JPH0297277A - Ac input automatic switching circuit - Google Patents

Abstract

PURPOSE:To prevent generation of overvoltage at the time of momentary break and reclosing and to improve reliability by providing a second switching element sensing an input voltage and adjusting the operation of an oscillator circuit. CONSTITUTION:At the time of 100V system input, a TRIAC TRK1 being one of switching elements is turned ON to conduct a double voltage rectification. At the time of 200V system input, the TRIAC TRK1 is turned OFF to conduct a bridge rectification by a diode bridge D1. In either case, a constant output voltage V0 is obtained as a terminal voltage of input capacitors C1, C2. A latch circuit is inserted between an input voltage sensing circuit and an oscillator circuit, and when an input voltage abruptly lowers by momentary break, the latch circuit stops oscillation by changing the specific terminal of the oscillator circuit from HI to LO level and reduces generation of overvoltage applied to the input capacitors from the momentary break to restarting.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an AC input voltage switching circuit in electrical equipment, and particularly to a method for detecting different input voltages and automatically controlling the operation of a rectifier circuit to correspond to the input voltage. This invention relates to an AC input automatic switching circuit for obtaining a DC constant voltage power source that can be selectively switched.

[Prior Art] Conventionally, when constructing a DC constant voltage power supply, an AC input voltage switching circuit is generally used. This AC input voltage switching circuit is equipped with a rectifier circuit that can switch the rectification method so that it can be used in response to different input voltages. A device configured to switch the rectification method is known. Today, as a commercial power source, single-phase AC 10
0■ and 200■ are mainly applied. Therefore, this type of AC input voltage switching circuit is equipped with a voltage doubler full-wave rectifier circuit, a bridge rectifier circuit, etc. to adapt to each of these input voltages, and these rectifier circuits are connected to each other using a changeover switch or a changeover connector. Switching is performed selectively in accordance with the input voltage at the time to prevent overvoltage from being applied to the capacitor of the input rectifier circuit and to stably obtain the required constant DC voltage. An electrolytic capacitor with large capacitance is used as the input capacitor.
This is because it is susceptible to overvoltage and significantly reduces the reliability of DC constant voltage power supplies.

Here, the manner in which overvoltage is applied to the input capacitor is as follows:
From the state of ■, the input 200 operates in a bridge rectifier circuit.
This is noticeable when switching to state (2). Such a situation occurs when a voltage abnormality such as a momentary interruption occurs in the input voltage source, and also occurs when a switching error is caused by an operator's malfunction.

In such a case, in conventional input voltage switching circuits, a connector such as a changeover switch or a changeover connector is provided as means for switching the rectification method corresponding to each input voltage, and selection and changeover is performed by manual operation. .

Therefore, for example, if electrical equipment is relocated due to the user's convenience and the commercial AC input is converted, if the changeover switch or changeover connector is incorrectly operated and the rectification method is selected incorrectly, the rectifier circuit There were problems such as overvoltage being applied to the input capacitor and damaging it.

In order to prevent this situation, it is possible to directly rectify the AC input voltage in advance and use the resulting DC as the input power source to operate the device, but there are problems such as the circuit becomes complicated and the manufacturing cost increases. .

Therefore, the present inventor previously developed an AC input automatic switching circuit for obtaining a DC constant voltage power supply that can detect the input voltage and automatically and reliably switch the rectification method in response to the input voltage without any time delay. We have discovered that it can be constructed using a pulse transformer or the like.

[Problem that the invention seeks to solve]

However, although the above-mentioned AC input automatic switching circuit using a pulse transformer or the like can solve the conventional problems, it still cannot sufficiently reduce the overvoltage generated in the input capacitor when the AC input is momentarily cut off.

A momentary power outage here refers to a momentary power outage in the AC input voltage, or
This refers to the phenomenon of voltage drop, which occurs during overloads, power outages, etc.

Therefore, the present invention uses transformation means such as a pulse transformer to turn on/off a switching element that changes the input rectification method.
In the AC input automatic switching circuit that performs OFF operation,
The purpose is to provide a highly reliable product that can prevent overvoltage from occurring during momentary power outages and restarts.

[Means for solving problems]

The present invention connects a bridge rectifier circuit and a pair of smoothing capacitors in series on the DC output side of the rectifier circuit, and connects one AC input end of the rectifier circuit to the connection point of the pair of smoothing capacitors. In a DC constant voltage power supply circuit configured to connect a switching element and turn on/off the switching element according to changes in AC input voltage to switch a rectifier circuit, the input voltage is detected by an input voltage detection circuit. The AC input automatic switching circuit is characterized in that it is provided with a second switching element that detects and adjusts the operation of the oscillation circuit.

In the present invention, a transistor, a thyristor, a tri-hook, etc. can be used as the second switching element, and by turning it on and off, a predetermined terminal of an IC constituting an oscillation circuit is switched between HI and LO. cormorant·
This constitutes a bench circuit.

EXAMPLES The present invention will be specifically explained below with reference to Examples, but it goes without saying that the present invention is not limited to these specific examples.

(Example) (Example 1) Fig. 1 shows an example of the AC input automatic switching circuit according to the present invention. When the tri-hook TRKI is turned on, voltage doubler rectification is performed, and when the 200-inch system is input, TRKI is turned off and bridge rectification is performed using the diode bridge D1.In either case, a constant output voltage ν0 is input. This is obtained as the terminal voltage of capacitors C, C2.

To open and close the gate of TRKI, the input voltage detection circuit drives and stops the oscillation circuit using the input voltage, and the output voltage is converted to DC voltage by the half-wave rectifier circuit consisting of diode D2, resistor R5, and capacitor C3 through the pulse transformer T1. Perform opening/closing operations.

The launch circuit according to the present invention is inserted between an input voltage detection circuit and an oscillation circuit as shown in FIG. By changing to f level, oscillation can be stopped, and the occurrence of overvoltage applied to the human-powered capacitor at the time of restarting from a momentary interruption can be reduced.

An embodiment of the input voltage detection circuit and launch circuit shown in FIG. 1 is shown in FIG. 2. The input voltage e is rectified by the input voltage rectifier circuit and compared with the Zener diode ZD, and if the input voltage is power fail, the photocoupler PCI operates to move the secondary side F1 coupler PCI and input it. From the voltage detection signal generation circuit to po
Issue a wer fail signal.

This photocoupler-based detection circuit is for input voltage detection.
It may be provided after C.

In FIG. 1, the input voltage is rectified and charged to capacitor C4. Here, the input voltage rectifier circuit can also use a diode bridge, D.

It is also possible to use a circuit configuration that is shared with

This voltage value is compared with the internal reference voltage of ICI, which is a voltage detection IC, to control the activation/stopping of the oscillation circuit. ICI
It is possible to use a commercially available IC, for example, an IC with a model name of MB3761 manufactured by Fujitsu ■.

This IC includes an operational amplifier that generates a high-level output signal when the AC input voltage becomes lower than a reference voltage, and generates a low-level output signal when the AC input voltage becomes higher than the reference voltage. Therefore, the selection of constants R6-R11 is a matter of design.

Zener diode ZD2 functions to stabilize the ICI power supply voltage VCC. A capacitor C5 is connected in parallel with this to delay the rise of VCC. This is to prevent malfunction.

Resistors R and □ are added to prevent chattering. In other words, the input AC voltage is converted to DC voltage by an input voltage rectifier circuit, and this converted DC voltage is used as the detection voltage, but since this DC voltage contains ripples, chattering occurs when switching the input AC voltage. There is a risk of causing

To prevent this, a resistor RIG is added to provide hysteresis to the switching voltage. The width of hysteresis is RI
It can be changed depending on the resistance value of O.

As IC2 in the oscillation circuit, conventionally used switching regulator ICs can be used, such as commercially available ICs such as Unitroad's UCl342, NEC's μPC494, and Texas Instruments' T.
L494 etc. can be used. The power supply voltage VCC of the oscillation circuit is preferably a separate power supply to ensure stable oscillation.

Various constants of the input/output circuit of ICI, which is an input voltage detection IC, can be designed according to the manufacturer's manual. I
In response to the output voltage from pin 7 of C1, the potential of pin 1 of IC2 is controlled by turning on and off the thyristor SRI. That is, when the input voltage drops abnormally due to a momentary interruption, SRI is turned on and divider resistor RI5. The potential of pin 8 of IC2 is set to the Lm level via R16, and oscillation is rapidly stopped.

The pulse transformer T2 generates and controls the gate voltage of the triac TRKI upon receiving a signal from the oscillation circuit. ■■ in the figure indicates a connection terminal.

The energy received from the pulse transformer T1 is rectified by the diode D4 and charged into the capacitor C5, which has the effect of stabilizing the operation of the ICI.

If there is no latch circuit surrounded by the two-dot chain line in Fig. 2 (before improvement), the terminal voltage of input capacitor C or C2 will vary from 200V to 100VI, as shown by the broken line in Fig. 5. If a momentary interruption occurs, 360
■ Jump up close.

Further, even when the input voltage is switched from 100 to 200, an overvoltage exceeding 400 is generated due to the delay in the operation of the oscillation circuit.

On the other hand, if the latch circuit according to the present invention is provided, the fifth
As shown by the solid line in the figure, overvoltage does not occur at all. Note that when the input voltage is switched from 100V to 200V, the terminal voltage of the input capacitor temporarily drops from the normal value of about 270V to about 180V, but the output voltage is not affected and stable operation continues.

(Embodiment 2) FIG. 3 shows a modification of the circuit shown in FIG. 1, in which the oscillation circuit is installed on the secondary circuit side.

Therefore, a photocoupler PCI is connected for electrical isolation and signal transmission between the negative side and the secondary side.

FIG. 4 shows an embodiment of the input voltage detection circuit in this case. This is almost the same as the case shown in Figure 2, but in order to stabilize the operation, dividing resistors Rz and R are added to the shunt regulator SRI.
+□ is connected, and the midpoint is fed back to the input side of the ICI. A shunt regulator, also called a shunt regulator, is a regulator that maintains a constant output voltage by controlling the current flowing through a voltage-dropping resistor connected in series with the load. can get.

A launch circuit similar to that shown in Figure 2 can be used.

〔Effect of the invention〕

According to the present invention, in an AC input automatic switching circuit provided with a control circuit that switches the rectification method in response to different AC input voltages, an AC input voltage can be properly detected with a simple circuit configuration, and the input AC voltage can be properly detected. In response to this, a switching element such as a triac can be turned on and off reliably without generating an overvoltage.

Therefore, it is possible to switch the rectifier circuit without making a mistake in the switching operation in response to changes in the AC input voltage, and it is possible to improve the safety of this type of input voltage switching circuit.
Abnormal voltage is not applied to the input capacitor, which has a remarkable effect on improving reliability.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the AC input automatic switching circuit according to the present invention, FIG. 2 is a circuit diagram showing an embodiment of the input sense pressure detection circuit shown in FIG. 1, and FIG. A circuit diagram showing another embodiment of the AC input automatic switching circuit according to the invention, FIG. 4 is a circuit diagram showing an embodiment of the input voltage detection circuit shown in FIG. 3,
FIG. 5 is a diagram showing the input capacitor terminal voltage waveform at the time of input voltage switching in the circuit shown in FIG. 1. Figure 1

Claims (3)

[Claims] (1) A bridge rectifier circuit and a pair of smoothing capacitors are connected in series on the DC output side of this rectifier circuit, and switching is performed between one AC input terminal of the rectifier circuit and the connection point of the pair of smoothing capacitors. In a DC constant voltage power supply circuit configured to connect elements and turn on/off the switching element according to changes in AC input voltage to switch a rectifier circuit, an input voltage is detected by an input voltage detection circuit. An automatic alternating current input switching circuit characterized in that a second switching element is provided to adjust the operation of the oscillation circuit. (2) The AC input automatic switching circuit according to claim 1, wherein the second switching element comprises a thyristor. (3) The AC input automatic switching circuit according to claim 1 or 2, wherein the on/off operation of the switching element is driven by a Paris transformer.