Newbie,Need help!!!12VDC to 24VDC flyback converter(multiple output)

hi,
I'm trying to design a flyback DC-DC converter which can provide up to 24V from a normal 12V,40Ah lead-acid battery that every car has. It can be used to run radios, small lights, relays, horns and other 24V accessories(multiple output) from a 12V vehicle.

I have done research about flyback topology, but both modes(discontinuous mode and continuous mode) have the identical circuit diagram. how to differentiate it and calculate those components?Which PWM IC chip for implementation for this converter?please recommended the circuit diagram.

I am totally no experience in this area.
PLS HELP!!! Thank you.

peggy said:

hi,
I'm trying to design a flyback DC-DC converter which can provide up to 24V from a normal 12V,40Ah lead-acid battery that every car has. It can be used to run radios, small lights, relays, horns and other 24V accessories(multiple output) from a 12V vehicle.

I have done research about flyback topology, but both modes(discontinuous mode and continuous mode) have the identical circuit diagram. how to differentiate it and calculate those components?Which PWM IC chip for implementation for this converter?please recommended the circuit diagram.

I am totally no experience in this area.
PLS HELP!!! Thank you.

Click to expand...

If you are completely new to power converter design, I'd suggest you start with an approach that gives you the big pieces of the puzzle. Check out National.com for their SIMPLE SWITCHER product portfolio, and their WEBENCH Power tool (look under apps). The Webench program should even give you a schematic and BOM to get you going.

Playing around with power supplies is a lot of fun, but if you haven't been exposed to the basic concepts like volt-second (charge) balance, then fiddling with a flyback could be an exercise in frustration.

This looked like a pretty well laid out paper for a good theoretical background on how flyback converters operate: The Flyback Converter

Hit Google for more explanations of SMPS topologies. And for a starter circuit, build up one from National, then analyze it and play with it to understand the concepts. Also, search on the forums here for the term "flyback"... you probably aren't the first one to come asking about them.

Thank you for your reply.
Attached is schematic diagram(LM2585).
https://obrazki.elektroda.pl/39_1299296704.jpg

Can i use this chip for my flyback converter for draw 0.8-1.5mA?
This device is available in 4 different output voltage versions: 3.3V, 5.0V, 12V, and adjustable.What is means adjustable and how to adjust?

I have a bit confuse after reach through so many information.
if no make your inconvenient, can u guide me step by step to design this converter since my theoretical background is very poor.
Thank you very much.

If you look at the schematic, you'll see that the feedback pin is tied directly to the flyback output voltage. In the schematic you attached, that would be a 12V version of the part. The control loop inside the chip will adjust the switching time/rate to keep the feedback pin at +12V. If you got a 3.3V version, then the chip would work to keep the feedback pin at 3.3V, instead.

Adjustable just means that the feedback pin will try to stay at some voltage (per the spec sheet, Vref is 1.23V). In this case, you would need to set up a simple resistive voltage divider to take your desired output voltage, and divide it down to 1.23V. If you wanted to have Vout = 8V, then you could use R1=6770 and R2=1230 ohms (or something close). The voltage divider would only steal 1 mA of output current to work correctly.

This device and schematic says it can handle +12V and -12V at 150 mA, so it should be more than capable of supplying your small current needs (around 2mA).

The easiest way to learn is to find a diagram, buy some parts, and start putting something together. I'm not a power converter designer, but I know the theory and general concepts well enough to get me by. I'm sorry, but I don't have the time to walk you through a design. That is something that takes several hours of time, even for an experienced designer.

When I was an undergrad, I started with a Simple Switcher and the basic schematic and made my first flyback, so it should be a pretty easy place to get started for about anyone.

Good luck!