JPH0621965B2 - DC constant voltage stabilizer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a DC constant voltage stabilizing device that supplies constant voltage DC power that is stable even against a temporary voltage drop in a DC power supply unit.

[Outline of the present invention]

According to the present invention, in a DC constant voltage stabilizing device, as a power source for a driver and a deviation detecting section, a DC power source section having a higher output voltage is provided separately from a DC power source section for supplying power to a power transistor. When the output voltage of the DC power supply unit that supplies power to the power transistor drops below the set voltage of this DC constant voltage stabilizer due to the provision of a conduction time limit circuit that limits the conduction time when a current flows. However, the constant voltage DC power can be supplied stably within the time limit.

[Conventional technology]

In recent years, in various electronic devices or electric products, the number of devices using a micro computer as a control system is increasing.

In general, devices other than the control system of equipment often return to normal operation when the voltage is restored even if the function is lowered or stopped due to a temporary voltage drop.

However, in the case of a digital control system using a peripheral device such as a microcomputer or RAM, a failure caused by a temporary voltage drop is often unrecoverable until it is reset, which disturbs control. Other devices may cause serious accidents such as burning due to abnormal heat generation or damage due to runaway.

Further, even if the fail-safe reset is activated, the work that has progressed halfway is stopped, resulting in loss of materials and time.

Therefore, in order to normally operate such a microcomputer and its peripheral elements, a DC constant voltage stabilizing device as shown in FIG. 4, for example, has been conventionally used.

This DC constant voltage stabilizing device includes a power transistor 1 that controls and outputs electric power from a DC power supply unit 4, a driver 2 that drives the power transistor 1, and a driver that detects a deviation of an output voltage from a set voltage. 2 and the deviation detecting section 3 for controlling the power source 2, the power of the power transistor 1, the driver 2 and the deviation detecting section 3 are all supplied from the same DC power supply section 4.

Further, as disclosed in, for example, Japanese Patent Application Laid-Open No. 47-35744, a constant voltage device provided with a second DC power supply for supplying a DC voltage to a driver is also proposed in addition to a DC power supply for supplying power to a power transistor. Has been done.

[Problems to be Solved by the Invention]

Even with such a conventional DC constant voltage stabilizing device, even if a failure such as a momentary voltage drop of the DC power supply unit 4 or an interruption of the AC power supply unit 7 occurs, the DC power supply unit 4 is not affected by the load current. Since the smoothing capacitor C ₄ has a large capacity, the electric power in the meantime is supplied from the smoothing capacitor C _4, and the output voltage of the DC power supply unit 4 slightly drops to the set voltage Vs of the constant voltage stabilizer. It had no effect.

However, the failure time such as interruption of the AC power supply 7 is further extended,
When the output voltage from the DC power supply unit 4 becomes equal to or lower than the set voltage Vs, it is unavoidable that the output voltage of the constant voltage stabilizing device also drops during that time.

In order to increase the stability against these obstacles, the time required for the output voltage to drop to the set voltage Vs by further increasing the capacitance of the smoothing capacitor C ₄ or increasing the output voltage of the DC power supply unit 4. There is a way to extend.

However, the former method increases the size of the smoothing capacitor C ₄ , and the latter method causes an increase in space and cost, such as a rating up of the withstand voltage and allowable power of the power transistor 1 and a large heat dissipation fin. I got it.

Further, the problem caused by the former method is described in JP-A-47-3.
When the output voltage of the DC power supply that supplies power to the power transistor becomes equal to or lower than the set voltage, as in the constant voltage device described in Japanese Patent No. 5744, the same constant voltage is output from another DC power supply having a higher output voltage through the driver. This can be prevented by supplying a load current of voltage.

However, in this case, it is necessary to use a transistor with a larger output than that of the power transistor, or a higher output voltage, because the supply voltage is high.
There is a problem similar to the latter method in that it causes an increase in space and cost such as an increase in the allowable power rating of the driver and an increase in the size of the radiation fin.

If a driver with a smaller output than the power transistor is used like a normal voltage regulator, destructive burning due to heat generation will occur over time when supplying a load current, which will cause an unrecoverable accident. Will be invited.

The present invention has been made in view of the above points, and it is an object of the present invention to improve stability against failures and to supply stable constant voltage DC power while suppressing space and cost.

[Means for Solving the Problems]

The present invention achieves the above object by detecting a power transistor that controls and outputs electric power from a first DC power supply unit, a driver that drives the power transistor, and a deviation of an output voltage from a set voltage. The driver includes a deviation detecting section for controlling the driver, and a second DC power source section for supplying a DC voltage higher than the output voltage of the first DC power source section to the driver and the deviation detecting section. In a DC constant voltage stabilizing device which is a transistor with a small output, a resistor having a high resistance value inserted in a circuit that supplies the output current of the deviation detection unit to the base of the driver and a resistance value It is composed of a parallel circuit of a bypass circuit in which a low resistance and a bypass capacitor are connected in series, and when a load current flows in the driver, An energization time control circuit for limiting the energization time is provided.

[Work]

In the DC constant voltage stabilizing device according to the present invention, the first and second DC power supply units cause the same voltage drop at the same time due to a failure of the AC power supply or the like, and the output voltage of the first DC power supply unit is the DC constant voltage. Even if the voltage is below the set voltage of the stabilizer, the second
Since the output voltage of the DC power supply part of the power supply is still higher than the set voltage, the driver operates so as to maintain a constant voltage instead of the power transistor, and the required load current is the second DC power supply. Since it is output from the section through the driver, stable constant voltage DC power is supplied to the load.

During this time, the load current flows directly to the driver, the internal power consumption suddenly increases, and heat is generated.Therefore, the allowable time is set in advance, and the energization is stopped when the load current flowing to the driver exceeds the allowable time. By providing such an energization time limiting circuit as described above, even if a driver having a proper rated power (a transistor having a smaller output than a power transistor) is used, the burnout can be prevented.

〔Example〕

 Hereinafter, examples of the present invention will be specifically described.

FIG. 1 is a circuit diagram showing an example of a DC constant voltage stabilizer according to the present invention, which includes a power transistor 1, a driver 2, a deviation detector 3 and first and second DC power supply units 4, 5.
And an energization time control circuit 6.

The AC power input from the AC power supply 7 is the power transformer 8
Is supplied to the primary coil L ₁ . A plurality of coils L ₄ and L ₅ are provided on the secondary side of the power transformer 8, and rectifiers D ₄ and D _{4 for} half-wave rectifying the outputs of the coils L ₄ and L ₅ , respectively.
₅ and the DC capacitors ₄ and ₅ which are independent of each other in combination with the smoothing capacitors C ₄ and C _{5 for} smoothing the output pulsating flow, respectively.
Make up 5.

The first DC power supply unit 4 supplies electric power to the collector of the power transistor 1 of the DC constant voltage stabilizer whose set voltage Vs is 5V, for example.

The second DC power supply unit 5 has an output voltage of 12 V to 15 V, for example, and supplies the driver 2 and the deviation detection unit 3 with a DC voltage higher than the output voltage of the first DC power supply unit 4.

Since the output voltage of the DC power supply unit is generally designed to be higher than the stabilized set voltage by about several volts or 10%, the output voltage of the first DC power supply unit 4 is about 7V.
The output voltage of the second DC power supply unit 5 is higher than the output voltage of the first DC power supply unit 4.

The deviation detection unit 3 is a circuit that detects a deviation of the output voltage with respect to the set voltage Vs and controls the driver 2.
Resistor R ₃ connected in series between (DC power supply unit 5) and ground
And a Zener diode ZD for outputting a reference voltage Vr, and a voltage dividing circuit composed of a variable resistor VR and a resistor R ₄ connected in series between a 5V output line and ground for detection voltage. An output voltage detection circuit that outputs Vd, a reference voltage Vr is input to the + input terminal, and a detection voltage Vd is input to the − input terminal, and a difference voltage between the detection voltage Vd and the reference voltage Vr is amplified and converted into a current. It is composed of a differential amplifier 9 for outputting.

The reference voltage Vr is a voltage corresponding to the detection voltage Vd when the output voltage is the set voltage Vs (5V in this example).

The driver 2 composed of an NPN medium output transistor has an emitter connected to the base of the power transistor 1, a collector connected to the output terminal of the DC power supply unit 5, and a base connected via the conduction time control circuit 6 to the differential amplifier 9 of the deviation detection unit 3. Output current of the differential amplifier 9 which is connected to the respective output terminals of the power amplifier 1 and is input to the base is amplified, and output as a drive current from the emitter to the base of the power transistor 1.

The emitter of the power transistor 1, which is an NPN type large output transistor, is connected to the 5V output line, and the collector is connected to the output terminal of the DC power supply unit 4. The drive current input to the base is current-amplified to a load current from the emitter.
Output to the V output line.

The energization time limit circuit 6 is configured by a parallel circuit of a bypass circuit formed by connecting a resistor R ₂ having a relatively low resistance value and a bypass capacitor C in series, and a resistor R ₁ having a relatively high resistance value. The bypass circuit limits the energization time when the load current flows through the driver 2.

The function of stabilizing the output voltage to a constant voltage by the feedback circuit composed of the power transistor 1, the driver 2 and the deviation detecting section 3 is well known, and therefore detailed description thereof will be omitted. A description will be given with reference to FIGS. 2 and 3.

2 and 3 are explanatory diagrams showing input / output currents of the power transistor 1 and the driver 2 when a regular voltage is supplied and when a voltage drop occurs, respectively.

The load current at the set voltage Vs of the DC constant voltage stabilizer is I _L , the current amplification factors of the power transistor 1 and the driver 2 (emitter grounding) are hfe ₁ and hfe ₂ , the emitter currents are I _E1 , I _E2 , and the base. The current is I _B1 , I
Assuming _B2 , there is a relationship of I _B1 = I _E1 / hfe ₁ I _B2 = I _E2 / hfe ₂ I _L = I _E1 and I _B1 = I _E2 .

As shown in FIG. 2, when the normal voltage is supplied, the power transistor 1 operates as a normal transistor, so I _E2 = I _B1 = I _E1 / hfe ₁ = I _L / hfe ₁ I _B2 = I _E2 / hfe ₂ = I _L / (hfe ₁ × hfe ₂ ), the emitter current I _E2 flowing through the driver 2 is much smaller than the load current I _L, and the base current I _B2 is also extremely small.

Therefore, the base current I _B2, that is, the output current of the operational amplifier 9 can be supplied through the resistor R ₁ having a relatively high resistance value.

However, when a voltage drop occurs and the output voltage of the DC power supply unit 4 becomes equal to or lower than the set voltage of 5 V as shown in FIG. 3, the power transistor 1 does not function as a transistor but acts as a simple diode, I _E2 = I _B1 = I _L I _B2 = I _L = hhe ₂ , the load current I _L itself supplied from the DC power supply unit 5 flows between C and E of the driver 2, and the base current I _B2 is also normal. The current will be ₁ time hfe.

Therefore, the required base current I _B2 cannot flow through the resistor R ₁ having a relatively high resistance value, and most of the base current is supplied through C and R ₂ of the bypass circuit. It is charged and the voltage across its terminals rises.

Here, the resistance value of the resistor R ₂ is the rapidly increased base current I _B2.
It is set low enough to drain the water.

If the voltage drop of the DC power supply unit 4 is restored in the meantime, it immediately returns to the normal case shown in FIG. 2 and the output line is not affected by the power supply voltage drop at all.

When the normal state is restored in this way, the electric charge charged in the bypass capacitor C is gradually discharged through the resistors R ₁ and R ₂ .

Should the voltage drop of the DC power supply unit 4 continue,
In order to maintain the load current _IL and maintain the output voltage at the set voltage 5V, the output voltage of the deviation detection unit 3 rises together with the voltage of the capacitor C, and when the output limit voltage is reached, the current flowing through the bypass circuit is stopped. The base current I _B2 is the resistance R
_It is reduced only to the current passing through ₁ .

Accordance connexion, emitter current driver 2 which is supplying the load current I _L in place of the power transistor 1 is also output, is limited to an extent slightly greater than the normal driver current, the voltage of the output line dividing connexion set voltage 5V The voltage drops to almost 0V.

As described above, the energization time limit circuit 6 is provided in the driver 2
When the load current I _L directly flows to the load current I _L , the energizing time is limited within the time limit determined by the increased base current I _B2 , the capacity of the bypass capacitor C, the output limit voltage of the differential amplifier 9, and the like. Since it operates, it is possible to prevent the driver 2 from being burnt out due to the heat generated by the sudden increase in internal power consumption.

Generally, the DC constant voltage stabilizer is designed to operate stably even with a continuous voltage fluctuation within the range of ± 10% of the AC power supply even if it is a conventional device, and various types of outlets, switches, etc. If the voltage change such as momentary interruption or momentary voltage drop due to contact failure is large but the time is short, it can be covered by the capacity of the smoothing capacitor of the DC power supply. Longer (eg, several H
_Z , about 0.1 seconds), the set voltage will be affected.

However, the frequency of the above-mentioned failures tends to decrease sharply as the failure time becomes longer than that of an instantaneous failure.

Accordingly, even if the time limit of the energization time limit circuit 6 is as short as, for example, about 0.2 seconds, it will be added to the fault tolerance time of the conventional example, so that the DC constant voltage stabilization is achieved. The stability of the device is dramatically increased.

Further, since the load current flowing through the driver 2 has a short energization time, the driver 2 may be a driver that has been conventionally used as it is or may be replaced with a driver having a slightly larger power capacity.

As described above, according to the present invention, it is possible to improve the stability of the DC constant voltage stabilizing device against a power failure while suppressing the space and cost.

In this embodiment, an example in which one power transistor is used has been described, but the present invention can be similarly applied to a large capacity output DC constant voltage stabilizer using a plurality of power transistors in parallel.

In addition, another DC power supply unit having a higher output voltage than that of the first DC power supply unit, for example, a device other than the control system can also be used as the second DC power supply unit to save parts and space.

Further, the present invention is not only applied to the power supply of the control system by the micro computer, but, for example, when there are a plurality of DC power supply units with different output voltages and a plurality of DC constant voltage stabilizers in the same device, the set voltage is The DC constant voltage stabilizing device that requires low and high stability may be configured so that the DC power supply unit that has a high set voltage or output voltage and does not require such high stability backs up.

〔The invention's effect〕

As described above, according to the present invention, it is possible to improve the stability against a power failure while suppressing the space and cost of the DC constant voltage stabilizing device.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIGS. 2 and 3 are also normal states thereof,
FIG. 4 is an explanatory diagram showing the input / output currents of the power transistor and the driver when a voltage drop has occurred, and FIG. 4 is a circuit diagram showing an example of a conventional DC constant voltage stabilizing device to which the present invention is applied. 1 ... Power transistor 2 ... Driver, 3 ... Deviation detection unit 4 ... First DC power supply unit, 5 ... Second DC power supply unit 6 ... Energization time limit circuit, 7 ... AC power supply 8 ... … Power transformer, 9… Differential amplifier

Claims (1)

[Claims] 1. A power transistor for controlling and outputting electric power from a first DC power supply unit, a driver for driving the power transistor, and a deviation detection for controlling a driver by detecting a deviation of an output voltage from a set voltage. And a second DC power supply unit that supplies a DC voltage higher than the output voltage of the first DC power supply unit to the driver and the deviation detection unit, and the driver is smaller than the power transistor. A DC constant voltage stabilizing device that is an output transistor, wherein a resistance having a high resistance value inserted in a circuit that supplies the output current of the deviation detection unit to the base of the driver, and a resistance having a low resistance value due to the resistance And a bypass capacitor connected in series to form a parallel circuit with a bypass circuit to limit the energizing time when a load current flows through the driver. A DC constant voltage stabilizing device having a conduction time control circuit.