AN2528 datasheet(10/21 Pages) STMICROELECTRONICS

部品番号	AN2528

部品情報	Very wide input voltage range 6 W SMPS for metering

PDF	21 Pages

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メーカー	STMICROELECTRONICS [STMicroelectronics]

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10 / 21 page

Base drive circuit design

AN2528

10/21

Figure 5.

DC current gain

Figure 6.

Dynamic collector-source saturation voltage

To maximize performances, a base capacitor CB has been inserted.

Note that, using the driving network shown in Figure 4, a quasi total recovery of energy to

drive the base is achieved. During the storage time the collector current comes out from the

base and is stored in the base capacitor. If the capacitor is small enough, the voltage across

it reaches the Vcc and after that the current flows to the Vcc capacitor.

To set the time duration of the base current spike, the following approximate formula is

useful:

Equation 12

Since RB=10 Ω (see below), if the peak has to be about 300 ns

Equation 13

The aim of RB is to dampen the ringing on the base current at the end of its peak. It is

chosen as a compromise between a damping effect and additional power dissipation on it.

peak

•

peak

•

-----------------

10nF

AN2528 データシート(PDF) 10 Page - STMicroelectronics