invert PWM output (18F4431)

webgiorgio · Joined: 02 Oct 2009 Posts: 123 Location: Denmark

Hi,
I use a 18F4431 to make a PWM on a six pulse two levels converter, using set_power_pwm_duty().
The gate driver works that when the output of the PIC is high, the switch is open.

Example of a transition:
-PWM1 is 1 and PWM2 is 0.
-PWM1 goes low
-dead time 500ns
-PWM2 goes up

Which in the power side became:
-IGBT1 is open, IGBT2 is close
-IGBT1 close
-dead time 500ns
-IGBT2 open

So...there is a short circuit! Exclamation

I would like to have the opposite of the signal which is actually generated in the pins PWM1 and PWM2. How can I do?

asmboy · Joined: 20 Nov 2007 Posts: 2128 Location: albany ny

i can't comment on the logic of of you program

but what you want is easy with 1/3 of a 74HCT04 connected between the PIC and your drive line ;-))

Ttelmah · Joined: 11 Mar 2010 Posts: 19346

Inversion is directly available in the chip.
It is controlled by the HPOL, and LPOL fuses. These control an inverter available for the high, and low output bits respectively. Section 17.11.2 in the data sheet. For CCS, these are:

freesat · Joined: 08 Feb 2011 Posts: 32

u can use xor with (
0xFF if 8 bit res
0x3FF if 10 bit res
0xFFF if 12 bit res

this way u dont need external components to invert.

Ttelmah · Joined: 11 Mar 2010 Posts: 19346

Er. No.
The original poster is talking about a hardware PWM output. You can't use XOR with this. Normally you would have to use an external inverter, as asmboy says.
However in the particular case involved of the ECCP, there are hardware inverters available inside the chip.

Best Wishes

webgiorgio · Joined: 02 Oct 2009 Posts: 123 Location: Denmark