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Power supply dual input voltage supply operation mode

Issue Time:2006-12-06
Dual input voltage supply operation mode
In the trend of international trade, it is more necessary to make the power adapter operate with the nominal input of 110V/220V. To meet these dual voltage requirements, a variety of techniques are available, including one or more, manual or automatic transformer tap conversion and selectable voltage doubling techniques. If you need to use auxiliary transformers and cooling fans, you also need to consider their connection in dual voltage applications.

The insulation of the auxiliary transformer and fan must ensure that the safety requirements can be met at the highest input voltage. Recently, a high-efficiency brushless DC fan has been developed, which can be powered by the output of the power adapter, which solves the problem of insulation and joint switching.

Double voltage technology with one or two connection switches is probably the most cost-effective and popular in power adapters. However, when applying this method, the design of the filter, input fuse and surge limit should also be considered. When switching the input voltage connection, the low voltage connector end will be subjected to large current stress, and the high voltage connector end will have to withstand higher. Voltage stress. To meet both of these requirements, a higher cost filter component is required, so unless the system really needs it, the dual voltage mode is generally not used.

Power supply maintenance time
One of the advantages of a power adapter over a linear regulated power adapter is that it can keep the output voltage constant for a short period of time after an AC power failure. The typical hold time is 20ms, but it still depends on the power supply fault at the moment. The position of the sine wave period, the size of the load, and the magnitude of the input voltage before the fault.

One of the main factors affecting the duration of the power supply is the historical process and amplitude of the power adapter voltage at the moment of power failure. The definition of the maintenance time in most standards is for the nominal input voltage and load, if the power adapter voltage is at the moment of power failure. Close to the minimum, the hold time will be much smaller.

A power adapter designed to maintain the output voltage for a long period of time with minimal input voltage, either because the size of the input capacitor is large or expensive, or because the power converter must maintain a constant output voltage at a much lower input voltage. And reduced efficiency. This usually results in low efficiency at nominal input conditions and should be considered when using low input voltages for long periods of time.

Synchronize
Sometimes the frequency of the power adapter is required to be synchronized, especially when the power adapter is used in the display, although the significance of synchronization in most cases is not certain, because proper shielding and filtering of the input eliminates the need for synchronization, but the system Power adapter engineers still often emphasize this.

The limitations on the design of synchronous power adapters are very strict, for example, systems that are inexpensive and variable in frequency cannot be used. In addition, the sync terminal is coupled to the driver circuit of the main converter, which provides a means of affecting the operational integrity of the converter.

The possibility of improperly or incorrectly synchronizing signals must be considered in the design of the synchronization system. The technology used should be as insensitive as possible to inappropriate use. The user should be aware that it is difficult to ensure that the power adapter is not damaged when incorrect or incorrectly defined synchronization signals are used. In order to avoid saturation when the device is damaged, most power adapters use an oscillator design that can only be synchronized to a higher frequency than the natural oscillation frequency, and the synchronization range is quite limited.

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