Modulator with switching voltage regulator

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Modulator with switching voltage regulator

Postby cableman » Mon Mar 13, 2006 9:44 am

Hi,
I came up with the idea,of making a very simple modulator(QRP)with an switching voltage regulator.
For example the LM2677 ADJ(there are a lot of types)
I want to try to feed the Feedback with an audiosignal on the reference voltage.
Maybe it is possible to put a few parallel.
Is there someone who has tryd it before?
I made an order of a sample of the LM2677.
It has to modulate a simple 12Watt transmitter(cristal-74HC240-IRF510)
Or do you say...don't even start,it won't work
Greetings Bert
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Postby WA2WVL » Wed Mar 15, 2006 10:15 pm

Cableman, it seems that it might work provided National has not limited the frequency response in the package. What I would do is put a resistor load on the output equal to your 12w transmitter dc voltage divided by the current it draws. Then I would add an op amp in the feedback loop where r2 is and drive the + side of the op amp with the feedback and drive the - side with capacitor coupled audio. Probably need dc bias on - since output cannot reach zero volts. I am not an expert on these matters but you have my thoughts.
Floyd

PS What DC voltage does your 12w transmitter run on?
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Postby WA2WVL » Wed Mar 15, 2006 11:40 pm

Cableman, I failed to mention that the output L and C must form a lowpass filter (maybe 10khz cutoff) to pass the audio. Common practice is a Butterworth design. Info available in the Radio Amateurs Handbook.
Floyd
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Postby WA2WVL » Thu Mar 16, 2006 8:17 pm

Cableman the LTC3780 might be useful since it is a Buck/Boost which means the output can swing above or below the input voltage.
Floyd
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Postby cableman » Fri Mar 17, 2006 8:10 am

Thanks for the info Floyd.
My sample request is not aproved,and all the switched regulators i can get here in Europe can not get under the 5V.
So now i thought of something new.
I want to use the IR2117 to drive 1 irfp240(or simular)
Now i am looking for a chip with audio in and PWM out.
Steve used 1 ,but i can't find it here.
So are there simular chips who can do the same.
I can build the other design of Steve but i want it as small as possible.
I build a SMD 15Watt transmitter of only 25x100mm
Here is a pic of the "monster"
Image[/img]
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Postby W1DAN » Fri Mar 17, 2006 9:45 am

Hi Cableman:

I have used an IR2117 in my early days. I had a problem with minimum pulse width (it would get to a small width, then disappear). That problem may have been with my charge pump cap being too small. So the IR2110 may be a good chip to use dispite my problem.

Steve uses a UCC25701 as noted here:

http://www.classeradio.com/simplified_pwm_generator.gif

I built Steve's full PDM modulator with great success, I notice that the diodes dissipate more power than the switching transistors.

I eventually want to play with the buck configuration and bi-phase PDM.

Good luck and keep us posed on your progress.

73,
Dan
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Postby cableman » Sat Mar 18, 2006 7:26 am

Hi Dan,
Yes i saw the schematic of Steve,but i cant buy the UCC25701 here.
That's my main problem here,to get the parts.
So as an absolute beginner at class E it is difficult for me to look for simular parts who will do the job too.
I am reading a lot on Steve's site and every time i understand a bit more of Class E and PWM.
This morning i found an nice little webshop,right here in Holland.
They sell the MC34151 PWM generator for about 1.5$
I think i try this one
They also sell the MC34151
Now i am looking for a suitable optocoupler.
Maybe someone can advise me?
This is the webshop....http://www.voti.nl/winkel/catalog.html ....under "overige IC's"
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Postby WA2WVL » Sat Mar 18, 2006 7:32 pm

Cableman, what voltage does your 12W amplifier run on. Is it 13.6?

Floyd
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Postby cableman » Sun Mar 19, 2006 4:12 am

Floyd,
Yes at carrier the voltage is 12V.
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Postby WA2WVL » Sun Mar 19, 2006 9:04 pm

Cableman:

TI is making a Class D Audio amplifier (TAS5424) designed for 13v but it is so new I couldn't find a data sheet.

Also SGC/Thompson Makes a 25 Watt Class D Amplifier 19.6mm wide.

Floyd
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