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S3F84B8_ALL-IN-ONE IH COOKER_AN_REV 0.00 1 OVERVIEW OF IH COOKER (IHC)
1-3
Comparator1/2/3 has only one input with an internal programmable reference level. It can lock the output of PWM
to a safe level. Besides the delay trigger function, PWM can realize anti-mis-trigger function as well. It prevents
the PWM from being triggered by unexpected noise. For more information about the cooperating mechanism of
the IH-PWM and four comparators, refer to the user’s manual.
1.3 SYSTEM PRINCIPLE
To make the system work reliably, the control of IH cooker can be divided into two major parts: heating and
protection.
1.3.1 HEATING
In earlie
r solutions, the output of LM339 controls the IGBT. On being filtered, the PWM output transforms into an
analog signal that sets the flip level of LM339. Therefore, only the duty determines the output power.
However, in a system with S3F84B8, the PWM directly controls the switch of IGBT and the width of valid output
level determines the output power. Therefore, the power is dependent on the system clock.
1.3.2 PROTECTION
Two
kinds of protection are available for the control of IH cooker: first is time sensitive protection, and the other is
acceptable protection that can be executed even after certain degree of delay.
Surge protection and IGBT over-voltage protection belong to the former class (time sensitive protection).
Therefore, these two signals use the integrated comparators. In this solution, PWM will be hard-locked when
surge protection is triggered. It stops the PWM with a safe output level until the software enables it again. Once
the voltage sensed at IGBT is beyond limitation, PWM will be soft-locked. This will make the PWM stop the current
cycle and reload PWMDATA with a preset safe value (PWMPDATA) to reduce the turn-on time of IGBT from that
instance.
Over-temperature, over-current, and over/under voltage protections belong to the latter class. They are realized by
AD conversion and software comparison.