JPH04165956A - Resonant converter - Google Patents

Abstract

PURPOSE:To prevent parasitic resonance between the junction capacitance of a rectifying diode and a resonant inductance by connecting a nonlinear inductor, exhibiting an inductance several times as high as the resonant inductance when the rectifying diode is not conducting, in series with the rectifying diode. CONSTITUTION:During an interval when the junction capacitance of a rectifying diode 5 contributes to parasitic oscillation, i.e., an interval when a rectifying diode 5 is not conducting, oscillation is induced with the junction capacitance of the rectifying diode 5 and the sum of the inductance in unsaturated region of a nonlinear inductor 10 and the inductances of primary and secondary resonant inductors 9, 9'. At that time, the inductance in unsaturated region of the nonlinear inductor 10 is selected so that the period of oscillation is substantially same as the maximum conduction width of a switching element 1 thus realizing a resonance circuit in which the rectifying diode 5 is conducted or nonconducted with zero voltage. According to the constitution, output control is carried out stably.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a resonant converter in which a switching element is switched in a substantially zero applied voltage state.

[Prior art]

Advances in power MO3FETs and IGETs have made it possible to perform high-power, high-frequency switching of power devices, and various power supplies with high efficiency and high functionality have already been put into practical use.

In recent years, resonant switching technology has attracted attention as a means of achieving higher frequency switching with higher efficiency, and numerous research reports have been published. The basic characteristics of various types of resonant converters have already been clarified using idealized models (for example, Tamotsu Ninomiya, Masatoshi Nakahara, Toru Itsuzuka, Kosuke Harada,
``Systematic analysis method of resonant converter'', pp857
~867, Journal of the Institute of Electronics, Information and Communication Engineers B-[, Vol.
J-72-B-1, No. 10. October 1989, etc.).

Actual switching semiconductor devices, especially power MO3FETs
has a large capacitance.

This may be a problem, but in a ZvS converter that switches the switching element with virtually no voltage applied, that is, with zero voltage (ZVS), MO
Since the SFET capacitance is used as the resonant capacitance or a portion thereof, there is no problem with the MOSFET capacitance.

However, the junction capacitance of the rectifier diode causes resonant inductance and parasitic vibration. This parasitic vibration may affect output control characteristics and become an obstacle to stable control.

To explain this point using a conventional flyback type ZvS converter as shown in FIG. Line N
1 and MO8FETl, current flows through transformer 3
to store energy.

At this time, the rectifier diode 5 is connected to the secondary winding N of the transformer 3.
Although it is reverse biased by the voltage induced in the rectifying diode 5 and does not conduct, parasitic vibrations occur due to the junction capacitance of the rectifying diode 5 and the resonance inductance mainly consisting of the leakage inductance of the transformer 3 and the wiring inductance. This parasitic oscillation occurs during the period (T) from when the rectifying diode 5 becomes non-conductive to when the rectifying diode 5 begins to conduct, as shown by ■5 and v5 in FIG. It also affects 1.

Here, in the case where a Schottky barrier diode is used as the rectifying diode 5 due to the necessity of using a diode with a small forward drop.

Since the junction capacitance increases, the vibration becomes even larger.

Next, when switching element 1 turns over.

The resonance inductance and the capacitance of the resonance capacitor 4 resonate (V4), and the energy stored in the transformer 3 is transmitted to the secondary winding N2 of the transformer 3, inducing a current. The current is rectified by a rectifying diode 5 and flows to a smoothing capacitor 6 and a load 7.

[Problem that the invention attempts to solve]

As can be seen from the above explanation, when the rectifying diode is non-conductive, its junction capacitance and resonant inductance cause parasitic vibration, and this parasitic vibration changes the output from the rectifying diode. If the change in output due to the phase of this parasitic vibration exceeds the change in output due to frequency control, the relationship between output and operating frequency will no longer be monotonic, and a reversal portion will occur where the output control characteristic with respect to the operating frequency becomes positive due to parasitic vibration. , stable control may not be possible.

In addition, especially in ZvS resonant converters, the peak current flowing through the rectifier diode is large, so in order to increase the efficiency of the low voltage output converter, a rectifier diode with a large die size is used to reduce the forward voltage drop as much as possible. It needs to be made smaller. In this case, the junction capacitance of the rectifying diode must become large, and the difference between the operating frequency and the frequency of the parasitic vibration becomes about one order of magnitude, and the adverse effects of the parasitic vibration become significant. Another method is to connect a snubber circuit in parallel to the rectifier diode to absorb parasitic vibrations, but in this case, the efficiency is greatly reduced.

[Means for Solving the Problems] In order to prevent such parasitic vibration between the junction capacitance of the rectifier diode and the resonant inductance, the present invention provides a method for preventing parasitic vibration between the junction capacitance of the rectifier diode and the resonant inductance. A resonant rectifier circuit is constructed by connecting a nonlinear inductor that provides an inductance several times larger than that of a rectifier diode in series.

[For production]

In this way, by connecting a nonlinear inductor that exhibits a larger inductance than the resonant inductance when the rectifier diode is not conducting in series with the rectifier diode, the period of parasitic vibration with the junction capacitance can be adjusted to the maximum conduction period of the switching element. Since it has a resonant rectifier circuit with the same level of vibration, it is not affected by vibration. Furthermore, since the present invention uses a nonlinear inductor that saturates in a small current region, the use of a nonlinear inductor as a rectifier diode does not substantially affect the output control characteristics.

〔Example〕

An embodiment of a resonant converter according to the present invention will be explained with reference to FIG.

In the figure, the same symbols as those shown in FIG. 8 indicate corresponding parts, and 8 indicates a diode connected in parallel to the switching element 1 and the resonance capacitor 4, and the switching element 1 is a MOSFET. In that case, the M
This is an internal diode of the OSFET, and in the case of other semiconductor devices, it is a separately connected diode. 9 and 9' are the primary side and 2 of the resonance inductance, which mainly consists of the leakage inductance of the transformer 3 and the wiring inductance.
These are resonance inductance means each indicating a next-side resonance inductance.

Reference numeral 10 denotes a saturable nonlinear inductor connected in series to the rectifying diode 5. In the non-saturation region, the inductance value of the resonant inductance means 9, 9'' is more than several times that of the rectifying diode 5. An inductance that resonates with the junction capacitance of the rectifier diode 5 is provided from the time of conduction to the turn-off of the switching element 1.

Reference numeral 11 denotes a control circuit, which turns on the switching element 1 after the voltage across it becomes zero, and outputs a control signal to control the off time of the switching element 1 according to the detected value of the output voltage. It is something.

Next, the operation will be explained using FIG. 2 as follows.

(1) Period T+ (t, ~t2) After the switching element 1 is turned on, the current flowing through the rectifying diode 5 5 is linear due to the relationship between the magnitude of the input/output voltage and the value of the resonance inductance means 9 and 9'. The maximum current value in the non-saturation region of the nonlinear inductor 10 decreases to 2 at time t1. Then, the nonlinear inductor 10 enters the non-saturated region from the saturated region.

(2) Period T 2 (t2-t3) At time t2, the current 5 flowing through the rectifier diode 5 becomes zero, the rectifier diode 5 becomes non-conductive, and its junction capacitance and resonance inductance means 9.9' A resonance with a large period occurs between the inductance of the nonlinear inductor IO and the inductance of the nonlinear inductor IO.

(3) Period Ts (ts~14) When the switching element l starts to turn off at time t3, the junction capacitance of the rectifying diode 5 and the resonance capacitor 4
capacitance and resonance inductance means 9.9'
, a resonance with a large period occurs with the inductance of the nonlinear inductor IO.

The output control of this converter is performed by controlling the turn-off time t3 of the switching element 1.

(4) Period T 4 (t4 to b) At time t4, the nonlinear inductor IO magnetically saturates, and its inductance becomes substantially zero. The state is at time t
Continues until just before 8. Therefore, the current 5 flowing through the rectifier diode 5 is equal to its junction capacitance, the resonance capacitor 4
capacitance and resonant inductance means 9.9'
, and the resonance is not affected by the nonlinear inductor 10.

(5) Period Ts (ts to ts) At time t6, the rectifying diode 5 becomes forward biased and becomes conductive. The current 5 flowing through the rectifying diode 5 increases until it reaches the point where it becomes a resonance between the capacitance of the resonant capacitor 4 and the inductance of the resonant inductance means 9, 9', and then begins to decrease.

(6) Period Te (t6 to 17) At time t6, the voltage across the switching element 1, that is, the voltage across the resonance capacitor 4 becomes substantially zero, the diode 8 begins to conduct, and the resonance ends. Thereafter, due to the relationship between the input/output voltage and the inductance of the resonance inductance means 9 and 9', the negative primary current 1 decreases toward zero until time t7, and the current flowing through the rectifier diode 5 decreases. I5 also decreases.

Here, between times t6 and t7, the rectifier diode 5 is conductive, and the voltage 1 across the switching element 1 is at zero, so by turning on the switching element 1 during this period, Can perform voltage switching.

(7) Period T 7 (t7 to tg) By turning on the switching element 1 between time t6 and t, at time t7, the primary current 1 passes through zero and becomes positive until time t8. increase On the other hand, a current I flows through the rectifying diode 5.

continues to decrease.

(8) Period Ts (ts・1+) At time t8, the current 15 flowing through the rectifier diode 5 reaches the maximum current value lff1 in the non-saturation region, completing one cycle and returning to one period T, and repeating the same operation. .

Here, during the period (t2 to t5) in which the junction capacitance of the rectifying diode 5 contributes to parasitic vibration, the inductance of the sum of the inductance in the non-saturation region of the nonlinear inductor IO and the inductance of the resonant inductor converted to the secondary side and the junction capacitance of the rectifier diode 5. In this embodiment, the inductance in the non-saturation region of the nonlinear inductor 10 is set on the secondary side so that the oscillation period is approximately the same as the conduction period of the switching element 1. It is selected to be larger than the sum of the converted inductances of the resonant inductors, and since the conventional parasitic vibration is incorporated as resonant rectification, stable output control can be performed.

This resonance during the reverse bias period of the rectifying diode 5 has the effect of reducing the frequency range for controlling the output power. That is, the magnetic flux of the nonlinear inductor 10 changes depending on the resonance phase of the rectifying diode 5, and the shorter the conduction period of the switching element 1, the more the nonlinear inductor 1
It operates in a wide range of magnetic flux state extending to the magnetic flux direction opposite to the magnetic saturation direction of the conduction direction of the rectifier diode 5 of zero.

Therefore, after the switching element 1 is turned off, the nonlinear inductor 10 is magnetically saturated and the time for flowing the output current from the rectifier diode 5 is delayed, resulting in a decrease in output.

Greater output control is possible with a smaller frequency change than in the case where there is no resonant circuit including this nonlinear inductor 10.

Furthermore, at the time of maximum conduction of the switching element 1, the magnetic flux of the nonlinear inductor IO returns almost to the saturation magnetic flux force in the conduction direction of the rectifier diode 5 due to this resonance. The rectifier diode 5 becomes conductive, and does not cause any adverse effects such as lowering the output.

An example of a nonlinear inductor 10 suitable for use in the above embodiments is a nonlinear inductor 10 in which a rectangular saturable inductor IOA and a linear inductor IOB are connected in parallel as shown in FIG. 3(A). Its magnetic properties are as shown in the same figure (B).

In addition, as another example, even if a gap is provided in the core of a rectangular saturable inductor, a nonlinear inductor with magnetic characteristics as shown in FIG. 3(B) can be obtained.

Next, FIG. 4 shows an embodiment in which the linear inductor 10 is biased.

FIG. 4(A) shows the winding W provided in the nonlinear inductor 10.
By connecting in series and a resistor R to both ends of the load 7, a DC current is caused to flow through the nonlinear inductance 10, and DC excitation is performed in the positive direction [B shown in FIG. 3(B). ] This is an example. As a result, the amount of magnetic flux change in the opposite direction up to magnetic saturation can be increased, so the core of the nonlinear inductor 10 can be made smaller.

Furthermore, since the nonlinear inductor 10 becomes magnetically saturated as soon as a current starts flowing through the rectifying diode 5, there is an advantage that the dead time in the non-control range [time (13 to ts) in FIG. 2] can be reduced. The same figure (B) as another example
As shown in FIG. 3, a winding W provided in a nonlinear inductor 10, an inductor L, and a capacitor C are connected in series to form a transformer 3.
The circuit may have a circuit configuration in which the diode D is connected to both ends of the secondary winding N2 of the transformer 3, and the diode D is connected between the secondary winding N2 of the transformer 3 via the capacitor C. Inductor L is for AC smoothing, and the value of capacitor C is selected to set the desired bias current. Further, since the bias current can control the reverse bias voltage waveform of the rectifier diode 5 and the conduction time of the rectifier diode 5, it is also possible to control the output voltage.

Next, each embodiment in which the output circuit has a different circuit configuration will be described. The primary circuit of the transformer may be a circuit with switching elements connected in a bush-pull type, a half-bridge circuit with a pair of capacitors and a switching element in a bridge configuration, or a circuit with switching elements in a bridge configuration. Therefore, it will be omitted.

FIG. 5 shows a center-tapped full-wave rectifier circuit configuration, in which nonlinear inductors 10a and 10b are connected to rectifying diodes 5a and 5b, respectively. These nonlinear inductors loa and 10b also have a period of parasitic oscillation between their junction capacitance and resonance inductance that is considerably larger than the switching period during the non-conducting period of each rectifier diode 5a and 5b, as in the above embodiment. Give an inductance of such value.

Figure 6 shows four rectifier diodes 5a, 5b,
5 c.

An example is shown in which nonlinear inductors 10 a , 10 b , 10 c , and 10 d are connected in series to rectifying diodes 5 a , 5 b , 5 c , and 5 d in a circuit in which 5 d is configured as a bridge. These nonlinear inductors 10a
, 10b, 10c, and 10d also perform the same function as in the above embodiment.

Next, in FIG. 7, two rectifier diodes 5a, 5b and two capacitors are connected to the secondary winding N2 of the transformer 3.
, C2 are connected to form a voltage doubler rectifier circuit configuration.

These nonlinear inductors IOa' and 10b also perform the same functions as in the previous embodiment, so their explanation will be omitted.

In addition, in two or more embodiments, the resonance inductance is mainly explained as the leakage inductance of the transformer and the wiring inductance, but a resonance inductor may be separately provided in the two circuits.

〔Effect of the invention〕

As described above, according to the present invention, during the period when the junction capacitance of the rectifier diode contributes to parasitic vibration, that is, during the non-conducting period of the rectifier diode, the inductance in the non-saturation region of the nonlinear inductor and the primary side and secondary side Either the inductance, which is the sum of the inductance of the resonant inductor on the side, and the junction capacitance of the rectifying diode are used to oscillate, or the non-saturation region of the nonlinear inductor is adjusted so that the oscillation period is approximately the same as the maximum conduction width of the switching element. Since the inductance is selected, the vibration operates as a resonant circuit that makes the rectifier diode conductive and non-conductive at zero voltage, and has no adverse effect on output control. Furthermore, since the nonlinear inductor is magnetically saturated when the rectifying diode is turned on, its inductance does not substantially affect the output characteristics.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of a resonant converter according to the present invention, Fig. 2 is a diagram showing voltage and current waveforms at various parts to explain an embodiment of the present invention, and Fig. 3 is a diagram showing an embodiment of the resonant converter according to the present invention. FIG. 4 is a diagram showing a preferred configuration and magnetic characteristics of a nonlinear inductor used in one embodiment of the present invention, and FIG. 4 is a diagram for explaining two other embodiments of the present invention. 5 to 7 are diagrams for explaining other embodiments of the present invention, FIG. 8 is a diagram showing a conventional resonant converter, and FIG. 9 is a diagram illustrating the voltages at various parts for explaining the conventional example. FIG. 3 is a diagram showing a current waveform. l - switching element; 2 - DC input power supply; 3 - transformer, 4 resonant capacitor. 5- rectifier diode, 7- load. 9.9″ - Resonance inductance. 10 – Nonlinear inductor, 11 – Control circuit. Patent applicant Origin Electric Co., Ltd. q; o. (A) t′ [Ito”

Claims (4)

[Claims] (1) A switching element whose conduction time is controlled by a control signal from a control circuit, a primary winding connected in series with the switching element and an input power supply, and a secondary winding connected to a load through a rectifier diode. A resonant converter comprising: a transformer having a transformer; a resonant inductance; and a resonant capacitor providing a resonant capacitance that resonates with the resonant inductance, the resonant converter switching the switching element with no applied voltage; Resonance characterized in that a nonlinear inductor that provides an inductance larger than the resonance inductance in a small current region is connected in series with the rectifying diode, and the rectifying diode is rendered conductive or non-conductive with zero applied voltage. shape converter. (2) The resonant converter according to claim (1), wherein the nonlinear inductor is a saturable inductor. (3) The resonant converter according to claim (1), wherein the nonlinear inductor comprises a saturable inductor and a linear inductor connected in parallel to the saturable inductor. (4) The resonant converter according to claim (1), wherein a DC bias is applied to the nonlinear inductor.