PTC Over-current
Protector
Features
  • Fast Switching
  • No Electrical
    Noise
  • Virtually
    Unlimited Life
  • Self  Resetting
  • No Contacts
  • Automatic
    Operation
  • Efficient
Options:
  • Encapsulation
  • Special Lead
    Configuration
  • Non-Standard
    Values
  

PTC OVER-CURRENT PROTECTORS

The PTC over-current protector is connected in series with the load which is to be protected. During normal operating conditions, the PTC remains in its low resistance state resulting in negligible attenuation to current flow. When a short circuit or over current condition occurs, the PTC will switch into its high resistance state thereby limiting the current flow in the circuit to a point well below the normal operating level. When the fault condition is removed, the PTC will return to its low resistance state allowing the current flow to recover to its normal level. RTI Electronics produces over-current protectors for a wide range of load protection applications.

Typical Applications

Some of the most popular applications of over-current protectors include:

  • Telephone Line Fault Protection
  • Transformer Protection
  • FHP Protection
  • Transistor Protection
  • Speaker Protection
  • Maximum Continuous Current (Icc) - One of the first considerations is the (Icc), the maximum amount of current. The PTC must be capable of conducting without switching into its high resistance state. See the over-current protectors specification sheet.
  • Minimum Switching Current (Is) - The second consideration is to determine the (Is), the minimum amount of current required to switch the PTC into its high resistance state. See the over-current protectors specifications.
  • Maximum Operating Voltage (Vmax) - Next calculate or estimate the voltage that will be across the tentatively selected thermistor when the device is switched into its high resistance mode (the thermistor's resistance in its high resistance mode will typically be greater by two to three orders of magnitude than its R@25°C value). If the voltage estimated is greater than the Vmax rating of the selected part then another selection with a higher Vmax rating must be made.
 
During normal operating conditions the PTC remains in its low resistance state resulting in negligible attenuation to current flow. When a fault such as short circuit or over-current condition occurs, the PTC will switch into its high resistance state which limits the current in the circuit to a point well below the normal operating level, therefore, protecting the load circuit components. When the fault condition is removed. The PTC will return to its low resistance state allowing the current flow to recover to its normal level.
 
PTC Over-Current Protector Specifications
  Base resistance             Reference
Dimensions
Part
Number		 (ohm) Tolerance (±) Maximum
Operating
Voltage
Vmax		 Maximum
Continuous
Current
(Amps)		 Minimum
Switching
Current
(Amps)		 Switch
Temp.
(Ref.)
(șC)		 Heat Capacity (Watt-Sec./șC) Dissipation Constant (mW/șC) D
Max.
Dia.
(In.)		 Lead
Dia.
(In.)		 S
Ref.
(In.)
SP5504D-1R0-120 1 20% 15 0.600 1.300 120 0.48 13 0.60 0.032 0.3
SP5004D-2R0-120 2 20% 25 0.440 0.900 120 0.39 12 0.55 0.032 0.3
SP4004D-3R3-120 3.3 30% 25 0.300 0.690 120 0.25 10 0.45 0.025 0.3
SP6709D-4R7-110 4.7 20% 132 0.290 0.650 110 1.59 16 0.70 0.032 0.0
SP4004D-5R0-110 5 20% 25 0.220 0.500 110 0.25 10 0.45 0.025 0.3
SP3505D-7R5-120 7.5 30% 50 0.180 0.400 120 0.24 8 0.40 0.020 0.2
SP5510D-100-110 10 30% 132 0.170 0.430 110 1.19 13 0.60 0.025 0.3
SP3505D-100-120 10 30% 50 0.150 0.350 120 0.24 8 0.40 0.020 0.2
SP2505D-200-120 20 30% 50 0.095 0.215 120 0.12 6 0.30 0.020 0.2
SP3510D-300-110 30 30% 132 0.075 0.190 110 0.48 8 0.40 0.020 0.2
SP3010D-500-110 50 30% 132 0.055 0.140 110 0.35 7 0.35 0.020 0.2
SP3010D-101-110 100 30% 132 0.040 0.100 110 0.35 7 0.35 0.020 0.2
SP2008D-251-120 250 30% 150 0.028 0.070 120 0.13 7 0.25 0.020 0.2
SP2010D-501-120 500 30% 250 0.020 0.050 120 0.16 7 0.25 0.020 0.2
SP2010D-102-110 1000 30% 300 0.012 0.032 110 0.16 7 0.25 0.020 0.2
SP2012D-152-110 1500 30% 350 0.010 0.026 110 0.19 7 0.25 0.020 0.2

*Maximum Continuous Current (Icc) - The maximum amount of current, expressed in AMPS, the PTC must be capable of conducting without switching into its high resistance state.

**Minimum Switching Current (Is) - The minimum amount of current, expressed in AMPS, required to switch the PTC into its high resistance state.

Note - The values for minimum switching current and maximum continuous current are for reference only. Mounting method and environmental conditions can affect these parameters. Please contact RTI Electronics Inc. for specific applications engineering assistance.

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RTI Electronics, Inc. 1800 E. Via Burton St. Anaheim, CA 92806-1213
Telephone: (714) 765-8200 • Fax: (714) 765-8201