The importance of lithium battery charging circuit and protection circuit
design. In the design of circuits using lithium batteries as power sources,
increasingly complex mixed-signal systems are required to be integrated into a
small-area chip, which inevitably raises low-voltage and low-power consumption
issues for digital and analog circuits. Therefore, the design of lithium battery
charging circuit and protection circuit is very important.
The necessity of lithium battery protection circuit
Due to the high energy density of lithium batteries, in the overcharged
state, the energy will be excess when the battery temperature rises, so the
electrolyte decomposes to produce gas, which can easily increase the internal
pressure and cause the risk of spontaneous combustion or rupture; conversely, in
the overdischarged state, The decomposition of the electrolyte causes the
battery characteristics and durability to deteriorate, reducing the number of
recharges and shortening the battery life. Therefore, the protection of lithium
batteries is very important. Lithium battery applications must have battery
protection chips to prevent battery overcharge, overdischarge and
overcurrent.
To sum up, the design of lithium battery protection circuit is very
important. We require lithium battery power protection chips to be able to
achieve the following most basic functions: overcharge protection,
over-discharge protection, over-current protection and short-circuit protection.
From the above application requirements of lithium batteries, it can be seen
that in order to improve the service life of lithium batteries and ensure the
safe use of batteries.
Lithium battery protection circuit needs to have the following
functions
(1) If the charging voltage exceeds the maximum allowed value of the
battery, a battery discharge circuit can be provided.
(2) If the discharge voltage is lower than the minimum allowed value of the
battery, a battery charging circuit can be provided. The battery is disconnected
from the external circuit, and the battery is disconnected from the external
circuit.
(3) If the charge and discharge current of the lithium battery is greater
than the limit value, cut off the connection between the battery and the
external circuit.
(4) When the lithium battery returns to normal state, the protection
circuit should be able to release the protection state accordingly so that the
battery can continue to work normally.
Things to note when designing lithium battery circuits
▲Overcharging and over-discharging lithium batteries will affect the life
of the battery.
▲Pay attention to the charging voltage and charging current of the lithium
battery. Then choose the appropriate charging chip.
▲Be careful to prevent overcharging, over-discharging, short-circuit
protection and other problems of lithium batteries.
▲After design, a lot of testing is required.
Design of lithium battery charging circuit management
When a lithium battery is charged, the potential applied to the two poles
of the battery forces the compound in the positive electrode to release lithium
ions and embed them in the carbon in which the negative electrode molecules are
arranged in a lamellar structure. During discharge, lithium ions are
precipitated from the carbon in the lamellar structure and recombine with the
compound of the positive electrode. The movement of lithium ions creates an
electric current. Although the principle is very simple, in actual industrial
production, there are many more practical issues that need to be considered: the
material of the positive electrode needs additives to maintain the activity of
multiple charges and discharges, and the material of the negative electrode
needs to be designed at the molecular structure level to accommodate more More
lithium ions; the electrolyte filled between the positive and negative
electrodes, in addition to maintaining stability, also needs to have good
conductivity and reduce the internal resistance of the battery.
When the lithium battery is in deep discharge, the charger must be required
to have a precharge process so that the battery can meet the conditions for fast
charging; then, according to the fast charging speed recommended by the lithium
battery manufacturer, which is generally 1C, the charger performs a constant
charge on the battery. During constant current charging, the battery voltage
rises slowly; once the battery voltage reaches the set termination voltage,
constant current charging is terminated, the charging current rapidly decays,
and charging enters the full charge process.
When we design products that require the use of lithium batteries, we need
to design a protection circuit for the lithium battery. Only on this basis can
we design the charging circuit. Lithium batteries require overvoltage charging
protection, overvoltage discharge protection, overcurrent discharge protection,
short circuit protection, etc. Therefore, when we design a lithium battery
protection circuit, we must at least achieve the above protection functions.
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