JPH0787733A - Stabilized power supply starting circuit - Google Patents

Abstract

PURPOSE:To reduce the loss of useless power generated in a starting circuit that supplies power through the input voltage Vi side to an output voltage control system when starting a stabilized power supply. CONSTITUTION:A starting circuit consists of a normal-on field-effect transistor 20 that extracts current from the input voltage Vi side and feeds it to a control system 10, voltage restricting means 9 to restrict a feed voltage Vs fed to the control system 10 to a specified value or less, and capacitor 8 charged through the feed voltage Vs. During start up of a stabilized power supply, the capacitor 8 is charged through the on-resistance of the transistor 20 to raise the feed voltage Vs. When the feed voltage reaches the specified value required for operating the control system 10, a gate bias is applied to the transistor 20 to sharply decrease the charge current (i) flowing through it from the peak value (ip). The feed current is kept at this decreased level throughout the operation of the stabilized power supply.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a starting circuit for supplying power from a side of an input voltage to a control system of an output voltage when starting a stabilized power supply such as a switching power supply.

[0002]

2. Description of the Related Art As is well known in a stabilized power supply, for example, a control system for PWM-controlling the on / off operation of the switching transistor to maintain a constant output voltage is required. Since it is necessary to configure a large number of circuit elements, it is customary to incorporate it into a one-chip integrated circuit. The power supply voltage for operating this integrated circuit device is easily obtained, for example, as its auxiliary output voltage after completion of the startup of the stabilized power supply, but it must be separately generated from the input voltage at least during startup. The starting circuit targeted by the present invention is used.

FIG. 4 (a) shows a typical conventional example of this starting circuit in a state of being incorporated in a stabilized power supply. The stabilizing power supply shown in the figure is a switching power supply, which rectifies an AC voltage Va of a commercial frequency of 100 to 220 V by a rectifying circuit 1 and a capacitor 2
The flyback type transformer 3 receives the smoothed and stabilized input voltage Vi by means of the switching transistor 4, and the diode 5 rectifies the voltage induced in the secondary coil 3b while interrupting the current flowing in the primary coil 3a. The output voltage Vo is output after being smoothed by the capacitor 6. The control system 10 incorporated in the chip of the integrated circuit shown by the block in the figure receives the actual value of the output voltage Vo, and the output voltage Vo is as usual. Then, the switching transistor 4 is controlled to be turned on and off so as to hold it at a predetermined set value.

The low-voltage power supply voltage Vs of about 5 to 15 V for the control system 10 is rectified by the diode 7 during the operation of the induced voltage of the auxiliary coil 3c of the transformer 3 and smoothed and stabilized by the capacitor 8. In order to generate this power supply voltage Vs at the time of start-up, a starter circuit consisting of a series circuit of a high resistance R receiving the input voltage Vi and a Zener diode 9 is provided as shown in the figure, and the power supply is limited to the latter Zener voltage or less. The voltage Vs is applied to the control system 10. When the power supply voltage Vs rises to a predetermined value at the time of starting the stabilized power supply by turning on the switch S, the control system 10 starts the on / off control for the switching transistor 4, and thereafter, the auxiliary coil 3c of the transformer 3 controls the control system. Supply voltage Vs and the current necessary for its operation are supplied to 10.

[0005]

As described above, the conventional starting circuit may have a very simple structure mainly composed of the resistor R.
There is a problem that a large power loss occurs in the resistor R during normal operation of the stabilized power supply. This will be described with reference to the characteristic diagram of the current i flowing through the resistor R shown in FIG. The vertical axis of the figure is the current i, and the horizontal axis is the voltage v at which the input voltage Vi rises when the stabilized power supply is started. When the voltage applied to the control system 10 reaches the vicinity of the predetermined power supply voltage Vs while charging the capacitor 8 while the voltage v rises after the switch Sw is turned on, a current is supplied from the auxiliary coil 3c side with the start of the operation. Therefore, the current i temporarily decreases after the passage of the small peak ip, but as the voltage v further rises, the current i immediately starts to increase and thereafter, as shown in the figure,
Increases linearly until it reaches a predetermined input voltage Vi.

As a result of the current i increasing linearly in this way, the current i becomes (Vi-Vs) / R and the resistance R becomes easy to understand during the operation of the stabilized power supply in which the voltage v is the input voltage Vi. The stationary power loss that occurs inside is (Vi-Vs) ² / R. As described above, when the AC voltage Va is 100 to 220V, the rectified voltage, the input voltage Vi is 140 to 310V, and the power supply voltage Vs is only 5 to 15V, so the difference Vi-Vs becomes large. The power loss in the resistor R becomes large. It should be noted that the current i in the resistor R will wastefully flow toward the Zener diode 9 when the consumption current of the control system 10 is supplied from the auxiliary coil 3c side during operation of the stabilized power supply.

To reduce this power loss, the resistance R may be set to a high resistance, but the resistance value is selected to be lower than the limit that can supply the current required for its operation to the control system 10 at the time of starting the stabilized power supply. Even with this limit resistance value, the current i flowing through the resistor R during operation of the stabilized power supply becomes larger than the current consumption of the control system 10, and the power loss in the resistor R is usually one digit higher than the power consumption of the control system 10. It becomes bigger than that.

An object of the present invention is to solve the above problems of the conventional technique and reduce the wasteful power consumption generated in the starting circuit.

[0009]

According to the present invention, the above-mentioned object is to control a control system by extracting a current from the input voltage in order to supply power to the control system of the output voltage from the input voltage side at the time of starting the stabilized power supply. An always-on field effect transistor to be supplied to the control system, a voltage limiting means for limiting the power supply voltage to the control system to a set value or less, and a capacitor constantly charged by the power supply voltage are provided, and the power supply voltage is necessary for the operation of the control system. After reaching such a predetermined value, it is achieved by applying a gate bias to the field effect transistor to reduce the current flowing therein.

A junction field effect transistor or a depletion type field effect transistor can be used as the always conducting field effect transistor in the above structure, and the voltage limiting means is a constant voltage circuit element such as a Zener diode. Is preferably used. Further, it is possible to supply the power consumption of the control system from the starting circuit of the present invention after starting the stabilized power supply, but it is desirable to supply this consumption current from the auxiliary output of the stabilized power supply as in the conventional case. In this case, it is preferable to apply a gate bias to the field effect transistor so as to bring it into a pinch-off state after starting.

In order to apply a gate bias to the field effect transistor so as to reduce its current, for example, by applying an input voltage to its drain and grounding the gate with its source connected to the feeding point for the control system, stability is achieved. The reverse bias may be applied to the gate of the field effect transistor by utilizing the rise of the power supply voltage at the time of activation of the switching power supply. In addition, the stabilizing power supply is a switching power supply, and the switching transistor is used together with the control system.
When incorporated in an integrated circuit of a chip, it is advantageous to incorporate the start-up circuit of the present invention in the same chip because a field-effect transistor of a constant conduction type can be manufactured in the same process as a switching transistor.

[0012]

The present invention uses the field-effect transistor in place of the conventional resistance for power supply, and pays attention to the fact that the field-effect transistor can be easily controlled by the gate from a low on-resistance state to a high off-resistance state, and makes it a continuous conduction type. By so doing, the charging of the capacitor is promoted due to its low resistance state at the start of starting the stabilized power supply, and the rising of the power supply voltage to the control system is accelerated while the upper limit value is limited by the voltage limiting means, and the power supply voltage operates as the control system operates. After reaching the predetermined value required for the gate bias, the field effect transistor is put into a high resistance state and the current flowing through it is throttled, so that the input voltage is much higher than the power supply voltage. The power loss is reduced to a negligible level compared with the conventional circuit.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention in the same manner as FIG. 4, where FIG. 1 (a) is a circuit diagram of a stabilized power supply including a starting circuit of the present invention, and FIG. 1 (b) is a field effect of the starting circuit. FIG. 6 is a characteristic diagram of a current flowing through a transistor, and the portions corresponding to those in FIG. 4 are denoted by the same reference numerals, and the description of the overlapping portions will be appropriately omitted. FIG. 2 shows the case where a junction type field effect transistor is used in the circuit of the present invention.
Figure (a) shows an example of the structure, and Figure (b) compares it with DMO.
It is a principal part expanded sectional view of the chip of an integrated circuit which each shows the constructional example of an S-type switching transistor. FIG. 3 is an enlarged cross-sectional view of a main part of an integrated circuit chip showing an example of the structure in the case where a depletion type field effect transistor is used in the circuit of the present invention in the same manner as FIG. 2 (a).

The stabilized power supply shown in FIG. 1 (a) is a switching power supply using a flyback type transformer 3 and the main circuit has the same configuration as that shown in FIG. In the example, the switching transistor 4 is incorporated together with the starting circuit of the present invention in the chip of the integrated circuit device 30 for the control system 10 which is surrounded by a dot-dash line in the figure, and further, in the example shown, the induction of the auxiliary coil 3c of the transformer 3 is induced. The diode 7 for the auxiliary output which receives the voltage is also incorporated therein. When the input voltage Vi is, for example, 310V, the switching transistor 4 needs a high withstand voltage of about 600 to 650V in addition to the margin for the input voltage Vi and the counter electromotive force generated in the primary coil 3a of the transformer 3, so that the DMOS is required. Or, it is customary to use a double diffusion type field effect transistor.

The drive circuit is composed of a field effect transistor 20 of a constant conduction type which replaces the conventional feeding resistor, a capacitor 8 which is the same as the conventional one, and a voltage limiting means 9. In the embodiment of FIG. Is a junction field effect transistor, and the voltage limiting means 9 is the same Zener diode as the conventional one. For example, the junction field effect transistor 20 receives an input voltage Vi at its drain, has its source connected to a feeding point for the control system 10, and has its gate grounded as shown to establish a reverse bias when the feeding voltage Vs is established. It is better to hang it. Further, the diode 7, the capacitor 8 and the voltage limiting means 9 are of course connected to the above-mentioned feeding point. When the input voltage Vi is 310V as described above, the junction field-effect transistor 20 has a margin of 45V.
It is desirable to have a breakdown voltage value of about 0V.

When the switch Sw is turned on at the time of starting the stabilized power supply, the voltage v shown in FIG. 1 (a) rises toward a predetermined input voltage value Vi, and the normally-conducting field effect transistor 20 is turned on at the beginning of this rise. The power supply voltage Vs which is set by the voltage limiting means 9 in the capacitor 8 by the flowing current i
However, in the starting circuit of the present invention, since the on-resistance value of the field effect transistor 20 is considerably lower than the resistance R of FIG. 4, a larger current i than the conventional one causes the rise of the feeding voltage Vs and the current to the control system 10. Supply is promoted. Therefore, the control system 10 starts operating at the time when the voltage v rises up to near the power supply voltage Vs, and the switching transistor 4
Is controlled on and off, the control system for the current is indicated by the broken line in FIG. 1 (b) via the diode 7 from the auxiliary coil 3c side.
Supply to 10 is started.

On the other hand, since a reverse bias is applied to the gate of the field effect transistor 20 at the same time when the power supply voltage Vs rises, the current i is throttled by this, and the control system is controlled from the auxiliary output side.
As shown in the figure, as the supply of the above-mentioned current is started at 10, after the peak ip has elapsed, it rapidly decreases to a small constant current ic, and this state causes the voltage v to rise to a predetermined input voltage value Vi. It is maintained until and after the operation of the stabilized power supply. Comparing this with the characteristics of the current i shown in FIG. 4 (b), it can be seen that the present invention can significantly reduce the current i flowing in the starting circuit during the steady operation of the stabilized power supply as compared with the conventional case. Further, along with this, the voltage limiting means 9 causes the power supply voltage Vs
Need only fulfill the role of keeping the value below the set value, and there is no need to supply a large current during operation as in the conventional case.

In the embodiment of FIG. 1, since the current consumed by the control system 10 is supplied as a constant current is from the auxiliary output side during the operation of the stabilized power supply, the field effect transistor 20 is reversely applied to its gate. It is advantageous to make the so-called pinch-off state during operation by the bias to narrow down the above-mentioned constant current ic to a very low level, and in this embodiment, the power loss in the starting circuit during operation is reduced to the number of power consumptions of the control system 10. It can be reduced to 1/10. When the auxiliary output is omitted, it is possible to easily configure the field effect transistor 20 so that the current i flowing in the gate biased state is narrowed down to the current consumption value of the control system 10.

FIG. 2A shows an example of a concrete structure of the junction type field effect transistor 20 of FIG. In this embodiment, the field effect transistor 20 is incorporated in the chip of the integrated circuit device 30 together with the switching transistor 4, so that
DMOS of switching transistor 4 shown in (b)
The structure will be similar to the structure so that it can be created in a common process. Therefore, the DMOS structure of FIG. 2B will be described first. The substrate 31 for the integrated circuit device 30 has, for example, a p-type 100
Use a high resistance material of ~ 200 Ωcm and L0COS on the surface.
An n-type well 21 is provided within a range surrounded by the film 32 and having an impurity concentration of, for example, 10 ¹⁶ atoms / cm ³ of several μm.
Diffuse to the depth of. Next, a gate 22 is provided on a predetermined portion of the surface of the well 21 via a thin gate oxide film 22a, and then a p-type channel layer 23 and an offset layer 25 are diffused.
The former has an impurity concentration of about 10 ¹⁷ atoms / cm ^{3 and is} , for example, 1.5 μm.
The latter is made to have a shallow depth of 1 μm with an impurity concentration of about 10 ¹⁶ atoms / cm ³ .

Further, an n-type source layer is provided on both sides of the gate 22.
26 is diffused at a high impurity concentration of 10 ²⁰ atoms / cm ³ or more to a depth of about 0.5 μm, and at the same time, a contact layer for drain.
Diffuse 28 with the same n-type and the same impurity concentration and depth. Next, the aluminum electrode film 33 is arranged in the required places to form the channel layer.
The source terminal S is derived from 23 and the source layer 26, the drain terminal D is derived from the contact layer 28, and the gate terminal G is derived from the gate 22 to complete the illustrated state.

The DMOS transistor 4 is an n-channel type, and is used in a state where the source terminal S is grounded and the drain terminal D is connected to the primary coil 3a of the transformer 3 as usual. When the gate terminal G receives a positive control voltage, an electron current flows from the source terminal S to the drain terminal D through the channel formed on the surface of the channel layer 23 below the gate 22. Further, at the time of off, the depletion layer mainly spreads in the well 41 below the offset layer 25, which is a double diffusion layer for the channel layer 23, and a high breakdown voltage of several hundred V is obtained. The transistor 4 can be provided with a current capacity of about 1 A or more, and a switching operation can be performed at a high frequency of several hundred kHz.

The junction field effect transistor 20 shown in FIG. 2 (a) has an n-type well 21 and a p-type well 21 similar to the DMOS structure.
Type offset layer 25 is provided as shown in the figure, and a p-type gate layer 24 is diffused in place of the channel layer 23 of the transistor 4 and an n-type contact layer 27 is diffused in place of the source layer 26 in the same process. Then, the electrode film 33 is provided to lead out the source terminal S and the drain terminal D from the contact layers 27 and 28, respectively, and lead out the gate terminal G from the gate layer 24.

The field-effect transistor 20 having such a structure is used in a state in which the drain terminal D receives the input voltage Vi, and the source terminal S and the drain terminal D thereof are not biased to the gate terminal G when the stabilized power source is started. The current i described above flows as a constant-conductivity-type resistor which is electrically connected between the two, but when a bias is applied to the gate terminal G after that, the n-type on the lower side from the p-type gate layer 24 and the offset layer 25. When a depletion layer extends vertically in the well 21 of FIG. 2 and narrows the current i, and the source terminal S is applied with the power supply voltage Vs and the gate terminal G is reverse biased by that amount, for example, as described above, pinch-off occurs. After entering the state, the current i is narrowed down to a very small value, and this state is of course maintained throughout the operation of the stabilized power supply.

As described above, the junction-type field effect transistor 20 shown in FIG. 2A can be easily incorporated into the integrated circuit device 30 in the same process as the switching transistor 4 having the DMOS structure, and the source terminal S thereof can be incorporated. The current flowing through the stabilized power supply after starting and during operation can be sufficiently narrowed down only by connecting the gate terminal G to the power supply point for the control system 10 and grounding the gate terminal G. In this field effect transistor 20, the withstand voltage of several hundreds of V required in the pinch-off state can be appropriately set by the lateral length of the preset layer 24 described above. Further, since the current capacity thereof may be relatively small, it may be formed in a laterally elongated shape having a small dimension in the front-back direction in the drawing.

In the embodiment of FIG. 3, the field effect transistor 20 of the always conducting type is constructed in the depletion type. As can be seen from the figure, the structure of this depletion type transistor 20 is different from the DMOS structure of FIG. 2 (b) only in that an n-type channel conductive layer 29 is diffused below the gate 22. The layer 29 is preferably diffused to a depth of 0.5 μm or less with an impurity concentration of 10 ¹⁶ to 10 ¹⁷ atoms / cm ³ , for example. The depletion type field effect transistor 20 also functions as a resistor that conducts in a state where the gate terminal G is not biased and allows the current i to flow, and when the feed voltage Vs is applied as a reverse bias to the channel conduction layer 29. Since the effect of conducting the channel is diminished, the current i is throttled in the non-conducting state or close to the non-conducting state, and this current limiting state is maintained throughout the operation of the stabilized power supply. As described above, according to the embodiment of FIG. 3, the field-effect transistor of the always conducting type has almost the same structure as the switching transistor to facilitate the incorporation into the integrated circuit, and the impurity concentration on the surface of the channel conducting layer 29 is appropriately set. The diaphragm effect for the current i can be easily controlled.

[0026]

As described above, in the start-up circuit of the present invention, the control system for the output voltage is supplied from the input voltage side when the stabilized power supply is started, so that the current is extracted from the input voltage side and supplied to the control system. An always-on field effect transistor,
A voltage limiting means for limiting the power supply voltage to the control system to a predetermined value or less and a capacitor charged by the power supply voltage are provided, and when the power supply voltage reaches the predetermined value necessary for the operation of the control system, By applying a gate bias and narrowing the current flowing through it, the following effects can be achieved.

(A) Taking advantage of the fact that a normally conducting field-effect transistor can be easily controlled by a gate bias from a low resistance state to a high resistance state, the current flowing through the stabilized power supply after starting and during operation is The power loss of the starting circuit can be reduced to a negligible level as compared with the conventional circuit. (b) A stabilized power supply that accelerates the rise of the power supply voltage to the control system while accelerating the charging of the capacitor at the start of starting the stabilized power supply by using the relatively low on-resistance when the field-effect transistor of the always-on type is on The startup time of can be shortened.

(C) Since the current flowing through the starter circuit during the operation of the stabilized power supply decreases, an extra current exceeding the current consumption of the control system does not flow into the voltage limiting means as in the conventional case, and the voltage controlling means operates. The current load can be reduced and the current capacity of the Zener diode for it can be set smaller than before. (D) By using a junction type or depletion type field effect transistor as an always conducting field effect transistor. , The DMOS structure and the switching transistor can be easily and economically manufactured in a common process when incorporated in an integrated circuit device for a control system.

As described above, according to the present invention, the power loss in the starting circuit is reduced to a negligible level as compared with the conventional case, the power conversion efficiency of the stabilized power source is improved, and the starting time is shortened to improve its performance. In addition, the starter circuit and the switching transistor are incorporated into a one-chip integrated circuit together with the control system, which is highly effective in increasing the economical efficiency.

[Brief description of drawings]

1 shows an embodiment of a starting circuit for a stabilized power supply according to the present invention, FIG. 1 (a) is a circuit diagram of a stabilized power supply including the circuit of the present invention, and FIG. 1 (b) is a field effect transistor of the starting circuit. It is a characteristic diagram of flowing current.

FIG. 2 relates to an embodiment in which a junction type field effect transistor is used as a field effect transistor of a constant conductivity type which constitutes a circuit of the present invention. FIG. 2A is a structural example thereof, and FIG. FIG. 4 is an enlarged cross-sectional view of a main part of a chip of an integrated circuit showing a structural example of a DMOS type switching transistor.

FIG. 3 is an enlarged cross-sectional view of a main part of an integrated circuit chip showing an example of the structure when a depletion type field effect transistor is used as the always conductive type field effect transistor constituting the circuit of the present invention.

FIG. 4 is a diagram showing an example of a starting circuit according to the related art, and FIG.
Is a circuit diagram of the stabilized power supply including the starter circuit, and Fig. 6 (b) is a characteristic diagram of the current flowing through the power supply resistance of the starter circuit.

[Explanation of symbols]

8 Capacitor constituting start-up circuit 9 Voltage limiting means constituting start-up circuit 10 Control system 20 Field effect transistor of conduction type constituting start-up circuit i Current flowing in start-up circuit Vi Stabilized power supply input voltage Vo Stabilized power supply Output voltage Vs Power supply voltage for control system

Claims (3)

[Claims] 1. A circuit for supplying power to a control system of an output voltage from an input voltage side at the time of starting a stabilized power supply, wherein a current is extracted from the input voltage side and supplied to the control system. An effect transistor, a voltage limiting means for limiting the power supply voltage to the control system to a predetermined set value or less, and a capacitor constantly charged by the power supply voltage are provided, and the power supply voltage becomes a predetermined value necessary for the operation of the control system. In the reached state, the starting circuit for the stabilized power supply is characterized in that the gate bias is applied to the field effect transistor so that the current flowing therein is narrowed. 2. The circuit according to claim 1, wherein after activation of the stabilized power supply, the auxiliary output voltage of the stabilized power supply is supplied to the control system, and the field effect transistor is gate-biased to be in a pinch-off state. The starting circuit for the stabilized power supply is characterized in that 3. The stabilized power supply start-up circuit according to claim 1, wherein a normally conductive junction field effect transistor is used as the field effect transistor.