Adrian,
Look closely at how the rectifier diodes are connected. They determine the polarity of the rectified and filtered +20V and -20V that feed the regulators. The polarized 2200uF filter capacitors must be connected in the direction shown or they might explode.
The same for the 7815 and 7915 regulators. The 7815 positive regulator must be connected in the positive part of the circuit, and the 7915 negative regulator must be connected in the negative part of the circuit. :lol:
The bridge rectifier with CT trafo - in this case - work as two independent two way rectifier: one pair diode with common cathode for +V out, another pair with common anode for -V out.
No, A 15V-0V-15V secondary gives peak voltages of +21.2V, -21.2V, +21.2V and -21.2V at a little less than full load. A transformer's output voltage is higher with less load. The voltage regulators provide a regulated +15V and -15V. The regulators need at least 17V to 18V minimum input to function properly.
When the top transformer terminal's voltage swings negative, then D2 conducts. When the bottom transformer terminal swings negative, then D3 conducts. Therefore it is full-wave.
Actually, since C3 is almost fully charged most of the time then D2 and D3 conduct only during the peak negative voltage of the transformer.
is there any software can draw n see the the waveform n measure the voltage?