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A BETTER BATTERY CHARGER

Part 2: Hardware and Software Implementation
by Thomas Richter

Start ý The Buck Converter ý Voltage Reference and Battery Temperature ý AT90S2333 Battery Charger ý ATtiny15 Battery Charger ý Charge Current ý Software Implementation ý User Settings ý Source Code ý INT Battery Function ý The Stable_ADC Function ý BC.H ý B_DEF.H ý Charge MethodýSLA.C ý Charge MethodýNiCd.C and NiMH.C ý Charge MethodýLilon.C ý Suggested Improvement ý Sources and PDF

CHARGE METHODýLiIon.C

Li-Ion batteries are the most advanced battery types to charge. The fast-charge starts at a constant current of 1 C (see Figures 14a and b ). This current is kept constant until a cell voltage level of 4.1 or 4.2 V, ý 50 mV is set. Then, the battery is charged with constant voltage until the current drops below Imin.

For an accurate measurement of the battery voltage (not the charge voltage), the PWM is turned off during voltage measurements. If the charge method then changes from constant current to constant voltage, the charge voltage is the relevant parameter to be measured. This is the reason why there are two voltage measurement modes, one with PWM turned off and one without.

The trickle charge of Li-Ion batteries is in principle the same as fast-charge (see Figure 15). The only differences are that the current is much lower than in fast-charge mode and the constant voltage phase of the trickle-charge mode is terminated by a timer (see the Charge Parameter Summary document).

Figure 15ýHere you can see the principle of trickle charging for lithium ion batteries.

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