JPS5886868A - Non-insulation type l-c resonance converter - Google Patents

Abstract

PURPOSE:To reduce switching loss by utilizing resonance action and forming the currents of a switching element and a diode in sine wave shape. CONSTITUTION:When an ON-cycle, both-end voltage of a capacitor 11 at a moment when a transistor 9 is at ON is under a state lower than input voltage. Accordingly, LC resonance charging currents flow through the capacitor 11 from an input power supply by LC resonance action. The maximum value is kept until the next OFF-cycle is started at both-end voltage of the capacitor 11. When a transistor 13 is at ON at OFF-cycle, the charge of the capacitor 11 is discharged to an output capacitor 5 by resonance action with a coil 14. Currents do not flow from the input side because the transistor 9 is at OFF, and currents do not flow through the input side from the output side.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a non-isolated DC-
Regarding improvement of DC converters, the chopper type shown in FIG. 1 is widely known as a conventional non-insulated DC-DC converter.
A rectangular wave pulse voltage converted from a DC input voltage 1 by the switching operation is applied to a smoothing circuit using a 4.5 LC, and the average DC voltage is taken out as an output. The input voltage, output voltage, switching period, and transistor on-width are each V+.

■. Assuming *T*Tox, the relationship expressed by the following equation (1) holds between these.

The output voltage is usually stabilized by fixing the period T and varying the on-width TON.

However, in the case of the conventional chopper method, the load on the transistor is a conductive load, and large currents are rapidly switched during turn-on and turn-off, resulting in large switching losses in the transistor and diode due to accumulated charge within the element. The disadvantages are that the radiation noise is large and has a high level across all harmonics, and that the transistors and diodes require surge suppressors to prevent reverse surges. Furthermore, these drawbacks become more noticeable as the frequency of the switching operation becomes higher, and thus become a fundamental factor that hinders the miniaturization of power supplies due to the increase in frequency.

The present invention eliminates the above drawbacks by switching a sine wave current using LC resonance, and provides a non-insulated DC that has low loss, high reliability, and can operate at a high frequency.
- It provides a DC converter.

The configuration of the present invention is that in a non-isolated 4DC-DC converter, a series circuit consisting of a first coil, a first switching element, a first diode, and a first capacitor is connected to both ends of an input power source, A series circuit consisting of a second diode, a second switching element, a second coil, and a second capacitor is connected in parallel across the first capacitor, and a load resistor is connected in parallel to the second capacitor. is characterized in that it is connected.

Next, the operating principle of the present invention will be explained. When the 0 element is turned on, charge is supplied from the input power source to the first capacitor due to the resonance effect of the first coil and the first capacitor. At this time, the second switching element is in the off state, and since the first diode is present, the first capacitor is discharged when it is charged to the maximum voltage value of the first resonance cycle, which is higher than the input power supply voltage. The maximum voltage is maintained as it is.

Next, when the first switching element turns off and the second switching element turns on, the charge moves from the first capacitor to the second capacitor due to the resonance between the first capacitor and the second coil. Take out the voltage across the capacitor No. 2 as an output.

After the first capacitor is discharged, the voltage across it becomes lower than the input voltage and the voltage across the second capacitor.
The first switching element is in an off state, and since there is a second diode, no current flows from the input and output.

Since the transmission power for one period is determined by the resonant waveform,
Transmission power can be controlled by varying the frequency.

Next, the present invention will be explained by way of embodiments with reference to the drawings.

FIG. 2 shows a circuit diagram of a non-insulated DC-DCw pumper according to the present invention. In FIG. 2, a coil 8, a transistor 9, a diode 10. Content? A series circuit consisting of a diode 12, a transistor 13, a coil 14, and a capacitor 5 is connected in parallel to the capacitor 11.

The output voltage of the converter is the voltage across the capacitor 5, and a resistor 6 is connected in parallel with the capacitor 5. The transistor 9.13 is driven by a control circuit 15, which turns the transistor 9.13 on and off alternately while changing its oscillation frequency to stabilize the detected output voltage.

Here, the period in which the transistor 9 is on and the transistor 13 is off is defined as an on cycle, and the opposite period is defined as an off cycle. The switching operation of this circuit consists of two cycles, an on cycle and an off cycle, and two cycles form one cycle.

In the above circuit configuration, first, during the on-cycle,
The voltage across the capacitor 11 at the moment the transistor 9 is turned on is lower than the input voltage, as will be described later.

Therefore, due to the LC resonance effect, an LC resonance charging current flows from the input power source to the capacitor 11, as shown in FIG. 3(1). At the end of the flow of the charging current at round gA, the voltage across the capacitor 11 assumes the maximum value of the resonance waveform as shown in FIG. 3 (3). Although this voltage is also higher than the input voltage, it will not be discharged to the input power supply because of the diode 10, and since the transistor 13 is off, it will not be discharged to the output capacitor 5. . Therefore, the maximum value of the voltage across the capacitor 11 is maintained until the start of the next off-cycle. Next, in the off-cycle, when the transistor 13 is turned on, due to the synergistic action with the voltage source 14, the voltage across the capacitor 11 is As shown, the capacitor 11 is discharged to the output capacitor 5. In the first cycle of this discharge resonance waveform,
As shown in Figure 3 (8), the minimum voltage of the capacitor 11 is lower than the input power supply voltage and the output voltage, but since the transistor 9 is off, the current from the input side is No current flows in, and no current flows from the output side to the input side (through the diode 12).

Now the input power supply voltage, the inductance of coil 8.14,
The capacitance and output voltage of capacitor 11 are VIN, respectively.
hg + 1114 + Ct+ + v, and if the time taken from the start of each cycle is t·n in the on-cycle and t@rt in the off-cycle, then the collector current Ice of the transistor 9 in the on-cycle and the OR Transistor 13 in cycle
The collector current 1c1m of is expressed by the following formula.

Here ■ cun and Vcnm are the maximum value in the on cycle and the minimum value in the off cycle of the capacitor 11, respectively. As can be seen from (2) and (8) above, the current flowing through each transistor has a sine wave shape. , the generated noise frequency is only the fundamental wave and there is no n-high blind control wave component. Furthermore, the currents in the transistor 2 star 9.13 and the diode 10.12 during turn-on and turn-off are zero, there is no switching loss, and there is no surge current. Therefore, even if the operating frequency is increased, there will be no increase in noise, surge current, or decrease in converter efficiency.

Note that if the frequency, load resistance, and maximum current of the transistor 13 are f, R, and lcxsM, respectively, the output power is expressed as the output voltage v, hiro-]. From the above equation, the output voltage V, is proportional to Jf, and conversely, the frequency f
It can be seen that by controlling the output voltage, the output voltage can be stabilized.

As explained above, according to the present invention, in a non-isolated converter, by making the current of the switching element and the diode into a sine wave shape by using the resonance effect,
There is no switching loss and the loss is low even when the frequency is increased, the noise is only the fundamental wave and does not contain high frequency components, and since no surge current flows, there is no need for a surge suppressor in the switching element or diode. 0

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional chopper-type DC-DC converter, Figure 2 is a circuit diagram of a DC-DC converter according to an embodiment of the present invention, and Figure 3 is a circuit diagram of a DC-DC converter according to an embodiment of the present invention. 5 is a time chart of voltage of a resonant capacitor. The symbols used in the drawings indicate the following. 1... Input power supply, 5... Output capacitor, 6... Load resistance, 8.14... Coil, 9.13... transistor, 10.12
... Diode, 11 ... Capacitor, 15 ... Control circuit.

Claims (1)

[Claims] In a non-isolated DC-DC converter, a series circuit consisting of a first coil, a first switching element, a first diode, and a first capacitor is connected across an input power source, and a series circuit consisting of a first coil, a first switching element, a first diode, and a first capacitor is connected across an input power source; A series circuit consisting of a second switching element, a second coil, and a second capacitor is connected in parallel across the first capacitor;
An input/output non-insulated type LC resonant converter, characterized in that a load resistor is connected in parallel to the capacitor.