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such a converter can be built with an LM2577 from national. Use it in flyback configurtion. Look at the datasheet for examples. National has also a software to calculate such converters (SimpleSwitcher).
An isolated system has to be built with a transformer. A DC/DC converter in an isolated configuration is a flyback converter. The input voltage is 'hacked' and sent to a transformer. It can move it to other levels (up or down) or even create more than one output voltage. One of these outputs is measured and the feedback path is often done by an optocoupler.
Such a system can be built with the LM2577. I give you an application note: **broken link removed**
hello
I need a dc-dc converter that convert 10-30VDC(unregulated ) to 5VDC and output current can be between 200-400mA.and 1000VDC isolation at minimum.
Traco Power (www.tracopower.com) has many DC/DC converters that meets (nearly) your requirements. The type TED2411 has an input range from 18..36VDC, an output voltage of 5V and 400mA. But the isolation voltage is only 500V. There are other types with higher isolation, but smaller input-range. But perhaps you'll find something.
The prices depend extremly on volume you need. Other manufacturers are Powerone, Artesyn, Power Innovations.
Don't forget Texas Inst. (formerly Burr-Brown)
Them have a lot of isolated DC-DC with built-in transformer
up to 1 A and isolation up to 7kV
Sample price - approx.15-20$
for a few kilo - approx 5-7$.
I think that if you have no experience about Dc/Dc converter, the best way is to start with a complete (monolithic) DC/DC converter as suggested by mr_ghz.
The parameter to know are:
-the range of input voltage (normally thi ranges are standard; for example 18-36V)
-the voltages and the relative output currents
-if it is necessary the isolation between input and output
An important parameter to consider is efficiency. Normally for the integrated Dc/Dc Coverter it is around 80%.
There are many manufacturers (Powerbox,Gaia,etc.) that propose their monolithic Dc/Dc Converter and some of them are cheaper especially if they come from oriental market like YDS.
Normally the integrated solution is much more expensive than a discrete solution, but for testing your project is better to have a reliable power supply.
In a second momet you can try to reduce the cost of your application either designing the Dc/Dc Converter by yourself (if you have time!) using the tools that many manufacturers make available on the net, like WEBENCH Tool by National Semiconductor, or you can ask third party to design and to realize the sample with your specification.
If you need the Dc/Dc Converter only for a project the best solution is the monolithic one.
If you need the Dc/Dc Converter for a market product the cheaper solution is the secod one.
most low cost dc-dc use uc3842 to design with flyback topology,the isolate can use transformer to realize it,because this design is complex,So you should to find a uc3842 application for it. www.ti.com have much application about it
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