Say i was to of made two circuits (i havnt, but pretend i had)
One circuit needed 12v, the other needed 4v... How do you go about attaching them so they use the same power sourcewithout wasting energy?

Im sorry if this is a silly question, but i have to learn such things somehow

Any links to sites or even breif answers will be apreciated

Edit: Im not 100% sure if this should be in this part of the forum, soz if it isnt...

 

You can only dissipate electricity via releasing energy, Light or Heat, what your asking for doesn't exits.

Just use a + regulator if your not modulating the signal, and be done with it
Or a simply Divider circuit via resistors, according to Ohms law of course.


-BaC

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A regulator is, indeed, what you're looking for.

However, a linear regulator will waste a lot of power in this situation. Say you're pulling 100mA on the 4V side, the 8V differential * 100mA = 800mW of power dissipated as heat by the regulator. A TO-92 package would probably be ok with that, check the spec sheets.

If you're concerned about wasting power though, you want to use a switching regulator. They can be up to 98% efficient in a step-down configuration in certain situations, though 85% or so is a more common value. The problem with a switching regulator is two-fold. One, it is more complex to design as it requires more components (most will need an inductor, two caps, a catch diode, and possibly a resistor or two). These components need careful selection and layout to minimize problem two: Noise. A switching regulator will almost invariable have noise at the switching frequency with a magnitude of 20-100mV or more. So if you're designing a noise-sensitive analog circuit, you may want to steer clear.

 

Agreed on all

-BaC

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Connect a switching regulator to the 12V supply.

4V sounds like an unusual voltage, are you sure it isn't 4.5V or 5V?

A Black regulator will do the job buy you need to change the zener to a 3.6V which will give you about 4.2V which should be alright.

http://www.romanblack.com/smps/smps.htm

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you can connect the two circuits in parallel and use the 12V power supply in parrallel with both circuits, but u will need to add a resistor in series with the circuit that needs 4Vs. Choose a resistor value based by Kirchoff's Voltage Law (KVL) that ensures that this resistance take 8V, so the other 4Vs would be for the circuit

 

A simple series resistor will only work for simple resistive loads as the current drawn doesn't change. A series resistor isn't any good if the circuit is something more complecated like a 555 timer as the current drawn changes the voltage will change. A series resistor also wastes a considerable amount of power and will only be 33.33% efficient in this case.

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I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong.

Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

 

What is the load for 12v and 4v? I mean the current from these voltage points.