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Old 22nd November 2008, 08:34 PM   #1
qsa is offline qsa  Germany
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Default Need assistance for additional devices in DC detect for Quasis NMOS 350 Amp


Im designing 350-500 Nnmos Power Amplifier PCB from Quasi

I want add to add in DC detect schematic from Quasi,

1. Protection Led, if Q5 and the realy turns off, (DC) Protect Led is turns on

2. Additional Overheat Protection, if Heatsink > 85 degress, Q5 and the realy is turns off, Protect Led is turns on

3. Additional Signal Led 1 pcs., if Amplifier have output power, green Led is turns on

I need assistance in schematic design because i dont have experience.

Who can help me to add additional devices ?

1. Attachment: schematic DC detect from quasi


Two 33K resistors and the two 22uF capacitors form a low (very low) pass filter .
A sustained positive voltage will turn on Q3. This turns Q4 off which turns off Q5 and the relay.
A sustained negative voltage causes Q1 to turn on. This turns on Q2 which turns Q4 off etc.
A very large negative or positive “music” swing could indeed trip the circuit; this could be a good or bad thing depending on the point of view.
The trip timing is dependant on the input voltage applied plus the value of the capacitors and resistors in the low pass filter. Increasing these values slows the reaction time and increases the restoration time.
As a bonus the 330K resistor and the 470uF capacitor provides a speaker connection delay (de-thump)
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Old 22nd November 2008, 10:43 PM   #2
qsa is offline qsa  Germany
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Heres is a sample schematic from PA AMP with Temperatur, Signal ...Protect
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