JPS5838067B2 - DC/DC converter control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for a DC/DC converter.

A DC/DC converter produces an output voltage that is the input voltage multiplied by a conversion ratio.

When a DC/DC converter is used in a DC stabilized power supply circuit, the conversion ratio is changed by a control signal in the opposite direction to the input voltage change, and the product of the input voltage and the conversion ratio, that is, the output voltage, is kept constant. It's starting to drip.

The control signal generation circuit generates DC/DC from an error amplifier etc.
A feedback signal based on the difference between the output voltage of the converter and its reference value is given, and the DC/DC
Generates a control signal (duty signal) suitable for the converter.

In conventional equipment, the control signal generation circuit is
It was designed to generate a control signal proportional to the back signal.

There is no problem with such a control signal generation circuit if the conversion characteristic of the DC/DC converter is linear, but if the conversion characteristic is non-linear, the loop gain changes depending on the input voltage value, and it may be difficult to turn on the power or This is inconvenient because the control may become unstable and oscillation may occur when the circuit is shut off.

In addition, in the case of feedback control, if the input voltage suddenly changes, the conversion ratio may not be able to be changed in time, causing a temporary change in the output voltage.
The core of the DC converter transformer may become saturated.

In order to prevent this phenomenon, conventionally the input voltage is fed to the control signal generating means so that the ET product is constant.
However, this is effective only when the conversion characteristic of the DC/DC converter is linear with respect to the control signal.

Conversion characteristics vary depending on the internal configuration of the DC/DC converter, and are not necessarily linear.
An input voltage fluctuation compensation means that is effective for DC/DC converters with arbitrary conversion characteristics is required.

An object of the present invention is to provide a control method that makes it possible to maintain a constant loop gain in feedback control and compensate for input fluctuations for a DC/DC converter with arbitrary conversion characteristics.

In the present invention, when the conversion characteristic of a DC/DC converter is given by a function f (x) of a control signal f”(Ky/
Ei).

The present invention will be explained below with reference to the drawings.

FIG. 1 is a conceptual diagram of an embodiment of the present invention.

In FIG. 1, CNV is an example of a DC/DC converter with nonlinear conversion characteristics, and includes a transformer T, a switching element S provided on the primary side thereof and driven by a control signal It consists of a diode D and a capacitor C provided on the next side.

This is known as an on-off type DC/DC converter, which stores energy based on the input voltage Ei in the transformer T when the switching element S is on, and releases it to the capacitor C through the diode D when it is off. It is.

The voltage of capacitor C is supplied to load RL as output voltage Eo.

The conversion characteristic of this DC/DC converter CNV is expressed as follows.

However, 1/n is the line ratio of Tofunu'r, and X has the unit of duty ratio.

A is an error amplifier that outputs a feed signal based on the difference between the output voltage Eo of the DC/DC converter CNV and the reference voltage ■8.
produces a backing signal y.

PWM is a control signal generation circuit, which is given a feed forward input voltage Ei and a feedback signal y, and generates an output signal represented by a function g (Eity) thereon.

The function g(Ei, y) is an inverse function of the conversion characteristics of the DC/DC converter, with Ky/Ei as the independent variable (
K is a constant).

That is, X-g (Ei, y) = f-1 (Ky/Ei) (2).

When f (x) is given by the above equation (1), it becomes.

The operation of the device configured in this way is as follows.

The output voltage Eo is expressed by the following formula. EO-Ei-f(x
)(4) It can be seen that control proportional to the feedback signal y is performed.

In other words, the loop gain of the feedback control is constant.

Furthermore, since the output voltage Eo is independent of the input voltage Ei from equation (6), fluctuations in the input voltage Ei are compensated for.

The conversion characteristics of the DC/DC converter CNV in FIG. 1 are expressed by a characteristic curve whose slope gradually increases as the control signal X increases, as shown in FIG. 2. Therefore, the conversion ratio f ( The rate of change of x) is obtained.

Therefore, the device shown in FIG. 1 becomes a DC stabilized power supply with a wide input range or a wide output range.

Of course, the DC/DC converter is not limited to the one shown in FIG.

Various control signal generation circuits PWM are used depending on the conversion characteristics of the DC/DC converter.

A control signal generation circuit PWM adapted to the conversion characteristics of the DC/DC converter CNV shown in FIG. 1 is configured as shown in FIG. 3, for example.

In Figure 3, CF is a comparator with two input terminals +,
The output voltage, that is, the control signal X, which becomes H and L, respectively, is generated depending on whether the voltage at the input terminal is larger or smaller than the voltage at the input terminal.

The feedback signal y from the error amplifier A is divided by resistors R3 and R4 and applied to the input terminal of the comparator CF.

The voltage of the capacitor CH is applied to the single power terminal of the comparator CF.

The capacitor CH is charged with current by the feedback signal y and the input voltage Ei through resistors R, R2, respectively.

The charge on capacitor CH is periodically discharged to zero by transistor Q.

In a range where the charging current can be regarded as a constant current, the voltage of the capacitor CH becomes a ramp voltage with a constant period T.

The operation of the circuit of FIG. 3 is as shown in FIG. 4. Depending on whether the lamp voltage V is smaller or larger than the partial voltage C of the feedback signal y, the output voltage of the comparator CF becomes H and H, respectively. The duty ratio X of the H portion with respect to the period T corresponds to the value of the feedback signal y.

Lamp voltage V.

is expressed by the following equation. At t=xT, V 2 matches the partial pressure value of the feedback signal y, so the following relationship holds true.

When the circuit constants are determined to satisfy Thus, the same functional characteristics as the above equation (3) are obtained.

Note that when the input voltage drops significantly, the duty ratio of the control signal X increases extremely or becomes unstable due to the input fluctuation compensation operation. It is sufficient to limit the voltage drop.

To do this, the input voltage E and the lower limit setting voltage E* may be applied to the resistor R2 through a high selector formed by a diode DI t D2 as shown in FIG.

As described above, in the present invention, when the conversion characteristic of the DC/DC converter is given by the function f(x) of the control signal The function f-1(Ky/
Ei).

Therefore, for a DC/DC converter with arbitrary conversion characteristics, the loop gain of feedback control can be kept constant and fluctuations in input voltage can be compensated for.

Since the loop gain of the feedback control is constant, stable feedback control can be performed, and unstable phenomena such as oscillations that occur when the power is turned on or off do not occur.

Furthermore, since fluctuations in input voltage are quickly compensated for by feedforward control, saturation of the transformer core does not occur.

In addition, an output voltage with a fairly constant voltage property can be obtained only by the feed forward control, and since this is further controlled by feedback control with a constant loop gain, an extremely stable output voltage can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a conceptual configuration diagram of an embodiment of the present invention, and Fig. 2 is a D C
An example of the conversion characteristics of a /DC converter, Figure 3 is an electrical connection diagram of an example of a control signal generation circuit, Figure 4 is an explanatory diagram of the operation of the circuit in Figure 3, and Figure 5 is an illustration of the circuit in Figure 3. These are some modified examples. CNV...DC/DC converter, A...
...Error amplifier, PWM...Control signal generation circuit, RL...Load.

Claims (1)

[Claims] 1. A transformer, a switch for turning on and off the current supplied from a DC power source to its primary coil, and means for rectifying and smoothing the induced voltage in the secondary coil when the switch is off, and outputting the rectified and smoothed voltage. an error amplifier that generates a signal proportional to the difference between the output voltage of the cono-converter body and a reference value of the output, and a signal proportional to the output signal of the error amplifier is applied to one input terminal, and A ramp signal formed by periodically resetting the time integral value of the sum of a signal proportional to the output signal of the error amplifier and a signal proportional to the voltage of the DC power supply that supplies voltage to the primary coil of the transformer. is applied to the other input terminal, and the DC/DC converter is provided with a comparator that compares the magnitude of the signals at both input terminals and generates a binary signal as a result of the comparison as a duty control signal for turning on and off a switch in the converter main body. control method.