AN2383 datasheet(21/39 Pages) STMICROELECTRONICS

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AN2383

Measurements at PWM frequency

Doc ID 12433 Rev 3

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Measurements at PWM frequency

The following scope waveforms were taken during the different working phases. These

signals are synchronized with the PWM signal, therefore running at PWM signal frequency.

The waveforms shown in Figure 12 and Figure 13 were taken while a 22 cm-diameter iron

pot filled with water was placed on the plate.

6.1

Powering the plate (with pot)

Figure 12.

Plate power-on (with pot on the plate)

The DC link voltage is applied to the plate and the 60 kHz PWM signal with 50% duty cycle

is applied to the half-bridge driver for half a second. UP-G and LW-G are the upper side gate

signal and the lower side gate signal, respectively. Of course they must be complementary

and there must be a certain dead time between the upper gate pulse and the lower one. The

dead time is set by hardware (L6384, resistor on pin 3).

Since the pot is on the plate, a certain current starts to flow through the plate (I-PLATE). The

unit in Figure 12 is expressed in volts, but the current probe connected to the scope is set at

20 amperes per division. This means that at plate power-on the system is already delivering

a 20 ampere peak-to-peak current.

PVM

UP-G

LW-G

I - PLATE

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