TSN 1-2450A instead of LM7905

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Vyper68
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Re: TSN 1-2450A instead of LM7905

Post by Vyper68 »

I am pleased I got to the bottom of it with Mikeb’s help. Sorry to hear about your Cumana Reborn issues HigashiJun, hope it works okay from now on.
Bazinga!

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mikeb
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Re: TSN 1-2450A instead of LM7905

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Vyper68 wrote:
Mon Sep 07, 2020 12:12 pm
I fitted the 2450A regulator again and the Atmos does boot if you short the Reset pin so I fitted a 4.7uf cap and had no joy but when I fitted a 10uf Capacitor the Atmos boots up so thanks to Mikeb for the tip on replacing the Cap with a higher value.
OK, so that shows you how slow the module is at achieving full voltage compared to a 7905 and a decent switch-on :)

It's probably buried in a datasheet for the module, somewhere, in the diagrams at the back!

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Re: TSN 1-2450A instead of LM7905

Post by Vyper68 »

mikeb wrote:
Mon Sep 07, 2020 4:44 pm
Vyper68 wrote:
Mon Sep 07, 2020 12:12 pm
I fitted the 2450A regulator again and the Atmos does boot if you short the Reset pin so I fitted a 4.7uf cap and had no joy but when I fitted a 10uf Capacitor the Atmos boots up so thanks to Mikeb for the tip on replacing the Cap with a higher value.
OK, so that shows you how slow the module is at achieving full voltage compared to a 7905 and a decent switch-on :)

It's probably buried in a datasheet for the module, somewhere, in the diagrams at the back!
It says startup time is 15ms at nominal vIn with constant resistive load and time for 10% to 90% of vOut is 10ms, how’s that compare to a normal 7905?
Bazinga!

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HigashiJun
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Re: TSN 1-2450A instead of LM7905

Post by HigashiJun »

Vyper68 wrote:
Mon Sep 07, 2020 3:43 pm
I am pleased I got to the bottom of it with Mikeb’s help. Sorry to hear about your Cumana Reborn issues HigashiJun, hope it works okay from now on.
Thank you. No worries, it works fine now.
HigashiJun

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mikeb
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Re: TSN 1-2450A instead of LM7905

Post by mikeb »

Vyper68 wrote:
Mon Sep 07, 2020 5:55 pm
It says startup time is 15ms at nominal vIn with constant resistive load and time for 10% to 90% of vOut is 10ms, how’s that compare to a normal 7905?
10ms of ramping up. OK. Well, I just checked an SGS-Thompson 7905 datasheet, there is no mention of time at all because it's going to be almost instant, it's just a pass-transistor and some feedback/monitoring circuit. Not a multiple-cycle charge-chucking design with inductors which take a few cycles to get going :)

For 1uF/2k2 original Oric reset circuit, it's about a 2.2ms time constant. So the processor is being released while things are struggling to start. 4.7uF is about 10ms -- as you found, marginal/not working. 10uF more like 22ms, and that works for you!

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iss
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Re: TSN 1-2450A instead of LM7905

Post by iss »

Correct! :)
Just to clarify mikeb's magic numbers: the time depends on the RC group charging/discharging constant i.e.
T=R*C, or in the 'standard' case T = 2200[ohms] * 0.000001[farads] = 0.0022[seconds] or 2.2ms ;).

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