AC and DC how to?

[Scott]

I would like to allow my circuit to take both AC or DC power. Does anyone have an example schematic on how to do this? Links? I am used to using a full bridge or just a regulator but never both.

Thanks in advance,
Scott

[NavMicroSystems]

If you have your circuit designed for AC (bridge rectifier + caps + regulator)
You can supply it with DC,
and you do not even have to care about the polarity of your DC supply
or voltage (AC or DC) as long as it is within the specs of your regulator

...I am used to using a full bridge or just a regulator but never both.

How do you ensure a clean and stable supply voltage of an AC powered circuit with only a bridge and no regulator?

[Scott]

Thanks!

I always have a regulator regardless AC or DC. I was not clear in my post. I have a bridge, cap and a standard LDO 12v regulator rated at 35V input. So if I connect it to a 24Vdc power supply it will be fine?

[NavMicroSystems]

Thanks!
...So if I connect it to a 24Vdc power supply it will be fine?

Yes, it will,
and even the DC polarity doesn't matter.

[NavMicroSystems]

I was not clear in my post. I have a bridge, cap and a standard LDO 12v regulator rated at 35V input.

Your post was very clear,
you said there is no bridge in combnation with a regulator:

I am used to using a full bridge or just a regulator but never both

[nomada]

Hi

Scott, Bruce is wright (as always), but do not forget that using a LDO with that voltage difference (24 volt to 12 volt) even a little current will generate a lot of heat at LDO metallic tab, please use a suitable heatsink.

Only wishing to help.

Best regards for both,

nomada

[nomada]

Hi

Just want to say that I mean to say RALPH (not Bruce) sorry about the confusion.

nomada

[tdavis80]

http://www.alessioviti.com/lcdprojects/basic_dc_dc.htm

The above link gives the basic circuit. A simple description of AC versus DC follows....

A/C is a voltage that slowly goes from full on, to off then full on again (but now in the opposite polarity). It 'alternates' between these 2 polarities. In north america, it happens 60 times a second.

The bridge reroutes the current so that the positive always swings onto the same pin, the negative always appears on the same pin. If you were to scope the 2 pins, you now have pulsating DC instead of AC. The pulsating is because although the bridge always routes the current to the proper pins, the bridge has nothing to reroute during that instant when the A/C swings from full + to full -. That zero voltage point is called the crossover point.

The capacitor C1 stores the charge during the 'full-on' phase so something is still left when the power is crossing the zero voltage phase. C1 should be large enough so that under no circumstance that the input voltage to the regulator drops below its requirements. With a 7805, you would want the voltage to stay above 7volts (to be safe). If you find that the voltage is not stable (has ripple), increase the value of C1 or simply throw another cap across the line.

C2 gives a cleaner noise-free bus. Not used to reduce ripple.

Consider DC to be really slow AC. If you circuit likes AC, it would probably like DC unless it feeds directly into a transformer.

[Scott]

Thanks to everyone it works fine. That is after I burned my hand on the regulator and had to add a larger cap to smooth out the ripple. I will add a heat sink and let the board run on the workbench for awhile to see what happens.

Scott

[NavMicroSystems]

...That is after I burned my hand on the regulator...
Scott

Scott,
that case you should really review your hardware design!

[CocaColaKid]

You might consider a switching regulator if heat is becoming an issue.