# How much power can a 7805 voltage regulator dissipate without a heatsink?

I am using a LM7805 linear voltage regulator.

Vin is 12 V Vout is 5 V (regulated)

My load is currently 100 mA. Without a heatsink, it's pretty hot.

Could i use a large heatsink to regulate 5 A?

Or what is the maximum output current with a heatsink for a 7805 linear voltage regulator?

• hmm, what does it saturate at? Commented May 28, 2020 at 5:27
• 1.5A (w/ heatsink) is a typical rule of thumb, but it depends on power not voltage. Power is (vin-vout)*I. Thus the max current depends on the heatsink. Within typical limitations of non-burning operating temp and non-huge heatsinks, 10W for an enclosed box and 20W for something that gets ventilation. With a fan and large heatsink, you might safely get 40W from a TO-220, but you're running up against case resistance and junction temp limits at that point. Commented May 28, 2020 at 20:49
• you could use the 7805 to feed a larger series pass transistor for a low cost "current boosted" 5v supply. You connect GND via a diode (instead of wire/solder), vout to the tranny's base, and vin to the collector. ~5v will then flow from the emitter. Commented May 28, 2020 at 20:52

No. Even if the output transistor did not saturate and even if you had a PERFECT, heatsink of infinite size and infinitesmal thermal conductivity, you could only manage 2.85A due to the junction-to-case thermal resistance being 5K/W at room temperature. So in reality you wouldn't even get 2.85A is unobtainable.

Datasheet lists peak current as 2.2A which is just that: a peak current, not continuous. Since there is no input voltage given, that's also probably right at dropout (i.e. minimum heating) and 12V to 5V is well beyond that so you would get significantly less than even 2.2A

• i see, with the next i am going to check the peak current! Commented May 28, 2020 at 5:28
• @kennethmods You won't get peak current unless you are near dropout and even then not continuously. Commented May 28, 2020 at 5:29
• @DKNguyen You left a door wide open. What could he get if he lowered the room temperature enough? (Hint: Limit is probably 0 K, though I would definitely be interested in any added thoughts considering still lower temps.) ;)
– jonk
Commented May 28, 2020 at 6:27
• @jonk Do consumer semiconductors even work below something like -50C? Commented May 28, 2020 at 13:11
• @DKNguyen I think nature still functions, somehow. But yes, they do. I've had some working below that temp, myself. Look up LNT CMOS.
– jonk
Commented May 28, 2020 at 13:22