MJL16218

6

Motorola Bipolar Power Transistor Device Data

DYNAMIC DESATURATION

The SCANSWITCH series of bipolar power transistors are

specifically designed to meet the unique requirements of hor-

izontal deflection circuits in computer monitor applications.

Historically, deflection transistor design was focused on mini-

mizing collector current fall time. While fall time is a valid

figure of merit, a more important indicator of circuit perfor-

mance as scan rates are increased is a new characteristic,

“dynamic desaturation.” In order to assure a linear collector

current ramp, the output transistor must remain in hard satu-

ration during storage time and exhibit a rapid turn–off transi-

tion. A sluggish transition results in serious consequences.

As the saturation voltage of the output transistor increases,

the voltage across the yoke drops. Roll off in the collector

current ramp results in improper beam deflection and distor-

tion of the image at the right edge of the screen. Design

changes have been made in the structure of the SCAN-

SWITCH series of devices which minimize the dynamic

desaturation interval. Dynamic desaturation has been

defined in terms of the time required for the VCE to rise from

1.0 to 5.0 volts (Figures 9 and 10) and typical performance at

optimized drive conditions has been specified. Optimization

of device structure results in a linear collector current ramp,

excellent turn–off switching performance, and significantly

lower overall power dissipation.

U2

MC7812

VI

VO

G

N

D

+

+

+

+

+24 V

C1

100

µF

C2

10

µF

C3

10

µF

R7

2.7 k

R8

9.1 k

R9

470

R10

47

C5

0.1

C4

0.005

R2

R510

R3

250

R6

1 k

R12

470

1 W

D1

MUR110

T1

LB

R4

22

Q4

DUT

VCE

CY

LY

C6

100

µF

R5

1 k

(IC)

(IB)

Q5

MJ11016

Q2

MJ11016

Q3

MJE

15031

R11

470

1 W

100 V

D2

MUR460

U1

MC1391P

%

OSC

VCC

OUT

GND

76

81

2

(DC)

BS170

Q1

SYNC

Table 2. High Resolution Deflection Application Simulator

R1

1 k

6.2 V

T1: Ferroxcube Pot Core #1811 P3C8

LB = 1.5

µH

Primary/Sec. Turns Ratio = 18:6

CY = 0.01

µF

Gapped for LP = 30 µH

LY = 13

µH

Figure 11. Deflection Simulator Circuit Base

Drive Waveform

TIME (2

µs/DIV)

IB1 = 2.2 A

Figure 12. Definition of Dynamic

Desaturation Measurement

TIME (ns)

tds

DYNAMIC DESATURATION TIME

IS MEASURED FROM VCE = 1 V

TO VCE = 5 V

1

4

5

0

3

2

06

8

4

210

IB2 = 4.5 A