JPH05304771A - Switching power supply device - Google Patents

Abstract

PURPOSE:To maintain stability and speediness within a closed loop fully for all operation conditions of a DC/DC converter. CONSTITUTION:A DC current which flows through a load 8 is detected by a current detection circuit 21, thus turning on or off an FET 22 according to the state of the load 8. Feedback phase compensation circuits 23 and 24 with different characteristics are constituted by the ON/OFF state of an FET 22, thus selecting the proper feedback phase compensation circuits 23 and 24 for control according to the change in the transfer function of a DC/DC converter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC converter having a feedback loop having a feedback phase compensation circuit.

[0002]

2. Description of the Related Art Generally, a switching power supply device having a DC / DC converter and a feedback loop is known, for example, from Japanese Patent Laid-Open No. 1-303055. Figure 4
Shows a conventional example of this type of forward switching power supply device, in which the DC input voltage Vi is applied to the primary winding of the transformer 1 which insulates the primary side and the secondary side from the NPN transistor. Switching element 2
The voltage induced in the secondary winding of the transformer 1 by the switching of the rectifier diodes 3 and 4 and the choke coil 5
By rectifying and smoothing by the rectifying and smoothing circuit 7 having a filter including the smoothing capacitor 6, a DC / DC converter that supplies a predetermined DC output voltage Vo to the load 8 from between the output terminals + V and -V is configured.

On the other hand, as a feedback loop for stabilizing the DC output voltage Vo, output terminals + V, -V and a load 8 are provided.
Remote sensing terminals + S, -S capable of correcting the voltage drop between them are provided, and voltage dividing resistors 9, 10 are connected in series between the remote sensing terminals + S, -S. Further, the connection point of the resistors 9 and 10 is connected to the inverting input terminal of the operational amplifier 11 via the resistor R1, and in the state where the output terminals + V, -V and the remote sensing terminals + S, -S are connected, respectively. , The DC output voltage Vo is divided by the resistors 9 and 10, and is detected by the error amplifier.
It is applied to 11 and is compared and amplified with the reference voltage E. And
The pulse width control circuit 12 controls the pulse conduction width of the switching element 2 based on the voltage comparatively amplified by the error amplifier 11 so as to keep the DC output voltage Vo constant.

Between the output terminal and the inverting input terminal of the error amplifier 11, a series circuit of a capacitor C1 and a resistor R2 and a resistor R3 are connected in parallel.
2, R3, the capacitor C1, and the resistor R1 constitute a feedback phase compensation circuit 13. The feedback phase compensating circuit 13 prevents DC / DC from rotating the phase of the filter by the choke coil 5 and the smoothing capacitor 6 beyond 180 °.
Overall closed loop gain due to converter and feedback loop −
By appropriately adjusting the frequency characteristics, it becomes possible to prevent the oscillation in the device and to continue supplying the stable DC output voltage.

[0005]

In the above-mentioned prior art, the continuous mode above the critical point at which the current of the choke coil 5 always continuously flows, and the discontinuity below the critical point at which the current of the choke coil 5 intermittently flows. Depending on the mode, DC /
The operating state of the DC converter is different, and the transfer function of the DC / DC converter changes before and after this critical point. However, in a normal case, the operation of the switching power supply device is often performed in the continuous mode of the choke coil 5, and the feedback phase compensation circuit 13 can maintain the stability in the closed loop to some extent in the continuous mode of the choke coil 5. In addition, the values of the resistors R1 and R2 and the capacitors C1 and C2 are appropriately set, and control is performed by a constant transfer function. Therefore, for example, when the choke coil 5 is in the discontinuous mode due to the dynamic fluctuation of the load 8 or the like, the frequency band of the feedback phase compensation circuit 13 is relatively narrow, and the response delay easily occurs.
Before and after the continuous and discontinuous modes of the choke coil 5, there was a problem that the stability and high speed of the entire device became insufficient.

Therefore, the present invention solves the above problems,
An object of the present invention is to provide a switching power supply device capable of sufficiently maintaining the stability and high speed of the entire device under all operating conditions of a DC / DC converter.

[0007]

According to the present invention, a DC input voltage is switched by a switching element and applied to a primary winding of a transformer, and a voltage induced in a secondary winding of the transformer is rectified and smoothed and output. DC / DC converter,
In the feedback loop for stabilizing the output voltage, the DC
In a switching power supply device including a feedback phase compensation circuit that suppresses phase rotation in a DC / DC converter, a plurality of the feedback phase compensation circuits having different characteristics are provided, and the feedback phase compensation circuit is provided according to a change in the transfer function of the DC / DC converter. The feedback phase compensation circuit is selectively switched.

[0008]

With the above construction, when the transfer function of the DC / DC converter, which is the main circuit, changes due to the dynamic fluctuation of the load, etc., the feedback phase compensation circuit is switched and selected by the change of this transfer function, and the DC / DC inverter and the feedback circuit are fed back. In a closed loop with the loop, its stability and speed are maintained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In FIG. 1, the same parts as those of FIG. 4 shown in the conventional example are designated by the same reference numerals, and detailed description of the common parts will be omitted.

A current detection circuit 21 for detecting the state of the load 8 by detecting the output current flowing from the rectifying / smoothing circuit 7 to the load 8 is inserted and connected to the output terminal -V line. Further, a series circuit of a junction type FET 22 and a capacitor C2 is connected between the output terminal and the inverting input terminal of the error amplifier 11 in place of the resistor R3 in FIG. 1, and the gate of the FET 22 and the current detection circuit 21 are connected to each other. By connecting the gate voltage to the FET 22 according to the state of the load 8 detected by the current detection circuit 21,
When ET22 is off, as shown in FIG.
1, R2 and a capacitor C1 constitute a feedback phase compensating circuit 23. On the other hand, when the FET 22 is on, another feedback phase compensating circuit 24 comprising resistors R1 and R2 and capacitors C1 and C2, as shown in FIG. The configuration is the same as that shown in FIG.

FIG. 4 is a block diagram of the switching power supply device shown in FIG. 1. For the DC / DC converter having the characteristic of the transfer function α, the transfer functions G (s) and G having different characteristics are shown. Feedback phase compensating circuits 23 and 24 having (s) ′ are provided as feedback loops, and each of the feedback phase compensating circuits 23 and 24 responds to changes in the transfer function α of the DC / DC converter by the FET 22 serving as a switch means. It is controlled so that it is selectively switched. The transfer functions G (s) and G (s) 'of the feedback phase compensation circuits 23 and 24 are s = j
Let ω be represented by the following formula.

[0012]

[Equation 1]

[0013]

[Equation 2]

However, in the equation 2,

[0015]

[Equation 3]

[0016]

Next, the operation of the above structure will be described. When the DC input voltage Vi is applied to the primary winding of the transformer 1, the voltage induced in the secondary winding of the transformer 1 by the switching of the switching element 2 is rectified and smoothed by the rectifying and smoothing circuit 7.
Is rectified and smoothed by and is supplied to the load 8 as a DC output voltage Vo. The DC output voltage Vo is divided by the resistors 9 and 10, and is detected and amplified by the error amplifier 11 in comparison with the reference voltage E. The pulse width control circuit 12 switches the switching element based on the comparison and amplified voltage. Controls the pulse conduction width of 2. At this time, the current detection circuit 21
When it is detected that the load 8 is in a heavy load state and the choke coil 5 has reached a critical point above the continuous mode,
The current detection circuit 21 turns off the FET 22 and performs the control by the feedback phase compensation circuit 23 having the characteristic of the transfer function G (s) having a wide frequency band, while the load 8 becomes no load or light load, When it is detected that the choke coil 5 has reached the critical point below the discontinuous mode, the current detection circuit 21 turns on the FET 22 to provide feedback having the characteristic of the transfer function G (s) 'with a narrow frequency band. Control by the phase compensation circuit 24 is performed. That is,
When the normal choke coil 5 operates in the continuous mode, the feedback phase compensation circuit 23 increases the gain and widens the frequency band to maintain stable and high speed in the closed loop, while the load 8 When the choke coil 5 is in the discontinuous mode due to the dynamic fluctuation of, the gain is reduced and the frequency band is narrowed by another feedback phase compensation circuit 24 in which the capacitor C2 is added to the feedback phase compensation circuit 23. Improves stability.

As described above, according to the above-described embodiment, the change of the operating state of the DC / DC inverter is detected by the current detection circuit 21 as the change of the output current flowing through the load 8, and the continuous or discontinuous mode of the choke coil 5 is detected. By switching the FET 22 on and off in accordance with, the appropriate transfer function G corresponding to the change of the transfer function α of the DC / DC converter
(S), G (s) 'feedback phase compensation circuit 23,
Even if the transfer function α of the DC / DC converter changes due to the dynamic fluctuation of the load 8, it becomes possible to perform control by selecting 24, and before and after the continuous and discontinuous modes of the choke coil 5, It is possible to sufficiently maintain stability and responsiveness in the closed loop.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, not only the combination of the current detection circuit and the FET in the embodiment, but also the other feedback means may detect the change in the transfer function of the DC / DC converter and switch the feedback phase compensation circuits. Further, each feedback phase compensation circuit can be provided at any position in the feedback loop. Furthermore, the switching element is not limited to a transistor, and a MOS type FET can be used.
The DC / DC converter and the feedback loop are adaptable to various types.

[0020]

INDUSTRIAL APPLICABILITY The present invention is a DC / DC converter for switching a DC input voltage by a switching element and applying it to a primary winding of a transformer, rectifying and smoothing a voltage induced in a secondary winding of the transformer, and outputting it. And a switching power supply device having a feedback phase compensation circuit that suppresses phase rotation in the DC / DC converter in a feedback loop for stabilizing the output voltage, a plurality of feedback phase compensation circuits having different characteristics are provided. The feedback phase compensating circuit is selectively switched according to the change of the transfer function of the DC / DC converter, and the stability of the entire apparatus is ensured under all operating conditions of the DC / DC converter. To provide a switching power supply device capable of sufficiently maintaining high speed and high speed It can be.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a switching power supply device according to the present invention.

FIG. 2 is a circuit diagram of the same choke coil in a continuous mode.

FIG. 3 is a circuit diagram of the same choke coil in a discontinuous mode.

FIG. 4 is a block diagram of the same as above.

FIG. 5 is a circuit diagram of a switching power supply device in a conventional example.

[Explanation of symbols]

 1 transformer 2 switching element 7 rectifying / smoothing circuit 12 capacitors 23, 24 feedback phase compensation circuit

Claims (1)

[Claims] DC / DC that switches a DC input voltage by a switching element and applies it to the primary winding of a transformer, rectifies and smoothes the voltage induced in the secondary winding of the transformer, and outputs it.
In a switching power supply device including a converter and a feedback phase compensation circuit that suppresses phase rotation in the DC / DC converter in a feedback loop for stabilizing the output voltage, a plurality of feedback phase compensation circuits having different characteristics are provided. A switching power supply device, which is arranged so as to selectively switch the feedback phase compensation circuit in accordance with a change in a transfer function of the DC / DC converter.