Vicor VI-J00 Family DC-DC Converters and Configurable Power Supplies - Manual (Page 32)

Design Guide & Applications Manual
For VI-200 and VI-J00 Family DC-DC Converters and Configurable Power Supplies
VI-200 and VI-J00 Family Design Guide Rev 3.5 vicorpower.com
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DESIGNING A BATTERY CHARGER
Vicor’s BatMod (current source module) enables designers
to easily build a compact, lightweight battery charging
system with commonly available parts. The BatMod
provides programmable output current and output voltage
capability. Since the BatMod allows the output voltage
and the charge current to be set independently, the
system design is greatly simplified.
Basic Battery Charger. Figure 11–3, shows a basic
charging circuit with a BatMod for the following
system requirements:
Battery voltage: 12 V
Float voltage: 13.8 V
Charge current: Adjustable 0 – 14.5 A
Setting the Float Voltage. Since the open circuit output
of a 12 V BatMod (VI-2x1-CU-BM) is 15 V, a trim resistor
(R3) is necessary to set the float voltage of 13.8 V.
Steps to determine the value of R3:
Solve for V TRIM :
(
V FLOAT
)
V REF = V TRIM
V NOM
(
13.8 V
)
2.5 V = 2.3 V
15 V
Solve for V R5 :
V
REF
– V
TRIM
= V
R5
2.5 V – 2.3 V = 0.2 V
Solve for I
R5
:
I
R5
= V R5 = 0.2 V = 20 µA
R5 10 k
Ω
Solve for R3:
V TRIM
= R3
I
R5
2.3 V
= 115 k
Ω
20 µA
A 13.8 V output requires a 115 k
Ω resistor.
Setting the Charge Current. The charge current can
be programmed from 0 to maximum (14.5 A) by applying
1 – 5 V to the I
TRIM
pin. To determine the voltage required
to produce a particular charge current, 10 A for example,
use the following formula:
4
(
Desired Charge Current
)
+ 1 = I
TRIM
voltage
Maximum Output Current
4
(
10 A
)
+ 1 = 3.76 V
14.5 A
To set the input voltage at I TRIM to 3.76 V, adjust the
potentiometer (R2) appropriately.
In Figure 11–3 the configuration will charge the battery
at a maximum of 10 A with a 13.8 V float voltage. Other
charge rates and float voltages may be similarly calculated.
If a fixed charge current is desired, the potentiometer can
be replaced with two fixed resistors. In applications requiring
tight control over the charging current, D1 can be replaced
with a precision reference.
Advanced Battery Charger. Many new battery technologies
require sophisticated charging and monitoring systems to
preserve their high performance and to extend their life.
The Bat Mod serves as an ideal building block for
constructing an advanced battery management system,
which typically incorporates a microprocessor-based
control circuit that is easily adapted for a variety of battery
chemis tries and monitoring functions. (Figure 11–4)
To maintain the optimum charge on the battery, the
control circuit independently adjusts the float voltage and
charge current in response to conditions during the
charge: the battery’s voltage, current, temperature and
pressure, and other pertinent parameters. It can also relay
battery status information such as capacity, charge and
discharge history, and cause of failure.
NOTE: A redundant control or monitoring circuit
must be included if failure of the BatMod or its
control circuit will result in uncontrolled charging of
the battery. Many new battery types are sensitive to
these conditions and may result in fire or explosion.
With its wide range of outputs, the BatMod offers
designers a simple, cost-effective solution to battery
charging for all major battery types.
11. Battery Charger (BatMod)