.

  The control circuit 10 generates control signals S1 to S5 based on the detection signals X1 and X2, the clock signal CLK, and the PWM signals P1 and P2. In the above configuration, the positive voltage Vp increases as the pulse width of the PWM signal P1 increases, and the absolute value of the negative voltage Vn increases as the pulse width of the PWM signal P2 increases. Since the PWM signal P1 and the PWM signal P2 are generated by comparing the triangular wave signal Vramp and the error signals Err1 and Err2, the magnitudes of the positive voltage Vp and the negative voltage Vn are adjusted by adjusting the gains of the amplifiers 16 and 17. Can be set.

  Next, the operation of the voltage conversion circuit 100 will be described. The operation of the voltage conversion circuit 100 is roughly divided into a first period Ta for generating the positive voltage Vp and a second period Tb for generating the negative voltage Vn. Further, each of the first period Ta and the second period Tb is It is divided into a charge period, a discharge period, and a stop period. FIG. 2 is a timing chart showing waveforms of respective parts of the voltage conversion circuit, and FIGS. 3 to 6 are explanatory diagrams for explaining ON / OFF of the transistors Tr1 to Tr5.

  As shown in FIG. 2, the clock signal CLK becomes a high level at the start of the first period Ta and the second period Tb. The triangular wave generation circuit 11 resets the level of the triangular wave signal Vramp in synchronization with the rising edge of the clock signal CLK. The PWM signal P1 is active (high level) only during a period corresponding to the error signal Err1, and the PWM signal P2 is active (high level) only during a period corresponding to the error signal Err2. The control circuit 10 sets the period in which the PWM signal P1 is active as the charging period of the first period Ta, and sets the period in which the PWM signal P1 is active as the charging period of the second period Tb.

  First, in the charging period of the first period Ta, the control circuit 10 activates the control signals S1 and S2 and deactivates the control signals S3 to S5. As a result, as shown in FIG. 3, the transistors Tr1 and Tr2 are turned on, and the transistors Tr3 to Tr5 are turned off. In the charging period, a current flows through a path such as the DC power supply circuit 20 → terminal T1, transistor Tr1, terminal T2, coil L, terminal T3, transistor Tr2, terminal T4, and ground. At this time, the first voltage V1, which is the voltage at one terminal of the coil L, is a positive voltage with respect to the ground, and the second voltage V2, which is the other voltage of the coil L, is the ground voltage (GND). During the charging period, the current IL flows into the coil L via the transistor Tr1, and as a result, the current IL flowing through the coil L gradually increases, and electric power is stored in the coil L.

  Next, the discharging period of the first period Ta starts from the end of the charging period and ends at the falling edge E1 of the detection signal X1. As described above, the detection signal X1 switches from the high level to the low level when the coil current IL becomes zero. Therefore, the discharging period of the first period Ta is a period from the end of the charging period until the coil current IL becomes zero. In the discharge period of the first period Ta, the control circuit 10 activates the control signals S3 and S4 and deactivates the control signals S1, S2, and S5. As a result, as shown in FIG. 4, the transistors Tr3 and Tr4 are turned on, and the transistors Tr1, Tr2, and Tr5 are turned off. In the discharging period, a current flows through a path of ground → terminal T4 → transistor Tr3 → terminal T2 → coil L → terminal T3 → transistor Tr4 → terminal T5. At this time, the second voltage V2 that is the voltage at the other terminal of the coil L is a positive voltage with respect to the ground, and the first voltage V1 that is one voltage of the coil L is the ground voltage (GND). In the discharge period of the first period Ta, the second voltage V2 is output as the positive voltage Vp from the terminal T5 via the transistor Tr4. The positive voltage Vp is generated by the electric power stored in the coil L during the charging period of the first period Ta.

  Next, the stop period of the first period Ta starts from the end of the discharge period and ends when the clock signal CLK becomes high level. During this period, the control circuit 10 activates the control signals S2 and S3 and deactivates the control signals S1, S4, and S5. As a result, as shown in FIG. 5, the transistors Tr2 and Tr3 are turned on, and the transistors Tr1, Tr4, and Tr5 are turned off. In the stop period, both the terminal T2 and the terminal T3 are grounded. Therefore, the first voltage V1 and the second voltage V2 of the coil L are ground voltages.

Next, the charge period and stop period of the second period Tb operate in the same manner as the charge period and stop period of the first period Ta.
Next, the discharging period of the second period Tb starts from the end of the charging period and ends at the falling edge E2 of the detection signal X2. As described above, the detection signal X2 is switched from the high level to the low level when the coil current IL becomes zero. Accordingly, the discharging period of the second period Tb is a period from the end of the charging period until the coil current IL becomes zero.
In the discharge period of the second period Tb, the control circuit 10 activates the control signals S2 and S5 and deactivates the control signals S1, S3, and S4. As a result, as shown in FIG. 6, the transistors Tr2 and Tr5 are turned on, and the transistors Tr1, Tr3, and Tr4 are turned off. In the discharging period, a current flows through a path such as terminal T6 → transistor Tr5 → terminal T2 → coil L → terminal T3 → transistor Tr2 → terminal T4 → ground. That is, a current flows in the direction of suction from the terminal T6. At this time, the first voltage V1, which is the voltage at one terminal of the coil L, is a negative voltage with respect to the ground, and the second voltage V2, which is the other voltage of the coil L, is the ground voltage (GND). In the discharge period of the second period Tb, the first voltage V1 is output as the negative voltage Vn from the terminal T6 via the transistor Tr5. The negative voltage Vn is generated by the electric power stored in the coil L during the charging period of the second period Tb.

  As described above, according to the present embodiment, when discharging the electric power stored in the coil L, the current is switched in the same direction as the charging period while the coil L is switched, and the positive voltage Vp is output. In this case, the current is discharged, while when the negative voltage Vn is output, the current is sucked, so that a positive and negative voltage can be generated using one coil L. In addition, the number of transistors can be reduced as compared with a conventional charge pump. In addition, according to the present embodiment, the magnitudes of the positive voltage Vp and the negative voltage Vn can be set independently.

<Modification>
The present invention is not limited to the above-described embodiments, and for example, the following modifications are possible.
(1) In the above-described embodiment, the comparator 13 detects whether or not the coil current IL in the discharge period of the first period Ta has become zero. However, the present invention is not limited to this, and the coil current IL is not limited thereto. Any means may be used as long as it can be monitored. In short, a detection unit for detecting the coil current IL may be provided in a current path through which the coil current IL flows. For example, the comparator 13 may be provided in parallel with the transistor Tr4.

(2) In the above-described embodiment, the comparator 12 detects whether or not the coil current IL in the discharge period of the second period Tb has become zero, but the present invention is not limited to this, and the coil current IL is not limited thereto. Any means may be used as long as it can be monitored. In short, a detection unit for detecting the coil current IL may be provided in a current path through which the coil current IL flows. For example, the comparator 12 may be provided in parallel with the transistor Tr5.

DESCRIPTION OF SYMBOLS 100 ... Voltage conversion circuit, T1-T8 ... Terminal, TR1-TR5 ... Transistor, L ... Coil, 10 ... Control circuit, 11 ... Triangle wave generation circuit, 12, 13, 17, 18 ... Comparator, DESCRIPTION OF SYMBOLS 15,16 ... Amplifier, 20 ... DC power supply circuit, 21-23 ... Capacitance element, S1-S5 ... Control signal, V1 ... 1st voltage, V2 ... 2nd voltage.

Claims (5)

A first terminal to which an input voltage is supplied;
A second terminal to which one terminal of the coil is connected;
A third terminal to which the other terminal of the coil is connected;
A fourth terminal to which a ground voltage is supplied;
A fifth terminal for outputting a positive voltage;
A sixth terminal for outputting a negative voltage;
A first switching element provided between the first terminal and the second terminal;
A second switching element provided between the third terminal and the fourth terminal;
A third switching element provided between the second terminal and the fourth terminal;
A fourth switching element provided between the third terminal and the fifth terminal;
A fifth switching element provided between the second terminal and the sixth terminal;
A control circuit for controlling the first to fifth switching elements on or off in a first period for generating the positive voltage and a second period for generating the negative voltage;
The control circuit includes:
In the charging period of the first period, the first switching element and the second switching element are turned on, the third switching element, the fourth switching element, and the fifth switching element are turned off,
In the discharging period following the charging period of the first period, the third switching element and the fourth switching element are turned on, the first switching element, the second switching element, and the fifth switching element are turned off,
In the charging period of the second period, the first switching element and the second switching element are turned on, the third switching element, the fourth switching element, and the fifth switching element are turned off,
In a discharging period following the charging period of the second period, the second switching element and the fifth switching element are turned on, and the first switching element, the third switching element, and the fourth switching element are turned off.
A voltage conversion circuit characterized by that.   The control circuit turns on the second switching element and the third switching element in a stop period following the discharge period of the first period and a stop period following the discharge period of the first period, and the first switching element The voltage conversion circuit according to claim 1, wherein an element, the fourth switching element, and the fifth switching element are turned off. A first detector that detects that the current flowing through the coil has become zero during the discharge period of the first period and outputs a first detection signal;
A second detector that detects that the current flowing through the coil has become zero during the discharge period of the second period and outputs a second detection signal;
The control circuit ends the discharge period of the first period based on the first detection signal, and ends the discharge period of the second period based on the second detection signal;
The voltage conversion circuit according to claim 1 or 2, wherein The first detection unit is a first comparator that compares the voltage of one terminal of the second switching element or the third switching element with the voltage of the other terminal,
The second detection unit is a second comparator that compares the voltage of one terminal of the second switching element or the third switching element with the voltage of the other terminal.
The voltage conversion circuit according to claim 3. First means for generating a first signal having a pulse width corresponding to a difference between the positive voltage and a target voltage;
A second means for generating a second signal having a pulse width corresponding to the difference between the negative voltage and the target voltage;
The control circuit controls the length of the charging period of the first period based on the first signal, and controls the length of the charging period of the second period based on the second signal;
The voltage conversion circuit according to claim 1, wherein the voltage conversion circuit is any one of claims 1 to 4.

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