Digital battery

With technological progress and social development, such as mobile phones, laptops, MP3 players, PDAs, handheld game consoles, digital cameras and other portable devices has become increasingly popular, there are many of these products is used in lithium-ion battery-powered, while Because the characteristics of lithium-ion batteries and other rechargeable batteries may be different, usually with an internal circuit, many people do not understand the role of the circuit this article will be the characteristics of lithium-ion Laptop battery and its protection circuit works to develop.

 

Li-ion battery is divided into two types of primary batteries and secondary batteries in some of the lowest power consumption in portable electronic products used primarily in a non-rechargeable lithium batteries, while in laptops, phones phones, PDAs, digital cameras and so on greater energy consumption electronic products use rechargeable secondary batteries, ie lithium-ion battery.

 

And nickel-cadmium and nickel-metal hydride battery compared to lithium-ion batteries have the following advantages:

1, high voltage, single-cell lithium battery voltage to 3.6V Ion, far higher than the nickel-cadmium and nickel-hydride battery voltage of 1.2V metal.

2 volume density, the density of its capacity Ni-MH batteries or nickel-cadmium batteries 1.5-2.5 times.

3, retention of load (eg, a small self-discharge) in place well after the loss of his ability is low.

4, long life, use the normal cycle of life can reach more than 500 times.

5, no memory effect, charging the former did not short-circuiting the remaining capacity, easy to use.

As the chemical properties of lithium-ion IBM ThinkPad R52 battery, under normal use, its internal energy and chemical energy conversion between the positive reaction of chemicals, but in certain circumstances, such as its overload, over discharge and over-current lead to the battery Internal chemical side-reactions, side effects increase, it will seriously affect battery performance and life, and may generate a large number of gas, so that the pressure increases the internal battery soon after the explosion that led to security problems, then all lithium-ion batteries need a protection circuit, used for charging the battery and the condition of the discharge of effective control and under certain conditions, off-line loading and unloading to prevent damage to the battery.

 

The next picture shows a typical lithium-ion battery diagram circuit protection.

 

As indicated above, the road safety cage with two MOSFET (V1, V2) and a control IC (N1) and a number of RC element composition. Control IC is responsible for monitoring the Dell Latitude D830 battery voltage and current loop, and control two MOSFET’s Gate MOSFET switches in the circuit play a role in, respectively, to control the charging circuit and discharge circuit turn on and turn -off, the capacitor C3 for delay, the circuit on the load protection, over-discharge protection, over current protection and short circuit the function of protection, its work principle is as follows:

 

1, the normal state

In normal circuit N1 of the state “CO” and “no” feet high output voltage, two MOSFETs are in a state of conduction, the battery can be free to load and unload, because of MOSFET on - resistance is very low, generally smaller than 30 cents in Europe, so the resistance has little effect on circuit performance.

The protection circuit of the State microA level of current consumption, typically less than 7μA.

 

2, over-charging protection

Requirements of the lithium-ion battery charging method of the constant voltage constant current /, in the initial presentation, a constant current charging and the charging process, increase the voltage to 4.2 V (based on different cathode materials, and some batteries require constant voltage value of 4.1V) for a constant voltage until the current is smaller and smaller.

 

The battery is charging if the charger circuit out of control, will continue after the battery voltage exceeds 4.2 V constant charging current, the battery voltage will continue to increase at this time, when the battery voltage is charged more than 4.3V, the battery chemistry of the side effects will be aggravated and may lead to cell damage or safety problems.

 

In the battery with a protection circuit when the control IC to detect the battery voltage reaches 4.28V (This value for the control IC has decided that a different IC have different values), the “CO” PIN will high voltage variation is zero voltage V2 to the end of his tour on foot, thereby reducing off the charging circuit, so that the battery charger can not charge, played overload protection. V2 comes at a time due to the presence of the diode VD2 body, the hp F4812A battery can discharge the diode external loads.

In the control IC to detect the battery voltage exceeds 4.28V to return the signal between the V2, there is a time delay, the length of delay time is determined by C3, usually set at 1 second or two, to avoid interference caused by false judgments.

 

3, over-discharge protection

The process of discharging the battery on the external load, its voltage will be gradually reduced as the discharge process when the battery voltage to 2.5 V, its capacity has been completely shine, this time the load if the battery continues to discharge, the battery lead to permanent damage.

 

The process of discharging the battery when the control IC to detect the battery voltage drops below 2.3V (the value used by the control IC, IC have various different values), the “DO” PIN will be strong voltage variation is zero voltage, so that V1 amended by the turn-off, reducing outside the discharge circuit so that the battery can no longer discharged into the charges, has been over-discharge protection. V1 comes at a time due to the presence of the body diode VD1, charger through the diode can be charging the battery.

 

Due to over-discharge protection of a state of the sony VGP-BPS2 battery voltage can be reduced, which requires the consumption of the circuit current protection is very weak now control IC enters a low power state, all of the Consumer Protection power circuit is less than 0.1μA.

In the control IC to detect the battery voltage is below 2.3V to send off the signal between the V1, but there is also a time delay, the length of delay time is determined by C3, generally set at 100 milliseconds, to avoid interference from True or False.

 

4, over-current protection

As the chemical properties of lithium-ion battery, the battery manufacturer provides its maximum discharge current should not exceed 2C (C = Battery capacity / hour) when the battery discharge current of more than 2C would cause permanent damage to the battery or the safety problem.

 

Charge the toshiba PA3191U-3BRS battery in the normal discharge process, the discharge current after a series of two MOSFETs, due to MOSFET on resistance, will produce a voltage at its ends, the voltage U = I * 2 * RDS RDS for single MOSFET on resistance, the IC control over the “V” pin of the voltage value for testing, where the load causes an exception for some reason, so that increases in current loop when the loop current is so large that U> 0.1V (the value of the control IC has decided that a different IC have different values), the “DO” PIN will be significant variation in voltage is a zero voltage, so that V1 disabled by the turn-on, cutting off the discharge circuit so that the loop current to zero, to play on-current protection.

In the control IC to detect over-current shutdown has to make between the signals V1, but there is also a time delay, the length of delay time is determined by C3, typically 13 milliseconds to avoid interference caused by false judgments.

In the process of control over, we can see that the value of the size of its over-current detection depends not only on CI control control value, but also depends on the MOSFET on resistance when the MOSFET on resistance, where most of the same control IC, the over-protection during the most value.

 

5, short-circuit protection

The process of discharging the apple A1079 battery to the load, if the loop is so large that U> 0.9 V (the value is determined by the control IC, IC have various different values), the control IC is considered that the load short-circuit the “DO” feet are rapidly changing the high voltage to zero voltage, so that V1 disabled by the turn-on, cutting and discharge circuit, playing short circuit protection. Short-circuit protection, a very short time period, usually less than 7 microseconds. ’s how it works with the methods of over-current protection is similar, but different in determining the length of time protection is not the same.

 

More detailed single-cell lithium battery operates ion protection circuit, multiple-series Lithium-principle of ion battery protection Similarly, will not go above the control circuits used in integrated circuits Series Ricoh R5421 Japan, in the circuit the battery real protection, there are many other types of control IC, such as S-8241 Seiko Japan Series, Japan Series MM3061 MITSUMI, the Taiwan-rich and crystal FS312 series FS313, the Taiwan AAT8632 series of analog technology, and so on, his works very much the same, but some differences in specific settings, some IC controls to safeguard the external circuit, the capacitor filter and the delay of chip capacitors to achieve its peripheral circuits can be very small, like Japan Seiko S-8241 series.

 

In addition to controlling IC circuit there is an important component, is the MOSFET, it acts as a switch in the circuit, because cascade directly between the VGP-BPS9/B battery and the external load, so it’s on the strength of the performance of cells are the impact of MOSFET with a choice of better quality, on-resistance is low, the internal resistance of the battery is low, with a transport capacity is also strong in the exercise of their electricity consumption is also less.

 

With the development of technology, portable devices get smaller and smaller, and as this trend of lithium-ion battery needs protection circuit size are becoming smaller in the last two years have seen the day in the control IC and MOSFET integrated protection of integrated circuit products, such as the series DA7112 dialog, and some manufacturers even the whole package of circuit protection in a small size of the IC, such as product MITSUMI company.