JPS5838405Y2 - Output voltage adjustment circuit for integrated circuit for constant voltage power supply - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an output voltage adjustment circuit for adjusting the output voltage of an integrated circuit for a constant voltage power supply.

Conventionally, as shown in FIG. 1, in a constant voltage power supply integrated circuit consisting of a series type constant voltage circuit, for example, the output side of a rectifier is connected between an input terminal IN and an input/output common terminal COM, A voltage control transistor T r 1 is connected in series to the load connected between the input/output common terminal COM and the input/output common terminal COM.
The emitter of the voltage fluctuation detection transistor T r 2 is connected to the reference voltage generation Zener diode Dz, and the transistor T r
By changing the base potential of transistor T r 2
By changing the collector current of the voltage control transistor T
The collector-emitter voltage of r1 is changed to compensate for the voltage fluctuation and stabilize the output voltage.

The output voltage can be adjusted by changing the value of the resistor Rat or Rb.

However, trimming within an integrated circuit (hereinafter simply referred to as IC) is relatively difficult, and in the case of a three-terminal configuration as described above, the nominal values of Zener diode Dz and resistors Ra and Rb are There was a problem in that the deviation occurred as a deviation in the 11 output voltages.

This invention was made to solve these conventional problems, and it is possible to accurately and easily adjust the output voltage of a constant voltage power supply IC, especially a three-terminal configuration constant voltage power supply IC. The purpose is to provide an output voltage adjustment circuit.

The feature of this invention is that the common terminal of a constant voltage power supply IC having an input terminal, an output terminal, and a common terminal is connected to the emitter of a transistor without being grounded, while the collector of this transistor is grounded. Further, a voltage dividing circuit is inserted between the output terminal and the ground point, and the voltage dividing point of this voltage dividing circuit is connected to the base of the transistor. While an input voltage is applied between the output terminal and the ground point, an output voltage corresponding to the voltage division state of the voltage dividing circuit is obtained between the output terminal and the ground point.

Embodiments of this invention will be described below with reference to the accompanying drawings.

FIG. 2 shows an embodiment of the adjustment circuit of this invention, which adjusts the output voltage of the constant voltage power supply IC shown in FIG.

In Fig. 2, input terminal 1a to which an alternating current voltage is applied
A rectifier circuit 3 is connected between , l and b via a switch 2, and a smoothing capacitor 4 is connected to the output side of this rectifier circuit 3.
One output terminal of the smoothing capacitor 4 is connected to the input terminal IN of the constant voltage power supply IC 5, and the other output terminal of the smoothing capacitor 4 is grounded.

In this case, since the input/output common terminal COM of the IC5 is not grounded, if the voltage across the capacitor 4 is Vin, the input terminal IN of this IC5 and the common terminal CO
The voltage Ein between the transistor 14 and the transistor M is the voltage obtained by subtracting the collector-emitter voltage VCE of the transistor 14, which will be described later, from the voltage Vin.

The base of the voltage control transistor 6 in the IC 5 is connected to the collector of the voltage fluctuation detection transistor 7, and the emitter of the voltage fluctuation detection transistor is connected to the input/output common terminal COM via the reference voltage generation Zener diode 8. There is.

A resistor 9 is connected between the collector and base of the voltage control transistor 6, and this resistor 9 is a load resistance for the transistor 7, and provides an appropriate bias to the two transistors 6 and 7.

Further, a resistor 10 is connected between the emitter of the voltage control transistor 6 and the emitter of the voltage detection transistor 7, and this resistor 10 is connected to a Zener diode 8.
This is a resistor for supplying current to the Zener diode 8, and is used to make the Zener current sufficiently larger than the emitter current of the voltage detection transistor 7 to prevent the Zener voltage Vz of the Zener diode 8 from changing.

A series circuit of a resistor 11 and a resistor 12 is connected between the emitter of the voltage control transistor 6 and the anode side of the Zener diode 8, and the connection point between the resistors 11 and 12 is connected to the base of the voltage fluctuation detection transistor 7. The base potential of this transistor 7 is set to be higher than its emitter voltage (reference voltage Vz generated by Zener diode 8) by base-emitter voltage VBF·1.

The IC5 having the above configuration has an output voltage Eo (output terminal OU
The collector current of the transistor 7 is changed by changing the base potential of the voltage fluctuation detection transistor 7 according to the fluctuation of the voltage between the voltage control transistor 6 and the input/output common terminal COM, and the collector-emitter voltage of the voltage control transistor 6 is changed. to compensate for voltage fluctuations and output voltage E.

It works to keep the value constant.

On the output side of IC5, there is an output voltage adjustment circuit 1 based on this invention.
This output voltage adjustment circuit 13 consists of a transistor 14 and a voltage dividing circuit 15, and the emitter of the transistor 14 is connected to the common terminal COM of IC5.
A voltage dividing circuit 15 is connected between the output terminal OUT of the IC 5 and the collector of the transistor 14.

The voltage dividing circuit 15 consists of a series circuit of a fixed resistor 16 and a variable resistor 17, and the slide terminal 1 of the variable resistor 17
7a (voltage dividing point of the voltage dividing circuit 15) is connected to the base of the transistor 14.

Then, output terminals 18a and 18 of the output voltage adjustment circuit 13
A voltage vO is generated between the load 19 and the load 19.

In this circuit of Fig. 2, IC5 is connected to its common terminal CO.
M operates with the transistor 14 connected to ground, or the voltage E obtained between its output terminal OUT and the common terminal COM.

is kept constant by the constant voltage operation of the IC5 itself.

On the other hand, the common terminal CO of IC5 is connected to transistor 1.4.
When the current of M flows into the ground point, collector-emitter voltages VC and E are generated.

Therefore, the voltage V.

becomes Eo+■cE. By the way, the collector-emitter voltage VCE is the base-emitter voltage VBE2 of the transistor 14 and the voltage E, as described later.

(These voltages are both constant voltages)
It can be expressed as the sum voltage of the voltage multiplied by a voltage division ratio of 5 and the voltage VBE2.

Therefore, the voltage V. can be adjusted according to the voltage dividing ratio of the voltage dividing circuit 15.

This will be explained in detail below using an equivalent circuit and equations.

3 is an equivalent circuit diagram of the circuit shown in FIG. 2, and FIG. 4 is a simplified version of the equivalent circuit shown in FIG.

In these figures, Rc is the voltage dividing point 17 of the voltage dividing circuit 15.
The resistance from a to the output terminal 18at, Rd is the voltage divider circuit 1
This is the resistance from the voltage dividing point 17a of No. 5 to the output terminal 18bt.

The base-emitter voltage of transistor 14 is vBE2
If the current flowing through Rd is id, then there is the following relationship: (1) o=Eo+vBE・2+1d−Rd (1).

If the current amplification factor hfe of the transistor 14 is sufficiently large, the base current of the transistor 14 flowing into the resistor Rd can be ignored.

In this (3X, voltage VBE2 is a constant value,
Also the voltage E.

As mentioned above, although there are individual variations during the manufacturing of IC5, it is a constant value, so the voltage V.

can be adjusted by changing the position of the slide terminal 17a of the variable resistor 17 and adjusting Rd/RC.

In this case, as mentioned above, the voltage VBE2tEO
Since both are constant, the voltage VO is naturally constant, that is, stabilized.

Here, each voltage Vin. Between Ein1EON vo, V in - V o = E in - E o... (4)
A relationship has been established.

In the above embodiment, the voltage dividing circuit is constructed by combining a fixed resistor and a variable resistor, but the invention is not limited to this, and for example, a field effect transistor may be used as a variable resistance element, The bias may be changed.

In addition, although a PNP type transistor is used in the above embodiment, if the voltage polarity at the output terminal of the constant voltage circuit is reversed, the N
An RN type transistor may be used.

Furthermore, although the above-mentioned embodiment adjusts the output voltage of a series-type voltage regulator, this invention also includes a parallel-type voltage regulator in which a voltage control transistor is connected in parallel to a load, and a parallel-type voltage regulator as described above. It can also be applied to a combination with a series type constant voltage circuit such as.

Furthermore, although the above embodiment relates to a three-terminal constant voltage circuit, this invention can also be applied to an output voltage adjustment circuit of a voltage circuit that generally operates to maintain the voltage between a pair of output terminals at a constant value. .

As is clear from the above description, the output voltage adjustment circuit of the integrated circuit for a constant voltage power supply according to the present invention can be implemented by using a transistor without grounding the common terminal of the IC for a constant voltage power supply having an input terminal, an output terminal, and a common terminal. while the collector of this transistor is grounded, and a voltage dividing circuit is inserted between the output terminal and the ground point, and the voltage dividing point of this voltage dividing circuit is connected to the base of the transistor, By pressing the button in this connection state, an input voltage is applied between the input terminal and the ground point, and an output voltage corresponding to the voltage division state of the voltage dividing circuit is obtained from between the output terminal and the ground point. Therefore, even if the output voltage of the integrated circuit for constant voltage power supply varies due to deviation from the Zener voltage of the Zener diode or the nominal value of the resistor, the same output voltage can be adjusted without impairing the constant voltage function. It can be adjusted with high precision.

In fact, the output voltage can be adjusted by changing the voltage dividing point of the voltage dividing circuit connected to the outside of the integrated circuit.
Output voltage can be easily adjusted.

Also, if this idea is applied to a three-terminal constant voltage power supply IC,
There is an advantage that there is no need to adjust the value of the output resistor in the IC, and that deviations in the Zener diode or resistor in the IC will not affect the output voltage.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional integrated circuit for constant voltage power supply, Fig. 2 is a circuit diagram showing an output voltage adjustment circuit of the integrated circuit for constant voltage power supply according to this invention, and Fig. 3 is a circuit diagram of the circuit shown in Fig. 2. The equivalent circuit diagram in FIG. 4 is a simplified equivalent circuit of the equivalent circuit in FIG. 3. 5... Integrated circuit for constant voltage power supply, 14... Transistor, 15... Voltage dividing circuit, IN, OUT, COM...
Input terminal, output terminal, and input/output common terminal of constant voltage circuit.

Claims (1)

[Scope of utility model registration request] An emitter or a collector connected to the common terminal of an integrated circuit for a constant voltage power supply configured to constant voltage a voltage between an input terminal and a common terminal and output it from between an output terminal and the common terminal. The voltage dividing circuit includes a grounded transistor and a voltage dividing circuit interposed between an output terminal of the constant voltage power supply integrated circuit and a ground point, and a voltage dividing point of the voltage dividing circuit is connected to the base of the transistor. An input voltage is applied between the input terminal of the integrated circuit for voltage power supply and the ground point, while an output voltage is output from between the output terminal of the integrated circuit for identified voltage power supply and the ground point. Output voltage adjustment circuit for integrated circuit for constant voltage power supply.