CN201467528U - Low cost and high reliability LED open protective circuit - Google Patents

Abstract

A low cost and high reliability LED open protective circuit comprises an LED, a capacitor Cout, an inductor L1, a first MOS transistor M1, a fly-wheel diode D1, a control chip and a transistor inverse feedback control module; the LED and the capacitor Cout are connected in parallel, and the anode of the LED is connected to power source Vin; one end of the inductor L1 is connected with the cathode of the LED; the drain of the first MOS transistor M1 is connected with the other end of the inductor L1, and the source of the first MOS transistor M1 is grounded via a first resistor R1; the anode of the fly-wheel diode D1 is connected with the drain of the first MOS transistor M1 and the cathode thereof is connected with the anode of the LED; the control chip is provided with an enabling terminal en and an output port gate and an output port cs, the output port gate is connected with the grid of the first MOS transistor M1 and the output port cs is connected with the source of the first MOS transistor M1; the transistor inverse feedback control module samples the output voltage at two ends of the LED and generate the output signals of the enabling terminal en output to the control chip to control the connection and disconnection of the first MOS transistor M1.

Description

A kind of LED open circuit guard circuit featuring low cost and high reliability

Technical field

The utility model relates to a kind of LED open loop protection circuit, more particularly, relates to a kind of LED open circuit guard circuit featuring low cost and high reliability.

Background technology

Fig. 1 is the schematic diagram of traditional LED open loop protection circuit.As shown in Figure 1, between power supply Vin and ground, be connected with decoupling condenser Cin; Resistor R 2 one termination power Vin, the negative pole of another termination voltage-stabiliser tube Z1, the positive pole of voltage-stabiliser tube Z1 connects the positive input terminal of optocoupler 12, the negative input end of optocoupler 12 is connected with the negative pole of the negative pole of LED, capacitor Cout and an end of inductance L 1, the positive pole of the positive pole of LED and capacitor Cout is connected the negative pole of receiving power supply Vin and sustained diode 1, and the positive pole of sustained diode 1 is connected to the drain electrode of the other end and the MOS transistor M1 of inductance L 1; The grid of MOS transistor M1 is connected to the gate output of control chip 11, and the source electrode of MOS transistor M1 is connected to the cs end of resistor R 1 and control chip 11; The other end ground connection of resistor R 1; The Enable Pin en of control chip 11 connects the positive pole of optocoupler 12 outputs; The minus earth of optocoupler 12 outputs.

When MOS transistor M1 conducting, inductance L 1 electric current increases, and node cs place voltage increases, and when node cs place voltage is elevated to a certain reference voltage, turn-offs MOS transistor M1; Inductance L 1 is by sustained diode 1, load LED discharge, and electric current reduces; Control chip 11 is opened MOS transistor M1 again by certain way again, forms one-period.When output LED open circuit, the conducting electric current is 0, thereby M1 normal open, output voltage V out can raise, and when it was worth up to certain value, voltage-stabiliser tube Z1 punctured, produce optocoupler 12 input currents, thereby optocoupler 12 output produces pull-down currents the en end is dragged down, and control chip 11 turn-offs MOS transistor M1, thereby keeps output voltage a more rational value.So prevent effectively that output produces high pressure when LED open a way, thereby prevent that effectively LED from being burnt out in connection moment.

In above-mentioned traditional open loop protection circuit, there are following two shortcomings: first, detect output voltage by voltage-stabiliser tube during open circuit, when being raised to, voltage produces the current direction optocoupler when being higher than the voltage-stabiliser tube rated voltage, thereby the en end of control chip 11 is dragged down, correspondingly turn-off MOS transistor M1, this detection mode has adopted optocoupler, thereby cost is higher; The second, need milliampere other electric current of level owing to drive optocoupler, so the high voltage stabilizing pipe of current level is less, and adopts the TVS pipe to replace voltage-stabiliser tube can reduce the reliability of protective circuit.

As seen, traditional LED open loop protection circuit cost height, reliability are low.

The utility model content

The purpose of this utility model is to solve the aforementioned problems in the prior, and a kind of LED open circuit guard circuit featuring low cost and high reliability is provided, to improve the cost performance of total system.

To achieve these goals, the utility model provides a kind of LED open circuit guard circuit featuring low cost and high reliability, comprising: the LED of connection parallel with one another and output capacitor Cout, and the positive pole of LED is connected to power supply Vin; Inductance L 1, the one end is connected with the negative pole of LED; The first MOS transistor M1, its drain electrode is connected with the other end of inductance L 1, and source electrode is via first resistor R, 1 ground connection; Sustained diode 1, its positive pole is connected to the drain electrode of the first MOS transistor M1, and negative pole is connected to the positive pole of LED; Control the control chip of the first MOS transistor M1 break-make, this control chip has Enable Pin en and output port gate, cs, wherein output port gate is connected to the grid of the first MOS transistor M1, and output port cs is connected with the source electrode of the first MOS transistor M1; It is characterized in that further comprise transistor negative feedback control module, this control module is sampled to the output voltage at LED two ends, and produce the output signal of the Enable Pin en that outputs to described control chip, to control the break-make of the first MOS transistor M1.

According to an embodiment of the present utility model, transistor negative feedback control module comprises the first bipolar transistor Q1, the second bipolar transistor Q2, second resistor R 2 and the 3rd resistor R 3, wherein the emitter of the first bipolar transistor Q1 is connected to the positive pole of described LED via second resistor R 2, the base stage of the first bipolar transistor Q1 is connected to described LED negative pole, the collector electrode of the first bipolar transistor Q1 is connected to an end of base stage and the 3rd resistor R 3 of the second bipolar transistor Q2, the emitter of the other end of the 3rd resistor R 3 and the second bipolar transistor Q2 is received ground altogether, and the collector electrode of the second bipolar transistor Q2 is connected to the Enable Pin en of described control chip.Wherein, the first bipolar transistor Q1 can be PNP transistor, and the second bipolar transistor Q2 can be NPN transistor.

According to another embodiment of the present utility model, transistor negative feedback control module comprises the second MOS transistor M2, the 3rd MOS transistor M3, second resistor R 2 and the 3rd resistor R 3, wherein the source electrode of the second MOS transistor M2 is connected to the positive pole of described LED via second resistor R 2, the grid of the second MOS transistor M2 is connected to described LED negative pole, the drain electrode of the second MOS transistor M2 is connected to the grid of the 3rd MOS transistor M3 and an end of the 3rd resistor R 3, the source electrode of the other end of the 3rd resistor R 3 and the 3rd MOS transistor M3 is received ground altogether, and the drain electrode of the 3rd MOS transistor M3 is connected to the Enable Pin en of described control chip.Wherein the second MOS transistor M2 can be the PMOS transistor, and the 3rd MOS transistor M3 can be nmos pass transistor.

The circuit module that the utility model adopts transistor and resistance to constitute replaces voltage-stabiliser tube of the prior art and optocoupler; not only realized open circuit protecting function; and because transistor and resistive technologies maturation, cost is low and reliability is high, thereby make low and reliability is high according to open loop protection circuit cost of the present utility model.

Description of drawings

Fig. 1 is the schematic diagram of traditional LED open loop protection circuit;

Fig. 2 is the schematic diagram according to the LED open circuit guard circuit featuring low cost and high reliability of the utility model one embodiment;

Fig. 3 is the schematic diagram according to the LED open circuit guard circuit featuring low cost and high reliability of another embodiment of the utility model.

Embodiment

Below, describe in detail in conjunction with the accompanying drawings according to preferred embodiment of the present utility model.

At first; for existing open loop protection circuit as shown in Figure 1; the Control Network that the technical solution of the utility model adopts transistor negative feedback control module to replace traditional voltage-stabiliser tube and optocoupler to constitute; by the output voltage at LED two ends is sampled; and generation outputs to the output signal of the Enable Pin en of control chip; control the break-make of the first MOS transistor M1, realize open circuit protecting function.

Particularly, as shown in Figure 2, LED is connected with output capacitor Cout is parallel with one another, the positive pole of LED is connected to power supply Vin, one end of inductance L 1 is connected with the negative pole of LED, the other end of inductance L 1 is connected with the drain electrode of the first MOS transistor M1, the source electrode of the first MOS transistor M1 is via first resistor R, 1 ground connection, the positive pole of sustained diode 1 is connected to the drain electrode of the first MOS transistor M1, the negative pole of sustained diode 1 is connected to the positive pole of LED, the break-make of the control chip 21 controls first MOS transistor M1, the output port gate of control chip 21 is connected to the grid of the first MOS transistor M1, and output port cs is connected with the source electrode of the first MOS transistor M1, and decoupling capacitor Cin is connected between power supply Vin and the ground.

Transistor negative feedback control module comprises the first bipolar transistor Q1, the second bipolar transistor Q2, second resistor R 2 and the 3rd resistor R 3.The emitter of the first bipolar transistor Q1 is connected to the positive pole of LED via second resistor R 2, the base stage of the first bipolar transistor Q1 is connected to the negative pole of LED, the collector electrode of the first bipolar transistor Q1 is connected to an end of base stage and the 3rd resistor R 3 of the second bipolar transistor Q2, the emitter of the other end of the 3rd resistor R 3 and the second bipolar transistor Q2 is received ground altogether, and the collector electrode of the second bipolar transistor Q2 is connected to the Enable Pin en of control chip.In the preferred embodiment, the first bipolar transistor Q1 is a PNP transistor, and the second bipolar transistor Q2 is a NPN transistor.

Among this embodiment, amplify output voltage V out, and in order to driving pulldown network, the Enable Pin en of control chip 21 is dragged down, thereby control the shutoff of the first MOS transistor M1 by the degenerative grounded emitter amplifier of emitter-base bandgap grading.Particularly, by second resistor R 2 and the first bipolar transistor Q1 output voltage V out is converted to electric current, this electric current flows into second resistor R 2 and produces voltage, the base stage of this voltage control second bipolar transistor Q2, thereby the generation pull-down current drags down the Enable Pin en of control chip 21, thereby turn-off the first MOS transistor M1 by control chip 21, thereby limited output voltage.Output voltage satisfies as lower inequality:

$V_{\mathrm{out}}\≤V_{\mathrm{be}1}+\frac{R1*V_{\mathrm{be}2}}{R2}\≈\frac{R1}{R2}*0.7V$

The voltage that the voltage that makes actual needs export by design limits less than following formula approximately; (connect moment) when then lamp connects suddenly and just can not burn out, and this protective circuit also can not trigger the normal function of the system of influence when operate as normal because of the impulse current of high pressure generation.

Fig. 3 shows according to another preferred embodiment of the present utility model, the difference of itself and preferred embodiment shown in Figure 2 only is, adopts the second MOS transistor M2 and the 3rd MOS transistor M3 to replace the first bipolar transistor Q1 and the second bipolar transistor Q2 respectively.Correspondingly, adopt the second MOS transistor M2 and second resistor R 2 that output voltage V out is converted into electric current and forms voltage on second resistor R 2, in order to control the conducting of the 3rd MOS transistor M3, thereby the Enable Pin en of control chip 31 dragged down turn-off the first MOS transistor M1, output voltage is limited when making open circuit.

Should be appreciated that; the technical solution of the utility model adopts the degenerative mode of emitter-base bandgap grading (source class) that output voltage is converted into electric current; and generation correspondent voltage oxide-semiconductor control transistors conducting on resistance; thereby the Enable Pin of control chip is dragged down; correspondingly turn-off the output switching tube, the restriction output voltage, thus realize open-circuit-protection; this protected mode adopts ripe transistor cheaply and resistance to realize, thereby reliability height and cost are low.

Described in this specification is preferred specific embodiment of the present utility model, and above embodiment is only in order to the explanation the technical solution of the utility model but not to restriction of the present utility model.All those skilled in the art according to design of the present utility model by the available technical scheme of logical analysis, reasoning, or a limited experiment, all should be within as the scope of the present utility model that claim defined.

Claims (6)

1. LED open circuit guard circuit featuring low cost and high reliability comprises: the LED of connection parallel with one another and output capacitor Cout, and the positive pole of LED is connected to power supply Vin; Inductance L 1, the one end is connected with the negative pole of LED; The first MOS transistor M1, its drain electrode is connected with the other end of inductance L 1, and source electrode is via first resistor R, 1 ground connection; Sustained diode 1, its positive pole is connected to the drain electrode of the first MOS transistor M1, and negative pole is connected to the positive pole of LED; Control the control chip of the first MOS transistor M1 break-make, this control chip has Enable Pin en and output port gate, cs, wherein output port gate is connected to the grid of the first MOS transistor M1, and output port cs is connected with the source electrode of the first MOS transistor M1; It is characterized in that further comprise transistor negative feedback control module, this control module is sampled to the output voltage at LED two ends, and produce the output signal of the Enable Pin en that outputs to described control chip, to control the break-make of the first MOS transistor M1.

2. LED open circuit guard circuit featuring low cost and high reliability as claimed in claim 1; it is characterized in that; described transistor negative feedback control module comprises the first bipolar transistor Q1; the second bipolar transistor Q2; second resistor R 2 and the 3rd resistor R 3; wherein the emitter of the first bipolar transistor Q1 is connected to the positive pole of described LED via second resistor R 2; the base stage of the first bipolar transistor Q1 is connected to described LED negative pole; the collector electrode of the first bipolar transistor Q1 is connected to an end of base stage and the 3rd resistor R 3 of the second bipolar transistor Q2; the emitter of the other end of the 3rd resistor R 3 and the second bipolar transistor Q2 is received ground altogether, and the collector electrode of the second bipolar transistor Q2 is connected to the Enable Pin en of described control chip.

3. LED open circuit guard circuit featuring low cost and high reliability as claimed in claim 2 is characterized in that, the described first bipolar transistor Q1 is a PNP transistor, and the described second bipolar transistor Q2 is a NPN transistor.

4. LED open circuit guard circuit featuring low cost and high reliability as claimed in claim 1; it is characterized in that; described transistor negative feedback control module comprises the second MOS transistor M2; the 3rd MOS transistor M3; second resistor R 2 and the 3rd resistor R 3; wherein the source electrode of the second MOS transistor M2 is connected to the positive pole of described LED via second resistor R 2; the grid of the second MOS transistor M2 is connected to described LED negative pole; the drain electrode of the second MOS transistor M2 is connected to the grid of the 3rd MOS transistor M3 and an end of the 3rd resistor R 3; the source electrode of the other end of the 3rd resistor R 3 and the 3rd MOS transistor M3 is received ground altogether, and the drain electrode of the 3rd MOS transistor M3 is connected to the Enable Pin en of described control chip.

5. LED open circuit guard circuit featuring low cost and high reliability as claimed in claim 2 is characterized in that, the described second MOS transistor M2 is the PMOS transistor, and described the 3rd MOS transistor M3 is a nmos pass transistor.

6. as each described LED open circuit guard circuit featuring low cost and high reliability among the claim 1-5, it is characterized in that, further comprise the decoupling capacitor Cin that is connected between power supply Vin and the ground.

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