JPH0398422A - Dc power supply circuit - Google Patents

Abstract

PURPOSE:To prevent the damage of circuit parts in a load positively by detecting the potential difference across a resistor inhibiting DC supply currents at a time when a power supply is turned ON and turning a switching means ON when the potential difference is brought to a certain value or less. CONSTITUTION:When potential at a point D gradually rises and the potential difference across a resistor R1 is brought to a set value or less, a transistor TR is brought to an OFF state, charging of a capacitor C3 in a timer circuit T1 is started, and timing is started by the timer circuit T1. When a set time expires and inversion input terminal voltage to a comparator U2 is made larger than reference voltage, an output from the comparator U2 is changed over from a High level to a Low level. Consequently, a current is made to flow through the phototransistor of a photo-TRIAC E3, and the contact of a relay K1 is brought to an ON state. Accordingly, current charged to a capacitor C1 is charged directly through the contact of the relay K1, thus completing soft charging.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a DC power supply circuit having a soft charge function for a load when power is turned on.

[Prior Art] Generally, when supplying DC power to a load, in order to prevent damage to capacitors, ICs, etc. in the load due to inrush current when the power is turned on, a resistor is used to suppress the inrush current while supplying power to the load. A so-called soft charge function is used, which charges the capacitor of the battery and supplies power directly after charging.

A conventional DC power supply circuit having such a soft charge function is shown in FIG. 3 (circuit diagram). This circuit uses a timer circuit T to perform circuit switching from power-on to after completion of soft charging. There is.

In Figure 3, l is the load to be supplied with DC power (
MC is a magnetic contactor that is turned on (closed) when the power is turned on.
DB is a rectifier circuit (DC power supply) that outputs DC power by rectifying the AC power (e.g., 3-phase 200 V) input via the magnetic contactors M and C through 3-phase full-wave rectification, and C1 is the load 1 and the rectifier circuit DB. A capacitor K1 is provided between the rectifier circuit D and smooths the DC power from the rectifier circuit D.
Relay (switching means) installed on the output side of B, R↓
is a soft charge resistor that is connected in parallel with relay K1 and suppresses the DC supply current when the power is turned on.

Further, K2 is a relay contact that turns on in conjunction with the on state of magnetic contactor MC, and T is a predetermined time t from when the power is turned on, that is, when relay contact K2 is turned on.
This timer circuit T is composed of a resistor R2, a capacitor C2, and a comparator U1. In this timer circuit T, a comparator U1 receives a voltage that rises at a predetermined time constant set by a resistor R2 and a capacitor C2 through an inverting input terminal, and compares it with a reference voltage v2. When the limit is exceeded, the output is changed from High level to Low level.
This is to switch to the level.

Furthermore, E1 has the output from comparator Ul as Lo%l
When the level is reached, it operates and switches relay K1 to the on state.
This is a phototrial drive. With the above configuration, the conventional circuit operates as shown in FIG. That is, when supplying power to the load 1, first the magnetic contactor MC is turned on. In conjunction with this, the relay contact K2 is also turned on. At this point, Relay K? is in the off state.

When the magnetic contactor MC is turned on, the input AC power (three-phase AC) is full-wave rectified by the rectifier circuit DB, and then passes through the resistor R1 to soft charge the capacitor Cl. At the same time, relay contact K2 is turned on, and charging of capacitor C2 in timer circuit T is started. The charging time depends on the resistance value of resistor R2 and capacitor C.
It is determined by the capacity of 2. As charging of the capacitor C2 progresses, the potential at point A rises, and after time t (predetermined time constant) has passed, the inverting input terminal voltage to the comparator U1 becomes larger than the reference voltage v2, the output of the comparator U1 changes from the High level. Switch to Lotz level. As a result, current flows through the phototransistor of phototriac El, turning on the triac of phototriac E1 and turning on (closed) the contact of relay K1.
become a state.

Therefore, the current that had previously been charged to the capacitor C1 through the resistor R1 is now directly charged through the contacts of the relay K1, and soft charging is completed at this point. [Problem to be solved by the invention] However, in the conventional DC power supply circuit described above,
As shown in FIG. 4, after the power is turned on, when a preset time te has elapsed by the timer circuit T, the capacitor Cl
Soft charging is completed regardless of the voltage level charged to the battery.

Therefore, if the primary impedance is larger than the expected value, soft charging may be completed before the voltage of capacitor CL has risen sufficiently (state where the potential difference ΔV shown in Figure 4 is large). In such a case, an overcurrent will flow through the rectifier diode and the contacts of the magnetic contactor MC, causing damage.

Further, for example, it cannot cope with a case where an open phase occurs in an external AC power source, and there is a possibility that circuit components in the load 1 may be damaged as described above.

Conventionally, in order to reliably avoid damage accidents such as those mentioned above,
The time t1 set by the timer circuit T should be long enough, but if it is set too long, the device (load 1)
The problem arises that it takes too long to start up.

The present invention has been made to solve the above-mentioned problems, and provides a DC power supply circuit that can reliably prevent damage to circuit components in a load while performing soft charging in the minimum necessary time. The purpose is to

[Means for Solving the Problems] In order to achieve the above object, the DC power supply circuit of the present invention includes a DC power supply, a switching means provided on the output side of the DC power supply, and a circuit connected in parallel with the switching means. A resistor for suppressing a DC supply current when the power is turned on and a detection means for detecting a potential difference across the resistor are provided, and the switching means is operated in response to a detection signal from the detection means to supply a predetermined DC supply current to the load. It is characterized by supplying

[Function] In the DC power supply circuit of the present invention described above, when the power is turned on to supply power from the DC power source to the load, the switching means is turned off, so that the power from the DC power source passes through the resistance. It is supplied to the load while being suppressed. At this time, the detection means detects the potential difference between both ends of the resistor, and when the potential difference becomes less than a certain value, the switching means is turned on, thereby supplying a predetermined DC supply current to the load.

[Embodiments of the Invention] A DC power supply circuit as an embodiment of the present invention will be explained below with reference to the drawings.
The figure is a timing chart for explaining the operation. Note that in FIG. 1, the same reference numerals as those already described indicate the same parts, so their explanation will be omitted. In this embodiment, as shown in FIG. 1, a photocoupler (detection means) E2 capable of detecting the potential difference across the soft charge resistor R1 (difference between the potential at point C and the potential at point D) is connected to the resistor R1.
are connected in parallel. This photocoupler E2 holds the transistor TR on the output side in the on state when the potential difference is larger than the set value V1, and turns off the transistor TR when the potential difference becomes smaller than the set value Ve. It operates to switch. The transistor TR is used to switch the inverting input terminal potential (potential at point E) of the comparator U2 of the timer circuit T1, which will be described later, to the ground, and is grounded in the on state and ungrounded in the off state.

Further, Tl is a timer circuit that starts counting a predetermined time t2 when the relay contact K2 is turned on and the transistor TR is turned off, and this timer circuit T1 is connected to the resistor R3.
, a capacitor C3 and a comparator U2. In this timer circuit T1, the comparator U
2 receives a voltage that rises at a predetermined time constant set by a resistor R3 and a capacitor C3 through an inverting input terminal and compares it with a reference voltage v2, and when the voltage exceeds the reference voltage v2, the output is changed to I. {This is for switching from high level to low level.

Further, E3 is a phototriac that operates when the output from the comparator U2 becomes Low level to switch and drive the relay K1 to the on state.

Since the DC power supply circuit of this embodiment is configured as described above, it operates as shown in Figure 2. That is, when supplying power to the load 1, first the magnetic contactor MC is turned on. In conjunction with this, the relay contact K2 is also turned on. At this point, relay K
1 is in the off state.

When the magnetic contactor MC is turned on, the input AC power (three-phase AC) is subjected to three-phase full-wave rectification in the rectifier circuit DB, and then passes through the resistor R1 to soft charge the capacitor C1. As a result, the potential at point D begins to rise. In this embodiment, the difference between the potential at point D and the potential at point C, that is, the potential difference across the resistor R1 is monitored by the photocoupler E2, and as shown in FIG. The transistor TR of the photocoupler E2 is kept in the on state until the following occurs. Therefore, even if the relay contact K2 is turned on when the power is turned on as described above, the potential at point E is O and the capacitor C3 is not charged. As the capacitor C1 is soft-charged, the potential at point D gradually rises, and when the potential difference across the resistor R1 becomes less than the set value Ve, the transistor TR turns off and the timer circuit Tl is turned off, as shown in Figure 2. Charging of the capacitor C3 is started, and the timer circuit T1 starts counting the time t2. This time t2 is determined by the resistance value of the resistor R3 and the capacitance of the capacitor C3. Capacitor C3
As charging progresses, the potential at point E rises, and after time t2, the voltage at the inverting input terminal to comparator U2 reaches the reference voltage v.
2, the output of comparator U2 becomes H
Switches from high level to low level.

As a result, current flows through the phototransistor of phototriac E3, turning on the triac of phototriac E3 and turning on (closed) the contact of relay K1.
become a state. Therefore, until then, the capacitor C1 is charged through the resistor R1? The current that was being used will be directly charged through the contacts of relay K1, and at this point soft charging is completed.

Here, since the potential at point C actually has a ripple as shown in FIG.
When the potential difference across the resistor R1 approaches the set value V, a chattering state may occur in which the resistor R1 repeatedly turns on and off.
Therefore, in this embodiment, a timer circuit T1 is provided to measure the time t2 after the transistor TR is turned off, and then complete the soft charge, thereby absorbing the flapping caused by the chattering. Since the timer circuit T1 has such a function, the set time t2 in this embodiment
is set much shorter than the set time t■ in the conventional timer circuit T.

In this way, according to the DC power supply circuit of this embodiment, the difference between the directly charged secondary side voltage level and the primary side voltage level, that is, the potential difference across the resistor R1, is applied to the photocoupler E.
2, and the soft charging of the capacitor C1 is completed after the potential difference between both ends becomes equal to or less than the set value V■.

Therefore, as in the past, if the potential difference between points C and D is too large due to impedance on the primary side or an open phase due to damage to the power on/off contact (contact of magnetic contactor MC), the relay K1 is no longer switched to the on state, and it is possible to reliably prevent overcurrent from flowing into the power supply circuit and damaging circuit components upon completion of soft charging.

In addition, the timing at which soft charging is completed changes depending on the potential difference across the resistor R1, and can be freely adjusted to the primary side voltage level, impedance, and circuit status, and the soft charging time after power is turned on changes. It can be minimized. [Effects of the Invention] As described in detail above, the DC power supply circuit of the present invention includes a detection means for detecting the potential difference across the DC supply current suppression resistor when the power is turned on, and the detection from the detection means According to the signal, the switching means (connected in parallel with the resistor on the output side of the DC power supply) is operated to supply a predetermined DC supply current to the load, so soft charging can be performed in the minimum necessary time. While doing so, it is possible to reliably prevent damage to circuit components within the load using a simple and inexpensive circuit.

[Brief explanation of drawings]

1 and 2 show a DC power supply circuit as an embodiment of the present invention, FIG. 1 is its circuit diagram, FIG. 2 is a timing chart for explaining its operation, and FIG.
FIG. 4 shows a conventional DC power supply circuit, FIG. 3 is a circuit diagram thereof, and FIG. 4 is a timing chart for explaining its operation. In the figure, ■-・Load, C 1 , C 3-・-・
Capacitor, DB-1 rectifier circuit (DC power supply). E2-
Photocoupler, E3---Phototriac, K
l-...Relay (switching means), K2--relay contact, MC-=magnetic contactor, R1--soft charge resistor. R3 - Resistor, T1 - Timer circuit. T.R. -・One transistor, U2...-Comparator.

Claims (1)

[Claims] A detection device includes a DC power supply, a switching means provided on the output side of the DC power supply, and a resistor connected in parallel with the switching means to suppress the DC supply current when the power is turned on, and detecting a potential difference between both ends of the resistor. A DC power supply circuit comprising means for operating the switching means in response to a detection signal from the detection means to supply a predetermined DC supply current to a load.