Example 2: Charging a Nickel Metal Hydride Battery
Pack
Battery Pack: 4.8V pack: 4 cells
@
1.2V, 1200 mAh
Charger Requirement: High-Quality Charge, Long Cell Life
The minimum input voltage required at full load is:
minimum V
supply
= N ( V
pk
) + V
reg
→
minimum V
supply
=
4(1.85V) + 1.25V = 8.65V
Fast PWM is recommended for a high quality charge.
The value of the discharge resistor for 0.2C is obtained via:
C = 1200 mAh
→
0.2C = 240 mAh
In order to discharge within 30 minutes, a current of 480 mA
will be required — resulting in a resistor value:
R
dischg
= 4(0.9V) / 480 mA = 7.5
Ω
The power dissipated by the discharge resistor is approxi-
mately 1.7 watts.
Note: V
reg
is the minimum input to output voltage drop across LM317.
Charger Settings for 4.8V Nickel Metal Hydride Pack
Jumper
Connection
Comment
Jumper
Connection
Comment
J1
Battery Pack
4 Ni-MH cells
J10
2-3
1200 mA Range
J2
N.C.
Disch. before charge
J11
13-14
Ni 4-cells Range
J3
NTC
Batt Pack Themistor
J12
13-14
Ni 4-cells Range
J4
Power Supply
minimum V
supply
= 8.65v
J13
7-8
1200 mA Range
J5
VCC
Ni-MH Battery
J14
5-6
Ni 4-cells Range
J6
VCC
Fast PWM Mode
J15
R
dischg
10
Ω
/ 10W Resistor
J7
Fast
Fast PWM Model
J16
N.C.
No J16 on Ref. Board
J8
Open
Attach NTC at J3
J17
N.C.
Only used in Slow
J9
7-8
1200 mA Range
J18
9-10
0.5C Topping
Example 3: Charging a Lithium-Ion Battery Pack
Battery Pack: 10.8V pack: 3 cells
@
3.6V, 1200 mAh
Charger Requirement: High-Quality Charge, Long Cell Life
A 3.6V cell develops a peak voltage of 4.1V when charging.
The minimum input voltage required at full load is:
minimum V
supply
= N ( V
pk
) + V
reg
→
minimum V
supply
=
3(4.1V) + 1.25V = 13.55V
Note: V
reg
is the minimum input to output voltage drop across LM317. For
multi-chemistry charging solutions, it is recommended that J6 be hard-
wired to V
CC
. Scaling resistors will have to be changed to accommo-
date 4.1V cells.
Charger Settings for 10.8V Lithium-Ion Pack
Jumper
Connection
Comment
Jumper
Connection
Comment
J1
Battery Pack
3 Li-Ion cells
J10
2-3
1200 mA Range
J2
N.C.
Maint. with auto-restart
J11
5-6
3 Li-Ion cells
J3
NTC
Battery Pack Thermistor
J12
5-6
3 Li-Ion cells
J4
Power Supply
minimum V
supply
= 13.55v
J13
7-8
1200 mA Range
J5
N.C.
Li-Ion Battery
J14
7-8
3 Li-Ion cells
J6
GND
4.1V /cell (see note)
J15
N.C.
Only Used for Ni-cells
J7
Fast
Fast PWM Mode
J16
N.C.
No J16 on Ref. Board
J8
Open
Attach NTC at J3
J17
N.C.
Only used in Slow
J9
7-8
1200 mA Range
J18
X
0.5C Topping
References
AN-1164 Application Note for LM3647
LM3647 Datasheet
Fairchild
Semiconductor
1N5401
data
sheet.
(http://
www.fairchildsemi.com/ds/1N/1N5401.pdf)
AN-1
165
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