Can't be practically heatsinked?
https://www.google.com/search?sxsrf=ALiCzsaeUVqwnOqCyEtOeS1KSg_Dlg4tZw:1669942294955&source=univ&tbm=isch&q=TO92+heatsink&client=firefox-b-1-d&fir=JpPInaLnYUMsqM%252CYAxXf7jhMUy_3M%252C_%253BC3trvQ1tJyVLjM%252CWw3saJtaRzBqDM%252C_%253BSXjAiYX8l7aauM%252C06grxW6JmGYPgM%252C_%253BPYeeGYp9Y2JLgM%252Cl14-IIyoCTMt5M%252C_%253BEuZoDXmClyyVRM%252Cwm57XPgqLjJuKM%252C_%253BKpe1BOJI3I2gVM%252CWMUKCzQTYB4HwM%252C_%253BLZBzFlwfmyqYsM%252CGsqtVv_-9dm8uM%252C_%253BmIjlFGgRyL_cMM%252CYe_LNPfPbwczEM%252C_%253BTi3qEgsPl505rM%252CdjC84Xld49ZRWM%252C_%253BhodvInlMlVMEuM%252CmybWFHMeaWJWTM%252C_&usg=AI4_-kSWIyPRxTvOKcGjvhTGfblIHyayyg&sa=X&ved=2ahUKEwjZyaTq29n7AhW0lGoFHdFVCYAQjJkEegQIGRAC&biw=1191&bih=616&dpr=1.4I don't know about the "Ali Express", no name ICs, but TI seems to have no problems with 100 mA if the Input Voltage is within 4 Volts of the Output. The TI datasheet clearly shows that THEIR TO-92 (Z) package can handle at least 400 mW in "free air" with short lead lengths (0.125"). So a TI LM78L05, with no heatsink, and an input Voltage of 9 Volts and a 100 mA load would dissipate 4 V x 0.1 A = 0.4 W. And that would be withing the spec. for heat in the package. I have designed circuits with those numbers and never had any problems, in spite of no additional (beyond the normal copper foil leads) heat sinks.
http://users.ece.utexas.edu/~valvano/Datasheets/LM78L05.pdfI have tested 78xx regulators with short circuits and no heat sinks for 12+ hours and they still worked like new. (note below) I would not hesitate to test a TI TO-92 LM78Lxx regulator with a 100 mA load, no heat sink, input V = output V + 4, and only short PC leads for as long as you wish. Or one by any other major manufacturer.
Now with 12 V as the Input, all bets are off. That's a 7 V drop and 7 V x 0.1 A = 700 mW. It WILL shut down. But all you need is a series dropping resistor if you must have 100 mA at 5 V from a 12 V supply.
If you are going to rip-off a component, you should meet ALL the original specs. That's my opinion and I am sticking to it. I do not buy from Ali Express and this only reinforces that practice.
For a linear supply some good rules of thumb are:
1. Transformer RMS, AC secondary Voltage = final regulated DC Voltage. Example: Regulated 12 VDC supply requires a 12V transformer.
2. Use a full wave rectifier.
3. Filter cap = I / (2 x F x Vr) where I = max current, F = line frequency, and Vr = desired P-P ripple Voltage.
4. Voltage regulator IC with recommended external components.
That provides for things like the diode drops and the needed head-room in most linear regulators. And it works with a 6.5 Volt transformer for a 5 V regulator. If you need 12 VDC and 5 VDC, get a center tapped, 12 V transformer and use the center tap for the 5 V supply.
Note: Many years ago when I was designing my first power supply with a 78xx regulator I just could not believe what I read on the data sheet about short circuit protection. So, after several quick tests for an instant and for seconds and then minutes, I shorted it and went home. The next day when I arrived at work I truly expected smoke, but when I removed the short it sprang back to life like nothing happened. And it was only a bit warm, definitely not hot. You gotta love a good design!
Yeah, TO-92 can't be practically heatsinked.
You need to calculate the actual maximum current. They can't give you one number because it varies depending on your use case: namely input voltage and ambient temperature.
Example: Let Vin=12V, Vout=5V, and Ta = 40 degC
From the LM78L datasheet:
* TO-92 RthJ-A (beware, datasheet has typo here, it says Tja they mean RthJ-A) = 158.7 degC/W.
* Recommended operating temperature max 125degC
* Absolute maximum junction temperature 125degC
RthJ-A means that when the device dissipates one Watt of power, temperature difference between the semiconductor junction (J) and ambient (A) will be 158.7 degC. So if our ambient is at 40 degC, the junction will be at 198.7degC, well over the absolute maximum. So clearly you can't dissipate 1W.
How much we can dissipate? Given Tj_max = 125degC and Ta = 40 degC, maximum difference between junction and ambient is Tja = 85 degC.
Let's plug this into RthJ-A and solve for the watts: 85degC / (158.7degC/W) = 0.53W.
The linear regulator dissipates (Vin - Vout) * I. With Vin=12V and Vout=5V: P = 7V * I. Solve for I = 0.53W / 7V = 75.7mA.
And of course, if they say Tj=125degC is "absolute maximum", you don't really want to run it that hot. (125 degC is surprisingly low for an absolute maximum, though, so no need to add massive margin). But I generally calculate for Tj_max = 110 degC or something like that, assuming I'm sure I have every detail in calculation covered. If I'm unsure about something, then of course add more margin.