By adding a JFET in cascode with a linear regulator (see the figure below), you can extend the regulator's input-voltage range. The regulator shown suits battery-powered applications, because its CMOS circuitry draws only 12µA maximum, regardless of the output-current level. The chip's VIN limit of 16.5V excludes some applications, however. Connecting the external JFET extends the circuit's input-voltage limit to the JFET's gate-source breakdown voltage. A J106 device, for instance, extends this limit to 25V. The J106 has a 6-ohm on-resistance, and IC1 has a minimum VIN/VOUT differential of 0.6V to 0.8V; thus, for low load currents, the combination can deliver a 5V output with chip inputs as low as 5.6V. The circuit can deliver 40mA at 5V with a 6.5V VIN. Replacing the J106 with a 2N4391 JFET increases the allowable input voltage to 40V. The 2N4391 has a 30-ohm on-resistance, so it delivers 40mA with a 2V in/out differential or 10mA with a 1V differential. Figure 1. Adding a JFET in cascode with a linear-regulator IC extends the allowable input voltage to 25V or 40V, depending on the JFET device used. A similar version of this article appeared in the July 12, 1990 issue of Electronic Design. 相关型号   APP 482: Dec 01, 2000 MAX666 Dual Mode™、5V可编程的、微功耗稳压器 完整的数据资料 (PDF, 376kB) 免费样品 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)。 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   下载，PDF格式 (23kB)  AN482, AN 482, APP482, Appnote482, Appnote 482