Hold-up Time


Hold-up time, in the context of power supplies, refers to the time a power supply unit (PSU) can maintain its output voltage within a specified range after the input power is lost or interrupted. It is a crucial parameter in power supply design to ensure the stability of the system, allowing devices connected to the PSU enough time to safely save data or switch to an alternative power source. Longer hold-up times provide better protection against voltage drops and short power outages.


The phonetic transcription of the keyword “Hold-up Time” would be: /ˈhoʊldˌʌp taɪm/Explanation: “Hold” is pronounced as /ˈhoʊld/, “up” is pronounced as /ˌʌp/ and “Time” is pronounced as /taɪm/.

Key Takeaways

  1. Hold-up Time refers to the duration a power supply can maintain its output voltage within the specified range without any input power.
  2. It is a crucial parameter in power supply design, as it ensures the uninterrupted operation of the device during power fluctuations or interruptions.
  3. Insufficient hold-up time can cause system malfunctions or data loss, leading to a negative impact on device reliability and performance.


Hold-up time is an important term in technology, particularly in the context of power supply systems.

It refers to the duration for which a power supply unit (PSU) can maintain its output voltage within the specified range, even after the input power is removed or interrupted.

This is a crucial aspect in ensuring the seamless performance of electronic devices, as it provides sufficient time for the device to properly switch to an alternative power source or execute a safe shutdown in case of power losses or fluctuations.

In essence, a power supply with a longer hold-up time offers greater reliability and stability in preventing data corruption, hardware damage, or system failure that may stem from unstable power conditions.


Hold-up time serves a critical purpose in the realm of power supply units (PSUs) in electronic devices, particularly in uninterruptible power supplies (UPS). The main objective of hold-up time is to ensure the continuous operation of these devices during brief power interruptions or voltage fluctuations. This transient period helps negate the possibility of data loss, hardware damage, or undesired shutdowns in mission-critical applications.

Moreover, a longer hold-up time is essential for environments with unstable power supply, as it allows ample time for the device to switch to an alternate power source, such as a battery or a generator, ensuring seamless operation without interruption. To maintain its efficacy, the hold-up time primarily depends on the design and components of the PSU or UPS.

Implementing energy-storing components like capacitors enables the system to store a sufficient amount of energy, affording it time to respond to varying power conditions. The hold-up time is accordingly influenced by the capacitance value and the quality of these capacitors.

Additionally, regulatory standards, such as those set by the International Electrotechnical Commission (IEC), serve as a guiding principle in determining the minimum hold-up time for different devices. A well-designed PSU with an adequate hold-up time contributes significantly to the overall reliability, durability, and performance of electronic systems.

Examples of Hold-up Time

Hold-up time refers to the duration a power supply unit (PSU) can continue supplying power to a system without input power before its output voltage drops below a specified threshold. This technology is crucial in ensuring the reliable and continuous operation of electronic devices during transient power interruptions. Here are three real-world examples highlighting the importance of hold-up time:

Uninterruptible Power Supplies (UPS) in Data Centers: In data centers, servers, and other important IT infrastructure need a continuous stream of power to maintain system stability and data integrity. Hold-up time is an essential feature in uninterruptible power supplies (UPS) devices, which provide emergency power when the main power source fails or fluctuates. The hold-up time allows the UPS to continue providing power to the servers while switching to backup power sources (like batteries or generators) and avoids any potential damage to the equipment or loss of data.

Medical Equipment: In hospitals and other health care facilities, medical equipment such as patient monitors, ventilators, and infusion pumps rely on a consistent power supply to maintain proper functionality and ensure patient safety. Hold-up time in these devices’ power supplies allows medical professionals time to save data or intervene in case of a power failure, ensuring patient care is not compromised.

Industrial Automation Systems: Manufacturing plants and production facilities make use of advanced automated systems to maintain process control and product quality. Unreliable power supply can lead to malfunctions or downtime in these systems, potentially causing significant losses or even accidents. Hold-up time helps manage minor disturbances or power fluctuations, maintaining operational continuity and reducing the risk of severe consequences caused by momentary power interruptions.

Hold-up Time FAQ

What is hold-up time?

Hold-up time refers to the amount of time a power supply can maintain its output voltage within a specified regulation range after the power input has been interrupted. This term is commonly used in power supply specifications to indicate how well the power supply can handle brief disturbances in the input power source.

Why is hold-up time important?

Hold-up time is important because it determines how a power supply will respond to sudden changes in the input voltage or brief power interruptions. It ensures the continuous and smooth operation of electronic devices by providing them with the necessary power during fluctuations in the input voltage or transient interruptions, preventing malfunctions, errors, or loss of data.

How is hold-up time measured?

Hold-up time is typically measured in milliseconds (ms) and is often specified at a particular output load and temperature. It is usually indicated in a power supply’s datasheet along with other essential features, such as input voltage, output voltage, and operating temperature. To measure hold-up time, the input power is interrupted, and the time taken for the output voltage to fall below a specified regulation limit is recorded.

What factors affect hold-up time?

Several factors can affect hold-up time, including the design of the power supply, the size and type of energy storage components, such as capacitors, the input voltage, the electrical load, and the operating temperature. In general, larger energy storage components can provide a longer hold-up time. However, this may result in an increased size and cost of the power supply.

How to improve hold-up time?

To improve hold-up time, you may consider using power supplies with larger energy storage components, such as capacitors, or opt for a power supply specifically designed to provide longer hold-up time. Switching to a power source with more stable input voltage can also help, as well as reducing the electrical load on the power supply, and ensuring that it operates within specified temperature limits.

Related Technology Terms

  • Power Supply Unit (PSU)
  • Switching Power Supply
  • Uninterruptible Power Supply (UPS)
  • Capacitor Discharge Time
  • Input Voltage Transients

Sources for More Information


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