(Lateral PNP have very poor h FE, so they aren't easy to use as output devices.) If you've been reading a lot from contemporary sources (contemporary of ♚723 that is it's ancient, and there is no reason or need to use it today, unless perhaps as a requirement for homework assignment or something), then it was true back then that the NPN process was most amenable to consumer production parts, and thus lateral PNP was the go-to method to create them, when they were required at all. Basically, nothing that's strong enough to matter here regulators are a very modest application. They actually perform better in some respects, or can, such as h FE being a little bit higher, but overall figure-of-merit tends to favor NPN. PNPs perform slightly poorer than NPN, on the order of about 10% in terms of overall conduction parameters IIRC.The additional process steps then cost more up-front (masks, production tuning) and per-part (more steps, somewhat lower yield). They may be more difficult in IC process, where either the collector is hard-wired to the substrate, or additional isolation wells have to be manufactured. ![]() PNPs aren't harder to manufacture, they're made inversely to NPNs - starting with p- instead of n- substrate (collector), epitaxy/diffuse n/p base layer, diffuse p+/n+ emitter layer and (degenerately doped) ohmic contacts, done.Conversely, NPN emitter followers tend to be lenient on stability, and have good PSRR (ripple on V IN is isolated by the collector impedance (Early effect)).Check stability and adjust compensation as needed. ![]() A direct substitution (as shown here, but without knowing anything else about the feedback network) is likely to cause oscillation.
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