JP2000312477A - Switching regulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve conversion efficiency by reducing the loss in a MOSFET used as an element for switching or an element for rectification. SOLUTION: A switching regulator obtains different DC output voltages, by stepping up or down the DC input voltage and it uses MOSFETs 101, 102 as an element for switching or an element for rectification, Each of the MOSFETs has an electrode for controlling the potential in a body region. This switching regulator is also provided with a control circuit 103, which inputs a signal synchronous with a signal inputted into the gate electrodes of the MOSFETs into the electrodes for controlling the potential in the body region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching regulator, and more particularly to a switching regulator that can increase or decrease a DC input voltage and output a DC output, and is applicable to a power supply such as a CPU.

[0002]

2. Description of the Related Art A configuration example of a conventional switching regulator will be described. FIG. 11 is a block diagram showing a buck converter using a conventional synchronous rectification method. As shown in FIG.
, A rectifying MOSFET 502, a control circuit 503 having terminals J and K, and an output filter 504. The terminal J is connected to the gate terminal of the MOSFET 501, and the terminal K is connected to the gate terminal of the MOSFET 502.

FIG. 12 is a waveform diagram showing signals output from terminals J and K of control circuit 503. As shown in the drawing, signals j and k output from terminals J and K of the control circuit 503 (hereinafter, referred to as gate signals) are MOSFET5
01 and 502 are input to the gate terminals, respectively. In general, in order to suppress a large current from flowing when the MOSFETs 501 and 502 are simultaneously turned on,
A predetermined dead time (T _dead ) is provided between the gate signals j and k of the MOSFETs 501 and 502.

The MOSFETs 501 and 502, which are switching elements or rectifying elements, are controlled by the gate signals j and k input from the control circuit 503, and repeat the on / off operation. The MOSFET loss is divided into conduction loss due to on-resistance and switching loss due to parasitic capacitance, ignoring the loss due to through current, and is expressed by the following equation.

[0005] ^{_{P = R on · I d 2}} + C iss · V g 2 · f (1)

Here, P is the total loss, R _on is the on-resistance, I
_d is the drain current, C _iss is the input capacitance, V _g is the gate drive voltage, and f is the switching frequency. As is apparent from the equation (1), it is understood that the reduction of R _on , C _iss , and V _g is effective in reducing the loss. In particular, the switching loss proportional to the switching frequency is caused by the gate drive voltage V _g
Is proportional to the square, it is necessary to reduce the gate drive voltage V _g.

[0007]

However, FIG.
As shown by the solid line in (a graph showing the relationship between the on-resistance and the gate voltage), since the on-resistance has a gate voltage dependency, when the gate voltage is low, the on-resistance does not sufficiently decrease, and the conduction loss is reduced. There is a problem of increasing.

On the other hand, as shown by the dotted line in FIG. 13, the gate voltage dependency of the on-resistance can be improved by setting the threshold voltage of the element low, but as the threshold voltage decreases, As a result, the leakage current during non-conduction is increased, resulting in an increase in loss. Although the apparent on-resistance can be reduced by connecting the elements in parallel, this method has a problem that the input capacitance increases and the switching loss increases.

The present invention has been made to solve such a problem, and a switching regulator capable of reducing the loss of a MOSFET used as a switching element or a rectifying element and improving conversion efficiency. The purpose is to provide.

[0010]

In order to achieve the above object, a switching regulator according to the present invention obtains a different DC output voltage by stepping up or down a DC input voltage, and obtains a switching element or a switching element. In a switching regulator using a MOSFET as a rectifying element, the MOSFET has an electrode for controlling the potential of a body region, and the MOSFET
And a control circuit for inputting a signal synchronized with a signal input to the gate electrode of T to an electrode for controlling the potential of the body region.

On the other hand, as another aspect of the present invention, the following configuration can be adopted. That is, the electrode for controlling the potential of the body region of the MOSFET and the gate electrode of the MOSFET may be connected via the diode. The electrode for controlling the potential of the body region of the MOSFET and the gate electrode of the MOSFET may be connected via a diode-connected MOSFET.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of operation of a switching regulator according to the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing a MOSFET used in the present invention. As shown in FIG. 1, a well 1 and diffusion layers 3 and 4 are provided on a substrate 1 made of bulk silicon, and a gate electrode 5 is formed on the well 2 via a gate oxide film.
Are provided on the diffusion layers 3 and 4, respectively.
And a drain electrode 7 are provided.
An FET is configured. Further, the well 2 is provided with a well electrode 8.

On the other hand, in the present invention, SOI (Silico
n On Insulator) A MOSFET formed on a substrate can also be applied. FIG. 2 is a diagram showing the structure of M formed on an SOI substrate.
FIG. 3 is a cross-sectional view illustrating an OSFET. As shown in FIG. 1, an insulator film 9 is formed on a substrate 1 made of silicon.
Diffusion layers 3 and 4 and body region 2a are provided thereon. A gate electrode 5 and a body electrode 8a provided via a gate oxide film are provided in the body region 2a, and a source electrode 6 and a drain electrode 7 are provided on the diffusion layers 3 and 4, respectively.

As described above, this embodiment is characterized in that a MOSFET having a well electrode or a body electrode is used. Although a MOSFET having a well electrode or a body electrode has been conventionally manufactured, conventionally, these electrodes are short-circuited with a source electrode and are not used as a control terminal of the MOSFET. Does not apply.

By the way, the threshold voltage of a MOSFET is generally expressed as follows.

[0016] _{V T = V FB + 2φ F} + {√ (2ε S ε 0 qN A (2φ F))} / C OX (2)

Φ _F = kT / q · ln (N _A / n _i ) (3)

Here, V _FB is a flat band voltage, φ _F
Is the Fermi level, ε _S is the relative permittivity of silicon, ε ₀ is the permittivity of vacuum, q is the elementary charge, N _A is the impurity concentration of the channel region, C _OX is the capacitance of the gate insulating film, and k is Boltzmann. The constant, T is the temperature, and _ni is the carrier density of the intrinsic semiconductor. Also, by changing the potential of the body region, equation (2) is described as follows.

[0019] _{V T = V FB + 2φ F} + {√ (2ε S ε 0 qN A (2φ F -V B))} / C OX (4)

Here, V _B is the potential of the body region.
As is apparent from equation (4), by controlling the potential V _B of the body region, it can be seen that control of the threshold voltage V _T. That is, by applying an appropriate potential to the body region only when the MOSFET is conducting, it is possible to simultaneously improve the on-resistance when conducting and suppress the leakage current when not conducting. In particular, if a configuration in which a well electrode or a body electrode is connected to a gate electrode is employed, threshold voltage control can be performed without increasing the number of control terminals of the MOSFET.

FIG. 3 is a graph showing the drain current-gate voltage characteristics of the MOSFET formed on the SOI substrate of FIG. 2 when the body electrode and the gate electrode are connected. The current value indicates a value per 1 μm of the channel width. As shown in the figure, by connecting the body electrode and the gate electrode, the threshold voltage is reduced and the drain current is increased.

FIG. 4 is a graph showing the dependence of the on-resistance on the gate voltage. The resistance value indicates a value per 1 μm of the channel width. As shown in the figure, by connecting the body electrode and the gate electrode, it can be understood that the on-resistance can be reduced even when the gate voltage is low. When the gate voltage is 1 [V], the ON resistance of the MOSFET according to the present embodiment is about one fifth of the ON resistance of a normal MOSFET.

As is apparent from the above description, the MOSF
The electrodes for controlling the potential of the body region of the ET are MOSFE.
By inputting a signal synchronized with the signal input to the gate electrode of T, it is possible to simultaneously reduce conduction loss and loss due to leakage current when not conducting,
The conversion efficiency of the switching regulator can be improved.

Next, an embodiment of the present invention will be described.

[0025]

FIG. 5 shows an example in which the present invention is applied to a synchronous rectification type buck converter. As shown in the figure, the present embodiment employs a MOSFET for switching.
T101, MOSFET 102 for rectification, and terminals A to
It comprises a control circuit 103 having D and an output filter 104.

The MOSFET 101 is a p-channel MOSFET for switching. MOSFET102
Is an n-channel MOSFET for synchronous rectification. The control circuit 103 is a circuit for supplying a control signal to the MOSFETs 101 and 102, and performs PFM control for changing a drive frequency or PWM control for changing a ratio of on / off time to obtain a desired DC voltage output. Has functions. The output filter 104 is a MOSFET 10
This circuit is a circuit that smoothes the rectangular wave generated by the first and second 102 and outputs a DC voltage, and is, for example, a smoothing filter including a coil, a capacitor, and the like.

FIG. 6 shows an example in which the present invention described above is applied to a one-stone forward converter. As shown in FIG.
A control circuit 202 having terminals E and F;
03, a rectifier circuit 204, and an output filter 205.

The MOSFET 201 is a p-channel MOSFET for switching. The control circuit 202
This is a circuit for supplying a control signal to the MOSFET 201, and has a function of performing PFM control for changing a drive frequency or PWM control for changing a ratio of on / off time in order to obtain a desired DC voltage output.

The transformer 203 is a circuit for transmitting a rectangular wave generated by the MOSFET 201 from the primary side to the secondary side. The rectifier circuit 204 is a circuit that rectifies the output of the transformer 203. The output filter 205 is a circuit that receives an output of the rectifier circuit 204 and outputs a DC voltage, and is, for example, a smoothing filter including a coil, a capacitor, and the like.

In these two embodiments, a control signal is supplied to each of the body electrode and the gate electrode. From the terminals A, B, C, and D of the control circuit 103, FIG.
Are output, and the control circuit 202 outputs the signals a, b, c, and d shown in FIG.
The signals e and f shown in FIG. 8 are output from the terminals E and F, respectively, to suppress the leakage current and the loss of the switching element. In the following description, the maximum value V _{g of the} gate input voltage
Is equal to the power supply voltage.

For the gate terminal of each MOSFET,
Rectangular waves a, c, and e having a maximum value of V _g [V] and a minimum value of 0 [V] are input from terminals A, C, and E of the control circuit. p
For the body terminal of the channel type MOSFET 101, the maximum value is V _g [V] and the minimum value is V _g −0. A signal b larger than 8 [V] is input.
For the body terminal of the n-channel MOSFET 102, the minimum value is 0 [V] and the maximum value is 0.8 [V] in synchronization with the signal c output from the terminal C from the terminal D of the control circuit 103. The following signal d is input.

For the above-mentioned reason, it is desirable to provide a dead time (T _dead ) between the rising and falling edges of the waveforms of the signals a and b and the signals c and d. The n-channel type MOSFET 201 shown in FIG.
Can be controlled by the same signals as the above-mentioned signals a and b, respectively.

[Second Embodiment] FIGS. 9 and 10 show a second embodiment of the present invention. That is, FIG. 9 shows a synchronous rectification type buck converter, and a switching MOSF.
ET 301, rectifying MOSFET 302, control circuit 303 having terminals G and H, and output filter 304
And diodes 305 and 306. FIG. 10 shows a single-pole forward type converter, which includes a switching MOSFET 401, a control circuit 402 having a terminal I, a transformer 403, a rectifier circuit 404, an output filter 405, and a diode 406.

In any case, a diode is inserted between the body electrode and the gate electrode in order to suppress a leakage current between the body electrode and the gate electrode. However, instead of connecting a diode, a diode-connected MOSFET can be used instead. According to the present embodiment, the switching and rectifying MOSFEs
This has the effect that leakage current and switching loss can be suppressed without increasing the number of control terminals of T.
As a matter of course, the number of terminals of the control circuit is reduced, and a simple configuration can be achieved.

The gate terminals of the MOSFETs 301 and 302 shown in FIG.
FIG. 12 in which the maximum value is V _g [V] and the minimum value is 0 [V].
By inputting the same signals as the signals j and k, the effect of the present invention can be obtained. The MOSF shown in FIG.
A signal similar to the signal k in FIG. 12 may be input from the terminal I of the control circuit 402 to the gate terminal of the ET 401.

[0036]

As described above, according to the present invention, the MOSF
The electrodes for controlling the potential of the body region of the ET are
A control circuit is provided for inputting a signal synchronized with a signal input to the gate electrode of the FET. Therefore, according to the present invention, it is possible to simultaneously reduce the conduction loss and the loss due to the leakage current at the time of non-conduction, thereby improving the conversion efficiency of the switching regulator.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a MOSFET applicable to the present invention.

FIG. 2 is a cross-sectional view showing another MOSFET to which the present invention can be applied.

FIG. 3 is a graph showing a relationship between a gate voltage and a drain current in the configuration of FIG. 2;

FIG. 4 is a graph showing a relationship between gate voltage and on-resistance in the configuration of FIG. 2;

FIG. 5 is a block diagram showing a synchronous rectification type buck converter (first embodiment).

FIG. 6 is a block diagram showing a one-stone forward converter (first embodiment).

FIG. 7 is a waveform chart showing signals a to d.

FIG. 8 is a waveform chart showing signals e to f.

FIG. 9 is a block diagram showing a synchronous rectification type buck converter (second embodiment).

FIG. 10 is a block diagram showing a one-stone forward converter (second embodiment).

FIG. 11 is a block diagram showing a conventional example.

FIG. 12 is a waveform chart showing signals j and k.

FIG. 13 is a graph showing a relationship between gate voltage and on-resistance in a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Well, 2a ... Body region, 3, 4 ... Diffusion region, 5 ... Gate electrode, 6 ... Source electrode, 7 ... Drain electrode, 8 ... Well electrode, 8a ... Body electrode, 9 ... Insulating film, 101, 102, 201, 301, 302, 401
... MOSFET, 103, 202, 303, 402 ... control circuit, 104, 205, 304, 405 ... output filter, 203, 403 ... transformer, 204, 404 ... rectifier circuit, 305, 306, 406 ... diode.

Continuation of the front page (72) Inventor Toshiaki Taniuchi 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo F-term in Nippon Telegraph and Telephone Corporation (reference) 5F048 AA05 AA07 AB07 AB10 AC03 AC10 BA16 BE03 BE09 BF17 CC06 CC13 5H006 CA02 CB03 CB07 CC08 DB01 HA08

Claims (3)

[Claims] 1. A switching regulator using a MOSFET as a switching element or a rectifying element to obtain a different DC output voltage by increasing or decreasing a DC input voltage, wherein the MOSFET controls a potential of a body region. And a control circuit for inputting a signal synchronized with a signal input to a gate electrode of the MOSFET to an electrode for controlling a potential of the body region. 2. The MOSFE according to claim 1, wherein an electrode for controlling a potential of the body region and the MOSFE.
A switching regulator, wherein the gate electrode of T is connected via a diode. 3. The MOSFE according to claim 1, wherein an electrode for controlling a potential of the body region and the MOSFE.
The gate electrode of T is a diode-connected MOSFE
A switching regulator, wherein the switching regulator is connected via T.