Hi!
So I have VERY limited experience with any sort of electrical engineering, but I need to design a part of a circuit to take an input voltage of ~24 V, and convert it to 12V. However, I need it to be controlled by an external input signal. So like when the converter receives an input current it will turn on and provide the output voltage. If someone could point me in the right direction for how to do this or what parts to use, it'd be much appreciated.

Also, from my limited knowledge, can't an op amp be used as a voltage amplifier? Why search for buck converters if you could just add some resistors to an op amp to get a designated output voltage?

Thanks! Pardon my ignorance.

 

You could use a simple LM7812 with its output controlled by a mosftet

 

You could use a simple LM7812 with its output controlled by a mosftet

Is there a more efficient method of doing this? Aren't linear regulators pretty inefficient?

 

How much current does your 12V load need?
Define this external input signal?

There are voltage regulators (switchers vs linear) with an "enable" pin to turn them on/of as needed..
Or yes a mosfet,etc.. could could be used as a switch..

Linear regulators are inefficient for the most part and a switch mode is much better.. But more complicated/higher part count typically. But there are "all in one" package switchers too..
Recom has those as well as others..

 

Is there a more efficient method of doing this? Aren't linear regulators pretty inefficient?

Yes, linear regulators are very inefficient (but with a "clean" output). You could also use a switch mode regulator, and a mosfet. And like mcgyvr just said, there are regulators out there that already have that "gating" feature that you want.

 

As for the op amp as a voltage amplifier, its output voltage would be limited by the voltage at its power pins. The only way to exceed a DC input voltage that I know of is by first turning DC to AC, and then increase AC voltage through a voltage multiplier or transformer (or switcher) and then turn AC back into DC.
BTW, an op-amp has very limited current capabilities at its output.

 

How much current does your 12V load need?
Define this external input signal?

There are voltage regulators (switchers vs linear) with an "enable" pin to turn them on/of as needed..
Or yes a mosfet,etc.. could could be used as a switch..

Linear regulators are inefficient for the most part and a switch mode is much better.. But more complicated/higher part count typically. But there are "all in one" package switchers too..
Recom has those as well as others..

Ok so I really don't know what I'm doing, sorry! But overall I'm designing a temperature control system. I want a microcontroller (MSP430?) to take input from an RTD and then have the microcontroller turn on some kapton heaters if the temp is below a certain threshold. The thing is I need to use a 24 V power supply to power the heaters (to simulate a typical cubesat power supply), so I need some way of stepping this down to 12 V only WHEN the microcontroller says to do so.
I'm not sure if this makes sense, but it's the basic idea!

The Kapton heaters (which will take the 12 V output) run on 2 mA

Thanks again !

 

The thing is I need to use a 24 V power supply to power the heaters (to simulate a typical cubesat power supply), so I need some way of stepping this down to 12 V only WHEN the microcontroller says to do so.
I'm not sure if this makes sense, but it's the basic idea!

That doesn't make sense. If you were controlling the heaters manually, wouldn't you just flip a switch between off and on, with "on" being 24V?

Your heaters must use far more than 2mA. Maybe you meant 2 amps?

You likely just need to control a MOSFET with your controller, and let the MOSFET switch power to the heaters. If you're asking about how to power your microcontroller, the inefficient linear regulator is a fine choice. The controller will use very little power and efficiency is not an issue. The heaters will see full 24V.

 

What else is the micro doing?
Do you know there are off the shelf devices (sold all over on ebay,etc..) that can control the heaters/read the temp,etc... for as little as $10 shipped to you..
Like this http://www.ebay.com/itm/10A-110V-Di...449329?hash=item20ffda49f1:g:~loAAOSw3ydVuZEX