Understanding the terminology and requirements related to the "holdup" time parameter can be valuable for system designers in the airborne industry.
Though holdup time parameters are valuable in other industries where power interruptions can cause problems, airborne systems have holdup requirements to ensure that they can continue to function during a power interruption. This can be particularly important during critical phases of flight, such as takeoff and landing. When there is a power interruption, the power supply within the equipment must have enough energy stored in reserve to continue to power the equipment for a certain duration of time. The "holdup time" is the amount of time that the equipment can maintain its function during a power dropout event. This prevents data loss, equipment damage and safety hazards.
In MIL-STD-704, a transfer operation refers to a switching process that changes the Airborne’s electrical power source from one to another. This transfer may cause a momentary interruption in the power supply to equipment that relies on it. In some cases, it is essential for this equipment to continue operating during the interruption. Therefore, meeting holdup requirements can ensure that critical systems can maintain their power supply during transfer operations. To meet the holdup requirement, the equipment may include energy storage components such as capacitors or batteries, which can supply power during a power interruption. These energy storage devices are being charged during normal operation so that they are ready to provide power during an interruption.
Power hold-up time solutions can be standalone modules or a feature incorporated in the power supply itself. Our products can be designed to meet any revision of MIL-STD-704 F.
The M2705 military power supply is a rugged three-phase AC to DC converter, that provides a single DC output of 270V, up to 1500W, with custom outputs available. This unit is sealed to protect against fluids, with a breather valve for condensation exhaust.
Holdup Output: 50mS @ 1500W
M4012 is a military-grade, 3U VPX, 28V DC-DC PSU card that provides six outputs per VITA 62 that is rated at 350W output power and 9-15 Joules of holdup for MIL-HDBK-704-8, LDC201 requirements.
Holdup Output: 50mS @ 250W
The M1255 hold-up power supply is meant to be installed in front of a power supply, and not a standalone. It is used for input voltage holding when a power failure occurs, such that if the input power returns to nominal limits in a defined period of time, the load can't tell that a power failure had happened. This unit is designed to be used with most of our DC/DC converters and DC/AC inverters (consult the factory for applicability to specific models).
More than 990 W/msec per 1 mF capacitance
M256 series DC-DC holdup units/ energy storage modules are known for their miniature size, high efficiency, wide input range and fixed switching frequency. They have external synchronization (250 +/- 10 kHz), included EMI filters, indication for input failure and hold-up activation and internal capacitor storage of at least 7 Joules. An external capacitor connection option for additional hold-up time is available.
Holdup Output: 50mS @ 140W
Holdup Output: 48J