Joyoung JYC-22F electromagnetic cooker pulse width signal output circuit

Joyoung JYC-22F electromagnetic cooker pulse width signal output circuit

Shown is the pulse width signal output circuit of Joyoung JYC-22F electromagnetic cooker. As can be seen from the figure, it is mainly composed of the B, C, D voltage comparators of IC
3 and peripheral components. IC3 D, that is, the output PWM signal of the LM339@ pin drives the gate control tube after passing through the driver amplifier
. If the circuit is abnormal, you should first check the output of the LM339@ pin. Then check the sawtooth wave signal at the LM339@ pin. If the signal is abnormal,
the peripheral components of LM339 and the DC voltage of each pin should be checked separately. If the peripheral components are normal and the power supply is normal, but the output signal is abnormal, the integrated circuit itself
is faulty and should be replaced with a new integrated circuit of the same model.
    In this circuit, the sawtooth wave generating circuit is mainly composed of C29, Ci2, R80, and D13 in the IC3C output circuit . When
the voltage at the left end of the heating coil resonant capacitor Cl is divided by R6, R7 and R4 and then added to the @ pin of the inverting input terminal of IC3C, the voltage at the right end of the capacitor c1 is
divided by R2, R1 and R82 and then added to the @ pin of the non-inverting input terminal of IC3C. When the voltage across the capacitor Cl is negative on the left and positive on the right, that is, when the collector voltage of the gate control tube
is the highest, the voltage comparator IC3C outputs a high level; when the voltage on both ends of the capacitor Cl gradually becomes positive on the left and negative on the right, the voltage comparator IC3C Output
low level. In this way, the synchronization pulse is output through IC3C, and then passes through the C29, C12, R80, and D13 circuits to form a sawtooth wave voltage, which is sent to
the @ pin of the reverse input end of the voltage comparator (pulse width modulation circuit) IC3D.
    The 5 V power supply provides a fixed voltage to the ⑦ pin of the voltage comparator IC3B through two voltage dividing resistors R75 and R76. Its @ pin is controlled by the
gate collector, that is, the conduction and cutoff of the gate control tube will cause the @ pin to form The pulse signal is synchronized with the collector of the gate control tube. This signal
is compared with the ⑦ pin and then the pulse signal is output from the ① pin. It is superimposed with the pulse width control signal and then sent to the @ pin of IC3D.
    After the sawtooth wave voltage of the reverse input terminal @ pin is compared with the power control level of the non-directional input terminal $11$, the @ pin of IC3D outputs a pulse signal
with adjustable pulse width . When the voltage controlled by the @ pin entering the pulse width is low, the pulse width output by the @ pin of IC3D is narrower: when the voltage controlled by the @ pin input by the @ pin is high, the pulse width output by the @ pin of IC 3D The pulse is wider.