AN1889

PWM driver

23/33

When sensing current in series with the power transistor, the current waveform will have a

large spike at turn on due to the intrinsic capacitance. As shown in Figure 11, a simple RC

filter is adequate to suppress this spike. Typical values are:

●

R16=1 k

Ω

●

C7=470 pF

7.5

ESBT gate drive

Series resistor R17 provides damping for a parasitic tank circuit. Resistor R19 shunts output

leakage currents to ground when the under-voltage lockout is active.

Figure 11.

ESBT fly-back schematic diagram

1

2

3

JP1

F1

D1

D2

D3

D4

GND

GND

JP2

GND

R1

R2W

R2

R2W

R6

R1/2W

R3

R2W

R4

R2W

R5

R2W

C3

D5

D6

R7

R1/2W

DZ1

C4

D7

VCC

7

VFB

2

COMP

1

VREF

8

RT/CT

4

OUT

6

SENSE

3

IC1

UC3842

R10

R11

R12

R13

C5

R14

GND

GND

R15

C6

GND

GND

C7

GND

R16

R17

Q1

R18

R1W

GND

3

6

5

10

8

1

TR1

D10

D8

R8

R1/2W

R9

R1/2W

+

C9

1

2

3

JP3

TOR1

D9

+

C10

GND

R19

10K

GND