JPH0524731B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a protection device for a power supply circuit having a rectifier circuit and a smoothing capacitor.

[Background of the invention]

As a countermeasure against inrush current, a structure is known in which a current-limiting impedance is inserted between the output side of the rectifier circuit 2 and the smoothing capacitor 3 as shown in Fig. 1, and a short-circuit is provided by a relay 5 as a short circuit during operation. It is. (Japanese Unexamined Patent Publication No. 58-9573) However, if the short circuit malfunctions, not only will the current limiting impedance 6 become abnormally heated, but also there will be a problem that sufficient power cannot be supplied to the load.

[Purpose of the invention]

The present invention has been made in view of these points, and it monitors the operation of the short circuit that short-circuits the current limiting impedance, and prevents the current limiting impedance from heating abnormally when the short circuit is not operating normally. In this way, a protection circuit for a power supply circuit is configured to suppress the current flowing through the current-limiting impedance.

[Summary of the invention]

That is, the present invention includes a rectifier circuit that inputs AC power, converts it to DC power, and outputs it, a smoothing capacitor that is connected to the output side of the rectifier circuit and smoothes voltage pulsations of the DC power, and an output of the rectifier circuit. A power supply circuit comprising: a current-limiting impedance connected between the smoothing capacitors and suppressing the charging current of the smoothing capacitor; and a short-circuit circuit that shorts both ends of the current-limiting impedance when activated. a standby means for outputting a signal after a predetermined time has elapsed based on a charging time constant determined by the current-limiting impedance and the smoothing capacitor from the time of input to the rectifier circuit; A short-circuit energizing means for activating the short-circuit circuit, and a voltage in either the current-limiting impedance or the smoothing capacitor in response to a signal from the standby means, which is generated in advance by a malfunction of the short-circuit circuit. a voltage detection means that outputs a signal when a predetermined value is reached; and a voltage detection means that responds to the input of the signal from the voltage detection means to prevent abnormal heating of the current-limiting impedance by controlling the current flowing through the current-limiting impedance. and a prevention means for suppressing the temperature to below a predetermined value.

The voltage detection means may be configured to detect the voltage across the smoothing capacitor, or may be configured to detect the voltage across the impedance.
Further, the blocking circuit may be configured to block the input side of the smoothing capacitor, or may be configured to block the output side of the smoothing capacitor.

Furthermore, the short circuit can be made non-contact by using a transistor, thyristor, etc.

[Embodiments of the invention]

The embodiment of the present invention shown in FIG. 2 will be described below. 1 is an AC power source, 2 is a rectifier circuit that rectifies the output of the AC power source 1, 3 is a smoothing capacitor that smoothes the output of the rectifier circuit, and 4 is an inverter as a DC load. 6 is a rectifier circuit 2 and a smoothing capacitor 3
This is a current-limiting impedance connected in series between the It is desirable to select the impedance value Z of this current limiting impedance to be much larger than the impedance value Zl of the load. Reference numeral 5 denotes a contact constituting a short circuit connected in parallel to the current limiting impedance 6, and is a contact that closes when the relay 5R is energized.

The relay 5a is connected to the AC power supply 1 in series with the energized close contact 9 of the auxiliary relay 9a.

8 is a timer as a standby means. This timer 8 is connected to the time constant determined by the smoothing capacitor 3 of the resistor 6, or
However, it is configured to output a signal when a predetermined time T has elapsed since charging was started by closing the contact 15.

Preferably, the predetermined time T is set to a time during which the smoothing capacitor 3 almost completes charging.

The output of this standby means 8 energizes the auxiliary relay 9R to close the contact 9, and energizes the relay 5R to close the contact 5.
While being used to close the circuit, it is also used as a command to start the operation of the voltage detection means 7. If necessary, a delay circuit is provided between the standby means 8 and the voltage detection means 7 so that the voltage detection means 7 outputs a detection signal after the contact 5 is closed. The voltage detection means 7 is configured to detect the voltage between both terminals of the smoothing capacitor 3.

When the voltage detection means 7 detects that the detected voltage is less than the predetermined value shown in equation (1), it cuts off the output of the base drive circuit 16 as a blocking means, stops the inverter 4, and closes the smoothing capacitor 3. As a result, new charging of the smoothing capacitor 3 is prevented.

V≒Zl/Zl+Z×E ……(1) However, E is the average value of the output voltage of rectifier circuit 2, 11
is an auxiliary power supply for the control circuit, and 15' is contact 1
This is a contact that operates in the same way as 5. The base drive circuit 16 is configured to operate after the energized close contact 9' of the relay 9R is closed.

Now, in the structure configured as above, contact point 1
5 is closed, power is supplied from the AC power supply 1 to the rectifier circuit 2. Due to this, smoothing capacitor 3
is charged via the impedance 6 to a value approximately equal to the average value of the output voltage of the rectifier circuit 2 with a time constant determined by the impedance 6 and the smoothing capacitor 3.

On the other hand, since the contact 15' is also closed along with the contact 15,
When the smoothing capacitor 3 completes charging, the standby means 8 outputs a signal to energize the relay 9R and close the contact 9. This energizes relay 5R, closes contact 5, and short-circuits impedance 6.

When the relay 9R is energized, the base drive circuit 16 also starts operating.

On the other hand, when a signal is output from the standby means 8, the voltage detection means 7 detects the voltage across the smoothing capacitor 3. As a result, if the voltage across both terminals of the smoothing capacitor 3 is equal to or higher than the predetermined value (V) in equation (1), the base drive circuit 16 continues to supply base signals to the inverter 4 in the scheduled order and continues operation. do.

However, when the short circuit 5 is not operating normally and the current limiting impedance 6 is not shorted, the voltage across the smoothing capacitor 3 cannot reach the predetermined value (V) shown in equation (1). Therefore, the voltage detection means 7 detects this and sends a signal to the base drive circuit 16 to stop the operation of the inverter 4.

Therefore, since no discharge occurs from the smoothing capacitor 3, no new charging is performed, and abnormal heating of the current limiting resistor 6 can be prevented.

Note that the standby means 8 functions to prevent the voltage detection means 7 from responding to the voltage across the smoothing capacitor 3 at the time of starting.

FIG. 3 shows a different embodiment of the invention. In this embodiment, current limiting impedances 6a and 6b are connected between the AC power source 1 and the AC input terminal of the rectifier circuit 2, and short circuits 5a and 5b are connected in parallel to the respective current limiting impedances.

In addition, the voltage detection means 7 has a current-limiting impedance 6
It is configured to detect the voltage drop of a. Therefore, in this case, when the short circuits 5a and 5b are operating normally, the voltage drop across the current limiting impedance 6a is almost zero, but when they are not operating normally, the voltage drop becomes larger than the predetermined value. .

Further, in this embodiment, when the voltage detection means 7 detects an abnormality, the relay 20R as a blocking means is operated to open the contact 20 which opens when energized.
It is configured so that a and 5b are opened.

〔Effect of the invention〕

As explained above, the present invention includes a rectifier circuit,
In a power supply circuit including a smoothing capacitor, a current limiting impedance, and a short circuit, a standby means;
Since short circuit energizing means, voltage detection means, and blocking means are provided, there is no malfunction when the power is turned on, and when the short circuit is not operating normally, the current flowing through the current limiting impedance is suppressed. Therefore, the current limiting impedance can be protected from abnormal heating.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an example of a conventional power supply circuit.
FIGS. 2 and 3 are circuit diagrams showing different embodiments of the protection device of the present invention. 3 is a smoothing capacitor, 5 is a short circuit, 6 is a current limiting impedance, 7 is a voltage detection means, 8 is a standby means, 16 is a base drive circuit as a blocking means, and 20 is a relay as a blocking means.

Claims (1)

[Scope of Claims] 1. A rectifier circuit that inputs AC power, converts it to DC power, and outputs it; a smoothing capacitor that is connected to the output side of the rectifier circuit and smoothes voltage pulsations of the DC power; A power supply circuit comprising: a current-limiting impedance connected between an output and the smoothing capacitor to suppress the charging current of the smoothing capacitor; and a short-circuit circuit that shorts both ends of the current-limiting impedance when activated. a standby means for outputting a signal after a predetermined time has elapsed based on a charging time constant determined by the current limiting impedance and the smoothing capacitor from the time when power is input to the rectifier circuit; and inputting a signal from the standby means. short-circuit energizing means for activating the short-circuit in response to a malfunction of the short-circuit; and short-circuit energizing means for activating the short circuit in response to a signal from the standby means; voltage detection means that outputs a signal when the resulting voltage reaches a predetermined value;
A protection device for a power supply circuit, comprising a blocking means for suppressing a current flowing through the current-limiting impedance to a predetermined value or less that prevents abnormal heating of the current-limiting impedance. 2. The power supply circuit protection device according to claim 1, wherein the blocking means is configured to receive a signal from the voltage detection means and cut off input to the rectifier circuit. 3. Claims characterized in that the blocking means is configured to input the signal of the voltage detection means and stop the switching operation of the inverter connected to the output side of the rectifier circuit. The power supply circuit protection device according to item 1.