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Old 17th March 2005, 04:14 PM   #21
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Default current sink capabilities

Hi all,


Smarmydog, why are you using the 3906's?, they can only sink 200mA, while the outputs of the sg3525 can sink 500mA. Do you really get a speed up at the mosfet turn-off placing that transitors instead running them directly from the controller?
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Old 17th March 2005, 04:38 PM   #22
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Good eye J.Carlos! The transistor in the actual circuit is an On Semi MPS6652. I grabbed the 3906 part from a Protel library and didnít change the part value. Iím with Alme Ė the magnetics design is where the real challenge is. Hopefully after I nail that I wonít need any special gate drive stuff.

-Casey Walsh
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Old 17th March 2005, 05:26 PM   #23
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Quote:
I grabbed the 3906 part from a Protel library and didnít change the part value
That's what I was thinking

By the way, did you notice an amplitud increment on the "noise" at the output voltage with that fastest turn-off time?, many car audio amplifiers that I have seen uses relatively long times to turn-on and turn-off their mosfets, maybe 'cause that's the way they meet EMC.


Greetings from Mťxico

Juan Carlos.
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Old 17th March 2005, 06:01 PM   #24
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I haven't scrutinized the conducted emissions on the battery connection yet, but I do have a CLC filter there that should help a bit.

-Casey Walsh
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Old 18th March 2005, 07:28 AM   #25
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Got my design now fellas. Going with a SG3525, with 3 IRFZ44 per rail, using the two inch toriod core from my blown amp (yes, its ferrite, 5 turns for each primary, and a +/- 60V output), got highspeed diodes from blown amp that still work(25nsec), and capacitors(about 10000uf on the input and 4500uf on each output rail), using a frequency of 37khz with the totem pole transistor out puts off the pwm and 10ohm resistors going into each... will get results back to you in a few weeks, maybe even with a few pictures...

two quick questions, input choke value(thinkin 100uH), and i read earlier in this thread that someone shorted the delay to reduce dead time to a minimum, is this advised???

michael
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Old 18th March 2005, 11:29 AM   #26
Alme is offline Alme  Ukraine
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Michael, I think such a choke 100uH, which will accept 50A (peak even more?) current without saturation, is quite large. Usually they use a choke in battery wire of up to 10uH to improve EMC. You will need its wire cross-section not less than 5sq.mm.
If you use some 2A transistor followers at PWM outputs, it's possible to decrease deadtime to its minimum. Without them, keep additional discharge resistor of say 100 ohm.
Also you can try to decrease switching frequency to some 27kHz (if there's really 2-inch core, you'll get slightly higher efficiency).
And report about your progression
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Old 20th April 2005, 12:47 AM   #27
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any progress on the pcbs yet?

I really want to build this but I'm not good enough at PCB design.
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Old 24th April 2005, 06:47 AM   #28
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Hi Everyone!,,

I am actually working on a 500W SMPS for a Tripath Class D Amplifier. The PCB layout is complete and I am awaiting the PCB from the manufacturer.

I am using a PSoC microcontroller to create a dual PWM with deadband at 200KHz. These signals are going into non-inverting 6A MOSFET drivers. The drivers switch the MOSFET through 4.7 Ohm gate resistors. The MOSFETs then switch on a custom wound toroidal transformer. Owen Columbus (diy member opc) painstakingly wound the transformer, which is composed of 22 primary turns and around 80 secondary turns, it's beautiful!

I have a bank of capacitors 26400uF 25V on the input a total of 40mH of power inductors and 5440uF capacitors for the output filter. The output is rectified with ultra high speed switching diodes. The DC voltage on both rails is monitored via a zener diode based feedback into an opto isolator. The output of the optoisolator is fed back into the microcontroller's ADC input. The PWM's period is then adjusted accordingly when the voltage starts to exceed the limit.

The problem with the design is the expense! The capacitors alone cost 50$, which all are surfacemount electrolytics. I have some pretty crazy via work and wire to solder to unmasked traces for it to handle the current..

I will test the design in roughly two weeks and will post the PCB here when complete with full part list and program. I can probably program some microcontrollers if someone is interested. I guess we will see how the SMPS performs first!

Steve
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Old 24th April 2005, 11:29 PM   #29
Eva is offline Eva  Spain
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I think it's quite a crazy idea to build such a circuit from scratch into quality finished boards without previous testing and prototyping
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Old 25th April 2005, 12:07 AM   #30
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Quote:

I think it's quite a crazy idea to build such a circuit from scratch into quality finished boards without previous testing and prototyping


No guts no glory baby
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