JP2729478B2 - converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a converter for converting a DC input voltage to obtain a DC output voltage.

[0002]

2. Description of the Related Art Converters having a configuration in which DC power is once converted to AC, and then transformed into an AC voltage by a transformer, rectified, and converted again into a desired DC voltage are widely used. Such a converter generally uses a commercially available converter driving integrated circuit (IC), and supplies a voltage stabilizing signal corresponding to an error signal between a detection voltage of a DC output voltage and a reference voltage to the converter driving IC. By providing the feedback loop, the switching element is driven by pulse width modulation so as to stabilize the DC output voltage.

[0003] If the conversion frequency of the converter is increased,
Since the capacitance of magnetic components such as transformers and capacitors decreases almost in inverse proportion to the frequency, the conversion frequency of converters has recently been increased to about 500 kHz, and the capacitors used have been reduced in capacitance. The technology to extend the life of the converter and to make it ultra-small by eliminating all electrolytic capacitors that have a change in capacity over time has become widespread.

[0004]

However, when a plurality of such converters are operated in parallel, the operating frequency component of another converter may appear in the output, and the inductor in the smoothing circuit of a certain converter may be cut off. Due to these effects, the ripple of the DC output voltage changes discontinuously,
If the DC output voltage ripple is detected by a resistor and a capacitor and phase compensation is performed, undesired fluctuations also appear in the voltage stabilization signal. Become stable.

Further, as described above, even in the case where the inductor in the smoothing circuit is not cut off in any of the converters, voltage phase delay elements such as storage of the switching element, inductor and capacitor of the smoothing circuit, and capacitor of the output voltage detecting circuit. As a result, the voltage stabilization signal given to the converter driving IC is delayed with respect to the driving signal output from the converter driving IC to the switching element, so that the operation of the converter also becomes unstable.

An object of the present invention is to reduce such unstable elements of the converter to such an extent that there is no practical problem, thereby stably operating a plurality of converters even in parallel operation.

[0007]

[Means for Solving the Problems] The first invention aims at eliminating the above-mentioned drawbacks, and according to the voltage levels of a DC power supply, a transformer, a switching element, and a voltage stabilizing terminal. A converter driving circuit for supplying a changing drive signal to the switching element, rectifying and smoothing the voltage of the secondary winding of the transformer to obtain a DC output voltage, detecting the DC output voltage, In a converter for applying a voltage corresponding to an error signal obtained by comparison with a voltage to the voltage stabilization terminal, a minute triangular wave voltage formed in synchronization with a drive signal output from the converter drive circuit is converted into a voltage. A converter characterized by applying a voltage superimposed on a voltage corresponding to an error signal to the voltage stabilizing terminal.

[0008] A second aspect of the present invention aims to eliminate the above-mentioned drawbacks, and provides a DC power supply, a transformer, a switching element, and a driving signal that changes according to the voltage level of a voltage stabilizing terminal. A DC drive voltage is obtained by rectifying and smoothing the voltage of the secondary winding of the transformer to obtain a DC output voltage, and detecting and comparing the DC output voltage with a reference voltage. And a semiconductor switch driven by the drive signal, wherein a resistor and a capacitor are connected in series to a voltage stabilization terminal of the converter drive circuit. Are connected to both ends of the capacitor, and a feedback current depending on a voltage corresponding to the error signal is caused to flow through the resistor and the capacitor. It is another object of the present invention to provide a converter characterized in that a voltage obtained by superimposing a minute triangular wave voltage due to charging and discharging of the capacitor on a DC voltage generated by the resistor is applied to the voltage stabilizing terminal.

[0009]

In FIG. 1 showing an embodiment of the present invention, the positive side of a DC power supply E is connected to a primary winding of a transformer T and a drain electrode of an FET Q1 which is a switching element in order. The negative side is connected to the source electrode of the FET Q1 and serves as a primary side common line. Here, an on / off signal such as a pulse width modulation signal, that is, a drive signal as shown in FIG. 2A is supplied from the output terminal a of the converter drive circuit U1 to the gate electrode of the FET Q1 via the resistor R5. Is done.

[0010] The converter drive circuit U1 is widely used as an off-the-shelf integrated circuit. Its internal circuit is
A reference oscillation circuit for setting a switching cycle of the converter, a triangular wave voltage generation circuit for generating a triangular wave voltage based on the reference oscillation circuit, a reference voltage source, and an error amplifier for constant voltage; The output level of the error amplifier and said 3
It comprises a comparator for comparing the waveform of the angular wave voltage generation circuit with a waveform, and a circuit for generating a drive signal such as a pulse width modulation signal based on the output of the comparator. FIG. 1 shows only the terminals directly necessary for the description of the present invention. That is, a drive signal output terminal a, a reference voltage source terminal b, voltage stabilization terminals c and d, a negative feedback terminal e, and a terminal for connecting a capacitor and a resistor for determining the cycle of the reference oscillation circuit, respectively. FIG. 2 illustrates g and f, and a ground terminal h.

The AC voltage appearing between the secondary windings of the transformer T due to the switching of the FET Q1 is rectified and smoothed by the rectifying diodes D1, D2, the inductor L and the capacitor C3 to obtain a desired DC output voltage. Are obtained at the output terminals t1 and t2 and supplied to the load RL.

[0012] The DC output voltage is determined by resistors R6 and R7.
And sent to the inverting terminal of the operational amplifier U2. The reference voltage Vref is equal to the operational amplifier U2.
Is applied to the non-inverting terminal of The output of the operational amplifier U2 is a voltage corresponding to the difference between the detection voltage of the DC output voltage and the reference voltage Vref, and the error signal is supplied to the light emitting section of the photocoupler PC via the resistor R5. The light signal modulates the conductivity of the light receiving transistor of the photocoupler PC to change the impedance of the light receiving transistor.

The light receiving transistor of the photocoupler PC has a resistor R2 and a capacitor C2 connected in series, and has a discharge signal from which a drive signal is supplied from an output terminal a of the converter drive circuit U1 via a resistor R3. PNP
The transistor Q2 is connected to the capacitor C2 via the resistor R4.
Are connected to both ends. On the other hand, the reference voltage generation terminal b of the converter drive circuit U1 is connected to the light receiving transistor of the photocoupler PC.

That is, as a structural feature of the present invention, a circuit including a capacitor C2, a resistor R4, a transistor Q2, and a resistor R3 forms a minute triangular wave forming circuit. Is connected in series to the resistor R2. Therefore, when this circuit configuration is provided, the capacitor C2 is connected to the voltage across the resistor R2.
Can be applied to the voltage stabilization terminal c of the converter drive circuit U1 as a voltage stabilization signal having a smaller unstable component than the conventional one.

Next, the operation will be described in more detail. The light receiving transistor of the photocoupler PC receives light corresponding to the error signal for stabilizing the output voltage, and conducts electric conductivity modulation.
The impedance changes depending on the magnitude of the error signal. Therefore, a current depending on the magnitude of the error signal flows from the reference voltage generating terminal b of the converter drive circuit U1 through the light receiving transistor of the photocoupler PC, the resistor R2, and the capacitor C2, and charges the capacitor C2. At this time, the transistor Q2 is off.

The transistor Q2 operates in response to a drive signal from the output terminal c of the converter drive circuit U1 so that the FET Q1
Operates complementarily. That is, the transistor Q2 is turned off by the high-level drive signal for turning on the FET Q1, and the transistor Q2 is turned on by the low-level drive signal for turning off the FET Q1, thereby discharging the electric charge of the capacitor C2 through the resistor R4. Therefore, since the capacitor C2 repeats charging and discharging every cycle of the drive signal of the converter drive circuit U1, a small triangular wave voltage starting from a substantially zero value is generated every cycle of the drive signal. A composite voltage having a waveform as shown in FIG. 2 (B) in which the thus-formed triangular wave voltage is superimposed on the voltage of the resistor R2 is applied to the voltage stabilizing terminal c of the converter drive circuit U1. . This small triangular wave voltage has an upward slope which can at least reduce the unstable component of the converter operation and the turn-off delay element of the switching element as described above.

As can be seen from the above description, in this embodiment, the voltage corresponding to the product of the feedback current corresponding to the error signal for stabilizing the output voltage and the resistance value of the resistor R2 corresponds to the magnitude of the feedback current. When the converter drive circuit U1 compares the stabilized voltage with the triangular wave voltage of the triangular wave voltage generating circuit to apply a voltage having a rising slope to the right, the two cross each other, that is, the time when the turn-off of the FET Q1 is determined. Can be made more stable than before. Therefore, the converter can be operated stably.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 3 shows a micro 3 in the circuit of this embodiment.
FIG. 3 is a diagram showing a relevant portion of the square wave forming circuit, wherein a drive signal from an output terminal a of the converter drive circuit U1 is a resistor R13;
Is divided by the resistor R14 and applied to the base of the transistor Q5. The transistor Q4 and the transistor Q5 are Darlington connected, and are configured to be able to drive the transistor Q4 with a small drive signal. on the other hand,
The constant voltage at the reference voltage generating terminal b of the converter drive circuit U1 is divided by the resistors R15 and R16 to give a constant potential to the base of the PNP transistor Q3. P
The collector and the emitter of the NP transistor Q3 are connected in series between the light receiving transistor of the photocoupler PC and the resistor R2, and the light receiving transistor and the resistor R of the photocoupler PC are connected between the base and the emitter of the PNP transistor Q3.
15 is connected.

In this circuit configuration, the light-receiving transistor of the photocoupler PC is subjected to conductivity modulation by the error signal for voltage stabilization, so that the voltage between the base and the emitter of the transistor Q3 changes, and the current flowing through the transistor Q3 is changed. Changes. This current flows through the resistor R2 and the capacitor C2, and the combined voltage obtained by superimposing the two voltages generated on the resistor R2 and the capacitor C2 is connected to the voltage stabilizing terminal c of the converter drive circuit U1. This circuit operates in the same manner as the circuit shown in FIG. 1, but has a higher response speed because the phototransistor of the photocoupler PC operates in the constant voltage mode as compared with the circuit shown in FIG. Further, the saturation voltage when the discharging transistor of the capacitor C2 is turned on can be reduced.

[0020]

As described above, the present invention provides a converter that combines a small triangular wave voltage formed in synchronization with a drive signal output from a converter drive circuit with a voltage corresponding to the error signal. Since it is applied to the voltage stabilization terminal of the drive circuit, unstable components of the converter operation and FET
The turn-off delay component of Q1 can be reduced.
Therefore, not only when the converter is operated alone but also when a plurality of converters are operated in parallel, the converter can be stably operated without causing any turbulence or the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a converter according to the present invention.

FIG. 2 is a waveform chart for explaining the operation of the converter according to the present invention.

FIG. 3 is a diagram showing another embodiment of the converter according to the present invention.

[Explanation of symbols]

E: DC power supply, T: Transformer C1-C5: Capacitor, D1, D2: Diode L: Inductor, R1-R16 ...
Resistor U1: Converter drive circuit, U2: Operational amplifier PC: Photocoupler, Q1: FET
(Switching element) Q2, Q3 ... PNP transistor, Q4, Q5 ... N
PN transistors t1, t2: output terminals of the converter, Vref: reference voltage RL: load

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-262081 (JP, A) JP-A-51-13515 (JP, U) Patent 2646021 (JP, B2)

Claims (2)

(57) [Claims] 1. A secondary winding of a transformer, comprising: a DC power supply; a transformer; a switching element; and a converter drive circuit for providing a drive signal to the switching element according to a voltage level of a voltage stabilizing terminal. A converter for rectifying and smoothing the voltage of the line to obtain a DC output voltage, detecting the DC output voltage, and providing a voltage corresponding to an error signal obtained by comparison with a reference voltage to the voltage stabilizing terminal; Wherein a voltage obtained by superimposing a minute triangular wave voltage formed in synchronization with a drive signal output from the converter drive circuit on a voltage corresponding to the error signal is applied to the voltage stabilizing terminal. converter. 2. A secondary winding of the transformer, comprising: a DC power supply; a transformer; a switching element; and a converter drive circuit for providing a drive signal to the switching element according to a voltage level of a voltage stabilizing terminal. A converter for rectifying and smoothing the voltage of the line to obtain a DC output voltage, detecting the DC output voltage, and providing a voltage corresponding to an error signal obtained by comparison with a reference voltage to the voltage stabilizing terminal; In the above, a resistor and a capacitor are connected in series to a voltage stabilizing terminal of the converter drive circuit, and a semiconductor switch driven by the drive signal is connected to both ends of the capacitor, and a voltage corresponding to the error signal is set. A dependent feedback current is passed through the resistor and the capacitor, so that a DC voltage caused by the feedback current and the resistor is reduced by a minute 3 due to charging and discharging of the capacitor. A converter, wherein a voltage obtained by superimposing an angular wave voltage is applied to the voltage stabilizing terminal.