JPS6098A - Disconnection detecting 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 [Technical Field of the Invention] The present invention relates to a disconnection detection circuit for lamps used in automobiles, for example.

[Technical background of the invention]

Generally, this type of circuit is constructed as shown in FIG. Figure 1 shows a two-lamp disconnection detection circuit. In the figure, "It" 2 is a lamp, Q+ and Qz are a pair of differential transistors whose emitters are commonly connected, and the base of this transistor Q is connected to the lamp. Ij l r L2 in parallel and connected to the ground point GND and resistor R
8 to the power supply Vcc, and the base of the transistor Q2 is connected to the reference voltage source Vref. The collectors Lt of the transistors Q+ and Qt are connected to the power supply Vcc via load resistors R, , R, respectively. Further, a first current source 11 is connected between the common emitter connection point of the L transistors Q+ and Qz and the ground point GND,
A differential amplifier is configured. The above transistor Q>, Q
The base of the transistor Q 3 y Q4 is connected to the collector of t. These transistors Q3. Q4 collector i'J,? , are connected to the IE source vCC, and their emitters are connected to Darlington-connected transistors Q, , Q6, respectively.The collectors of the transistors Qs and Qa are connected to the multi-collector transistor Q whose emitter is connected to the voltage σVee. , I are connected, respectively,
The base of this multi-collector transistor Q7 is connected to the collector of transistor Q. Resistors R3 and R4 are connected between the base and emitter of the transistors Q5 and Qa, respectively, and these transistors Qc
The emitters of pQ6 are commonly connected and connected to ground point GND via a second current source I2. moreover,
The collector of the I transistor Q0 is connected to the base of an output transistor Q8 connected between the power supply Vcc and the output terminal OUT. Note that the reference voltage iji% Vr
e f is set to about Vcc -0.1V, and resistor R1
, R2 are 5 KΩ, and current source I++12 is 70 Ω each.
A current of 200μ8 degrees flows.

Next, the operation in the above configuration will be explained. When lamps L and L2 are normal, that is, when they are not disconnected,
A current flows through the lamp Iy''2, and the base potential of the transistor Q is set to the reference ii Shobara Vref (D to the level (V
C! c-0,1'')j becomes lower, so the transistor Q
, is in the off state, and Q2 is in the on state. Also, transistor Q3? Q5 is on, Qa and Qa are off, Q7 is on, QB is off, and the output signal OUT is at a low level. Lamp L, some vl is R2
When the lamp is disconnected, the current flowing through the lamp becomes %, the base potential of the transistor Q1 rises, and the reference voltage source Vref
Since the potential exceeds , transistor Q+ is turned on, Q2 is turned off, and the output of the differential amplifier is inverted. As a result, transistors Qq and Q* are in the off state, Q4 p Qa is in the on state, Q7 is in the off state, Q,
is not in the ON state, and the output signal OUT is in the ON state. Therefore, by inserting a notification means such as a lamp or a buzzer between the output terminal 11 and the ground point, the lamp L,
Alternatively, disconnection can be reported. Note that the reason why the transistors Q3 and Qi are arranged in a Darlington connection configuration is that the following equation (1) must be satisfied in the circuit operation.

Vc c -R+bow B, -VBR, -Vnp,,'
(Vcc -V13E7-vcE, sat...
・(1) Ins 2l' Base current VBE of transistor Q3:
) Voltage between the base and emitter of transistor Qs VBB, : ) Voltage between base and emitter of transistor Q, VBET =) Voltage between base and emitter of transistor Q, VCE, sat: ) Saturation voltage between collector and emitter of transistor Q5 In (1), R1・l113 is minute and Vc
Since c is v+ (v+ is the voltage on the collector side of transistor Q+), transistor Qa.

If the potential of the common emitter connection point of Qa is v2, then V, -
The level of V is expressed by the following equation (2).

V I V 2 > VBB7 + VCE5 sat
(2) In other words, the second stage differential amplifier does not operate unless there is a potential difference of at least 2 VBB. [Problems in the Background Art] By the way, in such a disconnection detection circuit, the simplicity of the circuit There is a strong desire to reduce the number of elements and reduce costs by increasing the number of elements, and the circuit shown in Figure 1 above cannot be said to be sufficient. in,
The purpose is to provide a disconnection detection circuit that can simplify the circuit, reduce the number of elements, and reduce costs.

[Summary of the invention]

That is, in the third aspect of the present invention, a resistor f is inserted and connected between the resistor J+R2 and the power supply VCC in FIG. The next-stage differential amplifier is configured to operate using only a pair of differential transistors.

[Embodiments of the invention]

Hereinafter, a practical example of the present invention will be explained with reference to the drawings. In FIG. 2, the same reference numerals are given to the same components as in FIG. 1, and the explanation thereof will be omitted. The first of the pair. The collectors of the second differential transistors Ql and Q2 each have a second
．． One end of the third resistor "I+R2" is connected, and the other ends of these resistors R7 and R2 are connected to the power source Vcc via the fourth resistor R6.
The collector of Q2, Q2 is connected to a pair of third . The base of the fourth differential transistor Qo s Q:o (17) is connected to the collector of these differential transistors Qo, Q+. The bases of the multi-collector transistors Q7 each connected to the collectors thereof are connected to the collector of the transistor Q9v.

Next, the operation of C in the above configuration will be explained. It is assumed that the resistance value of the resistor R5 is 5Ω, and the other conditions are the same as in FIG. 1 above. When the lamps L, , L2 are normal, current flows through the lamps L, , L2, and the transistor Q+
The base potential of is the reference voltage [Vref J:) potential (V
cc -0,1v), so the transistor Q
, is off state, Qo is on state, Qlo is off state, Q
7 is on state M, and Q8 is off state. At this time, the transistor Q2 is in the on state, and the voltage Vc+ between the collector and emitter of the transistor Q2 is 2.
sBt is almost 0. IV, then transistor Q
The collector potential (3) of 2 is expressed by the following equation (3).

V3 = Vcc -Q, l V-VB++, +Vc
B2Ht= Vcc -VBE2- (3) Here, if VBE = Q, 7 V, the potential ■4 at the connection point between resistor R6 and resistor RIsR2 is V, = Vcc
-0.35V. Here v4=V, also Vcc-V, -'V++p, (Vcc-VIIE7
- VCEQsat and Schiff Vpc -0,35V -0,7V (Vcc -(3,
Since it is 7V-0, IV, it can operate even with a single-stage differential amplifier.On the other hand, when lamp L or L2 is disconnected, the base potential of transistor Q1 rises, and the reference voltage source Vref
Since the potential of the transistor Q is exceeded, the transistor Q is turned on.

is turned off and the output of the differential amplifier is inverted. As a result, the transistor Q9 is in an off state, Q+o is in an on state, Q7 is in an off state, Qs is in an on state, and the output signal OUT becomes ]. Therefore, output terminal 11
By inserting a notification means such as a lamp or a buzzer between the ground point GND and the ground point GND, disconnection of the lamp L or L2 can be notified. , , R can simplify the configuration of the differential amplifier at the next stage, thereby providing a disconnection detection circuit that can reduce the number of elements and reduce costs.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a conventional wire breakage detection circuit, and FIG. 2 is a diagram showing a wire breakage detection circuit according to an embodiment of the present invention. Vcc...power supply, GND...ground point, R8...first resistor, LI y R2...lamp (wiring to be measured),
■. ...first current source, Ql, Q2...first. Second differential transistors, R,, J...second . Third resistor, R3・
... Fourth resistor, Q9 + Qlo "Third and fourth differential transistors, Q7... Multi-collector transistor (constant current supply means), 12... Second current source, Q8...
・Output transistor.

Claims (1)

[Claims] A first resistor and the wiring to be measured are connected in series between the power supply and the ground point, the emitters are commonly connected to the first current source, and one base is connected to the connection point between the first resistor and the wiring to be measured; a pair of first and second differential transistors whose other bases are respectively connected to a reference voltage source; The second differential transistors each have one end connected to the collector of the second differential transistor. a third resistor, and these second . A fourth resistor connected between the other end of the third resistor and the power supply and the emitter of the first resistor are commonly connected. A pair of third . a fourth differential transistor; constant current supply means for supplying a constant current to the collector of the fourth differential transistor; a second current source connected to the common emitter of the fourth differential transistor; an output transistor that obtains an output from the collector of one of the fourth differential transistors;
A disconnection detection circuit that detects whether or not the wiring to be measured is disconnected.