Capacitor values with LM7806 regulator

The reason for the small value capacitors on the in and out legs is to shunt any AC noise to ground. The bigger caps(330uf/100uf) are used to keep the DC input and output voltages from varying with changes in the amount of current being drawn. If your 12VDC source is capable of 1/2 A or higher, then you really don't need the large caps. I'd use the small ones, however.  HTH----

The bigger cap is presumably to filter the ripple of the rectified power supplying the reg. Bigger is better here. 330 or 470 mic are good values to use, and they are readily available and cheap.

If your supply is already smooth clean DC, you don't need it.

The .1 mic on the output is to improve transient response in the case of a varying output load. Good to include this.

If you can tell me your load and your supply parameters I can run a filter cap size, and check your temp rise and whether you need a heat sink or not. I have a spreadsheet for this.

Rod

Thanks, guys, for the info.  I am doing this for my son.  It is a clean 12v supply that needs to drop to 6v to run a small relay, so we're not talking about a lot of power being drawn.  It wouldn't be that difficult to mount the tab to some metal object just to be safe.  I don't have exact current draw on the relay but I can find out tonight.

Thanks again guys - an easy to understand reply from both of you.

Mike

If you are just going to operate one relay, and don't intend to add anything else, this is a case where a resistor can be used in series as a voltage divider. You need a resistor that has the same resistance value as the relay coil.

On the other hand, 12 volt relays are very inexpensive. Unless you are locked into this particular relay for a reason, I would just use a 12 v relay.

If you just need it for a relay, a resistor is probably the easiest way.  Let's say the relay draws 50ma, and you want to drop the 12V to 6V.  A 100 ohm 1/2W resistor will do the trick here.

I see Arthur had the same idea.

Arthur & John - That would be easy to do, which would certainly simplify things.  I will be able to look at the relay tonight and see if it has any ratings and see what his application is.  We have to use this relay & can't substitute it.

Thanks so much for your input.  I appreciate your expertise.

Mike 

One more question - in my original configuration using the caps and the regulator, should the caps be polarized?  Thanks.

The large value caps(anything greater than 1uf) are usually polarized, with the negative side clearly marked on the case. the small value ones are not polarized.

As for the rating of the relay, the easy way to determine this if it's not documented is to simply apply 6 volts and measure the current using a common multi-meter.  Once you know the current, it's easy to compute the exact value of resistor you need.

I can't imagine why you'd want to bother with a regulator for this task.

I am with grj on this; a resistor is a cheap and dirty way to do this.

Regardless I can do the load calc for you once we know the coil resistance, or current drawn at 6 VDC.

If the source is clean filtered 12 VDC you don't need the big value cap; but I would still use the smaller one since the relay is intermittent operation.

Rod