FAQ

What are the basic differences between Fuzetec PPTC devices

1. Fuse: Resettability is the most significant difference between PPTC and traditional fuse, a PPTC device can provide overcurrent protection multiple times whereas the fuse must be replaced after a single fault occurred

2. CPTC: At the same rated current, PPTC has a faster trip time with smaller package and lower resistance in general.

3. Bi-metal breakers: The bi-metal disc inside this device will switch open when temperature is rise by fault condition. However, it can also automatically reset while the fault condition is still present, creating a hazard to user.
How quickly do PPTC devices reset?

1. Fuse: Resettability is the most significant difference between PPTC and traditional fuse, a PPTC device can provide overcurrent protection multiple times whereas the fuse must be replaced after a single fault occurred.
2. CPTC: At the same rated current, PPTC has a faster trip time with smaller package and lower resistance in general.
When will a PPTC device reset?

PPTC device generally start to reset when its temperature decrease to 90 ℃ , allow

80~90% rated current to pass through. Ambient temperature, current and voltage

across the PPTC device will affect the reset condition.
How fast is the trip time?

At low fault current, for example 2 x I_H , most devices will trip within 600 seconds; at higher fault currents, like 10 x I_H, the trip time will be much faster because of the power dissipation is not significant enough and the temperature of PPTC will rise rapidly. For more specific trip time, please refer to the PPTC typical time-to-trip curves.
How high will resistance rise when PPTC is in tripped state.

The resistance of the PPTC in tripped state depends on the following factors:

The voltage across the PPTC device

Power dispassion of the PPTC

R_{t =}V²/ P_d

In general, PPTC tripped resistance can rise above thousands of Ohm to hundreds K of Ohm.
What is the maximum body temperature of PPTC and the maximum ambient temperature PPTC can be used?

Maximum surface temperature of PPTC device can reach to 125 ℃ , but in most case, surface temperature won’t exceed 110 ℃ . PPTC has a lower surface temperature(125 ℃ ) in general, compared to CPTC(185 ℃ ) Typical operational range of PPTC is from -40 ℃ to 85 ℃ , some product families (FHT) can reach 125 ℃ .
What is the failure mode of PPTC device?

When PPTC device fail, it will keep in high resistance state and can’t perform PTC

behavior to return to low resistance. From circuit point of view, PPTC at tripped

state only allow minimal leakage current pass through the device and can be

consider as open circuit. With UL certification, Fuzetec PPTC device can be tripped

6,000 times and stay in tripped state for 1,000 hrs while exhibiting PTC behavior.
Voltage surge or inductive spikes

For sudden voltage surge or inductive spikes, if the duration is within 10

microseconds, normal time-to-trip won’t be fast enough to trip and the PPTC

should remain intact. If the duration of surge or spike is long enough to make PPTC

trip, it can potentially damage the PPTC device.
Use PPTC in parallel

Use PPTC device in parallel can provide some benefit like higher hold current with

lower resistance, however, the 2 PPTC must be identical and the placement must

be considered for better performance.
Use PPTC in series

Not recommended, since one PPTC device will always trip first and the other one

will remain untripped and provide no protection, it’s not very practical.
USE PPTC in AC application

AC-DC voltage conversion ratio might vary based on AC frequency, typical AC-DC

conversion equation is: AC = DC/0.636.
What does –R at the end of a SMD part number mean?

The –R at the end of a SMD part number indicate that that the SMD PPTC device

has half round hole structure at both side. This structure helps to improve

soldering process, reduce empty soldering and tombstone effect.
Resistance sorted(binned 0.5 ohm)

Some Fuzetec PPTC product can be supplied in resistance sorted variant.

“Binned 0.5” means in each bag, the resistance difference between every single

part is within 0.5 Ohm.

For example: If the product Spec is : R_min= 4 ohm, R_max= 8 ohm

The package will be sorted as:

Package 1, parts with 4.0, 4.3, 4.5 ohm.

Package 2, parts with 5.5, 5.7, 5.9 ohm.

.

.

Package 10, parts with 7.5, 7.7, 8.0 ohm
Why Low Rho PPTCs are Not suitable for Medium-Long lifecycle applications?

Due to the nature of Low Rho material, the rate of change of resistance is higher

than traditional carbon-base PPTC device after being used for a certain period of

time. Therefore Low Rho PPTC might not be suitable for mid-to-long life cycle

application, like automotive, medical and central office equipments. However, by

offering super low resistance and ensure low voltage drop, Low Rho PPTC device is

ideal for battery application and longer cable design.
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