JPS61245220A - Power supply circuit - Google Patents

Abstract

PURPOSE:To attain a power supply circuit with a compact size and low power consumption by detecting the change of the leakage magnetic flux of a transformer, etc. by a magnetic flux detecting circuit and comparing said change of the leakage magnetic flux with a reference signal for detection of an overcurrent. CONSTITUTION:The power is supplied to a load 6 from an AC power supply 1 via a transformer 2, a rectifying diode 3, a smoothing capacitor 4 and a limiting circuit 5 for output current. Then a detecting circuit 9 is added for detection of the leakage magnetic flux of the transformer 2 together with a reference power supply 8 and a comparator 7 which compares the signals sent from the circuit 9 and the power supply 8 with each other and outputs an overcurrent detecting signal. As the current flowing through the transformer 2 has the influence to the leakage magnetic flux of the transformer 2, this current is detected and the circuit 5 is actuated. Thus the overcurrent is prevented.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an overcurrent protection circuit for a power supply circuit.

, [Summary of the Invention] The present invention detects leakage magnetic flux of a transformer or inductor in a power supply circuit, and operates a current limiting circuit based on the difference from a reference signal, thereby eliminating the need for a resistor, etc. for current detection. In addition, the power loss caused by the current detection circuit is eliminated, making it possible to construct a highly efficient power supply circuit.

[Conventional technology]

In the conventional power supply circuit, the overcurrent protection circuit includes a regulator circuit 13, a current detection circuit 14 that detects the current flowing through the load 6, a reference signal generation circuit 15, a signal from the current detection circuit, and a signal from the current detection circuit and the A comparison circuit 7 that compares signals from the reference signal generation circuit and outputs an overcurrent detection signal.
and a current limiting circuit 5. This is a generally widely used method and is a well-known fact. In this method, a resistor, a current transformer, etc. have been used for the current detection circuit 14.

[Problems and Objectives to be Solved by the Invention Conventionally, as mentioned above, resistors, current transformers, etc. have been used in current detection circuits. However, in the case of using a resistor, a resistor is inserted in series with the load, which corrects the power loss caused by the inserted resistor. This power loss is extremely large, especially in small-capacity power supply circuits for small devices, and particularly in devices operated by batteries, it significantly shortens the battery life. Further, circuits using current transformers have the drawbacks of being large in size and high in cost.

The present invention is intended to solve these problems, and its purpose is to minimize the increase in power loss due to the insertion of a protection circuit, and to provide a low-cost, space-saving power supply circuit. The power supply circuit of the present invention is described in "Means for Solving the Problems."

a) In a power supply circuit having a transformer or inductor, b) Detecting leakage magnetic flux of the transformer or inductor,
a) a magnetic flux detection circuit that outputs a detection signal, C) a reference signal generation circuit that generates a reference signal, and d) a evaporative flux detection signal output from the magnetic flux detection circuit and a reference signal output from the reference signal generation circuit. Compare,
The present invention is characterized by comprising a comparison circuit that outputs an overcurrent detection signal, and a current limiting circuit that limits the output current.

[Effect]

Since the present invention is configured as described above, the magnetic flux detection circuit detects a change in the leakage magnetic flux of the transformer or inductor, and compares it with a reference signal to detect an overcurrent. This overcurrent detection signal can operate a current limiting circuit to prevent overcurrent.

[Example-1] The present invention will be described in detail below based on Examples.

Figure t41 is a block diagram of one embodiment of the present invention, and is an example of a circuit using the transformer 2. AC power supply 1, rectifier diode 5, smoothing capacitor 4, current limiting circuit 5 that limits the output current of the power supply circuit, load 6, leakage that detects leakage magnetic flux of the transformer and outputs a voltage or current signal corresponding to the leakage magnetic flux. It consists of a magnetic flux detection circuit 9, a reference power supply 8, and a comparison circuit 7 that compares the signals from the reference power supply and the leakage flux detection circuit and outputs an overcurrent detection signal. In this circuit, as long as current flows through the transformer, leakage flux will always exist. Since the leakage flux has a relationship with the current flowing through the transformer, it can be said that detecting the leakage flux is equivalent to detecting the current. Therefore, the leakage flux is detected and the leakage flux detection circuit Operating the current limiting circuit by comparing the detection signal with the reference signal can prevent overcurrent.Also, in this embodiment, the AC power supply 1 is connected to all AC power sources including commercial power supplies and switching power supplies. It refers to the power supply.

[Embodiment 2] FIG. 2 shows an embodiment of the present invention, which is a circuit for generating another DC voltage from a DC power supply. The configuration of this embodiment is as follows. A DC power supply 10, a regulator circuit 11 that creates all voltages other than the DC power supply 10, a load 6, an inductor 12 that serves as a filter to prevent fluctuations in the DC power supply 10 from being transmitted to the load 6, and a current flowing through the inductor. A leakage flux detection circuit 9 detects leakage flux and converts it into a current or voltage signal, a reference power supply 8, a current limiting circuit 5 for controlling the current flowing to the load 6, a detection signal from the leakage flux detection circuit and a reference. a comparison circuit 7 that detects an overcurrent by comparing it with a power supply 8 and operates the current control circuit;
In this embodiment, as in the first embodiment, there is a correlation between the current flowing through the inductor 12 and the leakage inductance, so overcurrent can be detected by detecting the leakage flux.

Therefore, the current limiting circuit can be operated due to overcurrent.

〔Effect of the invention〕

As described above, in the present invention, overcurrent detection is performed by detecting the leakage flux of a transformer or inductor that is correlated with the full load current, so the conventional overcurrent detection circuit is not necessary, and the overcurrent detection circuit is not required. Since the space occupied by the current detection circuit is no longer required and the power consumption of the overcurrent detection circuit is also eliminated, the power supply circuit can be miniaturized and power consumption can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the power supply circuit of the present invention, in which the power supply is AC and a transformer is used. FIG. 2 is a block diagram of an embodiment of the power supply circuit of the present invention, in which the power supply is direct current and an inductor is used. FIG. 3 is a block diagram of a conventional power supply circuit. 5... Current limiting circuit 7... Comparison circuit 8...
Reference power supply 9... Leakage flux blowing circuit 12...
・Inductor 14...: Current detection circuit 2...
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Claims (1)

[Claims] (1) a) In a power supply circuit having a transformer or inductor, b) Detecting leakage magnetic flux of the transformer or inductor,
A magnetic flux detection circuit that outputs a detection signal. c) A reference signal generation circuit that generates a reference signal. d) Comparing the magnetic flux detection signal output from the magnetic flux detection circuit and the reference signal output from the reference signal generation circuit;
A power supply circuit characterized by comprising: a comparison circuit that outputs an overcurrent detection signal e) a current limiting circuit that limits an output current.