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What is the safety of the switching power adapter?
time2006/09/27
- Switching power adapters are safer to do this: pulse-by-pulse over-power or over-current limiting, over-power-delayed shutdown protection, flyback overpower limiting protection, and constant power limiting protection.
During the new product development design of the switching power adapter, engineers usually add some protection measures to the new product designed to avoid short circuit or component damage during the use of the switching power adapter, which shortens the working life. In today's article, we will share four protection measures that will extend the life of the adapter. Let's take a look.
Method 1: Pulse-by-pulse superpower or overcurrent limit
In the development of new products for switching power adapters, pulse-by-pulse over-power and over-current limits are essential, and this is a super-power or over-current limit on pulse-by-pulse, which is a very effective output overload in practical applications. Protection method, which is often used in additional secondary current limiting protection. In previous switching devices, the input current was monitored in real time. If this current exceeds the specified limit current value, the turn-on pulse is terminated. In a non-continuous flyback converter, its current determines the power of the circuit. This type of protection circuit becomes a real power limit protection circuit.
Method 2: Super power delay shutdown protection
As a very effective output overload protection technology, the ultra-power delay shutdown protection has been widely used in power adapter products produced in China. In a time-delayed trip system, short-term transient current requirements are tolerated, and the power supply is turned off only when the current stress exceeds a safe value for a long time. The provision of short transient currents will not compromise the reliability of the power supply and will not have a significant impact on the cost of the power supply. Only long-term continuous current requirements will affect the cost and size of the circuit.
Method 3: Flyback Super Power Limit Protection
In addition to the two methods described above, the flyback ultra-power limit protection method is also an important measure to effectively ensure the safe operation of the switching power adapter. Currently, it is widely used in domestic adapter development and factory production processes. This protection technique is an extension of the upper speed form. In the adapter circuit using this protection method, there is a special circuit for monitoring the primary current and the secondary voltage, and reducing the power when the output voltage is lowered. In this way, the output current is reduced when the load resistance is lowered, and the secondary component is prevented from being subjected to excessive stress damage. The disadvantage is that the locking phenomenon occurs when used for a non-linear load.
Method 4: Constant Power Limit Protection
The constant input power limit protection method is the fourth kind of switching power adapter protection technology that we will introduce to you today. It is also a kind of output protection technology which is more common at home and abroad. In the development process of notebook adapters and mobile phone adapters, it is indispensable. The figure. The protection principle of this method is to protect the primary circuit by limiting the maximum transmission power. However, in a flyback converter, this technique hardly protects the secondary output components. For example, in a discontinuous flyback converter, the primary peak current has been limited, that is, the limited transmitted power is given.