JPH0217802B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention uses a thyristor (silicon-controlled rectifying element) as a voltage control element, and controls the output voltage by controlling its conduction angle. Concerning improvements in phase-controlled constant voltage power supply circuits.

[Prior Art] Conventionally, constant voltage power supply circuits have stabilized output by providing a variable impedance element such as a transistor between an input terminal and an output terminal, and changing the impedance of the variable impedance element according to the output voltage. Many so-called series regulator circuits were used to obtain voltage.

However, in such a series regulator circuit, a large amount of power is consumed by the variable impedance element, which causes problems such as heat dissipation and element casing, tends to increase the size, and has undesirable characteristics from an energy saving perspective. I was getting used to it.

Therefore, in order to improve this, an electronic switching element, such as a switching transistor, is used instead of a variable impedance element, and the ratio of its on time to off time, that is, the on-off duty ratio, is changed according to the output voltage. A so-called switching regulator circuit has been proposed and put into practical use, in which constant medical electrical characteristics are obtained by According to this switching regulator method, the power loss associated with voltage control is extremely small (if an ideal switching element can be obtained, the power loss is zero), and it is therefore highly efficient and compact and lightweight. This gives you the advantage of being able to
There is momentum for widespread adoption.

By the way, one example of a general use of a constant voltage power supply circuit is to obtain a stabilized DC power supply from an AC power supply, and it can be said that this is the case in most cases. In this case, the AC power source is first made into a pulsating current by a rectifier and then stabilized by a switching regulator circuit to obtain a DC voltage.

Therefore, we used a thyristor as an electronic switching element, turned it off using the input pulsation, and controlled the output voltage by controlling only the gate turn-off phase relative to the input pulsation phase. , a so-called phase-controlled type voltage power supply circuit was proposed.

An example of such a phase-controlled constant voltage power supply circuit is shown in FIG.

In the figure, 1 and 2 are input terminals to which AC voltage is supplied, 3 is a bridge rectifier, 4 is a resistor, 5 is a Zener diode for obtaining a constant voltage V _B , and 6
is a smoothing capacitor, 7 is a thyristor, 8 is a switching transistor for generating sawtooth waves, 9, 1
0 is a resistor, 11 is a protection diode, 12,1
3 is a resistor and a capacitor that constitute an integrating circuit for generating a sawtooth wave; 14 is a coupling capacitor; 15;
16 is a resistor forming a voltage divider for extracting a voltage proportional to the output voltage, 17 is a current limiting resistor, 18 is a transistor for voltage comparison, 19
is a Zener diode for generating the reference voltage _VB , 2
0 is a load resistor, 21 is a resistor for operating the Zener diode 19, 22 and 23 are capacitors and resistors that make up the differential circuit, 24 is an amplification transistor, 25 is an emitter resistor, 26 is a pulse transistor, and 27 is a startup 28 is a smoothing capacitor, and 29 is an output terminal.

Next, the operation will be explained with reference to waveform diagrams shown in FIGS. 2a to 2b. When an AC voltage is supplied to input terminals 1 and 2, a full-wave rectified voltage is obtained at a point a by a rectifier 3, and its waveform is a pulsating voltage as shown in FIG. 2a. This voltage at point a is supplied to the output terminal 29 every time the thyristor 7 conducts, and is supplied to the capacitor 28.
The DC output voltage V _O is obtained by smoothing the voltage.

Further, the voltage at point a flows through the resistor 4 to the Zener diode 5, is smoothed by the capacitor 6, and becomes a stable voltage V _B determined by the Zener voltage of the Zener diode 5, and the transistors 8, 18, 2
This serves as an operating power source for the control unit consisting of 4.

Further, the pulsating voltage at point a is divided by resistors 9 and 10 to a predetermined voltage, and then applied to the base of transistor 8 via diode 11.

Therefore, the transistor 8 becomes conductive only when the voltage V _B supplied to its emitter becomes larger than the pulsating voltage supplied to its base, and is cut off at other times, synchronizing with the pulsating voltage at point a. and turn it on and off repeatedly. When the transistor 8 is in the on state, the capacitor 13 is short-circuited and the voltage V _B is directly applied to the resistor 12. When the transistor 8 is in the off state, the voltage V _B charges the capacitor 13 and current flows through the resistor 12, so that the resistor 12 When the transistor 8 is on, the voltage becomes the same as the voltage V _B , and then when the transistor 8 is turned off, the voltage drops from the voltage V _B almost linearly to 0 voltage with a slope determined by the time constant of the resistor 12 and the capacitor 13. A sawtooth wave voltage is obtained which gradually decreases and then returns to the voltage V _B when the transistor 8 is turned on.

The sawtooth wave voltage obtained at this resistor 12 is supplied to the base of a transistor 18 via a capacitor 14, and the base of this transistor 18 is divided from the output voltage V _O by resistors 15 and 16. Since a direct current voltage is supplied to point b, the output voltage is changed to a sawtooth wave voltage as shown in Figure 2b.
A sawtooth wave signal b on which a voltage divided from V _O is superimposed appears and is applied to the base of the transistor 18 . Since the emitter of this transistor 18 is maintained at the reference voltage V _E by the Zener diode 19 and the resistor 21, the instantaneous value V _io of the sawtooth wave signal b is lower than the reference voltage V _E as shown in FIG. Transistor 1 only during the period of low
8 becomes conductive, and a rectangular wave signal as shown in FIG. 2c is generated at the collector resistor 20.

This rectangular wave signal is differentiated by a capacitor 22 and a resistor 23, amplified by a transistor 24, shaped into a phase pulse signal as shown in FIG.

In this way, the thyristor 7 is triggered to turn off at each cycle of the pulsating voltage being supplied to point a, and at each subsequent instant of near-zero voltage during each subsequent cycle, the thyristor 7 is triggered to turn off at the output terminal 29. It operates to supply intermittently.

Now, suppose that the output voltage V _O rises from a predetermined value for some reason. As a result, the DC voltage that is divided from the output voltage V _O by resistors 15 and 16 and superimposed on the sawtooth wave voltage also increases, so the average value _io of the sawtooth wave signal b increases, and the signal b becomes the reference voltage. V _E
The intersecting position changes and moves to the right in Figure 2b. In other words, 1 of the input pulsating voltage shown in a of the same figure
The position at which the sawtooth wave signal b begins to become lower than the reference voltage V _E is delayed during the cycle. Therefore, the phase of the phase pulse signal appearing at point d is delayed,
The time at which SCR 7 is triggered is also delayed and the conduction time of thyristor 7 during each cycle of pulsating voltage;
In other words, since the conduction angle decreases, the ratio of the time when the thyristor 7 is turned off to the time when it is turned on increases, and the output voltage V _O is controlled to be lowered.

Conversely, if the output voltage _VO decreases, the average value _io in FIG. 2b also decreases, and the sawtooth signal b moves downward in the diagram. Therefore, signal b is the reference voltage
Since the position lower than V _E is moved to the left, that is, to a position where the phase is advanced, and the phase of the phase pulse signal is advanced, the timing at which the thyristor 7 is triggered is at an early point in each thyristor of the pulsating voltage. As the conduction time increases and the cutoff time decreases, the output voltage V _O increases.

In this way, the circuit shown in Figure 1 has an output voltage of
It operates to stabilize V _O to a predetermined value.

In order to simplify the explanation, in the above explanation,
The base-emitter voltages of transistors 8 and 18 were ignored.

Also, the value of the output voltage V _O is the reference voltage V _E and the resistance 1
It can be arbitrarily selected depending on the voltage division ratio of 5.5 and 16, but this point is also well known to those skilled in the art, so it is omitted here.

Furthermore, the voltage division ratio by the resistors 9 and 10 is not made too large, and the time that the transistor 8 is on is shortened as much as possible within the range where the charge in the capacitor 13 can be sufficiently discharged when the transistor 8 is turned on. It goes without saying that it is practical to do so, so I just add it here.

As explained above, the phase-controlled constant voltage power supply circuit shown in Fig. 1 can fully utilize the characteristics of the thyristor, which are small in size and can control large currents, and can turn on the thyristor. Since control can be performed only by triggering at certain times, the circuit configuration is simplified, and a high-efficiency, low-cost constant-voltage power supply circuit can be obtained.There are few drawbacks of the series regulator system, so it is widely used. It is starting to be adopted.

[Problems to be Solved by the Invention] However, in the power supply circuit shown in FIG. 1, at startup, that is, when the power switch is turned on and pulsating voltage begins to be supplied to point 7 is not electrically connected because no trigger pulse is supplied to it. Therefore, the output voltage V _O is zero.

Therefore, in the operation explanation above, the output voltage
The situation is the same as when V _O drops extremely, so
After the power switch is turned on at point d, the phase of the phase pulse signal that first appears is also extremely advanced, and the thyristor 7 is triggered and conducts at the rising edge of each cycle of the pulsating voltage at point a, and the third
As shown in the figure, the output voltage ends up being much larger than the predetermined value _VO .

In theory, this large output voltage will cause a stabilizing operation to occur immediately after several cycles, and the output voltage will settle down to the predetermined value _VO , but there will be a transient high voltage during a few cycles from t ₀ when the power is turned on. It was not possible to suppress the output voltage from occurring.

Therefore, in order to eliminate this drawback to some extent, a method is known in which, for example, a starting resistor 27 is provided in the circuit shown in FIG.

If this resistor 27 is provided, even if the thyristor 7 is not conducting after the power switch is turned on, the voltage at point a will appear on the output terminal 29 side through this resistor 27, and even if it does not reach the predetermined output voltage _VO , b A DC voltage is applied to the point, which will prevent some of the extreme phase advances of the phase pulse signal. The lower the resistance value of this resistor 27 is, the more it is possible to suppress the transient rise in output voltage at startup, but on the other hand, the lower the resistance value of this resistor 27 is, the more this resistor 27 The power loss due to increases, and the output voltage V _O
In practice, it has been difficult to sufficiently suppress the transient rise in output voltage at the time of startup using this method because the stabilization characteristics of the output voltage are deteriorated.

This drawback becomes noticeable when the input voltage is relatively large compared to the output voltage V _O , and a large inrush current occurs at startup, damaging the rectifier or thyristor, or causing the load There was a risk of damage to the circuit.

SUMMARY OF THE INVENTION An object of the present invention is to provide a phase-controlled constant-voltage power supply circuit that eliminates the drawbacks of the prior art described above and prevents any transient increase in output voltage from occurring even during startup.

[Means for Solving the Problem] The above object is to provide first, second and third resistor voltage divider circuits connected in series between the output terminal and the ground for extracting the DC voltage to be superimposed on the sawtooth voltage. and a capacitor connected between the connection point of the first and second resistors and the output of the constant voltage circuit, and the connection point of the second and third resistors. At the same time, the voltage division ratio of the second and third resistors is determined so that the maximum value of the DC voltage that appears at startup is 1/2 of the voltage value of the sawtooth wave voltage, and the reference voltage is added to the voltage division ratio of the second and third resistors. This is achieved by setting the voltage division ratio to be larger than the voltage value.

[Function] The resistive voltage divider circuit works so that the DC voltage that rises with a predetermined time constant from the time of startup is superimposed on the sawtooth wave voltage, so that the phase of the phase pulse signal supplied to the thyristor is It progresses slowly, suppressing the transient voltage rise at startup.

[Example] Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 4 shows one embodiment of the present invention.
Parts that are the same as or equivalent to those in the circuit shown in the figure are given the same numbers.

The difference between the embodiment of the present invention shown in FIG. 4 and the circuit shown in FIG. 1 is that the resistor 16 for dividing the output voltage V _O in FIG. The connection point between these resistors 30 and 31 is set as a new voltage dividing point, and a capacitor 32 is provided between this point and the DC constant voltage V _B. 27 is the 4th
This is the only difference from the embodiment shown in the figure, and the other points are completely the same, so a detailed explanation will be omitted.

Next, the operation of this circuit will be explained.

An AC power supply is connected to the output terminals 1 and 2, and the pulsating voltage is full-wave rectified by the rectifier 3 (Fig. 2 a).
appears at point a, and the conduction/cutoff of the thyristor 7 is controlled by the phase pulse signal from the control section consisting of transistors 8, 18, and 24 (Fig. 2b,
c, d), the predetermined output voltage V _O is applied to the output terminal 29.
The operation up to the point where this is obtained is exactly the same as the conventional circuit shown in FIG.

The difference is that in the operation of the control unit during several cycles after the power switch is turned on, when the power switch is initially turned off, the charge in the capacitor 32 is discharged and becomes zero (others). The same goes for the capacitors, but they are not directly related to the operation of the present invention).

Therefore, when the power switch is turned on and a pulsating voltage (FIG. 2 a) appears at point a, the constant voltage V _B for operation is immediately built up by the resistor 4, Zener diode 5, and capacitor 6. So the voltage
From the V _B line, capacitor 32, resistor 31, 1
A charging current flows through the capacitor 32 through the path passing through the capacitor 32, and the current becomes a decay current determined by a time constant consisting of the capacitance of the capacitor 32 and the resistance value of the sum of the resistors 31 and 15. Therefore, immediately after the power switch is turned on, since the charge on the capacitor 32 is zero at first, the voltage _VB is directly applied to the series circuit of the resistors 31 and 15, and this voltage is divided by the resistors 31 and 15.
It appears at a point and is superimposed on the sawtooth voltage.

This can be explained using the waveform diagram of FIG. 5 as shown in A of the figure. That is, initially, the output voltage V _O
Since is zero, the voltage V _B appears as is at point b,
If we do not consider the sawtooth voltage, the voltage V _io at point b will attenuate due to the time constant determined by the capacitor 32 and resistors 31 and 15 as described above, so the initial value will eventually be changed to the initial value as shown by the dotted line _io . The attenuation voltage becomes V _B.

Note that at this time, the sawtooth wave voltage is
4, its average value is zero, and therefore it can be considered that V _io ≈ _io .

Therefore, what actually appears at point b is a sawtooth wave signal b, which is a sawtooth wave voltage superimposed on the voltage _io , as shown in _FIG. Since the phase pulse signal d is generated by comparison with the voltage IO, the sawtooth wave signal b does not cross the reference voltage _VE immediately after the power switch is turned on (time t ₀ ), and as the voltage _io attenuates, As shown in Figures 5A and 5B, the pulsating voltage a crosses the reference voltage V _E at the most delayed portion from the rising edge, and then at successively advanced phases. Therefore, the phase pulse signal d
The phase of VO also changes from the most delayed state to the most advanced phase, and the rise of the output voltage V _O occurs at the 6th phase.
As shown in the figure, after the power switch is turned on, the predetermined value V _O is not reached immediately, but rises due to the time constant of resistors 31 and 15 and capacitor 32, and the generation of transient high voltage is completely suppressed. become. Then, once the capacitor 32 is charged to approximately the voltage V _B , the voltage _io at point b becomes the voltage obtained by dividing the output voltage V _O by the resistors 30, 31 and the resistor 15, as in the case of Fig. 1. , output voltage V _O
The phase of the phase pulse signal d is controlled according to the change in the output voltage VO, thereby stabilizing the output voltage _VO .

At this time, the relationship between the voltage division ratios of resistors 15 and 31 is as follows: the resistance values of resistors 15 and 31 are R ₁₅ and R _{31 ,} respectively.
As V _B・R ₁₅ /R ₁₅ +R ₃₁ -1/2 (amplitude of sawtooth voltage) > V
Make it _E.

In this way, when the voltage V _io is superimposed on the first sawtooth wave voltage b after starting at time t ₀ in FIG.
It will no longer become lower than V _E , making it possible to reliably suppress the transient voltage rise at startup.

As described above, according to the present invention, it is possible to completely suppress the generation of a transient high output voltage when the power switch is turned on (at startup), and to reduce the power loss, while eliminating the drawbacks of the prior art. Moreover, a small and lightweight phase control type constant voltage power supply circuit can be obtained at a low cost.

[Brief explanation of drawings]

FIG. 1 is a wiring diagram showing a conventional phase-controlled constant voltage power supply circuit, FIGS. 2a to 3d and 3 are waveform diagrams for explaining its operation, and FIG. The wiring diagrams of the voltage power supply circuit, FIGS. 5A and 5B, and FIG. 6 are waveform diagrams for explaining its operation. 1, 2...Input terminal, 3...Bridge rectifier,
5... Zener diode for obtaining DC voltage V _B for operating the control section, 7... Thyristor for output voltage control, 8... Transistor for sawtooth wave generation,
15, 30, 31...Resistor forming a voltage divider for extracting control DC voltage, 18...Transistor for voltage comparison, 19...Zener diode for generating reference voltage, 24...Transistor for pulse amplification,
26...Pulse transformer, 32...Capacitor that provides a starting time constant.

Claims (1)

[Claims] 1. A full-wave rectifier circuit that rectifies AC voltage and outputs a pulsating DC voltage, a thyristor that connects the output of the full-wave rectifier circuit to an output terminal, a smoothing capacitor connected between the output terminal and ground, and a pulsating DC voltage. A sawtooth voltage generation circuit inputs a DC voltage and generates a sawtooth voltage synchronized with the pulsation frequency of the DC voltage, and superimposes a DC voltage proportional to the output voltage appearing at the output terminal on the sawtooth voltage. A resistive voltage dividing circuit, a pulse generating circuit that generates a phase pulse signal by comparing the output voltage of the resistive voltage dividing circuit with a reference voltage, and a DC constant for operation of the sawtooth wave voltage generating circuit and the pulse generating circuit. and a constant voltage circuit for supplying voltage, the constant voltage power supply circuit supplying the phase pulse signal to the gate of the thyristor to control the output voltage, the resistor voltage divider circuit is connected between the output terminal and ground. a resistive voltage divider consisting of a first, second, and third resistor connected in series;
and a capacitor connected between the connection point of the resistor and the output of the constant voltage circuit, and
The DC voltage is taken out from the connection point of the resistors, and the voltage division ratio by these second and third resistors is set such that the maximum value of the DC voltage that appears at startup is 1/2 of the voltage value of the sawtooth wave voltage. A constant voltage power supply circuit characterized in that the voltage division ratio is set to be greater than the voltage value obtained by adding the above-mentioned reference voltage.