The circuit of Figure 1 adopts a step-up (boost) dc-dc controller for use in a negative buck-regulator application. It was developed to power the laser diode in an optical amplifier/booster unit, a job for which no commercial IC was available at the time. The anode of the laser diode connects to ground, so the supply voltage must be negative, and it must deliver 160mA to 750mA. Figure 1. With an external op amp to invert its voltage feedback, this boost-mode dc-dc controller derives a regulated -3V from the -5.2V ECL supply. Although the boost-regulator IC operates in a buck-regulator circuit, its standard connections enable proper control of Q1. The output voltage, however, must be inverted by an op amp for proper voltage feedback: the load is referred to the most positive supply rail instead of IC1's ground terminal, so the controller must increase its duty cycle as VOUT (referred to that terminal) increases. The op amp therefore inverts the feedback signal and shifts it to match the 1.5V threshold internal to IC1. IC1 is configured in its non-bootstrapped mode, which provides an adequate gate-drive signal (ground to -5.2V) for the external MOSFET Q1. With VOUT set to -3V and the output current ranging from 160mA to above 700mA, the circuit's conversion efficiency ranges from 84% to as high as 87.5% (Figure 2). Figure 2. Efficiency for the Figure 1 circuit ranges from 84% to as high as 87.5%. A related idea appeared in the 11/9/95 issue of EDN. 我们期待您的反馈！ 喜欢？不喜欢？有待改善？或为我们提供建议？请与我们联系 — 我们将根据您的意见或建议改善我们的工作。 网页评价或提供建议 自动更新 需要自动接收最新发布的应用笔记吗？请订阅EE-Mail™ (English only)。 更多信息   APP 933: Nov 09, 1995 MAX1771 12V或可调、高效率、低IQ、升压型DC-DC控制器 完整的数据资料 (PDF, 1.6MB)   下载，PDF格式 (165kB)  AN933, AN 933, APP933, Appnote933, Appnote 933