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2.5.2.
Converter Driver and Flyback Converter
The converter driver consists of transistors V1438, V1413 and transformer T1404.
The converter itself consists of the converter transformer T1402.
- The converter driver (see Fig.
The circuit functions as follows:
The pulse-width of the square-wave current I 1 that i s applied t o the base of transistor V1438 is determined by
the integrated circuit D1402.
The frequency of the square-wave current i s 26 kHz approximately.
If transistor V1438 starts t o conduct
the period T I .
secondary winding of T I 4 0 4 (14).
The base current of V1413
Transistor V1413 will conduct and i t s collector current I 6 will increase to 4 A.
I f the transistor V1438 is blocked
Because of this sudden switch-off, the current 14 will be maximum a t this moment.
The current14 is in anti-phase with respect t o 1 2 and flows via diode V1437 to the supply voltage.
I n this way, the base current I 3 of V1413 becomes negative (-0,4 A ) during period 12, which rapidly blocks
The collector current I 6 of V1413 i s also switched o f f rapidly a t this moment. The energy present in the
transformer T I 4 0 4 is fed t o earth via diode V1419. This i s realised by the negative current 11 during period T3.
After
40
the procedure is repeated.
Resistor R1446 provides the base of V1413 with a d.c. current t o speed-up the switching-on of this transistor.
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A
2.9
Fig.
Converter-driver
2 . 9
8.14)
and
point A of Fig. 2.9), i t s collector current 12 increases to 0,4 A during
(see
will increase by the same amount as the collector current of V1438 a2).
point B of Fig. 2.9) i t s collector currentf2 i s switched off.
(see
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MAT 948
2-29
and to the
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