JPH01202018A - Voltage switching circuit - Google Patents

Abstract

PURPOSE:To obtain a voltage switching circuit reducing elements constituting the circuit by providing the circuit with a differential pair transistors(TRs) for outputting an input voltage or a reference voltage in accordance with the sizes of the input and reference voltages. CONSTITUTION:When the input voltage VIN and the reference voltage Vref3 is VIN>Vref3, a TR Q13 is turned on, a TR Q14 is turned off, the TRs Q13, Q15 act as a voltage follower circuit, and a voltage drop due to the TR Q13 is compensated by a level shifting TR Q15, so that a voltage equal to the input voltage VIN is outputted to an output terminal VOUT. In case of VIN<Vref3, the TR Q14 is turned on, the TR Q13 is turned off, the TRs Q14, Q15 act as a voltage follower circuit, and a voltage drop due to the TR Q14 is compensated by the level shift TR Q15, so that a voltage equal to the reference voltage Vref3 is outputted to the output terminal VOUT. Consequently, it is unnecessary to independently form a threshold voltage and two fixed reference voltages.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) This invention is applicable to, for example, an I
The present invention relates to a voltage switching circuit that is used in C and sets a reference voltage when switching between two different modes (for example, PAL/NTSC video formats).

(Prior Art) FIG. 2 is a circuit diagram showing a voltage switching circuit conventionally used in ICs of laser disc players. In the figure, Ql and Q2 are PNP transistors on the input side, forming a differential pair, and their emitters are commonly connected and connected to a power supply via a constant current source 11. Transistor Q1
．． The base of Q2 has a threshold voltage ■T)1.
An input voltage VIN is applied, and the transistor with the smaller voltage value becomes conductive.

Q3. Q4 is an NPN transistor, constitutes a current mirror circuit with transistor Q4 as a reference, and serves as a load. The collectors of transistors Q3, Q4 are connected to transistors Q1, . It is connected to the collector of Q2, and its emitters are each grounded.

Q5. Q6 is an NPN)-transistor and constitutes a differential pair. The common connection point of the emitters of these transistors is grounded via a constant current source (2).

And the base of transistor Q5 is the transistor Q2
The base of transistor Q6 is connected to the collector of transistor Q1, and the base of transistor Q6 is connected to the collector of transistor Q1.

Q7. Q8 is an NPN transistor, constitutes a voltage follower, and base i! Lightning voltage,. Outputs a voltage equal to fl to the terminal V. Output to Ul. These transistors Q7
．． The common emitter connection point of Q8 is connected to the collector of transistor Q5. A reference voltage ■ is applied to the base of the transistor Q7. fl is given, the collector and base of the transistor Q8 are connected, and their common connection point is the output terminal V. Connected to 1H.

Q9. Q10 is an NPN transistor, constitutes a voltage follower, and has a reference voltage V,. , 2 to the output terminal V. Output to Ul. These transistors Q9
．． The common emitter connection point of QIO is connected to the collector of transistor Q6.

A reference voltage Vif2 is applied to the base of the transistor QIO, the collector and base of the transistor Q9 are connected, and their common connection point is the output terminal (2). It is connected to lJl.

Ql 1. Ql2 is a PNP transistor, constitutes a current mirror circuit with transistor Q12 as a reference, and serves as a load. Transistor Q11. The emitter of Q12 is connected to the power supply. Transistor Q11
．． The collectors of Q12 are connected to the output terminal V and the collector of transistor Q10, respectively.

Next, the operation will be explained. First, the relationship between the input voltage VIN and the threshold voltage VdH is VIN>Vllll
The case will be explained below. In this case, transistor Q1
is ONL, and transistor Q2 is turned off. Therefore,
Transistor Q5 is 0FFL, transistor Q6 is ON
do. Transistor Q9 configuring the voltage follower. When Q10 is ONL, a voltage equal to the reference voltage V is output to the output terminal ef2.

On the other hand, when vIN<vTll, the transistor Q1 is OFFFL, and the transistor Q2 is ON. Therefore,
Transistor Q5 is ONL, transistor Q6 is OFF
do. Transistor Q7 configuring the voltage follower. Q8 is ONL, and the voltage equal to the reference voltage vref1 is the output terminal V. Output to U□. In this way, the output terminal ■. The output voltage of Ul is the reference voltage ■ or V
As a result, switching of the video format of the laser disc, etc. is performed.

[Problem to be solved by the invention]

Since the conventional voltage switching circuit is configured as described above,
Transistor Q5. The threshold voltage V1N, which is the reference for controlling the 0N10FF of Q6, is the reference voltage "rer1".
'v,. This has to be provided separately from f2, which poses a problem in that the number of elements constituting the circuit increases.

The present invention was made to solve the above-mentioned problems, and therefore, it is an object of the present invention to obtain a voltage switching circuit with fewer elements constituting the circuit.

[Means to solve the problem]

The voltage switching circuit according to the present invention consists of a pair of transistors, an input voltage is applied to the control electrode of one transistor, a reference voltage is applied to the control electrode of the other transistor, and the input voltage and the reference voltage are The configuration includes a differential pair that selectively outputs the input voltage or the reference voltage from a common emitter depending on the magnitude of the voltage.

[Effect]

The differential pair of transistors in this invention has an input voltage applied to the control 2a electrode of each transistor.

Since the input voltage or the reference voltage is selectively output depending on the magnitude relationship of the reference voltages, there is no need to provide a threshold voltage and two different reference voltages unlike the conventional circuit in order to switch and output two types of voltages.

(Embodiment) FIG. 1 is a circuit diagram showing an example of an actual seat according to the present invention. In the figure, the difference from the conventional circuit shown in FIG. 2 is that the differential pair transistor Q5. Eliminate Q6 and use differential pair transistor Q
5. Transistor Q1.Q6 controls 0N10FF.
Q2 and the reference voltage Vref1 in the voltage follower. ■、
. Transistor Q7.f2 is given. QIO is connected to one transistor each Q13. Q14 and transistors Q8 and Q9 were replaced with one transistor Q15. Transistor Q13. Q14 is an NPN transistor and forms a differential pair. These transistors Q
13. The emitters of Q14 are commonly connected, and this common connection point is grounded via constant current source I2 and is also connected to output terminal V 1 via level shift transistor Q15. The OUT collectors are also commonly connected, and this common connection point is the transistor Q11. It is connected to the collector of transistor Q12, which serves as a reference for the current mirror circuit made up of Q12. Transistor Q11 is a level shift transistor Q
It is connected to a common connection point between the 15 collectors and the base. The input voltage ■IN is applied to the base of the transistor Q13.
A reference voltage V is applied to the base of the transistor Q14, and ef3 is applied to the base of the transistor Q13 or Q1 depending on the magnitude of these voltages.
4 is ONL, and output terminal V from the common connection point of the emitters of these transistors Q13 and Q14. A voltage equal to the reference voltage Vrer1 or the input voltage ■■ is selectively outputted to Ul.

Next, the operation will be explained. First, the input voltage ■1N and the base Q
A case where the relationship between voltage Vref3 is VIN>Vref3 will be explained. In this case, transistor Q13 is ONL.
, transistor Q14 is turned off. Transistors Q13 and Q15 operate as a voltage follower circuit, and the level shift transistor Q15 compensates for the voltage drop caused by transistor Q13, so that the output terminal V
A voltage equal to the input UT voltage v1N is output.

Next, the case where vIN<vref3 will be explained.

In this case, transistor Q14 is turned ON and transistor Q13 is turned OFF. Then, the transistors Q14 and 015 operate as a voltage follower circuit, and the level shift transistor Q15 compensates for the voltage drop caused by the transistor Q14, so a voltage equal to the reference voltage V is outputted to the output terminal V. Ru.

In order to obtain an output voltage similar to that of the conventional circuit shown in FIG. 2 in this embodiment, for example, the reference voltage . , 1 is V,. , 2, the reference voltage ■ is made equal to the reference ef3 voltage V. As a result, the input voltage ef1 ■ becomes the reference voltage ■. , if it is smaller than 1, the voltage of the output terminal N becomes the reference voltage V, and the input type OUT
If the ref1 voltage V is the reference voltage V, the output terminal IN
The voltage of ref2 ■ becomes the reference voltage ■.

OUTr
ef2 [Effect of the Invention] As described above, according to the present invention, a differential pair transistor is provided that outputs an input voltage or a reference voltage depending on the magnitude of the input voltage and reference voltage applied to each control electrode. Unlike conventional circuits, there is no need to separately provide a threshold voltage and two fixed reference voltages to switch and output voltages, and the number of elements can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional voltage switching circuit. In the figure, ■ is the input voltage, and ■. f3 is the reference voltage N voltage, Q13. Q14 is a differential pair transistor. Note that the same reference numerals in each figure indicate the same or corresponding parts. Figure 1 Figure 2

Claims (1)

[Claims] (1) Consisting of a pair of transistors, an input voltage is applied to the control electrode of one transistor, a reference voltage is applied to the control electrode of the other transistor, and the input voltage is determined by the magnitude of the input voltage and the reference voltage. Alternatively, a voltage switching circuit comprising a differential pair that selectively outputs the reference voltage from a common emitter.