JPH04355661A - Charge pump circuit - Google Patents

Abstract

PURPOSE:To provide a charge pump circuit having excellent constant voltage characteristics by a method wherein a large charging efficiency is selected. CONSTITUTION:A plurality of unit circuits which are composed of a plurality of charge transfer capacitors 56-59 and 71-74 which are connected in series respectively, a plurality of charge switches 54, 55, 69 and 70 and charge transfer switch groups 60-67 and 75-82 are provided. ON's and OFF's of the charge switches 54, 55, 69 and 70 and the charge transfer switch groups 60-67 and 75-82 are controlled by a control circuit 85 so as to prevent charge timings from the respective charge transfer capacitors to an output capacitor 68 from overlapping each other.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge pump circuit which is a type of DC/DC converter.

0002

2. Description of the Related Art Conventionally, there has been a technique in this type of field, for example, as shown in FIG. This will be explained below using figures.

FIG. 2 is a circuit diagram showing an example of the configuration of a conventional charge pump circuit.

This charge pump circuit converts a voltage of +5V to a voltage of -5V, and has an input terminal 1 and a ground terminal 2, between which a +5V DC power source 3 is connected. Furthermore, a charging switch 4 and a charge transfer capacitor 5 are connected to both ends of the input terminal 1 and the ground terminal 2.
and a charging switch 6 are connected in series.

On the other hand, the connection point between the charging switch 4 and the charge transfer capacitor 5 is connected to the ground terminal 2 via the charge transfer switch 7, and the connection point between the charge transfer capacitor 5 and the charge switch 6 is connected to the ground terminal 2 via the charge transfer switch 7. is connected to a ground terminal 10 via a charge transfer switch 8 and an output capacitor 9. An output terminal 11 is drawn out from a connection point between the charge transfer capacitor 8 and the output capacitor 9.

Next, the operation will be explained with reference to FIG. Note that FIG. 3 is a time chart of FIG. 2.

First, from the state where the charging switches 4 and 6 and the charge transfer switches 7 and 8 are opened, the charging switches 4 and 6 are opened.
6 are closed at the same time, and the charge transfer capacitor 5 is charged from the power source 3 (period t1 in FIG. 3). Subsequently, the charging switches 4 and 6 are opened to ensure a break time (period t2). This break time means that if the charging switches 4, 6 and the charge transfer switches 7, 8 are closed at the same time, the charges on the power supply 3 side and the output capacitor 9 side will be continuous, and the voltage conversion function will no longer be achieved. So, it is time to control to prevent it.

After the break time has elapsed, the charge transfer switches 7 and 8 are closed simultaneously to charge the output capacitor 9 (period t3). This charging time is equal to the discharging time of the charge transfer capacitor 5. When charging of the output capacitor 9 is completed, a voltage of -5V is obtained at the output terminal 11.

Furthermore, after opening the charge transfer switches 7 and 8 and securing the same break time as described above (period t4)
By closing the charging switches 4 and 6 and repeating the second cycle of charging and discharging, the output capacitor 9 is charged at the timing shown in FIG. 3, and a voltage of -5V is continuously applied from the output terminal 11. can be obtained.

0010

However, in the charge pump circuit having the above configuration, the charging efficiency (t3/T) for the output capacitor 9 is less than 50%, as shown in FIG. Therefore, there was a problem that the output from the output terminal 11 had poor constant voltage characteristics and also had a small output current.

Further, although it is possible to convert the polarity of the voltage, for example from +5v to -5v, it is impossible to convert the absolute value, such as from -48v to +12v.

The present invention provides a charge pump circuit that solves the problems of the prior art, such as poor constant voltage characteristics, small output current, and inability to convert absolute values. be.

[0013]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the first invention provides a plurality of charge transfer capacitors connected in series, each of which charges a charge according to a predetermined input voltage;
a plurality of unit circuits including a plurality of charging switches for performing the charging, and a group of charge transfer switches for sequentially discharging charges at both ends of each of the charge transfer capacitors;
an output capacitor that sequentially charges charges from each of the charge transfer capacitors to generate a predetermined output voltage; and an output capacitor that sequentially charges charges from each of the charge transfer capacitors to generate a predetermined output voltage; and a control circuit that separates the timing of charge charging from the output capacitor to the output capacitor.

In a second invention, in the first invention, the rated values of the charge transfer capacitors are all set to be the same.

[0015] In a third invention, in the first or second invention, each of the charging switches and the charge transfer switch group is composed of a MOS transistor, a bipolar transistor, or an analog switch.

[0016]

[Operation] In the first invention, since the charge pump circuit is configured as described above, the charge transfer capacitor of any one of the plurality of unit circuits charges the output capacitor under the control of the control circuit. During this time, the charge transfer capacitors of other unit circuits are charged with the input voltage, and this charging operation is alternately switched among the plurality of unit circuits. This makes it possible to increase the charging efficiency of the output capacitor.

[0017] In the second invention, since the rated values of the charge transfer capacitors are all the same, the absolute value of the output voltage can be changed.

[0018] In the third invention, each charging switch and the charge transfer switch group are each composed of a MOS transistor, a bipolar transistor, or an analog switch, so that switching can be performed easily and accurately.

[0019] Therefore, the above problem can be solved.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram of a charge pump circuit showing a first embodiment of the present invention.

[0021] This charge pump circuit converts -48v to +
A DC power supply 53 of -48V (input voltage) is connected between the input terminal 51 and the ground terminal 52 to convert the voltage to 12V. Furthermore, an input terminal 51 and a ground terminal 5
Charging switches 54 and 55 are connected to both terminals of 2, respectively, and charge transfer capacitors 56 to 59 having the same rating are connected in series between the charging switches 54 and 55.

Furthermore, the connection point between the charging switch 54 and the capacitor 56 is connected to the ground terminal 64 via the charge transfer switch 60, and similarly, the connection point between the charging switch 54 and the capacitor 56 is
, capacitors 57, 58, and capacitors 58, 59 are commonly connected to the ground terminal 52 via charge transfer switches 61, 62, 63.

Furthermore, the connection points of capacitors 56, 57, capacitors 57, 58, and capacitors 58, 59 are connected via charge transfer switches 64, 65, 66, and the connection point of charge transfer switch 55 and capacitor 59 is connected to charge transfer switches 64, 65, 66. They are each commonly connected to one end of an output capacitor 68 via a transfer switch 67. The other end of the output capacitor 68 is connected to the ground terminal 52.

Here, the charging switches 54 and 55 and the charge transfer switches 60 to 67 are composed of MOS transistors, and the charging switches 54 and 55, the charge transfer capacitors 56 to 59, and the charge transfer switches 60 to 67 The first unit circuit is constructed by the following.

On the other hand, charging switches 69 and 70, charge transfer capacitors 71 to 74, and charge transfer switches 75 to 8 are connected between the input terminal 51 and the ground terminal 52.
A second unit circuit having the same connection configuration as the first unit circuit consisting of two unit circuits.
unit circuits are connected. An output terminal 84 and a ground terminal 83 are drawn out from both ends of the output capacitor 69.

In addition to the circuits described above, this charge pump circuit includes charging switches 54, 55, 69, and 70 and a charge transfer switch group 6.
A control circuit 85 for controlling switching operations of 0 to 67 and 75 to 82 is provided.

FIG. 4 is a time chart of FIG. 1, and the operation of FIG. 1 will be explained with reference to this diagram.

First, all the charge transfer switches 60 to
With charging switches 67, 75 to 82 and charging switches 69, 70 open, charging switches 54, 55 are closed. As a result, the charge transfer capacitors 56 to 59 are charged, and after the charging is completed, the charging switches 54 and 55 are opened (period t1). At this time, the voltage across each of the capacitors 56 to 59 is 48v/4=12v.

Next, after securing the break time t2, the charge transfer switches 60 and 64 are closed. Then, the charge on the capacitor 56 is transferred to the output capacitor 68. After the transmission is completed, the switches 60 and 64 are opened (period t3).

Similarly, after the break time t4 has elapsed, the switches 61 and 65 are closed in order to transfer the charge in the capacitor 57 to the output capacitor 68. After charge transfer is complete,
The switches 61 and 65 are opened (period t5). A similar operation is performed for the capacitors 58 and 59 using switches 62 and 66 and switches 63 and 67, and charge is transferred to the output capacitor 68 (period t6,
t7).

On the other hand, charge transfer capacitors 71 to 74 of the second unit circuit are similar to capacitors 56 to 74 of the first unit circuit.
While 59 is performing a discharging operation (period t3 to t7),
It is charged via charging switches 69 and 70. Therefore, after the discharging operation of the capacitor 59 by the switches 63, 67 of the first unit circuit is completed, the charging switch 69,
70 is opened, and after a subsequent break time t8, the capacitor 71 is first discharged by the switches 75 and 79 (period t9).

Thereafter, similarly, the discharge operation of the capacitors 72 to 74 is performed by the switches 76, 80 and the switches 77, 81.
, and switches 78 and 82 in sequence.

When the above-described series of operations is completed, charges as shown in FIG. 4 are injected into the output capacitor 68, and this is the result of the charge pump circuit of this embodiment. The output voltage will be +12v.

This embodiment has the following advantages.

(1) For example, while the first unit circuit is charging the output capacitor 68, the second unit circuit is charged from the power supply, and conversely, the second unit circuit is charging the output capacitor 68. While the capacitor 68 is being charged, the first unit circuit is controlled to be charged from the power source, and this is alternately switched, so that it is possible to increase the efficiency of charging the output capacitor 68. Become.

(2) Since the rated values of the charge transfer capacitors 56 to 59 and 71 to 74 of the first and second unit circuits were all the same, the absolute value of the output voltage was changed from -48V to +1
It can be converted to 2v.

FIG. 5 is a circuit diagram of a charge pump circuit showing a second embodiment of the present invention, in which elements common to those in FIG. 1 are given the same reference numerals.

This charge pump circuit is configured so that -12V can be obtained from the -48V power supply 3 at the output terminal 84.The difference from the first embodiment shown in FIG. 1 is that the charge transfer switch 60 -63, 64-67 are connected to opposite electrodes of charge transfer capacitors 56-59, respectively,
Similarly, one end of the charge transfer switches 75 to 78 and 79 to 82 is connected to the opposite electrodes of the charge transfer capacitors 75 to 78, respectively. By configuring like this,
After the same operation sequence as in the first embodiment, the output terminal 8
The output voltage generated in the fourth embodiment is -12V, and the output polarity is reversed from that of the first embodiment.

Note that the present invention is not limited to the illustrated embodiment, and various modifications are possible. For example, there are the following variations.

(1) In the above embodiment, the charge transfer capacitors were connected in series in four stages to obtain an output voltage of ±12V.
It is also possible to change the output voltage by changing the number of charge transfer capacitors connected. (2) Although the unit circuit is configured with two stages, a multi-stage configuration of two or more stages is also possible. (3) The charge transfer switches 60 to 63, 64 to 67, the charge transfer switches 75 to 78, 79 to 82, and the charging switches 54, 55, 69, and 70 may be replaced with devices other than MOS transistors, such as bipolar transistors, analog switches, etc. It may be composed of

[0041]

As explained in detail above, according to the first invention, while the charge transfer capacitor of any unit circuit is charging the output capacitor, the charge transfer of another unit circuit is stopped. The output capacitor is charged with the input voltage, and this charging operation is alternately switched between a plurality of unit circuits, so it is possible to charge the output capacitor without interruption, and the charging efficiency can be increased. This improves constant voltage characteristics and allows a large output current to be obtained.

[0042] In the second invention, since the rated values of the charge transfer capacitors are all the same, the absolute value of the output voltage can be made variable.

[0043] In the third invention, each of the charging switches and the charge transfer switch group is composed of a MOS transistor, a bipolar transistor, or an analog switch, so that switching can be performed easily and accurately.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a charge pump circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional charge pump circuit.

FIG. 3 is a time chart of FIG. 2;

FIG. 4 is a time chart of FIG. 1;

FIG. 5 is a circuit diagram of a charge pump circuit according to a second embodiment of the present invention.

[Explanation of symbols]

54, 55, 69, 70 Charging switch 56-59
, 71-74 Charge transfer capacitors 60-67, 7
5 to 82 Charge transfer switch 68 Output capacitor 85 Control circuit

Claims (3)

[Claims] 1. A plurality of charge transfer capacitors connected in series for charging electric charge according to a predetermined input voltage, a plurality of charging switches for carrying out the charging, and a plurality of charge transfer capacitors connected at both ends of each charge transfer capacitor. a plurality of unit circuits consisting of a group of charge transfer switches for sequentially discharging charges; an output capacitor that sequentially charges charges from each of the charge transfer capacitors to generate a predetermined output voltage; and each of the charge transfer capacitors; A charge pump circuit comprising: a control circuit that controls on/off of a switch and a group of charge transfer switches to separate charge timings from each of the charge transfer capacitors to the output capacitor. 2. The charge pump circuit according to claim 1, wherein the rated values of the charge transfer capacitors are all set to be the same. 3. The charge pump circuit according to claim 1, wherein each of the charging switches and the charge transfer switch group is each composed of a MOS transistor, a bipolar transistor, or an analog switch.