JPH03269265A - Power limitation detecting circuit - Google Patents

Abstract

PURPOSE:To detect a trouble causing circuit breakdown accurately by comparing the level of the output voltage of a multiplier with the level of a reference voltage, and outputting a detected limitation signal when the voltage at the level exceeding the reference voltage is inputted. CONSTITUTION:A current detecting means 11 converts a current to be detected I into the voltage and detects the voltage. A voltage to be detected V and the output voltage of the detection means 11 are multiplied in a multiplier 12. In a comparator 13, the level of the output voltage of the multiplier 12 and the level of the preset reference voltage are compared. When the output of the multiplier 12 at the level exceeding the reference level is inputted, the detected limitation signal is outputted. Then, a trouble can be detected even in the case wherein a power-supply voltage is largely changed and an output transistor might be broken even if the current is small. Thus, the trouble causing circuit breakdown can be detected accurately.

Description

[Detailed Description of the Invention] [Summary] Detects whether measured power exceeds a predetermined limit range.
Regarding FJ's power limit detection circuit, in order to more accurately detect circuit damage defects, we have developed a current detection means that converts the current into a voltage and detects the voltage to be detected. A multiplier that multiplies the output voltage of the current detection means and the output voltage of the @Fi device and a preset reference voltage are compared in level, and a limit is set when the output voltage of the multiplier is input at a level higher than the reference voltage. It consists of a comparator that outputs a detection signal.

[Industrial application field]

The present invention relates to a power limit detection circuit, and more particularly to a power limit detection circuit that detects whether or not measured power exceeds a predetermined limit range.

Amplifier output 1 - In order to operate with high reliability without damaging or deteriorating the transistor, the load current etc. must be within the limit range so that the transistor operates within the safe operating area (ASO). It is necessary to detect whether or not the limit has been exceeded.

[Conventional technology]

FIG. 4 shows a circuit diagram of an example of a conventional current limit detection circuit. In the figure, Tr is an NPN1 transistor (hereinafter referred to as output 1 transistor) in the output stage of the amplifier, its base is connected to input terminal 1, and its collector is a detection resistor R.
9, whose emitter is connected to the load R1-, and the power supply side terminal of the detection resistor R8 is connected to the non-inverting input terminal of the differential amplifier A1 via the resistor R1, and the detection resistor R8 is connected to the non-inverting input terminal of the differential amplifier A1. The connection point between output 1 and the resistor of transistor lr is connected to the inverting input terminal of differential amplifier A1 via resistor R2. Further, the output terminal of the differential amplifier Δ1 is connected to the output terminal 2, and is also connected to the inverting input terminal of A1 via a resistor R4. Further, the non-inverting input terminal of the differential amplifier A1 is grounded via a resistor R3.

In a circuit having such a configuration, the rector current and emitter current of the output I/transistor l'r change depending on the information signal input to the terminal 1. Since the collector current 1c of the output 1 to the transistor Tr is approximately equal to the emitter current flowing through the load RL, a detection voltage Vs (= It-・Rs
) occurs, this detection voltage Vs is connected to the resistors R+, R
2 to the differential amplifier A+, where it is differentially amplified.

In other words, the non-inverting input terminal of the differential amplifier A1 has v8·R3/ which is obtained by dividing the power supply voltage VB with resistors R1 and R3.
(R1-(-R3) voltage is input, differential amplifier Δ
A voltage VB-1t-.Rs is input to the inverting input terminal of No. 1. Therefore, when the current 11- from the differential amplifier A1 is smaller than the reference voltage expressed by VB・R+/((R+ −1−R3)・Rs), it is at the ll L II level, and when it is higher than the reference voltage, it is at the it H11 level. Voltage Vo
is taken out and output to terminal 2.

Therefore, the current 1 + - versus output voltage V of the current limit detection circuit of FIG. The characteristics of the circuit are as shown in FIG. 5, and when the output voltage Vo exceeds the reference voltage, this circuit detects it as an abnormal state in which the current 11- flows beyond a predetermined value.

(Problem to be Solved by the Invention) However, since the above-mentioned conventional circuit detects only the load current TL, if the power supply voltage Vo fluctuates for some reason under load fluctuations or poor power supply performance conditions, the voltage may change. It is not possible to detect that the voltage exceeds a predetermined value and may destroy the output 1 transistor Tr.

The present invention has been made in view of the above points, and an object of the present invention is to provide a power limit detection circuit that can more accurately detect circuit breakdown defects.

[Means to solve the problem]

FIG. 1 shows a basic configuration diagram of the present invention. In the figure, 11 is a single current detection stage, which converts the current 1 to be detected into a voltage and detects it, and 12 is a multiplier, which multiplies the voltage V to be detected and the output voltage of the current detection means 11. 11 Now. A comparator 13 compares the levels of the output voltage of the multiplier 12 and a preset reference voltage, and outputs a limit detection signal when the output signal of the multiplier Q device 12 whose level is higher than the reference voltage is input.

[Effect]

In the present invention, the multiplier 12 extracts a multiplied signal of the current l to be equivalently detected and the voltage V to be detected, that is, a signal corresponding to electric power. Therefore, this multiplier 12
By comparing the level of the output voltage with the reference voltage by the comparator 13, a limited detection output including not only the current to be detected but also the voltage to be detected can be obtained.

〔Example〕

FIG. 2 shows a circuit diagram of an embodiment of the present invention. In the same figure, the same components as in FIGS. 1 and 4 are designated by the same reference numerals.
In FIGS. 1 and 2, the explanation of which will be omitted, the differential amplifier A
The non-inverting input terminal of No. 3 is connected to the power supply terminal via the resistor R+, and the inverting input terminal thereof is connected via the resistor R2 to the connection point between the current detection resistor Rs and the collector of the output transistor Tr. Its output terminal is connected to the input terminal Y of the multiplier 12.

The multiplier 12 applies the power supply voltage Ve to the input terminal
Outputs a voltage with a value of 10i8. The output terminal / of the multiplier 12 is connected to the non-inverting input terminal of the comparator A4 via a resistor R6. In addition, the inverting input 9i of the comparator △4 is connected to the quasi voltage V ref via the resistor R7.
It is connected to the output terminal 2 via a resistor R5.

In the circuit configured as described above, a current IL corresponding to the current to be detected flowing through the load RL is detected in the form of a voltage VS across the current detection resistor RS. Therefore, the differential amplifier A
The power supply voltage Vn is supplied to the non-inverting input terminal of No. 3 through the resistor R1, and (VB-V
A voltage S) is supplied via the resistor R2, and thereby the above-mentioned detection voltage Vs is supplied to the input terminal Y of the multiplier 12 through the differential amplifier Δ3.

The multiplier 12 receives the current 1 to be detected inputted to the input terminal Y.
The detection voltage ■S obtained by converting + into a voltage is multiplied by the power supply voltage Vn to be detected inputted to the input terminal X, multiplied by 0, and the result is ■5-VB.
A voltage of /10 is generated and supplied from the output terminal Z to the non-inverting input terminal of the amplifier A4 via the resistor R6.

] Comparator A4 compares the levels of this input voltage 5-VB/10 with a preset reference voltage Vref, and when the human-powered type 1]] is smaller than the reference voltage Vrcf by 4c, the level is set to ``L'' level. When the voltage is equal to or higher than vrer, an output voltage V of the level 'I' is generated and output to the output terminal 2.

Therefore, the input/output characteristics of this embodiment are as shown in FIG. 3, and the reference voltage Vref' (=10-Vrc4
) or more is extracted from the multiplier 121,
11 A limit detection signal of HI+ level is output to terminal 2. The output voltage of the multiplier 12 is the current to be detected I
Since it is the product of L and detection 1 - power supply voltage VB, that is, a value that corresponds to the power, in this embodiment, if J:, power limit detection can be performed, and therefore, even though the current IL is small, the power supply voltage V
Limit detection can be performed even when the fluctuation of B is large.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a limited detection output that includes both current and voltage. It has the advantage of being able to detect cases where there is a risk of destroying the output transistor, and being able to be used as a protection circuit to prevent circuit damage caused by voltage.

13 is a comparator shows.

Claims (1)

[Claims] A current detection means (11) that converts the current to be detected into a voltage and detects it; and a multiplier (12) that multiplies the voltage to be detected and the output voltage of the current detection means (11), respectively. ), and a comparator that compares the output voltage of the multiplier (12) with a preset reference voltage and outputs a limit detection signal when the output voltage of the multiplier (12) is input at a level higher than the reference voltage. (13) A power limit detection circuit characterized by comprising the following.