Testing H745 Regulators

[Rob Jarratt]

> -----Original Message-----
> From: W2HX <w2hx at w2hx.com>
> Sent: 27 January 2022 00:11
> To: rob at jarratt.me.uk; Rob Jarratt <robert.jarratt at ntlworld.com>; General
> Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
> Subject: RE: Testing H745 Regulators
> 
> Any chance you have a second supply you can parallel with the one you're
> using? Some bench supplies are dual supplies and have a parallel mode so
> you can benefit from both sides of the supply and they can track the same
> voltage. Or just put two supplies in parallel with the same voltage set on
both
> 

It is already a twin PSU, I am using one half to power the AC input and the
other half to power the +15V input.

I do have a separate bench PSU I could use for the +15V and twin up the
actual twin PSU, so I might try that next.


> 73 Eugene W2HX
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> 
> 
> -----Original Message-----
> From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of Rob Jarratt via
> cctalk
> Sent: Wednesday, January 26, 2022 6:42 PM
> To: General Discussion: On-Topic and Off-Topic Posts
> <cctalk at classiccmp.org>
> Subject: Testing H745 Regulators
> 
> I am trying to test a couple of H745 regulators with a DC bench PSU and I
am
> having some problems with testing them.
> 
> 
> 
> My bench PSU is a twin unit so I can supply the +15V required as well as
the
> "AC" input using 20VDC from the other half of the bench PSU. The problem
is
> that I don't think the bench PSU can supply enough startup current to
allow
> the regulator to run. It can only supply 5A max.
> 
> 
> 
> I have seen with the H744s that if I put too big a load on them, then they
> can't start because of the heavy startup current required. I can start
them
> with a lower load and then add load once the regulator is running without
> breaching the current limit of the PSU.
> 
> 
> 
> With the H745s I have tried reducing the load to see if I can get them to
start,
> but a 10R load appears to be too much and the regulators draw the full 5A
> without outputting -15V.
> 
> 
> 
> I have two H745s, both exhibit the same behaviour. I suppose they could
> both have the same fault, but I am inclined to think that perhaps they
need a
> higher startup current than I can supply. Can anyone confirm this?
> 
> 
> 
> Thanks
> 
> 
> 
> Rob