![]() Circuit board is not very good at dissipating heat, if you put DPAK regulator on maybe 3-4 cm of copper, maybe the regulator will dissipate 1w and stay below around 90 degrees C So you need a heatsink and you can easily figure out how big of a heatsink you'll need. If you have 7.5v in, 5.0v out then at 0.5A your regulator will dissipate (7.5v-5.0v ) x 0.5A = 1.25w Now if you look at the table above, you can see that a TO-220 regulator will heat 50 degrees C over ambient temperature with every watt of heat produced, and your regulator will produce 1.25 watts, so it's only natural that your regulator will reach ambient temperature + 50 degrees C without any heatsink. Ĭode: Top Operating junction temperature range for L78xxC, L78xxAC 0 to 125 ☌ for L78xxAB -40 to 125☌ Table 2: Thermal data Symbol Parameter D²PAK DPAK TO-220 TO-220FP Unit R?JC Thermal resistance junction-case 3 8 5 5 ☌/W R?JA Thermal resistance junction-ambient 62.5 100 50 60 ☌/W So your regulator will dissipate the excess energy as heat. Should i go for another linear regulator and which one (needs to be low cost) or should i change design altogether and go for a step-down switching regulator? I also get a significant voltage drop at "higher" currents over 250mA Is it possible my LM7805CV is a fake? Unfortunately all i got in hand are a few 7805CV from ST which i dont know where i got them from, they might be laying around for several years. note that my current ambient temp is around 24C so operating in hotter environments or insides cases etc would also make things harder. I could possibly test every charging current selection from 60ma-1A with a variety of input voltages and provide a safe settings chart but even for this, i would need to know what is considered a "safe" temperature for the LM7805 to operate. The idea behind this module is to be able to use a variety of input sources and offer both battery output and boosted output on demand so it can serve as a real general purpose lithium battery charger/power supply for applications etc. What is a "safe" temperature for the LM7805 (I am even using the CV variant which should be able to handle 1,5A max current, more than enough for this application) I have soldered the regulator to the mounting hole on the PCBand its also grounded so it should work as a heat sink but i dont see any transfer of temperature to the PCB except directly around the hole. at VIN 7.5Volt and with charging current set i get readings on the regulator surface as high as 70-75 degrees C and with VIN of 12V it raises up to 95-100 degrees C. I am testing my tp4056flexadv module which works quite well when powered via USB (as expected, its a typical TP4056+protection configuration) but i am concerned about the LM7805 temperature. ![]()
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December 2022
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