Create a 20khz PWM signal with 5us dead time for driving h-bridge

Q&A Forum › Category: ESP32 › Create a 20khz PWM signal with 5us dead time for driving h-bridge

ENG asked 3 years ago

I want to create two opposite 20khz PWM signal with 5us dead time for driving h-bridge system, and this is my code.

const int ledPin1 = 12;
const int ledPin2 = 13;

int count = 0 ;
int num = 1 ;
void setup() {
pinMode(ledPin1, OUTPUT);
pinMode(ledPin2, OUTPUT);
}
void loop() {

count++;
switch(num){

case 1:
if(count<=10){
digitalWrite(ledPin1, LOW);
digitalWrite(ledPin2, LOW);
}
else if(count>10){
num=2;
}
break;

case 2:
if(count<=60){
digitalWrite(ledPin1, HIGH);
digitalWrite(ledPin2, LOW);
}
else if(count>60){
num=3;
}
break;

case 3:
if(count<70){
digitalWrite(ledPin1, LOW);
digitalWrite(ledPin2, LOW);
}
else if(count>70){
num=4;
}
break;

case 4:
if(count<=120){ 
digitalWrite(ledPin1, LOW);
digitalWrite(ledPin2, HIGH);
  }
else if(count>120){ 
num=1;
count=0;
         }

break;

}}

but when I test with an oscilloscope. I found some delay when ESP-32 run several cycles. Like the fig.

https://drive.google.com/file/d/1QNZ2ZZtjbOvogMMwLYnJ28dYrukNlOvS/view?usp=sharing

the delay make this wave wider then others, that is unacceptable.
How can I avoid this delay or the other way to create the signal with dead time.

6 Answers

0 Vote Up Vote Down

paulfjujo answered 3 years ago

hello,

Why not using PWM instead of processor cycles counts…
What is the Processor FOSC value (elementary count = cycle duration)
We can not see your figure !

0 Vote Up Vote Down

Sara Santos Staff answered 3 years ago

Hi.
To share a picture, please share a link to google drive, imgur or another server that can host images.
Regards,
Sara

0 Vote Up Vote Down

ENG answered 3 years ago

The image cannot be displayed, so I put the url below.I am trying to generate complementary signals with pwm, is there any examples to refer to?

0 Vote Up Vote Down

Sara Santos Staff answered 3 years ago

Hi.

As Paulo mentioned, have you tried using the PWM API instead?
https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/ledc.html

ESP32 PWM with Arduino IDE (Analog Output)

Or: https://github.com/JoaoLopesF/ESP32MotorControl

Regards,
Sara

0 Vote Up Vote Down

ENG answered 3 years ago

I solved my problem with MCPWM
Use mcpwm_deadtime_enable to generate a 5us dead time. And the signal is very stable.
Thanks for your help

#include "driver/mcpwm.h"
#include "soc/mcpwm_reg.h"
#include "soc/mcpwm_struct.h"

#define MOTO_GPIO1 12
#define MOTO_GPIO2 13

#define MOTOR_MCPWM_UNIT MCPWM_UNIT_0

void setup() {
mcpwm_gpio_init(MOTOR_MCPWM_UNIT, MCPWM0A, MOTO_GPIO1 );
mcpwm_gpio_init(MOTOR_MCPWM_UNIT, MCPWM0B, MOTO_GPIO2 );

#define MOTO_TIMER MCPWM_TIMER_0
mcpwm_config_t pwm_config;

pwm_config.frequency = 20000;
pwm_config.cmpr_a = 0;
pwm_config.cmpr_b = 0;
pwm_config.counter_mode = MCPWM_UP_COUNTER;
pwm_config.duty_mode = MCPWM_DUTY_MODE_0;

mcpwm_deadtime_enable(MOTOR_MCPWM_UNIT,MOTO_TIMER,MCPWM_ACTIVE_HIGH_COMPLIMENT_MODE,50,50);

mcpwm_init(MOTOR_MCPWM_UNIT, MOTO_TIMER, &pwm_config);
}

void loop() {
mcpwm_set_duty(MOTOR_MCPWM_UNIT, MOTO_TIMER, MCPWM_OPR_A,50);
mcpwm_set_duty_type(MOTOR_MCPWM_UNIT, MOTO_TIMER, MCPWM_OPR_A, MCPWM_DUTY_MODE_1);
mcpwm_set_duty(MOTOR_MCPWM_UNIT, MOTO_TIMER, MCPWM_OPR_B,50);
mcpwm_set_duty_type(MOTOR_MCPWM_UNIT, MOTO_TIMER, MCPWM_OPR_B, MCPWM_DUTY_MODE_1); 
}

0 Vote Up Vote Down

Sara Santos Staff answered 3 years ago

Great!
I’ll mark this issue as resolved. If you need further help, you just need to open a new question in our forum.
Regards,
Sara