hi
i have relay with coil activation voltage (24Vdc)
and my power supply output voltage is 12V(pc power supply)
how can i get the 24V from that power supply?
can i use voltage doubler?

 

If it has a +12 and -12 you can. +12 goes to + -12 is used instead of a ground.
The distance between +12 and -12 is +24.

 

A doubler will work, as long as it supplies sufficient coil current for the relay.

 

As far as a doubler circuit goes; if you're talking about trying to simply use a couple of diodes and caps, no - that's for AC.

In order to get 24v from a 12v supply, you'll need a "DC-DC converter", also called a "boost" or "step-up" converter.

A DC-DC converter or boost converter has a chopper circuit (oscillator) that provides current to an inductor via a diode. The current flows for a bit, and then is cut off. This causes the inductor to pass current through another diode at a higher voltage. It's actually quite an efficent process.

Here's a link to Wikipedia explaining the basics:
http://en.wikipedia.org/wiki/Boost_converter

 

As far as a doubler circuit goes; if you're talking about trying to simply use a couple of diodes and caps, no - that's for AC.

In order to get 24v from a 12v supply, you'll need a "DC-DC converter", also called a "boost" or "step-up" converter.

A DC-DC converter or boost converter has a chopper circuit (oscillator) that provides current to an inductor via a diode. The current flows for a bit, and then is cut off. This causes the inductor to pass current through another diode at a higher voltage. It's actually quite an efficent process.

Here's a link to Wikipedia explaining the basics:
http://en.wikipedia.org/wiki/Boost_converter

i think if i use the "boost" its need IGBT or MOSFET and trigger circuit
to get the duety cylce,isnt it?
if that true it will be more complicated that i need.
in other hand in my circuit i rectify 220Vac by full bridge rectifier
so i have 314Vdc,can i use voltage regulator to get the 24V,also i need 18Vdc too for another IC(MOSFET driver)?

 

No, You cannot use a simple voltage regulator to get your 24V nor 18V. Basic math dictates that even for a 25mA 24V supply, you'll get 7.25W dissipated from your regulator as heat. You will be very hard pressed to find any simple regulator that can accept that level of voltage anyways..

A 12V to 24V boost regulator is a simple approach, just check out www.national.com and use their power simulation software, it isn't as hard as you think.

Steve

 

thanks scubasteve_911
i get it
and that the schematic which dot from the national site.
thanks for all replays.

 

That's it You just need to follow closely with their bill of materials by buying the recommended component or an equivalent. Make sure you do this though, ie. their 10uH inductor isn't replaced by another one without checking the saturation and DCR.

Also, I'd layout according to their application notes or in the datasheet.

Steve

 

yes i should foolow the recommended components,i hope to finde it in my country shops!!!

hesham

 

in other hand in my circuit i rectify 220Vac by full bridge rectifier so i have 314Vdc,can i use voltage regulator to get the 24V,also i need 18Vdc too for another IC(MOSFET driver)?

This would work if you can use a separate transformer (or separate secondary winding) and second rectifier bridge for the lower voltages.

 

thingmaker3,
yes its able,by using 220:17 transformer to get 24dc then can use regulator or voltage divider to get 18Vdc.
thank you