Attaching circuits

blckscab · Sep 16, 2008

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...

BaCaRdi · Sep 17, 2008

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

blckscab said:
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...

mdwebster · Sep 19, 2008

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.

BaCaRdi · Sep 19, 2008

Agreed on all

-BaC

mdwebster said:
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.

Hero999 · Sep 20, 2008

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.

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

Jamjoom(EE) · Nov 1, 2008

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

Hero999 · Nov 1, 2008

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.

premkumar9 · Nov 10, 2008

blckscab said:
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...

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

Attaching circuits

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