Want to know more applications of step-up DC to DC converter

BlackMelon

Aug 7, 2012
188
Hello,

I'm gonna make the converter because it's my personal interest. In fact, I've known some of its applications already.. like allowing me to drive 48V DC motor from 12V battery but I don't see any significant usefulness of it... I don't know what can I do with high DC voltage.. (100V+). The circuit that I'm making is a power DC-DC converter (the maximum current and voltage is 8A and 120V with a large toroidal coil) so it's not suitable to use in cell phone or sth. small....

Could anyone tell me those applications?

BlackMelon

BobK

Jan 5, 2010
7,682
Photo flash comes to mind. These create a voltage of about 300V to set off the flash tube from a 1.5V battery.

For smaller voltages, an LED flashlight. A white LED needs about 3.3V. If you run off two 1.5V batteries with a boost converter, you can keep the LED going full speed even after the batteries can only deliver less than 1V, and this is indeed the way the better ones work.

Bob

KrisBlueNZ

Nov 28, 2011
8,393
You want to make a high-power DC-to-DC converter with an output of 120V at 8A but you don't have an application for it? I wouldn't do that! The usual way is to have the requirement first, then find something that fits that requirement.

In answer to your question, there are many useful applications for DC-to-DC converters, but for the one you're describing, a very good one is car audio, where the supply voltage is normally in the range 12~14V, roughly.

To deliver significant power into a speaker, you have to be able to apply significant voltage at significant current. With a supply voltage VS of 13V DC, say, this is a problem. One approach is the bridge-tied-load (BTL) method, where both ends of the speaker are driven from separate output stages that complement each other. This gives a theoretical maximum peak-to-peak voltage across the speaker of 2 × VS. This assumes that both output stages can swing fully between the supply rails, which is not the case, but I'll go with it.

So let's say that a BTL car audio amplifier can apply up to 26V p-p across the speaker. The RMS voltage will be 26 / 2 / sqrt(2) which is 9.2V RMS. How much power does this correspond to, for an 8Ω speaker? P = V2 / R = 10.6W. Now with 10.6 watts of subwoofer power, your car isn't going to trigger any earthquake warning systems.

One approach is to greatly reduce the speaker impedance. 9.2V RMS into an 8Ω speaker produces only 10.6W but into a 2Ω speaker, you get four times that, 42.4W. But 42W will barely even get you funny looks from other drivers when you pull up next to them at an intersection with your dubstep wound out to 11.

And reducing the speaker impedance causes another problem: significant loss of energy in the output stages and the speaker connectors and wiring, due to the very high currents.

So the best solution is to use an 8Ω speaker, but drive it at a higher voltage. To deliver, say, 200W into an 8Ω speaker, you need an RMS voltage of 40V! This is a peak voltage of about 57V. So even if you use the BTL trick, each output stage needs a power supply rail of at least 60V. That's where a high-power boost DC-to-DC converter is used, and you will find them in all of your big trunk-mounted subwoofer amps.

Of course you still need to draw a LOT of power from the car battery - including power to cover the inefficiencies in the boost regulator - and you need big fat wires there, but at least you can throw some big electrolytics in there to mitigate the power loss.

If you're looking for a good application of a high-power boost converter, that's the best one I know of.

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