PolySwitch PPTC Device Principals of Operation

PolySwitch PPTC Device
Principals of Operation
What they are, How they work, Where to use them
Using PPTCs to meet circuit protection requirements
Presented by
Jim Toth
Raychem Circuit Protection
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www.circuitprotection.com
What a PolySwitch™ Resettable PPTC Device is
Raychem Circuit Protection’s PolySwitch™ Polymeric
Positive Temperature Coefficient (PPTC) devices are
used to help protect against harmful overcurrent
surges and overtemperature faults.
Like traditional fuses, these devices limit the flow of
dangerously high current during fault conditions.
The PolySwitch device, however, resets after the fault
is cleared and power to the circuit is removed,
thereby reducing warranty, service and repair costs.
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How a PolySwitch device works
UNDER A FAULT CONDITION
UNDER NORMAL OPERATION
heats up
cools down
•
At the operating current
•
Many conductive paths
•
Very low resistance
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•
Excessive current causes
device to heat
•
Fewer conductive paths
•
High resistance
•
Cools down and resets
when fault removed
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Why is a PPTC useful?
Employed as series elements in circuit
Under normal operating conditions, the PPTC remains low in
resistance
When a fault occurs, the PPTC heats up and increases in
resistance thereby protecting the equipment from fault
PPTC resets when power is removed, and fault is cleared,
returning to low resistance state
.
I
Log Rs
Switched
I=V/Rs
Resistance of the
PolySwitch device
increases with
temperature
Normal I=V/RL
Rs
V
RL
RL
The PolySwitch device is in
series with the load
Temperature
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PolySwitch PPTC Device Mechanism
10
10
8
0.70
Resistance
6
0.65
4
10
10
2
0.60
0
Thickness
10
M.Heaney 11.92
-2
10
0.55
0
50
100
150
200
Temperature ( C)
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PolySwitch Resettable PPTC Device Functionality
A PPTC device acts like a fuse, however
it is a non-linear thermistor that limits current, so a small trickle
current will continue to flow through the circuit
Under most conditions the PPTC will not reset until power is
removed from the circuit
1Overtemperature
and overcurrent protection.
fuses are not designed for overcurrent protection, and generally require large currents to trip.
3Periodically attempts to reset until fault and/or power is removed, or resets to low resistance state when bimetal cools.
4Automatically resets to low-resistance state once the fault is cleared and power is removed.
2Thermal
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Resistance Relaxation for RXE075
Resistance Relaxation of RXE075
100000
10000
20 °C
Rf/Ri
1000
60 °C
100
10
1
0.1
1
10
100
1000
10000
Relaxation Time (Seconds)
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Effect of Extended Rapid Cycling
Cycle Life at 16V/100A - 5,000 cycles
RGE300
0.50
0.45
Resistance ( )
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Cycle Count
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Benefits & Features of PolySwitch™ Resettable PPTC Devices
Benefits
Reduced warranty and
service costs
Increased product reliability
Superior shock and vibration
withstand
Wide variety of applications
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Features
Remotely resettable
Testable
Solid-state
Wide variety of stock and
custom form factors
Low resistance devices available
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Typical Applications
Computers and peripherals,
USB ports, Firewire ports, disk drives
Rechargeable battery packs
Cell phones, MP3 players, DSC’s
Automotive electronics
Window and door lock motors, entertainment and GPS
systems
Telecommunications equipment
Faxes, modems, routers, central office switching
Electrical equipment
Security systems, solenoids, small and medium motors
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Sample Application: Automotive Electronics Applications
Since 1985, available as surface-mount and
radial-leaded devices to help protect:
Electronic modules, and junction boxes
Power and signal distribution systems
Automotive actuators for power windows,
mirrors, seat adjusters and door locks
Protective devices that can be located
strategically throughout the vehicle can help
reduce wire harness size and weight
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Sample Applications: DC Input Port Protection
Standard
DC Barrel Jack
•PDAs
Cell Phones
•Digital Cameras
•Portable DVD Players
•MP3 Players
Custom DC
Connector
•Portable Electronics
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DC Input Port Protection: Misconnections
The power supply can not be
guaranteed
DC Barrel Jack with
Reversible Polarity
+/- , -/+
Variable Voltage
Custom-to-Standard
Adaptor
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Custom Connectors are not
immune!
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Sample Application: POS
PolySwitch SMD device
Secondary side protection
Serial Port
TVB270SA &
TS250-130
Modem Line
Protection
PolySwitch
Strap device
Pack protection
PolySwitch LVR device
Primary side protection
Power Supply
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ROV
Varistor for Power Supply
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Sample Application: Industrial
Power Management
AC Mains
OC Protection
PolySwitch LVR device
Input Power
OV Protection
ROV
Comms I/O
OC Protection
PolySwitch
RXE, miniSMD
devices
Interface Protection
Analog I/O
OC Protection
PolySwitch
RXE/RTE/SMD
devices
Power Driver Protection
TRIAC, MOSFET, SCR
OC Protection
PolySwitch
LVR/RXE/RUE devices
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Sample Application: Synergies in Mobile Phones
PolySwitch Strap device
Battery Pack
Overcurrent
& Overtemperature
Protection
PolySwitch LVR device
Charger Overcurrent
Protection
PolySwitch
SMD Devices
Chip fuses
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Power Port OC
Protection
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Sample Application: Washing Machine Solenoid
Problem: Washing machine valve failure rate: 0.7%~3%
- Resulted in valve or controller board damage
Controlled by MCU
K
200
G
A2
~220V
PolySwitch
A1
TRIAC
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Visit us at www.circuitprotection.com and check out our complete
Circuit Protection solutions
PESD devices
Fuses
GDTs and ROVs
Portable
electronics
PolySwitch
Device family
Wide
Variety
of form
factors
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Telecom
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Q&A Session Begins Now
Resources & Links:
http://www.ttiinc.com/object/seminar_cp_resources.html