But assuming you have all your LEDs in parallel, each with a series current limiting resistor, and assuming each is pulling only 40 mA...question, is this a measured or calculated current draw? Because if your circuit is only a 320 mA load, the 7805 should be more than adequate.
Are there other circuits also involved that you didn't mention?
If not, then this is a troubleshooting issue, not a design issue. You need to verify the polarity of your LEDs. Also, what is the input voltage source? Batteries? Or a rectifier and transformer? Is the rectifier properly rated?
If this is a battery voltage source, is it new? Have you tried replacing it? I'm thinking likely your battery is going dead.
If none of this is the case, then verify the bias of all your diodes and make sure none of them are faulty. You might remove each diode one by one to see if one is shorted. Even a shorted resistor isn't an unreasonable failure. Do a physical check, touch each resistor and diode to see if one is getting too hot.
Use a multimeter. Take a measurement of all your voltage drops and find one that is behaving differently.
i have a 7805 feeding current to 8 blue leds each with 47ohm resistors. when i turn it on, my voltage drops to 1.8 after 10 seconds? any ideas????
oh and each led only is drawing 40mA
OK, you have a power supply.
First, I know it won't effect the normal operation of the circuit, but I think you should consider placing the resistors on the anode side of the LEDs. If you have a short circuit in your current configuration between and LED and resistor you have nothing to protect the diode from overcurrent. The resistors might be able to handle a short where the diodes won't.
Have you checked your filter capacitor? Take it out of the circuit and see if the problem goes away.
That doesn't seem right. (28V - 5V) * 0.32 = 7.36 Watts. It should burn your fingers without a heat sink! What is the input voltage to the 7805 when it's output voltage has dropped to 2.3V?no heatsink, since it doesnt use much power and it doesnt even heat up in the least.
after the filter cap (4700uF) i have 28V