JP2004326739A - Soft start circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soft start circuit which can be manufactured by a capacitor of a relatively small capacity value. <P>SOLUTION: The soft start circuit is equipped with a first current source whose input port is connected to a first voltage; a transistor whose first port is connected to an output port of the first current source and whose second port is connected to a second voltage; and a capacitor one port of which is connected to the output port of the first current source and the other port of which is connected to an input port of the transistor. By coupling the transistor and the capacitor, a ratio value of a soft start voltage generated by the soft start circuit and a time is reduced. Thus, by increasing an equivalent capacity value of the capacitor, the soft start circuit can be manufactured by the capacitor of a relatively small capacity value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a soft start circuit, and more particularly, to a soft start circuit in which an equivalent capacitance value of a soft start circuit is increased so that the soft start circuit can be manufactured with a capacitor having a relatively small capacitance value.

  The principle of the soft start circuit is to couple by using a resistance capacitance (RC) charging circuit and a control circuit. At the moment when the load is turned on, the current flowing through the load is utilized by using the resistance capacitance charging circuit. It is controlled to increase at a relatively slow speed, thereby controlling the current passing through the load, thereby preventing a large current load and other damage to the coupling circuit caused when the load is turned on with a slow power supply. The goal is to be able to control it.

The conventional soft start circuit is composed of a fixed current source 11 and a capacitor 12, as shown in FIG. 1, and a series node (Node) A between the current source 11 and the capacitor 12 is provided with a soft start voltage. It is a survey node.
Here, if the current of the current source 11 is I, the soft start voltage of the series node A is V, and the capacitance value of the capacitor 12 is C, the formula V (soft start) / T = I / C
As can be seen from the figure, since the current I is a fixed value, if it is desired to obtain a relatively small V (soft start) / T ratio in a fixed state of the soft start voltage V, the capacitance of the capacitor 12 should be sufficiently increased. Must be large. At present, as a normal capacitance value applied to a circuit of this type, since the magnitude is always between 1 nF and 0.1 uF, the volume of the capacitor corresponding to such capacitance value is a general electric appliance part circuit. However, if this technique is used for an integrated circuit (IC), the following two kinds of difficulties will appear if this technique is used for an integrated circuit (IC).
1. Since the volume of the capacitor having the above-mentioned capacitance value is too large, it cannot be matched with the manufacturing process of the integrated circuit, and the volume of the integrated circuit cannot correspond to the tide which is reduced every day.
2. If the capacitor is manufactured to meet the requirements of the manufacturing process size of the integrated circuit, there arises a problem that the capacitance value is not sufficient to exert the protection function of the soft start circuit.

  In view of the above problems, the present applicant has conducted intensive tests and researches to solve this problem, and finally has devised the "soft start circuit" of the present invention.

  A main object of the present invention is to design a soft start circuit by reducing the ratio of the soft start voltage and time generated by the soft start to the soft start voltage. By amplifying the effective value of the capacitor included in the start circuit, a capacitor having a relatively small capacitance value (that is, a relatively small volume) can be manufactured at the time of the soft start circuit.

To achieve the above object, a soft start circuit according to the present invention comprises a first current source having an input terminal connected to a first voltage, and a first terminal connected to an output terminal of the first current source. A transistor having a second end connected to the second voltage, a capacitor having one end connected to the output end of the first current source, and the other end connected to the input end of the transistor. Soft start circuit,
The transistor and the capacitor are coupled, and the ratio of the soft start voltage generated by the soft start circuit to time is reduced, thereby increasing the equivalent capacitance of the capacitor. -The start circuit can be manufactured with a capacitor having a relatively small capacitance value (corresponding to claim 1).

In the above soft start circuit according to the present invention,
The first current source is a current mirror;
The current mirror is coupled by two identical P-type MOS field effect transistors (MOSFETs),
The input end of the current mirror is connected to the input end of a second current source, the output end of the current mirror is connected to the first end of the transistor and one end of the capacitor, and the common source end of the current mirror is The output terminal of the second current source is connected to the first voltage, and the output terminal of the second current source is connected to the second voltage.

In the soft start circuit according to the present invention,
The first voltage is set higher than the second voltage,
The transistor is an npn-type bipolar junction transistor (BJT),
The first end of the transistor is a collector end, the second end of the transistor is an emitter end, the control end of the transistor is a base end, and / or the transistor is a Darlington transistor, wherein the Darlington transistor is The transistor is a coupling of a first npn-type bipolar junction transistor and a second npn-type bipolar junction transistor, and the base end of the first npn-type bipolar junction transistor is connected to the input terminal of the transistor. The emitter end of the first npn-type bipolar junction transistor is connected to the base end of the second npn-type bipolar junction transistor, and the collector end of the first npn-type bipolar junction transistor is connected to the Second npn-type bipolar junction And connected to the collector terminal of the transistor is configured first end of the transistor, the emitter terminal of the npn bipolar junction transistor of the second is the second end of the transistor (corresponding to claim 3).

To further achieve the above object, a soft start circuit according to another aspect of the present invention includes:
A current source having an output connected to the first voltage;
A first current mirror having an input connected to the input of the current source and a common source connected to a second voltage;
A first MOS field-effect transistor (MOSFET) having a source connected to the second voltage and a gate connected to a common gate of the first current mirror;
A second MOS field effect transistor having a drain end connected to the output end of the first current mirror and a source end connected to the first voltage;
A capacitor having one end connected to the output end of the first current mirror and the drain end of the second MOS field effect transistor, and the other end connected to the gate end of the second MOS field effect transistor;
An input terminal is connected to a drain terminal of the first MOS field effect transistor, a common source terminal is connected to the first voltage, and an output terminal is the other terminal of the capacitor and a gate terminal of the second transistor. A second current mirror connected to the first current mirror, the first MOS field effect transistor, the second current mirror, the second MOS field effect transistor, and the capacitor. The ratio between the soft start voltage and time generated by the soft star circuit is reduced by the coupling with the soft start circuit, thereby increasing the equivalent capacitance value of the capacitor, thereby making the soft start circuit relatively small. It can be manufactured with a capacitor having a capacitance value (corresponding to claim 4).

In the soft start circuit according to another embodiment of the present invention,
The first voltage is lower than the second voltage;
The first current mirror is coupled by two identical first P-type MOS field effect transistors;
The first MOS field effect transistor is a P-type MOS field effect transistor, and the aspect ratio of its channel is smaller than the channel aspect ratio of the first P-type MOS field transistor. Corresponding to).

Further, in the soft start circuit of the other invention of the present invention,
The second Moss field effect transistor is an N-type Moss field effect transistor;
The second current mirror is coupled by a first N-type MOS field-effect transistor and a second N-type MOS field-effect transistor;
The drain of the first N-type MOS field effect transistor is the input of a second current mirror, and the drain of the second N-type MOS field effect transistor is the output of the second current mirror;
The aspect ratio of the channel of the first N-type MOS field-effect transistor is larger than the aspect ratio of the channel of the second N-type MOS field-effect transistor (corresponding to claim 6).

Still another object of the present invention is to provide a soft start circuit comprising:
A current source having an output connected to the first voltage;
A first current mirror having an input connected to the input of the current source and a common source connected to the second voltage;
A first MOS field-effect transistor having a source terminal connected to the second voltage and a gate terminal connected to a common gate terminal of the first current mirror;
A second MOS field effect transistor having a drain end connected to the drain end of the first MOS field effect transistor and a source end connected to the first voltage;
A capacitor having one end connected to the drain end of the first MOS field effect transistor and the drain end of the second MOS field effect transistor, and the other end connected to the gate end of the second MOS field effect transistor; ,
An input is connected to the output of the first current mirror, a common source is connected to the first voltage, and an output is the other end of the capacitor and the gate of the second MOS field effect transistor. A second current mirror connected to the first current mirror, the first MOS field effect transistor, the second current mirror, the second MOS field effect transistor, and the capacitor. The ratio between the soft start voltage and the time generated by the soft start circuit decreases due to the coupling with the soft start circuit, thereby increasing the equivalent capacitance value of the capacitor. It can be manufactured with a capacitor having a small capacitance value (corresponding to claim 7).

In a soft start circuit according to another embodiment of the present invention,
The first current mirror is coupled by a first P-type MOS field-effect transistor and a second P-type MOS field-effect transistor;
A drain of the first P-type MOS field effect transistor is an input of the first current mirror, a drain of the second P-type MOS field effect transistor is an output of the first current mirror,
The aspect ratio of the channel of the first P-type MOS field-effect transistor is greater than the aspect ratio of the channel of the second P-type MOS field-effect transistor;
The first Moss field effect transistor is a P-type Moss field effect transistor;
The second Moss field effect transistor is an N-type Moss field effect transistor;
The second current mirror is coupled by a first N-type MOS field effect transistor and a second N-type MOS field effect transistor;
The drain of the first N-type MOS field effect transistor is the input of the second current mirror, and the drain of the second N-type MOS field effect transistor is the output of the second current mirror. ,
The aspect ratio of the channel of the first N-type MOS field-effect transistor is larger than the aspect ratio of the channel of the second N-type MOS field-effect transistor.

  The invention can be understood one step further by describing the best mode with reference to the accompanying drawings.

  FIG. 2 is a sketch of the soft start circuit according to the first embodiment of the present invention. As shown in the figure, the soft start circuit 20 is formed by coupling a current source 21, a current mirror 22, a capacitor 23, and an npn-type bipolar junction transistor (BJT) 24. The current mirror 22 is coupled by two identical P-type MOS field effect transistors 221 and 222, and the gate ends of the P-type MOS field effect transistors 221 and 222 are connected to each other, and the source ends are both high. Connected to voltage 25. The drain end of the P-type MOS field effect transistor 221 forms the input end of the current mirror 22, and the drain end of the P-type MOS field effect transistor 222 forms the output end of the current mirror 22.

  Alternatively, the input end of the current mirror 22 is connected to the input end of the current source 21, the output end of the current mirror 22 is connected to one end of the capacitor 23 and the collector of the npn-type bipolar junction transistor 24, and The terminal is connected to the base terminal of the npn-type bipolar junction transistor 24, and the output terminal of the current source 21 and the emitter terminal of the npn-type bipolar junction transistor 24 are both connected to the low voltage 26.

Here, as shown in FIG. 2, the constant current (the magnitude is I ') generated from the current source 21 is projected through the current mirror 22, so that the emitter of the npn-type bipolar junction transistor 24 The magnitude of the current flowing from the end is also I '. Due to the element characteristics of the npn-type bipolar junction transistor, the current flowing into the base of the npn-type bipolar junction transistor 24, the current flowing into the collector of the npn-type bipolar junction transistor 24, and the emitter of the npn-type bipolar junction transistor 24 are reduced. Since there is a linear relationship 1: b: (b + 1) between the current flowing out and the current flowing out, the magnitude of the current flowing through the capacitor 23 (that is, the current flowing into the base end of the npn-type bipolar junction transistor) is I ′ / (B + 1) and if b is large enough (between 100 and 200 for modern npn-type bipolar junction transistors), the magnitude of the current flowing through the capacitor 23 can be considered as I '/ b. By substituting this I '/ b into the current I of the formula V (soft start) / T = I / C,
V (soft start) / T = (I '/ b) / C,
V (soft start) / T = I '/ (bC) can be obtained.

It can also be considered that V / T = I '(bC).
As can be seen, when it is desired to obtain a relatively small V / T ratio under a condition where the soft start voltage V is fixed, if the soft start circuit according to the present invention is used, the equivalent capacitance value of the capacitor 23 is obtained. To make a soft start circuit with a sufficiently small ratio of soft start voltage to time (V (soft start) / I) by using a capacitor with a relatively small capacitance value. be able to.

  FIG. 3 is a circuit diagram showing a soft start circuit according to a second preferred embodiment of the present invention. As shown in the figure, the soft start circuit 30 is formed by coupling a current source 31, a capacitor 33, and a Darlington transistor 34. The current mirror 32 is coupled by two identical P-type MOS field-effect transistors, and the gate ends of the P-type MOS field-effect transistors 321 and 322 are connected to each other, and the sources are both high voltage. The drain end of the P-type MOS field effect transistor 321 forms the input end of the current mirror 32, and the drain end of the P-type MOS field effect transistor 322 forms the output end of the current mirror 32.

  The Darlington transistor 34 is coupled by two identical npn-type bipolar junction transistors 341 and 342, and the base end of the npn-type bipolar junction transistor 341 is the input end of the Darlington transistor 34. , Npn-type bipolar junction transistors 341 and 342 have their collector ends connected to each other and then connected to the output end of current mirror 32. The emitter end of npn-type bipolar junction transistor 341 is connected to the base end of npn-type bipolar junction transistor 342. And the emitter end of npn-type bipolar junction transistor 342 is connected to low voltage 36.

  Further, the current mirror 32 is connected to the input terminal of the current source 31, the output terminal of the current mirror 32 is connected to one end of the capacitor 33 and the common collector terminal of the npn-type bipolar junction transistors 341 and 342, and the other end of the capacitor. The terminal is connected to the input terminal of the Darlington transistor 34, and the emitter of the transistor 342 is connected to the low voltage 36.

Here, as shown in FIG. 3, the constant current generated by the current source 31 (the magnitude is I ″) is projected via the current mirror 32, so that the emitter terminal of the npn-type bipolar junction transistor 342 The magnitude of the current flowing out is also I ″. Due to the element characteristics of the Darlington transistor (the ratio value of the collector terminal and the base terminal of the npn-type bipolar junction transistor 341 is b, and the same applies to the npn-type bipolar junction transistor 342), the npn-type bipolar junction transistor 341 has Since there is a linear relationship 1: (b + 1) 2 between the current flowing in and the current flowing out of the emitter terminal of the npn-type bipolar junction transistor 342, the current flowing through the capacitor 33 (that is, the npn-type bipolar junction transistor 341) The magnitude of the current flowing into the base end of the capacitor 33 is I ″ / (b + 1) 2, and when b is sufficiently large (between 100 and 200 for a modern npn-type bipolar junction transistor), the current flowing through the capacitor 33 is Size of Can be as I "/ b2. By substituting this I ″ / b2 value into the current I of the formula V (soft start) / T = I / C, V (soft start) / T = (I ″ / b2) / C can be obtained.
Also, it can be considered that V (soft start) / T = I ″ / (b2C).

  As can be seen, if it is desired to obtain a relatively small V / T ratio under a condition where the soft start voltage V is fixed, if the soft start circuit according to the present invention is used, the equivalent capacitance value of the capacitor 33 is obtained. To make a soft start circuit with a sufficiently small ratio of soft start voltage to time (V (soft start) / I) by using a capacitor with a relatively small capacitance value. be able to.

  FIG. 4 is a circuit diagram showing a soft start circuit according to a third preferred embodiment of the present invention. The third embodiment differs from the first and second preferred embodiments in the circuit design of a complementary MOS (CMOS) manufacturing process in the third embodiment. As shown in FIG. 4, the soft start circuit 40 includes a current source 41, a 3P type MOS field effect transistor (42, 43, 44), a 3N type MOS field effect transistor (45, 46, 47), and a capacitor. 48. Among them, the aspect ratio of the channel between the drain and source terminals of the P-type MOS field-effect transistors 42 and 44 is the same as each other, but each is a multiple (n) of the aspect ratio of the channel of the P-type MOS field-effect transistor 43. The aspect ratio of the channel of the N-type MOS field effect transistor 45 is a multiple (m times) of that of the N-type MOS field effect transistor 46.

  As seen in FIG. 4, the source terminals of the P-type MOS field effect transistors 42, 43 and 44 are all connected to a high voltage 491, and the gate terminals of the three are connected to each other, and The drain of the MOS field effect transistor 42 is short-circuited in common. The drain terminal of the P-type MOS field-effect transistor 42 and the input terminal of the current source 41 are connected to each other, and the output terminal of the current source 41 is connected to the low voltage 492. Thus, both P-type MOS field effect transistors 42 and 43 form a current mirror with a current projection magnification of I / n, and both P-type MOS field effect transistors 42 and 44 have a single current projection magnification of 1 Make up the mirror.

  The N-type MOS field-effect transistor 45 is connected to the drain end of the P-type MOS field-effect transistor 43 in a short-circuit manner at the gate and drain ends, and the N-type MOS field-effect transistor 45 is N-type with a common gate end. A current mirror having a current projection magnification of 1 / m and a type MOS field effect transistor 46 are formed. The common source terminal is connected to the low voltage 492.

  Finally, the drain end of the N-type MOS field effect transistor 47 and one end of the capacitor 48 are connected to the drain end of the P-type MOS field effect transistor 44, and the gate end of the N-type MOS field effect transistor 47 and the other end of the capacitor are short-circuited. Both are connected to the drain end of the N-type MOS field effect transistor 46. The source end of the N-type MOS field effect transistor 47 is also connected to the low voltage 492.

  Here, as shown in FIG. 4, the constant current (the magnitude is I ′ ″) generated from the current source 41 is projected through a current mirror composed of P-type MOS field-effect transistors 42 and 44. Therefore, the magnitude of the current flowing out from the drain of the P-type MOS field-effect transistor is also I ′ ″. It should be noted that the current flowing out of the P-type MOS field-effect transistor is set to I ′ ″ / n by being projected through the current mirror composed of the P-type MOS field-effect transistors 42 and 43. The current is again projected through the current mirror formed by the N-type MOS field-effect transistors 45 and 46 so as to reduce the magnitude of the current flowing into the drain end of the N-type MOS field-effect transistor 46 by I ′. '' / (Mn). Since the ratio between the current at the drain end of the N-type MOS field effect transistor 47 and I ′ ″ / (mn) is extremely small, the magnitude of the current flowing into the capacitor 48 is I ′ ″ / (mn). Good.

(1) The magnitude of the current flowing out of the drain of the P-type MOS field effect transistor 44 is I ′ ″, and (2) the magnitude of the current flowing through the capacitor 48 can be regarded as I ′ ″ / (mn). , M and n are large enough (more than 25 in modern MOS field-effect transistors), the current value I ′ ″ / (mn) flowing through the capacitor 48 is determined by the formula V (soft start) / T = I / C Substituting for the current I,
V (soft start) / T = (I "'/ mn) / C,
Further, it can be regarded that V (soft start) / T = I ″ ′ (mnC).

  As can be seen, when it is desired to obtain a relatively small V / T ratio under a condition where the soft start voltage is fixed, if the soft start circuit according to the present invention is used, the equivalent capacitance of the capacitor 48 can be reduced. By making it possible to use a capacitor having an extremely small capacitance value by being able to amplify by mn times, a soft start circuit with a sufficiently small ratio of soft start voltage to time (V (soft start) / T) is used. Can be.

  As can be seen from the above three preferred embodiments, the arrangement of the soft start circuit according to the present invention is capable of amplifying the effective value of the large capacitor. Relatively low soft start voltage to time ratios can be reached with relatively low capacitance (ie, relatively low volume) capacitors. In other words, it is possible to control the rate of increase of the current passing slowly through the load, so that the system can operate more safely at the start. In particular, the soft start circuit according to the third preferred embodiment makes it possible to use a CMOS manufacturing process as an environment for implementing the circuit and combine it with a capacitor manufactured according to the requirements of the manufacturing process size of the integrated circuit. Capacitance value is large enough to provide the protection function of the soft start circuit, so that it can be effectively matched during the integrated circuit manufacturing process, which is in line with the world trend in which integrated circuits are becoming ever more compact. I can do it. Therefore, the present invention can surely solve the technical deficiencies of the conventional soft start circuit, and can achieve the object of the present invention.

  The above-described embodiment describes the technical means of the present invention more specifically. Naturally, the technical idea of the present invention is not limited to this, and a simple one by a person skilled in the art may be used without departing from the scope of the appended claims. Design changes, additions, modifications, substitutions, etc. all belong to the technical scope of the present invention.

It is a circuit sketch of the conventional soft start circuit. 1 is a sketch drawing showing a soft start circuit according to a first preferred embodiment of the present invention. FIG. 4 is a sketch showing a soft start circuit according to a second preferred embodiment of the present invention. FIG. 11 is a sketch showing a soft start circuit according to a third preferred embodiment of the present invention.

Explanation of reference numerals

  10, 20, 30, 40 ... soft start circuit 11, 21, 31, 41 ... current source 22, 32 ... current mirror 12, 23, 33, 48 ... capacitor 24, 341, 342 ... npn-type bipolar junction transistor 221 , 222, 321, 322, 42, 43, 44: P-type MOS field effect transistor 25, 35, 491 ... high voltage 26, 36, 492 ... low voltage 34: Darlington transistor 45, 46, 47 ... N-type Moss electric field Effect transistor

Claims (8)

A first current source having an input connected to the first voltage;
A transistor having a first end connected to the output end of the first current source, and a second end connected to a second voltage;
A capacitor having one end connected to the output end of the first current source and the other end connected to the input end of the transistor;
A soft start circuit comprising:
The transistor and the capacitor are coupled, and the ratio of the soft start voltage generated by the soft start circuit to time is reduced, thereby increasing the equivalent capacitance of the capacitor. The start circuit is made of a capacitor having a relatively small capacitance value;
A soft start circuit characterized by: The first current source is a current mirror;
This current mirror is coupled by two identical P-type MOS field effect transistors,
The input end of the current mirror is connected to the input end of a second current source, the output end of the current mirror is connected to the first end of the transistor and one end of the capacitor, and the common source end of the current mirror is Connected to the first voltage, and an output end of the second current source connected to the second voltage;
The soft start circuit according to claim 1. The first voltage is set higher than the second voltage,
The transistor is an npn-type bipolar junction transistor;
The first end of the transistor is a collector end, the second end of the transistor is an emitter end, the control end of the transistor is a base end, and / or the transistor is a Darlington transistor; The transistor is a coupling of a first npn-type bipolar junction transistor and a second npn-type bipolar junction transistor, and the base end of the first npn-type bipolar junction transistor is connected to the input terminal of the transistor. The emitter end of the first npn-type bipolar junction transistor is connected to the base end of the second npn-type bipolar junction transistor, and the collector end of the first npn-type bipolar junction transistor is connected to the collector end of the first npn-type bipolar junction transistor. Second npn-type bipolar diode And connected to the collector terminal of Nkushon transistor configured first end of the transistor, the emitter terminal of the npn bipolar junction transistor of the second is the second end of the transistor,
The source start circuit according to claim 1. A current source having an output connected to the first voltage;
A first current mirror having an input connected to the input of the current source, a common source connected to a second voltage, a source connected to the second voltage, and a gate connected to the second voltage. A first MOS field-effect transistor connected to a common gate end of one current mirror;
A second MOS field effect transistor having a drain end connected to the output end of the first current mirror and a source end connected to the first voltage;
A capacitor having one end connected to the output end of the first current mirror and the drain end of the second MOS field effect transistor, and the other end connected to the gate end of the second MOS field effect transistor;
An input terminal is connected to a drain terminal of the first MOS field effect transistor, a common source terminal thereof is connected to the first voltage, and an output terminal thereof is the other terminal of the capacitor and a gate terminal of the second transistor. A second current mirror connected to the first current mirror, the first MOS field effect transistor, the second current mirror, and a cup between the MOS field effect transistor and the capacitor. The ring reduces the soft start voltage and time ratio generated by the soft star circuit, thereby increasing the equivalent capacitance of the capacitor, thereby increasing the soft start circuit and relatively small capacitance. Can be made with capacitors,
A soft start circuit characterized by: The first voltage is lower than the second voltage;
The first current mirror is coupled by two identical first MOS field effect transistors;
The first MOS field-effect transistor is a P-type MOS field-effect transistor, and the aspect ratio of the channel is smaller than the aspect ratio of the channel of the first P-type MOS field effect transistor;
The soft start circuit according to claim 4. The second MOS field-effect transistor is an N-type MOS field-effect transistor;
The second current mirror is coupled by the first N-type MOS field-effect transistor and the second N-type MOS field-effect transistor;
The drain of the first N-type MOS field-effect transistor is the input of the second current mirror, and the drain of the second N-type MOS field-effect transistor is the output of the second current mirror. ,
The aspect ratio of the channel of the first N-type MOS field-effect transistor is larger than the aspect ratio of the channel of the second N-type MOS field-effect transistor.
The soft start circuit according to claim 4. A current source having an output connected to the first voltage;
A first current mirror having an input connected to the input of the current source and a common source connected to the second voltage;
A first MOS field effect transistor having a source terminal connected to the second voltage and a gate terminal connected to a common gate terminal of the first current mirror;
A second MOS field effect transistor having a drain end connected to a drain end of the first MOS field effect transistor and a source end connected to the first voltage;
A capacitor having one end connected to the drain end of the first MOS field effect transistor and the drain end of the second MOS field effect transistor, and the other end connected to the gate end of the second MOS field effect transistor; ,
An input is connected to the output of the first current mirror, a common source is connected to the first voltage, and an output is the other end of the capacitor and the gate of the second MOS field effect transistor. A second current mirror connected to
Wherein the first current mirror, the first MOS field effect transistor, the second current mirror, and the coupling between the second MOS field effect transistor and the capacitor provide the soft start circuit. The resulting lower ratio of soft start voltage to time reduces the equivalent capacitance of the capacitor, so that the soft start circuit can be made with a capacitor of relatively small capacitance.
A soft start circuit characterized by: The first current mirror is coupled by a first P-type MOS field-effect transistor and a second P-type MOS field-effect transistor;
The drain of the first P-type MOS field effect transistor is an input of the first current mirror, and the drain of the second P-type MOS field effect transistor is an output of the first current mirror. ,
An aspect ratio of a channel of the first P-type MOS field-effect transistor is larger than an aspect ratio of a channel of the second P-type MOS field-effect transistor;
The first Moss field effect transistor is a P-type Moss field effect transistor;
The second MOS field-effect transistor is an N-type MOS field-effect transistor;
The second current mirror is coupled by a first N-type MOS field-effect transistor and a second N-type MOS field-effect transistor;
The drain of the first N-type MOS field-effect transistor is the input of the second current mirror, and the drain of the second N-type MOS field-effect transistor is the output of the second current mirror. ,
The aspect ratio of the channel of the first N-type MOS field-effect transistor is larger than the aspect ratio of the channel of the second N-type MOS field-effect transistor.
The soft start circuit according to claim 7.

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