I am trying to build a 48 volt bldc controller. The problem is its only input supply will be 48 volt from battery so how i can step down this 48 volt to 5volt for my microcontroller and 12 volt to ir2110. I know there are linear voltage regulator are avialavail ke lm7805 and lm7812 but there max input voltage is 40 volt so if i use these regulator they probably will burn. I can use resistor to step down voltage but current rating will be low. Please suggest the best way to do this. And if anyone know what technique is used in standard 48 and 72 volt controller please suggest me.

 

There are couple of DC/DC Buck Converters available. For example, this one which is based on the XL7015.
Supply Voltage Input Pin. XL7015 operates from a 5V to 80V DC voltage.
Capable of driving a 0.8A load
Output Adjustable from 1.25V to 20V

 

I use these...
http://au.element14.com/recom-power/r-78hb12-0-5/converter-dc-dc-0-5a-12v-sip3/dp/1793166?st=R-78H
The R-78HB12-0.5 has a 12V output of 500mA and can stand 72Vin.
This 12V could feed a Traco Power 5V 1A version. TSR 1-2450
http://au.element14.com/tracopower/tsr-1-2450/converter-dc-dc-5v-1a-sip/dp/1696320?st=Tsr 1-2450
It can only handle 36Vin so that is why you run it off the 12V supply.
There are quite a few of these regs available now.

 

I have used simple R/C/Zener circuits with success before, especially in low current circuits such as this.
Max.

 

I have used simple R/C/Zener circuits with success before, especially in low current circuits such as this.
Max.

Can you give any examples

 

This is one example (not mine) that I use, this is the power end of a mains fed Treadmill controller.
The resistor is sized according to expected load, and within the zener rating.
Max.
A little faint but hopefully discernible.

 

A little more readable.
Max.