No Resistor from the 555 to the Base of the Transistor? How hard do you want to turn that poor Transistor on? If you disconnect pin 3 on the 555 and still have your 7805 (they DO need a heatsink) overheating, then you've damaged your 555.
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No Resistor from the 555 to the Base of the Transistor? How hard do you want to turn that poor Transistor on? If you disconnect pin 3 on the 555 and still have your 7805 (they DO need a heatsink) overheating, then you've damaged your 555.
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Thats another mistake, sorry. There is a 10K resistor between pin 3 on the 555 and the base of the transistor.
I use 7805s in every circuit i make that needs 5V and they never need a heatsink. Sometimes they do get slightly warm if a lot of things are running from them but still not enough to need a heatsink.
For testing i moved the 555 to a breadboard with a seprerate regulator and that regulator stayed cold. The one on the main board still got hot though which means its the IR emitters that are causing it to overheat. According to the datasheet they should be drawing 100mA each. Theres 2 of them but its about a 50% duty cycle so i would expect the average to be around 100mA. Lastnight my multimeter showed 102mA for the emitters and the 555 so i guess thats about right then as long as i put a heatsink on this regulator.
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Try it with the RS485 network disconnected. If the current drops, then use a 100 ohm, 1/4W resistor between the RS485 GND and this circuit's GND.
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You could still be drawing a lot of current due to mixing grounds. Try it with the network disconnected, including its GND.Originally Posted by The Master
Last edited by dhouston; - 13th September 2009 at 18:24.
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