On Thu, 06 September 2001, Alex Bligh wrote:
a wide frequency tolerance. The only problem you may run into is that some boxes are too clever by half, and autosense input frequency to determine output frequency.
Actually, its not being clever, its being cheap. If you use the input frequency to drive the output frequency, you don't need an extra crystal oscillator. Its cheaper, and results in fewer customer service calls about the clock running fast or slow. It also means, you can't just take a 50/Hz european UPS and plug it into an US plug at 220vac, and expect to still get 50/Hz out of it. When you plug it into the US grid, you'll get 60/Hz out. I spent a day troubleshooting a problem, until someone explained to me what was happening. That's why I now use a bench power supply, which explicitily generates the type of "international" power I want, instead of using a Rube Goldburg setup.