21-09-2019, 03:32 PM
Yeah, brain fart.
Looking more closely - now that I'm more awake after a bike ride with my son (who's nearly as fast as me, and it won't be long before he is) - I reckon the primary converter is definitely being controlled by the TL594. The transformer between the primary cap and the optocouplers is carrying the base or gate drive from the secondary side to the primary side. I would have spotted that sooner if I'd had the object in my hand - I'm not very good at seeing in 3D from the computer screen. But why are there 2 opto-couplers feeding back from secondary to primary? Obviously one must be for the standby supply, but if the TL594 is on the secondary side, why is there feedback back to the primary? I don't think it's to tell the PFC IC to throttle back in standby because it should do that natively (which is no-doubt why the SB supply is a bit lower when the main converter is not running - not that that matters, as the motherboard will be converting it down locally).
It's tempting to put it down as a strange or lazy choice, but in my experience it's best not to be such a smart-arse - there are often new tricks to be learnt from seemingly unconventional setups... But it is entirely possible that half of that primary-side chip is just not being utilised...
Something else on at the mo, but will see if I can make sense of the TL594 PCB later. Will be a lot easier with one in front of me, so might have to wait until next week.
Mike, a thought occurs before we get too far down this road - will it be quiet enough for the intended purpose? Even though it's only giving 12V, it should be easy enough to check at this point, before too much more effort is spent on further investigations...
Looking more closely - now that I'm more awake after a bike ride with my son (who's nearly as fast as me, and it won't be long before he is) - I reckon the primary converter is definitely being controlled by the TL594. The transformer between the primary cap and the optocouplers is carrying the base or gate drive from the secondary side to the primary side. I would have spotted that sooner if I'd had the object in my hand - I'm not very good at seeing in 3D from the computer screen. But why are there 2 opto-couplers feeding back from secondary to primary? Obviously one must be for the standby supply, but if the TL594 is on the secondary side, why is there feedback back to the primary? I don't think it's to tell the PFC IC to throttle back in standby because it should do that natively (which is no-doubt why the SB supply is a bit lower when the main converter is not running - not that that matters, as the motherboard will be converting it down locally).
It's tempting to put it down as a strange or lazy choice, but in my experience it's best not to be such a smart-arse - there are often new tricks to be learnt from seemingly unconventional setups... But it is entirely possible that half of that primary-side chip is just not being utilised...
Something else on at the mo, but will see if I can make sense of the TL594 PCB later. Will be a lot easier with one in front of me, so might have to wait until next week.
Mike, a thought occurs before we get too far down this road - will it be quiet enough for the intended purpose? Even though it's only giving 12V, it should be easy enough to check at this point, before too much more effort is spent on further investigations...
