Stability of gain of switch power source is analysed

As the electron, accuse oneself, spaceflight, communication, the technology such as medical apparatus and instruments is mixed to deepness ceaselessly the development of range, certainly will asks the power source of power supply of by a definite date wants to have taller stability, the linear that should have had not only namely adjusts rate, load adjustment rate has fast dynamic load to answer even. And these elements are concerned with operating ring road, operating ring road works commonly in laden condition, those who say lose feedback for voltage. If feedback operating ring was not used in transformer road (graph 1 in H part) , its transfer function is C/R=G commonly, among them G is input filter wave, the product of the factor such as part of wave of filter of power transformation, commutate (the form that its are cascade, express so in the article with G of total product factor) , can see the change that output follows the change of the input and becomes linear, but be in as a result of network of wave of rectification, filter of whole time domain nonlinear, actually this kind of change should be approximate at linear, should input the action that stabilized voltage cannot enrage very well when power source is changed so. What if feedback,annulus road designs is bad, the transient state of corresponding load is changed, annulus road cannot make seasonable and appropriate adjustment, so instant of output power source is met on the high side or on the low side, possible even meeting causes the oscillation of power source system, form attaint to issueing one class. If can be measured to annulus road,appear very important right now. So is annulus road section has how affect whole return? Product of series of AC-DC of referenced DELTA company, the annulus gain model that the carry in the share of control of feedback annulus road that next chart show puts, its transfer function is C/R=G/(1+GH) , among them G: Open loop gain. H: Feedback coefficient. One, the standard 　 with annulus stable gain by transfer function C/R=G/(1+GH) , the G of open loop gain of amplifier is the function of frequency, can reduce as the addition of frequency, also mix at the same time of amplifier phasic about, when GH=-1, criterion the cost that its pass is ∞ , namely gain is infinity, the input that can think random is small disturbs to be able to cause the infinity of output, if this is planted,the signal that outputs infinity arrives in feedback power transformation link, will naturally cause the oscillation that outputs finally, whole system is absent consequently stabilized voltage. The gain that says to be able to connect GH of beyond the mark analyse so and phasic the stability that will judge a system. Because become,oscillation is when GH=-1, having GH of phase shift ∠ so is 180 ° (the phase shift that has 180 ° because of negative feedback itself) , return gain | GH | =1 (0dB) .

Want to make carry puts stable need to satisfy the following requirement so: Phasic condition wants its phase shift to be less than 180 ° namely, want to have the surplus of 45 ° above namely, gain condition asks to have commonly - 12dB above surplus. 2.

Pass through frequency closes by 20dB/Dec. Relevant explanation later development introduces. 2, we can pass 　 of Bode graph foundation the stability that the frequency character of annulus gain GH will come judge a system, and return gain | GH | And the frequency character of GH of phasic difference ∠ can use return circuit Bode pursues (graph 2) will express, the phasic surplus in and systematic stability can pass Bode pursueing (Phase Margin) , gain surplus (Gain Margin) , pass through frequency (Crossover Frequency) will measure. Among them the action of 　 phasic surplus is to ensure fall in certain condition (change of voltage of the error that includes yuan of parts of an apparatus or appliance, input, laden change, temperature rise) the system can be stabilized, use in nominal below room temperature of input rated load, want to have 45 degrees surplus. If input span of power source, laden, temperature very big, phasic surplus should not be less than 30 degrees. Gain surplus to be close to not point of safes, think commonly - 12dB above is necessary. Pass through the speed that the size of width of frequency frequency band can reflect operating ring road to answer. Think width is wider commonly, its restrain ability to had been jumped over to what laden trends answers, too strong, owe strong smaller, restore time to be jumped over more fast, system thereby can stabler. But because get right half plane the influence 0 o'clock, and the bandwidth that raw material, carry puts cannot the limitation of the integrated element such as infinity, the bandwidth of power source also cannot rise without limit, take the 1/20~1/6 of switch frequency commonly. 3, the test 　 of annulus road is mixed to the gain of annulus road phasic measurement, we can use annulus road analyzer normally (FRA) or gain - phasic analyzer undertakes metrical. These instruments are to pass the imitate signal that obtains to sampling to undertake pretreatment, pass A/D changeover next, using DFT (disperse Fourier alternates) operation is gotten gain and phasic, use a curve finally (Bode Plot) express. Article general the annulus road analyzer with OMICRONI-LAB company (Bode100 country measures an electron) will do an analysis, basically undertake according to the join graph of below, what need an attention particularly is the position of infuse resistor, and size, measure an error to reduce, the experiment chooses the resistor of 10~100 Ω commonly, about disturb numerate through oscillograph in the process that we are checking the size of signal, the amplitude that also can use FRA is compressed (Amplitude Compression) the function will install, ask disturbing extent cannot exceed 5% of voltage nevertheless, measuring the outcome that come out otherwise is inaccurate. 4, stability checks case: The factor that affects product stability in understanding and decide criterion and how will detect after the product, the product outcome that can measure to place undertakes was analyticed. Below with DELAT company wide a product that controls series will do a test, test of part of actual ground connection sees as a result. Gain. In this case, seeing its gain surplus is - 9.

499dB, phasic surplus is 83deg, bandwidth is 20.

49KHz, but the phasic surplus of 83deg its trends owes damp, can pass pair of error amplifier to compensate a network to slide below a bit low frequency actually (Roll Off) will come true. Below the premise that assures phasic surplus, in 0dB the following gain can be pressed - 40dB/decade attenuation, thereby more be helpful for restraining high frequency interference, its are achieved optimal answer. The frequency with 0dB corresponding node is 20.

49KHz, if need taller bandwidth, can use capacitance of wave of less output filter to be able to produce lesser ripple tension, also can reduce the volume of the use of raw material and module power source so, make module power source becomes more energy-saving thereby. Considering very conservative gain and phasic surplus, also can be opposite of course the compensation link of error amplifier undertakes a few alter smally, reasonable elevator belt is wide, make the system achieves faster response, increase stability. Additional, in checking a process, the annulus road gain of switch power source and phasic normally the proposal is in carry for nothing, check respectively below half load and loaded to capacity circumstance. As to the choice of the power discretion of incentive signal, usually need is measuring the exchanges incentive signal power that an infuse wants when frequency is lower to be set a few higher, for example - 20dBm or - 30dBm. Test of ESR of the capacitance in process of annulus road test also is very important, and the Bode100 of annulus road analyzer of OMICRON-LAB company is as high as 40MHz frequency, great and convenient character of frequency of passive parts of an apparatus is measured. 5, summary: From feedback annulus road phasic angle told about gain how to measure stability of switch power source, give out the standard of stability, the understanding that Bode pursues, the use of FRA includes to link the measurement of character of road of sketch map, annulus, and the simple analysis of experimental result, offer ameliorative proposal finally. Of course systematic stability also can do qualitative analysis by time domain means, but can go up to be begged mensurably in frequency region however through annulus road analyzer piece, make more intuitionistic judgement to systematic function thereby. Especially in industry intense competition and client are handed in period it is very important to undertake to power source analysis of travel of frequency domain documentation appears below very brief case. Measuring switch power source to lose rate of feedback annulus Lu Pin to answer, the proposal uses analyzer of appropriative annulus road or vector network analyzer, be like Bode100, e5016B. CNC Milling