Can the LM7805 voltage regulator be used alone?--I'm trying to convert a 12v batttery to 9v for a sega nomad

Question

Can I just connect the output of the 12v battery to the LM7805, then run wires directly to the Sega system?

Answer 1

To start with, the LM7805 is designed to provide a 5 volt regulated output. While I have seen designs that trick the 7805 into producing other voltages, they all required additional components to make it work. To get a 9 volt output without additional components you will want to acquire a close cousin of the LM7805, the LM7809, which is a 3 terminal, fixed voltage regulator, exactly like the 7805 except it provides 9 volts DC instead of 5. There is a whole series of these regulators with various outputs. Note that the last 2 digits of the part number give the output voltage.

Answer 2

Wiki claims 850mA, so this is within the LM78xx 1 to 1.5A rating.

You want the LM7809, the 9V version. You also should use 2 caps, as shown on the datasheet below. In most applications, C1 is probably more needed. In your case, if you run just from a battery, c2 is more needed. You might be able to get away with no cap, but I would use at least c2. And, if in the car when the engine is running, it will dissipate 4W, so you need a good heat sink. If just a battery, maybe half that, but still probably needs a little heat sink.

Good luck.