Re: 'high voltage' adjustable regulator

Phil Guttridge G3TCU

I find the TL783 useful for e.g. deriving a low power bias supply from a 50V rail. Spec'd at 125V max input. Of course, with increasing voltage, there is an increasing need to be careful about dissipation.

73, Phil G3TCU

On 26/04/2020 11:31, Andy G4JNT via wrote:
A related general warning to all...

With the increasing use of higher supply voltages on PAs these days, 28V and upwards,  be careful what you feed small voltage regulators with, especially those for bias and control circuitry. Many low power low voltage regulators have a maximum input voltage rating that may be a fair bit lower than you'd expect.

The popular 78L05 and 78L033 devices, for example, are only specified for 30V max on the input, so in practice you shouldn't really be using them direct from even a 24V supply to allow some safety overhead.  And certainly not from a 28V rail.  And as for use on a 50V supply, there are only a few voltage regulators around rated 60V input and higher.  They do exist, but need searching-out

The adjustable LM317 family, including the L version, is a lot better in this respect, allowing 40V ACROSS it.   So this makes for a low cost solution for a two stage regulator; use an LM317 to drop 50V to, say, 18 - 20V, then your favourite fixed voltage reg to go from 20V down.

Just thought I'd mention it, as there seems to be quite a bit of construction of PAs and related stuff going on at the moment.

On Sun, 26 Apr 2020 at 11:13, Andy GD1MIP <gd1mip@...> wrote:
Ian 2E0IJH - Thanks. 

John G4TZR  - Thanks, I fully understand that Bert is busy and as I am not the original customer I again understand that his priority is to his business, himself and his paying customers. So I have no complaint whatsoever in the speed of his response or lack of.  My reason for mentioning that I have emailed him is because, in my experience whenever someone posts on a forum asking a Bert question, people always reply saying... email him.   

Thanks for commenting re the BIAS range, that puts my mind at rest, I will now just use 28v rather than finding ways to drop voltage.
Again thanks re the monitor volts, I assumed each unit was different so you'd get different readings on each amp produced, however my limited knowledge meant it was best to ask here for confirmation or is that comfort?

Testing so far has been on 28v for the PA and both 12 & 28v for BIAS, no difference noted. The unit runs remarkably cool, event before I have fitted fans I already know they will be needed only infrequently it isn't going to do much unless I try data.

Thanks Andy GD1MIP 


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