В 317 - "честный" эмиттерный повторитель на выходе, а в 1117/108х -
Шиклаи, имитирующий ОЭ. В результате - стабильности 317 посвящён
один абзац, а 108х - целый параграф. Или вот, цитата из "Linear Regulators: Theory
of Operation and
Compensation" app. note 1148:
Quasi-LDO Compensation
When evaluating the quasi-LDO regulator (Figure 3) for stability and compensation, it has some of the electrical characteristics of both the LDO and NPN regulator. Since the quasi-LDO uses an NPN pass device, it is in the
common-collector configuration which means it’s output device node (emitter) looks like a relatively low impedance.
However, because of the base of the NPN is being driven from a high-impedance PNP current source, the regulator
output impedance of a quasi-LDO is not as low as the NPN regulator with an NPN Darlington pass device (but is much
lower than a true LDO which drives the regulator output off the collector of a PNP).
This means that the troublesome power pole of a quasi-LDO is at a lower frequency than the NPN regulator, so some
compensation (output capacitance) is required to make a quasi-LDO stable. Of course, the pole is at a much higher
frequency than the LDO, so the quasi-LDO requires less capacitance and the ESR is not as critical.
For example, the LM1085 quasi-LDO rated for 3A of load current requires only 10 μF of Tantalum output capacitance
to assure complete stability over all line and load conditions. No ESR graphs are given, since the value of ESR is not critical as it is in an LDO.
Toчкa oпopы (29.04.2024 13:23, просмотров: 120) ответил Vit на На такое нарывался с LD1086. В той же схеме, с теми же нагрузками у
LM317B от той же ST гудёж не замечен. На практике никакие LM317 у
меня никогда не гудели. Зато когда-то приходилось применять
КР142ЕН12 - некоторые партии гудели, да ещё и тепловая защита в
таких часто не работала - тупо выгорали.