Hold-up power source?

• A. Five 1.5V C-cell batteries
• B. Three 9V batteries
• C. A single 28V battery
• D. A rechargeable 7.2V pack

Answer: (A)

A hold-up power source is meant to keep the essential circuits alive for a short time when the main supply fails, so the equipment can keep operating long enough to shut down safely or preserve memory. Five 1.5V C-cell batteries in series give about 7.5V, which matches the typical hold-up voltage needs and can supply a useful amount of current for the brief duration required. The other options are less suitable: three 9V batteries add up to about 27V but have high internal resistance and limited capacity, making them poor for sustaining current; a single 28V battery would require regulation to use safely and isn’t a common fit for quick-swap hold-up in small gear; a rechargeable 7.2V pack may not provide the needed headroom or immediacy of replacement for hold-up purposes.