AN2383 datasheet(14/39 Pages) STMICROELECTRONICS

14 / 39 page

How the system works

AN2383

14/39

Doc ID 12433 Rev 3

How the system works

4.1

Standby (system off)

As soon as the induction cooking system is plugged into the mains, the system is running

and the MCU goes into standby mode, or put simply, “system off”.

No controls or actions are taken, only the keyboard is scanned to capture a “button pressed”

event. The display shows "-".

In this status, putting or removing a pot from the plate has no impact on the system

functionality. The safety relay contacts are open, so no DC link voltage is applied to the

resonant tank.

4.2

System on

The system is turned on by pressing the on-off button (the first on the left in the user

interface).

Each time it is switched on the induction cooking system performs a sequence: safety relay

first, then plate power-on. The safety relay contacts close, which applies the DC link voltage

to the resonant tank.

At this point, the system temporarily powers-on the plate: a 60 kHz PWM signal is applied to

the half-bridge driver for half a second. During this time, if a pot is placed on the plate, or it is

there already, the system moves to the lowest operating power level, shown as "1" in the

user interface display. If however, no pot is detected on the plate, the system stops the PWM

signal. Another power-on sequence is performed after 10 seconds. After 5 unsuccessful

power-on sequences, the system goes back to standby mode.

When the PWM signal is applied to the half-bridge driver, the decimal point in the user

interface display turns on.

Once a pot is detected, the user can move through 9 working power levels by pressing the

buttons on the user interface. 1 is the lowest level, and 9 is the maximum.

4.3

Safety relay and fan management

The safety relay prevents the DC link voltage from being applied to the resonant tank when

the system is off. The relay contacts are connected in series with the plate, and they close

when the system is turned on. To prevent oscillation or undesired relay commutations, an

anti-bounce software routine is implemented. The relay turns off when the system turns off.

The fan helps the heatsink dissipate the heat while the system is working. It is turned on as

soon as the heatsink temperature reaches 55 °C. The fan stays on for at least one minute,

whether the system is on or in standby mode.

AN2383 датащи(PDF) 14 Page - STMicroelectronics