Question about my power source and a malfunctioning 555 timer IC?

Question

I'm using a rectifier which uses a center tap transformer (which is rated at 6.3V, .45A), two 400PIV diodes forming a full tap rectifier, one inductor (a 35A toroid coil) and a 1000uF, 16V electrolytic capacitor, the latter two used to filter the current, all leading to a 7805 +5VDC voltage regulator Now my question is (and please focus on the question and not the overkill of my 12V power source), is there any reason why my 5VDC generator refuses to work with and digital logic, i.e. CMOS? What I mean by "refuses to work" is burns up the chips, but if I put a 1k ohm current-limiting resistor in front of the voltage-in of the IC (for example, pins 8 and 4 on a 555 timer) which would deliver 5mA (5V/1000ohm=.005A=5mA) the IC doesn't even function, and the voltage input at pin 8 leaves pin 3 the same or, if I've grounded pin 1, at about 1/10 the voltage. Any help would be greatly appreciated, and if anyone has any suggestions for a power source better suited for CMOS projects, I'm open.

Answer 1

You don't have 12 volts to begin with. Even if the transformer windings were 6.3 volts from main terminal to center tap, as you have it wired up, you only have 6 volts. ALL regulators require a 3 volt "head space" in order for them to operate properly. That 7805 should be getting at least 8 volts in order for it to operate. If the transformer is capable of 12 volts, you need either a single diode for a half wave rectifier, or a 4 diode bridge to get the desired 12 volts. If you are smoking chips, then your wiring is wrong. You might want to stick to batteries until you understand AC based power supplies a lot better than what you do at this point.

Answer 2

See edits at bottom.

Let's start with the xformer. You need 4 diodes for a full wave rectifier. Get them and rewire, see Wiki for full wave rectifier to be sure it is hooked up right. Edit: If the 6.3V is across the entire winding, you need to use a voltage doubler circuit. Google voltage doubler to find it.

Now, put the inductor and cap filter in place. Use a 1k resistor load. What is the voltage measured on DC and AC scales? Should be about 11.5 to 12V on the DC scale.

Now, look at the 7805 datasheet:

http://www.national.com/ds/LM/LM340.pdf

  - it requires 7+ volts input

  - 5mA min. load

First, verify it is hooked up right per the first diagram, not the current source. Move the 1k resistor to be a load for the 7805. Check output voltage of 7805, should be 5V. Also check on AC scale, should be the same. Now, you should be ready to do the 555.

From your description of pins 8 and 4, sounds like you have it hooked up wrong. Pin 1 is the ground, you cannot operate the chip without this connected. Pin 3 is the output. Output low is a standard condition, maybe the chip is operating properly. There are a number of circuits you can make with the 555. Check the datasheet, select the circuit you need, and hook it up right:  http://www.national.com/mpf/LM/LM555.htm...

Now, everything should work. Your supply should be OK. I prefer to use old PC power supplies I pull. You can also buy cheap surplus units, either fixed or adjustable:

Look at 1st three surplus places:

http://amasci.com/surplus/surpcats.html

*****Edit*******

2 diodes with a center tap xfr gives 1/2 the voltage of the 4 diode bridge, but OK, you are getting 12V out, and I don't want to argue about the coil rating. Good deal so far. So, you have 5V from the regulator, indicating probably connected correctly. Good job!

Now, the1A to a 555 is crazy. Either the 1A is wrong, the 555 is shorted, or the chip is incorrectly biased. How are pin 3 and the others connected? One strange possibility is that the voltage at the chip is too low, making weird things happen. Most likely is reversed power and ground on chip.

OK, lets track down the 1A. First, looking from the top of the chip ("live bug", or with the leads pointing down) with the pin 1 mark on the top left, or the notch in the top center, pin 1 is on the top left, and pin 8 on the top right. Are these the ones you are using for power and ground? If not, look at datasheet, fix, and start over. By the way, check voltage on chip by a). put DMM on DC voltage, b). black lead in black plug, c). red lead in normal red plug (not 10A one), d). put black lead on pin 1 and red lead on pin 8. If negative voltage, you have it hooked up backwards, dumping all your current through forward biased substrate!

You sound like you know how the pins are numbered, so let's move on. Measure the voltage across the 1k resistors. Voltage across the pin 4 resistor should be zero. If not, let's put in a way bigger resistor, like 50k or 100k. Or, you should be able to disconnect pin 4 with no problem if you want.

Voltage drop across pin 8 resistor should be less than 1/2 volt. If it is over 2 or 3, you are indeed drawing huge current through it, which has to be going somewhere. The chip will not work correctly with a large drop across the resistor because it leaves too little voltage to run the 555 chip.

Use E=IR on resistor and voltage to calculate current. If low current, double check your 1A measurement, which must be wrong.

If high current, disconnect wires 3, 5, 6, 7, and recheck voltage drop across power supply resistor. By the way, I often put small resistors in series this way (say 1Ohm) in the ground or other lines, because measuring the voltage drop across the resistor directly gives the current without breaking into the circuit. You need to keep the resistors small to minimize effect on the chip. See where the current is coming from and going to.

Once you have the 555 properly powered, you can assemble the circuit you need from the datasheet.