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Registered Member #3451
Joined: Sun Nov 28 2010, 11:13PM
Location: United States
Posts: 100
I want to wind a simple transformer that will provide about 400 volts from a 12 volt battery.
Some questions: As far as driving it, will a spark gap - capacitor setup work? I don't think so, because there isn't enough voltage across the primary. If not, what kinds of semiconductor components are suitable substitutes?
Also, what kind of core should I have? I know that ferrite works best for higher frequencies and iron for lower, but it all depends on how I power it.
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
How much power/current do you want at the output? Do you want a DC output?
You are correct that a spark gap will not be a good choice at 12V. MOSFET is probably the best choice in this voltage range. The choice of topology depends on how much power you want to get out of the converter, for low power applications (less than 100-200W or so) flyback and forward converter topologies are the most common.
You probably want a ferrite or iron powder core. Flyback topologies call for either a gapped ferrite or iron powder. Other transformer switching topologies generally you want ferrite. Iron would have a lot of loss unless you used a very low switching frequency, and that would mean you have a larger core and higher ripple.
Registered Member #3451
Joined: Sun Nov 28 2010, 11:13PM
Location: United States
Posts: 100
wrote ...
How much power/current do you want at the output? Do you want a DC output?
Since I am using the output to charge a few capacitors, it must be DC. As for power, I don't think I will need anything more than ~100 watts.
wrote ...
You are correct that a spark gap will not be a good choice at 12V. MOSFET is probably the best choice in this voltage range. The choice of topology depends on how much power you want to get out of the converter, for low power applications (less than 100-200W or so) flyback and forward converter topologies are the most common.
What are some examples of flyback converters? Is this considered one?
wrote ...
You probably want a ferrite or iron powder core. Flyback topologies call for either a gapped ferrite or iron powder. Other transformer switching topologies generally you want ferrite. Iron would have a lot of loss unless you used a very low switching frequency, and that would mean you have a larger core and higher ripple.
How well would it work if I just used a ferrite rod?
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
wrote ... What are some examples of flyback converters? Is this considered one?
That's the basic idea, what distinguishes the flyback topology from other topologies is the arrangement of the transformer winding polarities and the direction of the output rectifier, which you can see here:
Many capacitor changing power supplies are desgined to output a constant current as it is the charging current which determines how much the capacitor heats up due to ESR. If you run an "open-loop" converter as in your link with a 555 that has no way to measure the output and adjust duty cycle then it will be running in constant power mode, at least initially, which results in higher charging currents which will increase heating though it could be okay still as long as the peak current is not too high.
A ferrite rod I don't think would make a good transformer, they radiate a lot of magnetic fields causing more interference, and the equivalent permeability is probably pretty small.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Mattski wrote ...
That's the basic idea, what distinguishes the flyback topology from other topologies is the arrangement of the transformer winding polarities and the direction of the output rectifier, which you can see here:
Er, no.
The polarities are merely incidental. The thing that *really* distinguishes the flyback from other transformer topologies is that a flyback uses a low permeability core in which it stores magnetic energy, and it uses the load voltage to determine how fast the current falls, giving it a high impedance output. A more conventional transformer uses a high permeability core, where any energy storage is incidental, where the winding voltage is basically determined by the input voltage, giving it a low impedance output.
In the flyback, the power transfer is limited to the storage energy * cycles per second. This makes the flyback an ideal topolgy for capacitor charging, it deals with the low impedance load automatically, and adjusts its output voltage automatically as the capacitor charges.
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400 volt transformer
