JPH0787736A - Series resonance converter - Google Patents

Abstract

PURPOSE:To prevent the operation frequency of a series resonance converter from changing greatly while reducing its switching loss even when its output frequency has lowered. CONSTITUTION:A series resonance converter is provided with a current transformer 41 in a resonance current route. The secondary side of the current transformer is connected to input terminals 3, 5 through a rectifier circuit 43, auxiliary switching element FET 45, and diode 47. When the output voltage is normal, the auxiliary switching element FET 45 is turned on to perform ordinary operation. When the output voltage lowers and the resonance current I has a longer trailing, the auxiliary switching element FET 45 is turned off to feed back part of the energy of the resonance current I to an input DC power supply 1, to reduce the current to zero quickly, thereby softly turning off the main switching elements IGBT 17 and 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a series resonant converter capable of constant voltage control without largely changing the operating frequency.

[0002]

2. Description of the Related Art A series resonance converter is composed of a series resonance circuit of an inductor and a capacitor and a semiconductor switching element. The switching element detects a time when a resonance current crosses zero and turns off at that time, so that a switching loss occurs. Also, it has a feature that the unnecessary radiation electromagnetic waves are significantly reduced.

An example of a conventional capacitor voltage clamp type series resonance converter is shown in FIG. Explaining according to this figure, the main circuit has capacitors 7 and 9 connected in series, and switching elements IGBT17 and 19 are connected in series to form a so-called half bridge circuit. The inductor 15, the primary winding of the current transformer 39, and the primary winding of the transformer 25 are connected in series at the midpoint of each arm of the. From the secondary side of the transformer 25, diodes 27 and 29 and a smoothing capacitor 31
A DC output is generated between the output terminals 33 and 35 via.

Regarding the ON signal of each switching element, the ON signal is generated in the control circuit 37 so that the voltage between the output terminals 33 and 35 is detected and a constant voltage output is obtained. Regarding the OFF signal, the current of the resonance circuit is detected by the current transformer 39 and sent to the control circuit 37, and the OFF signal is generated at the time when the detected value crosses zero. That is, the repetition frequency is controlled to control the time from off to next on.

[0005]

However, in such a conventional capacitor voltage clamp type series resonant converter, the output voltage is lowered, and as a result, the main transformer is used.
When the voltage of 25 drops, the power required for output is also small, so part of the resonance current becomes excess energy, and when the main switching element IGBT17 is on, IGBT17⇒transformer25⇒inductor15. ⇒Diode 11 ⇒IG
It will continue to flow in the loop of BT17, and it will take a considerable time to reach zero. As a result, the operating frequency may decrease, noise may be generated, and control may become difficult. For this reason, it was necessary to forcibly turn off the IGBT17, which is the main switching element, even if the current did not reach zero. However, when forced turn-off is performed, there is a problem that the loss of the main switching element, the required breakdown voltage, and the generated unwanted electromagnetic radiation increase.

It is an object of the present invention to obtain a circuit capable of softly turning off the main switching element in a series resonance converter even at a low output voltage without largely changing the operating frequency.

[0007]

In order to solve this problem, the present invention provides a capacitor voltage clamp type series resonance converter in which a current transformer is inserted at the current passing point of the resonance current and when the output voltage drops. It is proposed that a part of the resonance current is fed back to the input power source side through this current transformer.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A series resonance converter according to the present invention will be described with reference to FIG. In this converter, the DC power supply 1 is connected between the input terminals 3 and 5, and the conversion output is the output terminals 33 and 35.
It occurs between and. On the primary side, a clamping diode 11 is connected in parallel to the capacitor 7, a clamping diode 13 is connected in parallel to the capacitor 9, and these capacitors 7 and 9 are connected in series to input terminals 3, 5 Connected in between. Further, IGBTs 17 and 19 which are main switching elements of this converter are connected in series, and both ends thereof are connected between input terminals 3 and 5. Between the interconnection point of these IGBTs 17 and 19 and the interconnection point of capacitors 7 and 9, a primary winding 25a of a transformer 25 and a current transformer
The primary winding of 39, the inductor 15, and the primary winding of the current transformer 41 are connected in series. From the secondary windings 25b and 25c of the transformer 25, through the center tap double-wave rectification circuit by the diodes 27 and 29, respectively, and then through the smoothing capacitor 31,
Connected to output terminals 33 and 35.

The secondary winding of the current transformer 41 is a bridge type rectifier circuit.
It is connected to the AC side terminal of 43. This bridge type rectifier circuit
Regarding the DC side terminal of 43, the positive side is connected to the drain electrode of FET45, which is an auxiliary switching element, and is also connected to the input terminal 3 via the diode 47, and the negative side is connected to the source electrode of FET45 and the input terminal. Connected to 5.

The main switching elements IGBT17 and IGBT19 are driven on / off at high frequencies by drive circuits 21 and 23, respectively.
The drive circuits 21 and 23 are controlled by the signal from the control circuit 37. In order to stabilize the output voltage, the detection voltage between the output terminals 33 and 35 is sent to the control circuit 37 to generate a signal that determines the ON timing of the main switching elements IGBT17 and IGBT19. In addition, the current detection signal obtained from the secondary winding of the current transformer 39 is connected to the control circuit 37 to generate a signal that determines the OFF timing of the IGBT17 and the IGBT19 of the main switching elements. The control circuit 37 also supplies an ON / OFF signal to the FET 45 of the auxiliary switching element.

[0011]

[Description of Operation when Output Voltage is Normal] When the output voltage is normal, that is, when the detected voltage is higher than the set value, the signal generated from the control circuit 37 turns on the FET 45 of the auxiliary switching element. When the FET45 is on and the turns ratio of the primary and secondary of the current transformer 41 is 1: n, 1 / n of the main resonance current flows through the drain and source of the FET45 on the secondary side of the current transformer 41. . Since the secondary side of the current transformer 41 is short-circuited and the energy consumed here is extremely small, it has almost no effect on the operation of the resonant circuit. As shown in FIG. 2, the waveform at this time proceeds in a half period of the natural period of the resonant circuit with a rest period interposed.

[0012]

[Explanation of operation when output voltage is low] In the deep drooping region and low output voltage, the energy consumption of the resonant circuit is small, so the tailing of the current I of the IGBT17 (or 19, the same applies hereinafter) of the main switching element becomes long ( See Figure 3a). When the tail of this current I becomes longer and does not become zero even after a certain time τ1 from when the IGBT 17 is turned on, the FET 45 of the auxiliary switching element is turned off at time t1. By doing this, the secondary current of the current transformer 41 changes from the current transformer 41 to the rectifier 43 to the diode.
47 ⇒ DC power supply 1 ⇒ Rectifier 43 ⇒ Current transformer 41 and energy is returned to the input side DC power supply 1. In addition, since the FET 45 is turned off, the secondary side of the current transformer 41 is connected to the rectifier circuit 43.
The voltage of the DC power supply 1 on the input side is fixed via the diode 47. Therefore, the feedback power from the primary side to the secondary side of the current transformer 41 is Ei × I / n (where Ei is the voltage of the DC power supply 1, I is the current of the main transformer 25, and n is the number of turns of the current transformer 41). Ratio), and the current I of the IGBT 17 rapidly decreases to zero at time t2. (This effect is understood by comparison with the case where the conventional tailing of the waveform shown by the broken line in FIG. 3a is long.) Current transformer 39
Then, it is confirmed that the current of the main switching element has become zero (in this case, τ2 hours after the turning on of the FET 45), the main switching element 17 is turned off. Then, between the times t2 and t3, the FET 45 of the auxiliary switching element is turned on again. Here, the value of the period (τ1 + τ2) needs to be selected within a range of values shorter than the lower limit cycle of the audible frequency. As mentioned above,
The current can be turned off softer than forcibly turning off the main switching element.

[0013]

The present invention has the features described above,
Since the surplus energy of the resonant circuit is fed back to the input power source through the current transformer, the current of the main switching element can be softened to zero, and the loss of the switching element, breakdown voltage, and unnecessary radiated electromagnetic waves when turned off can be reduced. The effect is obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a series resonance converter according to the present invention.

FIG. 2 shows operation waveforms of the series resonant converter shown in FIG. 1, showing waveforms of various parts when the output voltage is normal.

FIG. 3 shows operation waveforms of the series resonant converter shown in FIG. 1, showing waveforms of respective portions when the output voltage is low.

FIG. 4 shows an example of a conventional series resonant converter.

[Explanation of symbols]

1 ... DC power supply 3, 5 ... Input terminal 7, 9 ... Capacitor 11, 13 ... Diode 15 ... Inductor 17, 19 ... IG
BT 21, 23 ... Driving circuit 25 ... Transformer 27 29 ... Diode 31 ... Capacitor 33 35 ... Output terminal 37 ... Control circuit 39 ... Current transformer 41 ... Current transformer 43 ... Diode 45 ... FET
47 ... Diode

Front page continuation (72) Inventor Katsuhiko Yamamoto 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Koichi Tanaka 1-1-6 Uchiyuki-cho, Chiyoda-ku, Tokyo Nihon Telegraph Phone Co., Ltd.

Claims (3)

[Claims] 1. A capacitor voltage clamp type series resonance converter in which a diode is connected in parallel to both ends of a resonance capacitor to prevent the voltage of the capacitor from being in the opposite direction, and a current transformer is inserted at a current passing point of the resonance current. , A series resonance converter characterized in that when the voltage of the main transformer drops, a part of the resonance current is fed back to the input power source side through the current transformer. 2. A pair of input terminals; a bridge circuit having both ends connected to the pair of input terminals, wherein a first capacitor, a first diode connected in parallel therewith, and a second capacitor.
Bridge circuit composed of an arm in which a second capacitor connected in series with a second capacitor connected in parallel with the above capacitor, and an arm in which a first switching element and a second switching element are connected in series; In a series resonant converter that consists of an inductor connected between the midpoints of the arms of the, and obtains output from the resonant current flowing through the inductor: A current transformer is provided in the path of the resonant current, and A series resonance converter comprising a feedback circuit connected to the input terminal of the. 3. The series resonance converter according to claim 2, wherein the feedback circuit is operated when the conduction period of each cycle of the resonance current exceeds a set value τ1.