JP2010244704A - Vehicle lamp lighting circuit - Google Patents

Abstract

An object of the present invention is to prevent an overcurrent from temporarily flowing into a load 3 after power is turned on and damaging the load 3.
A vehicle lamp lighting circuit includes a switching regulator 1 that converts input power into predetermined output power and supplies the output power to a load 3, and a current detection component 4 for detecting a current I _OUT flowing through the load 3. A feedback terminal FB to which a voltage indicating the magnitude of the current I _OUT detected by the current detection component 4 is applied, and a voltage applied to the feedback terminal FB is compared with a predetermined reference voltage to output power The switching control unit 2 that feedback-controls the magnitude of the current and the current detection component 4 only after the start of the supply of power to the switching regulator 1 and the switching control unit 2 until the switching control unit 2 is started. to apply a greater voltage Vp than the voltage representing the magnitude of the detected current I _OUT to feedback terminal FB And a overcurrent protection unit 5.
[Selection] Figure 1

Description

  The present invention relates to a vehicular lamp lighting circuit having a function of feedback-controlling a current supplied to a load.

  2. Description of the Related Art Conventionally, there is known a lighting control circuit that detects, based on a change in voltage applied to a light source, when an abnormality occurs in any of the light sources of each vehicle lamp (for example, Patent Document 1). reference). In Patent Document 1, a current smaller than the rated current is supplied from the switching regulator to the semiconductor light source for a certain period after the power switch is turned on. And the presence or absence of the leak failure accompanying the change of the forward voltage of a semiconductor light source is determined by comparing the forward voltage which generate | occur | produces from a semiconductor light source and the abnormality determination value in the said period. Also, if a current smaller than the rated current is supplied, the amount of decrease in the forward voltage of the abnormal semiconductor light source is larger than the amount of decrease in the forward voltage of the normal semiconductor light source. Yes.

Further, a vehicular lamp lighting circuit shown in FIG. 5 is conventionally known. When the switch SW is closed, power supply from the battery BAT to the switching regulator 51 and the switching control unit 52 is started. Then, the switching regulator 51 converts the input power into a predetermined output power and supplies it to the load 53 including the vehicular lamp. On the other hand, the current detection resistor 54 is connected in series to the load 53, and the switching control unit 52 generates a current I _OUT flowing through the load 53 from the voltage applied to the feedback terminal fb connected to the current detection resistor 54. The magnitude of the output power supplied from the switching regulator 51 to the load 53 is feedback-controlled.

JP 2007-200670 A

  Since the switching control unit 52 is configured by a component having an arithmetic processing function such as a microcomputer, a predetermined operation is required until stable operation is enabled after the power supply is started, that is, until the switching control unit 52 is started up. Time is needed. However, power supply to the switching regulator 51 is started at the same time as the switching control unit 52, and the switching regulator 51 starts to supply power before the activation of the switching control unit 52 is completed.

  Therefore, in a state where the switching control unit 52 cannot perform normal feedback control, output power is supplied to the load 53, and as shown in FIG. 5B, an overcurrent exceeding the maximum rated current of the load 53 is obtained. May flow temporarily and the load 53 may be damaged by this overcurrent.

  The present invention has been made in view of such a conventional problem, and an object of the present invention is to suppress a vehicle from temporarily flowing an overcurrent to the load after power is turned on and damaging the load due to the overcurrent. It is providing the lighting device lighting circuit.

  A feature of the present invention is that a switching regulator that converts input power into predetermined output power and supplies it to a load, a current detection component for detecting the magnitude of a current flowing through the load, and a current detection component A feedback terminal to which a voltage indicating the magnitude of the detected current is applied is provided, the magnitude of the voltage applied to the feedback terminal is compared with a predetermined reference voltage, and the output power supplied from the switching regulator to the load is compared. The magnitude of the current detected by the current detection component only after the switching control unit that feedback controls the magnitude, and after the supply of power to the switching regulator and the switching control unit is started until the switching control unit is started. Overcurrent protection unit that applies a voltage greater than the voltage indicating the voltage to the feedback terminal And summarized in that a vehicular lamp lighting circuit comprising a.

  A feedback terminal that provides a voltage greater than the voltage indicating the magnitude of the current detected by the current detection component only after the supply of power to the switching regulator and the switching control unit is started until the switching control unit is started. The switching control unit recognizes that a current larger than the current detected by the current detection component is flowing in the load, and reduces the output power supplied from the switching regulator to the load. . Thereby, it is possible to suppress the overcurrent temporarily flowing to the load after power is turned on and the damage of the load due to the overcurrent.

  In the feature of the present invention, the overcurrent protection unit feeds back a voltage higher than a predetermined reference voltage only after the supply of power to the switching regulator and the switching control unit is started until the switching control unit is started. The switching control unit may stop the supply of output power from the switching regulator to the load. As a result, it is possible to more strongly suppress the overcurrent temporarily flowing to the load after the power is turned on and the damage of the load due to the overcurrent.

  In the characteristics of the present invention, the switching regulator adjusts the magnitude of the output power by changing the ratio (duty ratio) of the on / off time of the first switching element, and the switching control unit includes the switching regulator and the switching regulator. Supply of output power from the switching regulator to the load with the ratio of the ON time of the first switching element set to zero only after the supply of power to the control unit is started until the switching control unit is started May be stopped. For a switching regulator capable of adjusting the magnitude of output power by changing the duty ratio of the first switching element, the ratio of the ON time of the first switching element is set to zero and the switching regulator is switched to the load. If the supply of the output power is temporarily stopped, it is possible to more strongly suppress the overcurrent temporarily flowing to the load after the power is turned on and the damage of the load due to the overcurrent.

  In the feature of the present invention, the overcurrent protection unit includes a resistor and a capacitor connected in series, and a potential between the resistor and the capacitor is applied to the control terminal, and the first electrode terminal is larger than a predetermined reference voltage. A second switching element to which a voltage is applied and the second electrode terminal is connected to the feedback terminal, and at the same time as the supply of power to the switching regulator and the switching control unit is started, The second switching element may be controlled to be turned on only during the period from the start of the application of voltage between the two terminals of the capacitor until the start of the switching control unit.

  The potential between the resistor and the capacitor changes with time after the application of the voltage is started. Therefore, by applying a potential between the resistor and the capacitor to the control terminal of the second switching element, the second switching element can be controlled to be in an on state for a predetermined period after the application of the voltage is started. it can. Therefore, by adjusting the size of the resistor and the capacitor, the second switching element is turned on only during the period from the start of power supply to the switching regulator and the switching control unit until the switching control unit is activated. Can be controlled.

  As described above, according to the vehicular lamp lighting circuit of the present invention, it is possible to prevent the overcurrent from temporarily flowing into the load after power is turned on and the load from being damaged by the overcurrent.

It is a circuit diagram which shows the structure of the vehicle lamp lighting circuit concerning embodiment of this invention. 6 is a graph showing changes over time in the open / close state of a switch SW, the voltage Vp output from the overcurrent protection unit 5, and the magnitude of the current _IOUT flowing through the load 3. It is a circuit diagram which shows the Example of the concrete circuit structure of the vehicle lamp lighting circuit shown in FIG. The open / close state of the switch SW, the voltage of the power supply terminal Vcc, the voltage V _R across the resistor Ra, the on / off state of the second switching element FET2, the voltage V _FB applied to the feedback terminal FB, the duty of the pulse signal OUT 6 is a graph showing a change over time in the ratio and the magnitude of the current I _OUT flowing through the load 3. FIG. 5A is a circuit diagram showing a configuration example of a conventional vehicular lamp lighting circuit, and FIG. 5B is a graph showing a change in the current I _OUT flowing through the load 53 after the power is turned on.

  Embodiments of the present invention will be described below with reference to the drawings. In the description of the drawings, the same portions are denoted by the same reference numerals, and description thereof is omitted.

  With reference to FIG. 1, the structure of the vehicular lamp lighting circuit according to the embodiment of the present invention will be described. The vehicular lamp lighting circuit according to the embodiment of the present invention includes a battery BAT that stores electric power supplied to the entire vehicular lamp lighting circuit, a switch SW connected in series to the battery BAT, and electric power stored in the battery BAT. For detecting the magnitude of the current flowing through the load 3, the load 3 to which the output power converted by the switching regulator 1 is supplied, and the switching regulator 1 for converting the input power to the predetermined output power A current detection resistor 4 as a current detection component and a switching control unit 2 that feedback-controls the magnitude of output power supplied from the switching regulator 1 to the load 3 based on the magnitude of the current flowing through the load 3. And an overcurrent protection unit 5 for suppressing the overcurrent from flowing through the load 3.

  The switching regulator 1, the switching control unit 2, and the overcurrent protection unit 5 are respectively connected in series to the battery BAT. Therefore, when the switch SW is closed, the electric power stored in the battery BAT is simultaneously supplied to the switching regulator 1, the switching control unit 2, and the overcurrent protection unit 5 to start the operation.

A load 3 and a current detection resistor 4 are connected in series on the output side of the switching regulator 1. The output power converted by the switching regulator 1 is supplied to the load 3 and the current detection resistor 4, and the current _IOUT flows. Examples of the load 3 include semiconductor light emitting elements (LEDs) and filaments used as various vehicle lamps such as headlamps, stop & tail lamps, fog lamps, and turn signal lamps.

The switching control unit 2 is composed of a component having an arithmetic processing function such as a microcomputer, and includes a feedback terminal FB to which a potential difference between both ends of the current detection resistor 4 is input. Since the potential difference between both ends of the current detection resistor 4 changes according to the magnitude of the current I _OUT , if the resistance value of the current detection resistor 4 is obtained in advance, the load applied from the voltage applied to the feedback terminal FB the magnitude of the current _{I OUT} flowing to 3 can be obtained. Thus, a voltage indicating the magnitude of the current I _OUT detected by the current detection resistor 4 is applied to the feedback terminal FB.

Then, the switching control unit 2 compares the voltage applied to the feedback terminal FB with a predetermined reference voltage, and sets the magnitude of the output power supplied from the switching regulator 1 to the load 3 so that there is no difference between the two. Feedback control. Thereby, the vehicular lamp lighting circuit can perform constant current control so that the magnitude of the current _IOUT becomes a predetermined constant value. Here, the “predetermined reference voltage” can be obtained from a predetermined constant value and the resistance value of the current detection resistor 4.

With reference to FIG. 2, the time change of the open / close state of the switch SW, the voltage Vp output from the overcurrent protection unit 5, and the magnitude of the current _IOUT flowing through the load 3 will be described. When the switch SW changes from an open state (OFF) to a closed state (ON), the electric power stored in the battery BAT starts to be supplied to each of the switching regulator 1, the switching control unit 2, and the overcurrent protection unit 5.

  Since the switching control unit 2 is composed of a component having an arithmetic processing function such as a microcomputer, a predetermined operation is required until stable operation is enabled after power supply is started, that is, until the switching control unit 2 is started up. Time is needed. However, power supply to the switching regulator 1 is started simultaneously with the switching control unit 2, and the switching regulator 1 starts to supply power before the activation of the switching control unit 2 is completed. Thus, the feedback control by the switching control unit 2 is delayed by the combination of the component constants in the switching regulator 1 and the setting of the switching control unit 2, and during this time (for example, several tens of msec), the switching regulator 1 is connected to the load 3. In some cases, a current exceeding the rated current may flow temporarily. A vehicular lamp made of an electronic component such as a semiconductor light emitting element (LED) may be damaged by a temporary overcurrent.

  The overcurrent protection unit 5 has a voltage higher than the voltage indicating the magnitude of the current detected by the current detection resistor 4 only for a certain period Ts after the switch SW is closed and the power supply from the battery BAT is started. A function of applying a large voltage Vp to the feedback terminal FB is provided.

The switching control unit 2 detects the current detection resistor 4 by applying a voltage Vp larger than the voltage indicating the magnitude of the current I _OUT detected by the current detection resistor 4 to the feedback terminal FB. Recognizing that a current larger than the current I _OUT applied to the load 3 is recognized, feedback control is performed so as to reduce the magnitude of the output power supplied from the switching regulator 1 to the load 3. In the example of FIG. 2, the voltage Vp applied by the overcurrent protection unit 5 is set to a voltage higher than a predetermined reference voltage, and the power supply from the switching regulator 1 to the load 3 is stopped until a certain period Ts elapses. is the magnitude of the current I _OUT to zero Te.

  The length of the certain period Ts is determined in advance according to the length of the period from when the supply of power to the switching regulator 1 and the switching control unit 2 is started until the switching control unit 2 is activated. As a result, the load 3 can be protected from a temporary overcurrent until stable operation is enabled after the power supply is started, that is, until the activation of the switching control unit 2 is completed.

Since the switching control unit 2 can perform normal feedback control in a state in which the switch SW is closed after the lapse of a certain period Ts, the overcurrent protection unit 5 does not output the voltage Vp, and the current detection resistor A voltage indicating the magnitude of the current I _OUT detected by the body 4 is applied to the feedback terminal FB, and feedback control by the switching control unit 2 described above is started.

  With reference to FIG. 3, the Example of the specific circuit structure of the vehicle lamp lighting circuit shown in FIG. 1 is described.

  The low potential side electrode of the battery BAT is grounded, and one terminal of the switch SW is connected to the high potential side electrode of the battery BAT. And the switching regulator 1, the switching control part 2, and the overcurrent protection part 5 are connected to the other terminal of the switch SW.

  The switching regulator 1 includes a flyback side DC / DC converter, inputs a pulse to the transformer 11, and generates an output voltage by mutual induction between the input side coil and the output side coil. The magnitude of the output power is adjusted by changing the ON / OFF time ratio (duty ratio) of the first switching element FET1 connected in series to the input side coil. Specifically, the pulse signal is repeatedly input to the control terminal of the first switching element FET1, and the magnitude of the output power is adjusted by changing the duty ratio of the pulse signal. In addition, the switching regulator 1 includes a protection diode 12 connected in series to the output side coil and a capacitor 13 connected in parallel.

  The switching control unit 2 includes a comparator CMP that compares a voltage applied to the feedback terminal FB with a predetermined reference voltage Vref, and a power supply terminal Vcc connected to the other terminal of the switch SW. The switching control unit 2 calculates the duty ratio of the pulse signal OUT according to the output from the comparator CMP, and outputs the pulse signal OUT to the control terminal of the first switching element FET1.

  In the overcurrent protection unit 5, the resistor Ra and the capacitor C connected in series, and the potential between the resistor Ra and the capacitor C are applied to the control terminal CT, and a predetermined reference voltage Vref is applied to the first electrode terminal FT. And a second switching element FET2 in which the second electrode terminal ST is connected to the feedback terminal FB.

Specifically, the other terminal of the switch SW is connected to the resistor Ra, and the other electrode of the capacitor C connected to the resistor Ra is grounded. The intermediate potential between the resistor Ra and the capacitor C is input to the control terminal of the second switching element FET2 via the resistor Rb. The other terminal of the switch SW is also connected to the first electrode terminal FT of the second switching element FET2, and the first electrode terminal FT has a battery voltage V _BAT as an example of a voltage higher than a predetermined reference voltage Vref. Is applied.

  In the second switching element FET2, a channel is formed when a predetermined negative voltage with respect to the first electrode terminal FT is applied to the control terminal CT, and a current flows between the first electrode terminal FT and the second electrode terminal ST. When no voltage is applied, the channel is not formed, and the current is cut off. This is an enhanced field effect transistor. The “predetermined negative voltage” refers to a voltage that is equal to or higher than a threshold voltage unique to the second switching element FET2. The “threshold voltage” is a minimum voltage required to form a general transistor channel.

4 shows the open / close state of the switch SW, the voltage at the power supply terminal Vcc, the voltage V _R across the resistor Ra, the on / off state of the second switching element FET2, the voltage V _FB applied to the feedback terminal _FB , the pulse 6 is a graph showing a change over time in the duty ratio of a signal OUT and the magnitude of a current I _OUT flowing through a load 3.

As shown in FIG. 4, at the same time as the switch SW is closed, the voltage at the power supply terminal Vcc rises to the battery voltage _VBAT . The potential between the resistor Ra and the capacitor C changes over time after the switch SW is closed and the application of the battery voltage _VBAT is started. Specifically, immediately after the application of the battery voltage V _BAT is started, the capacitor C does not store electric charge, so that the battery voltage V _BAT is applied to both ends of the resistor Ra. voltage applied is increased, the voltage V _R across the resistor Ra is reduced to zero.

Therefore, by setting larger than the threshold voltage _{V GS} of the battery voltage _{V BAT} second switching element FET2, only from the application of the battery voltage _{V BAT} is started in a predetermined time period Ts, the second switching element The FET 2 can be controlled to be on. Further, by adjusting the threshold voltage of the second switching element FET2 by adjusting the sizes of the resistor Ra and the capacitor C, the switching controller 2 after the power supply to the switching regulator 1 and the switching controller 2 is started. The second switching element FET2 can be controlled to be in an on state only until the time of starting.

When the second switching element FET2 is turned on, the battery voltage _VBAT is applied to the feedback terminal FB via the resistor Rc and the resistor Re. Since the battery voltage V _BAT is a voltage higher than the predetermined reference voltage Vref (in FIG. 4, twice the reference voltage Vref), the switching control unit 2 sets the ratio of the ON time of the first switching element FET1 to zero. To. As a result, the supply of output power from the switching regulator 1 to the load 3 is stopped, and the magnitude of the current _IOUT becomes zero.

When the voltage V _R across the resistor Ra in a predetermined period Ts has elapsed is less than the threshold voltage V _GS, the second switching element FET2 are changed to the OFF state, a voltage is applied to the feedback terminal FB V _FB becomes zero. The switching control unit 2 increases the on-duty to the maximum value (for example, 80%) of the duty ratio of the pulse signal OUT. Thereafter, a voltage indicating the magnitude of the current I _OUT detected by the current detection resistor 4 is applied to the feedback terminal FB, and normal feedback control by the switching control unit 2 is performed.

Since the switching control unit 2 can perform normal feedback control after a certain period Ts has elapsed, the switching control unit 2 follows the magnitude of the current I _OUT as indicated by P ₁ and P ₂ in FIG. And the occurrence of overcurrent is suppressed. Then, after the time Tc constant value current _{I OUT} (e.g., 100 mA) can be stabilized to.

  As described above, according to the embodiments and examples of the present invention, the following operational effects can be obtained.

As shown in FIG. 2, the current detected by the current detection resistor 4 is limited to Ts from the start of power supply to the switching regulator 1 and the switching control unit 2 until the switching control unit 2 is activated. applying a larger voltage Vp than the voltage representing the magnitude of I _OUT to feedback terminal FB. As a result, the switching control unit 2 recognizes that a current larger than the current I _OUT detected by the current detection resistor 4 is flowing in the load 3 and outputs power supplied from the switching regulator 1 to the load 3. Make it smaller. As a result, it is possible to suppress overcurrent from temporarily flowing to the load 3 after power is turned on (overshoot) and damage of the load 3 due to this overcurrent.

  By applying a voltage higher than the predetermined reference voltage Vref to the feedback terminal FB and stopping the supply of output power from the switching regulator 1 to the load 3, an overcurrent temporarily flows to the load after the power is turned on. And it can suppress more strongly that a load breaks by this overcurrent.

  With respect to the switching regulator 1 that can adjust the magnitude of the output power by changing the ratio (duty ratio) of the ON / OFF time of the first switching element FET1, the ON time of the first switching element FET1 If the ratio is set to zero and the supply of output power from the switching regulator 1 to the load 3 is temporarily stopped, the overcurrent temporarily flows into the load after the power is turned on and the load is damaged by the overcurrent. It can be suppressed more strongly.

  As described above, the present invention has been described by way of one embodiment and examples thereof, but it should not be understood that the description and drawings that form part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art. That is, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters according to the scope of claims reasonable from this disclosure.

DESCRIPTION OF SYMBOLS 1 Switching regulator 2 Switching control part 3 Load 4 Current detection resistor (Current detection component)
DESCRIPTION OF SYMBOLS 5 Overcurrent protection part 11 Transformer 12 Protection diode 13, C capacitor BAT Battery CMP comparator CT Control terminal FB Feedback terminal FET1 1st switching element FET2 2nd switching element FT 1st electrode terminal I Current which flows into _OUT load 3 OUT pulse signal Ra resistor Rb to Re resistance ST second electrode terminal SW switch Ts predetermined period V _BAT battery voltage V _FB voltage applied to feedback terminal V _GS threshold voltage Vcc power supply terminal Vref reference voltage

Claims (4)

A switching regulator that converts input power into predetermined output power and supplies it to a load;
A current detection component for detecting the magnitude of the current flowing through the load;
A feedback terminal to which a voltage indicating the magnitude of the current detected by the current detection component is applied; the magnitude of the voltage applied to the feedback terminal is compared with a predetermined reference voltage; A switching control unit that feedback controls the magnitude of the output power supplied to
Only after the supply of power to the switching regulator and the switching control unit is started until the switching control unit is started, the voltage is larger than the voltage indicating the magnitude of the current detected by the current detection component. An overcurrent protection unit that applies a voltage to the feedback terminal. A vehicular lamp lighting circuit.   The overcurrent protection unit applies a voltage higher than the predetermined reference voltage as a feedback terminal only after the supply of power to the switching regulator and the switching control unit is started and until the switching control unit is activated. The vehicular lamp lighting circuit according to claim 1, wherein the switching control unit stops supply of output power from the switching regulator to the load.   The switching regulator adjusts the magnitude of output power by changing a ratio (duty ratio) of ON / OFF time of the first switching element, and the switching control unit includes the switching regulator and the switching control unit. Only after the start of the supply of electric power to the time when the switching control unit is activated, the ratio of the ON time of the first switching element is made zero, and the output power from the switching regulator to the load The vehicle lamp lighting circuit according to claim 2, wherein the supply is stopped. The overcurrent protection unit is
A resistor and a capacitor connected in series;
A potential between the resistor and the capacitor is applied to the control terminal, a voltage higher than the predetermined reference voltage is applied to the first electrode terminal, and a second electrode terminal is connected to the feedback terminal. 2 switching elements,
At the same time as the supply of power to the switching regulator and the switching control unit is started, the application of a voltage is started between both terminals of the resistor and the capacitor connected in series, and the application of the voltage is started. 4. The vehicular lamp lighting circuit according to claim 2, wherein the second switching element is controlled to be in an on state only until the switching control unit is activated.

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