Battery charging regulator
Philips, IC Type TEA1100 uses the delta-peak principle to charge nickel-cadmium (NiCd) and nickel-metal-hydride (NiMH) batteries fast and effectively. The task of the delta-peak battery charging regulator is to ascertain and evaluate the change in the battery voltage: if the voltage at pin 7 drops 1% or more below the average maximum, charging is discontinued. The voltage at pin 7, according to the manufacturers’ data sheet, must be 0.385-3.85 V. Potential divider R4-R5 ensures that the battery e.m.f. corresponds to this range. The values of these resistors are given by:
R4/(R4+R5) < 2.14n;
The charging current, 4, is given by:
IC = 1•25Rsense/Rshunt’Rref.
where Rsense is R10; Rshunt is R8 parallel with R9, and Rref is R2. Timeout, TO, is a safety facility of the IC. If, for whatever reason, no maximum can be detected, the IC stops the charging after the timeout. This time constant is given by
TO = 226.0.93.RrefCosc,
where Cosc = C3. Note that both timeout and charging current are influenced by R2. When the charging current and timeout 0 are being determined, the value of R2 must, therefore, be fixed and that of C3 must be variable.
When the battery is fully charged, the TEA 1100 switches to the ‘maintain charge’ mode. In this mode, during 1/10 of the normal charging time 1/2 of the usual charging current flows (in other words, the battery is trickle-charged at 1/20 of the normal charging current). This trickle-charge current may be altered on the basis of the following formula:
Itrickie = I . 2 5Rsense I 1ORshuntRN•
The current is determined from the drop across the shunt resistor and switched by the transistors via pin 2 of ICI. Stability of the circuit is ensured by capacitor C2.
When no battery is connected to K1 or when a battery is being trickle-charged. DI flashes: when the voltage at pin 7 drops, the LED lights continuously.
The supply voltage at pin 12 must be 5.65-11.5 V. The quiescent current (when the outputs are all off) is some 4 mA. This IC enables many other applications: a number of these are given in Philips’ Data Sheet TEA1100 & TEA1100T.