JPH0419991Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to an inrush current prevention circuit for a DC/DC converter, and particularly relates to inrush current prevention during continuous re-opening operations of an input switch.

〔overview〕

This invention is designed to control the DC converter in a DC converter device equipped with an inrush current prevention circuit that limits the inrush current from the DC power supply with a series resistor when the input switch is turned on, and then shorts the series resistor with a relay contact. By prohibiting the circuit from operating below a predetermined power supply voltage, and by configuring the relay contact to operate depending on the presence or absence of AC output from this control circuit, no inrush current will occur even if the input switch is turned on immediately after being opened. It is designed to prevent this.

[Conventional technology]

In FIG. 2, which shows a block diagram of the conventional device, in order to limit the inrush current, the input switch 22 is closed, the input capacitor 25 is sufficiently charged via the inrush current prevention resistor 24, and then the inrush current is limited. , the relay 3 is activated by the output voltage of the limited power supply circuit 28 which is activated by the closing operation of the input switch.
0 is excited, the contact 23 is closed, and both ends of the inrush current prevention resistor are short-circuited to limit the inrush current.

In such a case, the open circuit voltage of the relay 30 is generally much lower than the operating voltage, so even after the input switch 22 is opened, the input capacitor 2
The relay does not open unless the discharge voltage of the input switch 5 becomes a considerably low voltage, and it takes more than one second for the contact 23 to open after the input switch is opened. However, the minimum interval between opening and closing of the input switch due to human operation is
It is extremely short, about 200ms. Therefore, if the opening and closing operations of the input switch are repeated too rapidly, the contact 23 of the relay will close after the input switch is released.
If the input switch is turned on again before the switch opens, an excessive rush current may occur.

[Problem that the invention attempts to solve]

As a result, there is a risk of welding of the input switch's contacts and malfunction of adjacent devices or logic circuits. To prevent this, it is necessary to specify in advance the time interval between when the input switch is released and when it is turned on again. There was a drawback.

It is an object of the present invention to eliminate such drawbacks and to provide a DC/DC converter device having an inrush current prevention circuit that follows the rapid re-opening operation of the input switch.

[Means for solving problems]

The present invention includes a DC converter circuit that generates DC current by converting input DC current into AC current, voltage conversion, and rectification, and an AC oscillator that branches the input DC current and uses it as a power source. A control circuit that provides an AC control signal to the circuit, a resistor connected in series to the input circuit of the DC converter circuit, a relay contact that shorts both ends of this resistor, and an input to the DC converter circuit and the control circuit. A DC/DC converter device comprising a relay circuit that keeps the relay contacts in an open state for a period of time from the start of supply of DC current until the activation of this control circuit, wherein the relay circuit The circuit is controlled depending on the presence or absence of an output, and is characterized by comprising a comparison circuit that stops oscillation of the AC oscillator of the control circuit when the voltage of the input DC current is below a predetermined value.

[Effect]

A relay circuit that controls shorting and opening of a resistor connected in series with an input circuit depends on the presence or absence of an AC control signal that controls a chopper of a DC converter. Further, when the input power supply voltage becomes lower than a predetermined value, control is performed to stop the oscillation of this AC control signal.

[Example] Next, an example of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of the above embodiment.

In Fig. 1, the input DC current of the input power source 1 is supplied to the DC converter 6 via the input switch 2, and the DC converter 6 converts this input DC current into an AC current, performs voltage conversion, and rectifies the DC current. is supplied to the load 7.

Furthermore, a control circuit 10 outputs an AC control signal to control the DC converter 6 using the input DC current as a power source, a resistor 4 connected in series to the input circuit of the DC converter 6, and a relay that shorts both ends of the resistor 4. A relay 15 is provided that keeps the relay contact 3 open for a period of time from when an input DC current is supplied to the contact 3, the DC converter 6, and the control circuit 10 until the control circuit 10 is activated.

Here, the feature of this invention is relay 15.
This is controlled by the presence or absence of the output of the AC control signal from the control circuit 10, and includes a comparison circuit 8 which stops the output of the AC control signal from the control circuit 10 when the voltage of the input DC current is below a predetermined value.

The control circuit 10 has two outputs; one is used to control the output of the converter 6 and the other is used to control the relay 15. Further, when the DC power supply voltage is low, the operation of the control circuit 10 is stopped without time delay by the comparison circuit 8.

Assuming that the input power supply voltage is V ₁ , the voltage at which the comparator circuit 8 operates is V ₂ , the capacity of the input capacitor 5 is C ₁ , the power consumed by the load 7 is P ₁ , and the converter efficiency is η, when the input switch is opened, Control circuit 10
The time τ ₁ until the output stops is expressed by equation (1).

τ ₁ = 1/2C ₁ (V ₁ ² −V ₂ ² )×η/P ₁ …(1) Also, the time τ ₂ from when the output of the control circuit 10 stops until the relay contact 3 is opened is the resistance It is determined by the resistance value R ₁ of R and the capacitance C ₂ of the capacitor 13, and its time constant τ ₂ is expressed by equation (2).

τ ₂ =R ₁ C ₂ (2) Therefore, the time τ 3 from when the input switch 2 is opened to when the relay contact 3 is opened is τ _{3 ≈τ 1} +τ ₂ (3).

Here, assuming that the time from when the input switch 2 is once opened to when it is suddenly turned on again is τ ₄ , the connecting/disconnecting operation of the input switch 2 is a manual operation, and usually τ ₄ ≧200 ms. Therefore, the values of τ ₁ and τ 2, that is, the capacitance of input capacitor 5 or capacitor ₁ , must be adjusted so as to satisfy the relationship τ ₃ ≒ τ ₁ + τ ₂ < τ ₄ (4).
By appropriately setting the capacity of 3, the time τ ₃ , that is, the period of operation time during which the relay 15 opens after the input switch 2 is opened, can be made shorter than the input switch operation time due to the input. Even if the relay 15 is suddenly turned on again, the contacts of the relay 15 can always remain open.

That is, even when the input switch is turned on again, the series resistor 4 is inserted between the input terminals, and the inrush current can be limited.

[Effects of the invention] As explained above, the present invention provides a DC/DC converter that has a highly safe inrush current prevention circuit that can reliably prevent inrush current even when the input switch is rapidly turned on again. You can get the equipment.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.
FIG. 2 is a block diagram of a conventional device. 1, 21... Input power supply, 2, 22... Input switch, 3, 23... Relay contact, 4... Resistor,
5, 25... Input capacitor, 6, 26... DC converter, 7, 27... Load, 8... Comparison circuit, 9, 28... Control power supply circuit, 10, 29...
Control circuit, 11, 12...Resistor, 13...Capacitor, 14...Transistor, 15, 30...Relay, 24...Inrush current prevention resistor.

Claims (1)

[Claims for Utility Model Registration] A DC converter circuit that generates DC current by converting input DC current into AC current, performing voltage conversion and rectification, and an AC oscillator that branches the input DC current and uses it as a power source. a control circuit that provides an AC control signal to the DC converter circuit; a resistor connected in series to the input circuit of the DC converter circuit; a relay contact that shorts both ends of the resistor; A DC/DC converter device comprising: a relay circuit that keeps the relay contact in an open state for a period of time from the start of supply of input DC current to the control circuit until the control circuit is activated; The circuit is controlled by the presence or absence of AC output of the control circuit, and is characterized by comprising a comparison circuit that stops oscillation of the AC oscillator of the control circuit when the voltage of the input DC current is below a predetermined value. DC/DC converter equipment.