JPH06121528A - Resonance dc-dc converter - Google Patents

Abstract

PURPOSE:To protect a transistor against breakdown due to a current, higher than a rated value, flowing through a switching element at the time of starting. CONSTITUTION:The resonance DC-DC converter comprises a resonance circuit for stepping the voltage up and down, a circuit for smoothing the voltage being stepped up or down through the resoance circuit, and a differential amplifier 22 producing the differential voltage between the smoothed voltage and a target voltage. The converter further comprises a VFO 23 for generating a frequency pulse corresponding to the voltage from the differential amplifier 22 and turning a transistor SW1 ON/OFF, and a limiter circuit 1 inserted between the differential amplifier 22 and the VFO 23 and lowering the output voltage from the differential amplifier 22 at the time of starting. Since the limiter circuit 1 limits output voltage from the differential amplifier 22 at a low level, the VFO 23 generates low frequency pulses based on the voltage thus limited and turns the transistor ON/OFF.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonance type DC-DC converter.

[0002]

2. Description of the Related Art Conventionally, there is a resonance type DC-DC converter of this type, for example, as shown in FIG.
This DC-DC converter is a current resonance type, and includes a DC power source E, a transistor SW1 as a switching element,
The non-return diode D, the resonance induction coil LR, the smoothing coil LF, and the output terminal 21 are connected in series.
The other end of the resonance capacitor CR whose one end is grounded is connected between the resonance induction coil LR and the smoothing coil LF. In addition, the smoothing coil LF and the output terminal 2
The other end of the smoothing capacitor CF, whose one end is grounded, is connected to the other end.

A DC power source E and a transistor SW
1. A resonance circuit is composed of the non-return diode D, the resonance induction coil LR, and the resonance capacitor CR.
Further, a smoothing circuit is constituted by the smoothing coil LF and the smoothing capacitor CF.

The output terminal 21 and the resonance capacitor CR
One end of a resistor R1 is connected between and. Resistance R1
The other end of is connected to the inverting input terminal of the operational amplifier A. The non-inverting input terminal of the operational amplifier A is connected to the DC power supply Vref. The voltage value of the DC power supply Vref is output from the output terminal 21, and is equal to the target voltage value. Further, one end of the resistor R2 is connected between the resistor R1 and the inverting input terminal of the operational amplifier A. The other end of the resistor R2 is connected to the output terminal of the operational amplifier A. The resistors R1 and R2 and the operational amplifier A constitute a differential amplifier 22 as output means.

The output side of the operational amplifier A is connected to a variable frequency oscillator (hereinafter referred to as VFO) 23 as a control means. The base of the transistor SW1 is connected to the VFO 23, and the transistor SW1
1 is turned on / off based on the frequency pulse generated from the VFO 23. In addition, V
The frequency pulse generated by the FO 23 is output based on the output voltage from the operational amplifier A.

[0006] The conventional DC-D constructed as described above.
In the C converter, the transistor SW1 is turned on.
The power supply voltage is converted into a pulse voltage by the off operation. At this time, the transistor SW1 includes the resonance induction coil LR and the resonance capacitor C of the resonance circuit during the ON operation.
R causes a sinusoidal current to flow. Therefore, the on / off operation of the transistor SW1 is zero current switching. Then, by this on / off operation, the power supply voltage is stepped down by the resonance circuit and is intermittently input to the smoothing circuit. The reduced voltage is smoothed by the smoothing capacitor CF and output to the output terminal 21 and the operational amplifier A.

The operational amplifier A outputs a voltage corresponding to the difference between the output voltage and the target voltage to the VFO 23. VFO
23 outputs a high frequency pulse when the difference between the output voltage and the target voltage is large relative to the voltage, and outputs a low frequency pulse when the difference is small to turn on / off the transistor SW1. Therefore, the VFO 23 changes the timing of the on / off operation of the transistor SW1, and the output voltage is always maintained at the target voltage.

Therefore, especially when the switching power supply is started up, the output voltage is 0 V, so that the VFO 23 turns on / off the transistor SW1 with the maximum frequency pulse.

[0009]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the C-DC converter, when the transistor SW1 is turned on / off with a maximum frequency pulse when the power supply is activated, a current higher than the rated current may flow through the transistor SW1 and destroy the transistor SW1.

That is, at startup, the current flowing through the transistor SW1 is the current I flowing through the smoothing coil LF.
It is equal to LF and the output voltage is equal to the voltage VCF of the smoothing capacitor CF. Therefore, if the smoothing capacitor CF has a large capacitance, the transistor S
When W1 is turned on / off, the current ILF becomes a value not less than the rated current of the transistor SW1 before the voltage VCF reaches the target voltage. Therefore, the current ILF destroys the transistor SW1.

This operation will be described with reference to the time chart of FIG. 4. For example, at timing t1, VFO2
The transistor SW1 is turned on by 3. By this ON operation, the voltage VCR of the resonance capacitor CR begins to rise gradually in a sinusoidal manner. Along with this, the smoothing coil LF
Current ILF and voltage VCR of resonance capacitor CR
Gradually begins to rise. Then, at the timing t2 when the current (not shown) flowing through the transistor SW1 becomes “0”, the transistor SW1 is turned off.

By this off operation, the resonance capacitor CR
The voltage VCR of the voltage starts to gradually decrease in a sinusoidal manner. With the change of this voltage VCR, the current ILF of the smoothing coil LF
Reaches a peak value and then gradually begins to fall.

Then, before the current ILF becomes "0", the transistor SW1 is turned on again at the timing t3 by the next high frequency pulse of the VFO 23. Then, the current ILF starts rising again without completely becoming "0" within the off period. With this rise, the voltage VCF
Also rises. When it is turned off at the timing t4, the current ILF starts to gradually decrease after reaching the peak value. The peak value of the current ILF at this time is larger than the previous peak value.

Subsequently, similarly, the transistor SW1 is turned on / off at timings t5 and t6, and turned on / off at timings t7 and t8. Then, the current ILF continuously rises and the transistor SW
The rated value of 1 will be exceeded. At this time, the transistor SW1 is destroyed by the current ILF exceeding the rated value before the voltage VCR reaches the target voltage.

An object of the present invention is to provide a resonance type DC-DC converter capable of preventing a current exceeding a rated value from flowing through a switching element and damaging the element at startup.

[0016]

In order to solve the above problems, the present invention comprises a direct current power supply, a switching element, an induction coil, a resonance capacitor, etc., and based on the on / off operation of the switching element, A resonance circuit for boosting / decreasing the voltage generated between the terminals of the capacitor, a smoothing coil, a smoothing capacitor, etc., and a smoothing circuit for smoothing the voltage boosted / decreased by the resonance circuit; Output means for outputting the difference between the desired voltage and the target voltage as a voltage, and drive means for turning on / off the switching element by generating a frequency pulse relative to the voltage output by the output means. In a resonance type DC-DC converter including: a voltage output from the output means between the output means and the driving means at the time of starting. And gist in that a limiting means for made.

[0017]

By virtue of the above-mentioned configuration, in the present invention, no voltage is applied to the smoothing capacitor of the smoothing circuit at the time of start-up, and it is "0". In this state, the voltage output from the output means has a high value. The limiting means drops the voltage to limit it to a low value. Then, the drive means generates a low frequency pulse based on the limited voltage value to control the switching element to be turned on and off.

Then, the voltage is stepped up / down between the resonance capacitor terminals of the resonance circuit based on the ON operation of the switching element. Along with this step-up / down, the current of the smoothing coil increases and the voltage of the smoothing capacitor also increases. Then, the voltage of the resonance capacitor drops based on the OFF operation of the switching element. Along with this drop, the current of the smoothing coil drops and becomes “0” within the off period. Therefore, the current of the smoothing coil does not exceed the rated value of the current flowing through the switching element. As a result, it is possible to prevent the switching element from being damaged by the flow of a current exceeding the rated value.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is embodied in a current resonance type DC-DC converter will be described below with reference to FIGS.

The same components as those of the prior art are designated by the same reference numerals and the description thereof will be omitted. As shown in FIG. 1, in this embodiment, a resistor R3 is connected in series between the operational amplifier A and the VFO 23. Further, one end of the resistor R4 is connected between the resistor R3 and the VFO 23. The other end of the resistor R4 is connected to the other end of the switch SW2 whose one end is grounded. In this embodiment, the resistors R3 and R4 and the switch SW2 constitute a limiter circuit 1 as a limiting means.

When the switch SW2 is turned on, the limiter circuit 1 divides the voltage output from the operational amplifier A by the resistors R3 and R4 and outputs it to the VFO 23. Therefore, a voltage suppressed to a value lower than that of the limiter circuit 1 is input to the VFO 23. Therefore, the VFO 23 outputs a low-frequency pulse by the amount that the voltage is suppressed to a low value, and turns on / off the transistor SW1. That is,
The transistor SW1 is turned on and off with a low frequency pulse because the current ILF is "0" every time at startup.
This is to secure a sufficient off period to become. Then, in order to secure the OFF period, that is, in order to output the low-frequency pulse from the VFO 23, the limiter circuit 1 applies the limiting voltage input to the VFO 23 to the voltage dividing resistor R3.
It is preset in R4.

The switch SW2 is also connected to the timer circuit 2 which also constitutes a limiting means.
The timer circuit 2 is on / off controlled by the timer circuit 2.

The timer circuit 2 turns on the switch SW2 on the basis of a start signal output from a control circuit (not shown), and at the same time, starts the start time (t) of the converter.
0), the counting operation is started, and the preset t1
Time goes up when it reaches 1 hour. During this t11 time, the limiter circuit 1 applies a low frequency pulse to the transistor SW.
It is the time required for the voltage VCF to reach the target voltage sufficiently by turning ON / OFF 1 and is a value obtained in advance experimentally or experimentally. When the timer circuit 2 counts up, the counting operation is stopped and the switch SW2 is turned off at the same time.

Next, the operation of this embodiment will be described with reference to FIG.
Follow the instructions below. Initially, no voltage is applied to the smoothing capacitor CF and the voltage VCF is "0".

First, at the timing t0 at the time of start-up, the timer circuit 2 turns on (closes) the switch SW2 and starts the counting operation. At this time, the operational amplifier A outputs a voltage having a large value corresponding to the difference between the output voltage “0” and the target voltage to the VFO 23. At this time, since the switch SW2 is closed, a voltage drop occurs in the limiter circuit 1, and a voltage lower than the voltage from the operational amplifier A (voltage divided by the resistors R3 and R4) is output to the VFO 23. . Then, the VFO 23 outputs a low frequency pulse at timing t1 by the voltage suppressed to this low value to turn on the transistor SW1.

By this ON operation, the resonance capacitor CR
The voltage VCR of the voltage gradually increases in a sinusoidal manner. Along with this, the current ILF of the smoothing coil LF and the voltage VCR of the resonance capacitor CR begin to gradually rise. And
At timing t2 when the current (not shown) flowing through the transistor SW1 becomes “0”, the transistor SW1 is turned off.

By this off operation, the resonance capacitor CR
The voltage VCR of the voltage starts to gradually decrease in a sinusoidal manner. With the change of this voltage VCR, the current ILF of the smoothing coil LF
Reaches a peak value and then gradually begins to fall and becomes “0” in the off period. This is because the VFO 23 outputs a low-frequency pulse, so that the off period of the transistor SW1 becomes long. At this time, the smoothing capacitor CF
The voltage VCF of V is maintained at a constant value.

Next, the transistor SW1 is turned on at the timing t.
At 3, the switch is turned on again. Then, since the current ILF is completely "0" in the off period, it starts to rise from "0" again. With this rise, the voltage VCF
Also rises from the aforementioned constant value. Then, the timing t
When the off operation is performed at 4, the current ILF starts to gradually decrease after reaching the peak value and becomes “0” within the off period.

Similarly, the transistor SW1 is turned on / off at timings t5 and t6, and turned on / off at timings t7 and t8. Further, the on / off operation is performed at the timings t9 and t10. Then, each time the transistor SW1 is turned off, the current ILF becomes "0" within the off period. Therefore, the current ILF continuously rises and the transistor SW
The current flowing through 1 does not exceed the rated value. The voltage VCF rises and reaches the target voltage after the timing t10.

Eventually, the timer circuit 2 counts up at the timing t11. Based on this count-up, the timer circuit 2 stops the counting operation and turns off (opens) the switch SW2. At this time, since the voltage VCF has reached the target voltage, the operational amplifier A is not operated and the output of the frequency pulse from the VFO 23 is stopped. Therefore, the voltage VCF is maintained at the target voltage when the load is not driven. After that, the voltage VCF
, The output voltage of the operational amplifier A is output to the VFO 23 as it is based on the fluctuation, and the normal voltage control for the fluctuation of the voltage VCF is performed.

As described above, in this embodiment, the limiter circuit 1 is provided between the operational amplifier A and the VFO 23 so that the switch SW2 is closed at the time of startup. Therefore, the transistor SW1 is turned on / off by the low-frequency pulse output from the VFO 23. Therefore, unlike the conventional case, the off operation period becomes longer and the smoothing coil LF
Current ILF becomes "0" within that period. As a result,
The current ILF does not exceed the rated value of the current flowing through the transistor SW1, and it is possible to prevent the transistor SW1 from being damaged.

Further, since the limiter circuit 1 is composed of the resistors R3 and R4 and the switch SW2, it is possible to prevent the transistor SW1 from being damaged with a simple structure.

Further, since the current ILF is kept low at the time of startup, the transistor SW1 having a small load capacitance and a low cost can be used. Further, it is possible to reduce the size and cost of the resonance induction coil LR.

The present invention is not limited to the above-mentioned embodiments, but may be carried out as follows without departing from the spirit of the present invention. (1) In the above embodiment, the current resonance type DC-DC converter is embodied, but the voltage resonance type DC-DC converter may be embodied. (2) In the above embodiment, the switch SW2 is turned on / off at the timing set by the timer circuit 2, but a latch circuit is provided instead of the timer circuit 2 to turn on / off the switch SW2. You may do it. In this case, the latch circuit is connected to the output side of the operational amplifier A. Therefore, when the operational amplifier A outputs a large voltage corresponding to the difference between the output voltage "0" and the target voltage at startup, "1" is stored and the switch SW2 is turned on. Further, when the operational amplifier A outputs the voltage “0” due to the output voltage reaching the target voltage, “0” is stored and the switch SW2 is turned off. (3) The transistor SW1 as the switching element in the above embodiment may be an element such as a bipolar transistor or a static induction transistor. (4) Switch S of the limiter circuit 1 in the above embodiment
W2 is not particularly limited, and a semiconductor switching element such as a relay, a transistor and a thyristor may be used. (5) In the above embodiment, the resonance induction coil L of the resonance circuit.
Although R and the smoothing coil LF of the smoothing circuit are connected in series, a transformer may be provided between the resonance induction coil LR and the smoothing coil LF.

[0035]

As described above in detail, the resonance type DC of the present invention.
The -DC converter has an excellent effect that it is possible to prevent the damage of the switching element due to the flow of the current of the rated value or more at the time of startup.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a current resonance type DC-DC converter in an embodiment embodying the present embodiment.

FIG. 2 is a timing chart showing the operation of the current resonance type DC-DC converter in one embodiment.

FIG. 3 is an electric circuit diagram showing a current resonance type DC-DC converter in a conventional example.

FIG. 4 is a timing chart showing an operation of a current resonance type DC-DC converter in a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Limiter circuit as limiting means, 2 ... Timer circuit as limiting means, 22 ... Differential amplifier as output means,
23 ... VFO as drive means, E ... DC power supply, SW1
... Transistor as switching element, LR ... Resonance induction coil, CR ... Resonance capacitor, LF ... Smoothing coil, CF ... Smoothing capacitor

Claims (1)

[Claims] 1. A resonance circuit, which comprises a DC power supply, a switching element, an induction coil, a resonance capacitor, and the like, and which boosts / decreases the voltage generated between the terminals of the capacitor based on the on / off operation of the switching element, A smoothing circuit configured by a smoothing coil, a smoothing capacitor, and the like, for smoothing the voltage stepped up and down by the resonance circuit, and outputting the difference between the voltage smoothed by the smoothing circuit and the target voltage as a voltage. A resonance type DC-DC converter comprising: an output means; and a drive means for generating a frequency pulse corresponding to a voltage output by the output means to turn on / off the switching element, the output means and the drive means And a limiting means for lowering the voltage output by the output means at the time of startup, a resonance type DC-DC converter. Data.