Arduino/Genuino High Voltage Power Supply : Sungmod

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Arduino/Genuino "Sungmod"

A high Voltage Power Supply for Photodiodes

The prototype

ระวัง ไฟฟ้า แรง สูง !

You have been warned ...

✈ Motivation

Some Photodiodes in our lab used for e.g. a Photon Counter need a High Voltage Bias. This design uses two identical power transformers (connected back to back) to generate a mains-isolated high voltage of approx. 300 V. This method was the preferred solution of my (now retired) colleague, Mr. Paul Studerus. So consider this design somehow as a tribute to yet another engineer with "Guru-Status", crossing my professional career.

✈ The Design

The Block Diagram of the "Sungmod"

The design is straightforward. As the dissipated power is very small, we used a linear regulator (IRF740/840). The High Voltage (approx. 300V) is generated with two identical transformers, were the low voltage side is connected back to back.

The Setpoint is generated by an AD5667R (Dual, 16-Bit nanoDACs® with 5 ppm/°C On-Chip Reference, I2C® Interface). A single Opamp (OPA140) controls the output voltage therefore, that it pulls the gate of the main transistor down. It is pulled up by a pnp transistor injecting approx. 1 mA into the gate.

The current is measured with a 1 Ω shunt. The voltage drop across it is amplified with a LT1789CS8-1 (Micropower, Single Supply Rail-to-Rail Output Instrumentation Amplifier) and then fed to an analog input of the Arduino. One could realise a current limit by that in software, but the prototype hasn't got that feature.

A look inside. And yes, the interesting components are below the ribbon cable :-)

✈ Downloads

✈ Test Sketch for Arduino/Genuino Nano

Double click on code to select ...

/* ////////////////////////////////////////////////////////////////// 

ARDUINO/Genuino Nano Sketch for Sungmod
https://www.changpuak.ch/electronics/Arduino-Sungmod.php
A High Voltage Power Supply for Photodiodes
Software Version 5.1
28.07.2019, Alexander Sse Frank
USEFUL:
learn.adafruit.com/adafruit-gfx-graphics-library/graphics-primitives

////////////////////////////////////////////////////////////////// */

#include <Adafruit_GFX.h>
#include <Adafruit_SH1106.h>
#include <Wire.h>

// DISPLAY

#define OLED_MOSI  11
#define OLED_CLK   12
#define OLED_DC    9
#define OLED_CS    8
#define OLED_RESET 10




Adafruit_SH1106 display(OLED_MOSI,OLED_CLK,OLED_DC,OLED_RESET,OLED_CS);

#if (SH1106_LCDHEIGHT != 64)
#error("Height incorrect, please fix Adafruit_SH1106.h!");
#endif

// ROTARY ENCODER

const int RotaryEncoder1 = 4 ;   // PRESSED
const int RotaryEncoder2 = 2 ;
const int RotaryEncoder3 = 3 ;

volatile bool LEFT = false ;
volatile bool RIGHT = false ;
volatile bool READY = true ;

// /////////////////////////////////////////////////////////////////////
// SUBROUTINES DAC AD5667R
// /////////////////////////////////////////////////////////////////////

// Pin 6 = ADDR is on GND >>> A0 = 1, A1 = 1
// Only VOUTA is used

const byte DAC_ADR = 0x0F ;
const float VoltFactor = 206.221 ;
const float MaxVolt = 270.000 ;
const float MinVolt = 0.000 ;
float SetVolt = 259.0 ;

void WriteDAC(byte cmd, unsigned int payload) 
{
byte lsb = payload & 0xFF ;
byte msb = (payload & 0xFF00) >> 8 ;
Wire.beginTransmission(DAC_ADR) ;  
Wire.write(cmd) ;   
Wire.write(msb);  
Wire.write(lsb);                  
Wire.endTransmission();
}

void UpdateVolt() 
{
unsigned int Setpoint = 0x0000 ;
Setpoint = (int)(SetVolt * VoltFactor) ; 
WriteDAC(0x10, Setpoint) ; 
Serial.println(Setpoint,DEC) ;
}



// /////////////////////////////////////////////////////////////////////
// D I S P L A Y
// /////////////////////////////////////////////////////////////////////

float Current = 0.0 ;
const int CurrentPin = A6 ;
int CursorPos = 2 ;  
int CurrBuff[32] ;      // STORES RAW VALUE
int CurrBuffPoint = 0 ;
const int MaxCurrBuffPoint = 31 ;
const float CurrentMuly = 5.0 / 1023.0 ; 


void ReadCurrent()
{
int CurrBuffSum = 0 ;

CurrBuffPoint += 1 ;
if(CurrBuffPoint > MaxCurrBuffPoint) CurrBuffPoint = 0 ;
CurrBuff[CurrBuffPoint] = analogRead(CurrentPin) ;
CurrBuffSum = 0 ;
for(int i = 0 ; i < MaxCurrBuffPoint; i++)
{
CurrBuffSum += CurrBuff[i] ;
}
Current = CurrentMuly * (float)CurrBuffSum / MaxCurrBuffPoint ; 
Serial.println(Current,3); 
}


void UpdateDisplay()
{
ReadCurrent() ;
display.clearDisplay() ;
display.setTextSize(1) ;
display.setTextColor(WHITE) ;
display.setCursor(0,0); display.print("*****  SUNGMOD  *****") ;
display.drawLine(0, 12, 128, 12, WHITE) ;

display.setTextSize(2) ;
// VOLTAGE
display.setCursor(10, 21);
if (SetVolt < 99.999) display.print(" ");
if (SetVolt < 9.999) display.print(" ");
display.print(SetVolt,3);
display.setCursor(104, 21);
display.print("V");
// CURSOR
display.setCursor(10, 26);
if(CursorPos == 1) display.print(" ");
if(CursorPos == 2) display.print("  ");
if(CursorPos == 3) display.print("    ");
if(CursorPos == 4) display.print("     ");
if(CursorPos == 5) display.print("      ");
display.print("_");
// CURRENT
display.setCursor(10, 45);
if(Current < 99.999) display.print(" ") ;
if(Current < 9.9999) display.print(" ") ;
display.print(Current,3);  
display.setCursor(104, 45);
display.print("mA");

display.display() ;
}



// /////////////////////////////////////////////////////////////////////
// S E T U P
// /////////////////////////////////////////////////////////////////////


void setup() 
{
Serial.begin(115200);

Wire.begin() ;

pinMode(RotaryEncoder1, INPUT_PULLUP) ;
pinMode(RotaryEncoder2, INPUT_PULLUP) ;
pinMode(RotaryEncoder3, INPUT_PULLUP) ;

// YELLOW
attachInterrupt(digitalPinToInterrupt(RotaryEncoder2), 
RotaryEncoderISR2, FALLING) ;
// GREEN
attachInterrupt(digitalPinToInterrupt(RotaryEncoder3), 
RotaryEncoderISR3, FALLING) ;

// INIT OLED
display.begin(SH1106_SWITCHCAPVCC) ;

// SHOW STARTUP SCREEN
display.clearDisplay() ;
display.setTextSize(1) ;
display.setTextColor(WHITE) ;
display.setCursor(0,0);
display.println("*****  SUNGMOD  *****") ;
display.drawLine(0, 12, 128, 12, WHITE) ;
display.setTextSize(1) ;
display.setCursor(0,21) ;
display.println("A HIGH VOLTAGE") ;
display.setCursor(0,33) ;
display.println("POWER SUPPLY FOR") ;
display.setCursor(0,45) ;
display.println("PHOTODIODES.") ;
display.setCursor(0,57) ;
display.println("BUILT 23.10.2021") ;
display.display() ;


// DAC AD5667R
// RESET ALL
WriteDAC(0x28, 0x0001) ;
// POWER UP CHANNEL A
WriteDAC(0x20, 0x0001) ;
// SETUP LDAC PIN = BOTH DISABLED
WriteDAC(0x30, 0x0003) ;
// SWITCH ON REFERENCE
WriteDAC(0x38, 0x0001) ;

delay(999) ;

UpdateVolt() ;
UpdateDisplay() ;
}


// /////////////////////////////////////////////////////////////////////
// M A I N 
// /////////////////////////////////////////////////////////////////////

void loop() 
{
// KEY ROTATED ?
// //////////////////////////////////
if(LEFT)
// //////////////////////////////////
{
switch (CursorPos)
{
  case 0 : 
	if((SetVolt - 100.0) >= MinVolt) SetVolt-=100.0 ;
	break ;
  case 1 : 
	if((SetVolt - 10.0) >= MinVolt) SetVolt-=10.0 ;
	break ;
  case 2 : 
	if((SetVolt - 1.0) >= MinVolt) SetVolt-=1.0 ;
	break ;
  case 3 : 
	if((SetVolt - 0.1) >= MinVolt) SetVolt-=0.1 ;
	break ;       
}  
UpdateVolt() ; 
delay(59) ;
READY = true ;
LEFT = false ;
RIGHT = false ;
}


// //////////////////////////////////
if(RIGHT)
// //////////////////////////////////
{    
switch (CursorPos)
{
  case 0 : 
	if((SetVolt + 100.0) <= MaxVolt) SetVolt+=100.0 ;
	break ;
  case 1 : 
	if((SetVolt + 10.0) <= MaxVolt) SetVolt+=10.0 ;
	break ;
  case 2 : 
	if((SetVolt + 1.0) <= MaxVolt) SetVolt+=1.0 ;
	break ;
  case 3 : 
	if((SetVolt + 0.1) <= MaxVolt) SetVolt+=0.1 ;
	break ;       
}
UpdateVolt() ;
delay(59) ;
READY = true ;
LEFT = false ;
RIGHT = false ;
}


// //////////////////////////////////
// KEY PRESSED ?
// //////////////////////////////////
if(!digitalRead(RotaryEncoder1)) 
{
CursorPos += 1 ;
if(CursorPos > 5) CursorPos = 0 ;
delay(199) ;
}    


UpdateDisplay() ;
delay(59) ;


}


// /////////////////////////////////////////////////////////////////////
// INTERRUPT SERVICE ROUTINES
// /////////////////////////////////////////////////////////////////////

void RotaryEncoderISR2()
{
// YELLOW
if(READY)
{
LEFT = false ;
RIGHT = false ;
byte autre = digitalRead(RotaryEncoder3) ;
if (autre > 0) RIGHT = true ;
if (autre < 1) LEFT = true ;
}
}

void RotaryEncoderISR3()
{
// GREEN
if(READY)
{
LEFT = false ;
RIGHT = false ;
byte autre = digitalRead(RotaryEncoder2) ;
if (autre > 0) LEFT = true ;
if (autre < 1) RIGHT = true ;
}
}


// /////////////////////////////////////////////////////////////////////
// END OF FILE.
// /////////////////////////////////////////////////////////////////////

✈ Performance

Voltage Drift @ 259.0 V, current drawn was 1.0 mA. First 9 hours after Power On.

A note on Arduino Nano :
We first used the Nano Every, but it turned out, that the 5 V regulator (MPM3610) was somehow unable to supply the AD5667R. Switching to the original Nano (LM1117IMPX-5.0) solved this problem. (Without redesigning the board).

✈ Share your thoughts

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t₁ = 7299 d

t₂ = 260 ms