JPH0534228Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a power supply device, and particularly to a DC voltage monitoring circuit thereof.

[Conventional technology]

First, an example of a conventional power supply device will be explained with reference to FIG.

In the figure, 1 is a 3-phase AC power supply, 2 is a 3-phase full-wave rectifier that rectifies the 3-phase AC voltage, 3 is a filter for reducing the ripple of the 3-phase full-wave rectified DC voltage, and 4 is a transformer. , 5 is a switching element connected in series to the primary winding of the transformer, 6 is a rectifier circuit that rectifies the voltage between the secondary windings of the transformer, 7
is a high frequency filter circuit, 8 and 8' are DC output terminals,
9 is a DC voltage monitoring circuit connected between terminals A and B on the output side of filter 3; 10 is a voltage that detects the voltage between output terminals 8 and 8' and generates an error signal between the detected voltage and the reference voltage; detection/control circuit,
Reference numeral 11 denotes a drive circuit that provides a drive signal to the switching element 5 via a DC insulation transformer 12.

In such a circuit, when the switching element 5 changes from the on state to the off state, the switching element 5 receives a _voltage (approximately 2.5 V _E ) is applied. Therefore,
In order to prevent switching element 5 from being damaged due to an increase in DC voltage V _E due to the effects of lightning surges, monitor circuit 9 monitors the voltage between terminals A and B, and ensures that the voltage exceeds a set value. At this time, the monitoring circuit 9 provides an off signal to the drive circuit 11 to prohibit the drive circuit 11 from supplying a drive signal to the switching element 5 . This drive stop continues until the voltage between terminals A and B drops to a predetermined value, and as a result, switching element 5 and the like are protected from damage due to overvoltage.

Further, the off signal generated by the DC voltage monitoring circuit 9 may be used to open a circuit breaker 13 provided between the AC power source 1 and the rectifier 2, as shown by the dotted line. Furthermore, although the example of monitoring the input voltage has been described in FIG. 4, a case where the DC voltage monitoring circuit 9 is connected between the output terminals 8 and 8' and the DC output voltage is monitored in exactly the same manner as described above. There is also.

Representative examples of such a monitoring circuit 9 are shown in FIGS. 5 and 6.

The monitoring circuit 9 shown in FIG. 5 has terminals A,
It consists of resistors R ₁ to _{R 7} connected between B, a constant voltage diode ZD, an operational amplifier OA, and a photocoupler PC. In this circuit, during operation, current always flows from terminal A to terminal B via resistors R ₂ and R ₃ and resistors R ₁ , R ₄ and R ₅ , and operational amplifier OA is connected to resistor R ₃ Compare the voltage drop across R5 and _R5 , and when the voltage drop across resistor _R3 exceeds the voltage drop across resistor _R5 due to the increase in voltage between terminals A and B, its output changes from high level to low level. . Accordingly, a current flows from the terminal A to the operational amplifier OA via the resistor R ₁ , the light emitting diode of the photocoupler PC, and the current limiting resistor R ₇ , and the photocoupler PC generates the aforementioned drive stop signal. As the voltage between terminals A and B drops, the voltage drop across resistor R ₃ causes a voltage drop across resistor R ₅ which divides the output voltage of operational amplifier OA between feedback resistor R ₆ and resistor R ₅ . , the output of the operational amplifier OA changes from a low level to a high level, and the photocoupler PC is deenergized. Note that the constant voltage diode ZD is for providing a constant power supply voltage to the operational amplifier OA, and is indispensable for the operation of the operational amplifier OA.

Next, the monitoring circuit 9 shown in Fig. 6 is equipped with a dedicated DC power source PS. The operation of this circuit is almost the same as that of the conventional example, so it will be omitted. In this circuit, too, a current is always applied from terminal A to terminal B via resistors _R2 and _R3 .
A current flows through ZD'.
This is a Zener diode that provides a reference voltage to the OA.

[Problem that the invention attempts to solve]

As can be seen from the above description, the circuit shown in FIG. 5 has the disadvantage that current always flows from terminal A to terminal B via resistors R ₁ , R ₂ and the like, resulting in large power loss. Furthermore, since an operating voltage is required for the operational amplifier OA, this further increases power loss and increases the number of parts.

In addition, in the case of the circuit shown in Figure 6, it requires a power supply PS, so the price must be high, and the resistance
Since current is always flowing through R ₂ , R ₄ , etc.
This circuit also had the drawback of large power loss. And the power loss in these circuits can amount to more than 1% of the output, for example, the efficiency
In a 90% or more power conversion device, the power loss in the circuit 9 accounts for 10% or more of the loss of the entire device and cannot be ignored.

[Means for solving problems]

The device includes first and second constant voltage diodes connected in series together with a resistor between DC voltage monitoring terminals, and a switch circuit connected thereto.

[Effect]

If the voltage between the DC voltage monitoring terminals is lower than the voltage corresponding to the sum of the breakdown voltages of the first and second voltage regulator diodes, the switch circuit will not turn on and current will essentially flow through the voltage monitoring circuit. Therefore, no power loss occurs. Furthermore, when the monitored voltage exceeds the voltage corresponding to the sum of the breakdown voltages of the first and second voltage regulator diodes,
These constant voltage diodes break down, turning on the switch circuit and outputting a drive stop signal.

〔Example〕

FIG. 1 shows a DC voltage monitoring circuit 9 according to the present invention.
An example of this will be described.

In the figure, the constant voltage diodes ZD ₁ and ZD ₂ each consist of one or a plurality of Zener diodes connected in series, and have preselected breakdown voltages V ₁ and V _2, respectively. These constant voltage diodes ZD ₁ and ZD ₂ are connected in series together with resistors R ₁ , R ₂ and R ₃ , and transistors are connected to these.
A switch circuit SW consisting of T ₁ , T ₂ , diode D, photocoupler PC, and resistors R ₄ to R ₆ is connected.

Next, the operation of this circuit will be explained.

(1) The voltage V _AB between terminals A and B is the voltage (V ₁ + V ₂ )
If it is lower, this is a normal state, and both the voltage regulator diodes ZD ₁ and ZD ₂ do not break down, so the switch circuit SW is not turned on.

(2) When the voltage V _AB increases further and becomes V _AB ≧ (V ₁ + V ₂ ), both constant voltage diodes ZD ₁ and ZD ₂ break down, and the current flows from terminal A to resistor R ₁ ,
It flows to terminal B via constant voltage diodes ZD ₁ , ZD ₂ and resistors R ₂ , R ₃ . Along with this the resistor R ₃
A voltage drop occurs at , which forward biases transistor T ₂ and turns it on. Turning on transistor _T2 causes current to flow through resistors _R5 and _R6 , forward biasing transistor _T1 and turning it on. The current flowing through the transistor _T1 is the current flowing through the diode D and resistors _R2 and _R3 , and the current flowing through the resistor _R4 and the photocoupler PC.
The current flowing through the light emitting diode and the former gives positive feedback to the transistor _T2 ,
The latter energizes the photocoupler PC to output an off signal. Here, when the transistor T ₁ and the diode D are conducting, the voltage regulator diode ZD ₂ is bypassed by them, and the voltage across it is equal to the collector-emitter voltage V _CE of the transistor T ₁ and the diode D
The voltage will be equal to the sum of the forward drop _VF . This voltage is naturally smaller than the breakdown voltage V ₂ of the voltage regulator diode ZD ₂ .

(3) When the voltage V _AB starts to fall and becomes V ₁ ≦ V _AB < V ₁ + V ₂ , the voltage regulator diode ZD ₁ remains in the breakdown state, and the resistor R ₁ and the voltage regulator diode ZD ₁ are A current that can keep the switch circuit SW in the on state flows through the switch circuit SW. Therefore, the photocoupler PC outputs an off signal.

(4) When the voltage V _AB drops further and becomes V _AB < V ₁ , the voltage regulator diode ZD ₁ , which has been in a breakdown state until now, is released from that state and stops passing current. Therefore, the switch circuit SW is also turned off, and no off signal is generated from the photocoupler PC.

FIG. 3 shows these situations, where the breakdown voltage V ₂ of the constant voltage diode ZD ₂ gives hysteresis to the on-off operation of the switch circuit SW. Diode D is important in creating this hysteresis, and this is the transistor
By forming a bypass path for the voltage regulator diode ZD ₂ together with T ₁ and playing the role of providing positive feedback to the transistor T ₂ , at the same time, it prevents current from flowing from the voltage regulator diode ZD ₂ side to the resistor R ₄ side. Ensures ON operation of transistor T ₂ when voltage regulator diode ZD ₂ breaks down.

Next, another embodiment of the present invention will be explained with reference to FIG.

The switch circuit SW in this example is a thyristor.
Consisting of Th ₁ and photocoupler PC, it is extremely simplified. Since the operation of this circuit is almost the same as that of the previous embodiment, a detailed explanation will be omitted, but the voltage V _AB between terminals A and B is the sum of the breakdown voltages V ₁ and V ₂ of the constant voltage diodes ZD ₁ and ZD ₂ , respectively. When a voltage equal to is exceeded, thyristor Th ₁ turns on. Due to its thyristor characteristics, thyristor Th ₁ is kept in the on state even if no gate current flows through the voltage regulator diode ZD ₂ , so the voltage V _AB drops below the breakdown voltage V ₁ of the voltage regulator diode ZD ₁ . ,
When the breakdown radio wave of the constant voltage diode ZD ₁ stops flowing and the current flowing through the thyristor Th ₁ drops below its holding current, it turns off. In this circuit as well, the hysteresis of the on-off operation of the switch circuit SW, that is, the voltage difference thereof, is determined by the breakdown voltage _V2 of the constant voltage diode _ZD2 .

In the above embodiment, a photocoupler was used as a means for transmitting the OFF signal, but it is of course possible to use ordinary means such as a transformer or a resistor if there is no need for direct current isolation. It is.

[Effect of idea]

As described above, the present invention provides the following practical effects.

(1) As long as the monitored voltage does not exceed a voltage equal to the sum of the breakdown voltages of the first and second voltage regulator diodes, virtually no current flows through the voltage monitoring circuit, so the power of the voltage monitoring circuit decreases. Loss can be significantly reduced.

(2) Since there is no need to have a dedicated power source for the pressure monitoring circuit, the circuit configuration can be simplified and power loss can be further reduced.

(3) Since the breakdown voltage of the second voltage regulator diode determines the hysteresis of the voltage monitoring circuit's on-off operation, the breakdown voltage It is determined only by the size of the voltage, which makes it possible to monitor the voltage accurately and to simplify the design.

(4) Overvoltage conditions are detected using a combination of voltage regulator breakdown and a simple switch circuit, so malfunctions are less likely to occur due to noise.

[Brief explanation of the drawing]

1 and 2 are views showing different embodiments of the present invention, FIG. 3 is a view for explaining the present invention, FIG. 4 is a view showing an example of a power supply device, and FIGS. FIG. 6 is a diagram showing different examples of conventional voltage monitoring circuits. 5...Switching element, 9...DC voltage monitoring circuit, 11...Drive circuit, SW...Switch circuit, _ZD1 , _ZD2 ...First and second constant voltage diodes.

Claims (1)

[Scope of utility model registration request] In a power supply device that includes at least an inverter section that converts DC to AC by switching one or more switching elements using a drive pulse signal, a first and a second inverter are connected in series together with a resistor between DC voltage monitoring terminals. when a voltage exceeding a voltage approximately equal to the sum of the breakdown voltages of the first and second voltage regulating diodes is applied between the terminals, the voltage regulating diode turns on and generates an off signal; A power conversion circuit comprising: a switch circuit that turns off and stops generating the off signal when the voltage between the terminals falls below the breakdown voltage of the first voltage regulator diode.