JPH0615295Y2 - Power supply protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a protection circuit for a power supply device, and more particularly, to a protection circuit for a DC power supply stabilization device or the like that copes with a sudden voltage drop or the like on the load side. Regarding

[Conventional technology]

In a power supply circuit, when the inrush current of the circuit is large, a circuit having a large-capacity capacitor C in the load and a large voltage is applied, as a means for lowering the level of the inrush current, for example, as shown in FIG. As shown in (a), a resistor R is connected in series to the output side of the drive circuit A, and the input end of the protection circuit B is connected between the resistor R and the large-capacity capacitor C. As described above, the input terminal of the protection circuit B such as a cutoff circuit is connected between the drive circuit A and the resistor R.

[Problems of conventional technology]

In the above circuit, depending on the value of the resistor R, the input voltage V for operating the protection circuit B when the load side is short-circuited
The condition for detecting ₁ becomes severe, and there is a problem that the protection circuit B may be delayed in operation or may not operate.

That is, in the circuit shown in FIG. 3A, the voltage V ₂
Rises with a time difference of t = CR due to the capacitance of the resistor R and the capacitor C as shown in FIG.
As shown in the figure (b), it is necessary to extend the forced driving time t ₀ of the limit value of V ₂ (threshold voltage of the protection circuit) V _x to t ₁ , which causes various problems. .

That is, as the above-mentioned adverse effect, when the power source is started with the load side short-circuited, the forced drive time t ₁ becomes long as shown in FIG. 4C, so that the high voltage state of V ₁ remains for a long time. Subsequently, the power supply circuit A is adversely affected by high heat generation and the like. The shorter as possible forced drive time t ₁ and will eliminate this adverse effect, V ₂ is given in a forced drive time t ₁ limit value V _x
There is a problem that the power does not turn on as shown by the dotted line in FIG.

Further, in the circuit shown in FIG. 3 (b), as shown in FIG. 4 (b), although the rise of V ₁ was earlier, even drastically voltage V ₂ was lowered by such as a short circuit of the load The resistance R causes a small change in V ₁ , and therefore the protection circuit B may not operate at all as shown in FIG. There is a defect that the element of the circuit A may be broken.

[Problems to be solved by the device]

Therefore, the present invention aims to provide a protection circuit for a power supply device that can reduce the input of the inrush current on the load side even when the inrush current is large, and can quickly respond to the fluctuation of the load voltage. It was done for the purpose.

[Means for Solving the Problems]

That is, the gist of the present invention is that in a circuit that outputs a DC power source via a drive circuit, two resistors having different resistance values are connected to the output side of the drive circuit, and a resistor having a large resistance value is connected to the drive circuit side. Is connected in series, and the input terminal of the drive circuit protection circuit is connected between the two resistors.

〔Example〕

 Next, this invention will be described with reference to examples.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.
(A) and FIG. 2 (b) are graphs showing the operational characteristics of the embodiment of the present invention.

A protection circuit 1 for a power supply circuit according to the present invention includes a resistance value R ₁ , R _{2 at} an output side A of a drive circuit 2 in an output circuit of a DC power supply via a drive circuit 2 such as a stabilized DC power supply circuit. Of the two resistors 3 and 4 having different resistances R ₁
A resistor 3 having a large (> R ₂ ) is connected in series as the drive circuit 2 side, and a protection circuit 5 for the drive circuit 2 having a function of interrupting in accordance with the voltage, for example, between the two resistors 3 and 4. The input terminal 5A of is connected.

[Action]

As shown in FIG. 1, assuming that the voltage between the drive circuit 2 and the resistor 3 is V ₁ and the voltage on the load side is V ₂ , R = R ₁
From + R ₂ On the other hand, if the voltage across the resistors 3 and 4 is X _x That is, the voltage when the load side is short-circuited is controlled by R ₂ as is clear from the above formula.

In the above, if R ₁ <R ₂ , then V _x ≈V ₁
Therefore, it becomes difficult to detect the voltage change.

Therefore, it is essential that R ₁ > R ₂ .

If this state is shown by a graph, it becomes as shown in FIGS. 2 (a) and 2 (b).

That is, the rising characteristics of the load side when the current inrush by two resistors R _1, R _2, next to V ₂ shown in FIG. 2 (b),
The rising characteristic of the detection voltage becomes V _{x due} to the resistor R _{2 in the} above equation.

Then, when the load short-circuit is V _x late to lowering of the load voltage V ₂ is lowered the descending order with respect to V ₂ is relaxed delay of rise characteristics, the detection is rapid,
For example, as shown in FIG. 2B, if the circuit break is activated when the voltage _reaches V _xo , the drive circuit 2 is cut off after the time t _xo .

[Effect of device]

Since the invention and the configuration as described above are adopted, the voltage change detection capability is V _x =, even though the overall resistance R (= R ₁ + R ₂ ) can be a high resistance value. Therefore, the inrush current can be surely detected, and at the same time, when the load side is short-circuited, it is possible to react quickly to operate the protection circuit. Further, the invention of the present application can be implemented by simply dividing the conventionally used resistor into two resistors, and thus has various practical effects such as easy implementation.

[Brief description of drawings]

FIG. 1 is a block diagram of the configuration of an embodiment of this invention, and FIG.
(A) and (b) are graphs showing the operation characteristics of the circuit of the present invention, FIG. 3 (a) (b) is an explanatory block diagram of a conventional example, and FIG. 4 (a) (b)
(C) and (D) are graphs showing the action characteristics of the conventional example. 1 ... Power supply circuit protection circuit, 2 ... Drive circuit, 2A
...... Output side, 3,4 ...... Resistance, 5 ...... Protection circuit, 5A ...
… Input end.

Claims (1)

[Scope of utility model registration request] 1. In a circuit for outputting a DC power supply via a drive circuit, two resistors having different resistance values are connected in series on the output side of the drive circuit, with a resistor having a large resistance value as the drive circuit side. A protection circuit for a power supply device, comprising an input terminal of the drive circuit protection circuit connected between the two resistors.