Hi all,
I am working on a design which uses TPA3130D2 in PBTL configuration to drive 4 ohm load. Requirement is 30W mono output, 70Hz to 18KHz, supply is car battery which is then boosted to supply 24V to the IC.
I have almost finished the design. Now customer wants to add requirement of 8 ohm and 100V output. So I have some problems now:
- My filter is already calculated for 4 ohm, it is 15uH and 2x 2.2uF for BD mode. Now how do I do to support 8 ohm as well as 4 ohm in the same output? I tried different values (in calculation) but it seems I have to due with slightly picking for 8 ohm and slightly over damped for 4 ohm load. I found none of the value can meet the requirement of +1/-3dB frequency response at 18KHz for both 4 ohm and 8 ohm. I see many product in market can support both 4 and 8 ohm same output, what do they do?
- To adapt with 4 ohm and 8 ohm, I think the circuit will have to somehow detect the load and set the gain accordingly, eg. we should have 15.5Vrm for 8 ohm and 10.9Vrms for 4 ohm at rated power?
- For 100V output, it is more problematic. I have gone through some posts on this forum: this and this. I see 2 major problems:
+ The IC may shutdown at low frequency (maybe < 400Hz) at high power output due to core saturation. Filtering out the low frequency is not possible to me because I have frequency range down to 70Hz. Can you confirm the back to back capacitor can solve this or do you suggest other solutions?
+ What happen if user sometime connects some different loads at the secondary, let's say 10W speaker, then 2 x 10W speakers in parallel. Will my filter still be able to do the job?
+ Can I use the conventional audio transformer which has 3 outputs: 4 ohm, 8 ohm, and 100V for this Class D amp output?
Sorry for many questions, I am new to the audio design.
