Generate stable 3.3V OR 5V from 20-134v DC supply for AMC1200

Thread Starter

ManeGote

Joined Jan 5, 2024
4
Hi, I would like to generate a stable 8mA or above supply for a fully-differential isolation amplifier. I used a 5v zener diode with a 6.8 kΩ (SMD 0603 package) resistor and it will burn out at higher voltages. my circuit experiences voltages from 20v to 134v. I'm using LCSC.com as my electronics distributor and they have a limited range of LDO one of which can accept my 134v max but will not work under 50v so I'm not sure what other ways i can power the AMC1200 and have such wide input voltage.
Screenshot 2024-01-04 185223.png
 

Sensacell

Joined Jun 19, 2012
3,445
Replace the resistor with a simple transistor current source.

Mind the power dissipation at high voltage levels- the source will need to burn 1.3 watts at 134V input, assuming a 10 mA current.
I would use a ~ 6 volt Zener and a garden variety 5V LDO to get a clean, well regulated output.
The only part that needs to be rated for high voltage is the transistor.

If you cannot afford the power loss, it gets much more complex.
 

Thread Starter

ManeGote

Joined Jan 5, 2024
4
Replace the resistor with a simple transistor current source.

Mind the power dissipation at high voltage levels- the source will need to burn 1.3 watts at 134V input, assuming a 10 mA current.
I would use a ~ 6 volt Zener and a garden variety 5V LDO to get a clean, well regulated output.
The only part that needs to be rated for high voltage is the transistor.

If you cannot afford the power loss, it gets much more complex.
thank you for this answer, would you be able to link me to a resource which discusses this? or a schematic of this? I'm a beginner to understanding these concepts
 

ronsimpson

Joined Oct 7, 2019
3,037
I have used 3-pin linear regulators for years. Some in the 400V to 150V input range are listed here. If you have 8mA in the regulator and 100V across it that is 800mW. So the regulator will run hot.
TL783CKTTR
TL783CKCSE3
NCP781BMN033TAG
NCP785AH33T1G
Oh, you want isolated. These are not isolated but might give you an idea.

You could use a linear regulator to turn the 20 to 135V to 12V and I use some small 12 to 3.3/5V isolators at 1 or 2Watts.
 

Thread Starter

ManeGote

Joined Jan 5, 2024
4
I have used 3-pin linear regulators for years. Some in the 400V to 150V input range are listed here. If you have 8mA in the regulator and 100V across it that is 800mW. So the regulator will run hot.
TL783CKTTR
TL783CKCSE3
NCP781BMN033TAG
NCP785AH33T1G
Oh, you want isolated. These are not isolated but might give you an idea.

You could use a linear regulator to turn the 20 to 135V to 12V and I use some small 12 to 3.3/5V isolators at 1 or 2Watts.
Your message gave me an idea, i already have 5v which powers my MCU and other bits that are isolated from the high voltage. so i was wondering what if i used a 5v isolator such as B0505S-1WR3 which claims to provide 200mA and make the output ground common to the AMC. thus my MCU will stay isolated but the AMC will get power. would this type of thing work?
Screenshot GOODIEX-01-05 194414.png
 

Sensacell

Joined Jun 19, 2012
3,445
IReg.JPG

If you cannot find the Depletion Mode MOSFET, this circuit will also work with more common parts.
Almost any NPN transistor and a MOSFET rated for the voltage.
Vout goes to your 3 terminal LDO regulator
 
Top