# From 40V-100Vdc to 8V-12Vdc to 5Vdc

#### Vindhyachal Takniki

Joined Nov 3, 2014
517
1. I have a voltage range of 40V-100Vdc & have to make 5vdc from it and power a microcontroller with it. Max current is 700ma.
2. Since have to measure analog so I want to first make a voltage of around 8-12Vdc then use a linear regulator like LM7805 to make 5Vdc.
3. I need module only. SO I checked for dc-dc buck. they are very costly >$100. 4. For lost cost option I see some people use a resistor & zener first to drop the voltage but I didnt find this good solution. 5. Ground of 40V-100Vdc should be same as of 5vdc & system should be non-isolated. Any low cost solution for this. I want module based system in this. Thread Starter #### Vindhyachal Takniki Joined Nov 3, 2014 517 #### crutschow Joined Mar 14, 2008 24,928 You could roll your own for cheaper than an off the shelf module.. I doubt that's true in general. #### crutschow Joined Mar 14, 2008 24,928 4. For lost cost option I see some people use a resistor & zener first to drop the voltage but I didnt find this good solution. That would dissipate 60W for a 10V @ 700mA output from a 100V supply, so that's not a good solution. #### mcgyvr Joined Oct 15, 2009 5,394 I doubt that's true in general. My comment there was that they could use discrete parts,etc.. and make their own/pcb,etc... if there is any decent volume it would certainly be cheaper than$40..
Now I did not include Design/Testing,etc.. costs into that..