JPH0228117Y2 - - Google Patents

Description

[Detailed description of the invention] (Technical field) The present invention relates to a lamp breakage detection circuit that detects a breakage in an automobile lamp, etc., and notifies the user of the breakage by turning off an indicator light that is normally lit. It is.

(Prior Art) A conventional example is shown in FIG. That is, a transistor Q ₁ as a lamp blinking switch and detection diodes D ₁ and D ₂ are connected between the power source E ₁ and the lamp L ₁ ,
The control signal of the switch circuit S is applied to the base of the transistor Q ₁ via the resistor R ₁ , while the forward voltage drop of the diodes D ₁ and D ₂ is applied to the base of the transistor Q _2.
Light emitting diode as an indicator light to turn on and off and confirm that the lamp is lit when it is turned on.
I am trying to make LED ₁ light up. Note that R ₂ and R ₃ are resistances.

In the above circuit configuration, when the transistor Q ₁ is turned on by the control signal of the switch circuit S, the lamp L ₁ lights up and a current flows, which is transmitted to the transistors D ₁ and D _2.
is detected as a forward voltage drop. This voltage drop turns on transistor _Q2 , which turns on the light emitting diode.
LED ₁ is lit. This lighting indicates that the lamp _L1 is in the lighting state.

If lamp _L1 is burnt out, the base potential of transistor _Q2 will rise and the transistor
Q ₂ turns off and light emitting diode LED ₁ turns off.
When the light emitting diode LED ₁ turns off while the switch circuit S is in operation, it is known that the lamp L ₁ is disconnected.

However, in such a circuit configuration, two detection diodes D ₁ ,
Since _D2 is connected, not only does the amount of heat generated in the diode, that is, the loss, increase, but also the voltage applied to the lamp _L1 is reduced, reducing the lighting effect.

(Purpose of the invention) An object of the invention is to provide a lamp breakage detection circuit that can reduce the influence on the lamp circuit.

(Summary of the invention) This invention is a lamp lighting circuit that connects a transistor as a lamp blinking switch between the power supply and the lamp, and turns it on and off according to the control signal of the switch circuit to control the lighting and extinguishment of the lamp. , a detection diode inserted into the main circuit to detect the lamp current, a resistive voltage divider circuit connected between the emitter and collector of the transistor, and a voltage divided by the voltage divider circuit. , a detection transistor that is turned off when the transistor is on and turned on when it is off, and in the on state of this detection transistor, its V _CE saturation voltage is applied between the emitter and the base, turning it off, and in the off state, the V of the transistor of the lamp circuit is The sum of _{the CE} saturation voltage and the voltage drop of the detection diode is added between the emitter and the base, and the base current flows through the lamp to turn on the indicator light transistor, and when this transistor is turned on, it lights up. and a light emitting diode to notify that the lamp is in a lit state, and since there is only one detection diode, the detection part is less sensitive in terms of heat generation and voltage applied to the lamp. This reduces the effect that the lamp has on the lamp circuit.

(Example) Figure 1 shows an example of the present invention.
Connect transistor Q ₁ as a blinking switch between E ₁ and lamp L ₁ to complete the main circuit (lamp circuit)
constitutes a part of the main circuit, such as a transistor
One detection diode D ₁ between Q ₁ and lamp L ₁
are connected. The transistor _Q1 is turned on and off by a control signal applied from the switch circuit S through the resistor _R1 .

Further, a voltage dividing circuit including resistors R ₄ and R ₅ is connected between the emitter and collector of the transistor Q ₁ ,
The base of the detection transistor _Q2 is connected to the voltage dividing point. The emitter of the detection transistor Q ₂ is connected to the emitters of the transistor Q ₁ of the main circuit and the indicator light transistor Q ₃ , and the collector is connected to the base of the transistor Q ₃ , and the detection transistor Q ₂ is connected to the emitter of the transistor Q 3 for the indicator light. is connected to the cathode of diode _D1 . And the transistor
The collector of Q ₃ is connected to the power supply E ₁ (−) terminal via a resistor R ₃ and a light emitting diode LED ₁ as an indicator light.

Next, the operation will be described. When switch circuit S turns on, transistor _Q1 turns on and lights up.
Current flows through L ₁ and lamp L ₁ lights up. As the transistor Q ₁ turns on, the voltage across the series circuit of resistors R ₄ and R ₅ becomes the V _CE saturation voltage of the transistor Q ₁ , and the detection transistor Q ₂ is in an off state due to insufficient base voltage. At this time, the sum of the V _CE saturation voltage of the transistor Q 1 and the voltage drop of the diode _{D 1 is applied between the emitter and base of the transistor Q 3 for the} indicator light, and the transistor Q 3 is turned on. this transistor
When Q ₃ is turned on, light emitting diode LED ₁ lights up, and a message indicating that lamp L ₁ is lit is displayed.

When the switch circuit S is turned off, the transistor
Q ₁ is turned off, a large voltage is applied to the series circuit of resistors R ₄ and R ₅ , and detection transistor Q ₂ is turned on. Therefore, the V _CE of the transistor Q ₃ becomes the V _CE saturation voltage of the detection transistor Q ₂ , and the transistor Q ₃ is turned off. Therefore, light emitting diode
LED ₁ turns off.

If the switch circuit S is on, the lamp
If _L1 is disconnected, the base current circuit of transistor _Q3 is interrupted due to the disconnection of lamp _L1 , transistor _Q3 is turned off, and light emitting diode _LED1 is turned off. That is, when the switch circuit S is in an operating state, turning off the light emitting diode LED ₁ means that the lamp L ₁ is disconnected, which indicates that the lamp is disconnected.

(Effects) As described above, according to the present invention, one detection diode is inserted in the main circuit through which a large lamp current flows, and the forward voltage drop is the sum of the forward voltage drop and the V _CE saturation voltage of the transistor in the main circuit. The transistor for the indicator light is turned on and off by the V _CE of the transistor in the main circuit, and the V _CE saturation voltage of the detection transistor is used to control the off state, and the lamp is included in the base current circuit. Lamp burnout can be detected using a single detection diode, reducing heat generation and power loss. Furthermore, since the voltage drop in the detection section is reduced, the voltage applied to the lamp is less reduced, and the influence on the lamp circuit, which is caused by reducing the illumination effect, can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a lamp burnout detection circuit according to the present invention, and FIG. 2 is a circuit diagram showing a conventional example. E ₁ ...power supply, L ₁ ... lamp, Q ₁ - _{Q 3} ... transistor, R ₁ - _{R 5} ... resistance, D ₁ ... detection diode, S ... switch circuit, LED ₁ ... light emitting diode .

Claims (1)

[Scope of utility model registration request] A transistor as a lamp blinking switch is connected between the power supply and the lamp, and this is turned on and off by the control signal of the switch circuit to turn on and off the lamp.
A lamp lighting circuit that controls turning off the lamp includes one detection diode inserted into the main circuit to detect the lamp current, a resistive voltage divider circuit connected between the emitter and collector of the transistor, and this voltage divider. There is a detection transistor that receives a divided voltage from the circuit and turns off when the transistor is on and turns on when it is off. When the detection transistor is on, its V _CE saturation voltage is applied between the emitter and base, turning it off and turning it off. Then, the sum of the V _CE saturation voltage of the transistor in the lamp circuit and the voltage drop of the detection diode is added between the emitter and the base, and the base current flows through the lamp, turning it on. and a light emitting diode that lights up when the transistor is turned on to notify that the lamp is in a lighting state.