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.

 

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.

 

Heat-Sink and large through-hole Transistor-Package, or, custom designed SMPS.
Take your pick.
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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

 

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.

 

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?

 

Sounds like a job for a depletion MOSFET such as DN2540.

 

I

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

 

Here's another way to do it ..........
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5v isolator such as B0505S-1WR3 which claims to provide 200mA

I am using that part and others with more spacing from input to output. I think you have the best answer.

 

I am using that part and others with more spacing from input to output. I think you have the best answer.

I have used this part in my design and it is working. so i will use this part from now on. however @LowQCab , @Sensacell and @Ian0 have answered my original question of how to generate a stable voltage from a high voltage supply with a wide input range.

 

Seems like a simple diode (D1) could be used to isolate the 5 volt supply like this:

 

Seems like a simple diode (D1) could be used to isolate the 5 volt supply like this:
View attachment 311889

What does this diode do for you? explain this "isolation" you need? I am not understanding the requirements?

 

What does this diode do for you? explain this "isolation" you need? I am not understanding the requirements?

Not my thread!

 

Not my thread!

Right! sorry.