JP2630221B2 - DC-DC converter - Google Patents

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 DC-DC converter having a voltage higher than the input voltage and capable of driving an avalanche diode (APD).
The present invention relates to a DC-DC converter capable of obtaining an output voltage of a high level and using a switching element having a low withstand voltage.

[0002]

2. Description of the Related Art With the advance of integration in communication equipment,
Power supplies are also required to be smaller and thinner.
There is an increasing demand for miniaturization of an on-board power supply used by being mounted on a printed circuit board.

[0003] The D used as an on-board power supply
Conventionally, as a first technique, a polarity inversion type DC that can obtain an output voltage having a polarity opposite to an input voltage has been used for a C-DC converter.
As a second technique, there is a step-up DC-DC converter having the same polarity with respect to the input voltage and obtaining an output voltage higher than the input voltage. There is a step-down DC-DC converter capable of obtaining an output voltage having a polarity lower than the input voltage, and a fourth technique is a power supply circuit described in Japanese Patent Application Laid-Open No. 54-9716.

FIG. 2 is a circuit diagram of a conventional polarity inversion type DC-DC converter, FIG. 3 is a circuit diagram of a conventional step-up DC-DC converter, and FIG. 4 is a conventional step-down DC-D converter.
FIG. 5 is a circuit diagram of a C converter, and FIG. 5 is a basic circuit diagram of a power supply circuit described in the above publication.

More specifically, in the polarity inversion type DC-DC converter according to the first prior art, referring to FIG. 2 , the collector C is connected to the ground terminal Q and the ground terminal Z on the negative side through the input terminal P. A transistor 8 as a switching element 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 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 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 and driving the transistor 8 for switching;
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, so that the current I flowing when the transistor 8 is on is
Transistor 8 stores energy when _ON
Is turned off, an inductor 9 that functions to induce a back electromotive force by the stored energy to make the rectifying element conductive and to flow the current I _OFF ,
Connected to one end d of an inductor 9 and one end of a load 7 whose anode side is connected to one end of a smoothing element and one end of an output terminal W and the other end is connected to a ground terminal Z and a ground terminal Q. A diode 5 serving as a rectifying element which conducts when turned off and becomes non-conductive when the transistor 8 is turned on, one end connected to the anode side of the diode 5 and one end of the load 7 through the output end W, and the other end grounded And a capacitor 6 as a smoothing element connected to the terminal Q and the ground terminal Z.

Next, the operation will be described. When the transistor 8 is turned on, an input voltage V _IN from the input DC power supply 1 is applied to both ends of the inductor 9, a current _ION 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 the triangular waveform, the current change △ I
_ON means that the inductance of the inductor 9 is L, the on time of the transistor 8 is T _ON, and the voltage between the collector C and the emitter E of the transistor 8 is V _CE = 0.

[0007]

[0008]

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

[0010]

## EQU1 ## However, when the transistor 8 is on, the rectifying diode 5 does not conduct, so that the energy E is not supplied to the load 7.

When the transistor 8 is turned off while the current I _ON is flowing through the inductor 9, the current I _ON
The energy E stored in the inductor 9 while the transistor 8 is on while maintaining the _ON state induces a back electromotive force in the inductor 9, and the back electromotive force causes the rectifying diode 5 to conduct, thereby causing the current I _OFF to flow. 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 a polarity opposite to that of the input voltage V _IN is obtained across the load 7. At this time, the current I flowing through the inductor 9 and the diode 5
_{The OFF} current change ΔI _OFF is obtained by assuming that 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.

[0013]

## EQU1 ##

Considering a case where the currents I _ON and I _OFF flowing through the inductor 9 are continuous, a change in the current flowing through the inductor 9 during the period between T _ON and T _OFF , that is, ΔI _ON and ΔI _{ON
Since OFF} is equal, from the equations (1) and (3),

[0016]

## EQU1 ##

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

[0019]

Here, for simplicity of explanation, V
_{Assuming that 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 rises} higher than the input voltage V _{IN. ON} <T
_{When OFF} , the output voltage V _OUT falls below the input voltage V _IN , but is generally used when T _ON > T _OFF .

When the transistor 8 is off, the voltage V _CE between the collector C and the emitter E of the transistor 8 is as follows: V _CE = (V _IN + V _D + V _OUT ) (6) For this reason, the transistor 8 needs to have a withstand voltage exceeding the voltage V _CE between the collector C and the emitter E in the equation (6).

Next, a step-up type DC according to a second conventional technique is described.
Referring to FIG. 3 , the -DC converter has one end e connected to the plus side of the input DC power supply 1 having the minus side connected to the ground end Q and the ground end Z through the input end P, and the other end d to one end of the switching element. the energy switching element is that accumulated in the off together connected to one end of the rectifying element Suinchingu element stores energy by a current I _oN flows when on induce a back EMF current is conducting rectifying device an inductor 9 which functions to flow the I _OFF, end a is controlled to a periodic control signal having a rectangular waveform inputted from connected to the ground terminal Q and the ground terminal Z and the control input terminal R to the other end b A drive circuit 2 that outputs a switching drive signal and supplies it to the base B of the transistor 8 to switch and drive the transistor 8 is connected to the collector C. An input connected to the other end d of the capacitor 9 and one end of the rectifier element, and an emitter E connected to the ground terminal Q and the ground terminal Z and controlled by a switching drive signal supplied from the drive circuit 2 and supplied through the inductor 9. A transistor 8 as a switching element for switching an input voltage VIN from the DC power supply 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 connected to one end of a smoothing element and an output end W.
The other end of the diode 5 is connected to one end of a load 7 connected to the ground terminal Z and the ground terminal Q through the terminal, and conducts when the transistor 8 is off, and becomes non-conductive when the transistor 8 is on. And a capacitor 6 as a smoothing element having one end connected to one end of the load 7 through the cathode side of the diode 5 and the output end W, and the other end connected to the ground end Q and the ground end Z.

Next, the operation will be described. When the transistor 8 is turned on, an input voltage V _IN from the input DC power supply 1 is applied to both ends of the inductor 9, a current _ION 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 waveform, and the current change ΔI _ON
Is the inductance of the inductor 9 as L, the on time of the transistor 8 as T _ON and the collector C of the transistor 8
−If the voltage between the emitters E is V _CE = 0,

[0024]

## EQU1 ## At this time, the energy E stored in the inductor 9 is

[0026]

## EQU1 ## However, when the transistor 8 is on, the rectifying diode 5 does not conduct, so that the 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, the current I _ON
The energy E stored in the inductor 9 while the transistor 8 is on while maintaining the _ON state induces a back electromotive force in the inductor 9, and the back electromotive force causes the rectifying diode 5 to conduct, thereby causing the current I _OFF to flow. , The energy E stored in the inductor 9 is equal to the DC voltage V _{IN of the} input DC power supply 1.
5 and a capacitor 6 for smoothing
And a positive output voltage V _OUT having the same polarity as the input voltage V _IN is obtained at both ends of the load 7.

At this time, the current change ΔI _OFF of the current I _OFF flowing through the inductor 9 and the diode 5 is _equal to the load 7
Assuming that the output voltage at 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 drop voltage of the diode 5 is V _D.

[0030]

## EQU1 ## 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 between T _ON and T _OFF , that is, ΔI _ON
And △ I _OFF are equal, so from equations (7) and (9),

[0032]

## EQU1 ##

From the equation (10), the relationship between the input voltage V _IN and the output voltage V _OUT is obtained.

[0035]

And V _D = 0 for simplicity of explanation.
Then, the output voltage V _OUT becomes a voltage boosted from the input voltage V _IN . For example, the output voltage V _OUT under the condition of T _ON = T _OFF becomes twice the input voltage V _IN .

When the transistor 8 is off, the voltage V _CE between the collector C and the emitter E of the transistor 8 is as follows: V _CE = (V _D + V _OUT ) (12) For this reason, the transistor 8 needs to have a withstand voltage exceeding the voltage V _CE between the collector C and the emitter E in the equation (12).

Subsequently, the step-down type D according to the third conventional technique is used.
Referring to FIG. 4 , the C-DC converter has a collector C connected to a positive side of an input DC power supply 1 having a negative side connected to a ground terminal Q and a ground terminal Z through an input terminal P, and switching supplied from a base B. A transistor 8 serving as a switching element that switches the input voltage VIN of the input DC power supply 1 under the control of the drive signal and outputs the input voltage VIN to the emitter E, one end a of which is connected to the ground end Q and the ground end Z, and A driving circuit 2 that is controlled by an input rectangular wave periodic control signal, outputs a 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; The other end e is connected to one end of the smoothing element and the output end W, and the other end is connected to 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 flow the current I _OFF was induced to conduct a rectifying element, a cathode side connected to one end d of the emitter E and the inductor 9 of the transistor 8 and the anode side is connected to the ground terminal Q and the ground terminal Z And when the transistor 8 is off, the transistor 8 is turned on.
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 end is connected to the ground end Q and the ground end Z. And a capacitor 6 as a connected smoothing element.

Next, the operation will be described. When the transistor 8 is turned on, 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 , a voltage of V _IN −V _OUT is applied to both ends of the inductor 9. A current _ION 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 is represented by the inductance of the inductor 9 being L, the on time of the transistor 8 being T _ON, and the collector C-emitter E of the transistor 8. Assuming that the inter-voltage is V _CE = 0,

[0040]

## EQU1 ##

At this time, the energy E accumulated in the inductance 9 is:

[0043]

Is as follows.

When the transistor 8 is turned off while the current I _ON is flowing through the inductor 9, the current I _ON
The energy E stored in the inductor 9 while the transistor 8 is on while maintaining the _ON state induces a back electromotive force in the inductor 9, and the back electromotive force causes the rectifying diode 5 to conduct, thereby causing the current I _OFF to flow. 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]

Is as follows.

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 between T _ON and T _OFF , that is, ΔI _ON and ΔI _{ON
Since OFF} is equal, from the equations (13) and (15),

[0050]

Is as follows.

From the equation (16), the relationship between the input voltage V _IN and the output voltage V _OUT is obtained.

[0053]

Here, for simplicity of explanation, V
_{Assuming D} = 0,

[0055]

As a result, the output voltage V _OUT becomes 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 , for example.

The voltage V _CE between the collector and the emitter of the transistor 8 when the transistor 8 is off is as follows: V _CE = (V _IN −V _D ) (19) For this reason, the transistor 8 needs to have a withstand voltage that exceeds the voltage V _CE between the collector C and the emitter D in Expression (19).

Further, referring to FIG. 5 which is a basic circuit of the power supply circuit of the fourth prior art, the collector C through the input terminal P is connected to the negative side at the ground terminal Q and the ground terminal Z.
Connected to the positive side of the input DC power supply 1 connected to the 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 to output to the emitter E A transistor 8 having one end a connected to the ground end Q and the ground end Z and controlled by a rectangular wave periodic control signal inputted from the control input end R to output a switching drive signal to the other end b; And a driving circuit 2 for switching driving the transistor 8 by supplying it to the base B, one end e of which is connected to one end of the rectifying element, the other end d of which passes through one end of the smoothing element and the output end W, and the other end of which is the ground end Z and the ground. An intermediate tap f connected to one end of the load 7 connected to the terminal Q and provided between the windings M ₁ and M ₂ is connected to the emitter E of the transistor 8. When the transistor 8 is turned on and the transistor 8 is turned on, the current I _ON flows to store energy, and when the transistor 8 is turned off, the stored energy induces a back electromotive force to make the rectifier element conductive so that the current I _OFF flows. And an anode connected to one end e of the inductor 4 and an anode connected to the ground terminal Q and the ground terminal Z.
A diode 5 as a rectifying element which conducts when the transistor 8 is off and becomes non-conductive when the transistor 8 is on, and one end connected to one end of the load 7 through the other end d of the inductor 4 and the output end W Are connected to a ground terminal Q and a ground terminal Z, and a capacitor 6 as a smoothing element.

Next, the operation will be described. Transistor 8 is turned on when the winding M ₁ side of the inductor 4 the current I _ON flows through the transistor 8 and Condesa 6,
When energy is accumulated in the inductor 4 and the input voltage from the input DC power supply 1 is V _IN and the output voltage across the load 7 is V _OUT between the other end a of the inductor 4 and the intermediate tap d, V _IN − A 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 waveform, and the current change ΔI _ON is determined by setting the inductance of the winding M ₁ of the inductor 4 to L ₁ and the ON time of the transistor 8 to T ON. _{Assuming that the} voltage between _ON and the collector C-emitter E of the transistor 8 is V _CE = 0,

[0060]

Is obtained.

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

[0063]

Is obtained.

Here, if the transistor 8 is turned off while the current I _ON is flowing through the inductor 4, this current I _ON
The energy stored while the transistor 8 is on to maintain the _ON state induces a back electromotive force in the inductor 4, and the rectifying diode 5 conducts due to the back electromotive force to cause a current I _OFF to flow through 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, current change _ΔI of current I _OFF flowing through diode 5, inductor 4 and load 7
_OFF, winding M ₂ side of the inductor 4 the inductance L
Assuming that the off time of ₂ and the transistor 8 is T _OFF and the forward drop voltage of the diode 5 is V _D ,

[0067]

Is obtained.

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

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 between T _ON and T _OFF , that is, ΔI _ON and ΔI _{ON
Since OFF} becomes equal, from the equations (20) and (22),

[0071]

Is obtained.

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

[0074]

As a result, the output voltage V _OUT becomes the input voltage V _IN
The output voltage V _OUT under the condition of T _ON = T _OFF and L ₁ = L ₂ becomes the input voltage V _{IN, for example.}
2/3. Further, under the same conditions, the formula (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) Furthermore the stepped-down voltage proportional to the ratio of the inductance L ₁ and the inductance L ₂ by providing an intermediate tap f 4.

[0076] The collector of the transistor 8 when the transistor 8 is turned off - voltage V _CE between the emitter voltage across winding M ₁ of the inductor 4 the voltage across the V _L1 and the winding M ₂ and 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, the collector C−
The voltage V _CE between the emitters E is lower by V _{L2 than the} voltage V _CE between the collector C and the emitter E in the equation (19) of the conventional step-down DC-DC converter. That is, V _CE
Is provided with an intermediate tap on the inductor 4 so that the winding M
Decreases in proportion to ₁ and the turns ratio between winding M _2, it requires only that the breakdown voltage of the partial transistor 8 is 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 -It is not smaller than a DC converter.

[0078]

In the polarity-reversal type DC-DC converter of the first prior art, T _ON = T
Under the _OFF condition, the output voltage V _OUT becomes the input voltage V _IN
And a voltage higher than the input voltage V _IN cannot be obtained. In addition, (V _I N +
Since a withstand voltage of (V _D + V _OUT ) is required, a switching element with a low withstand voltage cannot be used.

Further, a step-up type DC according to the second prior art
In the −DC converter, under the condition of T _ON = T _OFF , the output voltage V _OUT can obtain a voltage approximately twice as high as the input voltage V _IN , but the switching element has (V _D + V _OUT ) Therefore, a switching element having a low withstand voltage cannot be used.

Further, a step-down type D, which is a third prior art,
In the C-DC converter, the output voltage V _OUT is about half of the input voltage V _IN under the condition of T _ON = T _OFF , and the switching element needs a withstand voltage of (V _IN + V _D ). In order to obtain a high output voltage V _OUT , the input voltage V _IN increases accordingly, and a switching element with a low withstand voltage cannot be used.

Further, in the power supply circuit according to the fourth conventional technique, by providing the inductor 4 with the intermediate tap f, T _ON = compared to the conventional step-down DC-DC converter.
Under the same conditions of T _OFF , the output voltage V _OUT is
Further steps down in proportion to the ratio of the inductance L ₁ and the inductance L _2, also the switching element (V _IN +
Since a withstand voltage of (V _D -V _L2 ) is required, the input voltage _VIN increases to obtain a high output voltage V _OUT, and a switching element with a low withstand voltage cannot be used.

[0082]

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

[0083]

[0084]

[0085]

Next, the present invention will be described with reference to the drawings. Referring to FIG. 1, which shows 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 supply 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 a switching drive signal supplied from the gate G. Input DC power supply 1
N-type channel MOS F as a switching element for switching the input voltage V _IN
ET (Metal Oxide Semiconductor)
to Field Effect Transist
or) a switching drive signal is output to the other end b, and one end a is connected to the grounding end Q and the grounding end Z and controlled by a rectangular wave-shaped periodic control signal inputted from the control input end R to output the switching driving signal to the other end b. MOS to supply to gate G of FET3
A drive circuit 2 for switchingly driving the FET 3;
Is connected to the ground end Q and the ground end Z, the other end d is connected to one end of the rectifying element, and an intermediate tap f provided between the windings M ₁ and M ₂ is connected to the drain D of the MOSFET 3. The energy is stored by the current I _ON that is connected and flows when the MOS FET 3 is on, and the back electromotive force is induced by the stored energy when the MOS FET 3 is off to make the rectifying element conductive so that the current I _OFF flows. And a load 7 whose cathode side is connected to the other end d of the inductor 4 and whose anode side is connected to one end of the smoothing element and the other end to the ground end Z and the ground end Q through the output end W. It is connected to one end and conducts when MOS FET3 is off,
A diode 5 serving as a rectifying element that becomes non-conductive when the FET 3 is turned on, one end of which is connected to one end of the load 7 through the anode side of the diode 5 and the output end W, and the other end is connected to the ground end Q and the ground end Z. And a capacitor 6 as a smoothing element connected to

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

[0087]

Is as follows. At this time, the energy E stored in the inductor 9 is

[0089]

## EQU10 ## However, since the rectifying diode 5 does not conduct when the MOS FET 3 is on, this energy E is not supplied to the load 7.

Here, the current I flows through the winding M ₂ of the inductor 4.
Turning off the MOS FET 3 _{when ON} is flowing, the current energy transistor 8 in an attempt to maintain the I _ON is accumulated in the period of the on E induces a back electromotive force in the inductor 4, a counter electromotive force The rectifying diode 5 conducts and the 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 that of the input voltage _VIN is applied to both ends of the load 7. The voltage V _OUT is obtained.

At this time, current change _ΔI of current I _OFF flowing through inductor 4, diode 5 and load 7
_OFF, the inductance of the windings M ₁ of the inductor 4 L
_1, the inductance of the winding M ₂ of the inductor 4 L _2,
Assuming that 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]

Is obtained.

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

Considering the case where the current flowing through the inductor 4 is continuous, the amount of change in the current flowing through the inductor 4 during the period between T _ON and T _OFF , that is, △ I _ON and △ I _OFF , become equal. 28) and equation (30),

[0097]

Is obtained.

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

[0100]

In order to simplify the explanation, V _D
= 0, the output voltage V _OUT becomes a voltage boosted from the input voltage V _IN . 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, when the output voltage V _OUT in Expression (32) is compared with the output voltage V _OUT in Expression (5) of the conventional polarity inversion type DC-DC converter under the same conditions, Expression (3)
By direction of the output voltage V _OUT at 2) is provided with a center tap f on the inductor 4 than the output voltage V _OUT in equation (5), the voltage boosted twice. 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 This will be described quantitatively below.

MOS when MOS FET3 is off
Drain D- source S voltage V _DS of the FET3 is, when the voltage across the winding M ₁ of the inductor 4 the voltage across the V _L1 and winding M ₂ and _{V L2, V L2 = V D} + V OUT -V L1 (34) V _DS = V _IN + V _L2 (35) From the equations (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]

The following is obtained.

Here, the drain D−
The source-to-source voltage V _DS becomes smaller by V _{L1 than the} collector-to-emitter E voltage V _CE in equation (6) of the conventional polarity inversion 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 pronounced when higher high voltage output voltages are 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 output voltage V _{OUT of} 100V
3 of breakdown voltage V _DS is 100V, and the compared to the breakdown voltage V _CE = 200V conventional without the center tap of the same conditions of the polarity inversion-type DC-DC converter of the transistor 8 100V
Is generated. The withstand voltage and the withstand voltage difference are the values when each element is used just below the absolute maximum rating.
Normally, since the derating is used at about 70%, this withstand voltage difference is further increased to 130 V, so that the effect of providing the intermediate tap f is large.

[0107]

[0108]

[0109]

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As described above, according to the present invention, by providing an intermediate tap in the inductance element, it is higher than the input voltage and, for example, about 100 V which is sufficient for driving an avalanche photodiode (APD). , And a low breakdown voltage transistor can be used as the switching element, so that the size of the on-board power supply can be reduced. This effect becomes more pronounced in proportion to obtaining a higher high output voltage.

[Brief description of the drawings]

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

FIG. 2 is a polarity-reversal type DC-DC converter of a first conventional example.
FIG.

FIG. 3 is a circuit diagram showing a step-up DC-DC converter according to a second conventional example.

FIG. 4 is a circuit diagram showing a step-down DC-DC converter of a third conventional example.

FIG. 5 is a circuit diagram showing a power supply circuit of a fourth conventional example.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-219461 (JP, A) JP-A 4-259 (JP, A) JP-A-50-60712 (JP, A) JP-A-54- 104252 (JP, A) JP-A-62-178168 (JP, A) JP-A-60-117690 (JP, U) JP-B-41-5773 (JP, B1) US Patent 4,720,667 (US, A) US Patent 4,720,668 (US, A)

Claims (1)

(57) [Claims] 1. An input DC power supply having the other end connected to a common line.
A first electrode is connected to one end of the switch to switch from the second electrode
The input direct input to the first electrode by a driving signal
The DC voltage from the power supply is switched and output to the third electrode.
A transistor connected to the common line and having one end connected to the common line and periodically connected to the control input end.
A control signal is input and the other end of the switching drive signal
And outputs the same to the second electrode of the transistor.
A tapping means provided between the first winding and the second winding;
And the other end opposite to the tap is connected to the common line, and
Connect the other end of the second winding opposite to the tap to a rectifying element.
Connected to one end and the tap is connected to the transistor
When the transistor is on by connecting to the third electrode of
Energy stored and energy stored when off
Of the load whose other end is grounded through the rectifying element.
An inductance element to be supplied to one end of the second winding of the inductance element;
Connected to one end opposite to the
Connected to one end of the load and the transistor
The rectifier, which is non-conducting when on and conducting when off.
Element and one end connected to the other end of the rectifying element and one end of the load
And the other end is connected to the common line and the energy stored in the inductance element input through the rectifier element.
And smoothes the input DC power supply across the load.
The smoothing element for obtaining a DC output voltage having a polarity opposite to a DC voltage.
And a DC-DC converter comprising: