JPH0261046B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a constant voltage power supply device that applies a predetermined power to a load, and in particular, a constant voltage power supply device that detects a load applied voltage,
The present invention relates to a feedback phase control type constant voltage power supply device that compares this with a set value and controls the voltage application phase section to the load according to the difference between the two.

[Conventional technology]

This type of constant voltage power supply uses a switching transistor or a grid-controlled rectifier (thyristor).
A unidirectional switching (TRIAT: bidirectional switching) is connected to the power supply in series with the load, detects the load voltage or load current, compares its time-series smoothed value (average value or effective value) with the target value, and calculates the difference between the two. ,
That is, the on-period of the switching transistor or the on-phase of the lattice-controlled rectifier is controlled based on the amount of error. The accuracy of constant voltage control mainly depends on the detection accuracy of load power. Therefore, various load power detection means have been proposed in the past (Japanese Patent Publication No. 49-9818, Japanese Patent Application Laid-open No. 50-50916, Japanese Patent Publication No. 50-50916, Japanese Patent Publication No. 50-50916,
No. 52-36204, Utility Model No. 7342, Special Publication No. 1983-
No. 40873, Japanese Patent Publication No. 150022, Publication No. 17774
Publications, etc.). Conventionally, the load power detection means is a transformer or a photocoupler, since alternating current is applied to the load, and these are used to cut off the load AC power system and the load power detection circuit.

[Problem to be solved by the invention]

In the conventional method of detecting the load applied voltage using a transformer, the transformer itself has disadvantages such as being heavy and
There are problems such as the volume required, and the problem that if there is a DC component in the load voltage, it is not detected, resulting in a detection error. In the conventional example using a photocoupler,
There are detection errors due to changes in the characteristics of the photocoupler, that is, changes in temperature and changes over time. Furthermore, power control is performed in which the switching element is turned off at the zero-crossing point of the AC power supply and turned on between the zero-crossing points, increasing the load power by shifting the on-phase forward and lowering the load power by shifting the on-phase forward. Approximately the second half of the half wave is the energizing period, so
When the number of loads that require this type of phase control increases, the current peak appears only in the second half of the half-wave of the AC power supply, distorting the AC power supply current and worsening the power factor. Adversely affects driving.

The present invention aims to improve these conventional problems.

[Means to solve the problem]

In order to achieve the above object, in the present invention,
The AC power supply voltage is full-wave rectified by a diode bridge, a load and a transistor switching circuit are connected in series between the DC output terminals of the diode bridge, and a pulsating DC voltage is applied to them, and a resistor is connected to the load. Connect in parallel and use this resistor to detect the load voltage. Then, the phase control device turns on the transistor switching circuit using the zero-crossing point of the AC voltage as the starting point of conduction, compares the voltage of the resistor with a set value, and turns on the transistor switching circuit at a phase according to the difference between the two. The non-conducting phase of the transistor switching circuit is shifted in the direction in which the voltage of the resistor matches the set value.

[Effect]

According to this, the device becomes smaller and lighter than the case where a transformer is used, and the DC component of the load voltage can also be detected. There is no change in characteristics like with a photocoupler, and stable and highly accurate load voltage detection is performed. In addition, since only one of the emitter and collector of the switching transistor in the transistor switching circuit is always connected to one end of the load, the emitter and collector are alternately switched to the load according to the application of AC positive and negative voltages. This does not cause damage to the switching element, which is often the case when connecting devices.

In addition, power control is performed in which the switching transistor is turned on at the zero-crossing point of the AC power source and turned off between the zero-crossing points, and the load power is lowered by shifting the off-phase forward, and the load power is increased by shifting the off-phase backward. Approximately the first half of the AC half-wave is the energizing period, so if there is another load that performs conventional phase control where the second half is the energizing period,
Instead of concentrating the carrying current only in the second half of the half-wave of the AC power supply, on the contrary, the carrying current is dispersed over the entire half-wave period to correct the distortion of the alternating current, improving the power factor and Adverse effects on electrical equipment are suppressed.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

〔Example〕

FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows voltages at various parts thereof. In this embodiment, the exposure lamp of the copying machine is the load _L0 , to which the transistor switching circuit 10 is connected, and these loads _L0 and the circuit 10 are connected in series to the full-wave rectifier diode bridge _DB1. Connected between the DC output ends. A commercial alternating current voltage AC is applied to the alternating current input terminal of the diode bridge DB ₁ .

A lamp voltage detector 20 is connected in parallel to the load L ₀ . Detector 20 is a resistor connected in series.
Consisting of R ₆ and R ₇ with a load at their connection point
A voltage appears that is proportional to the voltage at L ₀ . In this embodiment, an error amplifier 30, an inverting amplifier 31, an effective value detection circuit 32, a comparator 33, a lighting command circuit 3
4, power synchronization circuit 36 and sawtooth wave generator 3
5 constitutes a phase control device. commercial exchange
AC is stepped down by a transformer T ₁ , rectified by a full-wave rectifier diode bridge DB _{2 ,} and applied to the power synchronization circuit 36 and the transistor switching circuit 10 . On the other hand, commercial AC is stepped down by a transformer _T2 , rectified by a full-wave rectifier diode bridge _DB3 , and applied to capacitors _C6 and _C7 . In addition,
One of the transformers T ₁ and T ₂ may be omitted and one transformer may be used in common. The output of the DC power supply circuit 40 composed of these elements is an error amplifier 30, an inverting amplifier 31, an effective value detector 32, a comparator 33,
The signal is applied to the lighting command circuit 34, the sawtooth wave generator 35, and the lighting signal generator 50.

Next, the operation of each part of the circuit shown in FIG. 1 will be explained with reference to FIG. The voltage of the load L ₀ is detected by the resistor R ₇ , inverted by the amplifier 31 and applied to the effective value detection circuit 32 . The effective value detection circuit 32 generates a voltage (hereinafter referred to as a load voltage signal) at a level indicating the effective value of the load voltage on its capacitor _C3 .
The load voltage signal is applied to error amplifier 30. The amplifier 30 compares the load voltage signal with a target signal Vref indicating the brightness of the lamp, generates a voltage with a polarity and level indicating the difference between the two, that is, an error signal, and outputs the voltage to the positive phase input terminal (+) of the comparator 33. to be applied.
The output of the lighting command circuit 34 is further applied to the positive phase input terminal (+). When the diode _D12 of the lighting command circuit 34 is energized by the lighting instruction signal (plus constant level) and emits light, the transistor Tr ₉ is turned off, and the positive phase input terminal (+) of the operational amplifier OP3 of the comparator 33 is grounded. more blocked. That is, when there is no lighting command, the circuit 34 connects the positive phase input terminal (+) of the amplifier OP3 to the ground, and outputs the error signal.
The application to OP3 is cut off, but when there is a lighting command, an error signal is applied to OP3.

The operational amplifier OP3 of the comparator 33 produces a positive voltage when the error signal is greater than the output a of the sawtooth generator 35, thereby energizing the light emitting diode _D8 of the transistor switching circuit 10. Since the output of the amplifier OP3 becomes a negative voltage when the output a of the generator 35 is higher than the error signal,
Diode D ₈ does not light up. Power supply synchronization circuit 36
The light emitting diode D ₃ emits light at a point other than the zero cross point of the commercial AC, and the sawtooth wave generator 35
will charge up capacitor _C5 while diode _D3 is on, and when _D3 stops emitting light, the capacitor will charge up.
Since C ₅ is discharged, the output a of the generator 35 is
It is a sawtooth wave that reaches the ground level at the AC zero-crossing point and then gradually increases in level until the next zero-crossing point. Therefore, the output of OP3 is at a positive level from just before the AC zero cross point until the sawtooth wave level exceeds the error signal level, and then becomes a negative level until just before the next zero cross point _. lights up from just before the commercial AC zero-crossing point until the sawtooth wave level exceeds the error signal level, and then turns off until just before the next zero-crossing point.

In the transistor switching circuit 10, while the diode _D8 is on, the phototransistor _Tr1 is on, and the transistor _Tr2 is off, and a step-down rectified AC voltage is applied to the base of the transistor _{Tr3 .} is turned on, so the switching transistor Tr ₄ is turned on and current is applied to the load L ₀ . Diode D ₈
When the light emission stops, the phototransistor Tr ₁ turns off and the transistor Tr ₂ turns on, and this transistor Tr ₂ connects the base of the transistor Tr ₃ to ground, so the transistor Tr ₃ turns off, and therefore the switching transistor Tr ₄ is turned off and the load L ₀ is no longer energized. As described above, the switching transistor Tr ₄ becomes conductive at the zero-crossing point of the commercial AC AC, turns non-conductive between the zero-crossing points, and then the conduction period is controlled by phase control, and the load voltage detected by the resistor R ₇ is adjusted according to the error signal level. The energization of the load L ₀ is controlled (the switching phase of the transistor Tr ₄ to OFF) so that the effective value of becomes the target level Vref.

While the switching transistor Tr ₄ is on, the resistor 50 of the lighting signal generator 50 and the light emitting diode D ₄
is connected between the DC output terminals of the diode bridge DB ₁ in the same way as the load L ₀ , so the diode D ₄ emits light. When diode _D4 emits light, phototransistor _Tr7 becomes conductive, which turns off transistor _Tr8 . Transistor Tr ₈
The emitter is the signal output end, and this is
It becomes a negative potential while voltage is applied to the load _L0 .
When no voltage is applied to the load _L0 , it becomes a positive potential. Therefore, the ignition signal generator circuit 50 outputs one pulse per AC half-wave while energizing the load _L0 .
Produces a bipolar pulse of pulses. This pulse is used as a lighting monitor signal.

Note that in this example, the resistor for detecting the load voltage is
Although an inverting amplifier 31 is inserted between R ₆ and R ₇ and the effective value detection circuit 32, this inverting amplifier 31 can be omitted. When doing so, for example, the positive DC output end of the diode bridge DB ₁ is disconnected from the ground, and the collector of the transistor Tr ₄ is connected to the ground.

〔Effect of the invention〕

As described above, according to the present invention, a full-wave rectified commercial AC wave is applied to the series circuit of the load L ₀ and the transistor switching circuit 10. Switching transistor of transistor switching circuit 10
Tr ₄ has one of its collector and emitter loaded with L ₀
In addition, the other transistor is fixedly connected to one pole of the power supply DB ₁ , and the emitter and collector are not alternately connected to the load as in the conventional case, so that the switching transistor Tr ₄ will not be destroyed. Since the full _- wave rectified wave DB ₁ is applied to the load L ₀ and the switching transistor Tr ₄ in this way, the load voltage can be detected by the resistors R ₆ and R _{7 .} It also detects the DC component of the load applied voltage.
Therefore, not only is the device smaller and lighter than when a transformer is used, but the accuracy of load voltage detection is also improved. Moreover, when compared with the conventional example in which a photocoupler is coupled to the load and the load power is detected by optical conversion, there is an advantage that the temperature dependence is small and the change over time is small.

In addition, switching transistor Tr ₄ is turned on at the zero-crossing point of the AC power supply and turned off between the zero-crossing points, and power control is performed in which the load power is lowered by shifting this off phase forward, and the load power is increased by shifting it later. In this case, approximately the first half of an AC half-wave becomes the energizing period, so if there is another load that performs phase control where the energizing period is in the second half, it is necessary to apply current only during the second half of the half-wave of the AC power supply. The distortion of the alternating current is corrected by dispersing the current throughout the half-wave period without concentrating it, improving the power factor and suppressing the adverse effects on other electrical equipment.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a time chart showing voltage waveforms at various parts thereof. 10: Transistor switching circuit (transistor switching circuit), 20: Lamp voltage detector (resistance) (30-60: Phase control device), 50: Lighting signal generator, L ₀ : Lamp (load), DB ₁ : Full wave rectifier diode bridge (rectifier means).

Claims (1)

[Claims] 1. A rectifier for full-wave rectification of an alternating current voltage; a transistor switching circuit connected in series with a load between output terminals of the rectifier; a resistor connected in parallel to the load; and the alternating current. The transistor switching circuit is made conductive with the zero-crossing point of the voltage as the starting point of conduction, and the voltage of the resistor is compared with a set value, and the transistor switching circuit is made non-conductive at a phase corresponding to the difference between the two, so that the voltage of the resistor increases. A constant voltage power supply device comprising: a phase control device that shifts the non-conducting phase of a transistor switching circuit in a direction that matches a set value.