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Class D Switching Power Amplifiers and Power D/A conversion

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Old 15th September 2012, 12:54 PM   #31
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After these mods, the amp on the current heatsink and PSU(2x58VDC around 400-500VA) idles slightly above ambient, not much but enough to be noticable, the IR2110 does get hot much not hot enuf to worry about, i'd call it normal.

Before it was stone cold regardless of runtime or abuse.

A video: Improved feedbackless Class D amplifier - YouTube
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Old 15th September 2012, 01:25 PM   #32
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After these mods, the amp on the current heatsink and PSU(2x58VDC around 400-500VA) idles slightly above ambient, not much but enough to be noticable, the IR2110 does get hot much not hot enuf to worry about, i'd call it normal.

Before it was stone cold regardless of runtime or abuse.

A video: Improved feedbackless Class D amplifier - YouTube
Ok, so your new dead time is already in the region of slight shoot through.
That is helpful for low distortion and helpful to handle the hard switching of the body diode.
The downsides are EMI and the theoretic risk of a thermal runaway (Threshold voltage is decreasing at higher temperatures...).
Unexpected but true all my class D builds were pretty forgiving and never showed thermal runaway.
You can easily check this, by heating it up with a hairdryer and see if it cools down again or above a certain temperature would start to heat up more and more by itself.

Another topic for optimization are snubbers, but in order to design them properly you would need detailed measurements of Ugs and Uds under hard switching....
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Old 18th September 2012, 06:27 PM   #33
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I am curious how your IR2110 has not blown up. You appear to be hitting the Lin and Hin with 85V. Did you actually build something a little different to that schematic in post 7?
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Old 18th September 2012, 07:20 PM   #34
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Those inputs are only seeing around 12V, the level shifters i used have been widely used on this forum by others, even simulation shows that only around 12V are preset at the IR2110 input pins.
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Old 18th September 2012, 07:57 PM   #35
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My simulation shows the HV rail voltage is seen at the junction of the collector and resistor, which makes sense looking at the circuit. I tried using other resistor values by the way and it still gave 35V at the junction.

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Old 18th September 2012, 08:18 PM   #36
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My simulation shows the HV rail voltage is seen at the junction of the collector and resistor, which makes sense looking at the circuit. I tried using other resistor values by the way and it still gave 35V at the junction.

Click the image to open in full size.
LM311 and THS4001 are not the same. What do you think R9 and R10 are used for on the original schematic?
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Old 18th September 2012, 08:22 PM   #37
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Yes they are because the device has open collector outputs. OK, so I will try inserting a resistor between the emitters and the op-amps.
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Old 18th September 2012, 08:34 PM   #38
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Thank you. Sometimes you look at a circuit for so long you can miss an obvious point.

I tried 470 ohm resistors with 2.2k but this gave me waves about 16.5V, 750 ohm gave me the 10V I wanted.
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Old 20th September 2012, 01:01 PM   #39
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There is no way to achieve fast switching or low EMI with the parts shown in the pictures. Current loop areas are insanely big, suitable for <10Khz switching only. Use TO-220 or TO-247 and SMD.
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Old 20th September 2012, 04:20 PM   #40
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WRONG!! Please do not make comments like that without proof to back them up!

I swept a tuner from lowest (LW around 200kHz, up to FM 108MHz) and i could not detect the amp anywhere, and its switching happyly at around 200kHz.

Sure it may not meet the EMI standards for beeing allowed to be sold commercially in stores, but its been running for over a week now with no complaints about EMI/RFI disturbance, and to be honest, i cannot tell it apart from any of my other amplifiers which are all commercial class AB ones.
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