60v power regulator for MCU required

[johnny78]

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

 

[johnny78]

Thats the max you can put thru the Zener. That would occur (not in your case)
when load got disconnected and Zener had to absorb all the current coming
thru Zener Rv in circuit. Thats a calculation you also do on reg circuit design
to see if you have that problem.

Regards, Dana.

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 Jun 5, 2023 ---

Thats the max you can put thru the Zener. That would occur (not in your case)
when load got disconnected and Zener had to absorb all the current coming
thru Zener Rv in circuit. Thats a calculation you also do on reg circuit design
to see if you have that problem.

Regards, Dana.

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 Jun 5, 2023 ---

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 Jun 5, 2023 ---

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

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 Jun 5, 2023 ---

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 Jun 5, 2023 ---

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 Jun 5, 2023 ---

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

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

--- Updated Jun 5, 2023 ---

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 Jun 5, 2023 ---

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 Jun 5, 2023 ---

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 Jun 5, 2023 ---

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

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 ?

 

[johnny78]

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 Jun 5, 2023 ---

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 Jun 5, 2023 ---

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 Jun 5, 2023 ---

View attachment 183188View attachment 183189
is it right the calculations this way ?or i've missed something else again ?

--- Updated Jun 5, 2023 ---

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 ?

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 Jun 5, 2023 ---

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 ?

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

 

[danadakk]

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.

 

[johnny78]

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.

View attachment 183192

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.... :

View attachment 183193

Regards, Dana.

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

 

[danadakk]

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

Regards, Dana.

--- Updated Jun 5, 2023 ---

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 Jun 5, 2023 ---

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

 

[johnny78]

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

yes i figured that i need only 100nF cap from Aref pin to GND

View attachment 183198



Regards, Dana.

--- Updated Jun 5, 2023 ---

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 Jun 5, 2023 ---

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

thanks for help
Johnny