September 27, 2023

What is switch redundancy? Detailed explanation of backup power supply

Most switches on market today, especially older switches, use only one power supply. If power supply fails (for example, a power outage), switch will not work properly, and even network will be paralyzed. Redundant power supplies are ideal solution to this problem. A switch with a redundant power supply can greatly improve stability of network and ensure uninterrupted operation of equipment. So what is a redundant power supply and why should a switch use a redundant power supply? This article will answer these questions in detail.

1. What is a standby power supply?

Generally, power supply redundancy can be implemented in form of power redundancy, cold redundancy, parallel current split N+1 redundancy, hot redundancy, etc. Power redundancy means that maximum load capacity of power supply exceeds actual load, which is not of great importance for improving reliability.

Redundant cold standby means that power supply consists of several modules with same functions, and one of them provides power under normal conditions. In event of a failure, redundant module starts working immediately. The disadvantage of this method is that there is a time lag for power switching, which can cause a power surge.

2. Redundant power connection

The traditional scheme for designing a redundant power supply is to connect two or more power supplies to anodes of diodes, respectively, and output them in parallel on power rail in form of an "OR gate". One power supply can work one or more power supplies can work at same time. Failure of one of power supplies will not affect output of power rail due to unidirectional conduction characteristics of diode.

In a real backup power system, total current is relatively large, up to tens of amperes. Given power consumption of diode itself, Schottky diodes with lower voltage drop and higher current are usually chosen, for example SR1620-SR1660 (rated current 16 A). Typically, these diodes also require a heatsink to facilitate heat dissipation.

The traditional solution using diodes is simple in design, but has inherent disadvantages: high power consumption, high heat dissipation, need to install heatsinks and large volume. Due to large current in circuit, diode is in forward conduction mode most of time, and power consumption caused by its voltage drop cannot be ignored. The Schottky diode with lowest voltage drop also has 0.45 V. At high current, such as 12 A, power consumption is 5 W, so special attention should be paid to problem of heat dissipation.

The new backup power circuit now uses a high power MOSFET instead of a diode in traditional circuit. The internal conduction resistance of a MOSFET can reach several mΩ, which greatly reduces voltage drop loss. In high power applications, not only a more efficient solution is achieved, but also absence of need for an energy-saving heatsink, which saves significant board area and reduces heat dissipation sources for device. Transistors in application circuits must be controlled by professional microcircuits.

3. How a redundant power supply helps users optimize their network

The benefits of switches with a redundant power supply include two aspects: ensuring uninterrupted operation of switch and supporting hot swapping.

1. Ensure smooth operation of switch to increase network availability.

The switch ships with two power modules. During its operation, if one power module unexpectedly loses power, other power module will immediately take over power supply function of equipment and perform a smooth transition, thereby ensuring uninterrupted operation of equipment and increasing high availability of system.

Note. As mentioned earlier, local redundant (N+1) power solutions take some time to complete power transfer, which can lead to network outages. Therefore, it is recommended to select appropriate backup power configuration mode according to your actual needs.

2. Support for hot swapping and flexible deployment.

Typically, a switch has two or more hot-swappable power supplies. This means that if one of power supplies fails, user can replace power supply without stopping device. Users only need to unplug failed power supply and then plug in new power supply.

4. Do I need to buy a switch with a redundant power supplyI when buying a switch?

As mentioned above, redundant power supply can provide various conveniences for network users, such as high availability of equipment, hot swap support, etc., and can also effectively avoid unnecessary downtime or data loss caused by accidental damage to power supply. However, price difference between conventional switches with a single power supply and switches with a redundant power supply is small. Buying a switch with a redundant power supply is smart choice these days. However, fact that this redundant design takes up more space on device itself cannot be ignored, so it is recommended that you choose appropriate product according to your actual needs.


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