Add external MOSFET to 34063 boost converter.

[chris917]

Hi everyone,

I'm a UBC engineering student entering my second year this fall, found this forum and looks like a pretty sweet resource.

I guess I'll jump right into it. What I'm trying to do is add an external MOSFET (or other switching device) to the 34063 buck/boost converter. I plan to use a very basic setup (an example from the datasheet) to power an inverter from several li-poly battery packs I have lying around. So the requirements for the power supply are ~7.4v boosted to 13.8v, at several amps (up to 10 likely).

My question is: what would be a good choice for the switching device? Are there any other considerations that should be taken when using this IC for higher current applications?

Thanks alot!

 

[Chippie]

Try Google.........At least the MC34063
data sheet...

 

[chris917]

Datasheet doesn't have any recommendations, just a sample circuit without any values.

 

[schmitt trigger]

The MC34062 can either sink OR source current. To efficiently drive a power Mosfet you need to sink AND source current; in other words a device with a totem pole output.

In the past I've used the TC1410 Mosfet driver from Microchip with good results.

 

[Mr RB]

Just put your Li battery packs in series?

That will do your 7v to 14v conversion with 100% efficiency and no parts...

 

[Chippie]

Just put your Li battery packs in series?

That will do your 7v to 14v conversion with 100% efficiency and no parts...

Ahhh...so often the simplest of solutions are easily missed...

4 lipo cells will give around 14v....Just make sure you dont over discharge them...(3volts/cell is the normal cut off)

 

[Iceman_Chris]

Ahhh...so often the simplest of solutions are easily missed...

4 lipo cells will give around 14v....Just make sure you dont over discharge them...(3volts/cell is the normal cut off)

Yeah I've done that in the past, but I've been told that this should be avoided due to mismatched impedences on the individual cells. Is this BS?

Regardless of this specific application, I'm still interested in using a 34063 w/ external transistor for a project or two.

 

[chris917]

Oops posted under old account ^^