JPS61199416A - Short-circuiting protection circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application in Industry-1-] The present invention relates to a short-circuit protection circuit that cuts off conduction of an output element when an overcurrent in the output element is detected.

[Prior Art] Conventionally, as this type of short-circuit protection circuit, for example, the one shown in FIG. 2, which is packaged in an IC package, is known.

In this circuit, the output of the comparator 3 and the detection signal of the detection circuit 1 operate the Yamao transistor 7, which is an output element. When an overcurrent flows through the output transistor 7, that is, when an overcurrent flows through the load 22 connected to the output terminal 21, the potential of the overcurrent detection resistor 6 rises and the transistor 8 becomes conductive. When the charging/discharging capacitor 5 connected to the input terminal of the comparator 3 starts discharging due to the conduction of the transistor 8, the output of the comparator 3 closes the gates 1 and 2 and forcibly prohibits the conduction of the output transistor 7. Therefore, the potential of the overcurrent detection resistor 6 decreases. Since the transistor 8 becomes non-conductive due to this potential change, the charging/discharging capacitor 5 is charged by the power supply 23 via the resistor 4. This capacitor 5
When the voltage of the comparator 3 becomes higher than the reference potential due to the charging of The output transistor 7 can now be operated.

[Problem to be solved by the invention] However, in such an IC packaged short-circuit protection circuit, a capacitor of the required capacity is generally not connected to the IC.
Since the capacitor 5 cannot be formed in the form fg', the capacitor 5 becomes an external signal through a connecting pin. As a result, capacitor pins must be placed on the IC package, which increases the overall size of the IC package and increases its manufacturing costs. There was a problem with the increase in

SUMMARY OF THE INVENTION Accordingly, one object of the present invention is to provide a short-circuit protection circuit that is configured so that no capacitor is required and is suitable for use as a Tokan circuit.

In order to achieve the objective 1-1, the present invention includes an output element operated by a detection signal, an overcurrent detection circuit that detects an overcurrent of the output element, and an overcurrent detection circuit that detects an overcurrent of the output element. A memory circuit that stores a signal indicating that there is an overcurrent detected by the detection circuit, and a prohibition on guiding the detection signal to the output element when the memory circuit stores the signal indicating that there is an overcurrent. The present invention is characterized in that it includes a prohibition circuit and a signal generation circuit that generates a signal to periodically release the memory of the memory circuit.

[Function 1] Therefore, the present invention is a method for storing overcurrent of an output element by converting it into a digital circuit using a flip-flop or the like. While the conduction of the element is prohibited, the overcurrent memory of the flip-flop is periodically released by a pulse from a pulse generation circuit or a frequency-divided pulse thereof.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, which is applied to a photoelectric switch 24.

To explain the schematic configuration of this circuit, 16 is a detection circuit 14
This is an output transistor as an output element that is operated by a detection signal supplied from the antenna gate 1 through the gate 1 and gate 15. Reference numeral 17 denotes an overcurrent detection resistor that detects when the current flowing through the load 22 of the output transistor 16 is overcurrent, and this resistor 17 constitutes an overcurrent detection circuit with transistors 18, 19, inverter 13, etc. . 12
is a flip-flop that stores a signal indicating an overcurrent obtained by the overcurrent detection circuit. The memory of the flip-flop 12 is cleared by the output of the frequency dividing circuit 11 which divides the output of the pulse generating circuit IO.

Next, an example of the operation of the circuit shown in FIG. 1 will be explained.

When the pulse generating circuit 10 sends pulses to the light projecting element 9 such as an LED, the light emitted from the light projecting element 8 is completely received by the light receiving element 20. Depending on the detection state of the light receiving element 20, the detection circuit 14 generates an ON-OFF signal corresponding to the detection state.

Now, when the signal from the detection circuit 14 is applied to the base of the output transistor 16 through the AND gate 15,
Output transistor 16 becomes conductive.

At this time, when an overcurrent flows through the output transistor 16, that is, when an overcurrent flows through the load 22, the potential across the overcurrent detection resistor 17 increases by -1. As this potential rises, transistors 18 and 18 operate to generate an overcurrent detection signal. This overcurrent detection signal is supplied to the CR terminal of the flip-flop 12 via the inverter 13, so the flip-flop 12 is cleared, and the output Q of the flip-flop 12 closes the antagonal gate 15. As a result, the supply of the signal from the detection circuit 14 to the base of the output transistor 16 is stopped, so that the output transistor 16 changes from a conductive state to a non-conductive state.

Note that the transistor 18 disables the conduction of the lJj transistor 16 during the transmission delay time from when an overcurrent flows until the output transistor 1B disables conduction.

On the other hand, the pulse from the pulse generation circuit 10 that generates the driving pulse for the light emitting element 8 is frequency-divided by the frequency dividing circuit 11, and the frequency-divided pulse periodically passes through the flip-flop 12.
Since the overcurrent memory is canceled, Antogame 1/15 opens. Therefore, the output signal from detection circuit 14 is applied to the base of output transistor 16, causing output transistor 16 to conduct. Note that if the pulse period of the pulse generator 10 is long enough to protect the output transistor 16, the frequency dividing circuit 11 as shown in FIG. 1 is not necessary.

As described above, according to this embodiment, the overcurrent detection of the flip-flop 12 is memorized and the memorization is canceled by using the light projection and the pulse. This eliminates the need for external capacitors, thereby reducing the number of pins required for external capacitors when packaging an IC.

[Effects] As described above, according to the present invention, a memory circuit is provided that stores a signal indicating that an overcurrent has been detected, and a pulse generation circuit that periodically releases the memory of the memory circuit is provided. This eliminates the need for a capacitor when packaging the present invention into an IC package, and eliminates the need for external terminals for the capacitor, thereby making it possible to reduce the size and weight of the entire device.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional circuit. l...Detection iJj circuit, 2...And gate, 3...Comparator, 4...Charging resistor, 5...Charging/discharging capacitor, 6...Overcurrent detection resistor, 7... Output transistor, 8... Discharge transistor, 8... Light emitting element, 10... Pulse generation circuit, 11... Frequency divider circuit, 12... Flip-flop, 13... Input transistor. , 14... Detection circuit, 15... AND gate, 16... Output transistor, 17... Overcurrent detection resistor, 18... Output element protection transistor, 18... Overcurrent detection signal transmission transistor 20...light receiving element, 21...output terminal, 22...load, 23...power supply, 24...photoelectric switch.

Claims (1)

[Claims] 1) An output element operated by a detection signal, an overcurrent detection circuit that detects overcurrent of the output element, and a signal indicating that the overcurrent detected by the overcurrent detection circuit is stored. a storage circuit; a prohibition circuit that prohibits the detection signal from being guided to the output element when the storage circuit stores a signal indicating an overcurrent; and a prohibition circuit that periodically cancels the storage of the storage circuit. A short-circuit protection circuit comprising a signal generation circuit that generates a signal. 2) The short circuit protection circuit according to claim 1, wherein the signal generation circuit is a pulse generation circuit for generating a detection signal. 3) The short circuit protection circuit according to claim 1, wherein the signal generation circuit is a pulse frequency dividing circuit for generating a detection signal. 4) The short circuit protection circuit according to claim 1, wherein the memory circuit is a flip-flop.