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Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Hi guys, I run into limitation of the enable pin of UCC gate drivers. I experience this problem: Once I set the PWM based interrupter to frequencies over few KHz my coil stops working.
My point is to achieve something similar I already did before but using two TL4894 instead. I used one of TLs to drive the coil in a fixed resonant frequency (170KHz) and the second one was driving the power supply of the first one over FET transitor. The second TL494 was set to 50 KHz with 25% duty cycle and PW audiomodulated. The coil reproduced sounds quite well but with strong 50Hz distortion because it was running in half rectified mains mode – here you can hear my voice reproduced by the coil . Why I cannot use the same approach for the enable pin of UCC? I mean simply setting the interrupter to 50 KHz and audiomodulate it’s PW?
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
Hi Mates,
The ENBL pin on the UCC is significantly slower than IN. I observed this when I had thought it was clever to wire IN/ENBL together to simplify my PCB layout.
Steve Conner also had poor performance from the ENBL pin using it for a dead-time application, IIRC. If you've already made your PCB, you may be able to get away with some mickey-mouse logic on IN, instead.
Tie your ENBL to VCC, put a 10k resistor in series with IN, and allow your ENBL signal to pull it down through a 1N4148, and see if that works any better.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I think the delay time of the enable input of the UCC is something like 60ns vs. 30ns of the input pin. I think you wont notice that in real life... Are you using some kind of feedback? Maybe it doesn't have the time to lock at such high interrupter frerquency.
@Blackplasma: Your circuit can't be used with two UCCs in push-pull configuration, because pulling the interrupter input down results in one UCC output high and the other low, however you want to have both low.
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
Here's the relevant thread with Steve's note: Generating deadtime, second post - ENBL pin is clearly quite picky, avoid where possible...
Dr. Kilovolt wrote ...
@Blackplasma: Your circuit can't be used with two UCCs in push-pull configuration, because pulling the interrupter input down results in one UCC output high and the other low, however you want to have both low.
Thanks Jan, you're right - I only get away with it because I'm hardcore and only use noninverting UCCs on principle.
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Problems with PWM audiomudulation over UCC37321 enable pin
