JPH07111778A - Dc-dc converter - Google Patents

Abstract

PURPOSE:To provide an on-board power supply that generates a higher voltage than an input voltage, for example an output of about 100 V, using a low- voltage withstanding switching element. CONSTITUTION:A DC-DC converter includes an MOSFET 3 for switching an input DC voltage (VIN) from a source using a switching drive signal applied to a gate (G) and generating an output to a drain (D), a driving circuit 2 controlled by a cyclic rectangular control signal for generating the switching drive signal to the gate (G) of the MOSFET 3, and an inductor with a terminal (d) connected to a diode 5 and a middle tap (f) connected to the drain (D) of the MOSFET 3 for storing energy during an on-time of the MOSFET 3 and feeding the energy to a load 7 during an off-time of the MOSFET 3. In addition, the DC-DC converter includes a diode 5 that is in a non-conductive state during the on-time of the MOSFET 3, while the diode 5 is in a conductive state during the off-time, and a capacitor 6 for smoothing the energy stored in the inductor through the diode 5 and generating an output voltage (VOUT) across both sides of a load 7.

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, and more particularly to a voltage higher than an input voltage and 100V which can drive an avalanche diode (APD), for example.
The present invention relates to a DC-DC converter that can obtain an output voltage of a high level and can use a switching element having a low breakdown voltage.

[0002]

2. Description of the Related Art Due to advances in integration in communication equipment,
There is a demand for smaller and thinner power supplies, and above all,
The demand for miniaturization of the on-board power supply mounted and used on the printed circuit board has become strict.

D used as this on-board power supply
In the C-DC converter, conventionally, as a first technique, a polarity reversal type DC that can obtain an output voltage having a reverse polarity with respect to an input voltage
-There is a DC converter, and the second technology is a step-up DC-DC converter that can obtain an output voltage having the same polarity as the input voltage and higher than the input voltage. The third technology is the same as the input voltage. There is a step-down DC-DC converter that can obtain an output voltage that is polar and lower than the input voltage. Further, as a fourth technique, there is a power supply circuit described in JP-A-54-9716.

FIG. 3 is a circuit diagram of a conventional polarity inversion type DC-DC converter, FIG. 4 is a circuit diagram of a conventional step-up type DC-DC converter, and FIG. 5 is a conventional step-down type DC-D converter.
6 is a circuit diagram of a C converter, and FIG. 6 is a basic circuit diagram of the power supply circuit described in the above publication.

More specifically, referring to FIG. 3, in the polarity reversal type DC-DC converter which is the first conventional technique, the negative side of the collector C is connected to the ground terminal Q and the ground terminal Z through the input terminal P. A transistor 8 connected to the positive side of the input DC power supply 1 and controlled by a switching drive signal supplied from the base B to switch the input voltage V _IN of the input DC power supply 1 and output it to the emitter E; One end a is connected to the ground end Q and the ground end Z and is controlled by a rectangular wave-like periodic control signal input from the control input end R to output a switching drive signal to the other end b to the base B of the transistor 8. A drive circuit 2 for supplying a switching drive to the transistor 8;
One end d is connected to the emitter E of the transistor 8 and one end of the rectifying element, and the other end e is connected to the ground end Q and the ground end Z, and the current I flowing when the transistor 8 is on.
Transistor 8 as well as store energy by _ON
Is off, an inductor 9 which functions to induce a counter electromotive force by the stored energy to conduct a rectifying element to flow a current I _OFF, and a transistor 8 on the cathode side
Is connected to one end of a load 7 which is connected to the emitter E and one end d of the inductor 9 and whose anode side is connected to one end of the smoothing element and the output end W and the other end to the ground end Z and the ground end Q, respectively. A diode 5 as a rectifying element which is conductive when off and non-conductive when the transistor 8 is on, one end of which is connected to the anode side of the diode 5 and one end of the load 7 through the output terminal W, and the other end of which is grounded. The capacitor 6 as a smoothing element is connected to the terminal Q and the ground terminal Z.

Next, the operation will be described. When the transistor 8 is turned on, the input voltage V _IN from the input DC power supply 1 is applied to both ends of the inductor 9, a current I _ON flows through the inductor 9 and the transistor 8, and energy is stored in the inductor 9. At this time, the current I _ON flowing in the inductor 9 increases in a triangular wave shape, and the current change ΔI
_ON means that the inductance of the inductor 9 is L, the on time of the transistor 8 is T _ON, and the collector C-emitter E voltage of the transistor 8 is V _CE = 0.

[0007]

[0008]

At this time, the energy E stored in the inductor 9 is

[0010]

[0011] However, the energy E is not supplied to the load 7 because the rectifying diode 5 does not conduct when the transistor 8 is on.

If the transistor 8 is turned off while the current I _ON is flowing through the inductor 9, this current I _ON
The energy E stored in the inductor 9 while the transistor 8 is on to maintain the _ON state induces a counter electromotive force in the inductor 9, and the counter electromotive force causes the rectifying diode 5 to conduct so that the current I _OFF flows. , The energy E stored in the inductor 9 is discharged through the diode 5 and the smoothing capacitor 6, and a negative output voltage V _OUT having the opposite polarity to the input voltage V _IN is obtained across the load 7. Current I flowing through inductor 9 and diode 5 at this time
_{The OFF} current change ΔI _OFF is expressed by the following formula: _OFF time of the transistor 8 is T _OFF , inductance of the inductor 9 is L, and forward voltage drop of the diode 5 is V _D.

[0013]

[0014]

Considering the case where the currents I _ON and I _OFF flowing through the inductor 9 are continuous, the change in the current flowing through the inductor 9 during the period T _ON and T _OFF , that is, ΔI _ON and ΔI
_Since it is equal to _OFF , from equation (1) and equation (3),

[0016]

[0017]

When the relationship between the input voltage V _IN and the output voltage V _OUT is _calculated from this equation (4),

[0019]

In order to simplify the explanation, V
_{When D} = 0, the output voltage V _OUT becomes equal to the input voltage V _IN when T _ON = T _OFF , and when T _ON > T _OFF , the output voltage V _OUT is boosted higher than the input voltage V _IN , and _ON <T
_{When OFF} , the output voltage V _OUT is lower than the input voltage V _IN , but it is generally used with T _ON > T _OFF .

The voltage V _CE between the collector C and the emitter E of the transistor 8 when the transistor 8 is off is V _CE = (V _IN + V _D + V _OUT ) ... (6) Therefore, the transistor 8 needs to have a withstand voltage exceeding the collector C-emitter E voltage V _CE in the equation (6).

Next, a step-up DC which is the second conventional technique.
Referring to FIG. 4, in the -DC converter, one end e is connected to the plus side of the input DC power supply 1 whose negative side is connected to the ground end Q and the ground end Z through the input end P, and the other end d is one end of the switching element and The current I _ON, which is connected to one end of the rectifying element and flows when the swinging element is on, accumulates energy, and when the switching element is off, the stored energy induces a counter electromotive force to bring the rectifying element into conduction. An inductor 9 that functions to flow I _OFF , one end a of which is connected to the ground end Q and the ground end Z and is controlled by the rectangular wave-shaped periodic control signal input from the control input end R to the other end b. The drive circuit 2 which outputs a switching drive signal and supplies it to the base B of the transistor 8 to switch drive the transistor 8 and the collector C are inductors. Input connected to the other end d of the switching element 9 and one end of the rectifying element and connected to the ground terminal Q and the ground terminal Z with the emitter E being controlled by the switching drive signal supplied from the drive circuit 2 and supplied through the inductor 9. A transistor 8 as a switching element for switching the input voltage V _IN from the DC power source 1, an anode side is connected to the other end d of the inductor 9 and a collector C of the transistor 8, and a cathode side is one end of the smoothing element and an output end W.
The other end is connected to one end of the load 7 connected to the ground terminal Z and the ground terminal Q, and the diode 5 as a rectifying element becomes conductive when the transistor 8 is off and non-conductive when the transistor 8 is on. And a capacitor 6 as a smoothing element, one end of which is connected to the cathode side of the diode 5 and one end of the load 7 through the output end W, and the other end is connected to the ground end Q and the ground end Z.

Next, the operation will be described. When the transistor 8 is turned on, the input voltage V _IN from the input DC power supply 1 is applied to both ends of the inductor 9, a current I _ON flows through the inductor 9 and the transistor 8, and energy is stored in the inductor 9. At this time, the current I _ON flowing through the inductor 9 increases in a triangular wave, and the current change ΔI _ON
Is the inductance of the inductor 9 is L, the on time of the transistor 8 is T _ON, and the collector C of the transistor 8 is
-If the voltage between the emitter E is V _CE = 0,

[0024]

[0025] At this time, the energy E stored in the inductor 9 is

[0026]

[0027] However, when the transistor 8 is on, the rectifying diode 5 does not conduct, so this energy E is not supplied to the load 7.

If the transistor 8 is turned off while the current I _ON is flowing through the inductor 9, this current I _ON
The energy E stored in the inductor 9 while the transistor 8 is on to maintain the _ON state induces a counter electromotive force in the inductor 9, and the counter electromotive force causes the rectifying diode 5 to conduct so that the current I _OFF flows. , The energy E stored in the inductor 9 is the DC voltage V _{IN of the} input DC power supply 1.
Superimposed on the diode 5 and the smoothing capacitor 6
And a positive output voltage V _OUT having the same polarity as the input voltage V _IN is obtained across the load 7.

At this time, the current change amount ΔI _OFF of the current I _OFF flowing through the inductor 9 and the diode 5 is _equal to the load 7
If the output voltage across both ends is V _OUT, the off time of the transistor 8 is T _OFF , the inductance of the inductor 9 is L, and the forward voltage drop of the diode 5 is V _D ,

[0030]

It becomes Considering the case where the currents I _ON and I _OFF flowing through the inductor 9 are continuous, the change in the current flowing through the inductor 9 during the period T _ON and T _OFF , that is, ΔI _ON
Since ΔI _OFF is equal to ΔI _OFF , from equation (7) and equation (9),

[0032]

It becomes

When the relation between the input voltage V _IN and the output voltage V _OUT is obtained from the equation (10),

[0035]

For the sake of simplicity, V _D = 0
Then, the output voltage V _OUT becomes a voltage higher than the input voltage V _IN , and for example, the output voltage V _OUT under the condition of T _ON = T _OFF becomes twice the input voltage V _IN .

The voltage V _CE between the collector C and the emitter E of the transistor 8 when the transistor 8 is off is V _CE = (V _D + V _OUT ) ... (12) Therefore, the transistor 8 needs to have a withstand voltage exceeding the collector C-emitter E voltage V _CE in the equation (12).

Next, a step-down type D which is the third conventional technique.
Referring to FIG. 5, the C-DC converter is a switching device in which a collector C is connected to a positive side of an input DC power supply 1 whose negative side is connected to a ground terminal Q and a ground terminal Z through an input terminal P and is supplied from a base B. A transistor 8 as a switching element which is controlled by a drive signal to switch the input voltage V _IN of the input DC power supply 1 and outputs it to the emitter E, and one end a of which is connected to the ground terminal Q and the ground terminal Z and which is also a control input terminal R The drive circuit 2 which is controlled by the rectangular control signal having a rectangular wave shape and outputs the switching drive signal to the other end b and supplies the switching drive signal to the base B of the transistor 8 to drive the transistor 8 for switching, and the one end d is a transistor. 8 is connected to the emitter E and one end of the rectifying element, and the other end e passes through one end of the smoothing element and the output end W and the other end is the ground end Z. It is connected to one terminal of the load 7 to be connected to the pre-ground terminal Q transistor 8 as well as storing energy by the current I _ON flowing when the transistor 8 is turned on the counter electromotive force by the accumulated energy in the off An inductor 9 which functions to induce a rectifying element to conduct a current I _OFF , a cathode side thereof is connected to an emitter E of the transistor 8 and one end d of the inductor 9, and an anode side thereof is connected to a ground terminal Q and a ground terminal Z. When the transistor 8 is off
Diode 5 as a rectifying element which becomes non-conductive when is on, one end is connected to one end of the load 7 through the other end e of the inductor 9 and the output end W, and the other ends are connected to the ground end Q and the ground end Z. It is composed of a capacitor 6 as a smoothing element to be connected.

Next, the operation will be described. When the transistor 8 is turned on, assuming that the input voltage from the input DC power supply 1 is V _IN and the output voltage across the load 7 is V _OUT , the voltage V _IN −V _OUT is applied across the inductor 9 and the inductor 9 and The current I _ON flows through the transistor 8,
Energy is stored in the inductor 9. At this time, the current I _ON flowing through the inductor 9 increases in a triangular waveform, and the current change ΔI _ON has the inductance L of the inductor 9, the ON time of the transistor 8 T _ON, and the collector C-emitter E of the transistor 8. If the voltage between the two is V _CE = 0,

[0040]

It becomes

The energy E accumulated in the inductance 9 at this time is

[0043]

It becomes

If the transistor 8 is turned off while the current I _ON is flowing through the inductor 9, this current I _ON
The energy E stored in the inductor 9 while the transistor 8 is on to maintain the _ON state induces a counter electromotive force in the inductor 9, and the counter electromotive force causes the rectifying diode 5 to conduct so that the current I _OFF flows. , The energy E stored in the inductor 9 is discharged through the diode 5 and the smoothing capacitor 6, and a positive output voltage V _OUT having the same polarity as the input voltage V _IN is obtained across the load 7.

The current change △ I _OFF current I _OFF through the diode 5 and the inductor 9 at this time, T _OFF OFF time of the transistor 8, the inductance of the inductor 9 the forward voltage drop of the L and the diode 5 V _D
Then,

[0047]

It becomes

Considering a case where the currents I _ON and I _OFF flowing through the inductor 9 are continuous, the change in the current flowing through the inductor 9 during the period T _ON and T _OFF , that is, ΔI _ON and ΔI
_Since it is equal to _OFF , from equation (13) and equation (15),

[0050]

It becomes

When the relationship between the input voltage V _IN and the output voltage V _OUT is _calculated from this equation (16),

[0053]

In order to simplify the explanation here, V
_{If D} = 0,

[0055]

Therefore, the output voltage V _OUT is equal to the input voltage V _IN
The output voltage V _OUT under the condition of T _ON = T _OFF becomes half of the input voltage V _IN .

The collector-emitter voltage V _CE of the transistor 8 when the transistor 8 is off is V _CE = (V _IN −V _D ) ... (19) Therefore, the transistor 8 needs to have a withstand voltage exceeding the collector C-emitter D voltage V _CE in the equation (19).

Further, referring to FIG. 6 which is a basic circuit of the power supply circuit of the fourth conventional technique, the collector C through the input end P is on the negative side at the ground end Q and the ground end Z.
Is connected to the plus side of the input DC power supply 1 connected to and is controlled by the switching drive signal supplied from the base B to switch the input voltage V _IN of the input DC power supply 1 and output it to the emitter E. The transistor 8 has one end a connected to the ground terminal Q and the ground terminal Z and is controlled by a rectangular wave-shaped periodic control signal input from the control input terminal R to output a switching drive signal to the other end b to output the transistor 8 To the base B of the rectifying element and the other end d is connected to one end of the rectifying element and the other end d passes through one end of the smoothing element and the output end W and the other end is the ground end Z and the ground. An intermediate tap f, which is connected to one end of the load 7 connected to the end Q and is provided between the winding M ₁ and the winding M _2, is connected to the emitter E of the transistor 8. Energy is accumulated by the current I _ON which is connected and flows when the transistor 8 is on, and when the transistor 8 is off, a back electromotive force is induced by the accumulated energy and the rectifying element is made conductive to flow the current I _OFF . And the cathode side is connected to one end e of the inductor 4 and the anode side is connected to the ground terminal Q and the ground terminal Z.
The diode 5 as a rectifying element which is conductive when the transistor 8 is off and non-conductive when the transistor 8 is on, and one end of which is connected to one end of the load 7 through the other end d of the inductor 4 and the output end W and the other end. Is composed of a capacitor 6 as a smoothing element connected to the ground terminal Q and the ground terminal Z.

Next, the operation will be described. When the transistor 8 is turned on, the current I _ON flows through the transistor 8 and the capacitor 6 on the winding M ₁ side of the inductor 4,
Energy is stored in the inductor 4, and between the other end a of the inductor 4 and the intermediate tap d, when the input voltage from the input DC power supply 1 is V _IN and the output voltage across the load 7 is V _OUT , V _IN − The voltage of V _OUT is applied. At this time, the current I _ON flowing through the winding M ₁ of the inductor 4 increases in a triangular wave shape, and the current change ΔI _ON is the inductance L ₁ of the winding M ₁ of the inductor 4 and the ON time of the transistor 8 is T 1. _{When ON} and the collector C-emitter E voltage of the transistor 8 are V _CE = 0,

[0060]

It becomes

The energy E stored in the inductor 9 at this time is

[0063]

It becomes

If the transistor 8 is turned off while the current I _ON is flowing through the inductor 4, this current I _ON
The energy accumulated while the transistor 8 is on to maintain the _ON state induces a counter electromotive force in the inductor 4, and the back electromotive force causes the rectifying diode 5 to conduct so that a current I _OFF flows and the inductor 4 flows in the inductor 4. The stored energy E is discharged through the diode 5 and the smoothing capacitor 6, and a positive output voltage V _OUT having the same polarity as the input voltage V _IN is obtained across the load 7.

At this time, the current change amount ΔI of the current I _OFF flowing through the diode 5, the inductor 4 and the load 7 is ΔI.
_OFF is the inductance L on the winding M ₂ side of the inductor 4.
₂ and the off time of the transistor 8 is T _OFF and the forward voltage drop of the diode 5 is V _D ,

[0067]

It becomes

However, L ₁ + L ₂ = L, and L is the inductance at both ends of the inductor 4.

Considering a case where the currents I _ON and I _OFF flowing through the inductor 4 are continuous, the change in the current flowing through the inductor 4 during the period T _ON and T _OFF , that is, ΔI _ON and ΔI
_Since it is equal to _OFF , from equation (20) and equation (22),

[0071]

It becomes

Here, in order to simplify the explanation, V _D = 0
When the relation between the input voltage V _IN and the output voltage V _OUT is _calculated from the equation (23),

[0074]

Therefore, the output voltage V _OUT is equal to the input voltage V _IN
The output voltage V _OUT under the conditions of T _ON = T _OFF and L ₁ = L ₂ is the input voltage V _IN.
2/3 of that. Furthermore, under this same condition, equation (24)
The output voltage V _OUT when compared with the output voltage V _OUT in the conventional step-down DC-DC converter of the formula (18) in the inductor than the output voltage V _OUT at the output voltage V _OUT has the formula (18) in equation (24) By providing the intermediate tap f at 4, the voltage is further reduced in proportion to the ratio of the inductance L ₁ and the inductance L ₂ .

Further, the voltage V _CE between the collector and the emitter of the transistor 8 when the transistor 8 is off is defined as the voltage across the winding M ₁ of the inductor 4 is V _L1 and the voltage across the winding M ₂ is V _L2 . _{Then, V L1 + V L2 = V} D + V OUT ...... from (25) _{(25), V L2 -V D} = V OUT -V L1 ...... (26) _{Therefore, V CE = V I N- (} V L2 _{-V D) = (V I N} + V D) -V L2 ...... becomes (27).

Here, collector C- in equation (27)
The voltage V _CE between the emitters E becomes smaller than the voltage V _CE between the collector C-emitters E in the formula (19) of the conventional step-down DC-DC converter by V _L2 . That is, V _CE
The winding M by providing the inductor 4 with an intermediate tap
_It becomes smaller in proportion to the winding number ratio between ₁ and the winding M _2, and the withstand voltage of the transistor 8 is accordingly small. However, this is, in order to obtain the same output voltage V _OUT to a conventional step-down DC-DC converter, since it is necessary to increase the input voltage V _I N, eventually breakdown voltage of the transistor 8 is conventional step-down DC -No smaller than a DC converter.

[0078]

In the polarity reversal type DC-DC converter which is the first conventional technique, T _ON = T
Under the _OFF condition, the output voltage V _OUT is equal to the input voltage V _IN
, And a voltage higher than the input voltage V _IN cannot be obtained. Further, the switching element (V _I N +
Since a breakdown voltage of V _D + V _OUT ) is required, a low breakdown voltage switching element cannot be used.

In addition, a boosting type DC which is the second conventional technique.
In the −DC converter, under the condition of T _ON = T _OFF , the output voltage V _OUT can obtain a voltage about twice higher than the input voltage V _IN, but on the other hand, the switching element has (V _D + V _OUT ). Since a high breakdown voltage is required, a low breakdown voltage switching element cannot be used.

Furthermore, the step-down type D which is the third conventional technique
In the C-DC converter, under the condition of T _ON = T _OFF , the output voltage V _OUT becomes about half of the input voltage V _IN , and the switching element requires a withstand voltage of (V _IN + V _D ). In order to obtain the high-voltage output voltage V _OUT , the input voltage V _IN increases correspondingly, and the low breakdown voltage switching element cannot be used.

Furthermore, in the conventional power supply circuit of the fourth technique, by providing the inductor 4 with the intermediate tap f, T _ON = T is lower than that of the conventional step-down DC-DC converter.
Under the same condition of T _OFF , the output voltage V _OUT is
Is further stepped down in proportion to the ratio of the inductance L ₁ and the inductance L ₂ of the switching element, and (V _IN +
Since a withstand voltage of (V _D −V _L2 ) is required, the input voltage V _IN becomes large to obtain a high output voltage V _OUT , and a low withstand voltage switching element cannot be used.

[0082]

DC-DC according to the present invention
The converter has a first electrode connected to one end of an input DC power supply whose other end is connected to a common line, and a DC voltage from the input DC power supply input to the first electrode according to a switching drive signal from the second electrode. A transistor for switching and outputting to a third electrode, a first electrode connected to the common line, a periodic control signal input from a control input end, and a switching drive signal output to the other end; A tap between the first winding and the second winding, and a switching drive means for supplying the first winding to the common line at one end of the first winding opposite to the tap; The other end of the transistor opposite to the tap is connected to one end of a rectifying element, and the tap is connected to the third electrode of the transistor to store energy when the transistor is on and to turn off the energy. An inductance element that supplies the stored energy to one end of a load whose other end is grounded through the rectifying element, and one end of which is connected to one end of the inductance element opposite to the tap of the second winding, and The other end is connected to one end of a smoothing element and one end of the load, and the rectifying element is non-conductive when the transistor is on and is conductive when the transistor is off, and one end is the other end of the rectifying element and one end of the load. Connected to the common line and the other end connected to the common line to smooth the energy stored in the inductance element that is input through the rectifying element, and has a polarity opposite to the DC voltage of the input DC power source across the load. And the smoothing element for obtaining a DC output voltage.

Further, in the DC-DC converter according to the present invention, a tap is provided between the first winding and the second winding, and the first winding is provided.
One end of the winding opposite to the tap is connected to one end of an input DC power supply whose other end is connected to a common line, and the other end of the second winding opposite to the tap is connected to one end of a rectifying element. Also, the tap is connected to the third electrode of the transistor to store energy when the transistor is on, and the stored energy when the transistor is off, the other end of which is connected to a common line through the rectifying element. An inductance element to be supplied to the common line, a switching drive means having one end connected to the common line, a periodic control signal input to a control input end, a switching drive signal output to the other end, and the switching drive signal being supplied to the base of the transistor; The three electrodes are connected to the common line and are driven by the switching drive signal from the switching drive means input from the base so that the collector receives the input. A transistor for switching the DC voltage from the input DC power supply supplied through the tap of the inductance element, one end of which is connected to the other end of the inductance element and the other end of which is connected to one end of a smoothing element and one end of the load. A rectifying element that is non-conductive when the transistor is on and conductive when it is off,
One end of which is connected to the other end of the rectifying element and one end of the load and the other end of which is connected to the common line to smooth energy stored in the inductance element that is input through the rectifying element and to both ends of the load. And the smoothing element for obtaining a DC output voltage having the same polarity as the DC voltage of the input DC power supply.

Further, in the DC-DC converter according to the present invention, the transistor is a field effect transistor, and the source, the gate and the drain correspond to the first electrode, the second electrode and the third electrode, respectively.

[0085]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. Referring to FIG. 1, which illustrates a first embodiment of the present invention, D
In the C-DC converter, the source S is connected to the positive side of the input DC power source 1 whose negative side is connected to the ground terminal Q and the ground terminal Z through the input terminal P and is controlled by the switching drive signal supplied from the gate G. Input DC power supply 1
N-channel MOS F as a switching element for switching the input voltage V _IN of
ET (Metal Oxide Semiconductor)
tor Field Effect Transist
or 3), one end a of which is connected to the ground end Q and the ground end Z and which is controlled by a rectangular wave-like periodic control signal input from the control input end R to output a switching drive signal to the other end b. Supply to the gate G of FET3 and MOS
The drive circuit 2 for switching driving the FET 3 and one end e
Is connected to the ground terminal Q and the ground terminal Z, the other end d is connected to one end of the rectifying element, and an intermediate tap f provided between the winding M ₁ and the winding M ₂ is connected to the drain D of the MOS FET 3. Energy is accumulated by a current I _ON which is connected and flows when the MOS FET 3 is on, and when the MOS FET 3 is off, a counter electromotive force is induced by the accumulated energy to turn on a rectifying element to flow a current I _OFF . Of the load 4 whose cathode side is connected to the other end d of the inductor 4 and whose anode side is connected to one end and the output end W of the smoothing element and the other end to the ground end Z and the ground end Q, respectively. It is connected to one end and conducts when the MOS FET3 is off.
A diode 5 serving as a rectifying element that becomes non-conductive when the FET 3 is on, one end of which is connected to the anode side of the diode 5 and one end of a load 7 through an output end W, and the other ends of which are a ground end Q and a ground end Z. And a capacitor 6 as a smoothing element connected to.

Next, the operation will be described. MOS F
When ET3 is turned on, the input voltage V _IN from the input DC power supply 1 is applied to the intermediate tap f on the winding M ₂ side of the inductor 4, and the current I _ON flows through the winding FET M ₂ of the inductor 4 through the MOS FET 3. Energy is stored in the inductor 4. At this time, the current I _ON flowing in the winding M ₂ of the inductor 4 increases in a triangular wave shape, and the current change ΔI _ON changes the inductance of the winding M ₂ of the inductor 4 to L ₂ , MOS.
If the ON time of the FET 3 is T _ON and the source S-drain D voltage of the MOS FET 3 is V _DS = 0,

[0087]

It becomes At this time, the energy E stored in the inductor 9 is

[0089]

It becomes However, the energy E is not supplied to the load 7 because the rectifying diode 5 does not conduct when the MOS FET 3 is on.

Here, the current I is applied to the winding M ₂ of the inductor 4.
When the MOS FET 3 is turned off while _ON is flowing, the energy E accumulated while the transistor 8 is on in order to maintain this current I _ON induces a counter electromotive force in the inductor 4, and this counter electromotive force causes The rectifying diode 5 conducts and a current I _OFF flows, the energy E stored in the inductor 4 is discharged through the diode 5 and the capacitor 6, and a negative output having a polarity opposite to the input voltage V _IN is output across the load 7. The voltage V _OUT is obtained.

At this time, the current change amount ΔI of the current I _OFF flowing through the inductor 4, the diode 5 and the load 7 is ΔI.
_OFF turns the inductance of winding M ₁ of inductor 4 to L
₁ , the inductance of the winding M ₂ of the inductor 4 is L ₂ ,
When the output voltage V _OUT across the load 7 and the off time of the MOS FET 3 are T _OFF and the forward drop voltage of the diode 5 is V _D ,

[0093]

It becomes

However, L ₁ + L ₂ = L, and L is the inductance at both ends of the inductor 4.

Considering a case where the current flowing through the inductor 4 is continuous, the change in the current flowing through the inductor 4 during the period T _ON and T _OFF , that is, ΔI _ON and ΔI _OFF , is equal to 28) and the equation (30),

[0097]

It becomes

When the relationship between the input voltage V _IN and the output voltage V _OUT is obtained from this equation (31),

[0100]

Therefore, in order to simplify the explanation here, V _D
= 0, the output voltage V _OUT becomes a voltage higher than the input voltage V _IN , and for example, T _ON = T _OFF and L ₁ = L
Output voltage V _OUT at the ₂ conditions will be twice the input voltage V _IN. Further comparing this under the same conditions the output voltage V _OUT in the formula (32) and the output voltage V _OUT in the conventional polarity inversion-type DC-DC converter of the formula (5), the formula (3
The output voltage V _OUT in 2) is doubled by providing the intermediate tap f in the inductor 4 as compared with the output voltage V _OUT in the equation (5). This means that the input voltage V _IN for obtaining the same output voltage V _OUT and the withstand voltage of the MOS FET 3 as the switching element are smaller than the input voltage V _{IN of} the conventional polarity inversion type DC-DC converter and the withstand voltage of the transistor 8. It means that you can finish. This will be described quantitatively below.

MOS when FET 3 is off
The drain-source voltage V _DS of the FET 3 is V _L2 = V _D + V _OUT −V _L1 where V _{L1 is the} voltage across the winding M ₁ of the inductor 4 and V _L2 is the voltage across the winding M _2. (34) V _DS = V _IN + V _L2 (35) From the formulas (34) and (35), V _DS = (V _IN + V _D + V _OUT ) −V _L1 (36) .

[0103] Further representative of the V _DS of the formula (36) the number of turns of winding M ₁ turns of n ₁ and winding M ₂ as n _2,

[0104]

It becomes:

Here, the drain D- in the equation (36)
The source S voltage V _DS becomes smaller by V _{L1 than the} collector C-emitter E voltage V _CE in the equation (6) of the conventional polarity reversal type DC-DC converter. That is, V _DS
Decreases in proportion to the turn ratio between the number of turns n ₂ turns n ₁ and the winding M ₂ windings M ₁ by providing an intermediate tap f to the inductor 4, requires the breakdown voltage of the minute MOS FET 3 is small. This is more remarkable when a higher high voltage output voltage is obtained. For example, the above _{T O N = T OFF, L} 1
= L ₂ , n ₁ = n ₂ and V _D = 0,
MOS FET for obtaining 100V output voltage V _OUT
The withstand voltage V _DS of 3 is 100 V, which is 100 V as compared with the withstand voltage V _CE = 200 V of the transistor 8 of the conventional polarity reversal type DC-DC converter in which the intermediate tap is not provided under the same condition.
Withstand voltage difference occurs. The withstand voltage and the withstand voltage difference are the values when each element is used at the absolute maximum rating.
Normally, the derating is used at about 70%, and the withstand voltage difference further increases to 130 V. Therefore, the effect of providing the intermediate tap f is great.

FIG. 2 showing the second embodiment of the present invention.
Referring to, in the DC-DC converter, one end d is connected to the plus side of the input DC power supply 1 whose negative side is connected to the ground end Q and the ground end Z through the input end P, and the other end e is connected to one end of the rectifying element. And winding M ₁ and winding M
_An intermediate tap f provided in the middle of ₂ is connected to one end of the switching element to accumulate energy by the current I _ON flowing through the winding M ₁ when the switching element is on, and to accumulate the energy when the switching element is off. An inductor 4 which functions to induce a counter electromotive force by the generated energy to make a rectifying element conductive and to flow a current I _OFF ;
One end a is connected to the ground end Q and the ground end Z and is controlled by a rectangular wave-like periodic control signal input from the control input end R to output a switching drive signal to the other end b to supply it to the switching element. A drive circuit 2 for switching-driving a switching element, and a drain D connected to an intermediate tap f of an inductor 4 and a source S connected to a ground terminal Q and a ground terminal Z to control a switching drive signal supplied from the drive circuit 2. And a P-channel MOS FET 3 as a switching element for switching the input voltage V _IN from the input DC power supply 1 supplied through the winding M ₁ of the inductor 4, and the anode side is connected to the other end d of the inductor 4 and One end of the load 7 whose cathode side is connected to one end of the smoothing element and the output end W and the other end to the ground end Z and the ground end Q The diode 5 as a rectifying element which is connected and conducts when the MOS FET 3 is off and non-conducts when the MOS FET 3 is on, and one end of which is connected to one end of the load 7 through the cathode side of the diode 5 and the output end W The other end of the capacitor 6 is connected to the grounding terminal Q and the grounding terminal Z and serves as a smoothing element.

Next, the operation will be described. MOS F
When ET3 is turned on, the input voltage V _IN from the input DC power supply 1 is applied between one end e of the inductor 4 and the intermediate tap f, and the winding M _{1 of the} inductor 4 and the MOS FET 3
A current I _ON flows through the inductor 4 and energy is stored in the inductor 4. At this time, the current I _ON flowing in the winding M ₂ of the inductor 4 increases in a triangular wave shape, and the current change ΔI _ON causes the inductance of the winding M ₂ of the inductor 4 to be L ₂ , MOS.
If the ON time of the FET 3 is T _ON and the source S-drain D voltage of the MOS FET 3 is V _DS = 0,

[0109]

It becomes: At this time, the energy E stored in the inductor 4 is

[0111]

[0112] However, the energy E is not supplied to the load 7 because the rectifying diode 5 does not conduct when the MOS FET 3 is on.

Here, the current I is applied to the winding M ₁ of the inductor 4.
_{If the} MOS FET3 is turned off while _ON is flowing, the MOS FET3 tries to maintain this current I _ON.
Energy E accumulated in inductor 4 during the period when is on
Induces a back electromotive force in the inductor 4, and the back electromotive force causes the rectifying diode 5 to conduct, causing a current I _OFF to flow, and the energy E accumulated in the inductor 4 is input to the input DC power supply 1
Of overlapping with dc voltage V _IN and discharged through condenser 6 for the diode 5 and a smoothing, at both ends of the load 7 positive output voltage V _OUT of the input voltage V _IN with the same polarity can be obtained.

[0114] current change △ I _OFF current I _OFF flowing through the inductor 4 and diode 5 in this case, L ₁ the inductance of the windings M ₁ of inductor 4, the output voltage of the load 7 across V _OUT and MOS FET 3 If the off time of is T _OFF ,

[0115]

[0116] Considering the case where the currents I _ON and I _OFF flowing through the inductor 4 are continuous, the change in the current flowing through the inductor 4 during the period T _ON and T _OFF , that is, ΔI _ON
And ΔI _OFF are equal, the equation (38) and the equation (4
From 0),

[0117]

It becomes:

However, L ₁ + L ₂ = L, and L is the inductance at both ends of the inductor 4.

When the relationship between the input voltage V _IN and the output voltage V _OUT is obtained from this equation (41),

[0121]

Therefore, the output voltage V _OUT is equal to the input voltage V _IN
The output voltage V _OUT under the conditions of T _ON = T _OFF and L ₁ = L ₂ is the input voltage V _IN.
3 times the voltage. Furthermore, under this same condition, equation (4
The output voltage V _OUT in 2) is compared with the conventional boost inverting DC-
Compared to the output voltage V _OUT at DC converter of formula (11), than the output voltage V _OUT towards the output voltage V _OUT in equation (42) in equation (11), the inductor 4 by providing the intermediate tap f The voltage is further boosted 1.5 times. This means that the input voltage V _IN for obtaining the same output voltage V _OUT and the withstand voltage of the MOS FET 3 as the switching element are smaller than the input voltage V _{IN of} the conventional step-up DC-DC converter and the withstand voltage of the transistor 8. It means to finish. This will be described quantitatively below.

MOS when FET 3 is off
The voltage V _DS between the drain D and the source S of the FET 3 is V _IN + V _L2 = V _D + V _OUT −, where V _{L1 is the} voltage across the winding M ₁ of the inductor 4 and V _L2 is the voltage across the winding M _2. V _L1 (43) V _DS = V _IN + V _L2 (44) From the formulas (43) and (44), V _DS = (V _D + V _OUT ) −V _L1 (45) .

Further, the V _DS of this equation (45) is set to the winding M ₁
Let n _{1 be} the number of turns of M and n _{2 be} the number of turns of winding M ₂ .

[0125]

[0126]

Here, the drain D- in equation (45)
The source S voltage V _DS becomes smaller by V _{L1 than the} collector C-emitter E voltage V _CE in the equation (12) of the conventional step-up DC-DC converter. That, V _DS is by providing an intermediate tap f to the inductor 4 becomes smaller in proportion to the turn ratio between the number of turns n ₂ turns n ₁ and the winding M ₂ windings M _1, the breakdown voltage of the minute MOS FET 3 Can be small. This is more remarkable when a higher high voltage output voltage is obtained. For example, the above T _ON = T _{OF F} , L ₁
= L ₂ , n ₁ = n ₂ and V _D = 0,
MOS FET for obtaining 100V output voltage V _OUT
The withstand voltage V _DS of 3 is 66.7 V, which is 33.3 V as compared with the withstand voltage V _CE = 100 V of the transistor 8 of the conventional step-up DC-DC converter in which the intermediate tap is not provided under the same condition.
Withstand voltage difference occurs. The withstand voltage and the withstand voltage difference are the values when each element is used at the absolute maximum rating.
Normally, the derating is used at about 70%, so the difference in withstand voltage becomes larger and becomes 43.3V.
The effect of providing the intermediate tap f is great.

In the above, in the first and second embodiments, the case where the MOSFET is used as the switching element has been described, but the JFET (junction) is used.
Even if a FET is used, even if a transistor is used, the collector C, the base B, and the emitter E of the transistor may be connected to correspond to the source S, the gate G, and the drain D of the FET. Can be achieved in the same way.

The configuration and operation in the case where a positive DC voltage V _IN is applied between the input terminal P and the ground terminal Q to obtain a negative DC voltage V _OUT between the output terminal W and the ground terminal Z will be described. However, on the contrary, a negative DC voltage V is applied between the input terminal P and the ground terminal Q.
_{Apply IN} and apply a positive DC voltage V between output W and ground Z
_{In order} to obtain _OUT, by replacing the MOS FET 3 with an N channel one and a P channel one, and reversing the direction of the diode 5 between the cathode side and the anode side, the same configuration and the same operation as described above are realized. can do.

[0130]

As described above, according to the present invention, by providing the inductance element with the intermediate tap, the inductance is higher than the input voltage and, for example, about 100 V which is sufficient for driving the avalanche photodiode (APD). Since a high voltage output voltage can be obtained and a transistor with a low withstand voltage can be used as a switching element, the on-board power supply can be downsized. This effect becomes more prominent in proportion to obtaining a higher high voltage output voltage.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a DC-DC converter of a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a DC-DC converter according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a polarity reversal type DC-DC converter of a first conventional example.

FIG. 4 is a circuit diagram showing a step-up DC-DC converter of a second conventional example.

FIG. 5 is a circuit diagram showing a step-down DC-DC converter of a third conventional example.

FIG. 6 is a circuit diagram showing a power supply circuit of a fourth conventional example.

[Explanation of symbols]

 1 Input DC power supply 2 Drive circuit 3 MOS FET 4 Inductor 5 Diode 6 Capacitor 7 Load

Claims (3)

[Claims] 1. A first electrode is connected to one end of an input DC power supply, the other end of which is connected to a common line, and a switching drive signal from the second electrode is used to input to the first electrode. A transistor that switches a DC voltage and outputs the same to a third electrode; one end of the transistor that is connected to the common line and that receives a periodic control signal from a control input end and that outputs the switching drive signal to the other end; A switching driving means for supplying the two electrodes and a tap are provided between the first winding and the second winding, and one end of the first winding opposite to the tap is connected to the common line and the second winding is connected. The other end of the winding opposite to the tap is connected to one end of a rectifying element and the tap is connected to the third electrode of the transistor to store energy when the transistor is on and to turn off the energy. An inductance element for supplying the stored energy to one end of a load whose other end is grounded through the rectifying element, and one end connected to one end of the inductance element opposite to the tap of the second winding, and The other end is connected to one end of a smoothing element and one end of the load, and the rectifying element which is non-conductive when the transistor is on and conducts when the transistor is off, and the other end of the rectifying element and one end of the load Connected to the common line and the other end connected to the common line to smooth the energy stored in the inductance element that is input through the rectifying element, and has a polarity opposite to the DC voltage of the input DC power source across the load. A DC-DC converter, comprising: the smoothing element that obtains a DC output voltage. 2. A tap is provided between the first winding and the second winding, and one end of the first winding opposite to the tap is connected to one end of an input DC power supply whose other end is connected to a common line. Shikatsu and the second
The other end of the winding opposite to the tap is connected to one end of a rectifying element and the tap is connected to a third electrode of a transistor to store energy when the transistor is on and store the energy when the transistor is off. And an inductance element that supplies the energy to one end of a load, the other end of which is connected to a common line through the rectifying element, and one end of which is connected to the common line and a periodic control signal is input to the control input end and which is connected to the other end. Switching drive means for outputting a switching drive signal and supplying it to the second electrode of the transistor, and driving to the switching drive signal from the switching drive means that connects the third electrode to the common line and is input from the second electrode The DC voltage from the input DC power source that is supplied to the first electrode through the tap of the inductance element is switched. A transistor that has one end connected to the other end of the inductance element and the other end connected to one end of a smoothing element and one end of the load, and is non-conductive when the transistor is on and conductive when it is off. A rectifying element, one end of which is connected to the other end of the rectifying element and one end of the load and the other end of which is connected to the common line to smooth energy stored in the inductance element input through the rectifying element. A DC-DC converter comprising: a smoothing element that obtains a DC output voltage having the same polarity as the DC voltage of the input DC power supply, across the load. 3. The DC-DC converter according to claim 1, wherein the transistor is a field effect transistor, and the source, the gate, and the drain correspond to the first electrode, the second electrode, and the third electrode, respectively.