JPH0377111A - Constant voltage generating device - Google Patents

Abstract

PURPOSE:To reduce the power consumption in a stand-by state by obtaining the stand-by voltage from the voltage of another level at a stand-by/non-stand-by state. CONSTITUTION:The 1st rectifying means 1C, 3C and C1 rectify the AC power output into the 1st DC voltage, and the 2nd rectifying means 1d, 3b and c2 rectify the AC power output into the 2nd DC voltage lower than the 1st DC voltage. A constant voltage transforming means 4 is connected to the outputs of both 1st and 2nd rectifying means 1C - C1 and 1d - c2 respectively and transforms the given rectified output into the constant voltage. Then a means 9 is added to secure the connection between the 1st rectifying means 1C - C1 and the means 4 in response to the stand-by state command signal received from outside. In such a constitution, the outputs of the 2nd rectifying means 1d - c2 which obtain the 2nd DC voltage lower than the 1st DC voltage are given to the means 4 in response to said stnd-by state command signal at a stand-by state. As a result, the power consumption is reduced in the stand-by state and the margin can be increased to the level fluctuation of the full-wave rectified voltage due to various factors.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a constant voltage generator, and particularly relates to a constant voltage generator that can reduce power consumption in a standby state.

[Prior Art] Many electrical products generally include functional parts to which AC voltage supplied from an external AC power source, such as a 100V commercial power source, cannot be directly applied. Therefore, such electrical products have a power supply circuit that is a constant voltage generator that converts the AC voltage supplied from an external AC power source into a predetermined constant voltage required by the above-mentioned functional parts and outputs it. including.

For example, a power supply circuit of a VTR (video tape recorder) converts an AC voltage supplied from an external AC power source into a plurality of types of constant voltages, and supplies these to predetermined functional units, respectively.

FIG. 2 is a circuit diagram showing the general configuration of a VTR power supply circuit.

Referring to the figure, a VTR power supply circuit 200 is connected to an external 10
A transformer 2 is composed of a primary coil 1a to be connected to a 0V AC power source, a transformer core 1b, a secondary coil IC, and a secondary coil 1d having a larger number of turns than the secondary coil 1c,
A diode bridge 3a in which four diodes constitute a bridge circuit is provided between both ends of the secondary coil 1c, a ripple prevention filter capacitor C1 is provided between one end of the diode bridge and ground, and a secondary coil 1d. A diode bridge 3b, in which four diodes constitute a bridge circuit, is provided between both ends of the diode bridge 3b, a ripple prevention filter capacitor C2 is provided between one end of the diode bridge 3b and ground, and an output terminal 8a,
8b, and 8C. The other ends of diode bridges 3a and 3b are both grounded.

The power supply circuit 200 further includes a voltage regulating circuit 4 provided between the capacitor C1 and the output terminal 8a, and a voltage regulating circuit 5 provided between the capacitor C1 and the output terminal 8b.
and a constant voltage circuit 6 provided between the capacitor C2 and the output terminal 8c, and connected to the constant voltage circuits 5 and 6,
The switching unit 7 receives a control signal CTL from a control unit such as a microcomputer built in the VTR.

The operation of this power supply circuit 200 will be explained below.

The AC voltage supplied to the primary coil 1a by the external AC power supply leads to the secondary coils 1c and 1d via the transformer core 1b as an AC voltage at a lower level. Since the number of turns of the secondary coil 1c is greater than that of the secondary coil 1d, the level of the AC voltage drawn to the secondary coil 1c is higher than the level of the AC voltage drawn to the secondary coil 1d. The AC voltage drawn to the secondary coil 1c is full-wave rectified by the diode bridge 3a and the capacitor c1. Similarly, the AC voltage introduced into the secondary coil 1d is full-wave rectified by the diode bridge 3b and the capacitor C2.

Hereinafter, the voltage obtained by full-wave rectification of the AC voltage derived to the secondary coil 1c will be referred to as the full-wave rectified voltage on the secondary coil IC side, and similarly the AC voltage derived to the secondary coil 1d will be referred to as the full-wave rectified voltage on the secondary coil IC side. The voltage obtained by full-wave rectification is called "full-wave rectified voltage on the secondary coil ld side."

The constant voltage circuit 4 converts the full-wave rectified voltage on the secondary coil IC side into a constant voltage of 5 V and outputs it to the output terminal 8a. The constant voltage circuit 5 converts the full-wave rectified voltage on the side of the secondary coil 1c into a constant voltage of 12V and outputs it to the output terminal 8b. A constant voltage circuit 6 sets the full-wave rectified voltage on the secondary coil d side to a constant voltage of 5V.
and output to output terminal C.

Constant voltage circuit 4, 5. and 6 are all similarly configured. That is, the voltage regulating circuits 4, 5° and 6 are connected to NPN transistors Q7, Q2, . and Q4, and the transistor Q7. Zener diodes Di, D are provided between the bases of Q2 and Q4 and the ground.
2. and D3, and transistor Q7. Q2 and Q4
A resistor r1. is provided between the base and the collector of the resistor r1. ．． r2.
and r3.

In the voltage regulating circuit 4, the full-wave rectified voltage on the side of the secondary coil 1C is applied to the collector of the transistor Q7 and is also applied to the Zener diode D1 via the resistor r1 to bring it into a breakdown state.

As a result, the Zener diode D1 outputs a constant breakdown voltage, fixing the base of the transistor Q7 at a constant voltage. As a result, the full-wave rectified voltage applied to the collector of transistor Q7 is output as a constant voltage of 5V from the emitter of transistor Q7. In other words, the full-wave rectified voltage on the secondary coil IC side is 5
The voltage is made constant by V.

Similarly, in the voltage regulator circuit 5, the transistor Q2, whose base voltage is fixed by the output voltage of the Zener diode D2, which receives the full-wave rectified voltage on the secondary coil IC side via the resistor r2, operates on the secondary coil IC side. The full-wave rectified voltage is made constant to 12V. This constant voltage of 12V is the output terminal 8
b.

Similarly, in the voltage regulator circuit 6, the transistor Q4, whose base voltage is fixed by the output voltage of the Zener diode D3, which receives the full-wave rectified voltage on the secondary coil ld side via the resistor r3, The full-wave rectified voltage (about 7 V) on the side of the secondary coil 1d, which is lower than the full-wave rectified voltage on the IC side, is made constant to 5 V. This constant voltage of 5V is the output terminal 8
It is derived into C.

The switching unit 7 has a collector connected to the base of the transistor Q2, an emitter connected to the ground, and a control signal CTL.
an NPN transistor Q3 having a base that receives the control signal CTL through the resistor R4, a collector connected to the base of the transistor Q4, an emitter that is grounded, and a base that receives the control signal CTL through the resistor r6.
N-type transistor Q5, resistor r5 provided between the base of transistor Q3 and ground, and transistor Q5.
and a resistor r7 provided between the base of and ground.

When the control signal CTL becomes high level, the base voltages of transistors Q3 and Q5 rise, and both transistors Q3 and Q5 become conductive. Due to the conduction of the transistor Q3, a current flows from the base of the transistor Q2 to the ground via the transistor Q3, and the base voltage of the transistor Q2 decreases. As a result, transistor Q2 becomes non-conductive, so transistor Q
A constant voltage of 12V is not derived from the output terminal 8b from the output terminal 8b.

Similarly, when the transistor Q5 becomes conductive, a current flows from the base of the transistor Q4 to the ground via the transistor Q5, and the base voltage of the transistor Q4 decreases.

As a result, the transistor Q4 becomes non-conductive, so that the constant voltage of 5 V is not derived from the transistor Q4 to the output terminal 8c.

Conversely, when the control signal CTL becomes low level,
The base voltages of transistors Q3 and Q5 drop, and both transistors Q3 and Q5 become non-conductive. Therefore, no current flows from the bases of transistors Q2 and Q4 to ground, and transistors Q2 and Q7
The base voltage of will not drop. Therefore, transistors Q2 and Q4 are in a conductive state and output terminals 8b and 8
Constant voltages of 12V and 5V are derived from C, respectively.

In this way, whether or not a constant voltage is derived to the output terminals 8b and 8C is controlled by the control signal CTL. On the other hand, when an AC voltage is supplied to the primary coil from an external AC power source, a constant voltage of 5V is always derived from the transistor Q7 to the output terminal 8a.

Between the output terminal 8a and the ground, there are functional parts that should be constantly supplied with a constant voltage, such as a microcomputer that controls various motors and recording circuits, etc., which will be described later, and related peripheral circuits, which are included in the VTR. Provided as load L1, output terminal 8b
A load L2 is provided between the VTR's recording/reproducing circuit, tuner, capstan motor, drum motor, and other functional units to which a constant voltage is appropriately supplied.

Between the output terminal 8C and the ground, there is an I for signal processing of the VTR.
A circuit section that operates by appropriately receiving a relatively low constant voltage such as C is provided as a load L3.

By the way, if the level of the AC voltage supplied to the primary coil 1a momentarily drops for some reason while AC voltage is being supplied from an external AC power source, the output terminals 8a, 8b will be affected accordingly. .

and 8C to load Ll, L2. and the level of the voltage supplied to L3 also decreases. Loads L2 and L3 are V
Since these are the recording system circuits, motors, etc. of the TR, a slight drop in the voltage supplied to these will only cause disturbances in the reproduced image. On the other hand, the load L1 connected to the output terminal 8a includes a microcomputer that outputs the control signal CTL. Microcomputers are generally configured to be automatically reset by a momentary drop in the voltage supplied to them. Therefore, when the voltage drawn to the output terminal 8a momentarily drops, the microcomputer is reset and the control signal CTL is no longer supplied to the switching section 7. As a result, a phenomenon occurs in which the functions of the functional units connected to the output terminals 8b and 8c that record and reproduce images stop functioning.

Moreover, even when the level of the AC voltage supplied to the primary coil 1a is stable, the full-wave rectified voltage manually input to the voltage regulating circuit 4 that supplies a constant voltage to the load L1 connected to the output terminal 8a If the constant voltage to be supplied to the other loads L2 is derived in common from the above, the load current flowing to the other loads L2 may change due to resistance value fluctuations of the other loads L2. In such a case, the current flowing into the voltage regulator circuit 5 that supplies constant voltage to the other load L2 fluctuates, so the voltage at the connection point between the voltage regulators 4 and 5, that is, the voltage on the secondary coil IC side, changes. The level of the full-wave rectified voltage fluctuates, and the voltage supplied to the load L1 connected to the output terminal 8a, that is, the microcomputer, etc. fluctuates.

As can be seen from the above, microcontrollers are sensitive to instantaneous level drops in the AC voltage supplied to the primary coil 1a, and
There is a risk of being reset due to fluctuations in the load current flowing through the load that receives a constant voltage derived from the alternating current voltage derived from the next coil.

In order to reduce this risk, it is necessary to increase the level of the full-wave rectified voltage that is input to the voltage regulator circuit that derives the constant voltage supplied to the microcontroller, so that the output voltage of the voltage regulator circuit is higher than that of the microcontroller. What is necessary is to increase the amount of reduction in the level of the full-wave rectified voltage required to lower the voltage to a value that resets the voltage.

Therefore, among the secondary coils 1c and 1d of the transformer 2, the voltage regulating circuit 4 that derives a constant voltage to the output terminal 8a connected to a microcomputer etc. is connected to the secondary coil IC side that derives a high level AC voltage. A full-wave rectified voltage of is given.

[Problems to be Solved by the Invention] As described above, in conventional power supply circuits, a voltage regulating circuit for supplying a predetermined voltage to a functional part that always requires a predetermined constant voltage requires a high total voltage. A wave rectified voltage is input. This causes the following problems. Refer to FIG. 2 for the following explanation. The voltage regulating circuit is a second
This corresponds to the voltage regulating circuit 4 in the figure.

The voltage regulating circuit 4 includes a secondary coil 1 included in the transformer 2.
2 to derive the higher level AC voltage of C and 1d
A high full-wave rectified voltage, usually about 17V, is applied to the next coil IC side. Therefore, this high full-wave rectified voltage is reduced by the transistor Q7 of the voltage regulating circuit 4 to a constant voltage of 5V, which is considerably lower than that. Therefore, a large amount of heat P corresponding to the difference between the high full-wave rectified voltage and the low constant voltage is generated at the collector of the transistor Q7. In other words,
The collector loss of transistor Q7 increases.

However, when the control signal CTL is at a high level, that is, when the constant voltage is not supplied to the output terminals 8b and 8C, the constant voltage circuit 5 and the load L2 are electrically insulated. Therefore, in this case, the load L
The level of the full-wave rectified voltage on the secondary coil IC side does not change due to a change in the resistance value of the second coil. Furthermore, the fact that the load L2 is not connected to the voltage regulating circuit 5 means that the capacitor C1
This means a reduction in the total amount of load connected to the therefore,
In this case, the speed at which the level of the full-wave rectified voltage on the secondary coil IC side decreases due to the instantaneous decrease in the level of the AC voltage supplied to the primary coil 1a is determined by the control signal CTL.
is at a low level, that is, it is slower than when the voltage regulating circuit 5 and the load L2 are electrically connected. As a result, the amount of decrease in the full-wave rectified voltage on the secondary coil 1c side required to reset the microcomputer included in the load L1 is lower than when the voltage regulator circuit 5 and the load L2 are electrically connected. substantially larger.

In this way, the stability of the voltage derived from the output terminal 8a has a larger margin against fluctuations in the full-wave rectified voltage than when a constant voltage is supplied to the output terminals 8b and 8c.

As can be seen from the above, a constant voltage is applied only to the output terminal to which a constant voltage is always supplied (hereinafter, this output terminal is referred to as the standby voltage output terminal, and the voltage applied to the standby voltage output terminal is referred to as the standby voltage). In the state where the voltage is being supplied (hereinafter, this state will be referred to as a standby state), the standby voltage output terminal voltage has a sufficiently large margin with respect to fluctuations in the full-wave rectified voltage. However, the amount of collector loss in the transistor of the voltage regulating circuit that supplies a constant voltage to the standby voltage terminal is the same during standby and non-standby. This means that the amount of collector loss in the transistor of the voltage regulating circuit during standby is unnecessarily large. Therefore, the power consumption of the power supply circuit during standby becomes unnecessarily large.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a constant voltage generator that consumes less power during standby and has a greater tolerance to fluctuations in the level of the full-wave rectified voltage due to various causes.

[Means for Solving the Problems] In order to achieve the above objects, a constant voltage generator according to the present invention includes an AC power source and a first rectifier that rectifies the output of the AC power source into a first DC voltage. and the AC power output to the first
A second rectifying means for rectifying a second DC voltage lower than the DC voltage of a constant voltage means for adjusting the voltage to a constant voltage; and means for electrically connecting the rectifying means and the voltage constant means.

[Function] Since the constant voltage generator according to the present invention is configured as described above, the first rectifying means electrically connects the voltage regulating means in response to a standby state command signal from the outside during standby. connected to.

Therefore, during standby, the output of the second rectifier that derives the second DC voltage lower than the first DC voltage is given to the voltage regulator.

[Embodiment] FIG. 1 is a circuit diagram of a power supply circuit according to an embodiment of the present invention.

Referring to the figure, this power supply circuit 1.00 includes a transformer 2, diode bridges 3a and 3b, and capacitors C1 and C, similar to the conventional power supply circuit shown in FIG.
2, a standby voltage output terminal 8a to which a constant voltage of 5V should always be supplied as a standby voltage, output terminals 8b and 8C to which constant voltages of 12V and 5V should be supplied, respectively, as necessary, and a constant voltage to the output terminal 8a. A constant voltage circuit 4 that supplies 5V, a constant voltage circuit 5 that supplies a constant voltage of 12V to the output terminal 8b, and a constant voltage of 5V to the output terminal 8C.
and a control signal C"I7L given to the power supply circuit 100 as a standby state command signal that commands the power supply circuit 100 to enter the standby state.
The switching section 7 controls ON and OFF of the transistors included in the voltage regulating circuits 5 and 6 in response to the voltage regulation circuits 5 and 6.

When this power supply circuit 100 is applied to a VTR, for example, the control signal CTL is output from a microcomputer etc. built into the VTR, and the above-mentioned signals are connected between the output terminals 8a, 8b, and 8C and the ground. Such predetermined functional units are provided as loads Ll, L2, and L3.

The operations and functions of each of the circuit sections included in the power supply circuit 100 are similar to those in the conventional power supply circuit shown in FIG.

However, this power supply circuit 100 differs from conventional power supply circuits in that the input terminal switching section 1 is provided between the capacitor C1 and the voltage regulation circuit 4, and the input terminal switching section 1 is provided between the input terminal switching section 1 and the voltage regulation circuit 6. and a diode D20 provided.

The input voltage switching unit 9 includes a capacitor C1 and a transistor Q.
7, a resistor R1 connected between the base and emitter of the transistor Q20, and a resistor R2 and an NPN transistor provided between the base of the transistor Q20 and ground. The series connection of Q21 and the transistor Q
A resistor R3 and an NPN transistor Q22 provided between the base of the transistor Q21 and the ground, and the transistor Q2
2, and a resistor R6 connected between the base of transistor Q21 and the emitter of transistor Q20. The base of transistor Q22 receives control signal CTL via resistor R5. The cathode of diode D20 is connected to the collector of transistor Q20, and the anode of diode D20 is connected to the collector of transistor Q20.

Next, the operation of the input terminal switching unit 9 and the diode D20 when the external power is turned on will be described.

When the control signal CTL becomes high level, that is, when the power supply circuit 100 enters the standby state, the base voltage of the transistor Q22 rises and the transistor Q2
2 is in a conductive state. As a result, transistor Q2
A current flows from the base of transistor Q21 to ground, causing the base voltage of transistor Q21 to drop, and transistor Q21 becomes non-conductive. Therefore, no current flows from the base of transistor Q20 to ground via transistor Q21, and the base voltage of transistor Q20 does not drop. Therefore, transistor Q20 becomes non-conductive. Therefore, in this case, the full-wave rectified voltage on the side of the secondary coil Jc is cut off by the transistor Q20 and is not applied to the voltage regulating circuit 4. In other words, diode D20
The collector voltage of transistor Q20, which is applied to the cathode of transistor Q20, decreases. On the other hand, the collector voltage of the transistor Q4, that is, the full-wave rectified voltage on the side of the secondary coil 1d is applied to the anode of the diode D20. Therefore, as the collector voltage of transistor Q20 decreases, diode D20 becomes forward biased and becomes conductive. As a result, the full-wave rectified voltage on the side of the secondary coil ld is applied to the collector of the transistor Q20, that is, the collector of the transistor Q7 via the diode D20.

In this way, the secondary coils 1C and 1d, which derive the AC voltage at the lower level, are connected to the voltage regulator circuit 4 which supplies the constant voltage to the output terminal 8a, which should always be supplied with a constant voltage in the standby state. The full-wave rectified voltage on the coil 1d side is manually applied. Therefore, when the full-wave rectified voltage is converted to a constant voltage of 5 V in the voltage regulator circuit 4, the amount of heat generated at the collector of the transistor Q7 is the difference between the full-wave rectified voltage (for example, about 7 V), which is lower than the conventional one, and the constant voltage of 5 V. The amount corresponds to the difference, that is, the amount is smaller than before. In other words, in the standby state, the voltage regulating circuit 4
The collector loss of the transistor is reduced. As a result, the power consumption in the voltage regulator circuit 4 that supplies the standby voltage is reduced, and the power consumption of the constant voltage generator in the standby state is reduced.

Conversely, when the control signal CTL becomes low level,
In other words, in a non-standby state, the transistor Q
The base voltage of transistor Q22 drops and transistor Q22 becomes non-conductive. Therefore, the base voltage of transistor Q21 does not fall, and transistor Q21 becomes conductive.

Therefore, current flows from the base of transistor Q20 to ground via resistor R2 and transistor Q21.

As a result, the base voltage of transistor Q20 decreases and transistor Q20 becomes conductive. Therefore, the full-wave rectified voltage from the secondary coil 1C side is supplied to the collector of the transistor Q20. On the other hand, at this time transistor Q4
The full-wave rectified voltage on the secondary coil 1d side, which is lower than the full-wave rectified voltage on the secondary coil 1C side, is supplied to the collector of . Therefore, a reverse voltage is applied to diode D20, and diode D20 becomes non-conductive. As a result, only the full-wave rectified voltage on the secondary coil IC side is supplied to the collector of transistor Q20.

In this way, during non-standby, the input voltage to the voltage regulator circuit 4 is the full-wave rectified voltage of the secondary coil IC and the secondary coil IC that derives the high-level AC voltage, as in the conventional case. Become. Therefore, the tolerance of the voltage derived to the non-standby voltage output terminal 8a, especially the standby voltage output terminal 8a, against fluctuations in the full-wave rectified voltage on the secondary coil IC side is approximately the same as in the conventional case.

By the way, during standby, the voltage regulating circuit 6, which is commonly connected to the secondary coil 1d with the voltage regulating circuit 4, and the load L
3 is electrically insulated from transistor Q4 which is in a non-conducting state. Therefore, the full-wave rectified voltage on the secondary coil ld side does not vary due to variations in the resistance value of the load L3 or the like.

Furthermore, since the voltage regulating circuit 6 and the load L3 are electrically insulated, the total load connected to the capacitor C2 that compensates for the full-wave rectified voltage input to the voltage regulating circuit 6 is smaller than the state. During non-standby, the presence of loads L1 and L2 increases the total amount of load connected to capacitor C1 that compensates for the full-wave rectified voltage supplied to voltage regulating circuit 4. Therefore, if the AC voltage supplied to the primary coil 1a decreases for some reason, the speed at which the input voltage to the voltage regulating circuit 4 decreases will be longer than in the non-standby state. That is, when the AC voltage supplied to the primary coil 1a decreases, the period during which the level of the full-wave rectified voltage is compensated according to the discharge time constant of the capacitor C2 becomes longer. As in the past, this
This means that during standby, the margin against full-wave rectified voltage fluctuations due to the reset phenomenon of the microcomputer corresponding to load L1 is greater than during non-standby.

In this way, when the power supply circuit 100 is applied to a VTR or the like, the margin against fluctuations in the input terminal to the voltage regulator circuit due to the reset phenomenon of the microcomputer during standby and non-standby is maintained at the same level as before. . therefore,
According to the present embodiment, the power consumption during standby can be reduced sharply without deteriorating the operating margin of the load against input voltage fluctuations.

In this embodiment, when deriving the constant voltage, the AC voltage derived to the secondary coil was full-wave rectified, but the rectification method for the AC voltage derived to the secondary coil is not limited to full-wave rectification.

Note that the constant voltage generator according to the present invention can be applied not only to VTRs but also to any other electrical products.

[Effects of the Invention] As described above, according to the constant voltage generator according to the present invention,
During standby/non-standby, the standby voltage can be derived from different levels of voltage.

As a result, during standby, the constant voltage used as the standby voltage can be derived from a voltage at a lower level than during non-standby. Therefore, according to the constant voltage generator according to the present invention, power consumption during standby is reduced.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a power supply circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a general power supply circuit of a conventional VTR. In the figure, 2 is a transformer, 3a and 3b are diode bridges, 4, 5 . and 6 is a voltage regulating circuit, 7 is a switching section, 8a, 8b, and 8C are output terminals, 9 is an input terminal switching section, Q2 to Q5. Q7, Q21. and Q22
is an NPN transistor, Q20 is a PNP transistor, R1-R5 and "1 to "7 are resistors, C1 and C
2 is a filter capacitor, D1 to D3 are Zener diodes, and D20 is a diode. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. 2000 drawings

Claims (1)

[Scope of Claims] A constant voltage generator that takes a standby state in response to a standby state command signal from the outside, comprising: an AC power source; and a first rectifier that rectifies the output of the AC power source into a first DC voltage. means, a second rectifier for rectifying the output of the AC power source into a second DC voltage lower than the first DC voltage, an output of the first rectifier, and an output of the second rectifier. a constant voltage means connected to the first rectifying means and the first rectifying means and the first rectifying means for adjusting the applied rectified output to a constant voltage; and a means for electrically connecting the constant voltage generator.