Battery Charger Protection Functions

Whether you use a battery charger for your car, or you use a battery for other purposes, it's important to understand how to protect your battery. This includes recognizing what causes an overcharge, how to avoid a thermal runaway, and more.

Overcurrent protection is an important part of all electrical circuits. It protects equipment from current overloads and ground faults.

In addition to providing protection, overcurrent devices may also be used to diagnose an overcharge situation. Circuit breakers, fuses, and fusible links are the most common overcurrent protection devices. These devices are connected in series with the circuit they protect.

Fuses and circuit breakers are designed to interrupt a circuit when a current exceeds a preset threshold value. They are commonly used in low voltage systems. A fuse consists of two wires or strips encased in an insulator. The melted connection of the fusing strip can arc across and melt.

Fuses and circuit breakers can be found in almost all electronics products. They are used to protect personnel, conductors, and equipment from overcurrent or short circuits. If the circuit fails to perform, the fuses will blow and the device will be inoperable.

Batteries should be protected against overcurrent and overvoltage. Overcharge and overvoltage conditions can cause battery failures, explosions, and toxic fumes. Lithium-ion batteries, in particular, should be monitored and protected.

Battery charging circuits are vulnerable to problems such as a power source overload, a mismatched load, and a charging circuit that draws more current than permitted. To protect the battery and the equipment from these hazards, the battery pack should include an overcurrent protection function.

Lithium polymer battery packs are commonly equipped with a protective circuit that is designed to prevent overcharging and overdischarge. However, they are also susceptible to misuse. Charging a lithium polymer battery beyond its capacity can result in thermal runaway and other safety concerns. Ideally, a battery should not be charged over 1.5 times the battery's overcurrent charging protection current.

Testing the overcurrent protection function of a battery pack involves checking the circuit's response to overcurrent and overvoltage conditions. These tests should be conducted in a laboratory.

The overcurrent charging protection function is tested using a DC power source. Data is collected for one hour after charging stops. During this time, the battery's temperature and SOC level are measured. When the SOC level reaches 130% or more, the test is terminated. This allows for more accurate assessment of the battery's ability to resist overcurrent and overvoltage.

Over-discharge protection is one of the safety functions of a lithium ion battery charger. It occurs when the voltage of a lithium battery drops below a certain threshold. If the voltage reaches a level below this threshold, the battery will stop charging. The battery will eventually become a potential fire hazard.

Over-discharge protection is implemented in the form of an overcharge protection switch. The switch is connected in series between the positive side of the batteries and the output terminal of the battery.

The switch is accompanied by a control circuit that turns the switch on and off when the battery voltage reaches a certain minimum set point. A delay circuit is also included to prevent the FET from switching off prematurely.

In addition to the overcharge protection switch, there is also a voltage detection circuit that monitors the battery voltage. This circuit consists of a three-terminal integrated circuit (IC) controller. As shown in Fig. 2, the IC controls the over-discharge protection switch by interrupting the output voltage when the cell voltage drops below the over-discharge threshold.

This circuit also incorporates a parasitic diode to maintain the FET in an on state with respect to reverse current. It is complemented by a capacitor C21 that adds a small amount of time to the rise of the voltage at the gate of the FET.

When the over-discharge protection switch is turned off, the voltage at the output side of the switch is raised to the voltage at the charge-end. A thermal circuit breaker is also used to disable the battery input.

Another aforementioned component is the over-temperature protection function. This device is not as sophisticated as the over-discharge protection function.

An alternative design for the over-discharge protection function would be a microcontroller reading the temperature of the batteries and disabling the output. However, this option requires a lot of programming, which may be impractical for some applications.

Nevertheless, there are some over-discharge protection options that are useful and can be customized to meet a particular application. For example, in a multi-cell Li-ion battery charger, the over-discharge detection mechanism could be set to monitor all cells in the battery pack.

Over-temperature protection functions of battery chargers are critical to the performance and reliability of battery power management systems. The over-temperature condition is not only a safety hazard but also can be detrimental to the life of the battery. In order to prevent the occurrence of a thermal runaway, the battery must be shut down before the temperature reaches a level that is unfeasible.

Battery protection schemes typically offer two levels of protection. One is a thermal fuse and the other is a thermal shutdown feature.

The thermal fuse is a device that automatically switches off the charger if the temperature of the storage battery exceeds a predetermined threshold. Other features of battery chargers include over-voltage and reverse polarity protection.

There are other battery chargers that offer thermal shutdown features. However, these devices are too expensive to incorporate into a standard charger and require careful design to avoid a thermal shutdown. Instead, a thermal shutdown function can be implemented by connecting an NTC thermistor to a dedicated connection pin. A voltage-detecting circuit can then monitor the resistance of the thermistor to determine if the temperature is high enough to shut the battery down.

Batteries have a large temperature range. The difference between the temperature of the storage battery and the charger may be huge. This difference can cause over-charging or under-charging. Both of these can lead to damage to the battery.

In addition to the thermal fuse, the charger can include a voltage regulator. This allows the charger to maintain a constant voltage while keeping the current flowing into the battery below the maximum permissible value.

Battery chargers typically incorporate a patented plastic profile design that features rapid heat dissipation. It also includes an indicator light, a charging rate display, and six built-in protection functions.

The battery can also incorporate a thermistor to determine if the starting environment is too hot for the battery to absorb the charge. This temperature measurement is useful in monitoring circuits and in turn triggering an action to turn on a cooling fan or cutoff the charging.

Depending on the battery technology and the chemistry of the storage battery, there are several different protection functions. Some are implemented as part of the battery's power management system and others are integrated into the charger itself.

Thermal runaway is a dangerous condition that can occur in a battery. It causes the electrolyte in a battery to overheat and can lead to a fire that cannot be extinguished. This condition can be a result of an internal short circuit or an external short circuit. Fortunately, a battery charger has built-in protection against thermal runaway.

When the system starts charging the battery, it will first start monitoring the battery voltage. If the voltage does not increase, the system assumes that the battery is in thermal runaway mode. Then the charging current will increase until the battery is at a predetermined charge voltage.

When the charging current reaches a predetermined level, the system starts reducing the charge rate. This reduces the charging current to an amount that is safe for the battery. Once the current level reaches a certain threshold, the battery will be fully charged.

To prevent the possibility of thermal runaway, the battery charger will monitor the voltage and duty cycle of the charging current. If there is a deviation in the charging characteristics, the system will treat the anomaly as a problem and will reduce the charging rate.

The battery charger's software will also monitor the electrical charging parameters of the battery. When the battery voltage reaches a preset value, it will be checked to determine if there is a thermal runaway condition.

In a constant current mode, the duty cycle is checked every three or four consecutive values. When the duty cycle decreases, the di/dt counter is decreased and the DTlimit is increased.

During a constant voltage mode of operation, the di/dt counter is set to the nominal value. The voltage curve will have a positive slope. A thermal runaway condition is considered when the voltage fails to ramp up and the di/dt counter reaches a negative value.

In a constant voltage battery charger, the duty cycle is checked at fixed intervals. At a preset time, the system will reduce the charging current and then check the duty cycle again to see if it has decreased.

Thermal runaway can occur in lithium batteries. Although they are extremely efficient energy storage devices, their capacity can be diminished if they are left in a warm environment. Moreover, they are known to combust when exposed to lithium hydroxide. For this reason, Li-ion batteries must be stored at a temperature that is safe for the battery.

Battery charger output over voltage protection is a feature that helps ensure that the current flowing into the battery stays within a predetermined limit. This means that the charging circuit can shut off the output for a certain amount of time to avoid a malfunction that may cause an explosion.

Batteries can be very sensitive, and a failure of the charging circuit could lead to an explosion. Fortunately, there are a number of ways to prevent this from happening. First, the battery must be charged at a constant rate. The rate depends on the battery chemistry and how much of it is depleted. Second, the circuit must be designed to be able to withstand abnormal operation conditions.

A typical battery management system consists of a battery monitoring block and an overvoltage protection circuit. The protection mechanism protects the battery from damage during the charging process and against power-supply problems. It can be integrated with the charging circuit, or it can be implemented as part of the battery management system. Typically, this type of battery charger uses a linear regulator design, which aims to keep the current within the range of the battery terminal voltage envelope.

Another option is a battery management system that integrates continuous control and limiting control functions. This enables the charge current to scale back when the load exceeds the USB current limit. Also, the regulated 3.3V output supply can be used to provide an active-low undervoltage detection signal.

Another option for overvoltage protection is a comparator circuit. Using comparison operators in the microcontroller code, it is possible to ensure that the impressed voltage is lower than the maximum permissible voltage. The INA300 23 current-sense comparator can consume well under the 1mA maximum.

An ideal diode function can also be used to pause the charging process when the output voltage falls below a specified level. In this case, the ideal diode is a high performance diode that enables a second external PFET to connect between the OUT and BAT. When the OUT voltage falls below the BAT voltage, the ideal diode becomes active.

Some battery chemistries are very sensitive to impressed voltages. For example, lithium-ion rechargeable batteries are designed to charge at only one degC. When the terminal voltage drops below this level, the charging circuit must disconnect. Similarly, other chemistries expect a very small float voltage. However, when the voltage drops too low, the self-discharge rate increases. These chemistries also require the charging circuit to disconnect when the terminal voltage is reached.

Other issues can arise from the use of unregulated ac/dc adapters. Many electronic devices, including airplanes, glass panels, and even the charging ICs, are susceptible to damage when they are plugged into an unregulated supply.

One solution is to use a switch-mode power supply. These types of power supplies use a switch to monitor the voltage. If the voltage rises too quickly, the switch will recheck the voltage. But if the power supply is faulty, the switching power supply can be damaged.

Battery Charger Input Under-Voltage & Over-Voltage Protection

Battery charger input under-voltage & over-voltage protection is an important feature for a variety of applications. When the input voltage exceeds a certain threshold, the charger IC will disable the power supply. This can protect the load, device, or system microcontroller from damage. Depending on the design of the charger IC, temperature thresholds may also be implemented.

Over-voltage protection is less common than under-voltage protection. However, in some cases, the condition may cause malfunctioning of the circuit. It is best to implement this type of protection with caution. There are a number of factors to consider, such as the battery's charge current and temperature, the amount of power needed to maintain battery voltage, and the type of device being used. Ideally, the charger IC will implement configurable responses to the over-voltage situation. The charger IC will also need to be able to regulate its operation range.

Under-voltage protection is often less complex than over-voltage protection. Most designers simply do not concern themselves with this aspect of their designs. Rather, they focus on other aspects of their projects. In most cases, under-voltage conditions do not cause damage. But, some conditions may require more attention.

To implement under-voltage protection, a circuit is placed across the power supply. Then, a timer is used. This timer will automatically disconnect the load if the battery falls below a set threshold. The circuit is simple and easy to implement. The timer can be adjusted to accommodate different voltage values.

Another option is to use a crowbar circuit. A crowbar circuit is similar to a drop-crowbar. However, a crowbar doesn't consider the possibility of damage to the power supply. Rather, the crowbar's function is to prevent an over-voltage situation from occurring.

Generally, the over-voltage protection feature of a battery charger will be based on a JEITA battery standard. As a result, the battery pack manufacturer will have specified thresholds for different charge current levels. For example, the charger IC may be able to configure the minimum input voltage to 4.5V, the maximum input voltage to 20V, and the under-voltage threshold to 3V.

Other over-voltage protection features include thermal regulation and missing-battery detection. The charger IC can also prevent over-temperature by regulating the charging current. These safety features will ensure the battery is not damaged during charging.

There are several types of charger ICs, including buck, boost, and buck-boost chargers. Buck-boost chargers enable continuous charging while limiting the maximum charge current to a specific threshold. Both buck and boost chargers have a higher operating voltage than a buck charger. Therefore, they require a larger IC package. They can be used in portable applications.

Some charger ICs have an integrated I2C interface. This allows the device to easily configure different safety features. One such feature is the watchdog timer. During the charging process, the MCU must regularly reset the timer. If the timer fails to operate, the system microcontroller will be unable to respond.

Another type of battery charger IC is the switching charger. Switching chargers are generally more efficient and capable of handling higher currents. While this type of charger can cost more, it can also be a more convenient choice for some applications.

Battery Charger Short Circuit Circuit & Reverse Connection Protection

Reverse polarity battery connections can cause serious damage to batteries and portable electronic equipment. They can produce a spark, hydrogen gas, or discharge the battery completely. These can all be hazardous to your health and to your equipment. Here's how to prevent reverse battery connections and how to protect your battery charger from the effects.

To prevent reverse polarity battery connections, it's important to connect the positive to the negative terminals of the battery. This is to ensure that the battery will not overheat. In addition, the voltage from the negative side of the battery will gradually discharge the battery, causing a discharge cycle similar to the one that occurs with a capacitor.

Depending on the type of device you are using, you may need a battery reversal switch or mechanical safeguards. These can include a polarized connector or a one-way connector. Also, you may need to wear protective eyewear or rubber gloves.

Another simple approach to prevent battery reversal is to use a parallel diode circuit. It's easy to build and can protect high output impedance batteries from reverse installations. However, it needs to be able to handle a high current. The charge pump can also be a useful addition to help protect the load.

A reverse polarity battery connection is dangerous because the electrons are pulled from the negative to the positive side of the battery. This can cause the battery to discharge and can burn out the battery. As with other batteries, it can also lead to quick drainage and a short lifespan. Using a battery reversal switch can protect your battery charger and portable electronics from the effects of a reverse battery connection.

When a reverse battery is connected, the MP1 detects it. If the MP1 doesn't detect the connection, it will disable the MP2 primary pass device. During a reverse battery attach, the MN1 will generate a lot of power. This causes the MP2 to deactivate and the MP1 will then disengage. Similarly, if the battery is attached and the MP2 is disabled, the MP1 will stop the charger from running.

Another approach is to use an NMOS-based circuit. NMOS uses a latching memory element to determine whether the reverse battery is attached. While this method is simpler than a PMOS-based approach, it doesn't always connect to the battery. Even if it does, it's not always fast enough to prevent the MN1 from activating.

Alternatively, you can try a PMOS protection circuit. In this method, the battery is temporarily connected to the charger's output while the charger is off. By comparing the voltage from the battery terminal with the voltage from the charger output, you can determine whether the connection is permanent.

Finally, it's essential to disconnect the MN1 from the battery before it becomes too hot to disengage. Although it's not a fast process, it's very important. Several circuits have been developed to assist with this task. One of the best circuits includes R3 and R4. It's most effective for lower-voltage lithium-ion battery applications.