JP2003009531A - Voltage step-up transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of irregular burst voltage in the secondary side when a main switch is opened in a voltage step-up transformer including the main switch in the primary side to control ON and OFF of the output of the secondary side. SOLUTION: In the voltage step-up transformer TA including the main switch RY2 in the primary side to control ON and OFF of the output of the secondary side, a serial circuit S including a sub-switch RY3 and a resistor R is connected to a coil T1 in the primary side. When the voltage step-up mode is changed to the output cut-off mode, the sub-switch RY3 is closed and the coil T1 of the primary side is short-circuited via the resistor R in the serial circuit S.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a step-up transformer having a switch for turning on / off a secondary side output on a primary side, and more specifically, for turning off a primary side switch to disconnect a secondary side output. In addition, the present invention relates to a technique for preventing an abnormal impulse voltage from being generated on the secondary side.

[Prior art]

Like withstanding voltage testers and insulation resistance measuring instruments,
In a device that requires a high voltage (for example, 500 V, 5 kV, etc.), a step-up transformer is generally used as a means for boosting the voltage.

In order to ensure safety, this type of step-up transformer is provided with a switch for turning off the secondary side output except when necessary. The way of arranging the switch is roughly divided into the following. There are two ways.

Referring to FIG. 3, the basic structure will be described first. In this type of step-up transformer T, an AC voltage generator G is used as a voltage generation source, and a primary side of the AC voltage generator G is used. When the AC input voltage Vi is applied to the coil T1, the output voltage Vo boosted according to the coil winding ratio between the primary side and the secondary side appears in the secondary side coil T2.

In order to turn on / off the output voltage Vo, in the first conventional example of FIG. 3, a relay switch RY1 is provided on the secondary coil T2 side. On the other hand, in the second conventional example of FIG. 4, the relay switch RY2 is provided on the primary coil T1 side.

[0006]

According to the first conventional example, by turning off the relay switch RY1, the output voltage Vo can be set to zero volt regardless of the AC input voltage Vi. However, the relay switch RY
In No. 1, since the withstand voltage between contacts must exceed the output voltage Vo, an expensive relay switch is required, which is not preferable in terms of cost.

According to the second conventional example, the AC input voltage Vi applied from the AC voltage generator G to the primary side coil T1.
Is at most 250V, so relay switch RY2
Although a general-purpose relay switch can be used for this, there are the following problems to be solved.

That is, depending on the model of the AC voltage generator G, a minute DC offset voltage may be superimposed on the AC input voltage Vi. This DC offset voltage continues to be output even if the AC output of the AC voltage generator G is set to zero.

Therefore, when the relay switch RY2 is turned on (closed) and the AC input voltage Vi is applied to the primary coil T1, the DC current Idc due to the DC offset voltage flows through the primary coil T1 as shown in FIG. Since a transformer is generally an L load, it has an impedance with respect to alternating current, but shows almost only a resistance value specific to the coil wire with respect to direct current.

Therefore, for example, when the relay input RY2 is opened in a state where the AC input voltage Vi is set to zero and the output voltage Vo of the secondary coil T2 is turned off, Vi2 = L × d ( A counter electromotive force of (Idc) / dt (L is an inductance of the primary coil T1) is generated, and this voltage is transmitted to the secondary coil T2.

For example, in order to obtain an output voltage of 5 kV AC on the secondary side with respect to 100 V AC on the primary side, the turns ratio of the transformer is 1:50. According to the actual measurement, when the direct current Idc of 0.1 A is opened, 10 V
Since the above-mentioned counter electromotive force is generated, a large voltage of 500 V is generated on the secondary side and is output as it is, which is not only dangerous, but also may be damaged depending on the device connected to the secondary side. There is also.

The present invention has been made to solve the above problems, and an object thereof is to turn off a switch on a primary side in a step-up transformer having a switch for turning on / off a secondary side output on a primary side. The purpose of the present invention is to provide a step-up transformer in which an abnormal impulse voltage is not generated on the secondary side.

[0013]

In order to achieve the above object, the present invention provides a primary coil to which an AC input voltage is applied from an AC voltage generator, and a secondary coil which boosts and outputs the input voltage. In a step-up transformer in which a main switch is interposed between the primary side coil and the AC voltage generator, a sub switch and a current limiting resistor are provided between the main switch and the primary side coil. A series circuit including is connected in parallel to the primary side coil, and includes a control means for controlling ON / OFF of the main switch and the sub switch according to an output setting state of the AC voltage generator, The control means turns on the main switch and turns on the sub switch in the boost mode in which a predetermined AC input voltage is output from the AC voltage generator and a boost output is obtained from the secondary coil. Is turned off and the AC output of the AC voltage generator is set to zero to set the output cutoff mode for cutting off the output of the secondary coil from the boost mode, after turning on the sub switch. The main switch is turned off after a predetermined time.

The present invention is particularly effective when the DC offset voltage is superimposed on the AC input voltage output from the AC voltage generator.

That is, in the primary coil of the transformer,
Although a DC current due to the DC offset voltage flows, according to the present invention, since the sub switch is closed before turning off the main switch, the current flowing through the transformer flows through the current limiting resistor and is consumed.

Therefore, no back electromotive force is generated. At this time, a voltage is generated at both ends of the current limiting resistor, but the generated voltage can be suppressed to a small value by selecting the resistance value of the current limiting resistor.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the circuit diagram of FIG. 1 and the timing chart of FIG.

Also in this step-up transformer TA, an AC voltage generator G for generating an AC input voltage Vi containing a minute DC offset voltage is used as a voltage source in the same manner as in the second conventional example, and this AC voltage generator G is used. And the primary coil T
A relay switch RY2 is connected between the switch 1 and the switch 1.

The step-up transformer TA has a series circuit S on the primary side thereof, which includes a relay switch RY3 other than the relay switch RY2 and a current limiting resistor R. The series circuit S is connected in parallel with the primary coil T1 between the relay switch RY2 and the primary coil T1.

In this case, the relay switch RY2 is the main switch, the relay switch RY3 is the sub switch, and these switches RY2 and RY3 are controlled by the control circuit C.
Its opening and closing is controlled.

Next, the operation of the present invention will be described with reference to the timing chart of FIG. First, the control circuit C turns on the relay switch RY2 to generate the AC input voltage Vi from the AC voltage generator G to enter the boosting mode, and the secondary coil T2 outputs the output voltage Vo according to the winding ratio. Is obtained. In the boost mode, the relay switch RY3 is kept off.

At time t1, if the output of the AC voltage generator G is controlled to set the AC input voltage Vi to zero, the output cutoff mode for cutting off the secondary side output is entered, but from the AC voltage generator G, Since the DC offset voltage Va is continuously output, the DC current Ic is applied to the primary coil T1.
Flows. Therefore, in this state, the relay switch RY
When 2 is turned off, the counter electromotive force Vi2 is generated in the primary side coil T1 as in the second conventional example.

Therefore, in the present invention, the relay switch RY
The relay switch RY3 is turned on at time t2 before turning off the switch 2, and the relay switch RY2 is turned off at time t3 thereafter. That is, both the relay switches RY2 and RY3 are turned on from the time t2 to the time t3.

Even if the relay switch RY2 is turned off at time t3, the relay switch RY3 is turned on and the primary coil T
Since a closed loop including 1 and the current limiting resistance R is formed, the coil current Ic flowing on the primary side flows through this loop, is converted into heat energy by the current limiting resistance R, and disappears.

At this time, at both ends of the current limiting resistor R, L
A voltage of × d (Ic) / dt = Ic × R is generated,
By properly selecting the resistance value of the current limiting resistor R,
The voltage can be made sufficiently smaller than the counter electromotive force Vi2.

By the way, when the coil current Ic is 0.1 A,
Assuming that the resistance value of the current limiting resistor R is 3Ω, the voltage generated on the primary side has a peak value of 0.3 V, and even if the winding ratio between the primary side and the secondary side is 1:50, the secondary The peak voltage generated on the side is 15V. This voltage value is at least within the safe ultra-low voltage (SELV) range and is not a dangerous value.

In this way, before opening the primary side,
By short-circuiting the primary side through an appropriate resistor, unnecessary high voltage is not generated on the secondary side, and even if a relay switch is not placed on the secondary side, an output voltage on / off function equivalent to that is provided. Can be secured.

The relay switch RY3 is turned off at an appropriate time t4 before the output switch of the AC voltage generator G is turned on next. In the above embodiment, the relay switches RY2 and RY3 are automatically controlled by the control circuit C, but the control start point may be manually input.

Although a relay switch is used as the switch, the present invention is not limited to this.
For example, other mechanical contact type switches or semiconductor switches can be used. Further, it is applicable to a transformer having many coils such as a tertiary coil, as well as a transformer having only a primary coil and a secondary coil.

[0030]

As described above, according to the present invention,
In a step-up transformer having a main switch that turns on and off the secondary side output on the primary side, a series circuit including a sub switch and a resistor is connected in parallel to the primary side coil, and when the boost mode is changed to the output cutoff mode, By closing the sub switch and short-circuiting the primary side via the resistor in the series circuit, the main switch can be opened without generating an abnormal impulse voltage on the secondary side.

[Brief description of drawings]

FIG. 1 is a circuit diagram illustrating an embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation of the present invention.

FIG. 3 is a circuit diagram showing a first conventional example.

FIG. 4 is a circuit diagram showing a second conventional example.

[Explanation of symbols]

TA step-up transformer T1 primary coil T2 secondary coil G AC voltage generator RY2 relay switch (main switch) RY3 relay switch (sub switch) R Current limiting resistor C relay control circuit

Claims (2)

[Claims] 1. A primary side coil to which an AC input voltage is applied from an AC voltage generator, and a secondary side coil for boosting and outputting the input voltage, the primary side coil and the AC voltage generator. In a step-up transformer in which a main switch is interposed between the main switch and the primary coil, a series circuit including a sub switch and a current limiting resistor is connected in parallel to the primary coil. A control means for controlling ON / OFF of the main switch and the sub switch according to the output setting state of the AC voltage generator is provided, and the control means is a predetermined AC input voltage from the AC voltage generator. Is output to obtain a boosted output from the secondary coil, the main switch is turned on, the sub switch is turned off, and the AC output of the AC voltage generator is set to zero. When the output cutoff mode for shutting off the output of the secondary coil from the boost mode is set, the main switch is turned off after a predetermined time after turning on the sub switch. Boost transformer to do. 2. The step-up transformer according to claim 1, wherein a DC offset voltage is superimposed on the AC input voltage supplied from the AC voltage generator to the primary coil.