SHITSUSHIKIGENZONOGENZOEKINODOSEIGYOSOCHI

摘要

PURPOSE:To prevent the generation of an excessive concn. of a polarity charge control agent at a low temp. and to obtain an always good image by providing a switching circuit which cuts the polarity control agent supply signal generated from electrodes at a prescribed temp. or below. CONSTITUTION:A resistance R13 of the charge control agent existing between a pair of the electrodes appears in parallel with a variable capacitor C1. The oscillation frequency of a sine wave oscillator OSC is set at such an extra-low frequency at which the other impedance between the electrodes does not drop too much as compared with the resistance R13. Furthermore, the sine wave voltage from the oscillator OSC is divided by the resistances R13 and R1 and the voltage of the R1 is amplified A1. This output signal is subjected to removal of noise components by an LPF, then to integration INT and is compared with a reference voltage VREF in a voltage comparator VC. The adjustment of the charge control agent concn. can be executed simply by changing the reference voltage VREF and the detection sensitivity can be adjusted by the variable capacitor C1. The deviation output signal from the comparator VC is applied to a driving circuit D by which a relay RA2 is driven to stop the toner replenishment into the developing soln.