Electronics > Beginners
Scullcom function generator - component functions ?
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netdudeuk:
Hi
What is the purpose of C21 and R33 ?
Thanks
oPossum:
Reduce noise from the power supply getting in to the output.
bd139:
C21 is a decoupling capacitor. It reduces the impedance at AC on the junction of R33 and R15 therefore establishing a stable voltage there. The amplifier looks like a summing amplifier so this reduces the “wiggle” on the DC offset input at DC and allows AC to float on that DC level. At DC the capacitor is effectively open.
You can model this by drawing the circuit twice. Once with the capacitor shorted (at DC) and once when it’s open (at AC) and think about each case independently.
netdudeuk:
Thanks guys.
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