JPH0139126B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in power supply stabilization circuits.

Recently, ICs commonly referred to as 3-terminal regulators
A stabilized power supply element has been released and is widely used because it can provide a stabilized output with just one IC. But the maximum output current is 0.5A~1A
The output current of the power supply is relatively small. Therefore, when a larger output current is required, the current must be increased using a transistor or the like. FIG. 1 shows an example of this. In the same figure,
1 is a positive input terminal, 2 is a negative input terminal, 3 is an IC regulator, 3-1, 3-2, 3-3 are terminals of the regulator, 4 is a current increasing transistor,
5 and 6 are resistors, 7 is a transistor for protecting the transistor 4, 8 is a positive output terminal, and 9 is a negative output terminal. When the current increasing transistor 4 is added as in this conventional example, the transistor 4 will be destroyed when the output terminal is short-circuited unless a current limiting circuit consisting of the transistor 7 and the like is added. Further, at this time, the output current of the IC regulator 3 is used only by a factor of H _FE of the output current of the transistor, and there is a drawback that the entire output capacity of the IC regulator is not used.

FIG. 2 is a graph showing the output voltage and current characteristics of FIG. 1, in which the vertical axis shows the output voltage and the horizontal axis shows the output current.

Assuming that the output current of the circuit shown in Fig. 1 is I ₀ , the maximum output current is I _0nax , the resistance value of resistor 6 is R _E , and the base and emitter voltages of transistor 7 are V _BE7 , I _0nax ≒
V _BE7 /R _E.

The resistor 5 is used to limit the output current of the IC regulator 3. If the resistance value is small, it is necessary to use a transistor 7 with a large current, and if it is made large, the voltage regulation will deteriorate. For example, if the output voltage of the IC regulator 3 is _V3 , _the output voltage _V0 of the circuit shown in FIG. 1 becomes _V0 = _V3 - _R5.I0 / _hfe - _VBE4 .

Here, I ₀ : Output current R ₅ : Resistance value of resistor 5, h _fe : DC current amplification factor of transistor 4, V _BE4 : Base-emitter voltage of transistor 4, Output current I _{3 of IC regulator 3} is Ic /h _fe usually
Since I ₃ < I _3nax and up to I _3nax is not used, the ability of IC regulator 3 cannot be fully demonstrated.

The present invention solves the conventional drawbacks and provides a stabilized power supply that can obtain any output voltage with a simple circuit.

The present invention uses a simple circuit to limit the current of the transistor, and after the current of the transistor is limited, the current is supplied from the IC regulator, and the current is supplied from both the transistor and the IC regulator, so that the capacity of the regulator is fully utilized. It is something that can be demonstrated.

3 and 5 to 8 are circuit diagrams showing embodiments of the present invention, and FIG. 4 is a graph showing output voltage-current characteristics. In addition, Figures 3 and 5 to 8
Among the embodiments shown in the figures, FIG. 3 is a circuit diagram showing the basic configuration of the present invention, and FIGS. 5 to 8 show other embodiments. In the figure, 1 is a positive polarity DC input, 2 is a negative polarity DC input, 3 is a 3-terminal IC regulator, 4 is a transistor, 8 is a positive output terminal,
9 is a negative output terminal, 10 is a resistor, 11 is a diode, 12 and 13 are resistors, and 14 is a Zener diode.

The operations shown in FIGS. 3 and 5 to 8 will be explained below.

The voltage difference between the terminal voltage of the positive polarity DC input terminal 1 and the positive polarity output terminal 8 is V _ip , the low resistance value of the resistor 10 is R ₁₀ ,
The resistance values of resistors 12 and 13 are R ₁₂ and R ₁₃ respectively, the voltage of Zener diode 14 is V _Z , the output voltage of IC regulator 3 is V ₃ , the output current I ₃ is the maximum value of
Assuming I _3nax , the maximum output current I _0nax is: The current amplification factor of transistor 4 is h _fe4 , and the minimum voltage between the collector and emitter is V _CEnio .

I _0nax = {(V _ip − V _CEnio ) / R ₁₀ } + I _3nax However, (V _ip − V _CEnio ) / (R ₁₀・h _fe4 ) < I _3nax The output voltage V ₀ at this time is V ₀ = V ₃ −V _BE4 . When the output current I increases, the collector current of the transistor 4 increases. When this collector current I _T reaches I _T =(V _ip −V ₀ −V _CEnio )/R ₁₀ , the transistor 4 is saturated and the collector current I _T no longer flows. In this way, when the output current I ₀ exceeds the collector current _IT of the transistor 4, the output current I ₃ of the IC regulator 3 increases, and the current is supplied to the load until it reaches I _3nax . IC regulators are usually
Since it has an overcurrent detection circuit, if you try to flow more current than this, the constant voltage characteristic will be lost and the output voltage will decrease.
V ₀ decreases. In this state, the collector current _IT of transistor 4 increases again. This is because I _T =(V _ip −V _CEnio −V ₀ )/R ₁₀ and V ₀ becomes smaller. Finally, the collector current I _T of the transistor 4 becomes I _T =(V _ip −V _CEnio )/R ₁₀ .

That is, the maximum output current I ₀ with constant voltage characteristics
is I _3nax + I _{T and} I _T at this time is I _TO = (V _ip − _{V 0} − V _CEnio )/R ₁₀ . The output current I _0nax when the load is short-circuited is I _0nax = I _3nax + I _Tnax , and I _Tnax at this time is I _Tnax = V _ip /R ₁₀ .

As described above, according to the circuit of the present invention, up to the output current _I3nax of the IC regulator can be used, and when the load is short-circuited, the resistor _R10 provides short-circuit protection, so that the transistor 4 will not be destroyed.

FIG. 4 shows this characteristic.

V ₃ −V _3nax is the output voltage of IC regulator 3,
The output current characteristics are shown, where V ₀ −I _Tnax is the output voltage and collector current characteristics of transistor 4, and V ₀ −I _0nax is the output voltage and output current characteristics.

FIG. 5 is intended to compensate for the disadvantage that in FIG. 3, the output voltage between the positive output terminal 8 and the negative output terminal 9 is lower by V _BE4 than the output voltage V ₃ of the IC regulator 3. diode 11
This takes advantage of the fact that the forward voltage V _D of is approximately equal to V _BE4 .

6 to 8 are application examples in which a voltage other than the output voltage of the IC regulator 3 is obtained.

In FIG. 6, the output current is as follows. Let I 3-3 be the current flowing from _3-3 of IC regulator 3 to negative output terminal 9, and let V ₀ be the output voltage, then V ₀ = (V ₃ − V _BE ) + R ₁₃・(I _3-3 + V ₃ −V _BE4 /R ₁₂ ).

In FIGS. 7 and 8, V ₀ =V ₃ −V _BE4 +V _Z.

Figure 8 shows a Zener diode 1 in the circuit of Figure 7.
4 is added with a bias current supply resistor 12, and is used when the operating current of the Zener diode 14 is insufficient at I _3-3 .

As explained above, according to the present invention, it is possible to increase the current of a 3-terminal regulator, and the characteristics of the regulator can be fully demonstrated, and any output voltage can be obtained with a simple circuit in a voltage stabilized power supply. .

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional voltage stabilized power supply. Figure 2 is a graph showing the output and voltage characteristics of Figure 1.
5 to 8 are circuit diagrams showing embodiments of the present invention, FIG. 4 is a circuit diagram showing output voltage current characteristics according to the embodiment of the present invention, 3 is an IC regulator,
3-2 is the output of IC regulator 3, 3-3 is the IC
A common terminal of regulator 3, 4 is a transistor,
5 and 6 are resistors, 7 is a transistor, 10 is a resistor,
11 is a diode, 12 and 13 are resistors, and 14 is a Zener diode.

Claims (1)

[Claims] 1. In a DC voltage stabilizing circuit using a three-terminal IC regulator having a characteristic that the output voltage drops when an overcurrent is output, a resistor is provided between the input terminal of the IC regulator and the collector of the transistor. , the output of the IC regulator is connected to the base of the transistor, and the emitter of the transistor and the common terminal of the IC regulator are used as output terminals. 2. In a DC voltage stabilization circuit using a three-terminal IC regulator having a characteristic that the output voltage drops when an overcurrent is output, a resistor is connected between the input terminal of the IC regulator and the collector of the transistor, and the IC The output of the IC regulator is connected to the base of the transistor, the common terminal of the IC regulator is connected to a power supply common line through a diode, and the emitter of the transistor and the power supply common line are used as output terminals to stabilize the power supply. circuit. 3. The power supply stabilizing circuit according to item 2 above, using a Zener diode as the diode. 4. In a DC voltage stabilizing circuit using a three-terminal IC regulator having a characteristic that the output voltage drops when an overcurrent is output, a resistor is connected between the input terminal of the IC regulator and the collector of the transistor, and the IC The output of the voltage regulator is connected to the base of the transistor and this IC
A common terminal of the IC regulator is connected to the emitter of the transistor via a resistor, and a common terminal of the IC regulator is further connected to a power supply common line via a resistor, and the emitter of the transistor and the power supply common line are output. Power supply stabilization circuit used as a terminal. 5. In a DC voltage stabilizing circuit using a three-terminal IC regulator having a characteristic that the output voltage drops when an overcurrent is output, a resistor is connected between the input terminal of the IC regulator and the collector of the transistor, and the IC The output of the voltage regulator is connected to the base of the transistor and this IC
The common terminal of the integrated circuit regulator is connected to the emitter of the transistor via a resistor, and the common terminal of the integrated circuit regulator is connected to a common power line via a Zener diode, so that the emitter of the transistor and the common power line are connected. Power supply stabilization circuit used as output terminal.