JPH0866024A - Control circuit for dc/dc converter - Google Patents

Abstract

PURPOSE: To reduce the proportional gain sufficiently in PI control by controlling the input to a switching element drive circuit depending on the difference of output between a second secondary winding and an error amplifier circuit in the proportional integration control so that fluctuation in the DC output voltage has no effect on the input to the switching element. CONSTITUTION: In the proportional integration control, input to the drive circuit 3 for a switching element 2 is controlled depending on the difference between the output from an error amplifier circuit, being fed with an input depending on the output from the first secondary winding of an output transformer, and the output from the second secondary winding of the output transformer 1. Since a mechanism for producing a drive signal based on the differential voltage V between the DC output voltage P5 from a winding 20 dedicated for constant voltage and the output voltage from the error amplifier circuit is provided, the control circuit can decrease the proportional gain below 0 dB while performing PI control and means for imparting margin in the phase can be eliminated along with the adverse effect thereof.

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 control circuit, and more particularly to a control circuit for error-amplifying an output voltage of a DC / DC converter to control a switching element.

[0002]

2. Description of the Related Art FIG. 6 shows a general DC / DC converter control circuit in which a flyback converter is used as an example of a main circuit. Reference numeral 1 is a high-frequency transformer for supplying a DC input to another, 2 is a switching element for switching a DC input voltage so that power can be supplied to a load by the high-frequency transformer, and 3 is a drive circuit for driving the switching element 2. For pulse width modulation integrated circuit. OUT1, O
The UTs 2 are output circuits that are insulated from each other and each output DC power. 4, 5 are rectifier diodes, 6, 7
Is a smoothing capacitor and constitutes a rectifier circuit, and the output is a DC voltage. In the case of the output circuit OUT1, further inductor 8
And the capacitor 9 form a low-pass filter. 1
Reference numerals 0 and 11 denote resistors that divide the DC output voltage of the output circuit OUT1. Shunt regulator 1 with error amplification circuit
2 and the resistor 13 and the capacitor 14 to perform proportional-plus-integral control (hereinafter referred to as PI control). Reference numeral 15 is a resistor for obtaining a current for operating the shunt regulator 12,
16 is a photocoupler for transmitting a drive signal to the drive circuit 3,
Reference numeral 17 is a resistor for limiting the current flowing through the photocoupler 16, 18 is a resistor inside the pulse width modulation integrated circuit for power supply corresponding to the driving circuit, 19 is a capacitor, and the resistor 18 and the capacitor 19 make a low-pass filter. Is configured.

The operation of the conventional DC / DC converter control circuit will be described.

The main circuit stores a predetermined DC power (DC input voltage) applied between the terminals P and N, which are input terminals, in the high frequency transformer 1 while the switching element 2 is ON, and the switching element 2 Is turned off, the power accumulated in the high frequency transformer 1 causes OUT1, OUT
A voltage is generated in each winding on the second side. The voltage is converted into a DC voltage by a rectifying circuit including rectifying diodes 4 and 5 and smoothing capacitors 6 and 7. In particular, in the OUT1 winding, the high-frequency component is attenuated by the low-pass filter composed of the inductor 8 and the capacitor 9 to provide a DC output voltage.

The DC output voltage of the output circuit OUT1 is divided by the resistors 10 and 11 which are voltage dividing resistors to determine the divided voltage. When the voltage is higher than the reference voltage of the shunt regulator 12, the output voltage of the shunt regulator 12 becomes low and the current flowing through the resistor 17 and the issuing side of the photocoupler 16 due to the potential difference between the DC output voltage of the output circuit OUT1 and the shunt regulator. growing.
This current is photo-insulated by the photocoupler 16, the photo-isolated current is processed through the low-pass filter composed of the resistor 18 and the capacitor 19 so that the high-frequency component is attenuated, and is transmitted to the drive circuit 3. Feedback is applied to the switching element 2. As a result, the duty ratio of the switching element 2 decreases, and the DC output voltage of the output circuits OUT1 and OUT2 decreases.

On the other hand, the divided voltage is the shunt regulator 1
Shunt regulator 1 when lower than the reference voltage of 2
2 becomes high and the potential difference between the DC output voltage OUT1 and the output voltage of the shunt regulator 12 causes the resistor 1
7 and the current flowing to the light emitting side of the photocoupler 16 becomes small. This current is optically isolated by the photocoupler 16, transmitted to the drive circuit 3 through the low-pass filter, fed back to the switching element 2, the duty ratio of the switching element increases, and the DC output voltage of the output circuits OUT1 and OUT2 becomes To increase.

In this way, one of the plurality of DC powers on the output side is used to feed back the switching element 2 to change the duty ratio appropriately, and the DC output voltage of the plurality of windings on the output side is made constant. The voltage maintaining means is used. Therefore, the DC output voltages OUT1 and OUT2 can be kept constant even if the load of the main circuit fluctuates or the DC input voltage changes. Further, the DC output voltage of the main circuit 1 can be set to a desired voltage value by setting the resistors 10 and 11 to appropriate resistance values.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the C / DC converter control circuit, in order to obtain the drive signal from the difference voltage between the DC output voltage and the output voltage of the error amplifier,
The gain of the PI control performed by the error amplification circuit never falls below 0 dB.

In FIG. 7, resistors 10 and 13 are R10 and R13, respectively, and a capacitor 14 is 14,
The DC output voltage is P5, and the difference voltage between the DC output voltage and the output voltage of the error amplifier circuit is V. When the transfer function from P5 to V is calculated,

[0010]

[Equation 1]

[0011] FIG. 8 is a Bode diagram of the equation (1), and it can be seen that PI control is performed. From FIG. 8, the value of the proportional gain is 0 dB even if the value of R13 is 0, and cannot be less than that.

When the main circuit operation is in continuous mode, the gain is -40 dB / d after the break frequency of the main circuit.
It is attenuated by the slope of ec and the phase is delayed by -180 degrees. Since the gain of PI control is constant and there is no characteristic for returning the phase, conventionally, a means called phase advance compensation has been used because it has a phase margin at a point (crossover frequency) where the open loop transfer function crosses 0 dB. However, this causes the phase to return and the gain to increase, requiring the low-pass filter composed of the resistor 18 and the capacitor 19 of FIG. 7, or increasing the value of the capacitor 19 to break the low-pass filter. Unless the point frequency is made small and the gain is made low at a high frequency, there are adverse effects such as weakening against noise.

On the other hand, when the main circuit operation is in the intermittent mode, the gain is attenuated substantially uniformly at -20 dB / dec, so that the PI control gain is constant at the cross frequency, that is, if the phase lag is 0 degree. Can have a phase margin.
However, in the conventional PI control, the gain is 0 dB at high frequency.
Can't decay below. Therefore, in order to reduce the gain at high frequencies, a means for attenuating the gain is used by providing a low-pass filter (resistor 18 and capacitor 19) in front of the drive circuit. In this case, since the break frequency of the low-pass filter is made smaller than the crossover frequency to attenuate the gain, the characteristic of the control circuit becomes the characteristic of the low-pass filter after the break frequency. The low-pass filter is a first-order lag control, and the phase becomes constant with a delay of 90 degrees without taking a constant gain at a frequency equal to or higher than the break frequency as seen in the PI control. Therefore, since the main circuit is also delayed by 90 degrees, there is an adverse effect such as insufficient phase margin.

It is therefore an object of the present invention to provide a means for reducing the proportional gain of PI control to 0 dB or less so as to have a phase margin, and a DC / DC converter control circuit for eliminating the adverse effect of the means.

On the other hand, Japanese Unexamined Patent Publication No. 2-201614 describes that the circuit gain is reduced to stabilize the circuit operation. However, since the proportional control is performed in this method, the steady gain cannot be made high and the disturbance is disturbed. I was weak. Japanese Patent Laid-Open No. 3-4308 also describes a measure for stabilizing the output voltage, but this has a different circuit configuration when the output voltage is negative, and PI control is not performed. Further, in JP-B-61-32786, the control is performed by the difference voltage between the output of another power supply and the output of the error amplification circuit.
The purpose is to make the output voltage variable.
The difference voltage between the voltage being fed back and the error amplifier circuit is still affected by the output voltage. There is no substitute for controlling by the difference voltage between the voltage affected by the output voltage and the output of the error amplifier circuit only by adding the voltage of another power supply to the output voltage. Moreover, PI control is not performed.

A first aspect of the present invention provides a DC / DC converter control circuit which can prevent the input of a switching element drive circuit from being affected by fluctuations in a DC output voltage and can sufficiently reduce a proportional gain in PI control. With the goal.

The second invention is the output of the constant voltage circuit and the PI.
An object of the present invention is to obtain a DC / DC converter control circuit capable of performing a control according to a difference between outputs of an error amplification circuit that is performing control and sufficiently reducing a proportional gain in PI control.

According to a third aspect of the present invention, the proportional gain in the PI control is made sufficiently small by performing control according to the difference between the output of the constant voltage circuit which is a shunt regulator and the output of the error amplifying circuit which performs the PI control. DC / DC capable
The purpose is to obtain a converter control circuit.

According to a fourth aspect of the invention, the difference between the output of the voltage dividing circuit for dividing the DC output voltage and the output of the error amplifying circuit for performing PI control that maintains a predetermined voltage relationship with respect to the divided voltage of the voltage dividing circuit. It is an object of the present invention to obtain a DC / DC converter control circuit capable of performing appropriate control and sufficiently reducing the proportional gain in PI control.

A fifth object of the present invention is to obtain a DC / DC converter control circuit having a concrete structure excellent in practical performance capable of sufficiently reducing the proportional gain in PI control.

[0021]

According to a first aspect of the present invention, there is provided an output of an error amplifier circuit which is input according to an output of a first secondary winding of an output transformer and a second output of an output transformer. The proportional-integral control is performed by inputting to the drive circuit of the switching element according to the difference from the output of the next winding.

According to a second aspect of the present invention, proportional-integral control is performed by inputting to the drive circuit of the switching element according to the difference between the output of the error amplification circuit and the output of the constant voltage circuit.

According to a third aspect of the present invention, proportional-integral control is performed by inputting to a switching element drive circuit in accordance with the difference between the output of the error amplification circuit and the output of a constant voltage circuit including a shunt regulator.

According to a fourth aspect of the present invention, proportional-integral control is performed by inputting to the drive circuit of the switching element according to the difference between the output of the voltage dividing circuit and the output of the error amplifying circuit.

A fifth aspect of the present invention provides a specific configuration in which proportional-integral control is performed by inputting to a drive circuit of a switching element according to the difference between the output of the voltage dividing circuit and the output of the error amplifying circuit.

[0026]

In the DC / DC converter control circuit of the present invention, the difference voltage between the DC output voltage of the constant voltage winding and the output voltage of the error amplification circuit, or the output voltage of the constant voltage circuit and the output of the error amplification circuit. The control circuit has a mechanism for obtaining a drive signal by the difference voltage with the voltage and the difference voltage between the output voltage of the error amplification circuit and the voltage that is constant according to the characteristics of the error amplification circuit. 0d
It can be made smaller than B, and the means for providing a phase margin and the adverse effect of the means can be eliminated.

[0027]

【Example】

Example 1 FIG. 1 shows a main circuit using a flyback converter. Reference numerals 2 to 17 are the same as in the conventional example. Here, 1 is a high frequency transformer having three secondary windings, which is a transformer for output, has first, second and third secondary windings, and serves as a third secondary winding. It has a constant voltage winding 20. 21 is a rectifying diode, 22 is a smoothing capacitor, 23 is an inductor, and 24 is a capacitor. The inductor 23 and the capacitor 24 form a low-pass filter that passes only a very low frequency, and the output of this low-pass filter is connected to one end of the resistor 15 and the resistor 17. The other end of the resistor 15 is connected to the cathode side of the shunt regulator 12, and the other end of the resistor 17 is connected to the light emitting side anode terminal of the photocoupler 16. The anode terminal of the shunt regulator 12 is common to the ground of the DC output voltage and the DC output voltage of the constant voltage dedicated winding together with one end of the resistor 11.

In this embodiment, the operation of the voltage maintaining means for keeping the DC output at a constant voltage is the same as that of the conventional example, but one of the secondary windings of the high frequency transformer 1 is the constant voltage dedicated winding 20, Resistor 17 which is a drive signal and photo coupler 1
The current flowing to the light emitting side of 6 is generated by the potential difference between the output voltage of the low-pass filter formed by the inductor 23 and the capacitor 24 and the cathode terminal voltage of the shunt regulator 12 (output voltage of the error amplification circuit).

In FIG. 1, the DC output voltage is P5, the difference voltage between the DC output voltage of the constant voltage dedicated winding 20 and the output voltage of the error amplification circuit is V, and the resistor 10 is R10 and the resistor 13 is R.
If the capacitor 13 and the capacitor 14 are C14, the transfer function from P5 to V is given by the formula (2) because the DC output voltage of the constant voltage dedicated winding 20 does not change with frequency.

[0030]

[Equation 2]

FIG. 2 is a gain diagram showing the equation (2). As shown in FIG. 2, the proportional gain of the PI control can take a value of 0 dB or less when the values of the resistors 10 and 13 are appropriate. As a result, the drive signal is not directly affected by the fluctuation of the DC output voltage, and the gain of the control circuit unit can be made smaller than 0 dB. Since the DC / DC converter control circuit in this embodiment is provided with a winding for exclusive use of a constant voltage and a mechanism for obtaining a drive signal by the difference voltage between its DC output voltage and the output voltage of the error amplification circuit, the control circuit is a PI. While performing the control, the proportional gain can be made smaller than 0 dB, and various means for providing a phase margin in the open loop transfer function and the adverse effects of the means can be eliminated.

EXAMPLE 2 Main circuit of FIG. 3 (not shown) and 3 and 10 to 17
Is the same as the above-mentioned conventional example. 27, 28 and 29 are resistors, and 30 is a shunt regulator. Resistor 27,
The resistor 28, the resistor 29, and the shunt regulator 30 form a constant voltage circuit. The constant voltage circuit passes the DC output voltage through the resistor 27 and then the resistor 2 having an appropriate value.
The voltage is divided by 8 and the resistor 29, and the divided voltage is input to the reference terminal of the shunt regulator 30. The anode terminal of the shunt regulator 30 is common with the ground of the DC output voltage, and the cathode terminals thereof are the resistors 27 and 28.
Is connected to one end of the constant voltage and has a constant voltage, which is the output of the constant voltage circuit. The output of this voltage-regulating circuit and the resistor 15,
One end of the resistor 17 is connected, and the other end of the resistor 15 is connected to the cathode terminal of the shunt regulator 12 and the resistor 1
The other end of 7 is connected to the light emitting side anode terminal on the photo coupler 16 side.

In this embodiment, the operation of the voltage maintaining means for keeping the DC output voltage at a constant voltage is the same as that of the conventional example, but the drive signal is the output voltage of the constant voltage circuit and the cathode terminal voltage of the shunt regulator 12 ( It is obtained by the potential difference of the output voltage of the error amplifier circuit).

Therefore, as in the first embodiment, the proportional gain of the PI control can take a value of 0 dB or less when the values of the resistors 10 and 13 are made appropriate. The constant voltage circuit using this shunt regulator can be realized by a shunt regulator and three resistors, and the design is simpler than the provision of the constant voltage dedicated winding of the first embodiment. DC / DC of this embodiment
The converter control circuit includes a constant voltage circuit and a mechanism for obtaining a drive signal by the difference voltage between the output voltage of the constant voltage circuit and the output voltage of the error amplification circuit. Therefore, the control circuit performs proportional control while performing PI control. The gain can be made smaller than 0 dB, and various means for providing a phase margin in the open loop transfer function and the adverse effects of the means can be eliminated.

EXAMPLE 3 Main circuit (not shown) of FIG. 4 and 3 and 11 to 17
Is the same as the above-mentioned conventional example. Reference numerals 31 to 32 are resistors. The resistors 31, 32, and 11 are set to appropriate values to divide the DC output voltage into two levels. As shown in the figure, the divided voltages are V1 and V2. V1 is a shunt regulator 1 via a resistor 13 and a capacitor 14.
2 and the cathode terminal of the shunt regulator 12 in parallel with V1 and the resistor 15
And the resistor 17 and the light emitting side of the photocoupler 16 are connected in parallel. The voltage V2 is input to the reference terminal of the shunt regulator 12. The anode terminal of the shunt regulator 12 is common with the other end of the resistor 11 and the ground of the DC output voltage.

In this embodiment, the operation of the voltage maintaining means for keeping the DC output voltage at a constant voltage is the same as that of the conventional example, but V1 and V2 are maintained at a constant voltage due to the characteristic of the shunt regulator, so that The drive signal is obtained from the potential difference between the voltage and the cathode terminal voltage of the shunt regulator (output voltage of the error amplifier circuit).

In FIG. 4, resistor 11, resistor 13,
The resistor 17, the resistor 31, and the resistor 32 are respectively R13 and R
17, R31, and the capacitor 14 is C14. Assuming that the DC output voltage is P5 and the voltage across R17 is V17, and the DC output voltage P5 is 5V, the V2 voltage is
It is 2.5 because it is the reference terminal voltage of the shunt regulator 12. Therefore, R11, R31, R32
Must satisfy the relationship of R31 + R32 = R11. Further, V1 must have a voltage value so that the current flowing on the light emitting side of R17 and the photocoupler 16 is within the control range of the drive circuit 3. Therefore, R11, R31,
If R1 is 98% of DC output voltage, R32 is R3
It has a relationship of 1 = (R32 + R11) * 0.02.

The transfer function from P5 to V17 is

[0039]

(Equation 3)

It becomes FIG. 5 is a gain diagram of the equation (4). As can be seen from FIG. 5, frequency 1 / [(R17 + R13) * C14]
PI control can be realized after [rad]. Since the proportional gain is taken at the frequency before that, the low band gain that does not worsen the steady deviation is set to about dB. R
17 and R31 must satisfy R17 / R31 = 10A / 20. At the same time, R17 is a current limiting resistor on the light emitting side of the photocoupler 16, so it is necessary to take care not to exceed the control range of the drive circuit because it is too large.

By paying attention to the above points, P
The I control gain can be reduced to 0 dB or less. There is no need to use a dedicated winding for constant voltage as in the first embodiment.
It is possible to configure with one shunt regulator for PI control without using another shunt regulator as in the second embodiment.

The DC / DC converter control circuit of this embodiment is provided with a mechanism for obtaining a drive signal by the difference voltage between the voltage that is constant in the characteristics of the error amplification circuit and the output voltage of the error amplification circuit. While performing PI control, the proportional gain can be made smaller than 0 dB, and various means for providing a phase margin in the open loop transfer function and the adverse effects of the means can be eliminated. In addition, the DC / DC converter control circuit of this embodiment is provided with a mechanism for obtaining a drive signal by the difference voltage between the voltage that is constant in the characteristics of the error amplification circuit and the output voltage of the error amplification circuit, and the drive signal is When the gain is AdB, the value R17 of the resistor 17 connected to the light emitting side anode terminal of the photocoupler 16 has a resistance value 10A / 20 times the value R31 of the first voltage dividing resistor 31. , 1 / C14 (R13 + R17) [r
ad] PI control can be realized at a frequency or higher. In addition, the proportional gain in a wide area can be smaller than 0 dB. Therefore,
Various means for providing a phase margin in the open loop transfer function and the adverse effects of the means can be eliminated.

[0043]

According to the first aspect of the invention, the input of the switching element drive circuit can be prevented from being affected by the fluctuation of the DC output voltage, and the proportional gain in the PI control can be sufficiently reduced. A / DC converter control circuit can be obtained.

According to the second aspect of the invention, the input of the switching element drive circuit is changed by changing the DC output voltage by performing control in accordance with the difference between the output of the constant voltage circuit and the output of the error amplification circuit which performs PI control. It is possible to obtain a DC / DC converter control circuit that can be prevented from being affected by the above and can sufficiently reduce the proportional gain in PI control.

According to the third aspect of the invention, the input of the switching element drive circuit is controlled by the direct current by performing control according to the difference between the output of the constant voltage circuit including the shunt regulator and the output of the error amplification circuit for performing PI control. It is possible to obtain a DC / DC converter control circuit which can be prevented from being affected by fluctuations in the output voltage and in which the proportional gain in PI control can be made sufficiently small.

According to the fourth aspect of the invention, the output of the voltage dividing circuit for dividing the DC output voltage and the output of the error amplifying circuit for performing the PI control for maintaining a predetermined voltage relationship with respect to the divided voltage of the voltage dividing circuit. By performing control according to the difference, it is possible to prevent the input of the switching element drive circuit from being affected by the fluctuation of the DC output voltage, and to make the proportional gain in PI control sufficiently small. A control circuit can be obtained.

According to the fifth aspect of the present invention, the input of the switching element drive circuit can be prevented from being affected by the fluctuation of the DC output voltage, and the proportional gain in the PI control can be made sufficiently small. It is possible to obtain a DC / DC converter control circuit having an excellent specific configuration.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a DC / DC converter main circuit and a control circuit according to a first embodiment of the present invention.

FIG. 2 is a gain diagram showing characteristics of the DC / DC converter control circuit according to the first embodiment of the present invention.

FIG. 3 is a circuit diagram showing a DC / DC converter control circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a DC / DC converter control circuit according to a third embodiment of the present invention.

FIG. 5 is a gain diagram showing characteristics of a DC / DC converter control circuit according to a third embodiment of the present invention.

FIG. 6 is a circuit diagram showing a conventional DC / DC converter main circuit and a control circuit.

FIG. 7 is a circuit diagram showing a conventional DC / DC converter control circuit.

FIG. 8 is a gain diagram showing characteristics of a conventional DC / DC converter control circuit.

[Explanation of symbols]

 1 High Frequency Transformer 2 Switching Element 3 Driving Circuit 4 Rectifying Diode 5 Rectifying Diode 6 Smoothing Capacitor 7 Smoothing Capacitor 8 Inductor 9 Capacitor 10 Resistor 11 Resistor 12 Shunt Regulator 13 Resistor 14 Capacitor 15 Resistor 16 Photocoupler 17 Resistor 18 Resistor 19 Capacitor 20 Constant voltage winding 21 Rectifying diode 22 Smoothing capacitor 23 Inductor 24 Capacitor 25 Inductor 26 Capacitor 27 Resistor 28 Resistor 29 Resistor 30 Shunt regulator 31 Resistor 32 Resistor

Claims (5)

[Claims] 1. A switching element operated by a drive signal from a drive circuit, and an output transformer having a primary winding that receives DC power via the switching element,
The transformer includes first and second secondary windings provided in this transformer and an error amplifier circuit that is input according to the output of the first secondary winding. A DC / DC converter control circuit, wherein proportional-integral control is performed by inputting to the drive circuit according to a difference between an output and an output of the error amplification circuit. 2. A switching element operated by a drive signal from a drive circuit, and an output transformer having a primary winding that receives DC power through the switching element,
A secondary winding provided in this transformer, an error amplification circuit that is input according to the output of the secondary winding, and a constant voltage circuit that receives the DC output voltage from the output of the secondary winding as an input And a DC / DC converter control circuit for performing proportional-plus-integral control by inputting to the drive circuit according to a difference between an output of the constant voltage circuit and an output of the error amplification circuit. 3. The DC / DC circuit according to claim 2, wherein the constant voltage circuit is composed of a shunt regulator.
Converter control circuit. 4. A switching element operated by a drive signal from a drive circuit, and an output transformer having a primary winding for receiving DC power via the switching element,
A secondary winding provided in this transformer, a voltage divider circuit that divides a DC output voltage by the output of the secondary winding, and a voltage divider circuit that is input according to the output of the secondary winding. An error amplification circuit that maintains a predetermined voltage relationship with the voltage, and performs proportional-plus-integral control by inputting to the drive circuit according to the difference between the output of the voltage dividing circuit and the output of the error amplification circuit. A characteristic DC / DC converter control circuit. 5. A DC / DC converter control circuit having a DC / DC converter as a main circuit, which performs a switching operation of a switching element according to a drive signal from a drive circuit to transform a DC input voltage to obtain a DC output voltage, First, second and third resistors sequentially connected from the high potential side to the ground side to divide the output voltage;
Of the shunt regulator is connected to the cathode terminal of the shunt regulator via at least one capacitor, and the terminal of the second resistor is connected to the reference terminal of the shunt regulator. An error amplification circuit having an anode terminal common to the ground of the DC output voltage is provided, and the current flowing through the current limiting resistor is switched by the potential difference between the terminal voltage of the first resistor and the cathode terminal voltage of the shunt regulator. A DC / DC converter control circuit, characterized in that the resistance value of the current limiting resistor is sufficiently increased within a control range of the drive circuit while being transmitted to the drive circuit of the element.