Purely academic question: I have a little bridge rectifier made out of four 1N4001 diodes, being fed by a transformer putting out 12VAC. When I run it without anything else attached to it, the waveform looks like this:
If I stick a 10K resistor on there as a dummy load, that junk in every other cycle goes away:
What gives? Is there some capacitance in the diodes or something? And why is it every other cycle?
(I know my scope can take screenshots; I just can't find my USB drive.)
...And why is it every other cycle?
The asymmetry is likely due to transformer construction. First, be aware that these high impedance loads (like an oscilloscope) make coupling capacitances overly important - with realistic low-resistance loads on the bridge, capacitance influences voltage far less.
The step-down transformer likely has secondary winding laid over primary winding, so that there is some capacitance between windings. A LTspice circuit was set up with transformer windings 10:1 turns ratio...a capacitance (C1) between windings of 100pf was estimated. Not shown is some resistance in series with each winding (else LTspice fails because voltage sources driving pure inductance is forbidden):
