60Hz from ECCP in a PIC

[kender]

Folks,

I’d like to drive an H-bridge with 60Hz square waves with large dead time. This is for a DC to AC inverter.

I wonder. As long as PIC's clock is no faster than 13.1Mhz, it should be possible to generate such slow waveform with ECCP. Right :?:

Of course, there are other options for generating a slow square wave:
- generate the waveform with a timer ISR. 60Hz is pretty slow.
- separate hardware dead time generator (GAL or analog RC delay).

- Nick

 

[bigdogguru]

I’d like to drive an H-bridge with 60Hz square waves with large dead time.

I wonder. As long as PIC's clock is no faster than 13.1Mhz, it should be possible to generate such slow waveform with ECCP. Right :?:

Of course, there are other options for generating a slow square wave:
- generate the waveform with a timer ISR. 60Hz is pretty slow.
- separate hardware dead time generator (GAL or analog RC delay).

A PWM frequency of 60 Hz is at or below most PIC ECCP modules capabilities with commonly used system clock rates.

What is the specific model of PIC you intend on using in your design?

What control do you require over various characteristics of the PWM?

What other tasks are assigned to the device?

In past commercial projects, I have utilized a timer ISR to generate as many as a dozen independent channels of PWM in the 50Hz range.

I found it more advantageous to operate the PIC at a higher system clock and employ a timer ISR, rather than lower the system clock to a range where the CCP module can effectively generate 50Hz PWM. Of course, I'm basing this opinion on my own past experiences, as I do not know the fully details of your project.

BigDog

 

[kender]

Frankly, I’ve posted the original question primarily for the purposes of cultural enrichment.

The PIC could be PIC18F1220. Other than driving the 60Hz H-bridge, it will be sampling user inputs, temperatures. It wouldn’t be overloaded with tasks. Generating 50Hz with timer ISR would work.

- Nick

 

[andre_luis]

...Of course, there are other options for generating a slow square wave:
- generate the waveform with a timer ISR. 60Hz is pretty slow.

Don´t worry.

I had successfully designed an inverter for a sinusoidal output UPS at 60Hz w/ PIC16F877 PWM module, where steps changes were triggered by Timer Interruption. I used 32 steps per entire cicle, and an empirical dead time slower than 1ms.

 

[kender]

I had successfully designed an inverter for a sinusoidal output UPS at 60Hz w/ PIC16F877 PWM module, where steps changes were triggered by Timer Interruption. I used 32 steps per entire cicle, and an empirical dead time slower than 1ms.

Did your inverter work like a Class D amplifier?

 

[andre_luis]

Kender,



No analog circuitry were used. PWM generation were performed by software only, with duty-cicle timer mapped on a lookup table.

Bellow, you can find the tool I used for generate values to be stored at microcontroler memory :