JPH0681496B2 - Inrush current prevention circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inrush current prevention circuit for a capacitor input type circuit that inputs commercial alternating current, and in particular, inrush current prevention that operates effectively even in the case of short interruption of commercial alternating current. Regarding the circuit.

[Background of the Invention]

Examples of conventional inrush current prevention circuits for capacitor input type circuits that use commercial AC such as switching power supplies are as follows: "Design method of switching regulator and usage of power device", Seikodo Shinkosha, June 1981. As shown in Issue, P.154-155 etc., a parallel circuit of a resistor and a switch element is connected to the input source in series with the input capacitor, and the input source is connected through the resistor during the transition period A circuit is known in which power is sometimes supplied through a switch element.

However, in this conventional circuit, the timing of turning on / off the switch element is important, and if the timing is deviated, the intended inrush current prevention function cannot be achieved. For this reason, in order for this circuit to function sufficiently, it is necessary to monitor the input source or its equivalent and perform appropriate on / off control, but this point has not been fully considered. There was a problem that the control of turning on and off was not performed with attention to relatively short interruption of commercial AC input.

[Object of the Invention]

An object of the present invention is to provide a rush current prevention circuit which can sufficiently cope with any interruption of commercial AC input in a capacitor input type circuit such as a switching power supply which inputs commercial AC.

[Outline of Invention]

The present invention is a conventional in-rush current limiting element connected in series with an input capacitor and its element short circuit, a pulse generation circuit for generating a pulse synchronized with the frequency of the commercial AC input,
By providing a drive circuit for connecting or short-circuiting the current limiting element depending on the presence or absence of the pulse input,
This is an inrush current prevention circuit that can handle any momentary interruption of commercial AC input.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a circuit diagram showing an embodiment of an inrush current prevention circuit for a switching power supply circuit according to the present invention. This embodiment is an application example of the present invention to a switching power supply circuit, 1 is an input plug (outlet), 2A is a pulse generating circuit, 2 is a rectifying diode stack, 3 is a resistor, 4 is a zener diode,
5 is a photocoupler, 6A is a switching power supply circuit (conventional circuit), 6 is a rectifying diode stack, 7 is a resistor (current limiting element), 8 is an input capacitor, 9 is a diode, 10 is a transformer, 11 is a diode, and 12 is a choke coil. , 13 is a diode, 14 is a capacitor, 15 is a transistor, 16 is a thyristor (short circuit), 17 is a power output stabilization control circuit, 18 is a resistor, 19 is a transistor, 20A is a drive circuit, 20
Is a retriggerable one-shot multivibrator, 21,2
2 is an inverter, 23 is a NAND gate, 24 is an inverter,
A is the jump symbol.

First, in the switching power supply circuit (conventional circuit) 6A, the commercial AC input Vin from the input plug 1 is charged into the input capacitor 8 as an unstable DC through the rectifying diode stack 6. This DC charging voltage is applied to the switching transistor 15 driven by the power output stabilization control circuit 17.
Is converted to a high frequency voltage by the transformer, transferred to the secondary side through the transformer 10, and then the diodes 11 and 13 and the choke coil.
It is smoothed by 12 and the output smoothing capacitor 14 and returned to DC again. This DC output voltage Vout is fed back to the control circuit 17 for stabilizing the output voltage. As a rush current prevention circuit, a resistor (current limiting element) 7 and a thyristor (short circuit) 16 in parallel with the resistor 7 are connected in series to the input capacitor 8 in the power supply circuit 6A. When the switching transistor 15 operates, the transformer 10 is connected. The gate of the thyristor 16 is driven through the resistor 7 and the resistor 7 is short-circuited. Also transistor
When 15 is not operating, the thyristor 16 is cut off and the resistor 7 is connected.

There are two cases where the inrush current is generated in the power supply circuit 6A. The first is when the input plug 1 is inserted into the commercial AC supply unit (when the commercial AC input is turned on), and the second is when the commercial AC input Vin is momentarily interrupted and recovered (when the commercial AC input is interrupted). . In the first case, the conventional circuit has taken sufficient measures. That is, immediately after the commercial alternating current is turned on, the charging voltage of the input capacitor 8 is low, and the thyristor
16 cannot be driven as follows. If the control system of the control circuit 17 is operating with the DC-DC converted output with this charging voltage as an input, the switching transistor 15 should be driven because there is no voltage until the control system can fully operate. Therefore, the thyristor 16 is not driven.
Even if the transistor 15 can be driven, the driving voltage of the thyristor 16 is set to the number of turns of the transformer 10, so that power cannot be supplied enough to drive the thyristor 16 when the charging voltage of the input capacitor 8 is low. Furthermore, in practice, a commercially available power supply output stabilization control IC (control circuit 17
The following soft start function can be added from the outside to one component part), and by adding this soft start function, it is possible to more completely take measures against the inrush current suppression in the first case. This soft start function is a net transistor
It is a function to start the operation after waiting an arbitrary predetermined time after receiving the drive start signal of 15 and gradually increase the duty ratio.If the operation of the transistor 15 is further delayed by this soft start function, the duty ratio will be further increased. Is gradually increased, and the driving power of the thyristor 16 is not sufficient in the initial stage. When the thyristor 16 becomes drivable in this way, the charging voltage of the capacitor 8 is already in a steady state.

In the following second case, sufficient measures cannot be taken only by the conventional circuit having the above contents. That is, when the commercial AC input is interrupted and the charging voltage of the input capacitor 8 begins to drop,
The operation of the transistor 15 has a maximum duty ratio in order to secure an output voltage, and the thyristor 16 cannot be stopped unless the charging voltage of the input capacitor 8 is considerably reduced. Therefore, when the normal recovery occurs after a short interruption, the conventional circuit alone does not have the ability to suppress the inrush current. Therefore, in the present invention, even in the second case and for a short momentary interruption, the inrush current suppressing force is exerted as follows.

According to the present invention, therefore, a commercial AC input including the rectifying diode stack 2, the resistor 3, the zener diode 4, the photocoupler 5 as well as the resistor 18 and the transistor 19 in the above conventional circuit is monitored and the pulse synchronized with the frequency is monitored. Pulse generator circuit 2A that creates a one-shot multivibrator 20 and inverter connected to its output (interlace symbol A)
A drive circuit 20A in which a circuit for operating the control circuit 17 is added to the control circuit 17 unless a retrigger pulse is input for a set time of the one-shot multivibrator 20 including 21, 22, 24 and the NAND gate 23 is provided.

FIG. 2 is a signal waveform timing chart of the operation of each part of FIG. In FIG. 2, Vin is the waveform of the commercial AC input Vin, Va is the waveform of the output pulse signal Va of the pulse generation circuit 2A,
Vb is the waveform of the output signal Vb of the inverter 24, Vc is the waveform of the output signal Vc of the one-shot multivibrator 20, Vd is the waveform of the output signal Vd of the inverter 22, Ve is the waveform of the output signal Ve of the NAND gate 23, and Vf is the control. 6 is a waveform of the output signal Vf of the circuit 17. The operation at the momentary interruption of the commercial AC input in the second case of the present invention shown in FIG. 1 will be described with reference to FIG. The circuit of the rectifying diode stack 2, the resistor 3, the zener diode 4, and the photocoupler 5 of the pulse generation circuit 2A of FIG. 1 monitors the commercial AC input Vin such as the waveform Vin of FIG. 2 and, in the case of normal input, the photocoupler. The output of the light-receiving transistor 5 causes the commercial AC input Vin of the waveform Va in FIG. 2 via the resistor 18 and the transistor 19 connected to the low-voltage DC voltage Vcc.
A pulse signal Va synchronized with the AC frequency is obtained. Second
The period τ1 of the waveform Vin in the figure shows a momentary interruption of the commercial AC input Vin. The drive circuit 20A receives the pulse signal Va and first obtains the output signal Vb of the inverter 24 having the waveform Vb shown in FIG. The retriggerable one-shot multivibrator 20 receives the output signal Vb of the inverter 24 as a trigger pulse input and outputs the second signal.
The output signal Vc of the waveform Vc in the figure for a predetermined time is output.
From this output signal Vc, the output signal Vd of the inverter 22 having the waveform Vd shown in FIG. 2 is obtained, and from the output signal Vd and the output signal of the waveform Va of the inverter 21 shown in FIG. 1, the NAND gate 23 having the waveform Ve shown in FIG. To obtain the output signal Ve of. The power supply output stabilization control circuit 17 receives the output signal Ve and controls the output signal Vf. That is, when the output signal Ve of the waveform Ve of FIG. 2 is low level “L”, the output signal Vf of the control circuit 17 of the waveform Vf of FIG. 2 is turned off, and conversely the output signal Ve is of high level “H”. At the same time, the output signal Vf of the control circuit 17 turns on. However, even if the output signal Ve of the waveform Ve of FIG. 2 changes from the low level “L” to the high level “H” by the soft start function of the control circuit 17, the output signal of the control circuit 17 is accompanied by a predetermined time delay τ3. Vf will turn on. Further, the period τ2 of the output signal Vf of the waveform Vf of FIG. 2 is the commercial AC input V of the waveform Vin of the waveform of FIG.
Even if there is a momentary interruption during the period τ1 in the period τ2 from the moment when the momentary interruption starts, the one-shot multivibrator 20 operates as if there was no momentary interruption corresponding to the predetermined time and the period τ2.
Means the allowable interruption time. The operation of the switching transistor 15 is stopped during the off period of the output signal Vf of the control circuit 17 after the permissible instantaneous interruption time τ2, whereby the thyristor 16 is stopped.
Is stopped and the resistor 7 is connected, and the peak value of the inrush current at the time of recovery after the commercial AC input interruption is limited.

As described above, according to this embodiment, the commercial AC input is monitored by the switching power supply circuit 6A including the conventional resistor (current limiting element) 7 and its short circuit (thyristor) 16, and the pulse synchronized with the commercial AC frequency is detected. A pulse generating circuit 2A for generating a signal and a switching transistor 15 and therefore a thyristor 16 are controlled according to the presence or absence of the pulse signal to connect a resistor (current limiting element) 7 in series with the input capacitor 8 or short-circuit the resistor 7. By including the drive circuit 20A including the conventional power supply output stabilizing circuit 17, the instantaneous interruption detection can be accurately detected because the instantaneous interruption detection is pulse detection synchronized with the input commercial AC frequency. After the detection, a predetermined permissible instantaneous interruption time τ2 is provided so that the thyristor 16 of the short circuit is not opened within this permissible time. Resistance due to momentary interruption 7
It is possible to prevent power loss, heat generation, damage, etc., and to normally supply power to the load. Then, even when there is a short interruption of the commercial AC input, the allowable interruption time τ2
If there is more than this, be sure to use transistor 15 and therefore thyristor 16
The operation of is stopped and the resistor 7 is connected, so that the inrush current can be surely limited. Moreover, since the thyristor 16 is driven by the switching transistor 15 to drive the gate of the thyristor 16 via the transformer 10, the momentary interruption recovery inrush current is only the charging voltage of the input capacitor 8 and is equivalent to the load power. Since there is no overlap, the peak value of the inrush current can be suppressed accordingly. Although the current limiting element is described as the resistor 7 in the above embodiment, the current limiting element is not limited to the resistor and may be, for example, a thermistor. Although the short circuit is also made of the thyristor 16, it may be, for example, a triac, a relay or a transistor.

FIG. 3 is a partial circuit diagram showing another embodiment of the inrush current prevention circuit of the switching power supply circuit according to the present invention. This embodiment is another application example of the present invention to a switching power supply circuit similar to FIG. 1, 2B is a pulse generating circuit, 6B is an input part of a switching power supply circuit (conventional circuit) similar to FIG. 1, 25 Is a transformer, 26 is a rectifying diode stack, 27, 28 and 29 are resistors, and 30 is a transistor. The same reference numerals or symbols throughout the drawings indicate the same or corresponding parts. The pulse generation circuit 2B of FIG. 3 uses the photocoupler 5 for insulation between the primary and secondary circuits of the pulse generation circuit 2A of FIG. 1, but uses a transformer 25 to achieve the same purpose. . Others are the same as in FIG. The above two embodiments are examples of application to a switching power supply circuit, but the present invention is not limited to this and is generally applicable to any capacitor input type circuit for inputting commercial alternating current or the like.

〔The invention's effect〕

As described above, according to the present invention, it is possible to accurately detect the occurrence of a momentary interruption in a capacitor input type circuit using a commercial AC as an input, and to prevent loss of the current limiting element, heat generation, etc. within a permissible momentary interruption time to prevent a load. On the other hand, if the power supply can be continued normally and the interruption is longer than the allowable interruption time, the peak value of the inrush current at the time of recovery from the interruption can be surely suppressed. Since the recovery current inrush current is only the charging current of the input capacitor and there is no superposition of the load power, the peak value of the inrush current can be suppressed by that amount, so that there is an effect that the destruction and deterioration of the circuit element due to the current surge can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an inrush current prevention circuit according to the present invention, FIG. 2 is a signal waveform timing chart of each portion of FIG. 1, and FIG. 3 is a partial circuit diagram showing another embodiment of the present invention. Is. 1 …… Input plug, 2A, 2B …… Pulse generator circuit, 2 ……
Rectifier diode stack, 3 ... Resistor, 4 ... Zener diode, 5 ... Photocoupler, 6A ... Switching power supply circuit, 6 ... Rectifier diode stack, 7 ... Current limiting element (resistor), 8 ... Input capacitor, 10 …… Transformer, 15 …… Switching transistor, 16 …… Short circuit (thyristor), 17 …… Power output stabilization control circuit, 20A
...... Drive circuit, 20 …… One-shot multivibrator, 25 …… Transformer.

Claims (1)

[Claims] 1. A capacitor input type circuit for inputting a commercial AC input to an input capacitor through rectifying means and outputting load power through a switching element and a transformer, wherein the input capacitor is connected in series with the rectifying means and the input capacitor. A current limiting element connected to the current limiting element, a short circuit provided in parallel with the current limiting element and gate-driven via the transformer, and a pulse synchronized with the commercial AC frequency during normal operation by monitoring the commercial AC input. A pulse generation circuit that generates the pulse, and stops the operation of the switching element when a predetermined time elapses from the time when the pulse is input and the pulse input disappears, and the switching is performed with a predetermined time delay from the time when the pulse input is restarted. A rush current prevention circuit comprising a drive circuit for starting the operation of an element.