I have a bunch of comments and questions. TIA to anyone who has the patience to read them all and shed some light :-)
Quote:
quote (1)
Al Skierkiewicz, Post 22:
in the Jaguar, only the high side FET is PWM while the low side FET is ON for direction.
|
Would this only be for the tan Jag, not the black? see quote (4)
Quote:
quote (2)
Al Skierkiewicz, Post 22:
The Brake Mode will turn on both low side FET pairs in a zero throttle condition
|
In earlier posts, it was stated that for locked antiphase there would be a 50% fwd/rev duty cycle for a zero command. This would seem to preclude turning on both low-side FETs simultaneously unless there were special logic to override the locked antiphase for the zero-throttle condition. Perhaps you are referring to the tan Jags only?
Quote:
quote (3)
Al Skierkiewicz, Post 22:
The locked anti-phase that Eric refers to is a condition where the controller is supplying a 50% duty cycle of forward and reverse commands... Please note that this could be a relatively large current demand as current is flowing in the motor all the time.
|
The current in the motor under this condition should be very nearly zero. The current never has a chance to rise to appreciable levels since the voltage is changing directions so fast. The motor inductance is the key here.
Quote:
quote (4)
Gdeaver, Post 19:
Black jags switch different than tan jags. The tan jags are high side switchers. The black jags are locked antiphase. Allegro makes a nice fet full bridge automotive driver chip. The A3941K. The data sheet gives a good description of the different ways the Fet bridge can be driven. May be it will help.
|
"Black jags switch different than tan jags. The tan jags are high side switchers. The black jags are locked antiphase."
I'm not disputing what you said, but could you please provide a link to this information?
"Allegro makes a nice fet full bridge automotive driver chip. The A3941K. The data sheet gives a good description of the different ways the Fet bridge can be driven."
Are you saying that the Black Jags use the Allegro A3941K instead of the Fairchild FAN5109?
Quote:
quote (5)
Geek 2.0, Post 17:
That only makes too much sense, thanks. Where would you possibly draw the line for what works with locked antiphase?
|
It would depend on the motor inductance. Very low motor inductance would require a higher switching frequency. Very high motor inductance would allow a lower switching frequency.
Quote:
quote (6)
Geek 2.0, Post 15:
Okay, for the sake of education (and that I've exhausted the extent of Wikipedia's ability to have a page on every minuscule topic) could someone please give a better definition of locked antiphase? I understand that it's using a PWM where a 50% duty cycle is brake, 100% is full forward, 75% half, 25% half reverse, etc. But maybe an illustration or something to that effect?
|
I think what you described in quote (10) below would be locked antiphase.
Quote:
quote (7)
Geek 2.0, Post 8:
It just seems odd that it's running forward 75% of the time and backwards 25% of the time to go forward at 50%... wouldn't it make more sense to just go forward 50% of the time?
|
I believe EricVanWyck stated in post 11 that locked antiphase gives better fine speed control at low speeds. I'm not entirely sure why this is, perhaps Eric or someone else could elaborate.
Quote:
quote (8)
kamocat, Post 5:
On the Jaguar (unlike the Victor) the H-bridge switches between 12v and 0v, not 12v and "open".
|
Could you clarify what you meant by this? And how does it apply to locked antiphase, and coast mode?
Quote:
quote (9)
Geek 2.0, Post 1:
After carefully studying the datasheet http://media.digikey.com/pdf/Data%20...client_id=5042 for the MOSFET driver, I learned that if the signal coming into PWM is high, HDRV is high (opening the MOSFETs it controls) and LDRV is low (closing the MOSFETs it controls).
|
Is the FAN5109 used only in the tan Jag, or in the black as well?
Quote:
quote (10)
Geek 2.0, Post 1:
If the PWM square waves are inverse of each other (or any other alignment), when one is high and the other is low, current will flow (e.g. when the left side is high and the right is low, current will flow from Q1 to Q4). However, since the wave then inverts, it would then switch which MOSFETs are open, thus switching the motor direction...
|
Is this how the black Jag does locked antiphase, or does it use the Allegro driver?
Quote:
quote (11)
Geek 2.0, Post 1:
There is one other possibility still: What if they aren't putting a PWM input into the PWM pin, but rather the OD (Output Disable) and a HIGH or LOW into PWM, depending on motor direction?
OD pulls both HDRV and LDRV low (closing their MOSFETs) if it is low.
http://img.skitch.com/20100831-dgeux...3h7cmd5ece.jpg
When PWM is HIGH on the left side, then Q1 is open and Q3 is closed. If it is LOW, Q1 is closed and Q3 is open. The same goes for the other side. Then the PWM into OD would close whichever is open when it is low.
|
Does the Jag firmware ever drive the FAN5109 this way?
Is this the schematic for the Black Jag, or the Tan Jag, or both ?