How to Select the Current of Dual Power Transfer Switch

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In the design of a dual power pc automatic transfer switch, the most important is the current control module (TCM), because the current is not strong enough to meet all the requirements.

At both the input and output ends there is a resistor whose function is to limit the current to a specified range. This resistor is usually called a current limiting resistor (LOR) or a current limiting unit (LOC) or a current limiting unit (LU), and is used to control the output current.

A typical dual power transfer switch has two power supplies.

One is the output tube, which controls the on-off of one MOSFET, and the other is the input tube, which controls the other transistor in the off-off state.

A current-limiting circuit is needed to make both tubes open and close simultaneously and to enable the MOSFET to operate below the off break point.

This is the basic principle and application of the dual power transfer switch.

In practical application, we should pay attention to its working environment and requirements, such as working temperature, load, voltage level, frequency and other parameters meet the design requirements.


First, when we use the dual power transfer switch, we should pay attention to the size of the load to choose the current.

At the same time, if the load is a large current, then it is necessary to choose the appropriate current to meet the requirements of the large current.

In general, in the input voltage is equal to the output voltage and the load resistance, the greater the load, the greater the corresponding current.

For some relatively small power electronic products such as mobile phones, power consumption should be taken into account and the battery should not be used too big.


Two, for relatively small load, such as mobile phone battery (charging), computer host (power supply) such small load, if it is a mobile phone charging, we should consider the choice of appropriate current without affecting the normal work of the battery.


If it is a computer host power supply, in the choice of time to consider the rated power of the host.

This has to do with our battery capacity.

Because the current is large, so the current loss is large, the output power will be reduced accordingly; At the same time, a larger output current also means more heat, higher power requirements and increased system costs.

So in the choice of dual power switch must consider the current, switching frequency, input voltage and other factors.


Three, for a large load, such as computer motherboard, graphics card, CPU such high-power output equipment, in order to ensure that the equipment in a long time uninterrupted power supply process to continue to work, it is recommended to choose the appropriate current;

When the power of the equipment is not big, you can use a small output current, which not only ensures the stability of the circuit in a long time of continuous power supply, but also reduces the impact on the output components.

If the design does not consider the system in the uninterrupted power supply environment to work normally and need frequent operation, you can choose a larger current dual power switch.

When using dual power switches, be sure to pay attention to the following points:

1. Dual power switch is best to use a temperature protection model; 2. Ensure that the voltage is always within the safe range during use; 3. Try to use large current double power switch, can improve the circuit stability performance; 4. In the design, try to consider the long-term continuous power supply and continuous power supply demand for the output load, and consider its stability.


Four. If we need to supply power to equipment or other large loads:

· When two power supplies are needed, a dual power supply with the current between the two power supplies being 1.5 times the rated value, or rated current being 100A, or rated current being 2 times shall be selected.

· Power supply with high power factor and low load resistance should be selected when large current needs to be provided.

· If we need to power some equipment, we should use a dual power supply.

Five, if we do not have strict requirements on the working state of the equipment.

If the requirements of the device are very low, such as <50A current, <1A output power.

In order to avoid overload (such as too high), generally when the output power is very small, can not use large current or voltage.

We can only use dual power switch and current limiting resistor with relatively high rated current to meet the requirements.

If the rated current is relatively small, you can use a large current of the dual power switch.

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