Abstract: Substituting a shunt regulator (U1) for the usual transistor in this power-amplifier circuit improves the current-limit accuracy. Adding current-limiting circuitry to an emitter follower protects both the pass transistor and downstream circuitry from excessive current damage. The classic way to implement such current limiting is to add a ballast resistor between the pass transistor's emitter and the circuit output, and then monitor the resistor drop with a small-signal transistor. See R4 and Q2 in the power amplifier (or linear regulator) shown in Figure 1. Figure 1. A small-signal transistor (Q2) provides an output current limit for this power amplifier. Unfortunately, the base-emitter voltage of the small-signal transistor sets the current-limit threshold for this circuit. That VBE has a well-known temperature coefficient of -2mV/°C, which causes a substantial change in current limit across the operating temperature range. An adjustable shunt regulator (U1 in Figure 2) is preferable to the small-signal transistor for sensing current. This IC is chosen for its low-input threshold (0.6V), which is lower than that of common shunt regulators (1.25V to 2.5V). In addition, the IC's separate power-supply input allows it to maintain accuracy as the internal output transistor approaches saturation. Figure 2. Substituting a shunt regulator (U1) for Q2 in the Figure 1 circuit improves the current-limit accuracy. Figure 3 compares current-limit accuracies of the small-signal-transistor version of Figure 1 with the shunt-regulator version of Figure 2. The transistor version exhibits a 25% change in current-limit threshold over the operating temperature range, while the shunt-regulator provides better than 2% accuracy over that range (neglecting the temperature coefficients of the sense resistors). Figure 3. Current-limit accuracy versus temperature for the circuits of Figure 1 (top trace) and Figure 2 (bottom trace). A similar article appeared as a Design Idea in the February 2, 2006 edition of EDN. 의견을 보내주세요! 위 내용이 도움이 되셨나요? 여러분의 의견을 기다립니다 — Maxim은 보내주신 정정이나 제안사항을 반영하고 있습니다. 이 페이지를 평가하고 의견을 보내주십시오. 자동 업데이트 관심있는 분야의 애플리케이션 노트가 나올 때 자동으로 업데이트 받고 싶으세요? 그렇다면 EE-Mail™을 신청하십시오. 추가 정보   APP 3867: Jul 26, 2006 MAX8515 절연된 DC-DC 컨버터를 위한 넓은 입력의 0.6V 션트 레귤레이터 전체 데이터 시트 (PDF, 276kB) 무료 샘플   다운로드, PDF 형식 (34kB)  AN3867, AN 3867, APP3867, Appnote3867, Appnote 3867