While I'm at it, let me ask about level shifting:
Some class-D amps use a complimentary N and P channel output pair, while others use dual n-channel output devices with a level shifter. How does the level shifter work, and why is it needed?
Some class-D amps use a complimentary N and P channel output pair, while others use dual n-channel output devices with a level shifter. How does the level shifter work, and why is it needed?
Hi,
some of class D N-fet output stage amp divided to 2 parts:
1. input parts that may contain of audio input, triangle wave generator, and comparator. Most of Class D, the input parts referenced their signal to ground that may have (+) and (-) signal.
2. Output stage, contains of driver gates, N-fet, and filter. The gates are referenced their signal to each mosfet's drain.
Then we have two different voltage reference for two gate driver. One called low side that referenced to (-) rail and other high side referenced as floating point voltage.
Level shifter used to match the input stage and output stage.
some of class D N-fet output stage amp divided to 2 parts:
1. input parts that may contain of audio input, triangle wave generator, and comparator. Most of Class D, the input parts referenced their signal to ground that may have (+) and (-) signal.
2. Output stage, contains of driver gates, N-fet, and filter. The gates are referenced their signal to each mosfet's drain.
Then we have two different voltage reference for two gate driver. One called low side that referenced to (-) rail and other high side referenced as floating point voltage.
Level shifter used to match the input stage and output stage.
Hi,
My first amp i built used both N and P fets simply because it is technically easier, especially for a first build. It is not important to match them as in other amp classes because they are not operating in the linear region. They are there simply to switch as hard as possible from one rail to the other so as long as they do that anything will do. I now use N fets for both high and low side due to their cheapness and also it keeps down the cost of replacinng the outputs. The high side is rarther difficult to drive as you have to provide a bootstrap supply to takes its gate above the high side supply rail, this supply rides up and down on your fet bridge. Due to the high side FETs supply jumping up and down you need to supply a drive signal to its gate that also rides up and down as it will be referenced to the bridge. The way that i have accomplished this is to use magnetic couplers then a drive signal booster chip to ram the signal into the gate, all run off the bootstrap supply and referenced to the bridge. I tried one with opto's that worked but was not fast enough for my liking. This can also be acheived with conventional components but at high frequencys it is very hard to master. The Gate drive and level shifting for the power output stage is the hardest part of building this class of amplifier and it is what will make or brake your amp. If your designing one i wish you all the luck in the world. HAVE FUN😀
I did.
Regards
Mad.P
My first amp i built used both N and P fets simply because it is technically easier, especially for a first build. It is not important to match them as in other amp classes because they are not operating in the linear region. They are there simply to switch as hard as possible from one rail to the other so as long as they do that anything will do. I now use N fets for both high and low side due to their cheapness and also it keeps down the cost of replacinng the outputs. The high side is rarther difficult to drive as you have to provide a bootstrap supply to takes its gate above the high side supply rail, this supply rides up and down on your fet bridge. Due to the high side FETs supply jumping up and down you need to supply a drive signal to its gate that also rides up and down as it will be referenced to the bridge. The way that i have accomplished this is to use magnetic couplers then a drive signal booster chip to ram the signal into the gate, all run off the bootstrap supply and referenced to the bridge. I tried one with opto's that worked but was not fast enough for my liking. This can also be acheived with conventional components but at high frequencys it is very hard to master. The Gate drive and level shifting for the power output stage is the hardest part of building this class of amplifier and it is what will make or brake your amp. If your designing one i wish you all the luck in the world. HAVE FUN😀
I did.
Regards
Mad.P
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