in other words, bank on having at least 3A available on the 3.3V supply - have to leave room for error.So, to get 1A current output at 8V, you would need (8v*1A/90%)/3.3v=2.7A from the 3.3v supply - that is with a really efficient DC-DC converter.
Over-capacity is almost always a good thing.
The 90% figure is if a really, really good boost circuit were used. It would be safer to assume more like 75% to 80% efficiency, and then add on a 20% safety margin. That would give you a 3.88A input current requirement; pretty close to your estimate.
I need 40mA on my output and available is 800mA.It would help us to help you, if you will tell us what your 3.3v power supply is, how much current is available, and how much current that you need at your output voltage.
Keep in mind that to get 8v at a given current from 3.3v, it will require at least 2.43 as much current from the 3.3v supply. Also, the boost conversion will not be 100% efficient; 90% efficient is about the best you can hope for.
So, to get 1A current output at 8V, you would need (8v*1A/90%)/3.3v=2.7A from the 3.3v supply - that is with a really efficient DC-DC converter.
Much, much thank you and sorry because I am late with replay message.Okin,
Where are you located? In the USA?
Please put your general location in your user profile.
You can get there by clicking on the "User CP" link near the top of the page, and then "Edit Your Details". There is a spot for "Location" towards the bottom. Click the "Save Changes" button to store.
If you are in the States near a Radio Shack, we can whip something up quickly that you can use.
I guess you dont like the place? Or is it just difficult to get parts?Unfortunately I live in Croatia in Europe.
much thanks. I will try your advice. It is not a big problem for components here in Croatian. I can order everything but I must wait few days.I ran through the calculations for a similar device as the MC34063, but the efficiency was terrible due to operating from such a low voltage.
See the attached. You will probably have to substitute other transistors for the devices I used. I really have no idea what parts you can find/get where you are.
You may have to wind the transformer yourself. I suggest a ferrite toroid. You can find them in junked equipment. For example, computer power supplies have toroids in them.
by Jake Hertz
by Jake Hertz
by Jeff Child