Testing H745 Regulators

W2HX w2hx at w2hx.com
Wed Jan 26 18:10:49 CST 2022

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

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?





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