JPH0462609A - Stabilized power source circuit - Google Patents

Abstract

PURPOSE:To reduce the fluctuation of a limiting current caused by the change of the working temperature by connecting a temperature compensating circuit provided for an overcurrent protecting circuit to this circuit through the reference voltage. CONSTITUTION:A limiting current ID1 is secured. The potential VP is defined at a point P as VP=Vref-VBE1+VBE13, where VBE1 shows the base-emitter voltage of a transistor Tr1 and VBE1=VBE13 is satisfied. Therefore VP=Vref. Then ID1XRO1=Vref is satisfied in an ON state of a Tr13. Thus the current ID1 is shown by an equation I. In this equation I, the temperature coefficient of the reference voltage Vref is equal to about +20PPM/ deg.C with the temperature coefficient of an emitter diffused resistance R13 set at about -200PPM/ deg.C respectively. Therefore the temperature coefficient of the current ID1 is equal to about -200PPM/ deg.C as long as the temperature coefficient of the Vref is neglected. Thus the temperature coefficient is reduced by 1/2.5. As a result the fluctuation of the current ID1 is reduced even in a wide range of working temperatures and furthermore the safety is assured to the thermal runaway owing to the negative temperature characteristic secured.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a stabilized power supply circuit equipped with an overcurrent protection circuit, and particularly to a stabilized power supply circuit using a monolithic integrated circuit or the like.

<Prior Art> An example of a conventional stabilized power supply circuit will be described with reference to FIG.

FIG. 2 is a circuit diagram of a conventional stabilized power supply circuit.

This stabilized power supply circuit uses P as a voltage control transistor.
This is a constant voltage circuit that includes an NP type transistor Tr11 and connects input and output via the emitter collector of this transistor Tr11.As explained below, the base current of the transistor Trll is controlled by the control circuit 10. A constant voltage is supplied to a load (not shown).

The transistor Tr11 has an emitter connected to the input terminal A, a base connected to the collector of the transistor Tr12, and a collector connected to the output terminal B and grounded via a voltage dividing circuit 11 consisting of resistors R11' and R12. has been done. This voltage divider circuit! The connection point between the resistor R11 and the resistor RI2 is connected to the inverting input terminal of the differential amplifier 12. The differential amplifier 12 has a non-inverting input terminal connected to the reference voltage vref, an output terminal connected to the input terminal A via the constant current circuit 13, and connected to the pace of the transistor Tr12.

The emitter of the transistor Tr12 is connected to the overcurrent protection circuit 1.
It is connected to the grounded transistor TrlB through the emitter diffused resistor R18 of 4.
The emitter of the transistor Tr13 is grounded, and the collector is connected to the base of the transistor Tr12.

In the stabilized power supply circuit configured in this way, the output voltage V
Q is divided by the resistors R11''R12 in the voltage dividing circuit I+, and the feedback voltage VF is applied to the inverting input terminal of the differential amplifier 12.
is entered as . The differential amplifier 12 has a reference voltage vre.
The current output from the constant current circuit 13 is adjusted by comparing f with the feedback voltage VF.

Thereby, the pace current of the transistor Tr12 is adjusted. Therefore, the output voltage vo is controlled according to the change in the base current of the transistor Tr11fd.

Such control is performed so that there is no difference between the reference voltage Vref input to the differential amplifier 12 and the feedback voltage VF, so that the output voltage VQ is, as a result, equal to the reference voltage V
It is stabilized to a constant voltage according to ref. In other words, the output voltage v□ is determined by the voltage dividing circuit I
+, differential amplifier 12, and transistor Tr12, which are configured by feedback loops, perform negative feedback control to maintain a constant value.

Furthermore, in the above-described stabilized power supply circuit, when the output current IQ increases, the base current of the transistor Tr11 flows to the emitter diffusion resistor R13 via the transistor Tr12. The voltage generated across this resistor R18 is the pace-emitter voltage VBE18 of the transistor TrlB.
When TrlB is reached, transistor TrlB turns on and reduces the current to the pace of transistor Tr12. As a result, the base current of the transistor jr11 decreases and flows between the collector-emitter of the transistors T and r11.
Output current IQ is controlled.

Here, if the output current (emitter current) of the transistor Tr12 is Il, the above-mentioned current limitation is performed because the voltage drop across the emitter diffusion resistor R13
When the W pressure between the pace and the emitter of 1B becomes equal to VBE13 and the transistor Tr13 turns on, that is, I
R18"" Performed at VBE18.

Therefore, the emitter current ■1 is I1=VBE18/R
It is ls. At this time, the emitter current 11 is limited to the current I
Assuming D1, IDI = VBE18 / R+a
...Equation (1) Further, the output current IQ is expressed by the following equation.

10 "hFEll XII"' Formula (2) However, h FEI 1 is a transistor T rll
hFE.

Therefore, when the emitter current 11 of the transistor Tr12 reaches the value of the limit current IDI, the output current 0 is expressed by the following equation.

rQ = hFEll X IDI”
Equation (3) (Problem to be Solved by the Invention) By the way, normally, the temperature coefficient of the voltage VBE18 between the pace and emitter of the transistor Tr13 is about -3000P.
PM/°C, and the temperature coefficient of emitter diffused resistor R18 is +2000 PPM/°C. Therefore, from equation (1), the temperature coefficient of the limiting current IDI is approximately -5000P in total.
PM/°C, which is a large value. Therefore, under a wide range of operating temperatures, the limit current IDI fluctuates greatly,
There is a problem in that the output current IQ shown by the above-mentioned equation (3) cannot be stably obtained.

The above problems will be explained in detail below.

FIG. 3 is a diagram showing the operating temperature characteristics of the limited current IDI. In the figure, a and b are the characteristics of the conventional circuit.

The circuit setting conditions under which characteristic a was obtained are as follows.

V, e (= 1.26V, R11=2.8, Q, R1
2=400IQ.

R13=250. Transistor T rll (')h
FE=80° Also, the circuit setting conditions under which the characteristics were obtained are described below.

Vref=1.26V, R11=2.8Ω, R12
=400Ω.

R13=+50. bFE of transistor Tr11=
80° FIG. 4 is a diagram showing the overcurrent protection characteristics, and shows the current range of the output current IQ.

In the figure, the ranges a' and b' correspond to the characteristic a and characteristic a of the conventional example shown in FIG. However, a'
Both of and b' show only the range of output current IQ in the range of TJ from 25°C to 125°C.

Are aQ and bo the outputs when T j = 125°C? W
1 indicates the output current IQ when Tj=25°C.

As shown in Fig. 4, according to the conventional circuit shown in Fig. 2, under the circuit setting condition a', when Tj = 125°C, the output current IQ satisfies the rated IA as a stabilized power supply circuit. I can't. Furthermore, under the circuit setting conditions b', when Tj = 25°C, the output current IQ flows as much as 2.6A,
The overcurrent protection circuit 14 has no protective function.

In this way, in the conventional circuit, the temperature coefficient of the limiting current ID+ is as large as -5000 PPM/℃, so the limiting current II)1 fluctuates greatly under a wide range of operating temperatures, and as a result, the stable output current IQ The problem was that it was not possible to obtain

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a stabilized power supply circuit that can reduce fluctuations in limited current and obtain stable output current even under a wide range of operating temperatures.

Means for Solving the Problems> 01 In order to achieve the object, the present invention provides a voltage control transistor that controls an output voltage, and a voltage control transistor that controls a part of the negative feedback output voltage so that it becomes equal to a constant reference voltage. and a control circuit that controls the entire base current of the voltage control transistor, the control circuit including an overcurrent protection circuit that controls the output current, wherein temperature compensation for the overcurrent protection circuit is provided. It is characterized in that the circuit is connected from the reference voltage 0j■ to the overcurrent protection circuit from l~.

<Function> By connecting the temperature compensation circuit for the overcurrent protection circuit from the reference voltage to the overcurrent protection circuit, the base potential of the transistor in the overcurrent protection circuit is made to be the same as the reference voltage when the transistor is turned on. , so the temperature coefficient of the limiting current flowing into the base of the transistor is smaller than the conventional one by the amount that the temperature coefficient of the base-emitter voltage of the 01J transistor is canceled out, and the temperature coefficient of the limiting current flowing into the base of the transistor becomes smaller due to changes in the operating temperature. Fluctuations can be reduced, resulting in stable output current over a wide operating temperature range.

<Example> An example of the present invention will be described with reference to FIGS. 1, 3, and 4.

FIG. 1 is a stabilized power supply circuit diagram according to this embodiment. From F
, only the points that are different from the conventional example shown in FIG. 2 will be explained. Components with the same functions as those in the conventional example shown in FIG. 2 are designated by the same symbols.

In FIG. 1, as a temperature compensation circuit I5 for the overcurrent protection circuit 14, a resistor R1 is connected between the emitter GND of the transistor Tr 13, and a transistor T
At the connection point between the emitter of r13 and resistor R1, is the transistor T rxa connected between the same base and emitter? The emitters of [transistor Tr with voltage] are connected. Further, the base and collector of the transistor Trl are connected to a reference voltage ref I.

In the circuit as described above, the 7E current restriction that is performed when the output current IQ increases to 7 is that the voltage drop across the emitter diffusion resistor RI3 becomes equal to the base-to-J-mitter voltage VBEI8 K of the transistor Tr13, as in the conventional example. This is when the transistor Tr43 is turned on. Hereinafter, the limit current In+ is determined.

First, the potential Vp at point P is as follows.

VP-” “re(VBEI” “BEI3
In Equation (4) ff11~, VBEI is the base-emitter voltage of the transistor T'r1.

Here, since V BEI "" V BEI3, it becomes Vp"Vref.

Therefore, when the transistor Tr13 is turned on, I pHX
ROI””vref”’Formula (5
)late! 'i:, iI month= Vrer/ Ro 1=
- Equation (6) In Equation (6), the temperature coefficient of the reference voltage vref is about +20 PPM/°C, and the temperature coefficient of the emitter diffusion resistor R13 is about -2000 PPM/°C. Therefore, if the temperature coefficient of vref is ignored, the temperature coefficient of IDI is about -2000 PPM/°C, which is '/2.5 compared to the conventional example. Therefore, even in a wide range of operating temperatures, there is little variation in the limiting current IDI, and the temperature characteristic remains negative, so safety against thermal runaway is guaranteed as before.

The effects of this example will be specifically shown below.

FIG. 3 is a diagram showing the operating temperature characteristics of the limited current IDI. In the figure, C is the characteristic according to this embodiment.

For example, the circuit setting conditions for characteristic C are as follows.

V ref” 1.26 V, R11: 2,8
KΩ, R12=400Ω.

R13=50Ω, R1=5Ω, transistor T rl
hFE of 1=80° In FIG. 3, when compared with the characteristics a and b of the conventional example, it can be seen that characteristic C has a small slope of the limiting current IDI and has little variation over a wide range of operating temperatures.

FIG. 4 is a diagram showing overcurrent protection characteristics. In the figure, +d
/ indicates the current range of the output current IQ according to this embodiment,
co and C1 are Tj=125°C and Tj=25, respectively.
It shows the value of output current IQ at ℃.

In the figure, compared to the ranges a' and b' of the output current rO according to the conventional example, the current range B' is narrower, and the output current IO has less fluctuation and is stable. Therefore, the output current ■o does not exceed IA as in the current range a', and the output current IQ does not reach 2.6 A as in the current range b'.

<Effects of the Invention> As described above, according to the present invention, it is possible to realize a stabilized power supply circuit in which fluctuations in the limited current are small even in a wide range of operating temperatures, and therefore a stable output current can be obtained.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a stabilized power supply circuit according to an embodiment of the present invention, Figure 2 is a circuit diagram of a stabilized power supply circuit according to a conventional example, Figure 3 is a diagram of operating temperature characteristics of limited current, and Figure 4 is It is an overcurrent protection characteristic diagram. 10... Control circuit, +4... Overcurrent protection circuit, 15
...Temperature compensation circuit, "11...Voltage 5 control transistor, vref...Reference voltage. Agent: Patent attorney Ume 1) Katsu (and 2 others) No. 1m Fig. 2

Claims (1)

[Claims] 1. A voltage control transistor that controls an output voltage, and a control circuit that controls a base current of the voltage control transistor so that a part of the negative feedback output voltage becomes equal to a constant reference voltage, The circuit is a stabilized power supply circuit including an overcurrent protection circuit that controls an output current, and is characterized in that a temperature compensation circuit for the overcurrent protection circuit is connected from the reference voltage to the overcurrent protection circuit. Stabilized power supply circuit.