JPS5938756Y2 - Voltage switching circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage switching circuit suitable for use in electronic equipment such as a television receiver, and particularly to a voltage switching circuit suitable for integration into an integrated circuit.

Conventionally, television receivers used VHF''HF-na, UHF
A voltage switching circuit for switching and supplying voltage to the tuner is configured as shown in FIG. 1, for example.

That is, in FIG. 1, 11 is a UHF tuner,
High frequency amplifier circuit RF, local oscillator OSC.

Includes frequency mixer MIX, etc.

Further, 12 is a VHF tuner, which is a high frequency amplifier circuit R.
F, local oscillator OSC, frequency mixer MIX, etc.

Note that 13 and 14 are a UHF antenna and a VHF antenna, respectively.

On the other hand, the NPN type UV discrimination transistor Q1 has its base connected to the UV mode input terminal 15, its emitter grounded, and its collector connected to the power supply terminal 16 via resistors R1 and R2 in this order. .

The connection point of the resistors R1 and R2 is connected to the base of a PNP type transistor Q2 for cutting off the UHF tuner supply voltage, and the emitter of this transistor Q2 is connected to the power supply terminal 1.
6): The I-rector is connected to the power input terminal 17 of the UHF tuner 11, and is connected to a reference potential (for example, ground potential point) via a diode D in the forward direction and then via a resistor R3. .

In addition, the PNP type tuner supply voltage conduction transistor Q3 has an emitter connected to the power supply terminal 16,
The base is connected to the cathode of the diode D1 via the diode D2 in the forward direction, and the collector is connected to the first power input terminal 18 of the VHF tuner 12.

In the VHF tuner 12, the power line 19 of the high frequency amplifier circuit RF and the local oscillator O8C is connected to the first power input terminal 18, and the power line 20 of the frequency mixer MIX is connected via the second power input terminal 21. It is connected to the power supply terminal 16.

In this way, the VHF tuner 120 frequency mixed rootstock MIX is always supplied with a power supply voltage and set to be operable.
This is not only to perform a frequency conversion operation when the HF tuner 12 is activated, but also to perform an amplification operation on the frequency conversion output signal when the UHF tuner 11 is activated.

Therefore, a predetermined DC power supply voltage +V is applied to the power supply terminal 16.
c is applied to the U-■ mode input terminal 15.
1” according to HF reception mode and VHF reception mode, respectively.
A ``0'' logic level Moto voltage is applied.

Therefore, in the UHF reception mode, the mode voltage input "1" turns on the transistor Q1, and its collector current causes a voltage drop across the resistor R2, so that the transistor Q2 is forward biased and turned on.

Therefore, the power supply voltage +Vc is applied through this transistor Q2.
is supplied to the UHF tuner 11 and set to the UHF reception operating state.

At this time, the diode D1 is forward biased and turned on, and the terminal voltage of the resistor R3 is equal to the power supply voltage Vc.
Close to.

Therefore, the base current necessary for turning on the transistor Q3 does not flow through the transistor Q3 and the diode D2, and since the transistor Q3 is in the off state, the high frequency amplifier circuit RF and the local oscillator O8C of the VHF tuner 11 are in an inactive state.

On the other hand, in the VHF reception mode, the mode voltage input "0'" turns the transistor Q1 off, so that the base current necessary for the on operation does not flow through the transistor Q2, and the transistor Q2 remains off.

Therefore, the power supply voltage +Vc is not supplied to the UHF tuner 11, and the diode D1 is also in an off state.

Therefore, transistor Q3 and diode D2 are each biased in the forward direction, and transistor Q3 is turned on because a sufficient base current flows through the path from diode D2 to resistor R3 to ground.

And through this transistor Q3, the VHF tuner 1
The power supply voltage +Vc is supplied to the high frequency amplifier circuit RF of No. 2 and the local oscillator O8C, thereby setting the VHF receiving operation state.

However, the resistors R1 and R3, which have the function of determining the base currents of the transistors Q2'Q3, respectively, have the disadvantage that if they are set to too large a resistance value, the chip area of the integrated circuit will increase.

Conversely, setting it to a small value increases current consumption, which is undesirable, and fluctuations in the power supply voltage +VC
It greatly affects the fluctuation of the base current of tQ3, and the power supply voltage +
The stable operating range of the transistors Q2'Q3 with respect to VC fluctuations is narrowed, which has the disadvantage that it is not suitable for integrated circuit implementation.

The present invention has been developed in view of the above points, and by using a constant current circuit to supply the base current of the first and second load supply voltage exclusive transistors, there is no base current fluctuation due to fluctuations in the power supply voltage. The present invention provides a voltage switching circuit that enables stable voltage switching operation over a wide voltage range and is suitable for integration into integrated circuits.

An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 2, the control input terminal 31 is connected to the base of an NPN type transistor Q, and this transistor Q1
Its emitter is grounded, and its collector is connected to the emitter of a constant current source NPN transistor Q2 via a resistor R1.

The collector of this transistor Q2 is connected to the base of a PNP type transistor Q3 for cutting off the first load supply voltage, and is also connected to the power supply terminal 32 via a resistor R2.

The emitter of the transistor Q3 is connected to the power supply terminal 32, and the collector is connected to the power supply input terminal (not shown) of the first load circuit 33.

On the other hand, the PNP type transistor Q4 for conducting the second load supply voltage has its emitter connected to the power supply terminal 32 and its collector connected to the power supply input terminal (not shown) of the second load circuit 34.

The collector of the transistor Q3 and the base of the transistor Q4 are respectively connected to a diode D.
1 and D2 in the forward direction.

This collective connection point a is connected to the collector of an NPN type transistor Q5 for a constant current source, and the emitter of this transistor Q5 is connected to a reference potential point (for example, a ground potential point) via a resistor R3.

Furthermore, the reference voltage source 35 is, for example, a resistor (see R5 in FIG. 4).
and a Zener diode (see R5 in FIG. 4) in series, and is connected between the power supply terminal 32 and the ground potential point.

The terminal voltage of the Zener diode Dz, ie, the reference voltage Vz, is supplied to each base of the constant current source transistors Q2'Q5.

A predetermined DC power supply voltage Vc is applied to the power supply terminal 32 from a main voltage source (not shown), and the control input terminal 31 is supplied with a voltage in the first load selection mode and the second load selection mode, respectively. Correspondingly, switching control signals of logic levels 1" and "O'" are applied.

Therefore, in the first load selection mode, the switching control input "1" is applied to the base of the transistor Q1, and the voltage VZ necessary for ON operation is applied from the reference voltage source 35 to the base of the constant current source transistor Q2. Therefore, these transistors Q1 and Q2 are each in an on state.

In this case, the collector current of the transistor Q2 is a constant current determined by the base voltage Vz and the resistor R1, and part of this constant current flows as the base current of the transistor Q3.

Therefore, the transistor Q3 is also turned on, and the power supply voltage +Vc is supplied to the first load circuit 33 through this transistor Q3.

Since the reference voltage VZ is applied to the base of the constant t current source transistor Q, the constant current determined by this reference voltage Vz and the resistor R3 flows from the collector of the transistor Q3 to the diode D1 → transistor Q5 → resistor R3. →
Flows through the grounding path.

Therefore, the collector potential of the constant current source transistor Q5 is determined by the power supply voltage Vc, the collector-emitter saturation voltage VcES3 of the transistor Q3, and the diode D1.
This value is obtained by subtracting the forward voltage drop VD1, and this value is approximately close to the power supply voltage +Vc.

Therefore, the base current necessary for turning on the transistor Q4 does not flow through the transistor Q and the diode D2, and since the transistor Q4 is in the off state, the second load circuit 34 is not supplied with the power supply voltage +Vc.

On the other hand, in the second load selection mode, the switching control input "O" turns the transistor Q1 off.
Therefore, transistors Q2'Q3 are also each in an off state.

Therefore, the power supply voltage VC is not supplied to the first load circuit 33, and the diode D1 is also in an off state.

Therefore, transistor Q4 and diode D2 are each forward biased, and the base current of transistor Q4 is changed from diode D2 to transistor Q5 to resistor R3.
→Flows as a constant current in the grounding path.

Therefore, the transistor Q4 is turned on, and the power supply voltage +VC is applied to the second load circuit 3 through the transistor Q4.
4.

In the voltage switching circuit as described above, the control input "1"
91 or "0'", the first load supply voltage conduction transistor Q3 or the second load supply voltage conduction transistor Q4 is set to the on state, and the reference voltage is set as the base current of each of the transistors Q3'Q4. Constant current source transistor Q controlled by output reference voltage Vz of source 35
2. A constant current is supplied from Q5.

Therefore, even if the power supply voltage +Vc of the above circuit fluctuates, if the reference voltage Vz is selected sufficiently low compared to the power supply voltage Vc, the reference voltage Vz will hardly change with respect to fluctuations in the power supply voltage Vc. , the base current can be held constant.

Therefore, even if the fluctuation range of the power supply voltage +Vc is wide, transistors Q3'Q4 operate stably, and each load circuit 33°34
This has the advantage that stable voltage can be supplied to the circuit, and fluctuations in current consumption of the voltage switching circuit are small.

Furthermore, by selecting an appropriate value for the reference voltage Vz, the resistors R1 and R3 having a constant current determining function can be selected to values suitable for integration into an integrated circuit, and the chip area can be reduced.

In the case of an integrated circuit, the diode D1 is a diode-connected vertical NPN transistor as shown in FIG. 3a, for example.

In such a transistor, the reverse breakdown voltage between base B and emitter E is generally around 5 to 7V, which is small.
A base B-collector 0 diode with a high reverse breakdown voltage is used.

That is, when the transistor Q3 is off, the cathode of the diode D1 is connected to the transistor Q4 from the power supply voltage +Vc.
Base-emitter voltage VBE4 and diode D
Since a large voltage minus the forward voltage drop of 2 is applied, a large reverse breakdown voltage is required.

However, diode D1 as above is connected to transistor Q3.
When the current ib flows between the base and the collector as shown in Figure 3 during the on-operation, a parasitic P-N-
A P transistor is generated and a current ic flows toward the substrate.

Since this parasitic HFE is large and on the order of β-1, a wasteful current ic, which is almost the same as ib, flows to the substrate, increasing the power consumption of the diode.

Therefore, in order to prevent this, it is necessary to suppress the vertical direct current amplification factor HFE.

In Figure 3, the emitter, base, and collector of the P-N-P parasitic transistor are respectively E? , B'.

It is represented by pi.

For the diode D2, a diode connection of vertical NPN transistors is used like the above diode, but a B-E diode is used.

Further, the first load circuit 33 and the second load circuit 34 of the above embodiment
For example, when the current consumption is large as in the UHF tuner and VHF tuner shown in Fig. 1, when integrating the voltage switching circuit, a transistor Q for exclusive use of the load supply voltage is added.
3. If Q4 is PNP type, the current capacity may not be sufficient.

In such a case, a combination of a PNP transistor and an NPN transistor may be used to obtain sufficient current capacity.

FIG. 4 shows an example of a circuit for this purpose. In FIG. 4, the same parts as those in FIG.

That is, the collector of the PNP type transistor Q3 is connected to the base of the NPN type transistor Q6, the collector of this transistor Q6 is connected to the power supply terminal 32, and the emitter is connected to the tJHF tuner and the diode D1.

Further, the base of the PNP type transistor Q4 is connected to the power supply terminal 32 via the resistor R4, and the base is connected to the power supply terminal 32 via the resistor R4.
is connected to diode D2 in the forward direction.

The collector of the 1ffNP type transistor Q4 is connected to the base of the NPN type transistor Q7, the collector of this transistor Q7 is connected to the power supply terminal 32, and the emitter is connected to the VHF tuner.

Therefore, when switching control power "1" is applied to the base of transistor Q, transistor Q.

Q2'Q3 are each turned on, and the transistor Q
The collector current of 3 flows into the transistor Q6 as a base current, and this transistor Q6 is turned on, allowing a large current to be supplied to the UHF tuner.

At this time, part of the collector current of the transistor Q6 flows through the diode D.

→ Transistor Q5 → Resistor R3 → Ground.

Therefore, the collector potential of the transistor Q3 is a value obtained by subtracting the collector-emitter saturation voltage VCES3 of the transistor Q3, the base-emitter voltage VBE6 of the transistor Qa, and the forward voltage drop of the diode D from the power supply voltage 10 Vc. However, this value is almost close to the power supply voltage +Vc.

Therefore transistor Q4 and diode D2,
The base current required to turn on the transistor Q4 does not flow through D3, and the transistor Q4 is in an off state.

Therefore, transistor Q7 is also in an off state, and V
The power supply voltage +VC is not supplied to the HF tuner.

On the other hand, the switching control input "O"' is the transistor Q1.
, transistors Q1, Q2 and Q3 are respectively turned off, and therefore transistor Q6
is also turned off, and the UHF tuner has a power supply voltage of 10 V.
C is not supplied, and the diode D1 is in an off state.

At this time, transistor Q4 and diodes D2, D
3, the base current necessary for turning on the transistor Q4 flows, and this base current flows from the transistor Q5 to the resistor R.
3 → Flows as a constant current to the ground path.

As the transistor Q4 turns on, the transistor Q7 also turns on, making it possible to supply a large current to the VHF tuner.

In such a voltage switching circuit, as in the circuit shown in FIG. 2, the base currents of the transistors Q3 and Q4 are made constant by the transistors Q2 and Q5, so that the transistors Q3. The operation of transistors Q6 and Q7, which work together with Q4, is also stable against fluctuations in the power supply voltage +Vc.

Note that the transistor Q1 in each of the above embodiments may be replaced with another switch knob element.

As described above, according to the present invention, the base current of the first and second load supply voltage exclusive transistors is supplied by a constant current circuit, so that the base current does not fluctuate due to fluctuations in the power supply voltage and can be applied over a wide voltage range. A stable voltage switching operation is possible, and a voltage switching circuit suitable for integration into an integrated circuit can be provided.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional voltage switching circuit, Fig. 2 is a circuit diagram showing an embodiment of the voltage switching circuit according to the present invention, and Fig. 3 is a circuit diagram showing an embodiment of the voltage switching circuit according to the present invention.
Figures a and b are diagrams showing the structure and equivalent circuit of diode D1 in Figure 2, and Figure 4 is a circuit diagram showing another embodiment of the present invention. 32...Power supply terminal, 33.34...Load circuit, 35
...Reference voltage source, Q1-Q5...Transistor, D
,. D2...diode, R1-R3...resistance.

Claims (1)

[Scope of utility model registration request] The first type is the same type for PNP type or NPN type.
A first transistor Q3 for conducting load supply voltage and a second transistor Q4 for conducting load supply voltage, a main voltage source connected to each emitter of both transistors Q3'Q4, and each of said transistors. A first load circuit and a first load circuit to which the voltage from the main voltage source is supplied via transistors Q3 and Q4, respectively, or via separate transistors Q6 and Q7 which are switched and driven by the outputs of the transistors Q3 and Q4, respectively. a first diode D1 having one end connected to the power input terminal of the first load circuit and connected in a forward direction with respect to the power supply voltage supplied to the power input terminal; A second diode D2 is connected in a direction opposite to the first diode D1 between the other end of the diode and the base of the second transistor Q4, and both diodes D1. A third transistor Q5 has a collector connected to the connection point of D2, a base connected to the reference voltage source 35, and an emitter connected to the reference potential point via a resistor, and a collector connected to the base of the first transistor Q3. a fourth transistor Q whose base is connected to the reference voltage source 35 and whose collector is connected to the main voltage source via a resistor;
2 and the resistor connected to the emitter of the fourth transistor Q2 and the reference potential point, and switching according to the selection of the first load circuit case or the second load circuit to which the power supply voltage is to be supplied. A voltage switching circuit comprising a controlled switching element.