openinverter forum

I have a power stage that utilizes Active low. If I change pwmpol setting to active low it doesn’t change state of PWM. PWM channels seem to still be low at idle when they should be high. Parameter comment states setting needs PWM restart.Silly question but how do you PWM restart... and turn on Active low? Thank you for your time.

Hit stop button then start inverter in some test mode or with start input.

So what I have been doing is while inverter is stopped I change pwmpol parameter to Active low then store parameter using store button.I then start inverter by pulsing start at 12v putting inverter into Run Mode also tested in Manual Mode.When I give the inverter throttle I have no PWM on channels...the PWM drivers just rest at ground potential.I haven’t connected my encoder signals to inverter yet.I’m just testing inverter signals to gate drivers before I connect motor... could this be causing issues for Active low parameter?Also while in Active high channels only reach 1.6 volt peak at full throttle 4095.Is this normal peak voltage or should they be high at 3.3 volts?Thank you for your reply.

In active low mode the outputs are in open drain mode, i.e. they only pull down, not up. The typical applications are gate drive opto coupler whos anode is connected to 5 or 3.3V permanently and they are switched on by pulling the cathode low, typically via a resistor.
You can only see the true peak voltage in active high mode with a scope. If you measure DC at standstill you will get the average voltage of the 50/50 dutycycle i.e. 3.3V/2=1.6V

Okay I understand now ....I didn’t realize the outputs were open drain in active low.I had my led anode tied to open drain when anode should of been connected to vcc via resistor.I was thinking in active low the outputs were open collector and floating at Vcc.Thank you Mr. Huebner for your help.

Johannes if you allow.
Volt inverter works with active low signal in drivers.
I made a mistake drawing my test board for Volt inverter and i cant get my inverter chip to work. For testing i dont want to make another board....
Its pins are misplaced. So i decided to offset that by connecting pins directly by wire. To get good signal i will use 470R pullups on the lines. Do you think those will be enough or need i use larger pullups 220R?
You think Olimex will manage?

Second question is about normal line resistors. In original config those are 220R. So now i should delete them and just wire through yes?
Some pics of the setup and schematic.




tnx

Olimex can output 20mA in open collector mode, so 220 Ohm is a bit overload but should still work. It much depends on your driver how much pull-up you need if any at all. If your drivers anode is connected to 5V you could just wire it directly to Olimex with 220 Ohms. Leaf driver does that.

johu wrote: ↑Sat Feb 22, 2020 3:05 pm Olimex can output 20mA in open collector mode, so 220 Ohm is a bit overload but should still work. It much depends on your driver how much pull-up you need if any at all. If your drivers anode is connected to 5V you could just wire it directly to Olimex with 220 Ohms. Leaf driver does that.

What do you mean, do i need to protect Olimex or the pullup transistor?
I think i saw transistor there before the actual driver and we are pulling its base down when we start PWM.
Before i made an interface board that used SN74L inverter chip with pullups. I could just use positive signal with that setup...

I mean 220 Ohm pullup