CN103152928A - Load overvoltage protection circuit and control method thereof - Google Patents
Load overvoltage protection circuit and control method thereof Download PDFInfo
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- CN103152928A CN103152928A CN2013100544966A CN201310054496A CN103152928A CN 103152928 A CN103152928 A CN 103152928A CN 2013100544966 A CN2013100544966 A CN 2013100544966A CN 201310054496 A CN201310054496 A CN 201310054496A CN 103152928 A CN103152928 A CN 103152928A
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Abstract
The invention provides a load overvoltage protection circuit and a control method thereof. The load overvoltage protection circuit comprises a load overvoltage judging circuit, a load voltage detection circuit and a PWM (Pulse Width Modulation) control circuit. During the process of the control method, a stable power supply voltage is input into the load overvoltage judging circuit; a voltage detection signal of the load voltage detection circuit is overlapped onto the stable power supply voltage, and input into the load overvoltage judging circuit; a reference voltage is input into the load overvoltage judging circuit; a summation of the stable power supply voltage and the reference voltage is used as the reference voltage; when the voltage of the voltage detection signal of the load voltage detection circuit exceeds the reference voltage, the load overvoltage judging circuit sends out an overvoltage protection signal; and the PWM control circuit receives the overvoltage protection signal, so that a power tube switch is controlled for load overvoltage protection. Not only is the load overvoltage protection circuit simplified, but also the precise load voltage judgment can be realized; and moreover, the detection current is recycled, and the system efficiency is improved.
Description
Technical field
The present invention relates to load voltage protective circuit technical field, relate in particular to a kind of load overvoltage protective circuit and control method thereof
Background technology
In LED driver, the current-voltage relation of LED is all the exponential type relation with conventional diode, when the forward voltage that applies with less dv/dt rate of change, can cause having the forward current of larger di/dt rate of change.Therefore, keeping the LED current constant is the best approach of controlling LED.In the LED driver of constant current output, its output voltage should be the forward voltage sum of the LED of all series connection.In case the LED as load disconnects, the actual loading of step-down or buck LED driver will be transformed into the electric capacity in parallel with lead-out terminal so.Therefore, this electric capacity will be charged to input supply voltage rapidly, and this has surpassed the maximum working voltage of electric capacity and can cause safety problem, for example causes electric capacity to be blasted.Therefore should add overvoltage crowbar solving safety problem in LED driver, and be subject to the impact of large surge current when preventing between LED load and driver output loose contact.
Patent documentation formerly: the utility model patent CN202353850U of the People's Republic of China (PRC).
The schematic diagram of the open loop protection circuit of existing LED drive circuit employing is disclosed in patent documentation formerly; as shown in Figure 1; the agent structure of this LED drive circuit is a typical voltage-dropping type LED control circuit; partly formed by inductance 101, diode 102, power tube 103, PWM control unit 104 etc.; pwm control signal by 104 outputs of PWM control unit; make power tube 103 periodically open and turn-off, realize the purpose of constant-current driving LED load.
This LED drive circuit has adopted in order to realize the defencive function when LED opens a way the protection protective circuit that is comprised of a plurality of electronic devices and components, comprising: zener D1, D2, triode Q1, resistance R 1, R2, capacitor C 2 and metal-oxide-semiconductor Q2.The operation principle of this LED open-circuit-protection is as follows: after load LED open circuit; the PWM control unit will continue to send pwm signal; load voltage Vled on output capacitance (namely; voltage in Fig. 1 between LED+ and LED-) will continue to raise; this voltage Vled is by resistance R 1; zener D1 and triode Q1 convert electric current I c, Ic=(Vled-VD1-Vbe to)/R1, wherein Vbe is the emitter junction voltage of triode Q1.this electric current I c flows through a resistance R 2 that connects with ground, produce one with respect to ground, and voltage detection signal (Vled-VD1-Vbe) the * R2/R1 relevant with load voltage Vled, then utilize the threshold voltage vt h of this voltage detection signal and a metal-oxide-semiconductor Q2 to compare, when the voltage detection signal that is added in metal-oxide-semiconductor Q2 grid level during greater than its threshold voltage vt h, the drain electrode of metal-oxide-semiconductor Q2 will become low level, thereby close the PWM control unit, there is no pwm signal output, voltage on output capacitance just can not raise again, therefore realized the defencive function when LED opens a way, output capacitance and LED load have been protected.
The course of work by above-mentioned protective circuit can be derived, and the magnitude of voltage that obtains overvoltage protection is:
The shortcoming of above-mentioned existing overvoltage crowbar is: one, and circuit structure is complicated, in order to prevent vibration, frequency compensation capacitor C 2 need to be set; Its two, detect the output loading voltage signal and the electric current I c that produces flows to ground by resistance, could not recycle, reduced system effectiveness; Its three, the overvoltage protection threshold accuracy is not high, easily is subject to the impact of metal-oxide-semiconductor voltage threshold, overvoltage protection threshold value and metal-oxide-semiconductor technological parameter and temperature have relation.
Summary of the invention
In order to solve the shortcoming of traditional overvoltage crowbar, the present invention proposes a kind of simpler and efficient load overvoltage protective circuit, and this protective circuit is simple and reliable for structure, stable performance; The overvoltage protection threshold accuracy is high, does not change with flow-route and temperature; And can recycle the electric current that detects the output loading voltage signal and produce, improve system effectiveness.
According to a kind of load overvoltage protective circuit of the present invention, comprising:
The load voltage testing circuit, it is connected in parallel on load circuit two ends, and for detection of load voltage, described load voltage testing circuit is superimposed upon on a stable voltage, and exports the load voltage detection signal that and this voltage and load voltage all are correlated with;
The PWM control unit; comprise load overvoltage decision circuitry and pwm control circuit; wherein the load overvoltage decision circuitry receives described load voltage detection signal, described stable voltage and a reference voltage; and generation overvoltage protection signal; pwm control circuit receives described overvoltage protection signal; and produce control signal power ratio control switch, and make the voltage on output capacitance no longer increase, realize the load overvoltage protection.
Preferably, above-mentioned load overvoltage protective circuit is characterized in that, also comprises from the power supply circuit of input voltage power taking, and it produces stable supply voltage and powers to the PWM control unit.
Preferably, above-mentioned load overvoltage protective circuit is characterized in that, described stable voltage is the stable supply voltage that power supply circuit produces.
Preferably, above-mentioned load overvoltage protective circuit is characterized in that, described power supply circuit is by the 3rd resistance, and voltage-stabiliser tube and the second electric capacity form.
Preferably, above-mentioned load overvoltage protective circuit is characterized in that, described power supply circuit is by the open type device, and voltage-stabiliser tube and the second electric capacity form.
Preferably, above-mentioned load overvoltage protective circuit is characterized in that, described open type device is selected from JFET or depletion type MOS tube.
Preferably; above-mentioned load overvoltage protective circuit; it is characterized in that; the voltage detection signal relevant with load voltage of described load voltage testing circuit output is superimposed upon on the second electric capacity of described power supply circuit, and the electric current that the detection load voltage produces flows into power supply circuit by the second resistance and recycles.
Preferably, above-mentioned load overvoltage protective circuit is characterized in that, described load voltage testing circuit is comprised of a positive-negative-positive triode and the first resistance, the second resistance.
Preferably, above-mentioned load overvoltage protective circuit is characterized in that, described load voltage testing circuit forms by a P type metal-oxide-semiconductor with the first resistance, the second resistance.
Preferably, above-mentioned load overvoltage protective circuit is characterized in that, described load voltage testing circuit is comprised of a diode and the 4th resistance, the second resistance.
According to the high-end voltage-dropping type topological structure of a kind of power switch provided by the invention, comprise above-mentioned load overvoltage protective circuit.
Preferably, the high-end voltage-dropping type topological structure of above-mentioned power switch is characterized in that, also comprises power supply circuit, and described power supply circuit is by resistance, and voltage-stabiliser tube and electric capacity form.
Preferably, the high-end voltage-dropping type topological structure of above-mentioned power switch is characterized in that, described power supply circuit is by the open type device, and voltage-stabiliser tube and electric capacity form.
Preferably, the high-end voltage-dropping type topological structure of above-mentioned power switch is characterized in that described open type device is selected from JFET or depletion type MOS tube.
According to a kind of buck-boost type topological structure provided by the invention, comprise above-mentioned load overvoltage protective circuit.
Control method according to a kind of load overvoltage protective circuit provided by the invention comprises the following steps:
The first step: with a stable voltage input load overvoltage decision circuitry;
Second step: the voltage detection signal of load voltage testing circuit output is superimposed upon the load voltage detection signal that forms on described stable voltage, and input load overvoltage decision circuitry;
The 3rd step: with reference to voltage input load overvoltage decision circuitry;
The 4th step: after the voltage of the voltage detection signal of load voltage testing circuit surpassed described reference voltage, the load overvoltage decision circuitry was sent the overvoltage protection signal;
The 5th step: pwm control circuit receives described overvoltage protection signal, and the load overvoltage protection is carried out in the switch motion of power ratio control pipe.
Preferably, the voltage that the described first step is stable is the stable supply voltage that power supply circuit produces.
As seen, adopt load overvoltage protective circuit of the present invention and control method, not only the overvoltage protection threshold accuracy is high, does not need to carry out stabiloity compensation, and has recycled the detection electric current that detects load voltage and produce and powered to the PWM control unit.Therefore can realize following beneficial effect at least:
(1) protective circuit is simple and reliable for structure, there is no stability problem, and the element that uses has still less increased the reliability of system;
(2) the overvoltage protection threshold accuracy is high, does not change with flow-route and temperature;
(3) detect detection electric current that load voltage produces to the power supply of PWM control unit owing to having recycled, improved the efficient of system.
Description of drawings
Figure 1 shows that the theory diagram of the load overvoltage protective circuit that adopts prior art.
Fig. 2 A is depicted as the theory diagram according to the first embodiment of load overvoltage protective circuit of the present invention.
Fig. 2 B is depicted as the theory diagram of the load overvoltage decision circuitry of the load overvoltage protective circuit shown in Fig. 2 A.
Figure 3 shows that the theory diagram according to the second embodiment of load overvoltage protective circuit of the present invention.
Figure 4 shows that the theory diagram according to the 3rd embodiment of load overvoltage protective circuit of the present invention.
Figure 5 shows that the theory diagram according to the 4th embodiment of load overvoltage protective circuit of the present invention.
Figure 6 shows that the theory diagram according to the 5th embodiment of load overvoltage protective circuit of the present invention.
Figure 7 shows that the flow chart of the first embodiment of the control method of protecting according to load overvoltage of the present invention.
Reference numeral
101 first inductance; 102 first diodes; 103 first power tubes; 104 the one PWM control units; 105 first load overvoltage protective circuits; 200 the 2nd PWM control units; The 201PWM control circuit; 202 load overvoltage decision circuitry; 203 first power supply circuits; 204 power switchs; 205 first load voltage testing circuits; 206 second inductance; 207 second diodes; 208 load circuits; 209 first electric capacity; 210 first resistance; 211 first triodes; 212 second resistance; 213 the 3rd resistance; 214 second electric capacity; 215 Zener voltage-stabiliser tubes; 217 comparators; 218 reference voltage sources; 300 second embodiment; 301 second power supply circuits; 302 JFET; 400 the 3rd embodiment; 500 the 4th embodiment; 501 second load voltage testing circuits; 502 the 4th resistance; 503 the 3rd diodes; 600 the 5th embodiment; 700 workflow diagrams; 701 first steps; 702 second steps; 703 the 3rd steps; 704 the 4th steps; 705 the 5th steps.
Embodiment
Below in conjunction with accompanying drawing, the preferred embodiments of the present invention are described in detail, but the present invention is not restricted to these embodiment.The present invention contain any make on marrow of the present invention and scope substitute, modification, equivalent method and scheme.Understand for the public is had thoroughly the present invention, describe concrete details in detail in the following preferred embodiment of the present invention, and for a person skilled in the art, do not have the description of these details also can understand the present invention fully.Need to prove, discuss as load circuit although the application's advantage is based on LED in background technology,, load overvoltage protective circuit provided by the invention obviously also can be for the protection of the load circuit of other kinds type.
The first embodiment
With reference to figure 2A, be depicted as the theory diagram according to the first load overvoltage protective circuit of the first embodiment of the present invention, wherein said load overvoltage protective circuit is applied to power switch low side voltage-dropping type topological structure, and it comprises following part:
The second inductance 206, be connected to the power switch 204 between the second inductance 206 1 ends and ground, be connected to the load circuit 208 between second inductance 206 other ends and input voltage VIN, this load circuit 208 can be the load circuit that one or more LED light-emitting components consist of; And be connected to the common port of the second inductance 206 and power switch 204 and the second diode (as fly-wheel diode) 207 between input voltage VIN; And the system power supply power circuit 203 that is formed by the 3rd resistance 213, the second electric capacity 214 and Zener voltage-stabiliser tube 215; System power supply power circuit 203 provides stable supply voltage VCC for PWM control unit 200,
The load overvoltage protective circuit further comprises load voltage testing circuit 205, is connected in parallel on load circuit 208 and output filter capacitor 209 two ends, for detection of load voltage Vled.Load voltage testing circuit 205 one of output and stable supply voltage VCC, the load voltage detection signal OVI that load voltage Vled is correlated with, load voltage Vled on load voltage detection signal OVI and load circuit 208 is linearly proportional, as formula (1):
Wherein, described load voltage testing circuit 205 comprises the first triode 211, the first resistance 210 and second resistance 212 of positive-negative-positive.The base stage of this first triode 211 is connected in the second inductance 206 and load circuit 208 common ports, emitter is connected in the first resistance 210, collector electrode is connected in the 3rd resistance 213 and the second resistance 212 common ports, first resistance 210 other ends are connected in input voltage VIN, and resistance 212 other ends are connected in described stable supply voltage VCC; Wherein from one of collector electrode output and stable supply voltage, the load voltage detection signal OVI that load voltage Vled is correlated with.Alternatively, the first triode 211 of above-mentioned positive-negative-positive can be replaced with P type metal-oxide-semiconductor or diode.
The theory diagram of load overvoltage decision circuitry 202 is as shown in Fig. 2 B, and the input in the same way of a comparator 217 is load voltage detection signal OVI, and reverse input end is the positive pole that is superimposed upon the reference voltage source Vref on described stable supply voltage VCC.When the abnormal situation; load voltage Vled on load circuit 208 begins to raise; the load voltage detection signal OVI of load voltage testing circuit 205 outputs simultaneously also begins to raise; when load voltage detection signal OVI be elevated to add the reference voltage Vref sum higher than described stable supply voltage VCC after, comparator 217 output loading overvoltage protection signal OVP.
According to the first embodiment of a kind of load overvoltage protective circuit of the invention described above, the overvoltage protection threshold value of load voltage Vled is:
（2）
Wherein Vbe is the emitter junction voltage of triode 211, and Vref is input reference voltage, and R1 is the resistance value of the first resistance 210, and R2 is the resistance value of the second resistance 212, by the value of adjusting resistance R1 and resistance R 2, can set the overvoltage protection threshold value of expectation.
The second embodiment
With reference to figure 3; be depicted as the theory diagram 300 according to the second embodiment of a kind of load overvoltage protective circuit of the present invention; wherein said load overvoltage protective circuit is applied to power switch low side voltage-dropping type topological structure, and the difference of the embodiment shown in this embodiment and Fig. 2 A only is power supply circuit.
In a second embodiment, power supply circuit 301 is comprised of open type device 302, Zener voltage-stabiliser tube 215 and the second electric capacity 214.Described open type device 302 can adopt depletion type MOS tube or JFET etc., and that Fig. 3 adopts in this example is JFET.The end ground connection of JFET302, another termination input voltage VIN, the common port of the 3rd termination the second resistance 212 and triode 211, power supply circuit 301 provides stable supply voltage VCC for PWM control unit 205 by JFET302, the second electric capacity 214 and Zener voltage-stabiliser tube 215.
The 3rd embodiment
With reference to figure 4; be depicted as the theory diagram 400 according to the 3rd embodiment of a kind of load overvoltage protective circuit of the present invention, the difference of the embodiment shown in this embodiment and Fig. 2 A only is that described load overvoltage protective circuit is applied to the high-end voltage-dropping type topological structure of power switch.
The 4th embodiment
With reference to figure 5; be depicted as the theory diagram 500 according to the 4th embodiment of a kind of load overvoltage protective circuit of the present invention; the difference of this embodiment and the 3rd embodiment shown in Figure 4 only is the second load voltage testing circuit 501; in the 4th embodiment; described the second load voltage testing circuit 501 is by the 3rd diode 503; the 4th resistance 502 and the second resistance 212 form; still linearly proportional by load voltage detection signal OVI and the load voltage Vled on load circuit 208 that described the second load voltage testing circuit 501 obtains, as shown in the formula described:
Can be derived by following formula, the overvoltage protection threshold value of the load voltage Vled of the 4th embodiment of foundation a kind of load overvoltage protective circuit of the present invention is:
Wherein, VD is the conduction voltage drop of the 3rd diode 503, and Vref is input reference voltage, and VCC is stable supply voltage, and R2 is the resistance value of the second resistance 212, and R3 is the resistance value of the 4th resistance 502; By adjusting the value of R2 and R3, can set desired overvoltage protection threshold value.
The 5th embodiment
With reference to figure 6; be depicted as the theory diagram 600 according to the 5th embodiment of a kind of load overvoltage protective circuit of the present invention, the difference of the first embodiment shown in this embodiment and Fig. 2 A only is that described load overvoltage protective circuit is applied to a buck-boost type topological structure.
Figure 7 shows that described control method comprises the following steps according to the flow chart 700 of an embodiment of the control method of a kind of load overvoltage protective circuit of the present invention:
The first step: with a stable voltage input load overvoltage decision circuitry;
Second step: the voltage detection signal of load voltage testing circuit output is superimposed upon formation load voltage detection signal on described stable voltage, and input load overvoltage decision circuitry;
The 3rd step: with reference to voltage input load overvoltage decision circuitry;
The 4th step: after the voltage of the voltage detection signal of load voltage testing circuit surpassed described reference voltage, the load overvoltage decision circuitry was sent the overvoltage protection signal;
The 5th step: pwm control circuit receives described overvoltage protection signal, and the load overvoltage protection is carried out in the switch motion of power ratio control pipe,
Preferably, the voltage that the described first step is stable is the stable supply voltage that power supply circuit produces.
As indicated above according to embodiments of the invention, these embodiment do not have all details of detailed descriptionthe, do not limit this invention yet and only are described specific embodiment.Show, according to above description, can make many modifications and variations.These embodiment are chosen and specifically described to this specification, is in order to explain better principle of the present invention and practical application, thereby under making, the technical field technical staff can well utilize the present invention and the modification on basis of the present invention to use.The present invention only is subjected to the extremely restriction of four corner and equivalent of claims.
Claims (10)
1. load overvoltage protective circuit comprises:
Load voltage testing circuit (205), it is connected in parallel on load circuit (208) two ends, for detection of load voltage, described load voltage testing circuit (205) is superimposed upon on a stable voltage, and exports the load voltage detection signal that and this voltage and load voltage all are correlated with;
PWM control unit (200); comprise load overvoltage decision circuitry (202) and pwm control circuit (201); wherein load overvoltage decision circuitry (202) receives described load voltage detection signal, described stable voltage and a reference voltage signal; and generation overvoltage protection signal; pwm control circuit (201) receives described overvoltage protection signal; and produce control signal power ratio control switch, and make the voltage on output capacitance no longer increase, realize the load overvoltage protection.
2. load overvoltage protective circuit according to claim 1, is characterized in that, also comprises from the power supply circuit of input voltage power taking, and it produces stable supply voltage and powers to the PWM control unit.
3. load overvoltage protective circuit according to claim 1, is characterized in that, described stable voltage is the stable supply voltage that power supply circuit produces.
4. load overvoltage protective circuit according to claim 2, is characterized in that, described power supply circuit is by the 3rd resistance (213), and voltage-stabiliser tube (215) and the second electric capacity (214) form.
5. load overvoltage protective circuit according to claim 2, is characterized in that, described power supply circuit is by open type device (302), and voltage-stabiliser tube (215) and the second electric capacity (214) form.
6. load overvoltage protective circuit according to claim 5, is characterized in that, described open type device is selected from JFET or depletion type MOS tube.
7. load overvoltage protective circuit according to claim 1; it is characterized in that; the voltage detection signal relevant with load voltage of described load voltage testing circuit output is superimposed upon on the second electric capacity of described power supply circuit, and the electric current that the detection load voltage produces flows into power supply circuit by the second resistance (212) and recycles.
8. load overvoltage protective circuit according to claim 7, is characterized in that, described load voltage testing circuit is comprised of a positive-negative-positive triode (211) and the first resistance (210), the second resistance (212).
9. load overvoltage protective circuit according to claim 7, is characterized in that, described load voltage testing circuit forms by a P type metal-oxide-semiconductor with the first resistance (210), the second resistance (212).
10. load overvoltage protective circuit according to claim 7, is characterized in that, described load voltage testing circuit is comprised of a diode (503) and the 4th resistance (502), the second resistance (212).
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| CN2013100544966A CN103152928A (en) | 2013-02-20 | 2013-02-20 | Load overvoltage protection circuit and control method thereof |
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| CN2013100544966A CN103152928A (en) | 2013-02-20 | 2013-02-20 | Load overvoltage protection circuit and control method thereof |
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| CN103428970A (en) * | 2013-07-23 | 2013-12-04 | 美芯晟科技（北京）有限公司 | Non-isolated LED (light-emitting diode) driving circuit and control method |
| CN104093254A (en) * | 2014-07-22 | 2014-10-08 | 矽力杰半导体技术(杭州)有限公司 | LED overvoltage detection circuit, drive circuit and LED illuminating system |
| CN106714389A (en) * | 2017-02-16 | 2017-05-24 | 深圳市晟碟半导体有限公司 | LED (Light Emitting Diode) driving device and surge protection circuit and surge protection method of LED driving device |
| CN107544374A (en) * | 2017-06-05 | 2018-01-05 | 苏州天信德环保科技有限公司 | A kind of basic model total quantity monitoring instrument |
| CN107810618A (en) * | 2015-05-28 | 2018-03-16 | 飞利浦照明控股有限公司 | Compulsory large value capacitor electric discharge in current-collecting device |
| CN110730541A (en) * | 2018-06-29 | 2020-01-24 | 法雷奥汽车内部控制（深圳）有限公司 | Open circuit protection circuit for LED driver |
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| CN110730541A (en) * | 2018-06-29 | 2020-01-24 | 法雷奥汽车内部控制（深圳）有限公司 | Open circuit protection circuit for LED driver |
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Application publication date: 20130612 |