Package of this charger.
Charger’s appearance
Internal:
Front side of PCB
We see 4 ntc temperature sensors for battery overheat protection. 2 batteries share one sensor.
Back side of PCB
The input 12v voltage converted via a buck converter. This converter is made up by a LM393 voltage comparator and a RC circuit(RC oscillating circuit). This circuit also provides current limitation.
Every 4 slots shares one step down voltage converter. So there are 2 converters in total.
This photo shows the inductors ,capacitors and diodes of the step down convertor.
This is a group of current sense resistors. Three 150 milliohms resistors parallel to each other to make 50milliohms for the current sense of AA batteries, and another two 100milliohms resistors parallel to make up a 50milliohms, this resistors conneted in series to the current sense resistors for AA batteries to make up a 100milliohms in total. It makes the peak charging current of AAA battries are about 50% of AA battries.
Four slots share a group of current sense resistors. So two groups are required.
Battery discharge resistors. Four slots share one group.
TL431 and a triode make up a voltage regulator circuit (set to 5V output) for Microcontroller. The microcontroller is MC81F4104S manufactured by ABOV (South Korea).
Every 4 slots share one converter. Batteries are charged in turns. Charge currents are switched by N-MOSFETS . One NMOS for one slot.
CD4051 switching 4 ntc sensors to one pin of MCU.
The duty cycle of battery charging current is slightly below 25%. So that 4 batteries share the charge current in turns.
This is the result of a battery charge test. We use a non-LSD 2600mAh NiMH battery for this test. Charging from 0% to 100% takes about 25000s (6h56min40s).
We can see a minus delta V near the end of this charge. This indicates the charger use a -ΔV algorithm to determine the charging terminal.
This charger has a function called “Refresh”. It discharges a battery to 0% and then fully charges it to eliminate the “memory effect” and improve battery performance.
The ripple of the step down buck converter. It doesnt matter since it’s used only for battery charging rather than MCU’s VDD.
