JPS6231584B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an input/output non-isolated switching power supply.

Conventionally, a chopper system as shown in FIG. 1 has been widely known as this type of input/output non-isolated switching power supply. This applies a rectangular wave pulse voltage converted from a DC input voltage by the switching operation of the transistor 4 to a smoothing circuit consisting of L ₈ and C ₉ , and outputs the average DC voltage. The input voltage, output voltage switching period, and transistor on-width are V _i , V ₀ ,
Assuming T and T _ON , there is the following relationship between them.

V ₀ = T _ON /TV _i The output voltage V ₀ normally has a fixed period T and an on-width T _ON
It is stabilized by varying the

However, in the case of the conventional chopper method, the load of the switching transistor is an inductive load and a large current is suddenly switched at turn-on and turn-off, so the switching loss of the transistor and diode is large, the radiation noise is large, and there is also a considerable amount of noise. High level across harmonics,
There were drawbacks such as the need for surge suppressors for transistors and diodes to prevent reverse surges. In addition, these drawbacks become more noticeable as the frequency of the switching operation increases, and are therefore a fundamental factor that prevents the miniaturization of power supplies due to the increase in frequency.

The purpose of the present invention is to eliminate the above drawbacks by switching a sine wave current using LC resonance, and to provide a non-isolated input/output switching power supply that has low loss, high reliability, and can operate at a high frequency. It is about providing.

The input/output non-isolated switching power supply of the present invention has the following features:
A series circuit consisting of a first coil, a first switching element, and a first capacitor is connected to both ends of the input power supply, and a second capacitor is connected in parallel to the first capacitor.
The first diode is connected to a series circuit consisting of a switching element, a second coil, and a second capacitor, and a load resistor is connected in parallel with the second capacitor.

Next, an embodiment of the present invention shown in FIG. 2 will be described. In this example, a series circuit consisting of a coil 12, a transistor 13, and a capacitor 14 is connected across the input power source 1, and in parallel with the capacitor 14, a diode 15, a transistor 16, a coil 17,
A series circuit consisting of a capacitor 9 is connected. The voltage across the capacitor 9 is the output voltage of the power supply, and a load resistor 10 is connected in parallel with the capacitor 9. The transistors 13 and 16 are driven by a control circuit 18, which turns the transistors 13 and 16 on and off alternately while changing its oscillation frequency so as to stabilize the detected output voltage.

Here, the period during which the transistor 13 is on and the transistor 16 is off (1/2 cycle) is defined as a cycle, and the opposite period (1/2 cycle) is defined as a cycle. The switching operation of this circuit is a cycle,
One period is formed by two cycles.

In the above circuit configuration, the voltage across the capacitor 14 immediately before the transistor 13 turns on is 0 volts, as will be described later. Therefore, when the transistor 13 is turned on during the cycle, due to the LC resonance effect, as shown in FIG.
LC resonant current i _L12 is from input power supply 1 to capacitor 1
Flows into 4. At the time when this charging current finishes flowing, the voltage v _C14 across the capacitor 11 assumes the maximum value of the resonance waveform as shown in FIG.

Here, the inductance of the coil 12, the capacity of the capacitor 14, and the input voltage are L ₁₂ , C ₁₄ , and E
If t is the time when the origin is the start of the cycle, then the relationships of equations (1) and (2) below hold.

During the remaining period of the cycle π√ _{12 14} <t<T/2 (T is the switching period), capacitor C ₁₄ has been fully charged, but transistor 1
6 is turned off, and since the conducting direction of the transistor 13 is reversed, the capacitor 14 is not discharged to the input side and the output side, and the capacitor C ₁₄ maintains the maximum voltage v _{C14 (nax)} = 2E during charging.

Next, in a cycle (T/2<t<T), when the transistor 13 is turned off and the transistor 16 is turned on, the charge in the capacitor 14 is discharged to the capacitor 9 due to resonance with the coil 17. Third
i _L17 in the figure indicates this discharge current. During discharging, the voltage across the capacitor 14 becomes lower than the input voltage E and the output voltage V ₀ (voltage of the capacitor 9), but since the transistor 13 is off and the conduction direction of the transistor 16 is opposite, the input/output is No current flows from the capacitor C14 to the capacitor _C14 . Here, if the inductance of the coil 17 is _L17 , and the time from when the capacitor _C14 starts discharging until the voltage across it reaches 0 volts is τ _DC , then the current j _L17 of the coil 17 and the current across the capacitor _C14 is The voltage v _C14 and τ _DC are expressed by the following formulas (3) to (5).

However, E>V ₀ (6) As can be seen from Figure 3, when the voltage across the capacitor _C14 drops to 0 volts, the excitation current of the coil 17 reaches its maximum. The maximum excitation current I _L17n of the coil 17 is expressed by the following formula (7).

The excitation current of the coil 17 thereafter is the diode 15.
It is reset via . This reset period is τ
_RS , the current i of the coil 17 during this period _L17
and τ _RS are expressed by the following formulas (8) and (9).

i _L17 = I _L17n −V ₀ /L ₁₇ (tT/2−τ _DC )…
...(8) τ _RS =L ₁₇ I _L17n /V ₀ ......(9) After the demagnetization of the coil 17 is completed, the circuit operation remains stationary until the next cycle is started.

In the derivation of equations (3) to (9) above, the voltage across the capacitor 9, that is, the output voltage _V0 , is determined by the fact that the time constant of the discharge circuit consisting of the capacitor 9 and the resistor 10 is much larger than the period T. It is assumed that the voltage value is large and that the voltage value remains unchanged throughout the cycle.

As can be seen from the above explanation, since the current flowing through each transistor has a sine wave shape, the generated noise frequency is only the fundamental wave and there are almost no harmonic components.

Further, the currents of the transistors 13 and 16 during turn-on and turn-off are 0, and there is no switching loss or surge current. Therefore, even if the operating frequency is increased, the noise surge current will not increase or the power conversion efficiency of the power supply will not decrease.

Furthermore, if the frequency and load resistance are respectively R, the output power P ₀ is P ₀ = 1/2C ₁₄ V ² _C14(nax) = V ₀ ² /R...
...(10) Since V _C14(nax) = 2E, the output voltage V ₀ can be expressed as the following equation (11) from equation (10).

V ₀ = E√2 ₁₄ ......(11) From the above formula, the output voltage V ₀ is a function of R and E, and conversely, the frequency can be adjusted in response to fluctuations in the input voltage E or load resistance R. It can be seen that the output voltage V ₀ can be stabilized.

As explained above, the present invention utilizes resonance in an input/output non-isolated step-down switching power supply to make the current of the switching element into a sine wave shape, thereby eliminating switching loss and achieving low loss even when the frequency is increased. The noise is only the fundamental wave of the LC resonance frequency and contains almost no high frequency components.
Furthermore, since no surge current flows, it has excellent features such as eliminating the need for a surge suppressor in the switching element.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional example, FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 is a waveform diagram showing the operation of FIG. 2. 1...Input power supply, 2...Resistor, 3...Capacitor, 4...Transistor, 5...Diode,
6...Resistor, 7...Capacitor, 8...Coil, 9...Capacitor, 10...Load resistor, 1
1... Control circuit, 12... Coil, 13... Transistor, 14... Capacitor, 15... Diode, 16... Transistor, 17... Coil,
18...Control circuit.

Claims (1)

[Claims] 1 A series circuit consisting of a first coil, a first switching element, and a first capacitor is connected to both ends of an input power supply, and a series circuit consisting of a second switching element, a second coil, and a first capacitor is connected in parallel to the first capacitor. 1. An input/output non-isolated switching power supply, characterized in that a series circuit consisting of two capacitors and a first diode are connected, and a load resistor is connected in parallel with the second capacitor.