Control Protector. SFD-128B Datasheet

SFD-128B Protector. Datasheet pdf. Equivalent

SFD-128B Datasheet
Recommendation SFD-128B Datasheet
Part SFD-128B
Description Self Control Protector
Feature SFD-128B; SC Protector Self Control Protector Est. 1997/12/10 Rev.20 2002/11/27 Innovative way of safety con.
Manufacture Dexerials
Download SFD-128B Datasheet

Dexerials SFD-128B
SC Protector
Self Control Protector
Est. 1997/12/10
Rev.20 2002/11/27
Innovative way of safety control for Li-ion rechargeable battery
At any moment, SC Protector system monitors the voltage of Li-ion rechargeable battery and its heater
fuses the fuse at the same instant when the system detects the overcharge. Usual protection element
takes long time to work because it works due to temperature rise of battery cells.
The difference of SC Protector provides you high degree of freedom in the design of protection circuit.
1. Application
Typical application of protection for a Lithium ion rechargeable battery from overcharging is shown
in the figure below.
When the voltage between a and b exceeds the pre-set limit value, the output of the voltage detector
IC becomes high and the FET is switched on. As a result, current flow through the heater of the
protector, the fuses melt, and the battery stops to be charged any longer.
Since the two fuses cut-off the voltage supplies from the charger and the battery, the SC Protector
stops to be heated immediately and thus, the safety control protection is provided against both excess
voltage and excessive heating.
Sony Chemicals Corporation
SIP Division
1-11-2, Osaki, Shinagawa-ku, Tokyo, 141-0032 Japan
TEL+81-3-5435-3943 FAX+81-3-5435-3072

Dexerials SFD-128B
2. Characteristics of SC Protector
2.1. Necessity
2.1.1. Reliability of the protection circuit
All Li-ion rechargeable battery packs are
equipped with at least one protection
circuit (ex.IC+FET).
In this case, when an IC or FET breaks,
overcharge can’t be controlled any more,
and the temperature rise of the battery
cell can invite very dangerous
thermo-runaway leading to smoking or
The trouble of the IC and FET actually
Therefore, double protection is needed to
ensure the safety of Li-ion battery packs.
Basic circuit with troubles
Overcharge = Danger
IC for protection
FET FET Trouble?
2.1.2. The weak points of conventional double protection elements.
Protection devices such as temperature fuses and bimetals work by conducting the temperature
rise in the battery to the inside of it via package or lead wire. Hence, they have a disadvantage
that the response speed is slow, and the response speed fluctuates depending on the installation
location of the device.
These elements obstruct a cost reduction since it is incompatible with the reflow soldering due
to their structures, and must depend on manual soldering.
By using SC Protector, the battery cells won’t become dangerous condition even if IC or FET breaks.
2.2. Characteristics
1) One device can protect against
both overcharging and overcurrent.
Double protection circuit using SC Protector
SCP protects from overcharge
and over current = Safe
2) Protection against overcharging is
directly performed by the battery cell
voltage, ensuring high accuracy and Battery
quick response, and the response speed cell
does not fluctuate depending on the
location and condition of installation.
SC Protector
IC for protection
3) At the same time of protection
against overcharging, since it is
constructed to send current to the
heater via the fuse element, the fuse
element forcibly fused by the heating of the heater and, upon the cutoff of charging circuit,
the current to the heater automatically stops, and hence, SC Protector itself never
4) Abundant product lineup allows the selection of protector with optimal operating
voltage and operating current depending on the cell structure of battery pack, ensuring
high degree of freedom in the design of protection circuit.
5) It is compatible with automatic mounting using general-purpose chip mounter, and at
the same time, compatible with the reflow soldering, contributing to the reduction of parts
mounting cost.
SC Protector has the strong points as shown above and it meets the safety requirement without
spoiling the strong point of miniature of the Li-ion battery.

Dexerials SFD-128B
3. Relations between the fusion state and the operation mode
“The operation mode” can be estimated by the fusion state of the fuse element.
3.1. Heater operation
In the case of overvoltage, “Both two sides of the middle electrode” are fused by the heater
operation. Because the fuses are heated until the charge to the heater is stopped.
Only one side may be cut when the protection circuit is designed so that charging to the
heater stops by cutting of one side of the middle electrode.
For the heater operation, it is characterized as “Fuses like flow into the middle electrode.”
<Features of the heater operation>
!"Fuses like flow into the middle electrode
!"Both two side (or one side) is fused
3.2. Current operation
In the case of overcurrent operation, basically, “only one position of the fuse is cut” because
it is the same operation mode as the conventional electric current fuse. When the current
exceeds 50A, two positions are cut occasionally.
For the current operation, it is characterized as “The cutting position isn't fixed”, “It cuts
like bursting”.
<Features of the current operation>
!"Cutting position isn’t fixed
!"It cuts like bursting
!"One position is cut basically (Over 50A,
two positions are cut occasionally)

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