JP2003284328A - DC-DC converter current detection method and DC-DC converter using the method - Google Patents

Abstract

[PROBLEMS] To provide a current detection method of a DC / DC converter for performing current detection using a protection MOSFET which is always switched on, and a DC / DC converter thereof. A current detecting method of a DC / DC converter having a protection field-effect transistor (MOSFET) that is always in an ON state and disconnects a circuit when an abnormality occurs.
A predetermined on-gate voltage is applied between the gate and source of the MOSFET, and the drain current Id of the MOSFET is calculated from the voltage difference Vds between the drain and source of the MOSFET at this time.

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 particularly suitable for vehicle mounting.

[0002]

2. Description of the Related Art As a vehicle-mounted DC / DC converter, one proposed by our company (99P00205) shown in FIG. 9 is known.
In FIG. 9, this DC / DC converter is a DC power supply 1
And a first field effect transistor (hereinafter abbreviated as MOSFET) M1 connected to the DC power supply 1 and controlled to be turned on and off.
And is connected in series with this first MOSFET (M1).
Inductor L excited by turning on SFET (M1)
And a capacitor C for charging / smoothing the output current of the inductor L and a diode D2 (commutation) forming a commutation / discharge circuit of energy injected into the inductor L when the first MOSFET (M1) is off. The main circuit can be configured by including the omitted second MOSFET (M2).

Further, as a structure of the protection circuit, a DC power source 1
The voltage of is converted by the DC / DC converter, and the output of this converter is passed through the inductor L to the third MOSFET that is normally ON.
It is supplied to the battery 2 and the load RL via (M3). Also,
It is connected in series with the charging / smoothing capacitor C, and is connected to the ground (0V) through the normally-on fourth MOSFET (M4). Furthermore, when all the MOSFETs (M1 to M4) are off, the DC power supply 1 is connected between the drain and source of the first MOSFET (M1) and between the anode and cathode of the diode D2.
The circuit is configured so that the divided voltage by R21 and R22 is applied.

With this configuration, the on-duty control of the first MOSFET (M1) is controlled by a control circuit (not shown), so that appropriate charging control from the high voltage side battery (DC power source) 1 to the low voltage side battery (battery) 2 can be performed. And the load RL can be driven. Next, the protection circuit configuration will be described.
The third MOSFET (M3), which is always on, is a switch element required for protection when the low voltage side battery 2 is reversely connected, and is normally always on.

The fourth MOSFET (M4) is a switching element necessary for protection when the battery 1 becomes overvoltage, and normally operates always on, but when the voltage of the battery 1 rises abnormally. Turned off. That is, the first MOSF
When ET (M1) and 4th MOSFET (M4) are off, 1st MOSF
The voltage applied to ET (M1) and diode D2 is determined by the voltage dividing resistors R21 and R22 in the steady state, but when the capacitance of the capacitor C is large and the resistance value of the voltage dividing resistors R21 and R22 is large, the voltage of the capacitor C is large. Cannot change suddenly, so the fourth MOSFET (M
When 4) is on, the voltage applied to diode D2 can hardly change. Hence the battery 1
When the voltage rises above the overvoltage detection level, most of this voltage change is added to the switch element of the first MOSFET (M1). To avoid this phenomenon, when the voltage of the battery 1 exceeds the overvoltage detection level, the 4th MOSF
Turn off ET (M4). In this way, in the on-vehicle DC / DC converter, the third MOSFET (M3) and the fourth MOSFET (M4)
Is a circuit element that constitutes an indispensable and essential protection circuit function as a DC / DC converter and is always switched on in a normal control state.

In such a DC / DC converter, current detection is generally performed for the purpose of current control and overcurrent protection. As a method of detecting this current, a resistor Det1 connected in series with the inductor L shown in FIG.
Shunt resistance method or Det2 (Hall element) in the figure
The (2) Hall CT method shown in Fig. 10 and the (3) current transformer (AC-CT, DC-CT) method shown in Fig. 10B are known.

However, in these current detection methods, (1) the shunt resistance method has no problem when the current value handled is small, but the power loss generated in the shunt resistance cannot be ignored when the current value increases. (2) With the Hall CT method, DC current can be easily detected, but it is generally large in size and costly.

(3) With a current transformer (DC-CT, AC-CT) system,
The DC current transformer DC-CT method can detect DC current accurately, but it has the same problems in shape and cost as the Hall CT method. Further, although the AC current transformer AC-CT method is inexpensive, it has a problem that it cannot detect a DC current accurately because it can detect only an AC current. In addition, AC-C
Due to the inductance of T, the switching current change due to the on / off operation of the first MOSFET (M1) causes a voltage jump phenomenon, and the first MOSFET (M1) and commutation diode D2
May adversely affect.

[0009]

As described above, the conventional vehicle-mounted DC / DC converter has the third MOSFET and the fourth MOSF which are always switched on in the normal control state.
The ET is a DC / DC converter that constitutes a compulsory protection function.It also uses the shunt resistance method, Hall CT method, or current transformer (DC-CT) method for current detection for the purpose of current control and overcurrent protection. , AC-CT) methods have problems such as power loss caused by shunt resistance at large current, large shape and cost, and switching noise.

The present invention has been made in view of the above points, and an object thereof is to solve the above-mentioned problems by providing DC / DC
To provide a DC / DC converter using the current detection method of a DC / DC converter that can perform current detection by using a MOSFET for protection that is always required to be switched on as a converter. is there.

[0011]

In order to achieve the above object, a DC field-effect transistor (MOSFET) that is always on and has a protective field-effect transistor (MOSFET) that disconnects the circuit when an abnormality occurs
A method for detecting the current of a DC converter, in which a predetermined on-gate voltage is applied between the gate and source of the MOSFET,
At this time, the drain current of the MOSFET is calculated from the voltage difference between the drain and the source of the MOSFET.

According to this method, when a predetermined on-gate voltage is applied between the gate and source of the MOSFET,
The MOSFET is in the ON state and in this ON state the MOSFET is
Can be regarded as a resistance element. This on resistance value is
It has an on-resistance value within a certain range determined by the MOSFET. Therefore, the on-resistance value can be known by measuring the on-resistance value of the MOSFET with a predetermined on-gate voltage in advance, and the on-resistance value can be obtained by dividing the voltage difference between the drain and source of the MOSFET by the on-resistance value. The drain current of the MOSFET can be obtained.

First MOSFET for controlling on / off of DC power supply
And an inductor that is connected in series with this first MOSFET and is excited by an on-voltage, and the output current of this inductor is charged.
In a DC / DC converter including a smoothing capacitor and a diode or a second MOSFET that forms a commutation / emission circuit of energy injected into the inductor when the first MOSFET is off, in a series with an output terminal via an inductor Third MOSFET connected, fourth MOSFET connecting charging / smoothing capacity to power supply 0V, and third MOSFET or fourth MOSF
ET or current detection means for detecting a current from the drain-source voltage difference when the third MOSFET and the fourth MOSFET are conducting.

The current detecting means applies a predetermined on-gate voltage to the MOSFET between the gate and the source, and the voltage difference between the drain and the source at this time is leveled to a predetermined reference potential by a level shift amplifier. The conduction current of the MOSFET can be obtained by shifting. With such a configuration, a predetermined on-gate voltage is applied between the gate and the source to the protection switching element, the third MOSFET, and the fourth MOSFET that are always on. In this state, the third MOSFET and the fourth MOSFET are in the state of resistance elements, and the drain current of the MOSFET can be obtained by measuring the drain-source voltage difference of the MOSFET at this time and dividing by the ON resistance value. it can.

In particular, by measuring the drain-source voltage of the MOSFET using a level shift amplifier, the MOSF for measuring the gain of the level shift amplifier is measured.
By selecting so that it is inversely proportional to the on-resistance value of ET,
The output voltage of the level shift amplifier can be an output voltage proportional to the drain current of the MOSFET at a predetermined reference potential, for example, a potential unified with the power source 0V.

Further, the current detecting means measures the current.
It has a temperature sensor arranged in the vicinity of the MOSFET and a gain adjusting circuit for adjusting the gain of the level shift amplifier by the signal from this temperature sensor, and when the temperature of this temperature sensor rises, the overall gain is lowered, This overall gain can be increased when the temperature drops. Further, the temperature sensor of the MOSFET of the current detecting means can be configured by using a thermistor having a positive temperature characteristic with respect to temperature or a thermistor having a negative temperature characteristic.

With this configuration, the switch element (MOSFET)
The temperature dependence of the on resistance of the switch increases as the temperature rises, and the entire gain is corrected by the gain adjustment circuit that is added to the level shift amplifier using a thermistor that has a positive or negative temperature characteristic. It can be corrected including the temperature rise. Further, the current detecting means can have a filter circuit for filtering the detected current.

With this configuration, the drain-source voltage of the MOSFET can be divided by the on-resistance to detect the drain current of the MOSFET as an instantaneous value. However, the influence of the differential waveform due to the inductance component of the lead wire of the MOSFET circuit element can be filtered. It can be removed by the circuit.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a DC / DC converter according to the present invention will be described in detail based on an application example to a DC / DC converter suitable for vehicle mounting. FIG. 1 is a block circuit diagram of a DC / DC converter according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a level shift amplifier according to an embodiment, and FIG. 3 is a diagram showing an output current of a DC / DC converter and a capacitor C. FIG. 4 is a circuit diagram of a level shift amplifier having temperature correction means, FIG. 5 and FIG. 6 are temperature correction circuit diagrams according to one embodiment, and FIG. 7 is a detected current. 8 is a characteristic circuit diagram of the detected current, and the same members corresponding to FIGS. 9 and 10 are designated by the same reference numerals. (Embodiment 1) A field effect transistor (MOSFET) for protection that is normally on and disconnects a circuit when an abnormality occurs
A method for detecting current in a DC / DC converter having:
A predetermined on-gate voltage is applied between the gate and source of the SFET, and the drain current Id of the MOSFET is calculated from the voltage difference Vds between the drain and source of the MOSFET at this time.

According to this method, when a predetermined on-gate voltage is applied between the gate and source of the MOSFET,
The MOSFET is in the ON state and in this ON state the MOSFET is
Can be regarded as a resistance element. This on resistance value Ron
Has an on-resistance value Ron within a certain range determined by the MOSFET. Therefore, by measuring the on-resistance value Ron of the MOSFET in advance with the predetermined on-gate voltage, the on-resistance value
The Ron can be known, and the drain current Id (= Vds / Ron) of the MOSFET can be obtained by dividing the drain-source voltage difference Vds of the MOSFET by the ON resistance value Ron. (Embodiment 2) In FIG. 1, the DC / DC converter is
A first MOSFET (M1) for controlling ON / OFF of the DC power supply 1, an inductor L connected in series with the first MOSFET (M1) and excited by an ON voltage, and a capacitor C for charging / smoothing the output current of the inductor L. And a diode D2 or a second MOSFET (M2) that forms a commutation / release circuit of the energy injected into the inductor L when the first MOSFET (M1) is off, and is connected in series to the output terminal via the inductor L. 3rd MO
The SFET (M3), the fourth MOSFET that connects the charging / smoothing capacity C to the power source 0V, and the drain-source voltage difference Vds when the third MOSFET, the fourth MOSFET, or the third MOSFET and the fourth MOSFET (M4) are conductive. And a current detection unit 3 that detects Id.

The current detecting means 3 applies a predetermined on-gate voltage Vgson between the gate and the source of the MOSFET (third MOSFET (M3) and fourth MOSFET (M4)),
The drain-source voltage difference Vds at this time can be level-shifted to a predetermined reference potential (for example, 0V) by the level shift amplifier G1 to obtain the conduction current Id of the MOSFET.

With such a structure, the switching element for protection, the third MOSFET (M3) and the fourth MOSFET (M
Apply the predetermined on-gate voltage Vgson between gate and source in 4). In this state, the third MOSFET (M3) and the fourth MOSFET (M4) are in the resistance element state, and the drain-source voltage difference Vds3, V of the MOSFETs (M3), (M4) at this time is
The drain currents Id3 and Id4 of the MOSFETs (M3) and (M4) can be obtained by measuring ds4 and dividing by the ON resistance values Ron3 and Ron4.

In particular, the drains of the MOSFETs (M3), (M4)
Level shift amplifier G1 for measurement of source-to-source voltage Vds3, Vds4
The gain of the level shift amplifier G1 is measured by using the ON resistance value Ro of the MOSFET (M3), (M4) to be measured.
The output voltage Vo-j (Vo-3, Vo-4) of the level shift amplifier G1 is selected so as to be inversely proportional to n3, Ron4, so that the output voltage Vo-j (Vo-3, Vo-4) of the level shift amplifier G1 is the same as that of the standard voltage of 0V. It is possible to obtain output voltages Vo-3 and Vo-4 proportional to the drain currents Id3 and Id4 of the MOSFETs (M3) and (M4).
By converting Vo-3 and Vo-4 with a predetermined coefficient, the drain currents Id3 and Id4 can be read.

[0024]

Embodiment (Embodiment 1) Referring to FIG.
The level shift amplifier G1 constituting the
A differential amplifier circuit should be configured with a pair of resistors R1 and R2, and the other terminal of the resistor R2 on the input terminal (+) side of the operational amplifier Q1 should be connected to a reference potential, for example, 0 V power supply. You can

With this configuration, the level shift amplifier G1
The voltage Vd (drain voltage of the MOSFET (M3, M4)), Vs (source voltage of the MOSFET (M3, M4)) applied to the input terminals Vd, Vs of the differential voltage (Vd-Vs) is 0V as the reference potential. Output voltage Vo-j (Vo-3,
Vo-4) can be output. As described in the first embodiment, the MOSFET can be regarded as a resistance element in the ON state. MOSFET drain voltage is Vd and source voltage is Vd
s, Ron is the on-resistance value, the drain-source voltage difference Vds when the drain current of this MOSFET is Id is

[0026]

[Formula 1] Vds = Vd−Vs = Ron × Id ... (1) Therefore, the drain current Id can be obtained by detecting the drain-source voltage difference Vds and dividing this voltage difference Vds by the ON resistance value Ron.

The input / output characteristic of the level shift amplifier G1 shown in FIG. 2 can be expressed by the equation (2).

[0028]

[Formula 2] Vo-j = (R2 / R1) (Vd−Vs) (2) Therefore, the resistance ratio indicating the gain of the level shift amplifier G1 is, for example,

[0029]

[Equation 3] (R2 / R1) = (1Ω / Ron) ············· (3), the drain current Id can be obtained from the drain-source voltage Vds (= Vd-Vs) of the MOSFET. it can.

[0030]

[Equation 4] Id = (Vd−Vs) / Ron = Vo-j (A) (4) That is, under the coefficient condition of the equation (3), the level shift amplifier G1
The output voltage of can be read as it is with the output current of the MOSFET (unit is ampere A).

FIG. 3 shows an embodiment of the current detecting means 3.
In FIG. 3, the current detection means 3 (3A) in the illustrated example has two types of level shift amplifiers G1-3 and G1-4, and the level shift amplifier G1-3 has a drain voltage Vd3 of the third MOSFET (M3). And source voltage Vs3 are input, and this level shift amplifier G1
The gain of -3 is, for example, the third MOSFET (M3) expressed by the equation (3).
When selecting the resistance ratio (R2 / R1) that satisfies the Ron-3 relationship of
The output voltage Vo-3 can detect that a current obtained by replacing the detected voltage Vo-3 in amperes is flowing through the third MOSFET (M3). The level shift amplifier G1-4 has a fourth MOSFET (M
The drain voltage Vd4 and source voltage Vs4 of 4) are input,
If the gain of this level shift amplifier G1-4 is selected as the resistance ratio (R2 / R1) that satisfies the relationship of Ron-4 of the fourth MOSFET (M4) expressed by the equation (3), the output voltage Vo-4 becomes Detected voltage
The current obtained by replacing Vo-4 in amperes is the fourth MOSFET (M4).
Can be detected. Both output voltage Vo-
The sum (Vo-L) of 3, Vo-4 can be detected as the current flowing in the inductor L.

That is, the current Id detected by the third MOSFET (M3)
3 (Vo-3) indicates the output current of the DC / DC converter,
The current Id4 (Vo-4) detected by the SFET (M4) indicates the receiving / discharging current to the capacitance C, and the current Id3 (Vo-3) detected by the third MOSFET (M3) and the fourth MOSFET (M4 ) Current detected by Id4
The sum of (Vo-4) can be detected as a current IL flowing through the inductor L. (Embodiment 2) Further, the current detecting means 3 includes a temperature sensor (R) arranged near the MOSFET (M3, M4) for measuring the current Id.
T) and a gain adjustment circuit G2-T that adjusts the gain of the level shift amplifier G1 by the signal from this temperature sensor (RT),
It is possible to reduce the overall gain when the temperature T 1 of the temperature sensor (RT) rises, and increase the overall gain when the temperature T 1 decreases.

The temperature sensor (RT) of the MOSFET of the current detecting means 3 is a thermistor (RT-2, RT-4) having a positive temperature characteristic with respect to the temperature T or a thermistor having a negative temperature characteristic. It can be configured using (RT-1, RT-3). With this configuration, the ON resistance Ron of the switching element (MOSFET) is
Is a thermistor (RT-2, RT-4), (RT-1, RT-4) that has a positive or negative temperature characteristic with temperature dependence that increases with increasing temperature T.
By using (3) to correct the overall gain with the gain adjustment circuit G2-T added to the level shift amplifier G1, it is possible to perform the correction including the self-temperature rise of the switch element.

In FIG. 4, the current detecting means 3 having the temperature correcting means is, for example, the operational amplifier Q1 described in the first embodiment.
Level shift amplifier G1 consisting of resistors R1 and R2 paired with
Can be configured by adding a gain adjusting circuit G2-T to. This gain adjustment circuit G2-T is, for example, a fixed resistor R3, a fixed resistor R4 and a thermistor (RT1) shown in (A) of FIG.
By configuring the gain adjusting circuit G2-T with the voltage dividing circuit of and, the thermistor with negative temperature characteristics with respect to the temperature T
When the temperature T of the temperature sensor (RT) rises at (RT1), the entire gain can be lowered and corrected. Also the temperature
The thermistor (RT-2) that has a positive temperature characteristic with respect to T has the fixed resistor R5 and thermistor (RT2) shown in Fig. 5B,
The same correction can be performed by configuring the gain adjusting circuit G2-T with the voltage dividing circuit of the fixed resistor R6.

Further, in FIG. 6, the gain adjusting circuit G2-T
The gain adjusting circuit G2-T can be configured by inserting a voltage dividing circuit into the negative feedback circuit of the operational amplifier Q2. In (A) of FIG. 6, the voltage divided by the fixed resistor R8, thermistor (RT3), and fixed resistor R7 from the output of the operational amplifier Q2 is equal to the output signal of the level shift amplifier G1. On the other hand, by using the thermistor (RT3) having a negative temperature characteristic, it is possible to correct by lowering the overall gain when the temperature T 1 of the temperature sensor (RT) rises.
In addition, by using the thermistor (RT4) having a positive temperature characteristic with respect to the temperature T by the configuration of FIG. 6B, the overall gain when the temperature T of the temperature sensor (RT) rises Can be corrected by lowering.

In the above description, the temperature Id (Id3, Id4) detected from the drain-source voltage of each MOSFET (M3, M4) is temperature-corrected.
When the temperature of (3, M4) is not so different, the result of adding the currents Id3 and Id4 (for example, only one gain correction circuit by temperature may be provided for the output IL of FIG. 3. Further, In the description, the temperature sensor shows an example in which the detection gain is corrected by utilizing the temperature characteristic of the resistance value of the resistor, but for example, the temperature information is obtained by an infrared sensor or the like, and the current detection value The temperature information may be obtained by another method such as the correction of the gain to perform the correction.

Further, in FIG. 7, the current detecting means 3 is
A filter circuit for filtering the detection current Id can be included. The difference from FIG. 3 is that the current IL is filtered,
The point is that a filter circuit (G3-F) is added. With such a configuration, when a current is detected using the current detecting means 3 having no averaging means G3-F, for example, the current IL flowing through the inductor L shown in FIG. 1 has an actual value indicated by the solid line shown in FIG. On the other hand, the detected value is shown by the dotted line.

This phenomenon is caused by the fact that the drain voltage Vd and source voltage Vs of the MOSFET input to the level shift amplifier of the current detecting means 3 have an inductance L0 of the lead wire of the MOSFET.
This is because there is a detection error of L0 × (di / dt).
This detection error is a + error when the current IL increases.
It has Va and has a negative error Vb when the current IL decreases. Since the errors Va and Vb in the dotted line have the relationship of equation (5),

[0039]

(5) Va × ta = Vb × tb (5) As for the average value of the detection current IL, the waveform of the solid line and the waveform of the dotted line can be the same waveform. That is, for example, an accurate average value can be obtained by a low-pass filter G3-F such as a simple first-order lag filter formed of a resistor and a capacitor.

[0040]

As is apparent from the above description, according to the present invention, the drain-source voltage is used by using the protection MOSFET which is always required to be switched on and is essential as a DC / DC converter. Since it is possible to calculate the current by using the current amplifier, it is not necessary to add a new component to the part where a large current flows, and there is no increase in power loss or increase in inductance, and it has an operational amplifier, fixed resistance, and temperature coefficient. Current can be detected at low cost by adding only a resistor
A current detection method for a DC / DC converter and a DC / DC converter using the method can be provided.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of a DC / DC converter according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a level shift amplifier according to an embodiment.

[Figure 3] Output current of DC / DC converter and reception of capacity C
Arithmetic circuit diagram for computing discharge current and current flowing in inductor L

FIG. 4 is a circuit diagram of a level shift amplifier having temperature correction means.

FIG. 5 is a temperature correction circuit diagram according to one embodiment.

FIG. 6 is a temperature correction circuit diagram according to another embodiment.

FIG. 7 is a filter circuit diagram for filtering a detection current.

FIG. 8 is a characteristic waveform diagram of detected current

FIG. 9 is a block circuit diagram of a DC / DC converter according to a conventional technique.

FIG. 10 is a block circuit diagram of a DC / DC converter having current detection means according to a conventional technique.

[Explanation of symbols]

1 DC power supply 2 batteries 3 Current detection means M1 to M4 MOSFET L inductor C capacity RL load Vd, Vd3, Vd4 drain voltage Vs, Vs3, Vs4 Source voltage R21, R22 partial pressure resistance G1, G1-3, G1-4 Level shift amplifier Vo-3, V-4, Vo-L, VTj detection output R1 to R10 resistance RT1 to RT4 temperature sensor G2-T temperature adjustment Q1, Q2 operational amplifier G3-F Averaging means D2 commutation diode Det1, Det2, Det3 Current detection means

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Fumito Takahashi             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. (72) Inventor Takayuki Atsuta             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. F-term (reference) 5H410 BB04 CC02 DD02 EA11 EB01                       EB37 FF05 FF25 GG05 KK05                       LL06                 5H730 BB13 BB57 DD04 EE13 FD37                       FD57 FD61 FF01 FG01 XX03                       XX15 XX23 XX35 XX42

Claims (6)

[Claims] 1. A field effect transistor for protection (hereinafter referred to as MOSF) which is normally in an on state and disconnects a circuit when an abnormality occurs.
(Hereinafter abbreviated as ET) is a method for detecting current in a DC / DC converter, in which a predetermined on-gate voltage is applied between the gate and source of the MOSFET, and the voltage difference between the drain and source of the MOSFET at this time A method for detecting a current in a DC / DC converter, comprising calculating a drain current of the MOSFET. 2. A first MOSFET for controlling on / off of a DC power supply.
And an inductor that is connected in series with this first MOSFET and is excited by an on-voltage, and the output current of this inductor is charged.
A DC / DC converter comprising a capacitor for smoothing and a diode or a second MOSFET that forms a commutation / release circuit of energy injected into the inductor when the first MOSFET is off, in which the output terminal is connected via the inductor. A third MOSFET connected in series, a fourth MOSFET connecting the charging / smoothing capacity to a power source of 0 V, and a current from the drain-source voltage difference when the third MOSFET or the fourth MOSFET or the third MOSFET and the fourth MOSFET are conductive. Current detecting means for detecting,
A DC / DC converter characterized by comprising: 3. The DC / DC converter according to claim 2, wherein the current detection means applies a predetermined on-gate voltage to the MOSFET between the gate and the source, and the drain-source voltage difference at this time is applied. A DC / DC converter characterized in that a conduction current of the MOSFET is obtained by level-shifting to a predetermined reference potential with a level shift amplifier. 4. The DC / DC converter according to claim 2, wherein the current detecting means includes a temperature sensor, and a gain adjusting circuit that adjusts the gain of the level shift amplifier based on a signal from the temperature sensor. A DC / DC converter characterized in that, when the temperature of the temperature sensor rises, the overall gain is reduced, and when the temperature drops, the overall gain is increased. 5. The DC / DC converter according to claim 4, wherein the temperature sensor of the MOSFET of the current detecting means uses a thermistor having a positive temperature characteristic with respect to temperature or a thermistor having a negative temperature characteristic. , DC / DC converter characterized by the following. 6. The DC / DC converter according to any one of claims 2 to 5, wherein the current detecting means has a filter circuit for filtering the detected current. .