下面是其工作过程。当VIN打开且Q1关闭时，电流通过R3、CT和D2上拉稳压器参考端到参考电压。这个动作限制了VOUT 的dV/dt到CT通过串联电阻放电的速率，(R3+R1R2/(R1+R2))，使用公式R3=(VIN–VREF–1)/VOUT，R4=<20R3,和CT=COUTVOUT/(IMAX(R3+R1R2/(R1+R2)))，从而限制IMAX到任何需要值。例如，假定电路如图所示，COUT=100 μF，dV/dt=2500V/s，且IMAX=0.25A。在改进的上电序列后部，D1和D2从稳压器反馈网络中分离dV/dt电路，防止从输入到输出纹波电压的耦合。
Circuit limits dV/dt and capacitor inrush at regulator turn-on
Adding a simple circuit to the adjust pin of a regulator controls the dV/dt of the output voltage, limiting inrush current.
W Stephen Woodward, Chapel Hill, NC; Edited by Charles H Small and Fran Granville -- EDN, 10/11/2007
Unusual design constraints sometimes reveal the unfriendly side of everyday components and circuits. A case in point is the design of power-supply-regulation circuitry in which the primary power source has an absolute current-limit specification, such as spacecraft photovoltaic, or “solar,” panels and radioisotope-thermoelectric generators. Such applications require that you pay scrupulous attention to strict control of current consumption, including transient-current consumption, and infrequent consumption spikes, such as those that typically occur on power-up. The problem is that current-limited primary-power sources can suffer catastrophic voltage droop and shutdown in response to momentary overcurrent faults, even when the fault is brief. Common causes of such faults are the current spikes that charge the regulator output’s decoupling capacitor.
Unless the current limit of the regulator clips the resulting spikes, the spikes are equal to the regulator’s output-voltage rate of rise multiplied by the sum of the parallel output capacitances: IMAX="dV/dt"×COUT, where IMAX is the maximum current, dV/dt is a differential in voltage with respect to a differential in time, and COUT is the output capacitance. The math suggests that the best strategy for limiting the regulator’s turn-on maximum current is to limit dV/dt. The circuit in Figure 1 relies on this trick and works with industry-standard adjustable linear regulators, such as the popular low-dropout LM2941.
The basis of the dV/dt-limiting technique comprises the six added components: R3, R4, CT, D1, D2, and Q1. On power-up, the control current through R3, CT, and D2 delays the rise of the output voltage and thus prevents excessive maximum-current transients.
Here’s how it works. When VIN is on and Q1 is off, current through R3, CT, and D2 pulls the adjust pin of the regulator to the reference. This action limits VOUT’s dV/dt to the rate of CT charging through the series resistance, (R3+R1R2/(R1+R2)), and thereby limits IMAX to any desired value using the design equations R3=(VIN–VREF–1)/VOUT, R4=<20 R3, and CT="COUTVOUT/"(IMAX(R3+R1R2/(R1+R2))). For example, given the circuit constants in the figure and assuming COUT="100" μF, dV/dt=2500V/s, and IMAX="0".25A. At the end of the modified power-up sequence, D1 and D2 decouple the dV/dt circuit from the regulator’s feedback network, preventing the coupling of ripple voltages from the input voltage into the output voltage.