JPS5836590B2 - 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 multiplies the input voltage by a conversion ratio to produce nine output voltages.

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 a feed signal from the error amplifier based on the difference between the output voltage of the DC/DC converter and its reference value.
A back signal is applied, and a control signal (duty signal) suitable for the DC/DC converter is generated accordingly.

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

Such a control signal generation circuit has no problem if the conversion characteristic of the DC/DC converter is linear, but if the conversion characteristic is nonlinear, the loop gain changes depending on the input voltage value, and the power supply This is inconvenient because the control may become unstable and oscillation may occur when turning on or off.

The object of the present invention is to have a certain non-linear conversion characteristic (7) D
It is an object of the present invention to provide a control method in which the loop gain of feedback control is constant for a C/DC converter.

The present invention provides a converter that includes a transformer, a switch that turns on and off a 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. a main body, an error amplifier that generates a signal proportional to the difference between the output voltage of the converter main body and an output reference value; and a signal proportional to the output signal of the error amplifier is applied to one input terminal, A ramp signal formed by periodically resetting the time integral value of the sum of a signal proportional to the output signal and a constant value signal is applied to the other input terminal, and the magnitude of the signals at both input terminals is compared. The DC/DC converter is equipped with a comparator that generates a binary signal of the comparison result as a duty control signal for switching on/off in the converter main body.
The above objectives have been achieved by the control system of the DC-77 converter.

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

FIG. 1 is a conceptual block 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, and when the switching element S is on, the transformer T
It stores energy based on the input voltage Ei, and releases it to the capacitor C through the diode D when it is off.

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

This (7) conversion characteristic of DC/DC converter CNV is expressed as (c).

However, 1/n is the winding ratio of the transformer T, and X has the unit of duty ratio.

A is an error amplifier that generates a feedback signal y based on the difference between the output voltage Eo of the DC/DC converter CNV and the reference voltage VR.

PWM is a control signal generation circuit, and a feedback signal y
is given, for which it produces an output signal represented by the function g(y).

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

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

The output voltage Eo is expressed by the following equation. Next door! Feed
It can be seen that control is performed in proportion to the back signal y.

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

The conversion characteristics of the DC/DC converter CNV in FIG. 1 are expressed by a curve whose slope gradually increases as the control signal X increases, as shown in FIG. 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.

A control signal generating 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 +,
It determines the magnitude of the voltage applied to the input terminal, and generates an output voltage (H) or a control signal X, which becomes (H) or (L), respectively, 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 R, , R, 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.

Capacitor CH is charged with current by feedback signal y and constant voltage ER through resistors R, , R, 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 shown in Fig. 3 is as shown in Fig. 4, and the output voltage of the comparator CF is (H) depending on whether the lamp voltage vc is smaller or larger than the divided voltage value of the feedback signal y. and (L), and (H) for period T
The duty ratio X of the part is the feedback signal y
corresponds to the value of .

The lamp voltage VC is expressed by the following equation.

[Brief explanation of drawings]

Fig. 1 is a conceptual block diagram of an embodiment of the present invention, Fig. 2 is a DC/
An example of the conversion characteristics of a DC converter, FIG. 3 is an electrical connection diagram of an example of a control signal generation circuit, and FIG. 4 is an explanatory diagram of the operation of the circuit of FIG. 3. CNV...DC/DC converter, A...error amplifier, PWM...control signal generation circuit, RL...load.

Claims (1)

[Claims] 1. A switch that turns on and off a current supplied from a DC power source to a transformer and 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. a converter body, an error amplifier that generates a signal proportional to the difference between the output voltage of the 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 the error amplifier A ramp signal formed by periodically resetting the time integral value of the sum of a signal proportional to the output signal of the amplifier and a constant value signal is applied to the other input terminal, and the magnitude of the signal at both input terminals is determined. A control system for a DC/DC converter, comprising a comparator that compares the values and generates a binary signal as a duty control signal for turning on and off a switch in the converter main body.