I need a high current DC to AC
- Thread starter manie
- Start date
Manie: is that a colpitts osc? There are a few circuits. Simple ones are fine,
but may have problems being consistent if you build a million of them, may drift, and have sensitivity to supply voltage and load changes.
There are some sine synth chips out, mostly for RF work, but some go down pretty low, don't have any part numbers right now. I have used 2 improved techniques in the past, but if was to do today would probably hunt for a single chip that does it.
The first method used a crystal locked square wave clock to control a switched capacitor filter, the clock speed was about ten times faster than the "signal" freq, so you need two clocks. I was getting some tiny steps in the waveform, the manuf said it was because I did not have a ground plane board. Maybe, I just added an rc filter and it cleaned it up.
The second trick was a PIC chip spitting out a sine table into a D/A. I got clever and realized all I needed was 0-90 degrees data. For the second quadrant, played it backwards!
For the 3rd and 4th, repeat, but switch polarity. This solution actually was never used, it was for a giant UPS inverter. Just playing around...
Anybody like my amplifier??? It really is just an extension of the "boosted opamp" circuit you can find in databooks, the npn/pnp driver. It gets weird with the transformer coupling, but is fun. I've been building circuits and reading about them for 4 decades, ham radio, shortwave, Heathkits, school. Have never seen that config before. No one asked why there is no base resistor. It works without it. If the output pair (I think I paralleled a couple) is driving 10A, with a beta of 10, then a 1A base current is about right, which the EL2008 can supply. At lower loads it might be overdriven. If I make another one will try a base resistor. Any other suggestions are welcome.
but may have problems being consistent if you build a million of them, may drift, and have sensitivity to supply voltage and load changes.
There are some sine synth chips out, mostly for RF work, but some go down pretty low, don't have any part numbers right now. I have used 2 improved techniques in the past, but if was to do today would probably hunt for a single chip that does it.
The first method used a crystal locked square wave clock to control a switched capacitor filter, the clock speed was about ten times faster than the "signal" freq, so you need two clocks. I was getting some tiny steps in the waveform, the manuf said it was because I did not have a ground plane board. Maybe, I just added an rc filter and it cleaned it up.
The second trick was a PIC chip spitting out a sine table into a D/A. I got clever and realized all I needed was 0-90 degrees data. For the second quadrant, played it backwards!
For the 3rd and 4th, repeat, but switch polarity. This solution actually was never used, it was for a giant UPS inverter. Just playing around...Anybody like my amplifier??? It really is just an extension of the "boosted opamp" circuit you can find in databooks, the npn/pnp driver. It gets weird with the transformer coupling, but is fun. I've been building circuits and reading about them for 4 decades, ham radio, shortwave, Heathkits, school. Have never seen that config before. No one asked why there is no base resistor. It works without it. If the output pair (I think I paralleled a couple) is driving 10A, with a beta of 10, then a 1A base current is about right, which the EL2008 can supply. At lower loads it might be overdriven. If I make another one will try a base resistor. Any other suggestions are welcome.
Jglenn: C-boards are "just up the road" form me, well about 350kM (220 miles) !! Have spoken to the owner once regarding small production runs. He seems very capable. In your Bass amplifier, on the output stage, I will have to couple up to say +12, -12V or whatever voltage I think is good ? The EL2008 I must google to see about supplier etc. Could I use the Oscillator output straight into the amplifier stage ? Also, will Picaxe be able to do same as Pic chip on Sine table, maybe once into an EEPROM, then just read and feed DAC for Sine Wave ? With regard to circuit mods, don't think I can comment yet.... maybe in a few years.....
Dr.A: Good to know the "magic" works, but if outside Picaxe scope then I probably won't try it at this point. Jglenn seems to have done something similar already (see his post above).
Dr.A: Good to know the "magic" works, but if outside Picaxe scope then I probably won't try it at this point. Jglenn seems to have done something similar already (see his post above).
Jglenn: I believe its called a Wien-Bridge oscillator. The 4k7 resistor (collector load resistor) on Q2 also forms part of the series connection with the 100nF (right of Q2) and these are seried with 4k7 parrallel with 100nF (bottom right) again which is the classic Wien-Bridge structure. Feedback is from there back to base of Q1. Output (not on schematic - SORRY) is from junction between Q2 collector and its 4k7 load resistor and 0V.
The EL2008 is an older part, it seems available from the specialty houses, some want a $250 min order. There may be an equiv. I do have a couple around somewhere it you want to try one. In looking at digikey, I found a class D
amp which will run cooler:
http://search.digikey.com/scripts/DkSearch/dksus.dll
TPA032D01DCA
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-2461-5-ND
It will drive 10W into 4 ohm, costs $14, nasty package but can be soldered.
I also used some TO220 amps from LTC, can't remember the whole part #,
but was LT10XX something. The EL2008 was a lot more powerful. I'd search
some more now, but it is work, and it's friday!!!!!
Oh yeah, the LM324 input buffer of my design will accept almost
any input, there is a dc blocking cap, it's not much load impedance, just tie it to your circuits output and see what happens!
You might be able to get the PICAXE to generate a sinewave, but I'd start with simpler osc circuits like you have. Much less time, trouble, and cost. There is the old 8038 chip, but the sine wave is not exact. Or just cheat and use a step down xfmr off the mains, for testing.
amp which will run cooler:
http://search.digikey.com/scripts/DkSearch/dksus.dll
TPA032D01DCA
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-2461-5-ND
It will drive 10W into 4 ohm, costs $14, nasty package but can be soldered.
I also used some TO220 amps from LTC, can't remember the whole part #,
but was LT10XX something. The EL2008 was a lot more powerful. I'd search
some more now, but it is work, and it's friday!!!!!
Oh yeah, the LM324 input buffer of my design will accept almost
any input, there is a dc blocking cap, it's not much load impedance, just tie it to your circuits output and see what happens!
You might be able to get the PICAXE to generate a sinewave, but I'd start with simpler osc circuits like you have. Much less time, trouble, and cost. There is the old 8038 chip, but the sine wave is not exact. Or just cheat and use a step down xfmr off the mains, for testing.
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Who's looking ? Thats not cheating, its being either CLEVER or INVENTIVE ! Point is, you have to drive it somehow at sometime..... might as well work it out especially since you must "step up" again to reasonable voltage....
Problem here is that this output is a Sin Wave yes, but never crosses zero... +12V/0V so its a "sined" bit of DC, I need that zero crossing for 'TRUE" AC.
I have never heard of magic sinewaves before, but they look to me exactly like Class D outputs.
Commercial units operate in the Megahertz range and require fairly specialised hi-frequency components. But if you only need to amplify a 50Hz sine, then you should be able to brew your own using cheap components. Maybe an op-amp to generate the sine wave, another to generate a triangle, a comparator and a couple of power transistors.
I’m not sure how much power will be lost to harmonics in the transformer coil, but I think the problem get’s smaller with higher switching frequencies.
Commercial units operate in the Megahertz range and require fairly specialised hi-frequency components. But if you only need to amplify a 50Hz sine, then you should be able to brew your own using cheap components. Maybe an op-amp to generate the sine wave, another to generate a triangle, a comparator and a couple of power transistors.
I’m not sure how much power will be lost to harmonics in the transformer coil, but I think the problem get’s smaller with higher switching frequencies.
premelec
Senior Member
It's time to re-mention the PIC one bit sound generator -
http://www.romanblack.com/picsound.htm -
The magic sine stuff was written up in Circuit Cellar some years ago and is certainly interesting - I don't know what all the 1 to 5KW sine power inverters use these days but it could be something like this I think. I recently got a 14 W class D audio amp from China ($12US) to see if it would work well driving small motors and such... 2 channels...
http://www.romanblack.com/picsound.htm -
The magic sine stuff was written up in Circuit Cellar some years ago and is certainly interesting - I don't know what all the 1 to 5KW sine power inverters use these days but it could be something like this I think. I recently got a 14 W class D audio amp from China ($12US) to see if it would work well driving small motors and such... 2 channels...
Lemme know when the parts come! Don Lancaster is an old hobbyist writer, he had a column in Popular Electronics, until it failed. Hobby electronics is close to dead in the USA, compared to the 1950's to 70's. He did often have "different" concepts, I remember one about wavelets. Forrest Mims is another well known writer. He made the mistake of writing Bell Labs, describing his idea of a fiber optic cable with LED's at each end, used them as TRANSCEIVERS, seems they can send and receive. Surprise, the cops, lawyers, etc showed up at his house and searched it, seems Bell Labs had a top secret project going on that!
Manie, a full pwm synthesised sine wave is a lot more work, but audio amps can in theory do it, drive motors or transformers. Look up current mode switching power supplies, have an advantage over voltage mode. But your circuit layout will become critical, and the design difficulty goes up quite a bit. I'd stick with linear for now.
Manie, a full pwm synthesised sine wave is a lot more work, but audio amps can in theory do it, drive motors or transformers. Look up current mode switching power supplies, have an advantage over voltage mode. But your circuit layout will become critical, and the design difficulty goes up quite a bit. I'd stick with linear for now.
Here is an interesting inverter using the UC3525, another dated chip in my collection! Good theory on making the transformer. He never really says what output ac voltage he's getting, may be more than 120V. It is square waves.
http://www.fusor.net/board/getfile.php?bn=fusor_files&att_id=1044
http://www.fusor.net/board/getfile.php?bn=fusor_files&att_id=1044
Lot's of useful info in this PDF document: http://www.irf.com/product-info/audio/classdtutorial.pdf
Note. The filters shown on the output can probably be ignored for your app. Just dump the extra HF power into the transformer. It might run a little hotter, but it’s easier. If it runs too hot, you might need to reconsider filtering, or use higher frequencies, or both.
Note. The filters shown on the output can probably be ignored for your app. Just dump the extra HF power into the transformer. It might run a little hotter, but it’s easier. If it runs too hot, you might need to reconsider filtering, or use higher frequencies, or both.
Nice write up. But a class D amp is probably impossible for a beginner to build, without a good pcb. Good idea to get a demo board, or kit. Here is one, 20W
does not even need a heat sink.
http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=UAM2
Digikey may have some IR demo kits.
does not even need a heat sink.
http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=UAM2
Digikey may have some IR demo kits.