JPH03139168A - Series resonance converter - Google Patents

Abstract

PURPOSE:To suppress resonance current, even when output voltage drops through overcurrent protective operation, by setting switch ON interval approximately same as half of resonance period of a resonance circuit. CONSTITUTION:Since a second inductor 9 functions not to clamp a capacitor 5 at an input voltage or zero voltage, ON interval of first and second switches 6, 7 matches with half of the resonance period of a resonance circuit comprising a first inductor 8 and the capacitor 5, and thereby the characteristic impedance of the resonance circuit is set optimally. When the output voltage drops through overcurrent protective operation, voltage across a primary winding 12 decreases to cause increase of voltage Vcr across the capacitor 5, but since feedback current iH also increases voltage Vor drops to some constant level upon turn OFF of the switches 6, 7. Consequently, charging voltage and discharging voltage of the capacitor 5, controlled respectively through the switches 6 and 7, are suppressed resulting in suppression of current iR.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a series resonant converter used in a constant voltage power supply.

[Conventional technology]

In a series resonant converter, the waveform of the current flowing through the switch is sinusoidal due to the series resonant circuit, and when the switch is turned on,
The overlap of current and voltage when off can be significantly reduced. Therefore, it has the characteristics of high efficiency and low noise, and can be miniaturized by increasing the driving frequency. Such a converter was introduced in PCIlorlando in April 1983 by R
, tl, lligh published by Baker
Frequency Power Conversi
on With FET-Controlled
Re5onant Charge Transfer
Seen in r. The basic circuit diagram of the converter according to this report is shown in FIG. 5, and the operating waveforms of each part are shown in FIG.

The operation of Baker's converter will be explained below.

Due to the driving voltage g from the control circuit 18, the switch 6
turns on, and DC power supply 1 → switch 6 → inductor 8
→ Primary winding 12 → Capacitor 5 → DC power supply 1 loop, and capacitor 4 → Switch 6 → Inductor 8 → Primary winding 12 → Capacitor 4 loop, current flows, and resonance between inductor 8 and capacitor 4.5 This results in a sinusoidal current. This period is 1. When the voltage Ver of the capacitor 5 reaches the input voltage v1, the diode 2 becomes conductive 1, and a current flows through the loop of the inductor 8 -> the primary winding Ia12 -> the diode 2 -> the switch 6, and decreases linearly.

This period is L8. Switch 6 is off, switch 7
The same operation occurs even when is on. The output power Po of Baker's converter is given by the following equation.

Po=Vi''XCrXfsvMXy7 Here, Cr is resonance capacitance, fsw is drive frequency, and η is efficiency.

Even if the driving frequency is limited, the output power can be increased by increasing the resonant capacitance.

JP-A-61-185070 ``Power converter with series resonant circuit'' discloses a method for optimally adjusting the conduction period of a switch by detecting a resonant current and switching the switch on and off when the current is zero. is listed.

[Problem to be Solved by the Invention] In the case of the Baker's converter described above, the sum of tl and t is the on-period ton of the switch, but as the input voltage 1 increases, the period t increases, so the conduction period ton must be set taking into account the maximum input voltage. Therefore, since the on-period ton is considerably longer than the resonant half cycle of the resonant circuit, there is a point where the maximum driving frequency of the converter is limited.

Furthermore, if the output voltage is reduced by an overcurrent protection circuit during an overload such as a high-power shortening, there is a problem that the resonance current increases and the load on the power element increases (IEICE Technical Report Vol. 1.87) No. 169 pp23-28 (Refer to rectifier using series resonant converter).

Furthermore, the method described in Japanese Patent Application Laid-open No. 185070/1983 requires a current detector and several logic circuits, making the control circuit complicated and expensive.

Therefore, the main feature of the present invention is that in order to optimize the characteristic impedance of the resonant circuit, it is possible to set the switch on and the resonant half period of the resonant circuit to be approximately equal, and even when the output voltage drops due to overcurrent protection, the resonant current It is an object of the present invention to provide a series resonant converter that can suppress an increase in .

[Means to solve the problem]

The present invention provides first and second switching elements having one end connected to each other and the other ends connected to both ends of the DC input power source, and a second switch element having one end connected to each other and the other end connected to the DC input power source. A first and a second diode connected to both ends of the first and second diodes are inserted in series between a connection point of the first and second switch elements and a connection point of the first and second diodes. a transformer having first and second inductors and a primary winding; a capacitor having one end connected to the negative terminal of the DC input power source and the other end connected to a connection point between the transformer primary winding and the second inductor; The converter is a series resonant converter that includes a control circuit that drives the first and second switching elements at an operating frequency determined by the load, and a rectifier circuit and a smoothing circuit in the secondary winding of the transformer.

In the present invention, the first inductor 8 and the primary winding 12 of the transformer are connected in series and inserted between the connection point of the series switch 6.7 and the connection point of the capacitor 5. A second inductor 9 is inserted between the connection point of the capacitor 5 and the connection point of the series diode 2.3. It further includes a control circuit 18 that turns the switch on and off at a drive frequency determined by the load. Due to the action of the second inductor 9, the capacitor 5 is not clamped at the input voltage Vi and zero, so the on-periods of the first and second switches are
This can match the resonance half period of the resonance caused by the first inductor 8 and capacitor 5, and the characteristic impedance of the resonant circuit can be optimally set. Moreover, even when the output voltage drops due to current holding current protection, the resonance between the second inductor 9 and the capacitor 5 adjusts the voltage of the capacitor 5 before the first and second switches 6.7 are turned on. , it is possible to suppress an increase in resonance current.

In addition, in order to simplify the drive circuit, in a circuit where the second switch 7 is turned on immediately after the first switch 6 is turned off, another capacitor is connected to the second inductor in order to balance the positive and negative resonance currents. 9 in series.

Hereinafter, the present invention will be specifically explained with reference to Examples.

〔Example〕

(Example 1) Fig. 1 is an embodiment of the present invention, Fig. 2 is a waveform diagram of each part for explaining the normal operation of the embodiment of Fig. 1, and Fig. 3 is an output of the embodiment of Fig. 1. FIG. 4 is a waveform diagram of each part for explaining the operation at the time of a short circuit. The present invention will be explained in detail below.

The switch 6.7 is turned on and off by the control circuit 18 at a drive frequency determined by the load. The on-time of each switch is fixed within the control circuit 18, and the output voltage is controlled by varying the off-time period of both switches. A dedicated IC for the control circuit 18 is commercially available. First, when switch 6 is turned on, DC power supply 1 → switch 6 →
A current iR flows through the loop of inductor 8 → primary winding 12 → capacitor 5 → DC power supply 1, and due to the resonance of inductor 8 and capacitor 5, the current becomes a sinusoidal current.

When the voltage Ver of the capacitor 5 reaches the input voltage Vi, the diode 2 becomes conductive 1, and a feedback current iH flows through the loop of the capacitor 5 → inductor 9 → diode 2 → DC power supply 1 → capacitor 5, and due to the resonance of the capacitor 5 and inductor 9. , a sinusoidal current roars. The switch 6 is turned off after the half period of resonance between the inductor 8 and the capacitor 5 when the current iR becomes zero.

Next, when switch 7 is turned on, current iR flows through the loop of capacitor 5 → primary winding 12 → inductor 8 → switch 7 → capacitor 5. When the voltage Ver of the capacitor 5 reaches zero, the diode 3 becomes conductive and the capacitor 5→
Diode 3 conducts and current i flows through the loop of capacitor 5.
H flows.

The switch 7 is turned off after the timing when the current iR becomes zero.

When the output is short-circuited, the drive frequency is suppressed by the overcurrent protection circuit, but since the voltage across the primary winding becomes almost zero, the current flowing through the switch tends to increase. However, due to the resonance between the inductor 9 and the capacitor 5, the charging voltage of the capacitor 5 before the switch is turned on increases, so that an increase in the current flowing through the switch is suppressed.

FIG. 4 shows that switch 7 is immediately turned off after switch 6 is turned off.
is turned on, and a second capacitor 1o is connected in series with the inductor 9 in order to balance the positive and negative sides of the resonant current iR.

In this case, ■g8 in Figure 2. ■There is no downtime like there is in GS. Therefore, due to the asymmetry of the circuit, a phenomenon occurs in which the waveforms of the feedback current LH and the resonant current iR exhibit different peak values for positive and negative waves. This phenomenon is caused by the difference in Ver between the charging period and the discharging period of the resonant current iR to the first capacitor 5.

Therefore, when the second capacitor 10 is connected, the positive/negative imbalance of the feedback current iH1 resonant current IR can be compensated for by the action of its accumulated charge.

In the converter of the embodiment shown in FIG. 4, the input voltage DC200
~350cm, output DC24V, 12.5A specifications, efficiency reaches the highest 92.5%.

This is up to 80% by the Baker converter mentioned above.
It has extremely high efficiency compared to the current quantity and general rectangular waveform converter.

[Effects of inventions and ideas]

In conventional converters, when the input range is wide, the characteristic impedance of the resonant circuit must be low.
Although the efficiency of the skewer was low, according to the present invention, the characteristic impedance can be set optimally, so the efficiency can be significantly improved. Further, it is possible to suppress an increase in resonance current when the output voltage drops due to overcurrent protection operation, and to reduce the load on the switch element.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a waveform diagram of each part to explain the normal operation of the embodiment of FIG. 1, and FIG. 3 is an example of the embodiment of FIG. 1. 4 is a circuit diagram showing the second embodiment of the present invention, FIG. 5 is a circuit diagram showing the conventional method, and FIG. FIG. 3 is a waveform diagram of each part for explaining the operation of the conventional method. Figure 4 Figure 4 Engraving of drawings (no changes in content) Figure 1 Figure 2 Figure 6 Procedural amendment form, Procedural amendment form (Category 1, 1, Indication of case, 1999 Patent Application No. 276245 2, Title of the invention: Series resonant converter 3, relationship with the case of the person making the amendments Patent applicant office: 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Heisei Koru, 2g

Claims (3)

[Claims] (1) A DC input power source, first and second switch elements each having one end connected to each other and the other end connected to both ends of the DC input power source; a first and a second diode connected to both ends; a first and second diodes connected in series between a connection point of the first and second switch elements and a connection point of the first and second diodes; and a second inductor, a primary winding of the transformer, a capacitor having one end connected to the negative terminal of the DC input power supply and the other end connected to a connection point between the primary winding of the transformer and the second inductor, and the first and a control circuit for driving a second switching element at an operating frequency determined by the load, and a series resonant converter comprising a rectifier circuit and a smoothing circuit in the secondary winding of the transformer. (2) The series resonant converter according to claim 1, wherein the first inductor is replaced by a leakage inductance of the transformer. (3) The series resonant converter according to claim 1, wherein a second capacitor is connected and inserted in series between the second inductor and a connection point at the other end of the capacitor.