High Voltage Converter And Flashtube (Part 2)

1/*
2  High-Voltage Converter and Flash-Light
3  ======================================
4
5  Control a DC-DC converter to generate High Voltage for Flash and trigger flashlight  once the required 
6  working-voltage is reached. This project uses an Arduino  Micro (5V power) with Aref connected to a voltage 
7  of 4.096 Volts. Pin numbers  refer to the Arduino Micro Pin numbering
8
9  Revision History
10  ----------------
11  2017-06-12 wasc High voltage generation code
12  2017-07-09 wasc Added code for  triggering flash-light 
13  2017-07-28 wasc reformatted to fit with the published  paper
14
15  ------------------------------------------------------------------------------------------------------------------
16*/
17
18
19//  define constants and variables with global scope in this module
20
21// Part 1:  High Voltage boost converter
22const int PWM11 = 11;                  // this PWM  (Timer-Counter 0) can be configured to run quite fast, see setup()
23const int  HighVoltageInput = 6;        // Analog 6 input (A6) is used to read the high voltage  value
24const int MaxPulseWidth = 255;         // Maximum value for the pulse width  setting (hardware determined)
25const int BoostPulseWidth = 210;       // Pulse  width to be used in PWM when HV is generated 
26const int SleepPulseWidth = 3;         // Pulse width to be used in PWM when HV has reached working value
27const  int MaxHighVoltageValue = 445;   // this is the value to set the expected High Voltage  
28                                       // 110 = approx. 50V
29                                       //  220 = approx. 100V
30                                       // 445 = approx. 200V
31                                       // 560 = approx. 250V
32const int HVhysteresis  = 10;           // To ensure sufficient trigger pulse width for thyristor, trigger  pulse will end 
33                                       // only when high-voltage  has decreased by hysteresis value
34
35// part 2: electronic flash-tube
36const  int FlashPin = 7;                // Digital Pin 7 is used as output to fire the  flash
37
38
39
40// ----------------------------------------------SETUP-------------------------------------------------------------
41//  This function is executed one single time at the start of the microcontroller (HW&SW  initialisation)
42void setup() {
43
44  // Set Arduino Micro Pin D11 as PWM-output  and set the prescaler of Timer/Counter 0 to 1x to allow 65kHz
45  pinMode( PWM11,  OUTPUT);
46  TCCR0B = 0x01;                // This will result in a frequency of  about 65 kHz at PWM11
47                                // This changes the predefined  Arduino environment -- see hardware manual
48                                //  INFO: This changes also the delay() function which provides much shorter delays  now!
49
50  // use the 4.096 Volts reference at Aref pin
51  analogReference(  EXTERNAL );
52
53  // set Digital Pin 7 as output
54  pinMode( FlashPin, OUTPUT);
55  digitalWrite(FlashPin, LOW);  // Just to be sure the Thyristor will not be triggered  yet
56
57}
58
59
60
61// ------------------------------------------------------LOOP-------------------------------------------------------
62//  This function is executed repeatedly forever (make sure it can run through quickly  and will not be stuck in a waiting loop)
63void loop() {
64
65  // define some  variables to be used here
66  int PulseWidth;                     // the pulse  width to be set in the PWM, computed by algorithm below
67  int HighVoltageValue;               // the ADC reading for the high voltage 0 = 0V to 1023 = 409.5V
68  
69
70  // This is the control section to control the generation of the high-voltage.  A timer of the Arduino is used as PWM 
71  // to generate the pulses for the simple  boost converter. The microcontroller generates the pulses and controls the pulse  
72  // width to generate the desired high voltage value.
73
74  // measure the  high voltage value with analog input
75  HighVoltageValue = analogRead( HighVoltageInput  );                  // will be used for setting the required pulse width of the  PWM
76                                                                      //  as well as (in this sample code) to trigger the 
77                                                                      //  flash-light when working voltage is reached
78  
79  //now compute the required  pulse width
80  if (HighVoltageValue <= MaxHighVoltageValue) PulseWidth = BoostPulseWidth;  // Full Pulse width while high voltage is below target value.
81  else PulseWidth  =SleepPulseWidth;                                           // Once high voltage  reaches target voltage, reduce 
82                                                                              //  pulse width so far as to disable the Power FET
83                                                                       
84  // now set the PWM to the desired pulse width
85  analogWrite( PWM11, (MaxPulseWidth  - PulseWidth) );         // Note: Pulse is inverted by hardware to ensure proper  operation 
86                                                              // when  pin is tri-stated (e.g. at startup)
87
88 
89  // Trigger flash when expected  high voltage is reached. This results in a 'traffic flashlight'. 
90  // Here would  be the place to trigger the flash for another reason, e.g. based on an photosensor  signal, electrical contact etc.
91  if (HighVoltageValue >= MaxHighVoltageValue  )    digitalWrite(FlashPin, HIGH);                      // trigger flash when expected  voltage is reached
92  else if (HighVoltageValue < (MaxHighVoltageValue - HVhysteresis))  digitalWrite(FlashPin, LOW);     // stop trigger pulse only when the high voltage  
93                                                                                                      //  has decreased below the working voltage
94                                                                                           
95}
96
97
98INFORMATION
99Here  we use Arduino's Digital Output 7 is used for the generation of the trigger pulse  to fire the flash-tube. In this example code the pulse is started at the point in  time when the expected working voltage of the flash-tube is reached. To ensure a  sufficiently wide trigger pulse at the gate of the thyristor, the pulse will be  turned off only at the point in time, where we can be sure, that the thyristor is  fully conducting: This is the case, once the high voltage has been sinking by some  volts (HVhysteresis):
100if (HighVoltageValue >= MaxHighVoltageValue )    digitalWrite(FlashPin,  HIGH);
101else if (HighVoltageValue < (MaxHighVoltageValue - HVhysteresis))  digitalWrite(FlashPin,  LOW);
102This simple code results in a flash which is repeatedly firing (e.g. as  you find it in traffic warning lights). By changing the code you can easily fire  the flash under different circumstances, e.g. when an opto-coupler is activated  etc.
103