I wanted to verify whether B59810C0160A070 is the right component for my application. The circuit runs at 5V, and the current must not exceed 2.5A. I want the thermistor to activate at 2.5A to prevent overcurrent. The load is not continuous.
If I’m reading this datasheet right, this part is specified to trigger up to 10A at 160Vrms in No Greater Than 10 seconds, and ambient temperature will influence that time. They’re inexact slow blow devices, a lick your finger to detect the wind direction kinda thing.
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Could you point me to PTC thermistor where the trigger point is 2.5A at 5Vrms?
Does the max operating voltage play a factor in choosing a PTC thermistor that will trigger at 2.5A?
Hi @wil, based on what you’re describing it sounds like a PTC Fuse, or a Varistor might be more what you’re looking for.
The section for PTC Thermistors that B59810C0160A070 lives in is more for temperature detection, sensing and control, rather than circuit protection. For these devices we tend not to even have max current or operating voltage as specifications to sort or search by. Maybe another tech can chime in with more context but as I understand it they move too slow to be useful for suppressing a surge or protecting from overcurrent, and aren’t designed with those applications in mind.
The concern here is that PTC current protection devices as a class are among the sloppiest and slowest-responding over-current protection devices in use.
They’re entirely temperature-based, so the current that will cause a device to trip will vary significantly (and inversely) with temperature.
Per the datasheet excerpted below, the device’s notional switching current is 1.6A: this is the current flow expected to provoke a persistent change in device resistance within 10 seconds at some (unspecified) initial device temperature, presumably 25°C. Because of uncertainties in device behavior however, planning to operate significantly below that trip point during normal conditions is necessary; here a normal operating current of 800mA at most is suggested.
The device’s rated operating voltage is initially of no concern for choosing a device based on trip point; the device’s function is entirely temperature-dependent. Where it does become a question however is when the device “trips” and enters a high-temperature, high-resistance state. The device is kept in that state by the I2R power dissipation of the source voltage across the (elevated) device resistance, and as voltage increases, so does the fault-state power dissipation.
The post on thermistors here may have/point to additional useful information.
Hi guys, unfortunately I can’t use a fuse in this application.
Would I be better suited using a TVS diode?
A TVS is for voltage surge suppression, it will clamp the voltage but not limit the current.
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