Author ：Iflowpower – Portable Power Station Supplier
As long as it is a battery powered system, there is always this problem: you are wrong to install the battery, reverse polarity events, reverse polar events. System temporarily malfunction or permanent damage. The custom battery designed to fit the assembly helps to minimize the incorrect insertion and reverse polar opportunities, but is a Type AAA, AA type, C-type, and D-type cells.
Battery, or even CR123, CR2 and button lithium ion battery are also prone to failure. In the past, designers used mechanical structures to prevent electrical contact with battery terminals (if not inserted correctly). But the mechanical solution is far less.
They usually have special processing because the spring contacts are to control good mechanical components to ensure that it is good to be in contact with the battery correctly, but not inserted correctly. These narrow tolerances can result in long-term stability problems because the springs and contacts that must be used may be bent or faulty. Even normal use is normal, the normal insertion of the initial resend, can also cause contact fatigue, and limit the reliability over time.
But although these restrictions, mechanical solutions have always existed because they are the only practical ways that designers can use to prevent incorrect battery installations. Designed to prevent electrical solutions from reverse polarity incidents caused by reverse phase batteries from being disputed. Because of the pressure drop during normal operation, it is usually not selected using a series diode.
It is not a good idea using diode grounding settings because the reverse polarity event may cause battery hazard discharge for a long time and make diode overheat. Differential MOSFETs to be complex, and may not be optimized or specific to prevent reverse polarity. The key specifications of the evaluation performance in the reverse polarity event may be lost, and this may make the designer have to estimate the performance characteristics of the data table and guess the safety working time period, is worrying.
Moreover, depending on the MOSFET application, they may have a controller or other cost high function. Multifunction ICs are sometimes equipped with circuits that prevent reverse polarity, which typically significantly adds the complexity of the circuit because they work in a positive bias environment and then work or not damaged in the reverse polarity mode. Therefore, multi-function IC has brought huge performance and / or cost price.
Due to the cost-effective trade-off, the typical implementation has a relatively limited reverse bias function (-2V or -6V). A dedicated anti-polarity protection device is an effective way to prevent erroneous insertion batteries However, recently, the emergence of dedicated reverse polar protection devices supply more viable electrical options for designers. Special devices (such as devices supplied by flying sight) represent one of the methods of preventing reverse polarity and cost performance and performance, is the best choice for battery power supply systems.
Figure 1. Displayed circuits from preventing reverse polarity using dedicated devices. Figure 1: Preventing reverse polarity from using dedicated devices This simple setting continues to reliably.
Designed to minimally reduce the voltage loss, and respond quickly and effectively under reverse bias conditions. Overall cost is also good. SiteThetti diodes are usually cheaper than dedicated reverse polar protection devices, but once the operating current begins to increase, the total cost of Schottky method will begin to rise.
For cost-effective trade-off, dedicated reverse polar protection devices are likely to be the most attractive electronic approach. People will continue to make more mistakes on the battery, but designers prevent small unexpected ways will also change. After considering comprehensive, the dedicated reverse polarity protection device may completely replace complex mechanical solution over time.
The cause of reverse polarity and the measures that can be taken to this, no one wants their system to fail, even more serious fire burning. However, if the reverse polarity is allowed to break, the above situation may occur. The reverse polarity is a steady-state reverse bias or negative transient result.
This is a dangerous electrical situation, and once the system is factory factory, it is difficult to prevent. Reverse polarity is the actual threat in a variety of common applications, including mobile electronics, battery power systems, devices connected to automotive power supply, DC power toys, products with bucket jack connector, or any subjected to negative voltage heat Plug or inductance transient DC device. Systems that support USB connection and / or USB charging are particularly affected.
The following is some of the most common causes of reverse polarity:. In some cases, the charger has a reverse electrical contact or polarity can be set by the user, which leaving space for the error. ● Use the USB "Hot Plug" function bus to easily connect or disconnect the mobile device when it is charged, and the "hot plug" operation is new, the amplitude of the hot-swappable transient is also the same.
These inductance transients can swing bus to reverse polarity conditions. Although these swings are often very short, it is large. More than ± 20V voltage rail swing has been measured in "hot plug" operation.
This transient may affect the other devices on the disconnected device and the voltage rail. This problem will only be more serious when the charging current increases. ● The system that is powered by battery batteries that is not properly inserted can be faulty because the battery is not inserted correctly, and its positive negative is inserted.
This is especially true for AAA type, AA type, C-type, and D-type cells, or CR123, CR2 or butter lithium-ion batteries. If the battery is inserted correctly, the mechanical solution prevents electrical contact with the battery terminal, but these solutions must be molded from the mold and can withstand the contact fatigue after a period of time. ● Developing the use of wall plugs in our country, there are fewer power infrastructure in the world, and there is less protection requirements.
Therefore, power supply can transmit large voltage transients on the line. Indoor wiring makes the situation worse. In the past, traditional incandescent lamps can help absorb and suppress transient energy on the power line, but there is no other inhibitory feature such as new types such as LED and CFL.
Problems that have never been encountered by moving to LED and CFL. ● Insert the device into the car (or plane, train, etc.) In many cases, the power supply adapter in the transportation power supply includes reverse polarity, but there are exceptions, especially in low cost replacement products.
Uninformed users only put the device inserted into the lighter jack in the car, because he didn't realize that the lighter jack can cause the device failure. Since there are too many ways to trigger a reverse polar event, the designer must prevent the reverse polarity before the system will prevent damage to damage. The best protection method of the reverse polarity in the 100mA system is low current system - that is, the operating current is below 100mA or 200mA - covering various applications, from the security system and fire alarm to the building automation, public address and data network system.
These include many different working environment, and the designers cannot always predict where the system will use. According to the specific situation, the system may be exposed to steady-state reverse bias or negative electrical conditions such as negative transients, which may result in reverse polarity events and damage the system. The result may be as simple as the electrical failure, but if the situation is very serious, it may cause a fire.
Therefore, the negative effects of designers to prevent reverse polarity from bringing the negative effects of reverse polarity. There are many ways to achieve this, but about low current applications, its efficiency is usually less problematic. As long as the system can be resistant to power consumption and the operating voltage pressure drop is associated with each method, the two simple methods of series PN or Schottky diode can be used to achieve the purpose.
The series PN diode is designed to accept a larger series pressure drop (± 1V), or may have a high voltage reverse transient (> 200V), then use a series PN diode is a good choice. Figure 2 is supplied with a design example. This is a simple low-cost solution that can supply fast blocking, reset function and high breakdown voltage.
Figure 2: Series Diode Method This diode has the least power consumption, so fewer heat sinks, and low cost. The system will work normally as long as the device is hot during normal operation or possible fault conditions. Even so, this solution is not suitable for each design.
The cost advantage will soon disappear with the rise of the working current. Moreover, under the higher current, the larger the power consumption, the larger the diode needs, the more expensive, the thermal conductivity is better, and the heat dissipation structure is used. In addition, in a low voltage system (≤5V), the diode pressure drop may have an additional downstream booster circuit, which makes it expected to be a low cost method actually become very expensive.
Therefore, it is important to remember these several before using the PN diode method. The series of Schottky diodes is similar to but the application is a broader method is to use a series of Schottky diodes instead of the series PN diode. This pressure drop is lower (± 0.
6V) and the power consumption is less power. Figure 3 shows the setting of Schottky diode. This configuration provides excellent blocking, simple design import and low cost.
It can also be reset and may support relatively high breakdown voltage (> 200V). Figure 3: Sitexerry diode method pressure drop can reduce heat management requirements related to traditional PN diodes, and this may achieve smaller and lower packages. Despite this, it is still careful because it may still be too high because of the pressure drop regarding many applications.
Moreover, although the operating range of the Schottky diode is wide than the series PN diode, the best application of this method is still a current using a current below 200 mA and has a higher voltage (> 5V). Conclusion Which method is used, it is necessary to consider two important aspects of pressure drop and power consumption. Suppose these two parameters are within acceptable ranges, then two methods can effectively protect the low current system at low cost, which is damaged from reverse polarity events.
If the pressure drop or power consumption is problem, it can consider the source solution such as FRPF.
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