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S3F84B8_ALL-IN-ONE IH COOKER_AN_REV 0.00 2 HARDWARE IMPLEMENTATION
2-11
2.5 SYSTEM PROTECTION
2.5.1 SURGE PROTECTION
Figure 2-5
shows the circuit diagram for surge protection. In this figure, Surge_P specifies the negative input of
Comparator 1. Also, reference voltage is internally set as 0.55VDD. When surge takes place, that is, V Surge_P >
0.55VDD, the falling edge of comparator 1 can hard-lock the PWM output immediately to prevent the IGBT from
being burnt out by over current. The whole system then stops work and restarts after some delay.
2.5.2 IGBT OVER VOLTAGE PROTECTION
IGBT over voltage is mo
st likely to occur the moment when the pan is removed from the panel.
Figure 2-5
shows the voltage measurement circuit. In this figure, IGBT_V_P specifies the negative input of
Comparator 2. Also, reference voltage internally is set as 0.70VDD. When V Surge_P > 0.70VDD, the co-
operation of comparator 2 and IH PWM will soft-lock the PWM output immediately to prevent the IGBT from being
burnt out by over stress of the collector voltage. As a result, it makes the PWM stop the current cycle and reload
PWMDATA with a preset safe value (PWMPDATA) to reduce the turn-on time of IGBT.
2.5.3 OVER/UNDER VOLTAGE PROTECTION
Over/und
er voltage protection uses the voltage measurement signal. The protection takes place when the AD
conversion result is either too large or too small. The whole system then stops working until the power returns to
normal.