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Old 20th May 2002, 08:12 AM   #21
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Sorry about that, I zipped the wrong file...

Here is the correct one.
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File Type: zip schematic.zip (12.1 KB, 128 views)
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Old 20th May 2002, 12:58 PM   #22
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Default Here's 555 schematic

I used LMC555's at around 200KHz switching speed and an ordinary switching power supply mosfet (look for the lowest Rds(on) for better efficiency). The output of the second 555 goes to the mosfet (which drives the speaker). (You can use LM555's but they can't switch as fast as the CMOS LMC555)

You can use LMC556 instead of 2 LMC555's, it doesn't make a difference.

The 555's (or 556) has enough juice that you can breadboard the circuit and drive a (somewhere around 270 ohm) easy load for testing.

Put whatever LP filter circuit you want (frequency and order).

Have Fun!

On the national website, the 555 datasheet shows the building blocks. (Timer and PWM generator). You can also use the PPM circuit, but it didn't seem to work as well as the PWM circuit.

http://www.national.com/pf/LM/LM555.html
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File Type: gif switchmode.gif (3.1 KB, 363 views)
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Old 20th May 2002, 01:09 PM   #23
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Hi Matt MacBeth
How is the mosfet or mosfets hooked up?
I have only seen four transistor setups (H-bridge).


JasonL
Is there something special with the powersupply? Cant one just use a regular supply to drive PWM stuff?
I would more like to see the article from the magazine about the PWM amp.


AudioFreak
.bmp are really big and cant even be displayed in a web browser. If its a .gif or .jpg it will be alot smaller and probably fit the atachment limit.
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Old 20th May 2002, 01:26 PM   #24
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Default possible fet hookup

There are many ways to hook this up to a driver, a simple one is shown in the picture. For a better circuit, a 'real' driver circuit should be used.

Harris (Intersil?) and others make an H-bridge driver that should interface to this. There's even some with integrated FET's. The problem with making your own H-Bridge, is that if the 'top' and 'bottom' come on at the same time (overlap) this will damage the FET's. The driver IC's prevent this.

Anyways, on to the schematic.

P.S. sorry about the MS-Paint schematics (especially the choke)!
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File Type: gif fet.gif (1.7 KB, 347 views)
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Old 21st May 2002, 12:33 AM   #25
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Thank you, Matt Macbeth. I think I can increase the accuracy of the pulse stage by placing a PNP transistor. The transistor will make the capacitor charge fully instead of 25% to 75%.

For more information of what I'm talking about:
http://casemods.pointofnoreturn.org/pwm/741.html

The person took off from the trigger and left the output hanging. I'll use the output pin so I don't have to use an op-amp to smooth out the sawtooth waves. Though, I don't have an ocilloscope to see the effects.

I can also use 4011 NAND gates to generate the pulse but I'll stick with 555 timer for now.

AudioFreak, you said that you zipped the wrong one. Looks like there is a bug on DIYauido.com servers. I still got the same one and this time it is in GIF.
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Old 21st May 2002, 01:13 AM   #26
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I am well aware of the relative virtues are each file format .... as I explained above, i simply zipped the wrong file .... I had both a bmp and gif version of the schematic both are the correct schematic only the second is in a more friendly format. It is the protel file posted by JasonL simply converted to a format that we can all view.... if you look about 3 posts down from that you will see that i posted the correct gif file. I had to zip it not because of the size of the file but rather because of the physical size of the picture which exceeds that which is allowed to be directly displayed on this forum.
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Old 21st May 2002, 01:41 AM   #27
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Default See..

Here it is all i can doo ill try to make it more clear..

any one email me please ill send it to them i cant get the file small and ect ect
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Old 21st May 2002, 03:45 AM   #28
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Below is off topic:
The best way is to sign up for web site space. I suggest you don't go with geocities. Geocities might be on the top of the list on Google or Yahoo search results but the banner hovers over text. I have used Netfirms, 100megsfree, and 50megs. 50megs has decrease the features that it gives to the web designer since I left about two years ago. Netfirms is great for hotlinking or linking to other file types instead of HTM or HTML files. 100megsfree has 100 megabytes of space but no hotlinking. They do have a good looking control panel. There is Angelfire, Bravenet, Spaceports and many others. You can also make your web server if you have a broadband connection.
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Old 21st May 2002, 04:26 AM   #29
jleaman is offline jleaman  Belgium
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Default HAHah

i dont need webspace i have 3 servers that i can use but i choose not to rght now..
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Old 21st May 2002, 09:30 AM   #30
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I think this is what you guys are looking for. A quad op-amp, a couple of comparators, four FETs. The TC4428 is a TeleCom dual comparator. All the parts are available from Digi-Key.
http://www.linear-tech.com/pdf/lt1160.pdf
This has a low distortion triangle wave generator driving the fast comparator and the motor drive IC has shoot-thru protection. Figure 6 page 13. Distortion is a function of the switching frequency and the low pass filter. Another good read.
http://www.onsemi.com/pub/Collateral/AN1042-D.PDF
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