JPH0564359A - Voltage switching circuit - Google Patents

Abstract

PURPOSE:To apply a constant voltage to a load circuit by detecting voltage generated by the first or second power supply circuit, and controlling the operation of a switching circuit. CONSTITUTION:When an electronic equipment body is in a normal operation mode, the output voltage VB2 of the second power supply circuit 4 is detected by a voltage detector circuit 5, keeps a selector switch 6 in the opened state, and applies the output voltage VB2 of the second power supply circuit 4 to the lead circuit 2 of a microcomputer, etc. When the electronic equipment body is in a standby operation mode, the voltage detector circuit 5 detects low-level output voltage VB2 of the second power supply circuit 4, changes the selector switch 6 over to the closed state, and applies the output voltage VB1 of the first power supply circuit 3 to the load circuit 2 of a microcomputer, etc. This makes it possible to switch over power sources so as to make the output voltage constant automatically, and a voltage switching circuit of simple constitution can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage switching circuit used in an electronic device having a power saving function having a normal operation mode and a standby operation mode, and particularly, a microcomputer etc. even when the operation mode is switched. The present invention relates to a voltage switching circuit in which the voltage supplied to the load circuit is kept constant.

[0002]

2. Description of the Related Art Recently, in electronic equipment such as audio equipment and video equipment, a device having a power saving function having a normal operation mode and a standby operation mode has become widespread. Since such an electronic device is generally controlled by a microcomputer, it is necessary to switch the operation mode so that the voltage supplied to the microcomputer is constant even when the operating voltage of the device body changes. In addition to the microcomputer, there are some devices that must continue normal operation, such as display devices such as LEDs, even when the main body of the device is in a standby state. , It is necessary to supply a constant voltage.

FIG. 3 is a block diagram of a conventional device. In the normal operation mode, the changeover switch 6 including a transistor and a relay is opened, and the power supply voltage V _B2 (for example, 16 V) is supplied from the power supply circuit section 1 of the device body to the microcomputer 2.

When the device main body 1 enters the standby operation mode, the power supply voltage V _B2 drops significantly to several V and becomes too low as the power supply voltage of the microcomputer 2. At this time, changeover switch 6
A trigger signal is input from the outside to close the changeover switch 6. As a result, the power supply voltage V _B1 is supplied to the microcomputer 2 from the power supply circuit section 1 of the device body through the changeover switch 6.

[0005]

In the above-mentioned conventional apparatus, when the operation mode of the device main body is switched from the normal operation mode to the standby operation mode or vice versa, the output voltage V _OUT is generated by the external trigger signal. Therefore, if the switching timing is deviated, the output voltage V _OUT may fluctuate, which may cause a circuit such as the microcomputer 2 to malfunction, and noise such as an external trigger signal may cause a malfunction such as voltage switching. It was

[0006]

In order to solve the above problems, the present invention provides a first power supply circuit which generates a lower voltage in the standby operation mode than in the normal operation mode, and the first power supply circuit. A second power supply circuit that generates a lower voltage and a lower voltage in the standby operation mode than in the normal operation mode, and the first power supply circuit when switching between the normal operation mode and the standby operation mode. And a switching circuit configured to switch a second power supply circuit to supply a predetermined constant voltage to a load circuit that always needs to supply a constant voltage. Second
In this configuration, the voltage generated by the power supply circuit is detected to control the opening / closing of the switching circuit.

Further, a constant voltage generating circuit for generating a constant voltage is provided, and the switching circuit is provided with a potential difference between a voltage supplied from the first or second power supply circuit and a constant voltage generated from the constant voltage generating circuit. It is configured to control opening and closing.

[0008]

According to the above structure, when the electronic device is switched from the normal operation mode to the standby operation mode, both the first and second power supply circuits have a voltage lower than that in the normal operation mode. The switching circuit is detected and switched, and the high level voltage of the second power supply circuit derived in the normal operation mode is switched to the low level voltage of the first power supply circuit.

Contrary to the above, when the electronic device switches from the standby operation mode to the normal operation mode, both the first and second power supply circuits have higher voltages than those in the standby operation mode. To switch the switching circuit,
The low level voltage of the first power supply circuit is switched to the high level voltage of the second power supply circuit in the normal operation mode.

Therefore, a predetermined voltage can be derived from the output of the switching circuit irrespective of the change in the power supply voltage due to the switching of the operation mode, and the predetermined voltage can be supplied to the load circuit which always needs to supply a constant voltage. Can be supplied at all times.

[0011]

1 is a block diagram of the present invention, and FIG. 2 is a circuit diagram of an embodiment of the present invention. In FIGS. 1 and 2, 1
Is a power supply circuit section of an electronic device having a normal operation mode and a standby operation mode for power saving. The power supply circuit section 1 generates a high level potential of, for example, 120 V in the normal operation mode, and in the standby operation mode. For example, a first power supply circuit 3 that generates a low-level potential of 20V and a second power circuit 3 that generates a high-level voltage of 16V in the normal operation mode and a low-level voltage of 2V in the standby operation mode.
The power supply circuit 4 of FIG.

Reference numeral 2 is a load circuit such as a drive circuit of a microcomputer or an indicator which requires a constant voltage to be supplied to the electronic equipment main body in either a normal operation mode or a standby operation mode, and 5 is supplied to the load circuit 2. A voltage detection circuit for detecting the voltage to be applied, 6 is a changeover switch for selectively switching the voltage supplied from the first or second power supply circuit 3 or 4 according to the voltage detected by the voltage detection circuit 5. Is.

Reference numeral 7 is a switching element including a transistor T _N or the like provided between the first and second power supply circuits 3 and 4, and 8 is a Zener diode Z _D connected to a control element of the switching element 7. Constant voltage element such as 9
Is a resistor for driving a switching element, which is connected between the first power supply circuit 3 and the control terminal of the switching element 7.

Therefore, when the electronic equipment main body is in the normal operation mode, the voltage of the first power supply circuit 3 becomes about 120V,
In addition, the voltage of the second power supply circuit 4 becomes about 16V, and when the electronic equipment main body enters the standby operation mode, the output voltage of the power supply circuit unit 1 is lowered in order to reduce power consumption. Is about 20V, and the voltage of the second power supply circuit 4 is about 2V.

On the other hand, the load circuit 2 such as the microcomputer or the power source for the LED is always about 16 regardless of the operation mode of the device body.
A voltage of V shall be required. Now, when the electronic device main body is in the normal operation mode, in FIG. 1, the voltage detection circuit 5 detects the output voltage V _B2 of the second power supply circuit 4, keeps the changeover switch 6 open, and loads the microcomputer or the like. Circuit 2
Is supplied with the output voltage V _B2 (about 16 V) of the second power supply circuit 4.

When the main body of the electronic device enters the standby operation mode,
The voltage detection circuit 5 detects the output voltage V _B2 dropped to the low level of the second power supply circuit 4, switches the changeover switch 6 to the closed state, and loads the load circuit 2 such as a microcomputer with the first power supply circuit 3 Supply the output voltage V _B1 .

This operation will be described in more detail with reference to FIG.
It Now, the constant voltage of the constant voltage element 8 such as Zener diode
V_ZDIf set to about 16.5V, in normal operation mode
Is the output voltage V of the second power supply circuit 4._B2Is on the high level side
Since it is 16V, V_B2> V_ZD-V_BETH  However, V_BETHIs a transistor that constitutes a switching element
T_NBecomes the base-emitter voltage of the transistor T_NIs
As a result of reverse bias, the switching element 7 is in the open state.
Keep the output voltage V of the second power supply circuit 4_B2(About 16V)
It is supplied to the load circuit 2 such as a microcomputer.

When the electronic device main body is in the above-mentioned normal operation mode
When switching to the standby operation mode, the output of the second power supply circuit 4
Force voltage V_B2Switch to a low level voltage (about 2V)
Transistor T_NThe base current flows to the switch
The closing element 7 is closed. Therefore, the negative
Output voltage V supplied to packing circuit 2_OUTIs V_OUT= V_ZD-V_BE  And becomes about 16V.

As described above, the load circuit 2 is supplied with a constant voltage even if the operating voltage of the power supply circuit is switched depending on the operating mode of the device body.

Each voltage value in the above embodiment is an example, and the present invention is not limited to this, and the constant voltage V _ZD of the constant voltage element 8 and the output voltage V _B2 of the second power supply circuit.
The output voltage V _OUT to be supplied to the load circuit 2 can be arbitrarily set by arbitrarily setting the output voltage V _OUT . Further, in the above embodiment, the switching element 7 is controlled by detecting the voltage V _B2 of the second power supply circuit 4, but
The same operation can be performed by detecting the voltage V _B1 of the power supply circuit 3.

[0021]

Since the present invention is constructed as described above,
The power supply can be switched so that the output voltage automatically becomes constant by detecting the voltage fluctuation due to the switching of the operation mode, and there are few malfunctions due to noise and few malfunctions due to the switching timing, and a simple voltage switching. A circuit can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of an embodiment of the present invention.

FIG. 3 is a block diagram of a conventional example.

[Explanation of symbols]

 2 load circuit 3 first power supply circuit 4 second power supply circuit 5 voltage detection circuit 6 changeover switch 7 switching element 8 constant voltage element

Claims (2)

[Claims] 1. A first power supply circuit that generates a lower voltage in the standby operation mode than in the normal operation mode, a lower voltage than the first power supply circuit, and a standby operation than in the normal operation mode. A second power supply circuit that generates a lower voltage in the mode and a constant power supply by switching the first and second power supply circuits when switching between the normal operation mode and the standby operation mode And a switching circuit adapted to supply a predetermined constant voltage to a load circuit requiring the same, wherein the first or second voltage switching circuit is used.
The voltage switching circuit is characterized in that the switching circuit is controlled by detecting the voltage generated from the power supply circuit. 2. A first power supply circuit that generates a lower voltage in the standby operation mode than in the normal operation mode; and a standby operation mode that generates a lower voltage in the standby operation mode than in the normal operation mode. Second time to generate lower voltage
When the normal operation mode and the standby operation mode are switched, the first power circuit and the second power circuit are switched to supply a predetermined constant voltage to the load circuit that requires constant voltage supply. In a voltage switching circuit of an electronic device including a switching circuit adapted to supply the voltage, a constant voltage generating circuit for generating a constant voltage is provided, and the switching circuit is set to the voltage supplied from the first or second power supply circuit. A voltage switching circuit characterized in that opening / closing control is performed by a potential difference from a constant voltage generated from the constant voltage generating circuit.