JPS61195415A - Constant voltage power supply - Google Patents

Abstract

PURPOSE:To improve a high frequency characteristic and stability by making a constant current source take share of the fixed current component of a load current and therefore reducing the current capacity of an output transistor, etc. CONSTITUTION:A constant voltage power supply device consists of a differential amplifier 10, a drive amplifier 30 containing MOSFET 31 and 32, an output FET 33 and a constant current source FET 34 and supplies a load current IL to a load 24. Then the fixed current component IK equal to 1/2 maximum current IL having variable level is supplied to a load 25 through the FET 34 in the form of a constant current source. While the rest amount of current component is supplied to the load 25 from the FET 33 as the variable current component IV. Thus the input electrostatic capacities 35 and 36 of the amplifier 30 and the FET 33 are reduced down to half respectively. Thus both the high frequency characteristics and stability can be improved while maintaining the same current supply capacity as conventional.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to improvements in constant voltage power supplies. .

[Summary of the invention]

The present invention provides a constant voltage power supply device that connects the output terminal of an operational amplifier to an inverting input terminal and also supplies a reference voltage to a non-inverting input terminal. This reduces the load on the output transistor of the operational amplifier and reduces the input capacitance, thereby improving high frequency characteristics and stability.

[Conventional technology]

Conventionally, as shown in FIG. 3, when an input voltage e4 is supplied to the non-inverting input terminal (2) of an operational amplifier (1) and negative feedback is applied from the output terminal (3) to the inverting input terminal, the output It is known that the voltage e0 satisfies e0=e< and becomes a voltage follower with a voltage gain of 1. Also, a reference DC voltage Vr is applied to the non-inverting input terminal of the operational amplifier.

A constant voltage power supply device is also known in which a DC voltage equal to the reference voltage is obtained from the output terminal by connecting the two.

First, a specific example of the configuration of such a constant voltage power supply device will be described with reference to FIG. 4.

In FIG. 4, (A) shows the differential amplifier as a whole, and N-channel MO8F of the differential amplifier α4itt pair with
The sources of ET (iυ and (2) are connected together to the drain of N-channel MO8FET (2) as a constant current source, and the drains of both PETαD and (6) form a pair of current mirror circuits. P channel MO
It is connected to each drain of 8FETα→ and (G), respectively. Both FETα → and each of (2)? -) is FET (
14 drains in common, and both FETs
(1 → and (6) are both connected to a power supply terminal TP to which a predetermined external power supply voltage vDD is supplied.PE
The source of T(Ll) is grounded, and an appropriate bias voltage is supplied to r-t from a bias source (not shown).

Is it still FET (6)? -1 is supplied with a predetermined reference voltage V from a reference voltage terminal. This reference voltage Vr
, 1 tief is set smaller than the power supply voltage vDD. Further, the reference voltage terminal αη is also a non-inverting input terminal of the operational amplifier shown in FIG.
It is connected to the gate of D and the output terminal to form a negative feedback loop. Note that the %MO8FETs are integrated on the same semiconductor chip.

(2) is an inverting amplifier for body ''m, which consists of P channel MO8FIT 011 and N channel MO8FET (2
) are connected to each other, and the source of FET (211) is connected to the power supply terminal TP, and the source of FET 1221 is grounded. The gate is connected to the connection midpoint A of each drain of the differential amplifier (11 FETs (121 and (151), and the connection midpoint B of each drain of FE'llll and @ is an N-channel MO for output control.
Connected to the gate of 8PET@. The drain of FET (c) is connected to the power supply Kameko TP, and the source is the output terminal ■
and grounded through the load.

A load current IL is supplied from the output terminal (to) of the conventional constant voltage power supply device having such a configuration to the load (c). In this case, the load (c) is composed of an electronic circuit including a large number of semiconductor elements, and the load current IL varies depending on its operation.
Also, since the aforementioned negative feedback loop exists, a constant voltage vref is supplied to the load (c), and the electronic circuit operates stably.

[Problem that the invention seeks to solve]

By the way, in the conventional constant voltage power supply device as described above, when the load becomes large, in order to stably supply current, the output FET g3 and the drive amplifier that drives it are
The drive capability of each FET@, (2), that is, the current capacity of each FET, must be increased in accordance with the magnitude of the load current. In the case of MOSFET, the current capacity is proportional to the area (width) of the electrode of the FET itself, so FET @1),
In order to increase the current drive capability of (2) and (to), each FE11. @, we have to increase the area (width) of (goods).

However, this increase in area immediately affects each FET (2).

(a) and (2) lead to an increase in capacitance (c) and plow.

That is, both FETs 121) of the drive amplifier (a) and the input capacitance (2) of the drive amplifier (a) determine the time constant τ of the load circuit of the differential amplifier αQ, and the large-area output PET (to) input capacitance) is the time constant τ of the load circuit of the drive amplifier (a)
, determine.

If the values of both capacitances 4 and @ are respectively C26''27, then C24<<C27, so the relationship between the above-mentioned constants is τ, τ1.In this way, the drive amplifier (H)
If the time constant τ of the load circuit is large, the high frequency characteristics of the operational amplifier deteriorate, causing a problem that the control operation as a constant voltage power supply cannot follow rapid fluctuations in the load current.

The load also has a large capacitance, which determines the time constant τ1 of the load (2). This τ.

When the three time constants τ, τ, and τ mentioned above become close to each other, the constant voltage power supply becomes unstable), and in severe cases, it may oscillate, so it is necessary to take complicated measures such as phase equalization. The problem was that it had to be done.

In view of this, an object of the present invention is to provide a constant voltage power supply device with good high frequency characteristics and stability.

[Means for solving problems]

Is this invention an external power source? , and the inverting input terminal α of the operational amplifier including the output transistor (to) connected to
・At the same time, supply the reference voltage vrd to the non-inverting input terminal (material), and output the reference voltage vr from the output terminal (material)
Load current with voltage equal to ef! In a constant voltage power supply device designed to provide 11 fixed current components 1. At the same time, the fluctuating current component of the load current IL is supplied through the output transistor (to) of the operational amplifier! This is a constant voltage power supply device that supplies 7.

[Effect]

According to this configuration, the current capacity of the output transistor (2) can be reduced, the input capacitance is reduced,
High frequency characteristics and stability are improved.

〔Example〕

Hereinafter, one embodiment of a constant voltage power supply device according to the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1 shows the configuration of an embodiment of the present invention. In FIG. 1, parts corresponding to those in FIG. 3 are given the same reference numerals and redundant explanations are omitted. In FIG. 1, cIQ is a drive amplifier, and the MOSFETs 91 and are connected in the same way as the conventional device 0FET (c) and (2) in FIG.
FIT is designed to have a current capacity of 9ρ and 2). ) is N-channel MO8FE for buffer output.
It's T.

0FET in Figure 3), but with FET q
It is designed to have a current capacity of a bar. (b) is a P-channel MO8FET as a constant current source,
The source and? The lanes are respectively connected to the power supply terminal T and the output terminal -, and their f-) are directly grounded. This FIT (b), like the FET (to), is configured to have a strong current capacity of FIT El in the fIL3 diagram.

Since it is configured like this, in the example,
As shown in Figure 2, the load current 1 whose magnitude fluctuates
1, the fixed current component IK of the ring with the maximum value is supplied to the load (c) from the FICT e3J) as a constant current source, and the fixed current component IK of the ring with the maximum value is supplied from the load current IL! The fluctuating current component of the residual after subtracting the 7 is supplied from the output F]iT to the load. tb, full load current X.

Since the output FET 03 and the constant current FIT (b) share approximately the same amount, the □ current capacity of both FETs @ and -, that is, the area (width) of their electrodes, is the same as that of the conventional output FIT.
It suffices if it is W of that. Therefore, the output FI of this embodiment
The input capacitance (b) of T(2) is the output FET0 of the conventional example.
The input capacitance (2) of 1 is reduced.

In addition, in this embodiment, as described above, the output FET (to)
Since the current capacity of is reduced to that of the conventional example.

FIT (It and (to)) that drives the output FΣT (to)
The current capacity, that is, the electrode area is also F of the conventional drive amplifier ■.
Any A in ET (2) and (a) is sufficient. Therefore, the input capacitance (to) of the FET Cl0), (to) of the drive amplifier of this embodiment is equal to the input capacitance (to) Fl'l' @j, @O of the conventional example rr)114 dynamic amplifier (e). (2
) decreases to a bar.

In this way, since the input capacitances of the drive amplifier (2) and the output FET C (I) are respectively reduced, in this embodiment, the time constants of the load circuits of the differential amplifier (2) and the drive amplifier (to) are are respectively τ4.τ, to τ, / of the conventional example.
2. With a small τ of /2, high frequency characteristics and stability are improved while maintaining the same current supply capacity as the conventional example.

Conversely, if it is sufficient to maintain constant high frequency characteristics and stability, the current supply capability will be doubled.

In addition, in this example, the load current! The variable current component Iv and the fixed current component X]c are made equal, but
It goes without saying that the ratio of both components is appropriately set depending on the fluctuation state of the load current.

In addition, in the above embodiment, each MO8FET (l]
) to (g) and 0 to (b) are configured in a complementary manner, but each FET may be configured with only a P channel or only an N channel. In this case, constant current source FET (1
If 4 is used as a depression fi FIT, good constant current characteristics can be obtained.

Further, in the constant voltage power supply device according to the present invention, the constant current source circuit that shares the fixed current component of the load current is somewhat complicated;
Even if a bipolar transistor is used, the structure can be similar to the above embodiment.

〔Effect of the invention〕

As described in detail above, according to the present invention, the fixed current component of the load current is shared by the constant current source to reduce the current capacity of the output transistor, etc., so that the electrode area of the output transistor, etc., and therefore the input A constant voltage power supply device with reduced capacitance and improved high frequency characteristics and stability can be obtained.

[Brief explanation of drawings]

Fig. 1 is a wiring diagram showing an embodiment of a constant voltage power supply according to the present invention, Fig. 2 is a diagram for explaining the present invention, and Figs. 3 and 4 are basic diagrams of a conventional constant voltage power supply. It is a wiring diagram showing a configuration and a specific configuration example. (2) is an inverting input terminal, (B) is a non-inverting input terminal, a trout is an output terminal, (C) is a load, (
(to) is the output FE'l', (b) is the constant current source FET,
IL is the load current, I is the fixed current component, ! MA is a fluctuating current component, TF is an external power supply terminal, and Vref is a reference voltage.

Claims (1)

[Claims] An output terminal of an operational amplifier including an output transistor connected to an external power supply is connected to an inverting input terminal, and a reference voltage is supplied to a non-inverting input terminal, so that the reference voltage is output from the output terminal to the inverting input terminal. In the constant voltage power supply device, a constant current circuit is connected between the external power supply and the output terminal, and the fixed current of the load current is supplied through the constant current circuit. A constant voltage power supply device, characterized in that the constant voltage power supply device is configured to supply a variable current component of the load current through the output transistor of the operational amplifier.