JPH04161064A - Resonant dc-dc converter - Google Patents

Abstract

PURPOSE:To feed a power component, based on an overvoltage occurring in a switch, effectively back to the input or output side of a circuit by providing a circuit for inducing a power upon occurrence of an overvoltage in the switch and a circuit for feeding back the induced power. CONSTITUTION:Immediately after switching of a switch SW from an operating interval to a halt interval, energy stored in a coil L1 or a capacitor C4 in a resonance circuit or the energy stored in a coil, i.e., a winding Tn1, appears at the switch SW to produce an overvoltage VOVF. When the level of the overvoltage VOVF exceeds 4Vin (input voltage), a diode D7 is biased forward to feed the energy, absorbed through a transformer T2, back to the input side. In other words, the winding Tn1, which had been functioning as a choke coil, functions as the primary winding of the transformer T2 at that time.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for controlling the output of a conversion circuit by opening and closing the switch according to the input pulse train while providing a rest interval to the input pulse train led to the switch. , a resonant type D in which a current from a DC power source input through a choke coil is supplied to the conversion circuit to obtain a conversion output.
This invention relates to a C-DC converter, and is particularly designed to effectively prevent overvoltage from occurring at a switch.

[Conventional technology]

rcla+s E resonant Regulat
ed DC/DCPower ConveNers:A
nalysi+ Of Op! ra+ion+, and
Experimental Re5uHs a41.
5MH! J IEEE TRANSACTIONS
N POWERELECTRONIC5, VOL, P
E-1, No, 2. APRIL 1986, and U
SP No. 4.607.323 describes a resonant DC-D that controls the conversion output by changing the switching frequency of the switch.
C converter is described.

In addition, “Characteristics analysis of DC-DC converter using E-class resonant switch” (“IEICE Technical Research Report J
PE9D-22, VOl, 90 No174. Miko Institute of Information and Communication Engineers, published August 20, 1990) describes the basic configuration of a resonant DC-DC converter and the operation of the converter.

Furthermore, r6.4 Improving efficiency by improving the snubber circuit” ([Switching Regulator Design Know-how JP
175.176 published by CQ Publishing Co., Ltd., April 10, 1985) describes a snubber circuit that returns the absorbed power to the input power source, as shown in FIG. This circuit has a transformer T whose main winding N and feedback winding N2
are tightly coupled so that the terminal voltage of the winding N2 is proportional to the voltage of the winding N2, and the emitter-collector voltage Vc, which shows a rapid voltage rise every time the switching transistor Q is turned off, is such that Vc < 2 V. i N 1 /
When N2 is reached, diode D is made conductive and the above V
Clamping is performed so that c is less than the above 2ViN/N2.

[Problem to be solved by the invention]

The resonant DC-DC converter described in the above US patent publication describes the control of the conversion output by changing the switching frequency of the switch. There is no description of the provision of a rest period in the pulse train and the countermeasures against overvoltage that occurs at the start of the rest period.

In addition, the resonant DC described in the technical research report of the Institute of Electronics, Information and Communication Engineers
-For the DC converter, there is only a detailed explanation of the circuit operation, but there is no mention of the fact that the pulse train has a rest period as described above, and the countermeasures against overvoltage that occurs in the switch at the start of the rest period. do not have.

Furthermore, the snubber circuit shown in FIG. 4 is designed so that the diode D is forward biased with a high collector voltage that occurs every time the switching transistor Q is turned off, that is, during normal operation of the switching circuit.
The transformer T acts as a transformer in steady state, and the power returned to the input power supply side is the energy stored in the leakage inductance of the winding N1.

The present invention has been made in view of the above, and provides a rest period to the pulse train guided to the switch to control the conversion output, while supplying current from the DC power source to the conversion circuit via the choke coil, and converts the conversion output. The object of the present invention is to provide a resonant DC-DC converter that effectively feeds back electric power due to overvoltage generated in a switch immediately after a pulse train pauses, etc. to the input side or output side of the circuit. .

[Means to solve the problem]

The present invention has a conversion circuit in which a DC power source is connected to a series circuit consisting of a choke coil and a capacitor, a switch is connected in parallel to the capacitor, and a series circuit consisting of a resonant circuit and a load is connected in parallel, In order to control the output of the conversion circuit, the switch is opened and closed by the input pulse train while providing a rest period to the input pulse train led to the switch, thereby reducing the current from the DC power supply input through the choke coil. In the resonant DC-DC converter, which is supplied to the conversion circuit to obtain a conversion output, a winding transformer-coupled to the choke coil is configured to induce power by the overvoltage when an overvoltage occurs in the switch. a power induction circuit having;
and a power feedback circuit that feeds back the induced power to the input side or output side of the conversion circuit.

[Effect]

According to the present invention, the resonant DC-DC converter is operated by the pulse train supplied to the switch, and during this operating section, the power induction circuit having the winding transformer-coupled to the choke coil is not driven. , so no current is flowing.

This pulse train is given a rest period according to the output of the conversion circuit, and the output is controlled according to the relationship between the rest period and the operation period. Immediately after transitioning from the operating period to the rest period, the energy stored in the choke coil and the resonant circuit appears in the switch as an overvoltage.

When such an overvoltage occurs, electric power is induced in the power induction circuit by the current that generates the overvoltage, and is fed back to the input side or output side of the conversion circuit.

〔Example〕

FIG. 1 is a block diagram showing an example of a resonant DC-DC converter according to the present invention.

From the commercial power supply E to the capacitor C2 constitutes a DC power supply forming means, and the AC input from the commercial power supply E is connected to the diode D via the noise prevention choke coil CH and the capacitor C.
The signal is guided through a diode bridge consisting of C1 to D4 for full-wave rectification, and further smoothed by a capacitor C2 to provide a DC power source.

Note that a rectifier circuit that performs half-wave rectification may be used instead of the diode bridge.

Reference numeral 1 denotes a so-called 5oka l type conversion circuit, which is composed of a transformer T2 to a capacitor C5 (excluding Tn2 as described later).

The winding Tnl functions as a choke coil that stably supplies current from the DC power supply.

In this embodiment, this winding Tn□ is configured as a primary winding of a transformer T2, and a secondary winding Tn2 is provided on its secondary side. Note that the dot attached to each winding indicates the polarity of the winding.

A series circuit consisting of this winding Tn2 and diode D7 is connected to a DC power source. The operation of this circuit portion will be described later.

A series circuit consisting of the coil L□ and the capacitor C4 constitutes a resonant circuit. The capacitor C3 is for changing the characteristic impedance (related to the resonant frequency) of the resonant circuit. SW is connected in parallel to the capacitor C3, and is connected to gate drive transistors Q1 to Q, which will be described later.
This is a switch consisting of a power MO8h transistor, etc., which is switched by inputting an opening/closing pulse train signal from 6 to gate G.

The transformer T1 connects the secondary coils Tn4 and Tn5 via the primary coil Tn3 by the opening/closing operation of the switch SW.
This induces a voltage in the Diode D5. D6 and capacitor C5 are connected to the secondary coil Tn4. Tn5
This is to full-wave rectify and smooth the induced voltage.

Note that R1 is a load resistance connected to the output side.

A determination circuit 2 determines whether the output current supplied to the load resistor R5 exceeds a predetermined level, and is comprised of an output current detection resistor RD for detecting the output current and an operational amplifier A5.

The circuit consisting of resistor R6 and capacitor C6 smoothes the detection output of output current detection resistor RD, and the series circuit consisting of coil L2 and capacitor C7 further smoothes the smoothed detection output.

The operational amplifier A5 has a reference voltage (Fig. 2, g1
The smoothed detection signal is input to the inverting input terminal (corresponding to the control target level 10). The output current of the determination circuit 2 is at the control target level i. It is designed to output a high level for the following periods and a low level for a period of i0 or more (FIG. 2, C).

3 is an oscillation circuit composed of operational amplifiers A□, A2, resistors Rs, Rt, and capacitor Ct, and the period of the output pulse from the oscillation circuit 3 (FIG. 2, b) is determined by the operation and rest of the conversion circuit 1. This determines the maximum switching frequency.

4 is a vibrator XL and a capacitor Cs at both ends thereof.

C9 is an oscillation circuit consisting of a resistor Rf connected in parallel to the vibrator XL, an operational amplifier A4, and an operational amplifier A3 for oscillation output, which operates the switch SW to open and close, for example, a pulse train (the pulse train) having a frequency of about IMHz or 2MHz. 2, a) is output.

DFFI and DFF2 are both D-flip-flops.
The judgment output of the judgment circuit 2 is connected to the D1 terminal of the FFI.
A pulse signal from the oscillation circuit 3 is led to the terminal, and judgment information regarding the output current is transmitted to the next stage every cycle of the pulse signal.

In addition, the D2 terminal of DFF2 is connected to the Q1 output of DFF1 (
In Fig. 2, d), the oscillation pulse of the oscillation circuit 4 (Fig. 2, a) is led to the CK2 terminal, and switching between supplying and stopping the opening/closing pulse is done in accordance with the rising timing of the oscillation pulse a. It is transmitted to the next stage. Furthermore, this DF
Fl, 2 is designed to operate at the timing when the input signal to the CK□, CK2 terminal changes from low to high.

6 is an AND circuit, which outputs Q2 of the DFF2 mentioned above (Fig. 2,
e) and the output a of the oscillation circuit 4 are guided.

5 is a gate drive circuit composed of an inverter Lup, operational amplifiers A6-88, and transistors Q1-Q6. The inverter Lup converts the voltage of the output of the AND circuit 6 from, for example, 5v to 15v, and the converted voltage signal is current amplified by operational amplifiers A6 to A8, and further power amplified by transistors Q1 to Q6. In this way,
The output pulse f of the AND circuit 6 is power amplified and guided to the gate of the switch SW as a switching pulse signal.

Here, the function of the winding Tn1 will be explained.

When the voltage level induced across the secondary winding Tn2 is lower than the input voltage Vin (the voltage between the terminals of the capacitor C2), the winding Tnl acts only as an inductance because the diode D7 is reverse biased and does not operate. act.

On the other hand, when the voltage level induced across the winding Tn2 exceeds the input voltage Vin, the diode D7 is forward biased and acts as a secondary winding, so the winding Tnl acts as the primary winding of the transformer T2. Therefore, electric power is induced in the secondary winding Tn2 by the current flowing into the secondary winding Tnl.

By the way, in order to obtain a suitable level as a conversion output, when the conversion circuit 1 is operated so that the non-conducting time of both the switch SW and a diode (not shown) in the switch is 140 degrees or more, both ends of the switch SW Being able to suppress the voltage generated within 4 Vin,
Further, in consideration of various situations, the maximum permissible value of the voltage applied to the switch SW is set to, for example, 4 Vin.

In this case, if 4Vin is generated in the switch SW, -3Vin (=Vin-4Vin) is generated in the winding Tn.
n) will occur. At this time, the winding T
If Vin (the direction of each winding is reversed) occurs in n2, the diode D7 is biased and turned on, so the winding T
Since n1 acts as the primary winding of transformer T2, and T2 acts as a transformer, the energy (power) that attempts to increase the voltage generated at switch SW to 4 Vin or more is transferred to the secondary winding by the function of transformer T2. Winding T
It will be fed back from n2 to the input side.

That is, in order to generate Vin in the winding Tn2 when -3 Vin occurs in the winding Tnl, the turns ratio of the winding Tn and Tn2 may be set to 3.

On the other hand, when the winding ratio is 3 and the voltage generated in the switch SW is 4 Vin or less, the voltage generated in the winding Tn2 is less than Vin and the diode D7 is reverse biased, so T2 does not function as a transformer. Therefore, the winding Tn works as an original choke coil interposed at the input part from the power supply.

Next, the operation will be explained for each period using the time chart shown in FIG.

(1) During normal operation up to the time tx, that is, when the output current to the load R2 is within a suitable range, the discrimination circuit 2 outputs a high level as shown in waveform C, and during this time the Q1 output of the DFFI d is maintained at a high level.

Therefore, even if the pulse train a from the oscillation circuit 4 is input to the CK2 terminal of the DFF2, the Q2 output is maintained at a high level as shown in the waveform e. Therefore, the AND circuit 6 passes the pulse train a from the oscillation circuit 4, and the passed pulse train f is guided to the gate drive circuit 5 where it is subjected to level change and amplification processing. As a result, the switch SW is opened and closed by the pulse train f to operate the conversion circuit 1, and the load R
Supply output current to L.

(Even if the output current to the load R1 increases during the Htl-t2 period and the 8-power C of the discriminator circuit 2 changes to the low level at the time t2, the Ql d of the DFFl remains unchanged until the pulse signal B1 of the next cycle is generated. Since the output is maintained in the same state as in (1) above, the switch SW
is switched by the pulse train f to operate the conversion circuit 1 and continue to supply the output current to the load R0.

(3) After the output C of the t2-t3 period determination circuit 2 changes to low level, when the next period pulse signal B1 is generated, the Q1 output of the DFFI is
As shown in waveform d, it changes from the H/r level to the low level. Due to this change in the Q1 output d of the DFFI, when the oscillation pulse A immediately after this is input, the Q2 output of the DFF2 changes to a low level as shown in the waveform e. Therefore, the pulse train a from the oscillation circuit 3 is cut off by the AND circuit 6, and the supply of the pulse train a to the switch SW is stopped as shown by the waveform f. Therefore, since the operation of the conversion circuit 1 is stopped, the supply of output current to the load RL is stopped. After this stop (rest period), only the accumulated current of the capacitor C5 is supplied, so the output current gradually decreases.

In the above, when the opening/closing operation of the switch SW is switched from the operating section to the rest section, immediately after that, the coil of the 2-resonant circuit □ acts as a coil and the energy stored in the capacitor C4 is transferred to the winding Tn. The stored energy appears in the switch SW, and the overvoltage VOVF (
FIG. 2, signal Vsw) is generated. And this overvoltage V. When the level of VF attempts to exceed the above-mentioned 4Vin, diode D7 becomes forward biased and returns the energy absorbed via transformer T2 to the input side.

That is, the winding Tnl, which had previously worked as a choke coil, now works as the primary winding of the transformer T2.

(4) When the output current decreases during the period from ta to t4 and the output C of the determination circuit 2 returns to high level again (at the time of ta), the Dl terminal of DFFL changes to high level, but the next cycle's pulse signal B2 The same state as in (3) above is maintained until the occurrence of the pulse train a, and the supply of the pulse train a to the switch SW is stopped as shown in the waveform f. Therefore, since the conversion circuit 1 is maintained in a stopped state, the supply of output current to the load RL remains stopped.

(5) From time t4 to next period pulse signal B2 is generated (immediately before time 14), D
When the Q□ output trace of FFl changes to high level, the Q2 output e of DFF2 is caused by the pulse A2 input immediately after this.
changes to a high level, and the switch SW starts opening/closing operations by the pulse train f. Therefore, the conversion circuit 1 is operated and output current is supplied to the load RL. Therefore, the output current gradually increases.

In this way, the conversion output of this resonant DC-DC converter is controlled such that n (<m) consecutive pulses are thinned out from the m pulse train output within a predetermined time. , by changing the average value of the number of pulses supplied to the switch SW within the predetermined time period and the number of pulses thinned out in accordance with fluctuations in the conversion output.

In the above embodiment, the absorbed power is fed back to the input side, but the power can also be fed back to the output side.

FIG. 3 is a circuit diagram for this purpose, and corresponds to the first part of the conversion circuit in FIG. In FIG. 3, the same numbers as those in FIG. 1 are assigned the same functions.

In the figure, the diode D7 is connected between the positive electrode side of the winding Tn2 and the connection point between the rectifier diodes D5+D6.

Now, when the load voltage set by the turns ratio etc. of the transformer T1 is VO, by setting the turns ratio N2 of the winding Tn□ and the winding Tn2 to V o / 3 V in, the switch SW When the voltage generated in the winding Tn is 4Vin, the voltage generated in the winding Tn□ is 3Vin, and furthermore, the voltage generated in the winding Tn
From the above relationship, the voltage generated at 2 is the same as the load voltage vo
becomes. Therefore, when an overvoltage of 4 Vin or more occurs in the switch SW, the diode D7 is forward biased,
The power absorbed via the transformer T2 is fed back to the output side.

That is, the winding Tn1 functions as a choke coil when the voltage is 4 Vin or less, and functions as the primary winding of the transformer T2 when the voltage reaches 4 Vin.

It should be noted that the overvoltage V may occur immediately after switching the opening/closing operation of the switch SW from the rest period to the operation period. V.

However, this overvoltage ■. The energy feedback described above may also be applied to vs.

〔Effect of the invention〕

As explained above, according to the present invention, there is provided a power induction circuit having a winding transformer-coupled to a choke coil so as to induce power by an overvoltage generated in a switch, and an input of the induced power to the conversion circuit. Since it is equipped with a power feedback circuit that returns the power to the side or the output side, the energy stored in choke coils and resonance circuits that appears immediately after transitioning from an operating section to a rest section is absorbed without causing a voltage exceeding a predetermined level to be generated in the switch. However, since the power induced in the power induction circuit is fed back to the input side or output side of the conversion circuit, protection of the switch and efficient use of power can be achieved.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a resonant DC-DC converter according to the present invention, Fig. 2 is a time chart explaining the invention in detail, and Fig. 3 is feedback of induced power generated by overvoltage to the output side. FIG. 4 is a partial circuit diagram showing another embodiment of the conventional snubber circuit. DESCRIPTION OF SYMBOLS 1... Conversion circuit, 2... Judgment circuit, 3, 4... Oscillation circuit, 5... Gate drive circuit, 6... AND circuit, DFFl, 2... D-flip-flop, E ...
Commercial power supply, RL...Load, D7...Diode, C
2... Smoothing capacitor, T, T2... Transformer, Tnl... Winding (choke coil), T n 2
"'Winding, Ll, C4... Coil and capacitor that constitute a resonant circuit, SW... Switch, RD... Output current detection resistor, Vin... Input voltage, vO... Load voltage. Patent Applicant Matsushita Electric Works Co., Ltd. Representative Patent attorney Etsushi Kotani Patent attorney Chief 1) Seido Patent attorney Takao Ito

Claims (1)

[Claims] 1. A conversion circuit in which a DC power source is connected to a series circuit consisting of a choke coil and a capacitor, a switch is connected in parallel to the capacitor, and a series circuit consisting of a resonant circuit and a load is connected in parallel, and the conversion The current from the DC power supply input via the choke coil is converted by opening and closing the switch according to the input pulse train while providing a rest period to the input pulse train led to the switch to control the output of the circuit. A resonant DC-DC converter that is supplied to a circuit to obtain a converted output, and has a winding transformer-coupled to the choke coil so as to induce power by the overvoltage when an overvoltage occurs in the switch. A resonant type D characterized by comprising an induction circuit and a power feedback circuit that feeds back the induced power to the input side or output side of the conversion circuit.
C-DC converter.