Please see the attached schematic of the power supply that I have physically tested at my bench. I measured 150 mV rms of ripple across each of the smoothing capacitors of the unregulated power supply, capacitors C2 & C3. At Vout of U2 (the negative voltage linear regulator) I measure 0 volts of ripple, that is AC voltage. At Vout of U3 (the positive voltage regulator) I measure 150 mV rms of ripple. In other words, the positive regulator is not eliminating the ripple at its input pin.
It seems odd to me that I'm measuring substantial ripple at one output, but not at the other. So I'm wondering what I'm doing wrong that the positive regulator does not severely reduce the ripple at the output of the unregulated DC power supply. I don't believe that this is a result of a faulty L7815 as I have tested the circuit with two different L7815 and get the same result. Also the linear regulators are located less than 3 inches distant from the smoothing capacitors C2 and C3.
I feel like someone is trying to make me loony! Your advice is appreciated.
Pete
It seems odd to me that I'm measuring substantial ripple at one output, but not at the other. So I'm wondering what I'm doing wrong that the positive regulator does not severely reduce the ripple at the output of the unregulated DC power supply. I don't believe that this is a result of a faulty L7815 as I have tested the circuit with two different L7815 and get the same result. Also the linear regulators are located less than 3 inches distant from the smoothing capacitors C2 and C3.
I feel like someone is trying to make me loony! Your advice is appreciated.
Pete
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