JPS63109515A - Power supply system - Google Patents

Abstract

PURPOSE:To prevent production of a defect such as repetitive on/off state of an output voltage to an overcurrent such as a very short time rush current by using a constant current protection and a fold-back protection against an overcurrent as required. CONSTITUTION:When a current given to a load 8 is larger than a preset current, a current sensing means 3 gives an output to activate a timer circuit 5 and a current limit circuit 7. The current limit circuit 7 receives an output of the current sensing means 3 so as to control an output transistor (TR)4 to limit a current flowing to a load 8 within a range of a prescribed current thereby applying constant current protection of a power system. On the other hand, a timer circuit 5 operated by an output of the current sensing means 3 activates the fold-back protection circuit 6 when an output of new overcurrent detection is given from the current sensing means 3 after the elapse of its setting time, e.g., one sec thereby suppressing the load current to a low value and protecting the power system.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a power supply system, and particularly to overcurrent protection in a power supply system.

(Prior Art and its Problems) Conventionally, in power supply systems, overcurrent protection has been implemented to prevent the output current from the power supply from flowing into the load in excess of a set value.

Overcurrent protection means include current suppression circuits and foldback protection circuits.

As the basic circuit of the current suppression circuit is shown in FIG. 2, the voltage drop across the current detection resistor R8 is equal to the transistor 0! If the voltage between the base and emitter of
A part of the base current is shunted to the output terminal to keep the load current at a constant value. This method has the disadvantage that the control transistor consumes a large amount of power in the event of an output short-circuit or overload, and even if the current exceeds the rated current value, it can be suppressed to the set value, so it is not suitable for systems using solar cells as the power source. When used in a system in which current changes are large, the transistors used must have a sufficiently large capacity, which poses problems such as cost amplification.

Some fold-pack protection circuits are also called "fold-back protection" and are basically configured as shown in Figure 3, in which the load current increases and the resistance 1? When the voltage drop across se becomes larger than the voltage drop across resistor R3 and the voltage between the base and emitter of transistor Q3 becomes a condition for turning on transistor Q3, the protection circuit operates and reduces the output current, preventing overcurrent. This is a useful means for eliminating system failures such as continuing.

However, the foldback protection circuit operates even with a temporary inrush current, causing problems such as the output voltage repeatedly turning ON and OFF, which adversely affects transistors and loads, such as welding of contacts and malfunction of the system. Furthermore, when the load includes a capacitor with a large capacity, if the rush current generated when the switch is turned on is greater than a set value, the circuit operates and the current becomes small, causing a problem that the capacitor is not sufficiently charged.

In addition, when a foldback protection circuit is used in a general power supply system, the overcurrent activates the protection circuit to reduce the current and turn off the load, so the load is turned off again. Requires maintenance work.

However, in the case of a system using a solar cell as a power source, it is required to be an unmanned system or a system that does not require maintenance, so it is not practical to configure the system using only a foldback protection circuit.

SUMMARY OF THE INVENTION An object of the present invention is to provide a DC power supply system that can solve the above problems and provide appropriate protection against overcurrent generation.

(Means for Solving the Problems) In order to solve the above problems, the present invention includes a DC power supply,
A power supply system comprising a load receiving power from the power supply, comprising a current detection means for detecting a load current flowing from the power supply to the load, an output transistor, a current suppression circuit, a faultback protection circuit, and a timer circuit, When the detection means detects a current exceeding the set value, the current suppressing circuit is operated to control the current by the output transistor, and after a predetermined period of time has elapsed, when the current detecting means detects a current equal to or higher than the set value again, the current is folded. The back protection circuit and the output transistor are operated to perform current control.

(Function) With the above configuration, when an overcurrent is detected by the current detection means, the current suppressing circuit suppresses the current flowing to the load and performs constant current maintenance.

If an overcurrent continues to flow even after a predetermined period of time has elapsed after the current suppression circuit operates, the foldback protection circuit is operated, so that the load current is suppressed to a low level.

If no overcurrent is detected after a predetermined period of time has elapsed after the current suppression circuit operates, the faultback protection circuit does not operate and the current suppression circuit does not perform constant current control.

(Example) Hereinafter, the power supply system of the present invention will be explained according to the drawings.

FIG. 1 is a block diagram showing the configuration of a power supply system that is an embodiment of the present invention.

In the figure, 1 is a solar cell, 2 is a storage battery, 3 is a current detection means, 4 is an output transistor, 5 is a timer circuit, and 6
is a fold bank protection circuit, 7 is a current suppression circuit, 8 is a load, and 9 is a reverse current prevention diode.

The foldback protection circuit 6 and the current suppression circuit 7 are the second
The circuit illustrated in FIG. 3 and FIG. 3 is used. The output transistor 4 corresponds to the transistor Q4 shown in FIG. 3, which is the transistor shown in FIG.

The current detection means 3 corresponds to the resistor R5 shown in FIG. 2 and the resistor R5C shown in FIG. 3.

The current detection means 3 outputs an output when the current flowing to the load 8 is higher than a preset current value, and operates the timer circuit 5 and the current suppression circuit 7. Current suppression circuit 7
The output transistor 4 is controlled by the output of the current detection means 3 to suppress the current flowing through the load 8 within a predetermined current range, thereby providing constant current protection for the power supply system. On the other hand, the timer circuit 5 operated by the output of the current detection means 3 operates the fold pack protection circuit 6 when a new overcurrent detection output is received from the current detection means 3 after the set time, for example, 1 second has elapsed. The foldback protection circuit 6 suppresses the load current to a low value to protect the power supply system. Here, the setting time of the timer circuit 5 is set taking into consideration the time required to prevent the foldback protection circuit 6 from operating due to an overcurrent such as a supply current, and is suitably about 1 second.

In other words, if the overcurrent continues to occur after a predetermined period of time has elapsed, it is determined that there is some kind of fault in the system, and the foldback protection circuit 6 is activated, allowing the system to return to normal operation after the cause of the fault is removed.

In the above embodiment, the current suppression circuit and the fold bank protection circuit shown in FIGS. 2 and 3 are used, but the circuit used in the present invention is not limited to this, and the It may also be configured using other circuits that perform foldback protection.

Further, in the above embodiment, an example was explained in which a solar cell was used as the DC power source, but the power supply system of the present invention may use a DC power source other than a solar cell.

(Effects of the Invention) As described above, the power supply system of the present invention is configured to use constant current protection and foldback protection against overcurrent as necessary. Problems such as the output voltage repeating ON-OFF with respect to current do not occur.

■The foldback protection circuit works to reduce the collector current of the output transistor during overload, so the collector loss of the output transistor during overload is small.
It does not impose an excessive burden on the equipment.

■Furthermore, the system can be stably protected even when overload continues for a long time.

It has various effects such as

Therefore, the present invention can sufficiently exhibit its effects in a power supply system installed in a place where maintenance and adjustment are extremely difficult, for example, a power supply system using solar cells.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a power supply system showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of a current suppression circuit, and FIG. 3 is a circuit diagram showing an example of a foldback protection circuit. . 3...Power supply detection means 4...Output transistor...Foldback protection circuit 7...Current suppression circuit

Claims (1)

[Claims] A power supply system comprising a DC power supply and a load supplied with power from the power supply, comprising a current detection means for detecting a load current flowing from the power supply to the load, an output transistor, a current suppression circuit, a faultback protection circuit, and a timer circuit. and when the current detection means detects a current equal to or greater than a set value, a current suppression circuit is operated to control the current by the output transistor, and after a predetermined period of time has elapsed, a current equal to or greater than the set value is again detected by the current detection means. 1. A power supply system characterized in that the power supply system is configured to operate a foldback protection circuit and the output transistor to perform current control when the power supply system is switched on.