help with designing Programmable Power supply

Projects General Guidance
1

Hello All,
I need to design power supply with display which need to accurate and if possible clean output with less noise.
I read about some methods (PWM) or (ADC and DAC) or ( resistor network) . I do not know which method is better with my requirements.
I am not sure where to start with
Requirements

  • --There is no limit for Input voltage and current
  • ---Current output 0-3A (1mA resolution)
  • ---Voltage output 0-5vdc (1mV resolution)
  • ---Able to read input current and voltage to PSU circuit and output to load
  • ---Overvoltage and over-current protection (maybe send alert to Arduino)
  • ---Short circuit protection
  • ---Adjust output current and voltage via Arduino and keypad and rotary
  • --- I2c or SPI communication

Thank you

2

What is Your education and experience in electronics?

3

I am not sure where to start with

This is an advanced project... You have a lot of studying (and experimenting) ahead of you!

Regulated power supplies work by comparing the output voltage to a reference voltage in a feedback loop. The voltages can be scaled (with a voltage divider, etc.) so the reference doesn't have to match the output voltage. They just have to be proportional. Usually, that's done with a comparator circuit so you don't need need an ADC and you don't have to actually measure the voltage. But you do need a DAC to "program" the reference voltage.

Current limiting/control is similar except you need a current sensor (or "small resistor") to "convert" voltage to current. If you use a resistor the voltage regulation goes after the resistor to compensate for the voltage drop.

  • --There is no limit for Input voltage and current

What? 1,000V or 10,000V? There's always a voltage limit.

The current depends on the power supply design and the current/power-out. (You can't get more power out than you put-in.)

  • ---Current output 0-3A (1mA resolution)

A normal (constant voltage*) power supply can't also have fixed current (Ohm's Law). The current limit can be fixed or variable/programable. If you "try" to exceed the current limit either the voltage is reduced to hold at that current or the the voltage is cut-off (or nearly cut off) to cut-off the current (similar to a circuit breaker or fuse).

A constant-current* power supply adjusts the voltage as necessary to maintain the current. If the load is "too light" (resistance is too high) the voltage goes-up to the maximum of the particular power supply.

If you have a current-limited power supply you can "make" a constant-current power supply by setting the current limit and then setting the voltage to maximum. But of course you might not achieve the current depending on the maximum available voltage and the resistance of the load.

  • ---Voltage output 0-5vdc (1mV resolution)

1mV (or 1mA) resolution is not "easy" and you'll get voltage drop in the wires & connections.** There is something called a 4-wire connection where a separate pair of wires is use for voltage-monitoring. That way, the voltage drop across the current-carrying wires is automatically adjusted-for by the voltage regulator.

  • ---Overvoltage

Input voltage or output voltage? Output voltage is presumably already regulated. Input voltage protection is often used along with a fuse. That's called a "crowbar" circuit. The analogy is a crowbar dropped across the input (when voltage exceeds the limit), shorting it out and blowing a fuse.

and over-current protection (maybe send alert to Arduino)

That's already built-in to your current control/limiting.

  • ---Short circuit protection

Again, built into your current limiting.

  • In the case of a variable power supply the voltage (or current) isn't actually constant, but it's controlled and independent of the load.

** I'm testing some boards at work right now. The run at 5V and about 250mA. The power supply has voltage & current displays and variable voltage (with a knob, no "programming") but no current control, just current limiting somewhere over 1 Amp. When I compare the voltage at the power supply to the voltage on the board, I'm getting about 150mV of voltage-drop through the wires/connections. So, 1mV accuracy (from the power supply) would be useless... It is nice to have 1mV (or better) from the multimeter.

4

Railroader:
What is Your education and experience in electronics?

I have some electronic background

5

Sorry but it sounds like You're aiming above Your head like explained by @DVDdoug

Scale down the project and see what You can achieve.

6

Hi @DVDdoug , thank you for your help and comments

Regulated power supplies work by comparing the output voltage to a reference voltage in a feedback loop. The voltages can be scaled (with a voltage divider, etc.) so the reference doesn't have to match the output voltage. They just have to be proportional. Usually, that's done with a comparator circuit so you don't need need an ADC and you don't have to actually measure the voltage. But you do need a DAC to "program" the reference voltage

okay , I understand . But I don't know where to start with.
I saw some circuit they were using ADC to read voltage from input and output although they were using op-amp before sending voltage to ADC
Can I ask you do you have any website or circuit that I can start with and modified for my application ? thank you

Current limiting/control is similar except you need a current sensor (or "small resistor") to "convert" voltage to current. If you use a resistor the voltage regulation goes after the resistor to compensate for the voltage drop.

right ,
How about if I want to measure current with AD8418 or ina240 , etc.

What? 1,000V or 10,000V? There's always a voltage limit.

Up to 24V

A normal (constant voltage*) power supply can't also have fixed current (Ohm's Law). The current limit can be fixed or variable/programable. If you "try" to exceed the current limit either the voltage is reduced to hold at that current or the the voltage is cut-off (or nearly cut off) to cut-off the current (similar to a circuit breaker or fuse).

A constant-current* power supply adjusts the voltage as necessary to maintain the current. If the load is "too light" (resistance is too high) the voltage goes-up to the maximum of the particular power supply.

If you have a current-limited power supply you can "make" a constant-current power supply by setting the current limit and then setting the voltage to maximum. But of course you might not achieve the current depending on the maximum available voltage and the resistance of the load.

thank you for your explanation
I need current and voltage limit . which I need to change limit using microcontroller.

1mV (or 1mA) resolution is not "easy" and you'll get voltage drop in the wires & connections.** There is something called a 4-wire connection where a separate pair of wires is use for voltage-monitoring. That way, the voltage drop across the current-carrying wires is automatically adjusted-for by the voltage regulator.

right thank you for your information

Input voltage or output voltage? Output voltage is presumably already regulated. Input voltage protection is often used along with a fuse. That's called a "crowbar" circuit. The analogy is a crowbar dropped across the input (when voltage exceeds the limit), shorting it out and blowing a fuse.

Thank you , I saw some chip from Maxim and Analog device to protect input from overvoltage and over-current
, but I think "crowbar" circuit. is much better for power supply

  • Power supply is only limiting current and voltage
  • Do you think do I need close loop power supply ? for better result ?
7

Railroader:
Sorry but it sounds like You're aiming above Your head like explained by @DVDdoug

Scale down the project and see what You can achieve.

Hello @Railroader
Thank you for your comment
that's my problem I don't know which method is better for me before start digging more

because I saw some circuit using

  • PWM and op-amp
  • another circuit using DAC and ADC and other bits
  • another one couple of resistor driven by transistor to vary voltage output
  • maybe there are other methods which I haven't discovered yet

thank you again for your help .

8

Start building a variable voltage source. Then expand it to be able to provide some power.
You will have work to do but taking one step at the time, instead of a giant 3 foot jump, You will succeed.
Time and willingness from helpers is not totally unlimited.

9

The circuits on my pages here may be a useful starting point.

When you have worked your way though those you may realise what a challenge this project is!

You may then wish to change your design spec

  • --There is no limit for Input voltage and current ?what does this mean?
  • ---Current output 0-3A (1mA resolution)
  • ---Voltage output 0-5vdc (1mV resolution)
  • ---Able to read input current and voltage to PSU circuit ?WHY?

and output to load

10

johnerrington:
The circuits on my pages here may be a useful starting point.

When you have worked your way though those you may realise what a challenge this project is!

You may then wish to change your design spec

Thank you for your comment and link
I need to mention my input voltage is already converted to DC before feed into input of my Power supply
I am going to read your website. Thank you

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