JP2008029132A - Protection circuit of power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a structure of a detecting circuit becomes complicated especially when excess current occurs in a negative voltage-side, and that cost is raised when a floating power supply is adopted at the time of connecting a plurality of LED lamps in series and lighting them up. <P>SOLUTION: A power supply unit in a floating state has current detectors detecting unbalance of current balance on a positive voltage-side and the negative voltage-side when output of a negative power-side is shorted and excess current flows. Further, the main line of the power supply unit is interrupted by output of the current detectors serving as a protection circuit. Thus, unbalance can be detected in a detecting circuit disposed in a regular ground line. The structure of the detecting circuit can be simplified and cost can be reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a configuration of a power supply device when an LED lamp is used for illumination of an automobile, for example, a lamp in which a plurality of LEDs are used for a lamp used for one application such as a headlight. When some of the LED lamps are disconnected, it is highly possible that the entire lamp will be out of specification, so when all the LED lamps are connected in series and an abnormality such as a short circuit occurs, It is preferable to use wiring that can be easily detected.

  Therefore, depending on the number of LED lamps connected in series, a voltage higher than the power supply (nominal 12 VDC) originally provided in the automobile may be required. In such a case, a positive voltage power supply and a negative voltage are provided by an inverter or the like. The power supply is prepared and the necessary power supply voltage can be obtained by connecting both power supplies in series, but this is related to the monitoring of the state of the LED lamp and the response when an abnormality occurs .

  FIG. 5 shows an example of a protection circuit 90 of a conventional power supply device. In the figure, the reference numeral 80 indicates an overcurrent monitoring circuit, and the reference numeral 70 indicates a protection circuit. The overcurrent monitoring circuit 80 includes NPN transistors 81 and 82, a diode 83, resistors 84 and 85, and a comparator 86 including an operational amplifier. The protection circuit 70 includes NPN transistors 71 and 72, D-type transistors. The flip-flop 73 is composed of resistors 74 to 76 and a switch 77.

  With this configuration, when the supplied power exceeds a predetermined value, the voltage drop in the resistor 85 increases, the transistor 82 is turned on, and the transistor 81 is turned off. As a result, a current flows through the resistor 84 and the transistor 82 to the output terminal OUT, and the voltage V applied to the non-inverting input terminal “+” of the comparator 86 is applied to the inverting input terminal “−”. The output voltage of the comparator 86 becomes high level.

As a result, the flip-flop 73 operates, and the output signal thereof becomes a high level, the transistor 72 is turned on, and the transistor 71 is turned off accordingly, whereby the input terminal IN to the output terminal OUT is turned on. The energizing current is completely cut off. Reference numeral 77 denotes a reset switch. After the overcurrent state is resolved, the flip-flop 73 is reset by turning on the reset switch 77, and the transistor 72 is turned off to switch from the input terminal IN to the output terminal OUT. Restore continuity.
Japanese Utility Model Publication No. 06-024347

  However, as described above, the LED lighting circuit in recent years uses a positive voltage power source synchronized with an inverter circuit or the like, and a negative voltage power source, and an overcurrent protection circuit in a circuit for lighting the LED lamp in a floating state. Therefore, the overcurrent protection circuit on the positive voltage power supply side can be handled by the same overcurrent protection circuit as the conventional example described above, but when considering the overcurrent protection circuit on the negative voltage power supply side, There is a problem that the configuration of the overcurrent protection circuit is complicated and the cost is increased, for example, a negative voltage signal must be converted into a positive voltage.

  As a specific means for solving the above-described conventional problems, the present invention provides a power supply device in which a positive voltage power supply and a negative voltage power supply are connected in series and are in a floating state with respect to the main body power supply of the device. Overcurrent protection is provided by providing a current detection unit that detects imbalance in the balance when the output on the negative power supply side is short-circuited and overcurrent flows, and the main line of the main body power supply is shut off by the output of the current detection unit The problem is solved by providing a protection circuit for a power supply device that is in a floating state.

  According to the present invention, a current detection unit is provided for detecting an imbalance between the current flowing through the current sense resistor on the positive voltage power supply side and the current flowing through the current sense resistor on the negative voltage power supply side. This makes it possible to detect an unbalanced state in a floating state by the unit, simplify the configuration of the overcurrent protection circuit of this type of power supply device, and achieve an excellent effect in cost reduction.

  Below, this invention is demonstrated in detail based on embodiment shown in a figure. What is denoted by reference numeral 1 in FIG. 1 is a power supply device according to the present invention, and this power supply device 1 includes a power supply unit 2, an LED lamp connection unit 3, and a current detection unit 4. Is attached with a power shut-off unit 5 as necessary.

  The power supply unit 2 employs, for example, a step-up DC-DC converter circuit, and is formed by a positive voltage power supply 2a that boosts the power supply voltage of an automobile, the positive voltage power supply 2a, and a target circuit, element, and the like. A negative voltage power source 2b that inverts an output from the positive voltage power source 2a and outputs a substantially equal negative voltage is connected in series.

  At this time, the positive voltage power supply 2a and the negative voltage power supply 2b are connected to the vehicle body (not shown) on the ground side where the respective circuits are configured. This side is not connected to the vehicle body or the like, and is in a so-called floating state.

  Based on the configuration described above, the configuration of the current detection unit 4 of the present invention will be described. The power supply unit 2 is provided with a constant current circuit and the like, and in a state where no short circuit to the vehicle body occurs, a substantially constant current is output and is connected to the LED lamp connection unit 3. It is assumed that a predetermined range of current is supplied to the LED lamp 3a.

  As the current detection unit 4, first, a positive current sensing resistor 4 a is connected between the output of the positive voltage power source 2 a and the wiring of the LED lamp connection unit 3 on the side where the anode of the LED lamp 3 a is connected. Similarly, a negative-side current sense resistor 4b is connected between the output of the negative voltage power supply 2b and the wiring to which the cathode of the LED lamp 3a is connected.

  Here, as clearly shown in FIG. 1, since the plurality of LED lamps 3a connected to the LED lamp connecting portion 3 are all connected in series, a negative voltage is supplied from the positive voltage power supply 2a. In the wiring including the LED lamp connection part 3 up to the power source 2b, for example, the value of the flowing current is the same as long as no leakage current is generated due to contact with the vehicle body. Resistance value of sense resistor 4a) = (resistance value of negative-side current sense resistor 4b). Therefore, when the power supply device 1 is operating normally, the voltage drop across both sense resistors 4a and 4b has the same value.

  Next, in the present invention, a power supply high-voltage side resistor 4c and a power supply low-voltage side resistor 4d are inserted in series on the power supply unit 2 side of both sense resistors 4a and 4b, and between the positive voltage power supply 2a and the negative voltage power supply 2b. The voltage is appropriately divided and input to the + terminal of the comparator 4g as will be described later.

  Further, the LED high voltage side resistor 4e and the LED low voltage side resistor 4f are also inserted in series on the LED lamp connecting part 3 side of both the sense resistors 4a and 4b, and the LED lamp connecting part 3 is connected. The voltage is appropriately divided and input to the negative terminal of the comparator 4g.

  As the resistance value, since a positive potential is always input to the comparator 4g, the power supply low-voltage side resistor 4d and the LED are set to be higher than the resistance values of the power supply high-voltage side resistor 4c and the LED high-voltage side resistor 4e. In order to set the resistance value of the low-voltage side resistor 4f high and to prevent malfunction due to noise or the like, the “+” terminal of the comparator 4g is always set to be higher than the “−” terminal in the normal state. I do.

  A PNP transistor 4h is connected to the output of the comparator 4g. When the output from the comparator 4g becomes "L" level, the PNP transistor 4h is turned on, and the switch 5a of the power shut-off unit 5 is operated. The voltage applied to is cut off.

  In the power supply device 1 of the present invention, since the output of the negative voltage power supply 2b is a voltage obtained by inverting the waveform of the positive voltage power supply 2a, the positive and negative voltages rise from the power-on to the specified voltage. The voltage ratio divided by the power source high voltage side resistor 4c, the power source low voltage side resistor 4d, the LED high voltage side resistor 4e, and the LED low voltage side resistor 4f does not change, and for example, an output is generated in the comparator 4g. Such a malfunction does not occur.

  FIG. 2 shows an example of a detection circuit when an overcurrent is generated on the positive voltage power supply 2a side. The positive current sensing resistor 4a is shared, and a voltage drop caused by the positive current sensing resistor 4a is shown. Can be detected by conducting the PNP transistor Q1 and outputting it via the bias resistor R1 and the diode D1 and appropriately displaying it.

  FIG. 3 shows a power cutoff unit that shuts off the power supply of the entire power supply device 1 by an overcurrent signal from the positive current sense resistor 4a and / or the negative current sense resistor 4b detected as described above. 5 shows an example of the configuration of 5. When the above-described overcurrent signal is input, the P-channel FET Q2 serving as the switch 5a continues to be in an OFF state, and is turned on until the power is turned on again. Keep state.

  As described above, according to the present invention, the positive electrode of the positive voltage power supply and the negative electrode of the negative voltage power supply are provided with current sense resistors of the respective power supplies, and two sets of balance resistors sandwiching each of the current sense resistors. The level of the detection voltage is shifted, and the occurrence of an overcurrent accident due to a short circuit on the negative voltage power supply side in the floating state is also a simple configuration consisting of two sets of balance resistors consisting of four resistors and a comparator only. It is possible to detect and to simplify the circuit configuration.

  Furthermore, a circuit diagram in which the current detection unit is simplified is shown in FIG. The output of the positive voltage power supply 2a, the wiring to which the anode of the LED lamp 3a of the LED lamp connection part 3 is connected, the output of the negative voltage power supply 2b, and the wiring to which the cathode of the LED lamp 3a is connected Are divided by resistors R1 and R2, and an output line provided between the resistors R1 and R2 is connected to the power shut-off unit 5 via a diode D1. Thereby, similarly to the above embodiment, even when the output on the negative power supply side is short-circuited and an overcurrent flows, the overcurrent can be immediately cut off by the power cut-off circuit 5.

It is a circuit diagram which shows the protection circuit of the power supply device which concerns on this invention. It is a circuit diagram which shows the example of the overcurrent detection circuit by the side of the positive voltage power supply which shares the current sense resistor provided in the positive voltage power supply side. It is a circuit diagram which shows the example of the switch for power supply cutoff when generation | occurrence | production of overcurrent is detected. It is a circuit diagram which shows the other example of a current detection part. It is a schematic circuit diagram which shows the example of the overcurrent monitoring circuit of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Power supply device 2 ... Power supply part 2a ... Positive voltage power supply 2b ... Negative voltage power supply 3 ... LED lamp connection part 3a ... LED lamp 4 ... Current detection part 4a ... Positive electrode side current sense resistor 4b ... Negative electrode side current sense resistor 4c Power supply high voltage side resistor 4d Power supply low voltage side resistor 4e LED high voltage side resistor 4f LED low voltage side resistor 4g Comparator 4h PNP transistor 5 Power supply cutoff unit 5a Switch

Claims (4)

  In a power supply device in which a positive voltage power supply and a negative voltage power supply are connected in series and are in a floating state with respect to the main power supply of the device, the balance is unbalanced when the output on the negative power supply side is shorted and an overcurrent flows A protection circuit for a power supply apparatus in a floating state, characterized in that an overcurrent protection is performed by providing a current detection unit for detecting the power supply, and cutting off a main line of the main body power supply by an output of the current detection unit.   The current detection unit is configured to provide current sense resistors for the respective power supplies on the positive electrode of the positive voltage power supply and the negative electrode of the voltage power supply, and provide two sets of balance resistors sandwiching each of the current sense resistors. 2. The protection circuit for a power supply apparatus according to claim 1, wherein the detection voltage is level-shifted to enable detection in a floating state.   3. The protection circuit for a power supply apparatus according to claim 2, wherein the current sense resistor on the positive voltage power supply side is shared for detection of an overcurrent protection circuit on the positive voltage power supply side.   3. The protection circuit for a power supply device according to claim 2, wherein a set value at the time of overcurrent protection operation can be changed by making the balance resistance constant adjustable.

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