heat sink wasn't hot, but mosfets were very hot, i think thermal isolation was not able to transfer that amount of heat this fast. but as i understand mosfets shouldn't heat up as this without load and thermal isolation is not the main problem in my amp.
Like i said above, those thermal pads you used are useless!! They are made for computer harddrive coolers.
Apex,
please describe the operation of the overcompensated Bias Tempco and where to find that bias voltage circuit in the schematic.
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Bias resistor is about 230ohm (P1+R20 in parallel with R19) X 30mA (VAS current) = 7V (bias voltage). VAS current drop with heat (Q9 and Q10 are on main heatsink) and compensated bias (bias voltage drop).
Bias 200mA per mosfet on start (cold amp heatsink) drop to 120mA with hot heatsink and it's overcompensated but very safe for PA use.
I have changed thermal insulator to mica and again irfps get hot pretty quick (few seconds) and i cannot adjust bias in that time. And again... one pair down one pair left 🙂
With one pair and with no load i have adjusted bias to 20mV but when i connect load protection lamp lights up... and from +75/0/+75v left +13/0/-13v.
With one pair and with no load i have adjusted bias to 20mV but when i connect load protection lamp lights up... and from +75/0/+75v left +13/0/-13v.
D
Deleted member 148505
Hi,
Is this circuit fast enough to protect the output transistors in case of short circuit in speaker?
Thanks