JPH029378Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a voltage switching circuit that can obtain a current capacity corresponding to the voltage when switching the voltage. Conventionally, when switching the load voltage, the first step was to obtain the corresponding current capacity.
It was common to adopt a circuit configuration as shown in FIGS.

In the one in Figure 1, the voltage switching circuit SW
Set the desired voltage with the automatic voltage regulator AVR
In this method, the voltage of the DC power supply DC is accurately dropped to obtain an arbitrary load voltage ZV, but in this type of voltage switching circuit, the stabilization circuit is complicated, and the collector A transistor with large loss is required, which inevitably increases the cost. In addition, in the case shown in FIG. 2, when the load voltage is low, the load voltage is supplied by the transistor Q ₁₁ and the resistor R ₂₁ , and when setting the load voltage to a high load voltage, a voltage is applied to the signal input terminal B ₂ . In this method, the transistor Q ₁₂ is turned on and the resistor R ₂₃ is connected in parallel to the circuit at low voltage, thereby increasing the current capacity and increasing the load voltage ZV. This method has the advantage that the collector loss is smaller than the method shown in Figure 1, and low-cost transistors can be used, but when the voltage of the DC power supply DC fluctuates, the load voltage ZV However, it has the disadvantage that the voltage also fluctuates, so it cannot be used as a voltage switching circuit that requires stability.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, and to provide a voltage switching circuit that is low in cost and highly stable, and is particularly suitable for voltage switching circuits that require stability.

Embodiments of the present invention will be described below with reference to FIGS. 3 and 4.

Figure 3 is a block diagram showing the basic configuration. In the figure, 1A and 2A are current supply circuits connected in parallel between the DC power supply DC and the load Z, and the current supply circuit 1A is always in operation. be. In the example, there are two current supply circuits, 1A and 2A, but
Of course, it may be more than that. D ₁ and D ₂ are constant voltage elements connected in series between the current supply circuit and the ground, and the embodiment shows an example in which two of them are used. S ₁ indicates a switch for selectively switching the number of constant voltage elements D ₁ and D ₂ to be connected in order to switch the load voltage;
_S2 is _a switch for changing the number of connected current supply circuits 1A and _2A in conjunction with the switch _S1 so as to correspond to the number of connected constant voltage elements. It constitutes a circuit. The mutual connection point between constant voltage elements D ₁ and D ₂ can be grounded by switch S ₁ , and when switch S ₁ is turned off, the voltage characteristics of constant voltage elements D ₁ and D ₂ change. is combined and the load Z
Therefore, the load voltage ZV is set high.

On the other hand, since the switch _S2 is interlocked so that it is turned on when the switch _S1 is in the off state, the current supply circuits 1A and 2A are connected in parallel.
As a result, it is possible to cope with the increase in current caused by switching to a high voltage as described above, and it is possible to obtain a stable load voltage. Next is the switch
When S ₁ is turned on, the potential at the connection point between constant voltage elements D ₁ and D ₂ is lowered to ground potential, and the load voltage ZV is set low because the characteristics of constant voltage element D ₁ determine the load voltage ZV. The Rukoto.

On the other hand, since the switch _S2 is turned off, the current supply circuit 2A is disconnected from the load Z and no longer carries any current. However, as mentioned above, the load voltage
Since ZV is in a low voltage state, the current capacity of the current supply circuit 1A, which is always in operation, is sufficient.

FIG. 4 shows a specific example of the circuit configuration of the present invention,
_The current supply circuit 1A is composed of a transistor Q ₁ and a collector resistor R ₂ , and the current supply circuit 2A is composed of _a transistor Q ₂ and a collector resistor R ₃ .
A Zener diode is used as the

_Q3 is a transistor as a switching circuit, and B is a voltage switching signal input terminal. D ₃ is a diode for backflow prevention, R ₄ to R ₆ are resistors, M
is a DC motor as a load, and these are wired as shown in the figure.

First, when no voltage is applied to the voltage switching signal input terminal B, the collector and emitter of the transistor _Q3 are open, so the Zener diode _D1 ,
The Zener diodes _D1 and _D2 are connected in series without any influence on the connection point P between _D2 ,
Those voltage characteristics are combined and applied to ZV,
Set to high voltage. On the other hand, a voltage divided by resistor _R4 is applied to the collector of transistor _Q3 , and since the collector is connected to the base of transistor _Q2 via resistor _R5 , it is also applied to the base of transistor _Q2 . A voltage is applied, and conduction occurs between the collector and emitter of transistor _Q2 . As mentioned above, the transistor
Since Q ₁ is always conductive and bears the load current through resistor R ₂ , transistor Q ₂ and resistor R ₃ are connected in parallel to these circuits, increasing the current capacity and increasing the It can cope with the increase in current caused by setting the load voltage.

Next, when an appropriate voltage is applied to voltage switching signal input terminal B, conduction occurs between the collector and emitter of transistor _Q3 , and since the emitter is grounded, the collector also becomes ground potential and becomes a Zener diode.
A mutual connection point P between D ₁ and D ₂ is approximately at ground potential. Therefore, the load voltage ZV is the Zener diode
Since it is determined by the characteristics of _D1 , it is set to a low load voltage.

In addition, since the collector of transistor Q ₃ is at ground potential, the base voltage of transistor Q ₂ is also sufficiently lowered, and the collector of transistor Q ₂ ,
Although the emitter is in an open state, since the load voltage is set to be low, no current capacity is required, and only the capacity of the current supply circuit 1A, which is always in a conductive state, is sufficient.

Note that transistors Q ₁ and Q ₂ are for switching operation, so the voltage between the collector and emitter is low, and most of the load current is borne by the resistor.
This is done in R ₂ and R ₃ . A circuit that compensates the load current as the load voltage is switched in this way is ideal for use in DC motors whose rotational speed can be varied depending on the applied voltage, and for other purposes.
It is also suitable for switching the brightness of a display circuit.

With the configuration described above, even if the DC power supply DC is higher than the load voltage ZV,
Since most of the potential difference is borne by the resistance in the current supply circuit, a transistor with low collector loss can be used, which is economical.

Furthermore, since the transistor _Q2 of the current supply circuit operates only when the load voltage is set high, current consumption can be reduced when the voltage is set low. Furthermore, if configured as in the embodiment, most of the load current is borne by the resistor in the current supply circuit, so the maximum collector loss of the active element in the current supply circuit can be small, and costs can be reduced.

According to the voltage switching circuit according to the present invention, since the current supply circuit can be switched in conjunction with switching of the load voltage, it is possible to accurately supply the current capacity according to the load voltage, and the constant voltage characteristics are maintained. can get. Furthermore, when the voltage is set to a low voltage, unnecessary current supply circuits are disconnected, so power consumption can be reduced.

[Brief explanation of drawings]

1 and 2 show conventional voltage switching circuits, with FIG. 1 showing a block diagram and FIG. 2 showing a circuit diagram, respectively. 3 and 4 show an embodiment of the voltage switching circuit according to the present invention, and FIG. 3 is a block diagram,
FIG. 4 is a specific circuit configuration diagram. 1A, 2A: current supply circuit, D ₁ , D ₂ : constant voltage element, S ₁ , S ₂ : switch as switching circuit, R ₂ , R ₃ : resistor, Q ₁ , Q ₂ : transistor,
Q ₃ : Transistor as a switching circuit.

Claims (1)

[Scope of utility model registration request] A plurality of current supply circuits provided in parallel between a power supply and a load, a plurality of constant voltage elements connected in series between the current supply circuit and earth, and a plurality of constant voltage elements for switching the load voltage. a switching circuit for selectively switching the number of elements to be connected and, in conjunction with this, switching the number of the current supply circuits to be connected so as to correspond to the number of the constant voltage elements to be connected; A voltage switching circuit characterized in that it is configured to obtain a current capacity according to a load voltage.