Hi all,
I am building a simple bench power supply with a 12VDC and 5VDC output.
A 24VDC wall wart is fed into a 7812 regulator for 12VDC output. The output of the 7812 is also fed into the input of a 7805 regulator to provide a fixed 5VDC output. The 5VDC output also supplies power to 2 common ground LED panel meters; each draws 60mA.
Problem I am having is this. When nothing is hooked up to the outputs, I see 12V and 5V as expected. When I provide 5V to one panel meter, both regulators heat up quite a bit. But I have confirmed the actual current drawn is 60mA. When I connect both panel meters I have verified a current draw of about 120mA. However both regulators quickly become too hot to touch and will shut down after a few minutes. The inputs to the panel meters have not been connected.
Any ideas? Have I committed some faux pas by chaining two regulators? Any debugging ideas? I have broken the circuit in a few places to verify current draw and checked the voltages. Everything seems normal except the heat generated.
Thanks,
-- Dan
I am building a simple bench power supply with a 12VDC and 5VDC output.
A 24VDC wall wart is fed into a 7812 regulator for 12VDC output. The output of the 7812 is also fed into the input of a 7805 regulator to provide a fixed 5VDC output. The 5VDC output also supplies power to 2 common ground LED panel meters; each draws 60mA.
Problem I am having is this. When nothing is hooked up to the outputs, I see 12V and 5V as expected. When I provide 5V to one panel meter, both regulators heat up quite a bit. But I have confirmed the actual current drawn is 60mA. When I connect both panel meters I have verified a current draw of about 120mA. However both regulators quickly become too hot to touch and will shut down after a few minutes. The inputs to the panel meters have not been connected.
Any ideas? Have I committed some faux pas by chaining two regulators? Any debugging ideas? I have broken the circuit in a few places to verify current draw and checked the voltages. Everything seems normal except the heat generated.
Thanks,
-- Dan