JPH0226235Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a capacitor input type rectifying and smoothing circuit for various DC power supplies, and more specifically, a switch element is connected between the input end of a rush current prevention resistor and the other common line, and By controlling the conduction/non-conduction of the switch element with the discharge control section, the inrush current prevention resistor is used as a discharge resistor for the smoothing capacitor, and the charge stored in the smoothing capacitor is discharged when the power is cut off. The present invention relates to a capacitor input type rectifying and smoothing circuit that is devised so that voltage dangerous to the human body does not remain in the smoothing capacitor even if the casing is opened for repair or inspection by quickly discharging the battery.

In various DC power supply devices, one of the circuits for rectifying and smoothing AC input is a capacitor input type rectifying and smoothing circuit. The smoothing capacitor used here has a very large capacitance, and it varies depending on the input circuit configuration, output power capacity, etc.
It is used after being charged to a medium voltage of about several tens of volts or a high voltage of more than 100 to 200 volts. For this reason, an inrush current prevention resistor is provided on the input side of the smoothing capacitor in order to prevent an excessive charging current (usually called an "inrush current") from flowing immediately after the power switch is turned on. Also, immediately after the power switch is turned off, a large amount of charge is still stored in the smoothing capacitor and a high voltage remains, so it is important to remove the power supply casing for repairs, maintenance, or inspection. When opened, this smoothing capacitor is extremely dangerous to the operator.

A conventional capacitor input type rectifying and smoothing circuit of this type rectifies alternating current line input (AC) with a rectifying diode bridge 1, as shown in FIG. 1, for example.
It is configured to supply direct current output (DC) to the load side after smoothing with a large-capacity smoothing capacitor C. Usually, a discharge resistor with a relatively low resistance value is connected in parallel to the smoothing capacitor C. R ₁ is connected. In other words, with this discharge resistor R ₁ ,
When the power switch is turned off, the charge stored in the smoothing capacitor C is discharged as quickly as possible, and the terminal voltage of the smoothing capacitor C is forced to drop to zero.

However, in this case, if the resistance value of the discharge resistor _R1 is large, the smoothing capacitor C
The large amount of charge stored in the capacitor is slow to discharge, and there is a possibility that when the operator opens the case, a considerable amount of voltage may still remain in the smoothing capacitor. On the other hand, if the resistance value of the discharging resistor R ₁ is small, discharging will occur quickly when the power is turned off, but the discharging resistor R ₁ will also consume power even when the power supply is in normal operation. As a result, the efficiency of the power supply device deteriorates accordingly, and a large amount of heat is generated, making countermeasures troublesome.

Generally, the approximate resistance value of this discharge resistor _R1 is that the terminal voltage of the smoothing capacitor C will drop to a level that is not dangerous to the human body after about one minute has passed since the power switch is turned off. This discharge resistor must be
The value of R ₁ must be quite small, which has the drawback of increasing power loss during normal operation.

Further, between the rectifying diode bridge 1 and the smoothing capacitor C, a parallel circuit consisting of a switch element such as a thyristor TH and a rush current prevention resistor _R2 is usually installed. Here thyristor TH
is in the off state immediately after power is turned on, and the charging current to the smoothing capacitor C is connected to the inrush current prevention resistor R ₂
After the smoothing capacitor C has been charged to a certain extent, the thyristor TH becomes conductive to prevent power loss due to the inrush current prevention resistor _R2 . However, although this inrush current prevention resistor R ₂ is a fairly large component, it is required only immediately after power is turned on, and is completely unnecessary during normal operation of the power supply device.

The present invention was devised in view of the actual state of the prior art and to overcome its drawbacks, and its purpose is to suppress power loss as much as possible when the power supply device is in normal operation. In addition, when a worker opens the case to access the inside of the device for maintenance or repair after turning off the power switch, the charge accumulated in the smoothing capacitor has already been discharged. It is an object of the present invention to provide a capacitor input type rectifying and smoothing circuit which ensures sufficient safety for workers.

In this invention, the inrush current prevention resistor provided on the input side of the smoothing capacitor only needs to be present immediately after power is turned on, and its resistance value is set to a fairly small value.Furthermore, the smoothing capacitor The discharging operation only needs to be performed when the power is cut off, and its resistance value is quite low and may be approximately the same as the resistance value of the inrush current prevention resistor. Therefore, the inrush current prevention resistor is used as a discharge resistor. This was done with the focus on the fact that it can have multiple functions.

That is, the present invention, which can achieve the above objects, connects a switch element between the input terminal of the inrush current prevention resistor and the other common line, and allows a potential to remain in the smoothing capacitor.
In addition, a discharge control unit is provided that makes the switch element conductive when the AC input is lost, thereby preventing wasteful power loss during normal operation of the power supply, and quickly reducing the accumulation of the smoothing capacitor when the AC input is lost. This is a capacitor input rectifier and smoothing circuit designed to discharge electric charge using a resistor to prevent inrush current.

Hereinafter, the present invention will be explained in more detail based on the drawings. FIG. 2 is a circuit diagram showing the basic configuration of a capacitor input type rectifying and smoothing circuit according to the present invention. An alternating current input (AC) is rectified by a rectifying diode bridge 1, smoothed by a smoothing capacitor C, and supplied to the load side as a direct current output (DC). This smoothing capacitor C usually has a very large capacitance in order to perform a sufficient smoothing function, and in the case of line operation, a high voltage of 100 or more than 100 V or 200 or more V is used. A charge is applied and accumulated. Therefore, in order to prevent excessive current (rush current) from flowing into the smoothing capacitor C when the power is turned on, a rush current prevention resistor with a relatively small resistance value is installed between the diode bridge 1 and the smoothing capacitor C. A parallel circuit of R ₂ or a switch element such as a thyristor TH is incorporated. Here, as mentioned above, the thyristor TH is in a non-conducting state immediately after the power is turned on, and is then controlled to become conductive after a certain period of time has elapsed _. During normal operation, the thyristor TH conducts and operates to supply power to the smoothing capacitor C and the load side with almost no power consumption.

Now, in this invention, the inrush current prevention resistor
A discharge control unit that connects a switch element SW between the input terminal of _R2 and the other common line, and makes the switch element SW conductive when a potential remains in the smoothing capacitor C and there is no AC input. It has a configuration with 2. Here, the inrush current prevention resistor _R2 functions as a discharging resistor for discharging the charge accumulated in the smoothing capacitor C after the power switch is turned off. The switch element SW is in a non-conducting (OFF) state during normal operation of the power supply. The switch element SW may be any element as long as its conduction/non-conduction can be electrically controlled from the outside, but a transistor switch, for example, is suitable. Of course, it is also possible to use other electronic switches, such as thyristors, or electromagnetic relays. Further, the discharge control section 2
As mentioned above, it detects both that a potential dangerous to the human body remains in the smoothing capacitor C and that the AC input is lost due to shutting off the power switch, etc., and at that time, the switch element It performs an operation that makes SW conductive.

The operation of the circuit according to the present invention is as follows.
When the power is off, both the switch element SW and the thyristor TH are in a non-conductive state. Immediately after the power is turned on, the output rectified by the rectifier diode bridge 1 is current-limited by the inrush current prevention resistor _R2 , charges the smoothing capacitor C, and is supplied to the load side. When the terminal voltage of the smoothing capacitor C rises to a certain extent, the thyristor TH becomes conductive, and from that point on, the output rectified by the rectifying diode bridge 1 is supplied to the smoothing capacitor C and the load through the thyristor TH. . During normal operation of such a power supply, a large amount of charge is accumulated in the smoothing capacitor C at a considerably high terminal voltage. After that, when the AC input disappears due to shutting off of the power switch, etc., the discharge control section 2 operates to make the switch element SW conductive. As a result, the charge accumulated in the smoothing capacitor C is quickly discharged through the discharge route consisting of the inrush current prevention resistor _R2 and the switch element SW, and the terminal voltage of the smoothing capacitor C is applied to the human body. It rapidly reduces the amount to a point where it no longer poses a danger.

With this configuration, no power consumption occurs in the inrush current prevention resistor R ₂ during normal operation, except immediately after power is turned on or when the power is turned off. Also,
When the AC input is removed, the terminal voltage of the smoothing capacitor C quickly decreases, and there is no danger at all even if a worker opens the case and accesses the inside for maintenance, inspection, or repair. It is.

A specific embodiment of the capacitor input type rectifying and smoothing circuit according to the present invention is shown in FIG. Here, the second
The same reference numerals are given to the parts corresponding to the basic principle circuit diagram in the figure, and the explanation thereof will be omitted since it is redundant. In this embodiment, a transistor switch _Q1 is used as the switch element. Here, the configuration of the discharge control section 2 is as follows. The alternating current line input (AC) is rectified by two diodes _D1 , _D2 and passed through a current limiting resistor _R3 to a capacitor _C1.
is supplied to The capacitance of this capacitor _C1 is
This is very small compared to the capacitance of the smoothing capacitor C. The terminal voltage of capacitor _C1 is connected to the control transistor through base resistor _R4 .
Applied to the base of Q ₂ , the control transistor
_Q2 is connected in parallel between the base and emitter of the transistor switch _Q1 . As mentioned above, the transistor switch _Q1 is connected between the input terminal of the inrush current prevention resistor _R2 and the other common line, and its base is connected to a base bias circuit consisting of a resistor _R5 and a resistor _R6 . It is the composition.

The operation of the circuit shown in this embodiment is as follows. The operations of the inrush current prevention resistor R ₂ and the thyristor TH immediately after power-on and during normal operation are as described above. During normal operation of the device, the control transistor _Q2 is in a conductive state due to the potential charged in the capacitor _C1 , so that the base potential of the transistor switch _Q1 is approximately equal to the emitter potential. Therefore, it is in a non-conducting state. During normal operation of the power supply, current flows through the resistors R ₃ , R ₄ , R ₅ , and R ₆ , but since these resistors have fairly high resistance values, almost no power consumption occurs. Next, when the power switch is turned off, the AC input disappears and a fairly high terminal voltage remains in the smoothing capacitor C. As mentioned above, since the capacitance of the capacitor _C1 is small, if the power switch is turned off, the accumulated charge in the capacitor _C1 will be discharged by the base resistor _R4 and the control transistor _Q2 .
After a very short period of time, the control transistor
Q ₂ becomes non-conducting. Then, the divided voltage output of the base bias circuit consisting of resistors R ₅ and R ₆ is applied to the base of the transistor switch Q 1 and the base current flows into the base of the transistor switch Q ₁ .
Q ₁ becomes conductive. Therefore, the charge accumulated at the terminal of the smoothing capacitor C is rapidly discharged through the inrush current prevention resistor R ₂ and the transistor switch Q ₁ which is turned on, and the terminal voltage thereof quickly decreases. In this way, once the power switch is turned off, the terminal voltage of the smoothing capacitor becomes almost zero within a very short time, and the safety of workers accessing the inside of the device is sufficiently ensured.

Since the present invention is a capacitor input type rectifier and smoothing circuit configured as described above, the power loss during normal operation of the power supply is very small, which can contribute to improving the efficiency and miniaturization of the power supply, and it is necessary only immediately after the power is turned on. Since the inrush current prevention resistor is also used for discharging the smoothing capacitor when the power is turned off, it is possible to improve the efficiency of parts usage. When maintenance or repair is to be carried out, the electric charge accumulated in the smoothing capacitor is quickly discharged, so no dangerous voltage remains in the smoothing capacitor, and the worker is safe. It has many excellent effects, including ensuring sufficient safety.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of the prior art, Fig. 2 is a diagram explaining the principle of a capacitor input type rectifying and smoothing circuit according to the present invention, and Fig. 3 is a circuit diagram showing an example of its specific circuit configuration. be. 1... Rectifier diode bridge, 2... Discharge control unit, C... Smoothing capacitor, R ₂ ... Resistor for inrush current prevention, SW... Switch element, Q ₁ ...
Transistor switch, TH...thyristor.

Claims (1)

[Scope of utility model registration request] A capacitor input type rectifier and smoother comprising a rectifier diode that rectifies AC input, a smoothing capacitor that smoothes the output, and a rush current prevention resistor inserted between the rectifier diode and the smoothing capacitor. In the circuit, a switch element is connected between the input terminal of the inrush current prevention resistor and the other common line, and the switch element is made conductive when a potential remains in the smoothing capacitor and there is no AC input. A capacitor input type rectifying and smoothing circuit equipped with a discharge control section.