JP2599978B2 - Power supply circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device, and more particularly, to a power supply device having an input rectifier circuit for switching rectification of an AC input voltage between a full-wave rectification method and a voltage doubler rectification method. And rectification method switching means.

[Conventional technology]

FIG. 7 shows an example of the basic configuration of a switch control circuit and an example of a power supply device according to the prior art.

Generally, as AC input voltage, AC100V system (about 87V-132
V) and AC200V (about 174V to 264V). In order to prevent the applied voltage value to the switching transformer 12 from being drastically changed, when the input voltage is 100 V, the switch control circuit 15A operates to operate the rectification changeover switch 1.
6 to conduct and execute double voltage rectification, input voltage 200V
In the system, full-wave rectification is performed with the rectification changeover switch 16 in an open state.

Transistor 11 repeats on-off, and transformer 12
Based on the rectified voltage on the primary side, DC-DC conversion for generating a DC voltage on the capacitor 14 through the diode 13 on the secondary side is performed.

The switching transistor control circuit 10 controls the switching transistor so that the DC voltage on the secondary side becomes constant.
11 to control the on-off duty.

Also, the detection voltage V that can be obtained by dividing the rectified voltage by
The det is input to the switching transistor control circuit 10 as an undervoltage detection signal to detect that the rectified voltage is insufficient, and when the rectified voltage is insufficient, the switching transistor 11 is turned off, and the operation of the transistor 11 is performed. To stop. That is, the power supply transformer 12 is prevented from being saturated due to insufficient rectified voltage, and the switching transistor 11 is prevented from being destroyed.

In addition, a rectification switch 16 according to the voltage of the AC power supply
Conventionally, in order to automatically switch between the AC input voltage VA before rectification by the rectifier circuit by the switch control circuit 15A.
C is detected, and the switching of the rectification changeover switch 16 is commanded.

[Problems to be solved by the invention]

Considering that the switch control circuit 15A is incorporated in a portion after the rectification stage, a rectified voltage is necessarily used as the detection voltage. In the above prior art, the detection voltage and the reference voltage are simply compared, and if the detection voltage is low, the voltage is switched to the double voltage rectification, and if the voltage is high, the switching is switched to the full-wave rectification.

First, consider a case where an AC 100 V AC current is input. If the voltage is double-rectified, the rectified voltage becomes twice as high as the AC voltage, so that the rectified voltage becomes higher than the reference voltage. Then, the rectified voltage becomes lower than the reference voltage, and returns to the double voltage rectification. This switching was repeated, and there was a problem that the intended double voltage rectification could not be determined.

By simply doubling the reference voltage,
In the case of AC 200V AC voltage, double rectification and full-wave rectification occur repeatedly, and this does not solve the essential problem.

Therefore, the switch control circuit 15A is incorporated in a portion after the rectification stage, and the switching transistor control circuit
It was not possible to share a power supply with the like or to omit a rectifying / smoothing circuit for detecting an AC input voltage, and in particular, to integrate the switching transistor control circuit 10 into a one-chip IC.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a circuit type power supply device in which a switch control circuit for controlling switching of a rectification changeover switch can be incorporated in a portion subsequent to a rectification stage.

[Means for solving the problem]

Means for Solving the Problems In order to achieve the above object, the present invention provides a means for rectifying an AC input voltage that varies depending on an installation location, a means such as a switching regulator for converting a rectified voltage to a DC-DC voltage to obtain a predetermined DC output voltage, and a rectifier. In a power supply circuit including a rectification changeover switch for switching means to full-wave rectification or voltage doubler rectification, and a switch control circuit for operating the rectification changeover switch, the switch control circuit uses a rectification voltage as a detection voltage and a high and low reference. If the detected voltage is higher than the higher reference voltage, a command to switch to the full-wave rectification state is output to the rectification changeover switch, and if the detected voltage is lower than the lower reference voltage, the voltage is doubled rectified. Output a switching command to the rectification changeover switch, and when the voltage falls between the two reference voltages, a power supply circuit comprising means for maintaining the current operation command as it is. It is intended to draft.

The switch control circuit may include a delay circuit that issues a switching command to a rectification switch after a lapse of a predetermined time from the time when the rectified voltage exceeds a predetermined voltage.

[Action]

FIG. 1 is a block diagram showing a basic configuration of a power supply device according to the present invention. The switch control circuit 15 receives the detection voltage Vdet obtained by dividing the rectified voltage by the resistance bleeders 8 and 9. Further, the operation output state of the switch of the switch control circuit 15 itself is monitored. By doing so, the switch control circuit 15 determines the transition state of the operation output from the operation state of its own switch and the level of the rectified voltage.

Specifically, for example, the control circuit has a hysteresis characteristic shown in FIG. Next, this characteristic will be described.

First, two reference voltages (VH, VL, where VH> VL × 2)
Be prepared). When the rectification changeover switch 16 is open, the switch 16 is turned on when the rectification voltage becomes lower than VL. On the other hand, when the switch 16 is conducting, the switch 16 is opened when the rectified voltage becomes higher than VH.

Due to this hysteresis characteristic, an operation as shown in FIG. 3 can be performed. Hereinafter, the operation will be described step by step.

Here, AC200V system × 2>VH> AC200V system> VL and V
VH, VL so that H> AC100V system x 2>VL> AC100V system
It is assumed that has been selected.

First, consider the case where an AC 100 V AC voltage is input. When full-wave rectification is performed, the rectified voltage is equal to or lower than VL. In the full-wave rectification, since the switching circuit is in an open state, if the voltage is equal to or lower than VL, the switching circuit is made conductive and the operation shifts to the voltage doubler rectification. The rectified voltage is twice the AC voltage, but the rectified voltage is V
This double rectification is maintained as long as H is not exceeded.

On the other hand, if the voltage is doubled rectified, the rectified voltage is two times the AC voltage.
Doubled rectification is because the switching circuit is conducting,
As long as the rectified voltage does not exceed VH, the double voltage rectification is maintained.

Consider a case in which an AC 200 V AC voltage is input. In the case of double voltage rectification, the rectified voltage exceeds VH. In the voltage doubler rectification, since the switching circuit is in a conductive state, when the rectified voltage exceeds VH, the switching circuit is opened to shift to full-wave rectification. Here, the rectified voltage is detected again, and the full-wave rectification is maintained unless the rectified voltage becomes VL or less.

On the other hand, when full-wave rectification is performed, the rectified voltage is equal to or higher than VL. Since the switching circuit is open in the full-wave rectification, the full-wave rectification is maintained unless the rectified voltage drops below VL.

As mentioned above, even if the power supply voltage fluctuates due to an instantaneous power outage, 100V
Double voltage rectification can be maintained for system input voltage, and full-wave rectification can be maintained for AC200V system input.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. This embodiment is an embodiment using a memory circuit. Note that the operation state of itself is referred to inside the flip-flop 25.

The rectifier circuit includes diodes 2, 3, 4, and 5, and rectifies the AC input voltage VAC. The rectification changeover switch 16 is a switch for switching between full-wave rectification and voltage doubler rectification. When the switch 16 is opened, full-wave rectification is performed, and when the switch 16 is closed, voltage double rectification is performed. Reference numerals 6 and 7 denote smoothing capacitors for removing ripples after rectification.

Next, the configuration of the switch control circuit 15 will be described. Resistance 8,
9 divides the rectified voltage by resistance to create a detection voltage Vdet. The voltage is connected to the input terminals (+ side) of the comparators 22 and 23 at the next stage. VBB is an internal power supply. The reference voltages VL and VH are created by connecting resistors 19, 20, and 21 in series to the internal power supply VBB and dividing the resistors. The respective voltages are connected to the input terminals (− side) of the comparators 22 and 23 in the next stage. Comparator 2 with input of reference voltage VH
The output of 2 is connected to the set terminal (S) of the next-stage flip-flop 25, and the output of the comparator 23 connected to the reference voltage VL is inverted by the inverter 24 and connected to the reset terminal (R) of the flip-flop 25. The output (▲) of the flip-flop 25 is connected to the base of the transistor 26 for driving the relay 18. The relay 18 controls the opening and closing of the switch 16, and closes the switch 16 when the transistor 26 is on,
The switch 16 is set to open when the switch is off.

The following describes that the switch control circuit 15 of this embodiment has the characteristics shown in FIG. 2 and performs the operation shown in FIG. Also, it is assumed that VH> 2 × VL.

As an initial state, the determination is started from the point where the switch 16 is opened and full-wave rectification is performed.

First, the operation starts when the AC input voltage VAC is low and the full-wave rectified voltage is lower than VL. In this case, since Vdet is lower than VL, the outputs of the comparators 22 and 23 are respectively Low.
Level, the output of the inverter 24 becomes High level, and the flip-flop 25 is reset.
Level. Then, the transistor 26 is turned on, the relay 18 closes the switch 16, and the rectifier circuit performs voltage doubler rectification. The rectified voltage doubles and the detection voltage doubles.

Here, since VH> VL × 2 was selected, Vdet is 2
It doubles and may exceed VL but not VH. When Vdes exceeds VL, the output of comparator 23 goes high, but the output through inverter 24 is low. Therefore, the previous state of the flip-flop 25 is maintained, and the switch 16 remains closed.

Next, a case will be described in which the AC input voltage increases and Vdet, which has detected the doubled rectified voltage, becomes higher than VH.
In this case, the output of the comparator 22 goes high, the flip-flop 25 is set, and ▲ ▼ goes low,
Therefore, the transistor 26 is turned off, and the relay 18 opens the switch 16, so that the rectifying circuit shifts to the full-wave rectifying operation. The rectified voltage is half before opening switch 16,
Although Vdet is also halved, Vdet> VL is guaranteed because VH> 2 × VL was selected. Thus, the output of the comparator 22 is inverted and goes to a low level, but the output of the comparator 23 remains at a high level, the state before the flip-flop 25 is maintained, and the switch 16 remains open.

This time, a case will be described in which the AC input voltage decreases and Vdet, which has detected the full-wave rectified voltage, becomes lower than VH. In this case, the output of the comparator 22 becomes low level,
The output of the comparator 23 also becomes low level, and the flip-flop
25 is set and the state is inverted, and the output ▲ ▼ becomes high level. The transistor 26 is turned on, the relay 18 closes the switch 16, and the rectifier circuit shifts to the voltage doubler rectification operation. The rectified voltage is doubled, and therefore Vdet is doubled before switch 16 is closed, and the output of comparator 23 goes high. However, since VH> 2 × VL and VH> Vdet are guaranteed, the output of the comparator 22 remains low, the state before the flip-flop 25 is maintained, and the switch 16 is closed. Will remain. Hereinafter, the following operation is repeated according to the AC input voltage change.

According to the present embodiment, the operation having the characteristics shown in FIG. 2 and the operation shown in FIG. 3 can be realized. That is, it is possible to detect the voltage after rectification and accurately judge the situation, to perform voltage doubler rectification for an AC 100 V input and full-wave rectification for an AC 200 V input.

Although a relay is used as the switching element in the present embodiment, it goes without saying that a thyristor, a triac, or the like can be used.

By the way, when the AC voltage of 200 V is input while the switch 16 is conducting, that is, in the state of the voltage doubler rectification, a high rectified voltage by the voltage doubler rectification is generated until the switching to the full-wave rectification occurs. It is uneconomical to use a circuit element such as a capacitor with a high withstand voltage in accordance with this high voltage.

This can be solved by always operating and maintaining the switch 16 in the open state when there is no rectified voltage.

FIG. 5 shows a circuit for realizing this function. In this circuit, a voltage Ea formed by dividing the voltage VBB by resistors 27 and 28 is input to a comparator 29, and the output of the comparator 29 is set via an inverter 30 and an OR circuit 31 to a set terminal of a flip-flop circuit 25 ( S). Therefore, this circuit functions to maintain the flip-flop 25 in the set state when the detection voltage Vdet for detecting the rectified voltage is equal to or lower than the preset voltage Ea. By providing this reset circuit, double voltage rectification of the 200 VAC input voltage can be prevented beforehand, and a high withstand voltage circuit element such as a capacitor is not required, which is economical.

In addition, in order to prevent an excessive rush current from flowing into the smoothing capacitors 6 and 7 when the AC voltage is turned on, insert an inrush limiting resistor of about 10 ohms between the AC power supply and the bridge rectifier circuit at the beginning of turning on. There are often. in this case,
The rectified voltage gradually rises after the AC voltage is applied. If the state of the switching circuit is initialized to the open state,
Since the initial state is full-wave rectification, it is not necessary to change the state of the switching circuit when a 200 VAC system is turned on.

However, when there is an inrush limiting resistor, the rise of the rectified voltage at the time of AC input is slow, so that the setting of the switching circuit is performed when the rectified voltage does not reach the final value or less than VL. At this time, since the voltage is insufficient,
The transition to the conducting state, that is, the voltage double rectification is temporarily made. then,
The rectified voltage rises and exceeds VH, at which point the switching circuit is opened again to return to full-wave rectification and return to the desired state. This operation of switching the state twice and returning to the original state is an inherently unnecessary operation and is not desirable.

FIG. 6 shows a circuit for preventing the unnecessary operation.
This circuit keeps the switching circuit in an open state, that is, full-wave rectification, before the rectified voltage exceeds the set level, and operates to start setting the switching circuit after a certain time from when the rectified voltage exceeds the set level. It is a delay circuit. If a certain period of time is waited until the rectified voltage is appropriately stabilized, the unnecessary operation is eliminated at the time of AC200V input. In the case of AC100V input, the state is switched once from full-wave rectification and shifts to double voltage rectification as usual.

 Hereinafter, the operation of the initialization delay circuit of FIG. 6 will be described.

The rectified voltage when the AC input voltage is turned on is low, and the detection voltage Vd
While et is lower than the reference voltage Ea of the comparator 29, the output of the comparator 29 is low, the output of the inverter 30 is high, and the transistor 34
Is on, the voltage across capacitor 35 is almost 0 V, and comparator 37
, The output is high, the inputs of the OR circuit 38 are both high and the output is high, and the output of the OR circuit 31 is high.
Also goes high, maintaining flip-flop 25 in the set state.

The rectified voltage rises, and Vdet becomes the reference voltage Ea of the comparator 29.
, The output of the inverter 30 is low, the transistor 34 is off, and the input terminal of the OR circuit 38 connected to the inverter 30 is low. Constant current I ₀ begins to charge the capacitor 35, the terminal voltage of the capacitor 35 rises gradually. When this terminal voltage is still lower than the reference voltage (+ terminal) of the comparator 37, its output becomes high, so that the OR circuits 38 and 31 become high, and the flip-flop 25 maintains the set state.

When the charging voltage of the capacitor 35 exceeds the reference voltage of the comparator 37, the output of the comparator 37 becomes low, the output of the OR circuit 38 becomes low, and if there is no other set signal, the set terminal of the flip-flop 25 is It becomes low, and the switching is started.

In the case where the power supply of the power supply of the switch control circuit is obtained from the rectified voltage, the same effect can be obtained by using the rise of the power supply of the control circuit to start the delay circuit.

When the AC input voltage shifts from AC100V system to AC200V system, when the rectified voltage exceeds VH, it switches from voltage doubler rectification to full-wave rectification and the rectified voltage falls, but the rectified voltage is
It can be considered that the voltage rises slightly above VH transiently. This is a constraint on the power supply circuit design.

This constraint detects that the rectified voltage has exceeded VH,
While the voltage exceeds VH, the switching transistor 11 can be removed by stopping the operation.

The output of the comparator 22 in FIG.
By sending it to the switching transistor control circuit 10, the above object can be easily achieved.

In the power supply circuit, when the rectified voltage is insufficient, the magnetic flux of the iron core, the core, and the like of the power transformer 12 is saturated, and DC superposition occurs, and the switching transistor 11 is damaged. To prevent this, when the rectified voltage is insufficient, the operation of the switching transistor 11 is stopped.

For this purpose, it is necessary to detect the rectified voltage and send it to the switching transistor control circuit 10 as a transistor switching stop signal a as shown in FIG.

When the switching transistor control circuit 10 and the switch control circuit 15 are considered as ICs, in the conventional technology, the transistor switching control circuit 10 detects a rectified voltage, and the switch control circuit 15 detects an AC input voltage. Required two. According to the present invention, the same rectified voltage can be detected, and a one-chip IC having two control circuits mounted thereon can be used, so that the detection terminals can be shared. Since only one terminal is required, there is a merit of being economical.

〔The invention's effect〕

According to the present invention, it is possible to switch between full-wave rectification and voltage-doubled rectification by detecting a rectified voltage, so that this switch control circuit can be incorporated in a circuit section after the rectification stage. Therefore, the power supply is shared with the switching transistor control circuit and the like, and the rectifying and smoothing circuit for detecting the AC input voltage can be omitted. In particular, it is possible to make an IC chip IC with the switching transistor control circuit.

Also, before the rectified voltage exceeds the set level, the switching circuit is kept in an open state, that is, full-wave rectification, and a delay circuit that operates to start setting of the switching circuit after a certain time from when the rectified voltage exceeds the set level. In the case where full-wave rectification is to be set, there is no needless operation that temporarily shifts to voltage doubler rectification and then returns to full-wave rectification.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of a power supply device according to the present invention, FIG. 2 is an explanatory diagram showing hysteresis characteristics used in the FIG. 1 device, and FIG. 3 shows an example of operation of the FIG. 1 device. FIG. 4 is a circuit diagram showing an embodiment of the power supply device according to the present invention. FIG. 5 is a diagram showing an example of a circuit for initializing the state of the rectification changeover switch. FIG. 7 is a diagram showing an example of a circuit to be driven, and FIG. 7 is a diagram showing an example of the configuration of a conventional power supply device. 1 ... AC current, 2,3,4,5 ... Rectifier circuit diode, 6,7 ... Smoothing circuit capacitor, 8,9 ... Division resistor, 10 ... Switching transistor control circuit, 11 ... Switching transistor , 12 ... Transformer, 13
... Diode, 14 ... Smoothing capacitor, 15 ... Switch control circuit, 15A ... Conventional switch control circuit, 16 ... Rectifier switch, 18 ... Rectifier switch 16 drive relay, 19, 20, 21 ...
… Divider resistor, 22, 23… Comparator, 24… Inverter, 25… Flip-flop, 26 …… Transistor, 27, 28 …… Divider resistor, 29… Comparator, 30 …… Inverter, 31 OR circuit, 32, 33 Transistor, 35 Capacitor, 36 Constant current source, 37 Comparator, 38
…… OR circuit.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kenkichi Yamashita 5-2-1 Omika-cho, Hitachi City, Ibaraki Prefecture Inside the Hitachi, Ltd. Omika Plant (56) References JP-A-62-250872 (JP, A) Opened 63-87175 (JP, A) Opened 62-198884 (JP, U) Opened 60-114530 (JP, U) Opened 1-86481 (JP, U) Opened 61-7289 (JP, U) JP, U)

Claims (2)

(57) [Claims] 1. A means for rectifying an AC input voltage which differs depending on an installation location, a means such as a switching regulator for converting a rectified voltage from DC to DC voltage to obtain a predetermined DC output voltage, and a means for rectifying the rectifying means by full-wave rectification or In a power supply circuit including a rectification changeover switch for switching to voltage doubler rectification and a switch control circuit for operating the rectification changeover switch, the switch control circuit uses the rectification voltage as a detection voltage and has two reference voltages, high and low, If the detection voltage is higher than the higher reference voltage, a switching command to the full-wave rectification state is output to the rectification changeover switch.If the detection voltage is lower than the lower reference voltage, the state changes to the double-voltage rectification state. Output to the rectification changeover switch, and when the voltage falls between the two reference voltages, the current operation command is maintained as it is. Characteristic power supply circuit. 2. The power supply circuit according to claim 1, wherein the switch control circuit has a delay circuit for issuing a switching command to the rectification change switch after a lapse of a predetermined time from the time when the rectified voltage exceeds a predetermined voltage. A power supply circuit characterized by the following.