Just a quick question: will a 7805 supplied by a 12v power brick, pushing around 200mA need a heatsink, or will it stay cool? How about with something like... 7.5v?
I power my PIC with a 7805, regulating from a 9V wall wart (which my multimeter says outputs 13V) and outputs around 600mA. Completely cool to the touch.
A 78xx regulator in a TO-220 package without a heatsink will have its chip at a temperature very close to causing shutdown if it dissipates about 1.5W.
The one from National Semi says its max dissipation when it has a perfect heatsink is only 19W.
Whilst I agree, 100mA is guaranteed and 200mA is more typical. I'm just being picky what I mean is don't bank on it being able to supply 200mA but don't also bank on it limiting the current to 100mA.
The little 78L05 will get too hot then it will shut down. After it cools then it will start working again then it will shut down again. The thermal stress will probably break it.
A limit of 100 mA is pretty realistic for typical applications.
The junction temperature, that is related to the power, does matter.
If the dropout voltage is around 7 V, the current should be kept below that value. The thermal resistance of the TO-92 is about 230°C/W.
I agree but I think you've missed my point, which was don't also bank on it limiting the current to 100mA to protect the transformer and rectifiers powering it; most units will limit at 200mA or even more.
i need to run an lcd with backlight and a microcontroller and a medium sized seven segment display with a common 5v regulator. Total current consumption could be possibly around 600 mA . what regulator would be the best choice in terms of cost and performance...??
but whenever i use switch the backlight of lcd(16x2) ON the circuit becomes very dull and the alarm seems to cry weakly..
and in another circuit where i use a 128 x 64 lcd the circuit refuses to work at all when i swithc the backlight on...
but whenever i use switch the backlight of lcd(16x2) ON the circuit becomes very dull and the alarm seems to cry weakly..
and in another circuit where i use a 128 x 64 lcd the circuit refuses to work at all when i swithc the backlight on...