60v power regulator for MCU required

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johnny78

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hi Guys
i need to power an MCU on 60v supply
unfortunately the HV version on lm317 ot 2596 is not available
a friend suggested to connect 2 lm2596 on series for 60v input & use one output
But it didnt work
as a voltage devider to read the 60v dc on analog pin i have used 100k as R1 & 9,09k as R2
using voltage devider calculator & it works But do you have any ideas if i need to use another values?

any suggestion for 60v regulator?

thanks in advance
Johnny
 

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im sorry i woke up & was thinking all night i guess it was a mistake what i thought its the current i should think of
but i couldnt delete my reply before you read it
--- Updated ---

hi
im testing again with the 5mA test current but something wrong i guess

the input voltage is 5v
the output is 4.3v the zener Vz V
load current = what it should be ?
diode current = 5mA test current

thanks
--- Updated ---

is it right i should calculate the impedance of the Aref pin which its 32k to get the load current ?

would you please give me an example values to regulate 4.3v from 5v without any load (just to measure 4.3v on zener diode

thanks again
--- Updated ---


is it right the calculations this way ?or i've missed something else again ?
--- Updated ---

in the redcrab calculator i set the load current to 0.00016 A insted of mA & i've got 135.66 ohm seris resistor value
is thats right ?
 
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hi again
i've used 137ohm 1/4w resistor & i got 4.47v on the zener cathode
is it ok ?
when i placed the Atmega328 the reference voltage rised to 4.8v
why could it happen ?
--- Updated ---

johnny78 said:
hi again
i've used 137ohm 1/4w resistor & i got 4.47v on the zener cathode
is it ok ?
when i placed the Atmega328 the reference voltage rised to 4.8v
why could it happen ?
Click to expand...
its the Aref pin which have the VCC voltage on it also
i will check the Aref parameter settings & hope the MCU is not damaged
 
Last edited:

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The calc values you used OK, but not for worst case.

So as a refresher on getting to worst case......

Lets calc the Zener R, assuming no load for simplicity first.



So worst case we want 5 mA min thru the Zener.

So Rs = (Vin - Vz) / .005, but worst case is when Vin lowest, Vz highest,
so (Vinmin - Vzmax) / .005 = Rs. Best design would also include the drift
in these voltages over T. Lets ignore that for now.

Now whats the max current will run thru Zener ?

Iz = ( Vin - Vz ) / Rs, worst case when Vin is max, Vz is min, and Rs is min,
so Izmax = (Vinmax - Vzmin) / Tsmin. So we want a Zener rated with some
margin for this.

Worst case, Pz = Vz x Iz, worst case when they both are max,
so Pzmax = Vzmax x Izmax. So we want Zener rated with some
margin for this.

If load were shorted, therefore max power in Rs, Prsmax = Vinmax^2 / Rsmin,
we want a R rated for this power.

Now we can repeat this analysis with superposition with load current to make
life easier, I leave that up to you, to cover the load current addition.

Superposition Theorem | DC Network Analysis | Electronics Textbook

Read about Superposition Theorem (DC Network Analysis) in our free Electronics Textbook
www.allaboutcircuits.com

Rise in Aref pin when you connect Atmega, whats the reference set to ? If set to AVCC,
eg. +5, it would pull the pin up a little more.... :



Regards, Dana.
 
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hi
unfortunately the chip i was testing on its Aref pin is damaged so its dropping the 4.48v reference voltage to 1.8
i've tested another one & its ok
i think all the chips i have are damaged because i never used the Aref pin before & long time ago i read somewhere that i must connect the Aref pin to VCC

about the zener regulator worst case i will read about it again carefully
but the easiest solution is using 500mW resistor instead of 361mw Calculated & the diode power is 21.5mW & im using 500mW zener

i think i must keep this post as a reference for power calculations for later use
thank you all

best regards
Johnny
 
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If you are using internal reference I do not think you have to connect Aref to anything.





Regards, Dana.
--- Updated ---

A copy of this in your library good ref material. You can borrow it on archive.org

Zener Diode Handbook for sale | eBay

Get the best deals for Zener Diode Handbook at eBay.com. We have a great online selection at the lowest prices with Fast & Free shipping on many items!
www.ebay.com


Regards, Dana
--- Updated ---

Or this https://www.onsemi.com/pub/Collateral/HBD854-D.PDF
 
Last edited:

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danadakk said:
If you are using internal reference I do not think you have to connect Aref to anything.
Click to expand...
yes i figured that i need only 100nF cap from Aref pin to GND
thanks for help
Johnny
 

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