Simple DC/DC converter

[Scarr]

Hi,

I have 12v DC and want to lower this to between 4-5v DC 3A (pulsed < 3ms with a 20% duty cycle) with as small a footprint as possible, I have always used linear or switch mode regulators before but ideally want it smaller than these packages.

I looked at a zener but one that is 15w is huge, any other way of doing this?


Regards

Steve

 

[MikeMl]

What is the load? Is it inductive or resistive? How much voltage sag could you tolerate during the 3ms that the load is driven?

 

[Scarr]

Load

Hi MikeMI,

The load is resistive, a digital circuit MCU etc, as for vsag I suspect 2v max, it will be the MCU that dictates this and I have not selected this as yet. looking at a Attiny13 it's voltage range is 1.8-5v

Thanks

 

[Hero999]

A digital circuit is not purely resistive, it's a complicated load which changes resistance during operation.

I don't believe an MCU would require 3A.

What exactly are you driving? Isn't the MCU just what you're using to drive it with?

 

[MikeMl]

If you are switching the MCU's Vdd supply on-off, you will have to be careful with supply bypassing. If the bypass caps are large, then the surge current to charge them at the beginning of each pulse will be huge. Is that where the 3A requirement comes from? Surely the MCU will not require 3A?

Why turn off the power supply to the MCU at all? Just put it in a sleep state.

 

[Scarr]

I am.....

Hi again,

I am using MCU to control a power transistor using same input supply (5v) it peaks at 3A


Thanks

Steve

 

[Hero999]

Please post a schematic, this isn't making much sense.

 

[MikeMl]

Hi again,

I am using MCU to control a power transistor using same input supply (5v) it peaks at 3A


Thanks

Steve

Ok, so your problem has nothing to do with switching the MCU On/OFF. It is all about dropping 12V to 5V for the load being switched by the transistor?

I'm with Hero. Enough second guessing what you are trying to do. Just post a schematic...