The circuit of Figure 1 shows an alternative to opto-isolated feedback signals (the system shown is a 5V switching regulator). The zero (non-existent) line regulation of a push/pull, surface-mount transformer and driver (T2 and IC2) produces an isolated feedback signal (to pin 3 of IC1) proportional to the regulator's nominal 5V output. The result is a fully isolated dc-dc converter without the usual opto-isolator bandwidth constraints and aging characteristics. Figure 1. This fully isolated 5V switching regulator offers long-term reliability and ease of design. By alternately grounding each end of T2's center-tapped primary, the transformer driver (IC2) generates an ac signal proportional to the desired 5V feedback voltage. A diode bridge (CR2–R5) and capacitor (C4) convert this transformer's output to dc, and a diode-resistor network (CR1, R3, R4) compensates for the diode bridge's temperature coefficient. (You can substitute silicon signal diodes, such as 1N4148s, for the Schottky diodes.) The result is a zero-TC voltage slightly less than ½VOUT. Transformer T1 isolates VOUT. In response to a 5V output, the feedback network produces an isolated 2.404V (at IC1, pin 3) and introduces about 250ns of delay at 100kHz—the equivalent of 9° of phase shift. This bandwidth is sufficient for the control loop in most switching converters. Supply current for IC2 and the temperature compensation network together is about 6mA. Starting with a 5V, nonisolated transformer flyback converter in which VOUT connects directly to the top of C1 and R1, you can insert the isolated-feedback circuit (bottom of Figure 1) between VOUT and C1/R1. To accommodate this extra isolated-feedback circuit, simply reduce the value of R1 to ensure that the R1/R2 divider voltage is comparable to IC1's internal feedback reference (1.5V). The isolated converter's performance is virtually identical to that of the nonisolated converter, except for isolated-feedback-circuit power consumption. T2 provides 500VRMS isolation. (You can also get transformers with 1500VRMS isolation.) フィードバックをお寄せください。 内容に満足されましたか、あるいは満足されていませんか？もっと良いページにできると思いますか？あるいは、単なるコメントでも結構です。フィードバックをお待ちしています。—マキシムはお客様からいただく訂正、提案を元に改善していきます。 このページを評価し、フィードバックを送信する。 自動アップデート お客様が関心のある分野でアプリケーションノートが新規に掲載された際に自動通知Eメールの受信を希望する場合は、EE-Mail™にご登録ください。 その他の情報   APP 998: Jul 09, 1998 MAX770 5V/12V/15Vまたは可変、高効率、低IQ、ステップアップDC-DCコントローラ フルデータシート (PDF, 9.3MB) 無料 サンプル MAX845 PCMCIAアプリケーション用、絶縁型トランスドライバ フルデータシート (PDF, 224kB)   ダウンロード、PDFフォーマット (24kB)  AN998, AN 998, APP998, Appnote998, Appnote 998