JPH04344166A - DC-DC converter - Google Patents

Abstract

PURPOSE:To provide a DC-DC converter which has high efficiency, a small size, and a simple circuit configuration and can supply a stabilized DC voltage to industrial equipment for information, communication, OA, etc., and electronic equipment of consumer appliances, such as VTR, TV, etc., by using a single-winding transformer which is well coupled as compared with insulated transformers and requires a less amount of winding. CONSTITUTION:This DC-DC converter is provided with a switching means 3, secondary winding 4b of a transformer 4 which is connected to the primary winding 4a of a transformer 4 and added to the winding 4a, and a rectifying and smoothing circuit which is composed of diodes 6 and 7, a choke transformer 8, and a capacitor 9 and transmits the output of the secondary winding 4b to a load and the switching means 1, winding 4b, and rectifying an smoothing circuit are connected in series with a DC power source 1. The converter is also provided with a reset circuit which resets the transformer 4 when a switching means 3 composed of resetting winding 4c and diode 5 is turned off and a control means 11 which controls the on/off ratio of the means 3 so that the voltage across both ends of the capacitor 9 can become constant. In addition, the converter is constituted so that an arbitrary output voltage can be outputted from the capacitor 9 by generating a high voltage by superimposing a voltage induced across the secondary winding 4b upon an input voltage applied across the primary winding 4a.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-DC converter that supplies DC stabilized voltage to industrial equipment such as information, communication, and OA equipment, and electronic equipment such as consumer equipment such as VTRs and TVs.

0002

2. Description of the Related Art In recent years, as electronic devices have become more portable, battery-powered devices have been increasing, and the use of DC-DC converters for converting and stabilizing voltages supplied to electronic circuits is rapidly increasing. For portable equipment applications, there is a strong demand for smaller size and higher efficiency.

A conventional DC-DC converter will be explained below. FIG. 3 shows a circuit diagram of a conventional DC-DC converter, which is called a step-down converter. In FIG. 3, 1 is a DC power source such as a battery, which supplies input voltage to input terminals 2a and 2b, and connects a positive voltage to the input terminal 2a and a negative voltage to the input terminal 2b. 3 is a switching means such as a transistor;
One end is connected to the input terminal 2a, the other end is connected to the choke transformer 8, and the on/off operation is performed by the on/off pulse of the control circuit 11 to conduct or cut off the current. 8 is a choke transformer having one winding, one end of which is connected to the switch means 3, the other end of which is connected to the output terminal 10a, and stores and releases energy. A smoothing capacitor 9 is connected to both ends of the output terminals 10a and 10b to smooth the pulsating voltage into a DC voltage. 10a-10b are output terminals, and load 1
A positive voltage is supplied to the output terminal 10a, and a negative voltage is supplied to the output terminal 10b connected to the input terminal 2b. A diode 7 has a cathode connected to the connection point between the switch means 3 and the choke transformer 8, and an anode connected to the output terminal 10b, forming a current loop when energy is released to the output of the choke transformer 8. Reference numeral 11 denotes a control circuit which detects the output voltage between the output terminals, generates on/off pulses with a predetermined cycle, and adjusts the on/off duty ratio so that the output voltage is constant.

The operation of the DC-DC converter configured as described above will be explained in detail. The input voltage supplied from the DC voltage 1 is switched on and off by the switch means 3, and the choke transformer 8 is supplied with a voltage and cut off to supply a current. The current flowing through the choke transformer 8 is supplied to the load 12 via the output terminals 10a-10b, and the energy stored in the choke transformer 8 is supplied to the load 12 via the diode 7 when the switch means 3 is on and from the DC power supply 1 when the switch means 3 is off. By being released, the load 12 is continuously
supplied to The output voltage is fixed at a voltage value expressed as Vout=Vin×D (1) because the control circuit 11 constantly adjusts the on/off of the switch means 3 so that the output voltage is constant.

[0005] Here, Vin is an input voltage value, Vout is an output voltage value, and D is an on/off duty ratio. From the above equation (1), it can be seen that the output voltage value Vout is a step-down converter that cannot become higher than the input voltage value Vin because the on-off duty ratio D is less than 1. Therefore, if the input range is such that the input voltage value Vin is lower than the required output voltage value Vout, this converter cannot be used.

A so-called isolation transformer type feedforward converter, which is generally used in such cases, will be explained with reference to FIG. 4. In FIG. 4, the same parts as in FIG. 3 are denoted by the same reference numerals, and the description thereof will be omitted. 1 is a DC power supply, 2a-2b are input terminals,
7 is a diode, 8 is a choke transformer, 9 is a smoothing capacitor, 10a-10b are output terminals, 11 is a control circuit,
12 is a load. Reference numeral 3 denotes a switch means, one end of which is connected to the input terminal 2b and the other end connected to the primary winding 4a of the transformer 4, and is turned on and off by on/off pulses from the control circuit 11 to conduct or cut off current. A transformer 4 has a primary winding 4a, a secondary winding 4b, and a reset winding 4c. The primary winding 4a has one end connected to the input terminal 2a, the other end connected to the switch means 3, and transmits energy to the secondary winding 4b. The secondary winding 4b has one end connected to the choke transformer 8 via the diode 6, and the other end connected to the choke transformer 8 through the diode 6.
and supplies energy to the load side via the diode 6. The reset winding 4 c has one end connected to the input terminal 2 a and the other end connected to the input terminal 2 b via the diode 5 to reset the transformer 4 .

The operation of the DC-DC converter configured as described above is the same as that explained with reference to FIG. 3, so the explanation thereof will be omitted, and the operation of the transformer 4 will be explained here. When the switch means 3 is turned on, an input voltage is applied to the primary winding 4a, a voltage is induced in the secondary winding 4b, and current is supplied to the choke transformer 8 via the diode 6. Further, when the switch means 3 is turned off, the reset winding 4c releases excitation energy from the input terminal 2b through the diode 5 to the input terminal 2a, and resets the magnetic flux generated when the transformer 4 is turned on. In this case, the output voltage is
Vout=Vin×D(Ns/Np)...It is fixed at the voltage value shown by (2).

Here, Ns is the number of turns of the primary winding 4a, Np
is the number of turns of the secondary winding 4b. From the above formula (2), depending on the ratio of the number of turns Ns of the primary winding 4a and the number of turns Np of the secondary winding 4b, any output voltage value Vo can be determined regardless of the input voltage value Vin.
It can be seen that ut can be obtained. However, when using an isolation transformer such as the transformer 4, the coupling between the primary winding 4a and the secondary winding 4b is poor, resulting in a large leakage inductance and the energy transferred from the primary winding 4a to the secondary winding 4b. There is a problem that the amount decreases and the efficiency deteriorates.

A conventional system called a buck-boost converter that utilizes a plurality of switch means will be described with reference to FIG. In FIG. 5, the same parts as in FIG. 3 are denoted by the same reference numerals and omitted. 1 is DC power supply, 2a-2
b is an input terminal, 3 is a switch means, 7 is a diode, 8
is a choke transformer, 9 is a smoothing capacitor, 10a-1
0b is an output terminal, 11 is a control circuit, and 12 is a load. The diode 14 has a cathode connected to the output terminal 10a and an anode connected to the connection point between the switch means 15 and the choke transformer 8, and forms a current loop when energy is released to the output of the choke transformer 8, similar to the diode 7. Reference numeral 15 denotes a switch means, one end of which is connected to the input terminal 2a and the other end connected to the connection point between the choke transformer 8 and the diode 14, and is turned on and off in synchronization with the switch means 3 by the on/off pulse of the control circuit 11. Cuts off current conduction.

The operation of the DC-DC converter configured as described above will be explained. The input voltage supplied from the DC power supply 1 is switched on and off by the switch means 3 and 15, and the voltage is cut off from being applied to the choke transformer 8 to supply current. Energy is stored in the choke transformer 8 at the same time as the switch means 3 and 15 are turned on. Next, at the same time as the switch means 3 and 15 are turned off, the energy stored in the choke transformer 8 is released via the diode 7 and the diode 14, and is supplied to the load 12. Since the control circuit 11 adjusts the on/off of the switch means 7 and 15, which are turned on and off at the same time, so that the output voltage remains constant, the output voltage is expressed as Vout=Vin×{D/(1-D)} (3). Fixed to voltage value.

From the above equation (3), since the output voltage value Vout has an on-off duty ratio D of 1 or less, it can be seen that the converter is a buck-boost converter that can obtain any output voltage value Vout regardless of the input voltage value Vin. .

0012

However, with the conventional configuration described above, the step-down converter shown in FIG. 3 cannot be used when the input range is wide, where the input voltage may be lower than the output voltage. On the other hand, in the feedforward converter shown in FIG. 4, the coupling between the primary winding and the secondary winding of the transformer is poor, resulting in poor efficiency. Furthermore, in the buck-boost converter shown in FIG. 5, two stages of switching means are connected in series in the loop that supplies current to the output, and two stages of diodes are also connected in series, so the loss is higher than that of the step-down converter, resulting in lower efficiency. This poses problems such as deterioration and the complexity of the circuit configuration.

The present invention solves the above-mentioned conventional problems, and uses a transformer with a single-phase winding structure that has better coupling than an isolation transformer and requires fewer windings, making it possible to achieve high efficiency and miniaturization. It is an object of the present invention to provide a DC-DC converter with a simple circuit configuration.

[0014]

[Means for Solving the Problems] In order to solve this problem, the DC-DC converter of the present invention includes a switch means and a primary winding of a transformer connected in series to a DC input, and a switch means and a primary winding of a transformer connected in series to a DC input. A secondary winding of the transformer is added from the connection point with the winding, and a series circuit of a diode, a choke transformer, and a capacitor is connected from the secondary winding to the connection point of the input terminal and the primary winding. A second diode connected to a connection point between the diode and the choke transformer and a connection point between the input terminal and the primary winding, and an on-off ratio of the switch means are controlled so that voltages across the capacitor are constant. The device includes a control means and is configured to output the voltage across the capacitor to a load.

[0015]

[Operation] With this configuration, when the switching means is turned on, the voltage induced in the secondary winding is superimposed on the input voltage applied to the primary winding, thereby boosting the switching voltage and generating a voltage higher than the input voltage. By applying this voltage to the choke transformer, it is possible to obtain an output voltage higher than the input voltage.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit diagram of a DC-DC converter according to the present invention. In FIG. 1, the same parts as in FIG. 3 are denoted by the same reference numerals, and the description thereof will be omitted. In Figure 1, 1 is a DC power supply, 2a and 2b are input terminals, 3 is a switch means, 7 is a diode, 8 is a choke transformer, 9 is a smoothing capacitor, 10a and 10b are output terminals, 11 is a control circuit, and 12 is a load It is. A transformer 4 has a primary winding 4a, a secondary winding 4b, and a reset winding 4c. The primary winding 4a has one end connected to the switch means 3 and the other end connected to the input terminal 2b to store and release energy. The secondary winding 4b wound around the primary winding 4a has one end connected to the choke transformer 8 via the diode 6, and the other end connected to the switch means 3 to release energy. The reset winding 4c has one end connected to the input terminal 2a via the diode 5, and the other end connected to the output terminal 10b, thereby resetting the transformer 4.

Regarding the DC-DC converter configured as described above, the operation as a converter is the same as that explained with reference to FIG. 3, so a description thereof will be omitted, and the operation of the transformer 4 will be explained here. When the switch means 3 is turned on, a DC input voltage is applied to the primary winding 4a, and this voltage is applied to the secondary winding 4.
The voltage induced in b is superimposed, and current is supplied to the choke transformer 8 via the diode 6. Furthermore, when the switch means 3 is turned off, the reset winding 4c releases the excitation energy of the transformer 4 to the input terminal 2a via the diode 5, thereby resetting the magnetic flux. The output voltage is Vout=V
in×D(1+Ns/Np)...(4) is fixed to the voltage value.

Further, the operating waveforms of each part are as shown in FIG. That is, FIG. 2(a) shows the waveform of the voltage Vds across the switching means 3, and FIG. 2(b) shows the waveform of the voltage Vds across the switching means 3.
2(c) shows the waveform of the current Id of the diode 5, and FIG. 2(d) shows the waveform of the on/off pulse Vg of the control means 11.

[0019]

As described above, the present invention boosts the switching voltage by using a transformer with a single-phase winding structure, thereby increasing the output voltage value Vou higher than the input voltage value Vin.
Compared to a transformer that isolates the primary and secondary windings, the voltage of the secondary winding is superimposed on the voltage of the primary winding, so the number of turns in the secondary winding is small. The transformer can be made smaller, and since the primary winding is shared by a part of the secondary winding, coupling is good. Furthermore, since the circuit configuration is simple,
A DC-DC converter that can be downsized and highly efficient can be realized.

[Brief explanation of drawings]

[Fig. 1] Circuit configuration diagram of a converter in an embodiment of the present invention

FIG. 2: (a) Waveform diagram of the voltage Vds across the switch means in the embodiment of the present invention; (b) Current Id of the switch means in the embodiment of the present invention;
s waveform diagram (c) Waveform diagram of the diode current Id in the embodiment of the present invention (d) Waveform diagram of the on-off pulse Vg of the control means in the embodiment of the present invention

[Figure 3] Circuit configuration diagram of a conventional step-down converter

[Figure 4]
Circuit diagram of conventional feedforward converter

[Figure 5] Circuit configuration diagram of a conventional buck-boost converter

[Explanation of symbols]

1 DC power supply 2a-2b Input terminal 3 Switch means 4 Transformer 4a Primary winding 4b Secondary winding 4c Reset winding 5 Diode 6 Diode 7 Diode 8 Choke coil 9 Capacitor 10a-10b Output terminal 11 Control circuit 12 Load

Claims (1)

[Claims] 1. A switch means and a primary winding of a transformer are connected in series to a DC input, and a secondary winding of the transformer is added from a connection point between the switch means and the primary winding,
A series circuit of a diode, a choke transformer, and a capacitor is connected to the connection point between the input terminal and the primary winding from the secondary winding, and the connection point between the diode and the choke transformer, the input terminal, and the primary winding. a second diode connected to a connection point of the capacitor, and a control means for controlling an on-off ratio of the switch means so that the voltage across the capacitor is constant, and outputs the voltage across the capacitor to a load. converter.