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Old 3rd June 2003, 01:06 PM   #21
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Quote:
Originally posted by fr0st

Another forum member surgested that having inputs chokes would be a bad idea since they increase transients and that the switcher should get rid of any alternator hum on its own.
opinions?
if they suggest that an input choke increases transients then they haven't taken physics.
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Old 3rd June 2003, 01:20 PM   #22
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Default Re: Re: Re: 2kW Switcher

Quote:
Originally posted by BenY


Dan,
How do you select a toroid for 50Khz operation,What permiability should one select for optimal results?

Thanks.
Yuval.
I received the design manuals that Magnetics inc. publishes. They have all the info on how to select a core. Most ferrites will operate at 50Khz, it's just a matter of winding the transformer correctly.


Quote:
Originally posted by jackinnj
if they suggest that an input choke increases transients then they haven't taken physics.
Yes, I have taken physics, and I have tried filter chokes on the input to automotive amplifiers. I have done so with a scope on the input to the amplifier. If there is not enough input capacitance in the amplifier, with the high frequency currents the added inductance in the choke will see the transient currents from the switching transformer, therefore, generate transient voltages.

The noise on the amplifier is probably not getting through the power leads to the amplifier, it's most likely a ground loop issue between battery, head unit, and amplifier. Star grounding as suggested by one of the other members is the best solution.

-Dan
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Old 3rd June 2003, 02:21 PM   #23
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Default Ground Loops & Toroids

Ground Loops:

I have the worst time with alternator whine, and I can tell from experience that a good grounding shceme will take care of almost any anternator-induced whine. Yes indeedy, star-grounding is the best way to go, but it is a good idea to keep input grounds (on the primary side of the PSU) separate from the output grounds (the secondary, or audio side of the PSU) to further remove the audio circuitry from the noise source. then run a 10-ohm resistor from the RCA input jacks of the amp to vehicle (primary-side) ground to tie it all together. Bypass with a 0.01uF cap is there's still a little noise.

Toroids:

Amidon Associates of CA suggests that you use their ferrite material #77mix with a permeability of u=2000 @ 20kHz. They have a graph to extrapolate what permeability # to use at higher frequencies (like 45-50 kHz), and it is all pretty straightforward.

Best of luck![SIZE=1]
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Old 3rd June 2003, 06:57 PM   #24
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Default Re: Re: Re: Re: 2kW Switcher

Quote:
Originally posted by dkemppai


Yes, I have taken physics, and I have tried filter chokes on the input to automotive amplifiers. I have done so with a scope on the input to the amplifier. If there is not enough input capacitance in the amplifier, with the high frequency currents the added inductance in the choke will see the transient currents from the switching transformer, therefore, generate transient voltages.

-Dan
I meant the "power" connection "inputs" of the amplifier, sorry, my mistake. The transients go "every which way but loose".
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Old 4th June 2003, 12:22 AM   #25
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Default Re: Re: Re: Re: Re: 2kW Switcher

Quote:
Originally posted by jackinnj

I meant the "power" connection "inputs" of the amplifier, sorry, my mistake. The transients go "every which way but loose".
Also meant the power inputs. 12 volts in to the amp. The choke used was several paralled #12 coppers on a core...

Now, a low pass filter (choke in series with a good cap bank.. ..then you may be onto something! But, even then, I still think grounding is a more important issue.

I think we're on the same page I hope so, anyway

-Dan
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Old 4th June 2003, 01:53 AM   #26
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dkemppai,
can u please post the schematic of the 2kw switcher here? thanks
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Old 4th June 2003, 05:00 AM   #27
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Default Grounding Inputs & Outputs

I think we're all singing from the same sheet of music , and the coil/cap thingy is a great idea. Nuttin' like brute force where necessary!

What I mean wrt input/outputs is in the supply: 12V-side is the inpit, and the +/-V is the output side. The RCA inputs to the amp should be tied to the power supply's output ground, then to the psu's input (12V) ground via a 10 ohm resistor and a 0.01uf cap in parallel.

N8XO
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Old 4th June 2003, 08:54 AM   #28
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Is it possible to parrallel transformer primarys but not secondaries in having a transformer for each rail?
or... would it require to have a set of MOSFET's per transformer to eliminate any current sharing issues?
Thanks for all the tips
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Old 4th June 2003, 11:13 AM   #29
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Arrow Paralleling

Need Separate MOSFETS AND PWM Chip, too. Not to worry, though the PWM chips should be synchronizable. Master chip provides clock frequency to slave chip. Actually saves components on 2nd PWM chip.
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Old 4th June 2003, 03:15 PM   #30
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Default Push-Pull vs. Full Bridge topology issue

ai" :

"Problem with H-bridge is that you have two pairs of switching devices in series with each other, on each side of the transformer. Therefore conduction losses double, so it's not as efficient. H-Bridge is great at high input voltages, where currents are small, and conduction losses are minimal."

Be careful when making direct comparisons. Although the push-pull has only one FET conducting at a time, vs. two FETs for the full bridge, the FETs in the push pull circuit must withstand **twice** the supply voltage when off, as opposed to the full bridge topology, whose FETs only need withstand the supply voltage. Therefore, the push-pull topology requires FETs with twice the drain-source breakdown voltage rating vs. full bridge. Higher voltage FETs always have higher Rdson for the same die size. The result is increased conduction losses. Also, switching losses are higher for push-pull due to the double voltage present at drain to source. It is well known to all skilled in the art of SMPS design, that full bridge can handle higher power requirements better than push-pull. Although I feel that push-pull is a very good choice in this application, it is incorrect to assert that full bridge incurs greater losses. To say that full bridge is "not as efficient" is dead wrong. Why then, does every power supply OEM and designer insist on full bridge for the highest power requirements? As far as transformer isolated converters go, the pecking order has always been from lowest to highest power as follows. Flyback, forward, push-pull, half bridge, full bridge. I just thought I should set the record straight. Best regards.
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