CN202818086U

CN202818086U - Circuit inhibiting switching power supply from outputting overshoot voltage during power-on

Info

Publication number: CN202818086U
Application number: CN2012204010672U
Authority: CN
Inventors: 徐军; 严祖军
Original assignee: TPV Display Technology Wuhan Co Ltd
Current assignee: TPV Display Technology Wuhan Co Ltd
Priority date: 2012-08-14
Filing date: 2012-08-14
Publication date: 2013-03-20
Anticipated expiration: 2022-08-14
Also published as: TWM457343U

Abstract

The utility model relates to a switching power supply of a liquid crystal display product, and particularly relates to a circuit inhibiting the switching power supply from outputting overshoot voltage during power-on. The circuit comprises a power supply output end and a feedback end, and is characterized in that the power supply output end is connected to a capacitor, a reference end of a three-terminal shunt regulator of the feedback end is connected to a resistor, and the capacitor is connected with the resistor in series. The circuit provided by the utility model has the beneficial effect that the difficulty in solving an abnormal noise problem in a standby operating model is improved, and the circuit can enable parameters of the capacitance of the capacitor C11 and the resistance of the resistor R6 to be modified dramatically so as to solve the abnormal noise problem in the standby mode; and a circumstance that mainboard components are damaged or even burned because of severe overshoot voltage of 5V at the power-on moment is improved, and the reliability of products is promoted.

Description

A kind of circuit that suppresses Switching Power Supply output overshoot voltage when start

Technical field

The utility model relates to the Switching Power Supply of liquid crystal display product, concrete relates to a kind of circuit that suppresses Switching Power Supply output overshoot voltage when start.

Background technology

Fig. 1 is that available liquid crystal shows that product exchanges an example that turns direct current (AC-DC) power supply.This power supply structure is the inverse-excitation type framework, and two groups of Vout1 and Vout2 output is arranged.It is that the direct current of 5V is as the supply power voltage of the motherboard circuit of liquid crystal display product that Vout1 exports a representative value; Vout2 export a representative value for as: the direct current of 16V is as LED lamp tube drive circuit input supply power voltage.This Vout1 5V output is undertaken offering three-terminal shunt regulator behind the voltage sample by R8 and R9 resistance, as: the R end (reference edge) of TL431, after sampling by R8 and R10 resistance, this Vout2 16V output also offers three-terminal shunt regulator, as: the R end (reference edge) of TL431.After the reference voltage that it is 2.5V that the R of TL431 holds resulting sampled voltage and the inner voltage of TL431 compares, the output of the electric crystal of TL431 inside will be exported an electric current I ka, so that the input light-emittingdiode of IC902 optocoupler obtains an electric current I f=Ika-Ir14=Ika-Vf/R14, wherein Vf is IC902 optocoupler light-emittingdiode forward conduction voltage, be approximately about 1.2V, R14 is the resistance of resistance R 14.Determine the size of this optocoupler output electric crystal collector electrode and emitter current flowing Ic according to IC902 optocoupler light-emittingdiode If size, be Ic=If*CTR, wherein CTR is the optocoupler transmission ratio such as CTR=70%, the size of current of this Ic directly has influence on the voltage quasi position size of control chip IC FB feedback pin, and the voltage swing of FB pin will directly have influence on duty ratio (duty) size of pulse modulation (PWM) pulse square wave of this flyback power supply control chip IC1 Gate pin output, and the power conversion by Q1 N metal-oxide-semiconductor control transformer T1, thereby controlled output voltage to reach substantially invariable direct voltage.Fig. 1 has adopted 5V and the two feedback controling modes of 16V, but need comparatively accurate because 5V is the supply power voltage that offers motherboard circuit, so at present general 5V output voltage specification all is controlled at 5V(1 ± 5%) in, that is: 4.75V ~ 5.25V, and the 16V output voltage generally only offers the drive circuitry that the DC-DC Boost of LED fluorescent tube boosts, the circuit that present this DC-DC Boost boosts requires looser to input voltage range, (for example: the input voltage of the circuit that the above DC-DC Boost of output 30V boosts generally drop on about 12V-23V can) so general feedback circuit can be set to the primary feedback circuit with 5V output, 16V output generally be set to time feedback circuit.That is: this flyback power supply is the PWM Duty size that decides the output of control chip IC1 Gate pin by the fluctuation of detecting 5V output end voltage basically, thus the control transformer Energy Transfer.

Fig. 2 is another example that available liquid crystal shows product A C-DC power supply, adopts the single feedback controling mode of 5V.This AC-DC power supply product uses usually in multi-functional lcd products, also will offer the circuit supplies such as USB, Audio except offering mainboard work, so that the 5V output loading is larger.(that is: switch power supply system input AC mains after) 5V is arduous after start carries (Max loading) and 16V output is not eaten when carrying, if adopting two feedback circuits of Fig. 1 to produce easily the 5V output voltage is dragged down because the 16V output voltage rises by a relatively large margin, can make when serious the 5V instant power-down to as: below the 4V, so that the control chips such as the microcontroller of mainboard end (MCU) and picture processing chip (Scaler) can't work; If adopt the single feedback circuit of the 5V of Fig. 2,16V output this moment mainly is to rely on dummy load circuit ZD1, Q2, R11 ~ R13 to do the output voltage clamper.For the Energy Saving Control chip (such as logical good LD7750 control chip) of stand-by power consumption less than 0.1W Switching Power Supply scheme, for control chip itself more energy-conservation, the maximum current Ic with its FB pin (LD7750 is called the COMP pin) output is adjusted to 0.32mA, so that the electric current I f that optocoupler IC902 input diode flows through only is If=Ic/CTR=0.32mA/0.7=0.45mA(hypothesis CTR=70%); And TL431 itself requires the electric current of cathode terminal (K end) minimum when normal operation to be at least 1mA at present, so the resistance R 14 in parallel with optocoupler input light-emittingdiode needs to provide the electric current more than the Ir14=1mA-0.45mA=0.55mA at least, be that resistance R 14 resistance maximums can not surpass R14=Vf/Ir14=1V/0.55mA=1.8K, so an optocoupler input light-emittingdiode need resistance in parallel is about the resistance R 14 about 1K ~ 1.8K at present, and this resistance in parallel can have influence on the feedback speed of system, can make the feedback speed of reponse system slack-off, produce the 5V output voltage in overshoot voltage (Overshoot) problem of booting moment, when the parameter of other feedback circuit of power-supply system arranges when unreasonable, 5V will be more serious in the overshoot voltage phenomenon of booting moment, even mainboard (main board) end parts part is damaged, affect product reliability.The flyback power supply control chip for more energy-conservation, adopts burst mode (Burst-mode) control mode usually under standby mode.And the waveform of the feedback pin FB of control chip can have influence on pwm pulse radical and the PWM duty size of getting in the Burst-mode envelope of Burst-mode operating frequency, control chip Gate pin usually.Operating frequency is when the most responsive frequency band of 1KHZ ~ 4KHZ people's ear when Burst-mode, and transformer just produces different sound.Usually the resistance that needs to strengthen the appearance value of feedback pin direct-to-ground capacitance C11 and optocoupler light-emittingdiode input series connection resistance R 6 this moment can make the Burst-mode operating frequency drop on operating frequency section less than 1KHZ, and C11 appearance value strengthens and the increasing of R6 resistance makes feedback speed slack-off too, equally also can produce the 5V output voltage in overshoot voltage (Overshoot) problem of booting moment.

Summary of the invention

Technical problem to be solved in the utility model is to propose a kind of circuit that suppresses Switching Power Supply 5V output overshoot voltage when start for above-mentioned prior art, this circuit is so that this Switching Power Supply needs increase resistance R 14 to cause the switch power supply system feedback speed slack-off because solution TL431 negative electrode needs to flow through the 1mA electric current at least to anode tap when start, and need to be adjusted at when the Burst-mode operating frequency needs adjustment capacitor C 11 and resistance R 6 further to cause the slack-off problem of switch power supply system feedback speed under the standby mode less than 1KHZ, the 5V output voltage of Switching Power Supply still can not produce overshoot voltage (Overshoot) problem, guarantee that all electronic components of mainboard terminal circuit (Main board circuit) can be not destroyed because of problem of withstand voltage when Switching Power Supply is started shooting, thereby promoted the reliability of liquid crystal display product, reduced the market defect ratio of the mainboard (Main board) of lcd products.

The utility model solves the problems of the technologies described above the technical scheme that adopts: a kind of circuit that suppresses Switching Power Supply output overshoot voltage when start, include power output end and feedback end, it is characterized in that being connected with on the power output end electric capacity, the reference edge of the three-terminal shunt regulator of feedback end is connected with resistance, and electric capacity and resistance serial connection.

Such as Fig. 3, the utility model is in reference edge (R end) serial connection one resistance R 10 and the capacitor C 10 of IC3 TL431 at second group of output of inverse-excitation type Vout2, Vout2 begins to be the variation voltage that a larger linear gradient rises from 0V when utilizing start, make capacitor C 10 produce one electric current I=C10*dv/dt, this electric current I flows through current-limiting resistance R10 and TL431 reference edge over the ground during a resistance R 8, reference edge to this TL431 produces an additional voltage when starting shooting, so that the reference edge of TL431 obtained the voltage more than or equal to 2.5V in advance before Vout1 does not also reach normal output voltage 5V, so that TL431 internal electrical crystal conducting, thereby so that the input of IC902 optocoupler obtains an electric current I f, simultaneously so that the output of IC902 optocoupler obtains an electric current I c, this Ic electric current can make the current potential of the feedback FB pin of control chip IC1 be interrogated speed and drag down, so that the PWM square wave duty of control chip IC1 Gate pin output reduces, be that transformer output energy reduces, so that Vout1 becomes comparatively slow at the slope that voltage that a bit of voltage before also not reaching 5V rises.

The beneficial effects of the utility model are: not only improved 5V output overshoot voltage overshoot problem, and circuit design there are two large benefits: 1) improve the different sound solution of problem difficulty under the standy operation mode, examined filter to 5V output overshoot voltage overshoot problem so that C11 appearance value and R6 resistance parameter can not be made modification by a relatively large margin for the different mail topic of improving under the standy operation mode because of needs, and the different mail that the utility model can make C11 appearance value and the modification by a relatively large margin of R6 resistance parameter solve under the standby mode is inscribed in the past; 2) improving 5V causes the mainboard component wear even burns the improving product reliability at the serious overshoot voltage of booting moment.

Description of drawings

Fig. 1 is the example circuit diagram that available liquid crystal shows product A C-DC power supply;

Fig. 2 is another example circuit diagram that available liquid crystal shows product A C-DC power supply;

Fig. 3 is circuit diagram of the present utility model;

Oscillogram when Fig. 4 is first group of 5V output and second group of 16V output start;

Fig. 5 is the start timing waveform of Fig. 3 novel power supply;

Fig. 6 is the partial circuit diagram of Fig. 3 novel power supply control chip IC1 inside;

5V produced the schematic diagram of Overshoot phenomenon when Fig. 7 was the power panel start;

Fig. 8 arranges afterwards oscillogram of the capacitor C 10 of suitable parameter and a resistance R 10 for this power supply increases by one between the reference edge of Vout2 at TL431.

Embodiment

The utility model will be further described below in conjunction with accompanying drawing, but can not consist of restriction of the present utility model.

A kind of circuit that suppresses Switching Power Supply output overshoot voltage when start, include power output end and feedback end, it is characterized in that being connected with on the power output end electric capacity, the reference edge of the three-terminal shunt regulator of feedback end is connected with resistance, and electric capacity and resistance serial connection.

Embodiment 1 as shown in Figure 3, a kind of circuit that suppresses Switching Power Supply output overshoot voltage when start includes IC3 TL431 and Vout2 output, is connected with capacitor C 10 on the Vout2 output, the R end of IC3 TL431 is connected with resistance R 10, and capacitor C 10 and R10 serial connection.

Oscillogram when Fig. 4 is first group of 5V output and second group of 16V output start, when start, two groups of voltages of exporting all begin to rise from 0V, basically are the linear rising of certain slope, and the slope of second group of 16V output Vout2 rising is much bigger than first group of 5V output.

The below does the T1 time of concrete principle and action specification: Fig. 4 for when starting shooting to this new-type circuit, when the Vcc of control chip IC1 feeder ear voltage reaches Vcc (on) voltage, PWM IC control chip IC1 starts working, the Gate end pin of control chip IC1 will be exported the pwm pulse square wave that a duty ratio duty changes from small to big, and this process is referred to as again soft start (soft start);

The T2 time of Fig. 5 is when the pwm pulse duty cycle square wave will no longer increase behind certain value greatly; T1+T2 process Vout1 and Vout2 begin to be the linear rising of Different Slope from 0V.Slope when second group of output voltage V out2 rises as can be seen from Figure 4 is much bigger than Vout1, and when Vout2 voltage rose, it was the voltage variety at C10 two ends that capacitor C 10 will produce one electric current I=C10*dv/dt(dv at R8 resistance); Also produce one electric current I=Vout1/ (R8+R9) at R8 resistance when Vout1 voltage rises simultaneously, so produce the voltage of a voltage Vr=(I+ I) * R8=[Vout1/ (R8+R9)+C10*dv/dt] * R8 at R8 resistance.

In the T3 time of Fig. 5, when Vout1 voltage reach as: during 4.6V, Vr voltage has just reached the reference voltage Vref of its TL431 inside in advance; The base terminal voltage Vbe of TL431 internal electrical crystal begins to increase, so that this base terminal current Ib e also begins to increase, begin to produce an electric current I ka who begins to increase from 0A between the collector electrode of TL431 internal electrical crystal and the emitter, because the light-emittingdiode forward current If=Ika-Vf/R14(Vf of optocoupler IC2 input: the light-emittingdiode forward conduction voltage of optocoupler IC2 input, be approximately about 1.2V), so enter T3 constantly after the light-emittingdiode of optocoupler IC2 the one If electric current that begins to increase from 0A will be arranged, because the output of Ic=CTR*If(CTR optocoupler and the transmission ratio of inputting, as: CTR=70%), so the time will produce an electric current I c who is begun to increase by 0A at the output of optocoupler;

With reference to figure 6, the Vfb1 voltage of control chip IC1 inside is to be obtained by FB pin voltage Vfb conversion, Vcs2 voltage is to be changed after inter-process and obtained by the voltage that control chip current sense pin CS detecting comes, when the optocoupler output has electric current to flow through, the current potential Vfb of the FB pin of the control chip IC1 that is connected with optocoupler is dragged down, the Vfb1 current potential descends, and when the Ic electric current is larger, the Vfb1 of the FB pin current potential inside of control chip IC1 will be drawn lowlyer; The voltage of Vfb1 will controlled the time of the PWM high level ton of control chip IC1 Gate pin output, also namely: the size of controlling transformer T1 output secondary side output terminal energy.

As: when the Clock clock of control chip IC1 inside is sent the high level signal of a Vclk turn on, Q1 N-MOS manages conducting, transformer T1 produced one according to V=L*di/dt and substantially was the linear electric current that rises and flows through R2 resistance this moment, and via R3, the CS pin of control chip is provided after the C2 low-pass filtering, finally convert Vcs2 voltage to and Vfb1 voltage compares, when relatively to Vcs2 〉=Vfb1, control chip IC1 will export a low level signal from the Gate pin and make Q1 N-MOS turn off, until next clock Clock signal is when sending the high level signal of a Vclk turn on again, the again conducting of Q1 N-MOS pipe, so when Vfb1 voltage is lower, the turn on time of Q1 N-MOS is shorter, the turn off time is longer, and the electric energy that transformer T1 offers output is just less.

So in the T3 time, increase along with the feedback quantity of optocoupler IC2, the duty of the pwm pulse square wave of its control chip IC1 Gate pin output will reduce gradually, so that the rate of voltage rise of first group of output Vout1 and second group of output Vout2 output becomes slower, the slope of rising diminishes.

In the T4 time of Fig. 5: when the voltage of Vout1 output is raised to 5V, Vout1 and Vout2 are not all also eaten carries (loading), the FB pin of control chip IC1 will keep lower voltage, and the Gate pin of this control chip IC1 will still be exported the pwm pulse square wave of less duty.

5V produced the oscillogram of Overshoot phenomenon when Fig. 7 was Switching Power Supply plate start, Fig. 8 arranges the capacitor C 10 of suitable parameter and the oscillogram after the resistance R 10 for this Switching Power Supply in increase by between the reference edge of Vout2 at TL431, and this oscillogram can be found out: Switching Power Supply 5V output end voltage when start does not produce the Overshoot overshoot phenomenon.

The all outputs at power supply of the Switching Power Supply of two group outputs of liquid crystal display product solve all genus this patent protection range that produces the overshoot voltage problem when wherein one group of main output voltage is in start to string one resistance and an electric capacity between the reference edge of the three-terminal shunt regulator (as: TL431) of feedback end.The above person of thought, it only is preferred embodiments of the present utility model, but can not limit the scope that the utility model is implemented with this, the simple equivalence of namely generally doing according to the utility model claim and utility model description changes with modifying and all still belongs in the scope that the utility model patent contains.

Claims

1. one kind is suppressed Switching Power Supply is exported overshoot voltage when start circuit, include power output end and feedback end, it is characterized in that being connected with on the power output end electric capacity, the reference edge of the three-terminal shunt regulator of feedback end is connected with resistance, and electric capacity and resistance serial connection.