CIRCUIT DESCRIPTION

Figure 7 shows the block diagram of the TDA8140,

the circuit consists of an input transconductance

amplifier composed by Q1, Q2, Q3 and Q4.

The symmetrical output current is fed into the load

resistor R1 and R2 ; the two amplifiers V1 and V2

realize a floating voltage to current converter which

can drive 1.2A sink current and 2A source current

for a wide common output range.

So, the overall transconductance results into :

=

R1

+ R2

R3

⋅

1

R5

across the resistor R4 which provides an output

bias current of 140mA ; the control input determines

the turn ON/OFF function.

In the ON phase, Q5 shorts the external capacitor

the element realizes the transconductance func-

tion ; lower voltages are clamped by the D1/Q6

configuration.

For input voltages higher than 750mV, Q7 limits the

maximum output current at 1.5A peak.

input voltage, by this way, the output current de-

creases quasi linearly and the system stability is

reached.

During the flyback phase, the IC is disabled via the

sync. detector input ; this function with the limited

sink and source current together with the undervol-

tage turn-OFF and a chip temperature sensor en-

sure a complete protection of the IC.

In Figure 8 is shown the application diagram of the

TDA 8140, the few external component and the

automatic handling possibility ensures a lower ap-

plication cost versus the conventional approach

shown in Figure 4.

In Figure 9 is shown the currents and voltages

waveforms of the driver circuit of Figure 8, as to be

seen, the driving charge Ib

at minimum.

&

C

VOLTAGE

CONTROL

V < 7V

j

OVERTEMP.

PROTECTION

T < 150˚C

&

8

7

6

5

4

3

1

2

9

101112

13141516

Q9

V1

R2

R1

INPUT

TRANSCONDUCTANCE

AMPLIFIER

V2

Q10

Q11

R5

D2

Q7

Q6

R4

D1

Q1

Q4

Q3

R3

Q8

R6

Q2

Q5

I

1

I

2

REF

IN

V

V

= 750mV

OUTPUT

I

B

SENSE

INPUT

V

+

CC

PROTECTION

AND REMOTE

STANDBY INPUT

CONTROL

INPUT

SPECIAL

REMOTE

STANDBY

POWER GROUND

SENSE

GROUND

C

EXT

C

T

Figure 7 : Block Diagram of the Integrated Horizontal Driver

TDA8140

7/10