JPH02174555A - Dc/dc converter - Google Patents

Abstract

PURPOSE:To improve power conversion efficiency by arranging an auxiliary switch in parallel with a rectifying device, turning the auxiliary switch ON/OFF through an auxiliary winding provided for a reactor and connecting the rectifying element in parallel with a main switch element. CONSTITUTION:In case of a light load 17, i.e., in case of high resistance, reactor current crosses zero, but since an auxiliary switch 14 is turned by the voltage produced in the auxiliary winding of a reactor 15 current flows in minus direction. Consequently, when a diode 13 and the auxiliary switch 14 are turned OFF at next period ON interval of a main switch 12, current flows through a diode 18 to a DC power source 11 and excessive energy is returned from the reactor 15 to the power source 11 without requiring insertion of dummy load.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a DC-D device that steps up or steps down a DC voltage.
Regarding C converter.

(Prior Art) FIG. 5 is a circuit diagram showing a conventional D(,-DC converter of this type. In this conventional D(,-DC converter, direct current (DC), which is the output of the DC power supply 11, is By turning on and off with the main switch 42, a rectangular wave pulsating current is generated, and this pulsating current is smoothed by a smoothing circuit consisting of a diode (rectifying element) 43, a reactor 45, and a capacitor 16 to obtain a direct current of another voltage. Reference numeral 17 indicates a load, and this load 17 generally varies over time.

(Problem to be solved by the invention) In the conventional DC-DC converter described above, the load 1
7 is light (the resistance value of load 17 is large), and the reaction is 1~
When the current flowing through the reactor 45 becomes discontinuous, an abnormal phenomenon that cannot be determined only by the output voltage or the on/off time ratio of the main switch 42 occurs due to surplus energy stored in the energy storage reactor 45. Therefore, this kind of DC
- In the DC converter, the abnormal phenomenon is prevented by inserting a tummy load (a fixed resistor connected in parallel to the load 17). However, because the tummy load does not lose power, the conventional DC-DC converter in which the tummy load is connected in parallel to the main load cannot achieve very high power conversion efficiency.

(Means for Solving the Problems) The means provided by the present invention to solve the above-mentioned problems are as follows:
receiving direct current power at a first voltage;
An alternating current or pulsating current is generated by switching the TL current path on and off with a main switch, and the alternating current or pulsating current is smoothed by a smoothing circuit to generate direct current power of a second voltage, and the smoothing circuit is connected to an energy storage reactor. A DC-DC converter comprising a first rectifying element and a smoothing capacitor, the second rectifying element being connected in parallel to the main switch to the opposite pole Il'1g, and An auxiliary switching element connected in parallel with opposite polarity is provided with an auxiliary winding in the reactor 1 so that the auxiliary switching element is turned on when the main switch is off. The winding is connected to a control input terminal of the auxiliary switching element.

(Embodiments) FIGS. 1(a, 1c) to 1(c) are circuit diagrams showing embodiments of the present invention. These DC-DC converters are circuits that are modified by applying the present invention to conventionally known circuits, and elements that perform the same types of functions are given the same reference numerals. 11 is a DC power supply, 12 is a main switch, 13 is a rectifier, 14 is an auxiliary switch, 15 is a reactor 1 health, 16
is a smoothing capacitor, and 17 is a load. Main switch 12
receives a rectangular wave control signal with a constant frequency and alternately turns on and off. Rectifying element 13, reactor 1
5. The capacitor 16 constitutes a smoothing circuit. Here, taking the case of a step-down type as an example, the current waveform flowing through the reactor 15 is, if the smoothing capacitor 16 is large enough,
It will look like Figure 2.

That is, when the main switch 12 is on, the input voltage is E.
4. Set the output voltage to V. , the reactor interface is L
Then, the accelerator current 11. increases with a slope of (E, -V.)/L. Next, during the period when the main switch is off, the accelerator current decreases at a slope of -Vo/L. If the load 17 is light (the resistance value is large), the reactor current will cross O or the auxiliary switch 14 will be connected to the reactor 15.
Since it is turned on by the voltage generated in the auxiliary winding, current can flow in the negative direction. Therefore, when the main switch-on period of the next cycle comes and the diode 13 and auxiliary switch 14 are turned off, current flows toward the DC power supply 11 via the diode 18, causing a problem with conventional DC-DC converters. Excess energy from the accelerator is returned to the input power supply, eliminating the need to insert a tammy load.

FIGS. 3(a) to 3(c) are circuit diagrams showing other embodiments of the present invention, and these embodiments use power MOSFETs as switching elements. The power MO3FET has a parasitic diode as shown in the equivalent circuit diagram in FIG. Therefore, in the embodiment shown in FIG.
One power MO8FE T32 realizes the main switch and parallel diode, another power MO3FE""3
4 realizes a rectifying element and an auxiliary switch.

(Effects of the Invention) As explained above, in the DC-DC converter of the present invention, an auxiliary switch is provided in parallel with the rectifying element, and the
By turning the auxiliary switch on and off using an auxiliary winding installed in the main switch, and by connecting a rectifying element in parallel to the main swing element, a dummy load can be used to suppress the abnormal phenomenon of the reactor current discontinuous mode during light loads of the DC-DC converter. It can be prevented without insertion. Therefore, according to the present invention, there is no need to consume power by a dummy load, and a highly power efficient DC-DC converter can be realized.

[Brief explanation of the drawing]

Figures 1 (a) to (c) are circuit diagrams showing embodiments of the present invention, Figure 2 is a waveform diagram showing the current flowing through the reactor in the embodiment of Figure 1, and Figures 3 (a) to (c). (c) is a circuit diagram showing other embodiments of the present invention, and FIG.
FIG. 5 is an equivalent circuit diagram of the power MO3FET in the embodiment, and FIG. 5 is a circuit diagram of a conventional DC-DC converter. 11...DC power supply, 12.41...Main switch, 1
．． 3.43... Rectifying element, 14... Kamisuke switch, ]
, 5.45...Reactor 1~le, 16...Smoothing capacitor, 17...Load, 32.34...Power MO3F
E.T.

Claims (1)

[Claims] Receiving DC power of a first voltage, generating alternating current or pulsating current by cutting and intermitting the direct current path of the first voltage with a main switch, and generating the alternating current or pulsating current through a smoothing circuit. DC power of a second voltage is generated by smoothing, and the smoothing circuit is connected in parallel to the main switch with opposite polarity in a DC-DC converter comprising an energy storage reactor, a first rectifying element, and a smoothing capacitor. and an auxiliary switching element connected in parallel to the first rectifying element with opposite polarity, the reactor is provided with an auxiliary winding, and the time when the main switch is off is A DC-DC converter characterized in that the auxiliary winding is connected to a control input terminal of the auxiliary switching element so that the auxiliary switching element is turned on.