![]() L1, R6 & C2 make up an optional noise filter. Note that this circuit can only discharge C1 –it cannot charge C1 due to the presence of the lower diodes of BR1 that short the bias current(s) to circuit common. At that point, it begins to charge in the proper polarity for that half-cycle. To discharge C1 to zero volts as quickly as possible, the bias current through either R4 or R5 (depending upon polarity) quickly discharges the voltage across C1 to zero. At the beginning of each half-cycle when the line voltage changes polarity, the voltage across C1 lags in voltage and is of the opposite polarity. Note that the resistor values are different for the two line voltages indicated (115 /230VAC). I suggest that the experimenter try it with and without these components so the effect may be observed. ![]() However, if the voltage at the end of the cycle is insufficient to trigger the DIAC, the next half-cycle starts with C1 charged in the incorrect polarity so that it takes all the longer for C1 to discharge through zero and then charge to the opposite threshold.Īfter the DIAC initially fires, this condition changes substantially so that the phase delay angle is reduced and the lamp snaps on at a minimum brightness –sometimes brighter than desired. Before the DIAC triggering device fires, C1 must charge to 28 or so volts.
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