Show Posts
1
The RF Workbench / Class D audio amps - protection circuits
« on: April 27, 2023, 0339 UTC »
I've learned a lot from this forum, so thanks, first of all!
One thing is the use of class D amplifiers as modulators by connecting a class E PA directly to one of the H bridge (speaker) outputs. Beautiful hi-fi quality and couldn't be simpler or less expensive! I've been using the TPA3116 amplifiers to modulate 5-8 watt transmitters but have one of the TPA3118 jobs enroute. My question/problem is about the built-in protection circuitry which is common to both.
I've been getting frequent shutdowns that seem to be due to a DC Detect fault, which causes the outputs to go Hi-Z. The datasheet describes this fault: "A DC Detect Fault is issued when the output differential duty-cycle of either channel exceeds 60% for more than 420 msec at the same polarity." It could be triggered since we are applying a load to one output but not both - or it could be for some other reason as I'm just guessing, and know the amp hasn't run enough to be thermally related. I've had it happen at start-up and can often produce it by connecting an input device when the amplifier is powered-up and idle, thus both outputs are a 1/2 Vcc. There is no current draw until the transmitter is keyed but sometimes I see a brief current spike on power-up then the outputs fault. Other times it just stops randomly. Very annoying to say the least.
I'm curious to know if others have observed this and any suggestions as to how to deal with it would be appreciated, thanks.
Bob
One thing is the use of class D amplifiers as modulators by connecting a class E PA directly to one of the H bridge (speaker) outputs. Beautiful hi-fi quality and couldn't be simpler or less expensive! I've been using the TPA3116 amplifiers to modulate 5-8 watt transmitters but have one of the TPA3118 jobs enroute. My question/problem is about the built-in protection circuitry which is common to both.
I've been getting frequent shutdowns that seem to be due to a DC Detect fault, which causes the outputs to go Hi-Z. The datasheet describes this fault: "A DC Detect Fault is issued when the output differential duty-cycle of either channel exceeds 60% for more than 420 msec at the same polarity." It could be triggered since we are applying a load to one output but not both - or it could be for some other reason as I'm just guessing, and know the amp hasn't run enough to be thermally related. I've had it happen at start-up and can often produce it by connecting an input device when the amplifier is powered-up and idle, thus both outputs are a 1/2 Vcc. There is no current draw until the transmitter is keyed but sometimes I see a brief current spike on power-up then the outputs fault. Other times it just stops randomly. Very annoying to say the least.
I'm curious to know if others have observed this and any suggestions as to how to deal with it would be appreciated, thanks.
Bob