| 摘要 |
A temperature control circuit for a point-of-use water heater comprises a pulse charging circuit which includes a summing capacitor provided with a residual charge thereon at the beginning of each half cycle of an a.c. supply. The residual charge on the summing capacitor determines the pedestal charge on a timing capacitor and thereby the phase angle at which a ramp superposed on the pedestal fires a programmable unijunction transistor to provide a pulse for triggering switching means to supply a fraction of the a.c. supply to the heater each half cycle. The residual charge on the summing capacitor is determined each half cycle by the discharging thereof in accordance with a load current pulse feedback circuit and the output of a comparing circuit which compares the actual temperature of the water flowing past the heater with a desired set temperature.
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