JPH0619312Y2 - DC power supply circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to which the Invention belongs] The present invention relates to a DC power supply circuit that full-wave rectifies an AC power supply to supply power to a load, and particularly compensates for a momentary voltage drop or power failure of the power supply. DC power supply circuit capable of

[Prior Art and its Problems] Generally, when a DC power source obtained by rectifying an AC power source is fed to an inductive load such as an electromagnetic coil, the coil current is smoothed even if the DC output voltage has a ripple. There is no hindrance to its operation. Therefore, in such a case, in many cases, the rectified voltage is directly supplied to the electromagnetic coil.
However, such a DC power supply has a drawback that it is directly affected by the voltage fluctuation of the AC power supply and fluctuates.

For this reason, if an electromagnetic undervoltage trip device is connected to such a power source, the device will operate due to an instantaneous voltage drop or power failure that occurs only for a short period of several cycles when the AC power source is switched. There is a disadvantage. In order to prevent this, it is necessary to suppress the fluctuation of the voltage supplied to the load within a narrow range.

Conventionally, for this purpose, as shown in FIG. 1, a full-wave rectification circuit 2 in which the voltage of the AC power supply 1 is bridge-connected with a diode or the like.
Is directly rectified, the capacitor 3 is charged with the rectified voltage of the rectifier circuit, and the charging voltage of the capacitor 3 is supplied to the load when the rectified voltage decreases. If the capacity of the capacitor 3 is increased, it is possible to compensate for a momentary voltage drop or power failure.
For example, FIG. 2 shows changes in the rectified voltage V ₀ and the load voltage with respect to changes in the voltage of the power supply. The rectified voltage V ₀ during the period from t ₀ to t ₁ when there is no change in the AC power supply voltage in FIG.
Since the capacitor 3 is charged up to the peak value V _P of, the voltage V _P is supplied to the load. Next, in the period from time t ₁ to time t ₂ when the AC power supply voltage decreases and the peak value decreases, the voltage of the load 4 gradually decreases as the capacitor 3 discharges, as shown by the solid line. Of course, if the voltage of the AC power supply recovers at time t ₂ , the load voltage also recovers.

If a power failure occurs at time t ₃ , the voltage of the load 4 is fed from the capacitor 3 and gradually decreases as the capacitor 3 discharges. Therefore, the purpose can be achieved if the power failure is recovered before the terminal voltage of the capacitor 3 falls below the required value.

However, the voltage fed to the load by the DC power supply circuit that is not connected to the capacitor is substantially alternating source voltage and the average value V _a of the voltage full-wave rectification. If the effective value of the sine wave voltage is V, this V _a is Since the average value V _a of the full-wave rectified voltage is no effective value V so different sinusoidal AC voltage, the capacitor is charged to the peak value V _P of the rectified voltage the capacitor is connected. This peak value V _P is Is about 1.4 times the effective value of the sine wave voltage.
Of course, in the case of a small load power source such as the one discussed here, the internal impedance of the power source circuit is relatively large, so the load current also flows, so the voltage of the capacitor is not equal to the peak value _VP, and the time t _{0 in} FIG. It changes as shown by the solid line in the period from the time point t ₁ from, but not be reduced to an effective value level.

When using a battery to back up a power failure of an AC power supply, the voltage of this battery is usually selected to be approximately equal to the effective value of the AC power supply voltage, so connect the rectifier circuit directly to the AC power supply and smooth it to the DC side. In the case of a DC power supply circuit in which a capacitor is connected for power supply or compensation for momentary power failure, the DC output voltage becomes higher than the voltage of the backup battery, so that the backup battery cannot be used as it is.

In such a power supply circuit, in order to keep the DC output voltage at approximately the effective value of the AC power supply voltage, insert a transformer on the AC side of the rectifier circuit to adjust the AC input voltage of the rectifier circuit, or It is necessary to provide a voltage adjusting element such as a switching regulator on the output side to adjust the rectified voltage, but this has the drawback of increasing the number of parts and increasing the cost of the power supply circuit.

[Purpose of device]

The object of the present invention has been made in view of the above-mentioned points, and it is possible to compensate with a low voltage fluctuation rate when an instantaneous voltage drop or a power failure occurs in the AC power supply for a short time, and the DC output voltage in a normal state. It is an object of the present invention to provide a simple DC power supply circuit having a configuration capable of maintaining a value close to the effective value of the AC power supply voltage.

[Key points of device]

In order to achieve the above-mentioned object, the present invention includes an AC power supply, a full-wave rectifier circuit that rectifies an AC voltage of the AC power supply and supplies the load to a load, and an output terminal of the rectifier circuit connected in parallel with the load. A capacitor and a diode connected in series with this capacitor with a polarity that charges this capacitor,
The base voltage is kept at a constant voltage, and the collector-emitter circuit constitutes a DC power supply circuit with the discharge control transistor of the capacitor connected in parallel with the diode. According to this circuit, when the AC power supply is normal, , Since the voltage obtained by rectifying the voltage of the AC power supply by the full-wave rectifier circuit is applied to the load, the transistor is left in the non-conductive state because the load voltage becomes higher than the voltage applied to the base of the transistor for most of the period. The period in which the voltage of the capacitor is applied to the load is short. However, when the AC power supply voltage drops or power failure occurs, the voltage applied to the load drops below the constant voltage applied to the base of the transistor, and the base current flows through the transistor due to the voltage of the capacitor charged to the peak value of the rectified voltage. Flow, the transistor conducts,
The capacitor discharges through this transistor and a voltage corresponding to a constant voltage applied to the base of the transistor is supplied to the load to compensate for a momentary drop in power supply voltage or power failure. By doing this, the applied voltage of the load can always be kept close to the effective value of the AC power supply voltage, and it is possible to compensate with a capacitor in the event of an instantaneous voltage drop or power failure. It is possible to switch between the voltage and the battery.

[Example of device]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.
In the following wiring diagrams, parts having the same functions as those in FIG. 1 are designated by the same reference numerals as those in FIG. 1 to avoid redundant description, and in order to make the description easier to understand, the impedance of the power source, the diode, and the like. The internal resistance and the like of the transistor will be ignored in the description.

FIG. 3 is a connection diagram showing an embodiment of a DC power supply circuit according to the present invention. An AC power supply 1 is connected to an AC input terminal of a full-wave rectification circuit 2 in which four diodes are connected to a bridge. A capacitor 3 and a load 4 are connected to a DC output terminal 2 of the capacitor via a diode 5 having a polarity for charging the capacitor in series. The base of the transistor 6 is connected to the connection point of both the series circuit of the resistor 8 and the constant voltage diode 9 connected in parallel to the capacitor 3, and the base voltage is the Zener voltage V of the constant voltage diode 9.
_It is designed to be kept constant at _Z.

The waveform of the load voltage when the voltage of the AC power supply 1 is rectified by the rectifier circuit 2 and fed to the load 4 is plotted as time t on the horizontal axis.
Shown in the figure. In FIG. 4, the output of the full-wave rectification circuit 2 from time t ₀ to time t ₁ when the power supply voltage does not fluctuate is the full-wave rectification voltage V ₀ corresponding to the rated voltage of the AC power supply 1 (the full-wave rectification voltage including the dotted line portion). The instantaneous value of the wave rectified waveform), and the peak value is V _P. Therefore, the capacitor 3 has this peak value V
It is charged up to _P, and the charging voltage of this capacitor 3 is applied to the collector of the transistor 6. The transistor 6 is rectified voltage V ₀ is in non-conductive state so does not flow the base current while exceeds the Zener voltage V _Z of the constant voltage diode 9, the rectified voltage V ₀ is the Zener voltage V _Z
When it becomes lower, a base current flows and becomes conductive. That is, the transistor 6 is made conductive by the base current flowing through the diode 7 and the load 4 only for the period of Δt ₁ in FIG. Then, during this period of Δt ₁ , the capacitor 3 is discharged through the transistor 6, and a voltage equal to the base voltage of the transistor 6 (Zener voltage V _Z of the constant voltage diode) defined by the constant voltage diode 9 is applied to the load 4. Power is supplied, and the average value of the voltage having a waveform as shown by the solid line in FIG. 4 is supplied to the load throughout the entire period. Since this average value partially includes the discharge voltage of the capacitor 6, the average value is higher than the average value of the voltages that are just full-wave rectified.

At time t ₁ , when the power supply voltage drops and the rectified voltage drops to V ₀ ′ (FIG. 4) which is higher than the Zener voltage V _Z but lower than the rated voltage V ₀ , this rectified voltage V ₀ ′ is lower than the Zener voltage V _Z. The base current flows through the diode 7 and the load 4 only during the period of low Δt ₂ , and the transistor 6 becomes conductive. The period of Δt ₂ is longer than the period of Δt ₁ .

Also, further, rectified voltage V _{0 "drops} (Fig. 4) (rectified voltage V ₀ from V _0" may be considered to have fallen to), this rectified voltage V _{0 "is} also the peak value Zener Since it is lower than the voltage V _Z , the transistor 6 conducts for the entire period, and the load 4 is supplied with a constant voltage corresponding to the base voltage of the transistor 6 defined by the constant voltage diode 9 by discharging the capacitor 3. Time point t ₃
When the power supply voltage recovers and the rectified voltage returns to V ₀ , the load 4
Then, the average voltage of the rated rectified voltage V ₀ is the same as that at the time points t ₀ to t ₁ . If there 'blackout time t _4, the voltage fed thereto for subsequent load 4 becomes a voltage equal to the Zener voltage V _Z.

In this way, this DC power supply circuit can reduce the full-wave rectified voltage during a low period due to a change in the waveform during one cycle,
The full-wave rectified voltage is
As long as the voltage is lower than the base voltage of the transistor 6 kept constant, the transistor 6 is turned on to discharge the capacitor 3 and the load 4 is supplied with a voltage equal to the base voltage of the transistor 6. It is possible to maintain a voltage higher than the base voltage of 6.

FIG. 5 is a connection diagram showing a different embodiment of the present invention,
An AC power supply 1 is connected to a full-wave rectifier circuit 2, a DC output terminal of the rectifier circuit 2 is connected to a series circuit of a diode 5 and a capacitor 3, and a load. Diode 7
It is similar to the circuit shown in FIG. 3 in that the base of the transistor 6 is connected to the intermediate point of the series circuit of the resistor and the constant voltage diode which are connected in parallel with the capacitor 3 via the. However, it is different in that the collector-emitter circuit of the short-circuiting transistor 10 is connected between both ends of the constant voltage diode 9, that is, between the base of the transistor 6 and the negative electrode side of the DC output end of the rectifier circuit. At the base of this transistor 10, the voltage at the output end of the rectifier circuit 2 is divided
The voltage divided by 11 and 12 is applied. A diode 13 prevents the charging voltage of the capacitor 3 from being applied to the base of the short-circuiting transistor 10 when the transistor 6 is turned on.

In the circuit shown in FIG. 5, when power is supplied from the AC power supply 1, it is rectified by the rectifier circuit, and as shown in the voltage waveform diagram in FIG. 6, the capacitor 3 is a diode during the time t ₄ to t ₅ shown on the horizontal axis. Full-wave rectified voltage V ₀ via 13 and diode 5
Is charged up to the peak value V _P of this voltage, and this charging voltage is applied to the collector of the transistor 6. However, at this time, the transistor 10 is turned on when a voltage obtained by dividing the full-wave rectified voltage V ₀ is applied to its base and the divided full-wave rectified voltage exceeds the conduction voltage V _L ′ of the transistor 10. To short-circuit the constant voltage diode 9. The ratio of the voltage dividing resistors is selected so that the voltage of the entire voltage dividing resistor when the voltage divided by the voltage dividing resistor is V _L ′, that is, the power supply voltage is V _{L in} FIG. The value of the power supply voltage V for making this transistor 10 conductive
_{When L} is set relatively low, the transistor 10 conducts for almost the entire full-wave rectified voltage, and the full-wave rectified voltages V ₀ and V ₀ ′ are supplied to the load as they are. Only a small period of time t ₄ rectified voltage V ₀ as shown in FIG. 6 in the period of ~t ₅ falls below V _L △ t ₄ transistor 10 becomes non-conductive, the constant voltage by the charging voltage of the capacitor 3 The Zener voltage V _Z of the diode 9 is applied to the base to make the transistor 6 conductive, the capacitor 3 is discharged, and the voltage regulated by the Zener voltage V _Z is applied to the load 4 via the diode 7.
Is powered. Therefore, the voltage supplied to the load 4 has a waveform as shown by the solid line in FIG. Here, even when the rectified voltage drops to V ₀ ′ at time t ₅ , the transistor 10 becomes non-conductive only during the period of Δt ₅ where the rectified voltage V ₀ ′ becomes V _L or less regardless of the Zener voltage V _Z , and the capacitor 10 becomes non-conductive. The zener voltage V _Z of the constant voltage diode 9 is applied to the base by the electric charge of the capacitor 3 so that the transistor 6 becomes conductive and the capacitor 3
Is discharged and the voltage regulated by the Zener voltage V _Z is supplied to the load 4 via the diode 7. Here, when at time _{t 6} and the rectified voltage is restored to the load 4 _t 4 ~t ₅
A voltage equal to the voltage of the waveform shown by the solid line in the period is supplied. If a power failure occurs at time t ₇ , when the instantaneous value of the rectified voltage becomes _VL or less, the transistor 10 becomes non-conductive, the transistor 6 becomes conductive, and the constant voltage from the capacitor 3 via the transistor 6 is reached. A regulated voltage is supplied to the Zener voltage V _Z of the diode 9.

Here, the value V _{L of the} power supply voltage for turning on the transistor 10
Choosing a value close to zero volts will virtually instantly respond to a power failure. That is, since the circuit shown in FIG. 5 can be controlled so that the charging voltage of the capacitor 3 is discharged only during a power failure, the average voltage supplied to the load is the AC power supply voltage when the AC power supply is in a normal state. It can be close to the effective value of.

[Effect of device]

As described above, according to the present invention, a load is provided with a full-wave rectified voltage obtained by rectifying an AC power supply voltage and a voltage instantaneous value in one cycle of the rectified voltage due to charges of a capacitor charged by the rectified voltage. A voltage equivalent to the Zener voltage V _Z of the constant voltage diode is supplied through the transistor that discharges the capacitor only while the voltage is low. Therefore, when the power supply voltage drops only momentarily, the period in which the voltage of one cycle is low becomes long, so the Zener voltage V _Z supplied to the load is increased.
The period in which a considerable voltage is applied becomes longer, and the fluctuation of the average value of the load voltage can be suppressed to a low level with respect to the fluctuation of the power supply voltage. Furthermore, if the power supply voltage drops significantly or if there is a power failure, a voltage equivalent to the Zener voltage specified by the constant voltage diode is supplied to the load as the charge of the capacitor,
It is possible to compensate for brownouts and blackouts for several cycles. Furthermore, when the AC power supply is normal, the conduction period of the transistor that discharges the capacitor is extremely short, so only the rectified voltage is applied to the load, and the charging voltage of the capacitor is hardly applied, so the discharge of the capacitor is controlled. Only by providing the transistor circuit, the load voltage can be maintained at the average value of the rectified voltage close to the effective value of the AC power supply voltage without using a transformer or a DC voltage adjusting element having a complicated configuration. Therefore, it is possible to switch and use the battery power source selected to the DC voltage corresponding to the effective value of the AC power source voltage. If the base voltage circuit of the capacitor discharge control transistor is short-circuited by a short-circuiting transistor that is made non-conductive at approximately zero volts, the capacitor discharge period will be equal to the AC voltage when the AC power supply voltage is normal. Since it is an extremely short period of about 0 V, the increase in the average value of the rectified voltage applied to the load can be suppressed to a small value, and the load voltage can be made closer to the effective value of the AC voltage. . In addition, when a power failure or a voltage drop corresponding to a power failure occurs, it is possible to obtain an effect of instantly responding and reliably performing backup at the time of power failure.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an example of a conventional DC power supply circuit, and FIG.
1 is a voltage waveform diagram of the circuit shown in FIG. 1, FIG. 3 is a connection diagram showing an embodiment of a DC power supply circuit according to the present invention, FIG. 4 is a voltage waveform diagram of the circuit shown in FIG. 3, and FIG. Is a connection diagram showing an embodiment different from FIG. 3, and FIG. 6 is a voltage waveform diagram of the circuit shown in FIG. 2 ... Rectifier circuit, 3 ... Capacitor, 4 ... Load, 5 ...
... diode, 6 ... transistor, 9 ... constant voltage diode, 10 ... shorting transistor.

Claims (1)

[Scope of utility model registration request] 1. An AC power supply, a full-wave rectifier circuit that rectifies an AC voltage of the AC power supply and supplies the load to a load, and a capacitor connected in parallel with a load at an output end of the rectifier circuit.
This capacitor comprises a diode connected in series to the capacitor with a polarity for charging the capacitor, and a capacitor discharge control transistor in which the base voltage is kept constant and the collector-emitter circuit is connected in parallel with the diode. A DC power supply circuit characterized in that