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G0HZU_JMR · 13th Apr 2021, 1:17 am

Wow, I haven't seen that circuit in a few years! It's a low dropout 8V regulator circuit. This dates back over 40 years and the earlier Uniden radios that had this circuit could suffer temperature related instability in this circuit.

The 2SA473 is quite a fast device and Uniden had to add some decoupling caps to improve the stability on the early versions of this regulator circuit. From memory, the early version of this circuit (used on the mark 1 radios) can go unstable up in the MHz region without the extra caps.

The circuit shown looks to be the later version. It serves as a low dropout regulator plus it has a fairly wide loop bandwidth so it can filter out any input side noise and spurs at AF frequencies and higher.

13th Apr 2021, 1:17 am	#7
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: Superstar 360 Wow, I haven't seen that circuit in a few years! It's a low dropout 8V regulator circuit. This dates back over 40 years and the earlier Uniden radios that had this circuit could suffer temperature related instability in this circuit. The 2SA473 is quite a fast device and Uniden had to add some decoupling caps to improve the stability on the early versions of this regulator circuit. From memory, the early version of this circuit (used on the mark 1 radios) can go unstable up in the MHz region without the extra caps. The circuit shown looks to be the later version. It serves as a low dropout regulator plus it has a fairly wide loop bandwidth so it can filter out any input side noise and spurs at AF frequencies and higher. __________________ Regards, Jeremy G0HZU