# calculating if heat from regulator can start a fire or melt ffc

I have a flat flex cable (to a display module) close to a regulator (maybe the ffc are even touching the regulator) in a product I am making. Worried about if the regulator's heat will destroy the cable. the regulator's output is max 13V*0.1amp=> 1.3 watt (more likely half of that) and I understand the regulator is about 60% effective. regulator used (SOIC package) So 40% of 1.3 watt gives 0.52 watt (worst case) that goes to heat. Thermal Resistance RJA 160 °C/W

so 160°C/W * 0.52watt = 83 degrees celsius in temp rise? So the regulator will best case be 25 (ambient) +83 =108 degrees??? I guess not all heat is produced in the regulator. maybe some in diode or inductor. but still.... I'm I calculating this correctly? missing anything?

I have no idea how much heat a flat flex cable can handle. Do I need to prototype and test this or is there some way to know if this will be a problem?

Found this question to help with my reasoning above. But not sure if it applies here.

• the regulator is about 60% effective Explain that because in my view, this greatly depends on how you implement the complete DCDC converter and the input voltage. That MC34063 is also quite old. Also 60 % efficiency is quite poor. You would be much better off using a more modern DCDC converter (preferably on a module) with temperature protection and then too much heat should never be an issue. Nov 15, 2021 at 21:58
• I have no idea how much heat a flat flex cable can handle. Then how can anyone answer this question? Look in the datasheet of the flex cable or better: make sure that the flex cable cannot touch the regulator, use some Kapton tape. Nov 15, 2021 at 22:00
• well it´s dirt cheap and do the job. Generic design and same circuit sold by many companies. easy to get hold off. I don´t see how temperature protection would help. it´s not the regulator overheating I am worried about. It is that the heat melts something outside the circuit. Nov 15, 2021 at 22:02
• well maybe someone else maybe know how much a ffc usually can handle. I have contaced the company. I havenot gotten an answer yet. but I will. But that is not the main part of the question. the temp calculation is. Nov 15, 2021 at 22:06
• Some of that heat will be conducted by the SOIC pins. If you could use the DFN8 package with exposed pad, even better: RJA=80°C/W (twice as good as SOIC.) Nov 15, 2021 at 22:39