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Class D Switching Power Amplifiers and Power D/A conversion

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Old 21st April 2004, 01:00 AM   #11
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Default The Class-T Preamplifier

Finally I have gotten around to taking pictures. There have been a lot of you sending me emails with a lot of interest and I will do my best to get back to everyone. If you have questions feel free to email and I will answer them the best I can. The first set of pictures are of the simple preamplifier. It provides simple buffering, gain, and a 3 band EQ based on op-amp gyrators. Also on this board are the circuits for gain and balance. Also, there is a pair of relays that provide alternate signal routing and turns the four channels into a pair of higher power bridged channels. The bridging relay simply takes one of the input signals and applies it to two channels through buffers where one is inverting and one is non-inverting. The question some of you may have at this point is where are all the user controls? The appropriate analog signals run through a sort of ribbon cable to a slim circuit board which holds most of the controls. It will be seen a little later. So here are a couple of shots of the Class-T 4 Channel Preamplifier.

Once again the pictures are too big. Most are around 145kB. I will compress them a little in a couple days and post them here. Coming up next: The PFC front end to the power supply.
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Old 22nd April 2004, 01:36 AM   #12
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Default Class-T Preamplifier

This is a picture of the prototype preamp as described above.
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File Type: jpg preamp1.jpg (96.6 KB, 851 views)
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Old 22nd April 2004, 01:39 AM   #13
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Default Class-T Preamplifier

Another Picture!
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File Type: jpg preamp2.jpg (71.0 KB, 748 views)
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Old 22nd April 2004, 01:41 AM   #14
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Default Class-T Preamplifier

Another Preamplifier Picture...
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File Type: jpg preampbottom.jpg (65.6 KB, 668 views)
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Old 22nd April 2004, 01:49 AM   #15
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If you couldn't tell that particular board is only partially populated. There are a few components missing. I figure that I will show a picture of what a mostly populated system ends up looking like at a circuit board level.
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Old 22nd April 2004, 01:51 AM   #16
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Default Main Circuit Board

The main power supply is a ZVS switching supply with an off-line Active Power Factor Correction Front end.
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File Type: jpg mainboard.jpg (92.2 KB, 748 views)
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Old 22nd April 2004, 01:54 AM   #17
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Another Birds eye view of the circuit boards....what is not shown is the PFC Circuit which takes in the AC offline voltage from 90VAC to 270VAC @50-400Hz and turns it into a 400VDC bus for the input of the converter to draw from.
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File Type: jpg mainboard2.jpg (96.4 KB, 684 views)
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Old 22nd April 2004, 01:55 AM   #18
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The front set of controls on this prototype system. I keep stressing that thiss is a prototype because of the shady construction used to tweak and verify the design.
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File Type: jpg controlpanel.jpg (60.2 KB, 644 views)
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Old 22nd April 2004, 02:07 AM   #19
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Default Active Powe Factor Correction

The Active Power Factor Correction PreRegulator circuit provides a 400VDC bus voltage to be presented to the input to the proceding converter stage. The fundamental topology of this circuit is a continuous boost converter where the input in a rectified AC haversine and the output is a DC voltage with ripple. If you are not familiar with the boost topology it consists of a transistor switch, a diode, an inductor, and a capacitor. This particular PFC is designed to power limit at 1000W and does so. All of the magnetics on this and the rest of the circuits are custom designed and hand wound personally. The boost inductor here has a core material of High Flux MPP (moly permalloy powder) and solid 13AWG wire. The exact value of inductance is not as important as the current rating, the losses, and the amount of energy storage (ultimately proportional to inductance though). It is important that the components used be correctly rated including the diode bridge which will be exposed to 400V plus. This particular one is rated for 600V. Enought with the text....here is some pictures. I can answer any questions anyone may have.
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File Type: jpg pfc1.jpg (64.1 KB, 682 views)
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Old 22nd April 2004, 02:09 AM   #20
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Default Power Factor PreRegulator

Another view of the Power Factor Preregulator
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File Type: jpg pfc2.jpg (68.3 KB, 663 views)
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