JPS6229990B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a constant current power supply device, and more particularly, to a constant current power supply device having an emergency cutoff function in case a power supply operation is mistakenly performed when a load is disconnected.

Generally, power is supplied to repeaters on a balanced power transmission line using a constant current power supply device in order to provide stable power supply regardless of the number of repeaters or the distance of the transmission line. Therefore, in the event of a failure that opens the load, such as a break in the power supply cable, the load impedance becomes infinite and a high voltage is applied between the output terminals of the constant current power supply device. Since the current flowing through the inserted relay is cut off, the power supply is stopped by opening the contacts of this relay.

However, if the start switch of the constant current power supply device is pressed during a fault such as a break in the load cable, high voltage will be applied to the output circuit while the main start switch is pressed, so it was expected that the power outage would continue. Dangerous for workers etc.

FIG. 1 shows a block diagram of a conventional power supply device using a generally known self-excited converter system. In the figure, reference numerals 1 and 1' are input terminals, reference numerals 2 and 2' are output terminals, reference numeral 3 is a switching transistor, reference numeral 4 is a converter transformer, reference numeral 5 is a rectifier diode, and reference numeral 6 is a smoothing terminal. capacitor, reference numeral 7 is the first relay and 7' its contacts, reference numerals 8, 9 and 10 are resistors, reference numeral 11 is the reference voltage supply, reference numeral 12 is the comparator amplifier, reference numeral 13 is the control circuit; Reference numeral 14 is the activation switch, reference numeral 15 is the second
In the relay, 15' indicates its contact, and reference numeral 16 indicates the load. These switching transistor 3, converter transformer 4, rectifier diode 5, smoothing capacitor 6, and control circuit 13 constitute a generally well-known self-excited converter (Japanese Patent Publication No. 50-15281). Input terminals 1 and 1'
When the start switch 14 is applied with DC voltage applied to
When pressed, the second relay 15 is energized,
Its contact 15' closes. This allows output terminal 2
A constant current is supplied to the load through 2' and 2', and this constant current operates the first relay 7, and by closing the contact 7', power supply continues even if the activation switch 14 is released. It turns out.

A voltage proportional to the output current is generated across the resistor 10 inserted in series in the output circuit. This voltage is input to the comparator amplifier 12 together with the voltage of the reference voltage power supply 11 . Comparison amplifier 12 amplifies the difference between these two voltages and sends it to control circuit 13. The control circuit 13 controls the ratio between conduction (ON) and non-conduction (OFF) of the switching transistor 3 in accordance with the output of the comparison amplifier 12, thereby stabilizing the output current from the output terminals 2 and 2'.

In this conventional constant current power supply device, if the start switch 14 is pressed while the load is experiencing a load disconnection failure such as a cable break, the output terminals 2 and 2 will be turned on while the main switch 14 is turned on. It is dangerous for workers on the load side because high voltage is supplied between the

An object of the present invention is to provide a constant current power supply device that protects the human body by including a cutoff circuit that immediately terminates such a dangerous situation.

This invention includes a first switch connected in series to an input line that receives power from an input terminal, and when an output current exceeds a predetermined first value, the first switch is closed and the output current is adjusted to a predetermined value. a first current detecting means that opens the first switch when the current falls below a second value; a second switch connected in parallel with the first switch; an activation switch; The second switch is closed when the current flowing through the activation switch exceeds a predetermined third value, and the second switch is opened when the current flowing through the start switch falls below a predetermined fourth value. 2
current detection means, the start switch and the second
and current detection means connected in series, and means for connecting the serially connected current detection means in parallel with the input terminal on the input terminal side from the first switch. a capacitor connected in series with the switch and a resistor connected in parallel with the capacitor; and in an initial state, when the start switch is closed, the current flowing through the second current detection means is determined by the predetermined value. The capacitor has a capacity necessary for the current to flow at least the predetermined third value, and the current flowing to the second current detection means after the capacitor finishes charging is equal to or less than the predetermined fourth value. The constant current power supply device is characterized in that the resistor has a resistance value.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a block diagram showing one embodiment of the present invention. In the present invention, a capacitor 17 is inserted in series with the start switch 14, and a resistor 18 for discharging the charge of the capacitor 17 is inserted in parallel therewith. In the present invention, when the start switch 14 is pressed down, the second relay 15 is excited only for a moment when a direct current flows through the capacitor 17, and the contact 15' of this relay is closed to operate the converter, and the output terminals 2, 2' This output current operates the first relay 7 inserted in series in the output circuit, and its contacts 7'
Continuous power supply is performed by closing.

Therefore, if the start switch 14 is pressed down during a failure such as a load cable break, the charge will accumulate in the capacitor 18 from this press down until the current flowing to the second relay 15 falls to the lowest current. The second relay 15 is energized only during the contact 1
5' is closed, voltage appears between output terminals 2 and 2', but no output current is supplied, so the first relay 7
is not excited. Therefore, when a certain amount of charge is stored in the capacitor 17, the relay 15 opens its contacts 15'. Therefore, even if the start switch 14 is continued to be pushed in, the voltage between the output terminals 2 and 2' disappears.

As explained above, according to the present invention, in a load open state such as a wire breakage, even if the start switch 14 is kept on, voltage appears at the output terminals 2, 2' only for a moment, so that the operator can It is possible to obtain a constant current power supply device equipped with a protection function.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional constant current power supply device.
FIG. 2 is a block diagram showing one embodiment of the present invention. 1, 1'...input terminal, 2, 2'...output terminal, 3...
Switching transistor, 4... Converter transformer, 5... Rectifier diode, 6... Smoothing capacitor, 7... First relay, 7'... Contact of first relay, 8, 9, 10... Resistor, 11... Reference voltage power supply , 12... Comparison amplifier, 13... Control circuit, 14...
Start switch, 15...Second relay, 15'...Contact of second relay, 16...Load, 17...Capacitor, 18...Discharge resistor.

Claims (1)

[Claims] 1 A first switch connected in series to an input line that receives power from an input terminal, and when the output current exceeds a predetermined first value, the first switch is closed and the output current increases to a predetermined second value. a first current detection means that opens the first switch when the current falls below a value of a second current detection that closes the second switch when the current exceeds a third predetermined value and opens the second switch when the current flowing through the start switch falls below a fourth predetermined value; and means for connecting the start switch and the second current detection means in series, and connecting the series connection in parallel with the input terminal on the input terminal side of the first switch. A constant current power supply device including a capacitor connected in series to the start switch and a resistor connected in parallel to the capacitor;
The capacitor has a capacity necessary for the current flowing through the second current detection means to exceed the predetermined third value when the start switch is closed in an initial state, and the capacitor has finished charging. The constant current power supply device is characterized in that the resistor has a resistance value such that the current flowing to the second current detection means after the second current detection means is equal to or less than the fourth predetermined value.