On 31/05/2026 16:33, Dave McGuire via vcf-midatlantic wrote:
On 5/31/26 11:20, David Wade via vcf-midatlantic wrote:
Thanks folks! I have a spare step-up transformer. I just wasn't sure if providing the UK Atari STE a 240V / 60 Hz power source would be a problem as it's probably designed for a 240V / 50 Hz source.
Its a switched mode PSU so the first thing that happens is that the mains is rectified and used to charge a high-voltage capacitor. So I think it will be fine with 240v/60v.
Really the usual cause of problems is running a US designed setup on 110v/50hz. Transformers efficiency depends on frequency, which is why a SMPSU which runs a kHz can have such a small transformer
I'm sorry Dave but this is wholly incorrect. Switching power supplies typically don't use transformers to step down voltages;
I know, my bad. I meant to say... Opps pressed send too quickly. I meant to say :- Switched mode PSUs don't have issues with frequency. The usual cause of problems is running a US designed setup with a *linear *PSU on 110v/50hz in the UK because the transformer is less efficient and can overheat. This can be an issue with some Tandy Color Computers as the transformer runs warm anyway...
they chop the rectified incoming voltage using a chopper transistor driven by an oscillator, and control the pulse width such that the integrated voltage (area under the curve) is the target voltage. An integrating network and filtering follows the chopper to produce a steady DC voltage, and a voltage divider pick-off is compared against a reference voltage and used to control the PWM width in a feedback network, resulting in regulation to the desired output voltage. It is not a matter of converting the frequency higher so a smaller transformer can be used in a linear power supply arrangement. Then why does the Atari PSU have a transformer? It also puzzles me is that there is only one transformer, yet we have two output voltages, +5v and +12v. I can understand using PWM to control one voltage, but how do you keep one output at 12v and one at 5v when the load varies?
This is the schematic on my onedrive... PSU_ASP34-1.pdf <https://1drv.ms/b/c/277a0739f125010e/IQBqZ48f-MTZTKUuEUKJyzYqAa4emkFH5F386XGY203tiug?e=g8v068> I know your love for all things Microsoft knoweth no bounds, so it came from here, but I couldn't figure out what the real URL for the PDF was https://docs.dev-docs.org/htm/search.php?find=_s Dave
-Dave
Dave