EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: yabba235 on December 06, 2023, 06:44:04 pm
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Hi!
Put in my hand mini audio amplifier from China - it use HV amplifier chip from apex manufactury. It use very strange aplication of flyback conventer base on TL494 PWM driver. I cannot compare this system to any example of using this system found on the Internet - can someone help me and explain to me how it works?
I just wanted to make a similar power supply but I can't find any diagram that would correspond to this system.
I am attaching a photo of the board - the output is an FTDP 20n50 n-mosfet controlled in parallel from outputs e1 and e2.
I suspect that this is a copy of the power supply circuit from the Stax SRM-D10 portable amplifier. I don't know how the Chinese copied this system (there are no diagrams for me), but they managed to do it.[attachimg=1]
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pls straighten the mosfet we don't see under it
an serious smps application has one more transformer to do the tl494 coupling, in case of the main section who could blow, the tl494 get isolation
this circuit seems simple you could do a schematic yourself
and for sure you should have a feedback line who should from the xformer secondaries and goes back to the tl494, normally thru an optocoupler etc ...
but this circuit seems pretty cheap and cut on quality / functionality, and show us a zoomed out picture of this section, we may miss some parts
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A few photos:
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A fews photos more:
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This circuit has no optocoupler, only voltage divider from output voltage. I can't recognize configuration of error aplifiers from 494 chip - without cleer look track and pads seems is impossible recreate schematic.
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This circuit has no optocoupler, only voltage divider from output voltage. I can't recognize configuration of error aplifiers from 494 chip - without cleer look track and pads seems is impossible recreate schematic.
No BGA array parts so you can figure connectivity with ohmeter between pins. Not as easy as viewing bare board, but straightforward.
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I've seen a few TL494 based amplifier circuits. The PWM controller can be used open loop to provide the class D action. The internal error opamps might be used as audio gain stages (arrgh!).
You might not have a conventional TL494 application at all. Its not being used as a power supply circuit.
eg https://www.elcircuit.com/2018/03/diy-500w-class-d-tl494-switching.html (https://www.elcircuit.com/2018/03/diy-500w-class-d-tl494-switching.html)
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I've seen a few TL494 based amplifier circuits. The PWM controller can be used open loop to provide the class D action. The internal error opamps might be used as audio gain stages (arrgh!).
You might not have a conventional TL494 application at all. Its not being used as a power supply circuit.
eg https://www.elcircuit.com/2018/03/diy-500w-class-d-tl494-switching.html (https://www.elcircuit.com/2018/03/diy-500w-class-d-tl494-switching.html)
No, in this case TL494 work in "normal" mode, no D class audio aplifier.