Help with boost converter maths

[joshnz]

Hi everyone I'm attempting to build a boost converter for a 16port hub it's psu only has 5volts and it needs a new fan but 12v is a load cheaper than 5v fans.

I'm planing to use MC34063AP1G.

What I need help with please is converting this into something I can understand


For instance d = 3+(4-1)

[PCBONEZ]

Re: Help with boost converter maths

You are making a fan controller?
You know that's going to add heat too - right?
.
If you run a 12v fan on 5v it should run fine, just slower.
So use a higher RPM [or thicker] 12v fan and the 5v power source....
.

[PCBONEZ]

Re: Help with boost converter maths

Also check if these guys will ship to you.

http://www.allelectronics.com/make-a...ING-FAN/1.html

[joshnz]

Re: Help with boost converter maths

Not fan controller
1. I have developed a interest in boost buck conversion.
2. The fan I have got wont start on 5v.

Thanks for the site suggestion but they won't tell me the price to nz
Also I'm not sure I think the fan is 15mm thick and it's tight.

[mariushm]

Re: Help with boost converter maths

The psu of the 16 port hub may only provide a few amps of power on 5v.

Technically, you should have 16 x 0.5A to fully power those ports, so that would be about 8A. However, I doubt the psu of the hub delivers more than 3A of power, and at such load, it would probably not do quite 5v, but rather about 4.6v-4.8v

See for example this video, where a cheap chinese psu advertising 5v @ 1A can barely do 0.3A at about 4.6v :

http://www.youtube.com/watch?v=T88ej...qDogWgYQcamJzV

Next step is to keep in mind the efficiency of the step up converter which should be at about 70% ... so a 12v @ 0.15A fan would use about 2 watts of power, with the efficiency drop think of about 2.3 watts... at 5v that's already 0.5A of power.

as for the calculations, you have to do them one after another from top to bottom...

See https://cdn.badcaps-static.com/pdfs/...9237226842.pdf for a step down ...



Vf is about 0.35v which is typical for a schottky diode , f is the frequency of the oscillator which you pick between 24khz and 44 khz let's say you pick 32 khz... assuming minimum 4.7v at input

Vsat is in the datasheet...
Figure 4 shows the saturation voltage....

From there you just do the calculations making sure the measure units are the right ones.