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Four ways to make the power adapter safer
time2006/09/19
- Four methods to make the power adapter safer: pulse-by-pulse over-power or over-current limit, over-power delay-off protection, flyback overpower limit protection, and constant power limit protection.
Method 1: Pulse-by-pulse superpower or overcurrent limit
In the new product development process of the power adapter, the pulse-by-pulse super power and overcurrent limit are indispensable, and this is a super-power or over-current limit for pulse-by-pulse, which is a very effective output overload protection in practical applications. In this way, this technique 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 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.