JPH09298872A - Resonance type dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain prevention of overcurrent and switching frequency lowering by a simple circuit formation by changing the time constant setting resistance component of a pulse generating circuit according to error voltage for controlling off-time of a switching element. SOLUTION: A pulse duration control circuit 14 includes an error detection circuit 15. When the error voltage between the output voltage divided by a potential divider 15 and reference voltage 15b is amplified by a differential amplifier 15C, and it is applied to the base of a transistor 16, the current corresponding to it flows through the collector of the transistor 16. Therefore, it is equivalent to an apparent change of the combined resistance consisting of a parallel circuit of a resistor 17 and a resistor 18, and a resistor 19 which is connected to the parallel circuit in series. By the combined resistance and a capacitor 23, the time constant of off-time of a pulse generating circuit 20 is determined. The off-time can be restricted so as to become extremely short in case of overcurrent and become extremely long in case of small load current, therefore, it is possible to attain prevention of overcurrent and switching frequency lowering by a simple circuit formation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention converts a direct current input into an alternating current by switching with a switch element,
Resonant DC-D that converts this AC output into DC and outputs it
It relates to a C converter.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing a configuration of a conventional resonance type DC-DC converter. In the figure, a ripple removing capacitor 2 is connected between the input terminal 1 to which the DC input voltage Vin is input and the ground, and further between the input terminal 1 and the output terminal 3 from which the output voltage Vout is output. The choke coil 4 and the rectifying diode 5 are connected in series.

A switch element 6 is connected between the connection point of the choke coil 4 and the rectifying diode 5 and the ground, and an output smoothing capacitor 7 is connected between the output stage of the rectifying diode 5 and the ground. Has been done.

Further, the differential amplifier 8 detects a variation of the DC output voltage, and the output voltage divided by the voltage divider 9 is input to one input terminal of the differential amplifier 8 to obtain a difference. The reference voltage 10 is input to the other input terminal of the dynamic amplifier 8.

The differential voltage detected by the differential amplifier 8 is supplied to the pulse width modulation circuit (PWM) 11, and the pulse signal whose pulse width is modulated according to the differential voltage of the differential amplifier 8 is supplied to the switch element 6. It By switching the switching element 6 with this pulse signal, the DC input is chopped and converted into AC, the AC output is converted into DC by the diode 5, smoothed by the capacitor 7, and the output voltage Vout is output.

The PWM control of the DC-DC converter configured as described above is a pulse width modulation method which is performed by fixing the switching cycle and controlling the on / off time ratio (duty ratio) of the switching element 6.

In this control circuit system, the voltage divider 9 in the feedback system is used.
The output voltage divided by is compared with the reference voltage 10 by the differential amplifier 8, and the pulse width modulation circuit 11 is controlled by the difference voltage,
When the output voltage is low, the on-time pulse width is widened, and when the output voltage is high, the on-time pulse width is narrowed.
The output voltage of the power supply is stabilized.

[0008]

However, in the case of duty ratio control, since the switching frequency is fixed, an overcurrent protection circuit that prevents the output voltage from rising at a small load current, and
An overcurrent protection circuit such as overload or output short circuit must be added, which is disadvantageous in terms of cost and mounting.

Further, in the current resonance type DC-DC converter, the resonance frequency is fixed in correspondence with the on-time.
Stabilization of the output voltage is frequency control that stabilizes the output voltage by making the off time variable.

According to the present invention, by making the off time of the switch element variable, overcurrent protection and switching frequency reduction prevention can be easily realized at a low cost with a simple circuit configuration, and the reliability and safety are high. Current resonance type DC-
An object is to provide a DC converter.

[0011]

According to the present invention, there is provided a switching element for chopping a direct current voltage at a predetermined frequency to convert it into an alternating current, and a rectifier for converting the converted alternating current to a direct current and smoothing it to generate a direct current output voltage. Resonant DC with smoothing part
A DC converter that outputs a switching pulse signal of a predetermined frequency to the switch element; an error detection circuit that compares the DC output voltage with a reference voltage to detect an error voltage; and the pulse A time constant variable circuit for controlling the off time of the switch element by changing the time constant setting resistance component of the generation circuit according to the error voltage detected by the error detection circuit.

According to the present invention, when an overcurrent such as an overload or an output short circuit occurs, the time constant variable circuit determines the time constant of the pulse generating circuit so that the off time of the switch element does not become extremely short and the load is overloaded. Prevent current from flowing. Further, when the load current is small, the variable time constant circuit determines the time constant of the pulse generating circuit so that the off time of the switch element does not become excessively long, thereby preventing the switching frequency from decreasing.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is a switching element for chopping a DC voltage at a predetermined frequency to convert it into an AC, and converting the converted AC into a DC for smoothing. A resonance type DC-DC converter having a rectifying / smoothing unit for generating a DC output voltage, comprising: a pulse generating circuit for outputting a switching pulse signal of a predetermined frequency to the switch element; and the DC output voltage and a reference voltage. An off-time of the switching element is controlled by changing an error detection circuit for comparing and detecting an error voltage and a time constant setting resistance component of the pulse generation circuit according to the error voltage detected by the error detection circuit. And a time constant variable circuit for

According to a second aspect of the present invention, the variable time constant circuit includes a transistor for generating a current according to the error voltage from the error detection circuit, and a first resistor connected in series to the emitter of the transistor. , A second resistor connected in series to the collector of the transistor, and a third resistor connected in parallel to the series circuit of the transistor and the first resistor.

Therefore, when an overcurrent such as an overload or an output short circuit occurs, the transistor forming the variable time constant circuit is turned on, so that the time constant of the off time of the pulse generation circuit depends on the first to third resistors. Determined by combined resistance. This limits the off time from becoming extremely short, and prevents an overcurrent from flowing to the load.

Further, since the transistor forming the variable time constant circuit is turned off at the time of a small load current, the time constant of the off time of the pulse generation circuit is determined by the combined resistance of the second resistance and the third resistance. It This limits the off time from becoming extremely long and prevents the switching frequency from decreasing.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a configuration of a current resonance type DC-DC converter according to an embodiment of the present invention.
The same parts as those shown in FIG. In FIG. 1, a ripple removing capacitor 2 is provided between the input terminal 1 to which the DC input voltage Vin is input and the ground.
, And a choke coil 4 and a rectifying diode 5 are connected in series between the input terminal 1 and the output terminal 3 that outputs the output voltage Vout.

A resonance choke coil 12 and a switch element 6 are connected between the connection point of the choke coil 4 and the rectifying diode 5 and the ground, and between the output stage of the rectifying diode 5 and the ground. The output smoothing capacitor 7 is connected. Furthermore, the rectifying diode 5
A resonance capacitor 13 is connected in parallel with the resonance choke coil 12 and the resonance capacitor 13 to form a current resonance circuit.

Further, the pulse width control circuit 14 for controlling the switch element 6 compares the voltage obtained by dividing the output voltage Vout by the voltage divider 15a with the reference voltage 15b and detects the error voltage between them and the differential amplifier 15c. Error detection circuit 15 having
Having.

Further, the pulse width control circuit 14 generates a current according to the error voltage output from the error detection circuit 15, a PNP transistor 16, a resistor 17 connected in series between the emitter terminal of the transistor 16 and the Vcc power supply, A pulse signal is supplied to the resistor 18 connected in parallel between the collector terminal of the transistor 16 and the Vcc power supply for preventing switching frequency reduction, the resistor 19 connected in series to the collector terminal of the transistor 16 for preventing overcurrent, and the switch element 6. It has a pulse generation circuit 20 composed of a dual monostable multivibrator having an IC configuration.

Further, the capacitor 21 and the resistor 22 which are connected between the pulse generating circuit 20 and the Vcc power source and set the ON time of the pulse generating circuit 20, the pulse generating circuit 2
A capacitor 23 connected between 0 and the collector terminal of the transistor 16 to set the off time of the pulse generation circuit 20.
Is provided. In addition, the transistor 16 and the resistors 17 to 1
Reference numeral 9 constitutes a time constant variable circuit 24 for setting the time constant of the off time of the pulse generation circuit 20.

Next, the operation of this embodiment will be described. First, the time constant of the pulse generation circuit 20, that is, the on-time determined by the capacitor 21 and the resistor 22 corresponds to the resonance frequency of the resonance current by the choke coil 12 and the capacitor 13.

On the other hand, in the error detection circuit 15, the error voltage between the output voltage divided by the voltage divider 15a and the reference voltage 15b is amplified by the differential amplifier 15c, and this error voltage is applied to the base of the transistor 16. , A current corresponding to the error voltage flows in the collector of the transistor 16, so that it is equivalent to that the combined resistance of the parallel circuit of the resistors 17 and 18 and the resistor 19 serially connected to the parallel circuit has changed. Therefore, the time constant of the off time of the pulse generation circuit 20 is determined by the combined resistance and the capacitor 23.

That is, since the transistor 16 is completely turned on when an overcurrent such as an overload or an output short circuit occurs, the time constant of the off time of the pulse generation circuit 20 is a combination of the resistance 17, the resistance 18, and the resistance 19. It is determined by the resistance and the capacitor 23. This limits the off time from becoming extremely short and prevents an overcurrent from flowing to the load.

When the load current is small, the transistor 1
Since 6 is completely turned off, the time constant of the off time of the pulse generation circuit 20 is determined by the combined resistance of the resistors 14 and 19 and the capacitor 23. This limits the off time from becoming extremely long and prevents the switching frequency from dropping to the audible band.

As described above, according to the present embodiment, it is possible to limit the shortening of the off-time by the combined resistance of the resistors 17 to 19 at the time of overcurrent, and the resistor 1 at the time of a small load current.
It is possible to prevent the off time from being shortened by the combined resistance of 8 and 19 and prevent the switching frequency from decreasing.

[0028]

According to the present invention, the resistance component for setting the time constant of the pulse generation circuit is changed according to the error voltage detected by the error detection circuit to control the off time of the switch element, thereby preventing overcurrent. Further, it is possible to realize the prevention of the decrease of the switching frequency with a simple circuit configuration, which is advantageous in terms of cost reduction and mounting, and it is possible to obtain a resonant DC-DC converter having high safety and reliability.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a resonance type DC-DC converter according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a conventional resonance type DC-DC converter.

[Explanation of symbols]

 1 Input Terminal 2 Ripple Removal Capacitor 3 Output Terminal 4 Choke Coil 5 Rectifier Diode 6 Switch Element 7 Smoothing Capacitor 12 Resonance Choke Coil 13 Resonance Capacitor 14 Pulse Width Control Circuit 15 Error Detection Circuit 15a Voltage Divider 15b Reference Voltage 15c Difference Dynamic amplifier 16 Transistor 17 Resistor 18 Resistor 19 Resistor 20 Pulse generating circuit 21 Capacitor 22 Resistor 23 Capacitor 24 Time constant variable circuit

Claims (2)

[Claims] 1. A resonance type having a switch element for chopping a DC voltage at a predetermined frequency to convert it into an AC, and a rectifying / smoothing section for converting the converted AC into a DC and smoothing to generate a DC output voltage. A DC-DC converter, comprising: a pulse generation circuit that outputs a switching pulse signal of a predetermined frequency to the switch element; an error detection circuit that compares the DC output voltage with a reference voltage to detect an error voltage; A resonance, comprising a time constant variable circuit for controlling the off time of the switch element by changing the time constant setting resistance component of the pulse generation circuit according to the error voltage detected by the error detection circuit. Type DC-D
C converter. 2. The variable time constant circuit comprises a transistor for generating a current according to an error voltage from an error detection circuit, a first resistor connected in series to the emitter of the transistor, and a series connection to the collector of the transistor. 2. The resonance type DC- according to claim 1, wherein the resonance type DC- is constituted by a second resistor connected to the first resistor and a third resistor connected in parallel to a series circuit of the transistor and the first resistor. DC converter.