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Power adapter circuit operation in three states

Date:2019-04-20 Hits:257
Power adapter circuit operation in three states

In learning the power adapter circuit, to learn to analyze the circuit, start by understanding the three states of the circuit. There are three states of the circuit: the power adapter voltages in the three states of loading, short circuit, and no load are U=E-IR, U=0. U=E, the following describes the specifics of these three states.

 

1. Loading status

The load is the switch closure in the circuit, and current flows through the load. In this state, the relationship between the voltage of the power adapter terminal and the load current can be determined by the characteristics of the power adapter. According to the size of the load, it can be divided into three situations: full load, light load, and overload. The working state of the load under rated power is called rated working state or full load; the working state lower than rated power is called light load; the working state higher than rated power is called overload. Since the overload is very easy to burn the appliance, overload is not allowed in general.

 

2, short circuit

If the external circuit is turned on by a conductor whose resistance value is approximately zero, then the power adapter is in a short-circuit state. In this state, the current in the circuit (short-circuit current) IE/R. We know that the internal resistance of the power adapter is generally small, so the short-circuit current may reach a very large value, which will burn the power adapter and must be strictly prevented and avoided.

The most common way to prevent short circuits is to install a fuse in the circuit. The fuse in the fuse is made of a low-melting lead-tin alloy or silver wire. When the current increases to a certain value, the fuse is first blown, thereby cutting off the circuit.

 

In the short circuit state, the terminal voltage of the power adapter is:

U=E-IRE-E/R*R=0

It can be seen that the main feature of the short circuit state is that the short circuit current is large and the voltage of the power adapter terminal is zero.

It should be noted here that usually the internal resistance of the power adapter is basically constant and the value is small, so it can be approximated that the terminal voltage of the power adapter is equal to the power adapter electromotive force. In the future, if it is not specifically pointed out that the internal resistance of the power adapter is marked, it means that the internal resistance is small and can be ignored.

 

3. no load status

The no load circuit is that the no load circuit of the power adapter is disconnected somewhere, no current flows through the circuit, and the power adapter does not deliver power to the load. For power adapters, this state is called no load. The main feature of the open circuit state is that the current in the circuit is zero. The power adapter terminal voltage and electromotive force are equal.

These three states can be seen everywhere in our lives. For example, if the switch of the electric light is turned on and the electric light is bright, this is a state of passage. If the electric light is turned on, the refrigerator, air conditioner, rice cooker, TV, computer, Speakers, electric wok, then the load is more, the overload phenomenon occurs later, when the cable is overloaded, it is easy to smoke and catch fire. When the switch is closed, the light is off, which is an no load state. When the two wires (hot wire, neutral wire) are damaged by the mouse, causing the two wires to touch together, it will cause a short circuit. If there is an over current switch, the over current switch will work immediately. If there is no over current switch, then Immediately smoke and catch fire.

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