1997 Jan 20
4
Philips Semiconductors
Product specification
Vertical deflection power amplifier for
monitors
TDA4861
PINNING
SYMBOL
PIN
DESCRIPTION
V
P1
1
supply voltage 1
INP1
2
input 1 of differential input amplifier
INP2
3
input 2 of differential input amplifier
V
P2
4
supply voltage 2 for vertical output
stage
V-OUT
5
vertical output
SUB
6
substrate
FLB
7
flyback generator output
V
P3
8
flyback supply voltage 3
PCO
9
pulse circuit output
Fig.2 Pin configuration.
handbook, halfpage
TDA4861
MEH360
1
2
3
4
5
6
7
8
9
VP1
VP2
VP3
INP1
INP2
SUB
PCO
FLB
V-OUT
FUNCTIONAL DESCRIPTION
Differential input amplifier
The differential sawtooth input signal (coming from a ramp
output of the TDA4850 for example) is fed to the input at
pins 2 and 3. The non-inverted signal is attached to pin 3.
The vertical feedback signal is superimposed on the
inverted input signal on pin 2.
Vertical shift is applied at the inputs in a power-less way
(see Fig.1).
Flyback generator
Signals for the flyback generator and the pulse circuit are
generated in the flyback driver stage. The flyback output
consists of a Darlington transistor and a flyback diode.
The flyback generator can operate in two modes:
1. An external supply voltage is applied for the short
flyback time, thus the power dissipation is minimum
(see Fig.1).
2. The flyback voltage is generated by doubling the
supply voltage (see Fig.5). The 100
µ
F capacitor C2
connected between pins 4 and 7 is charged up to V
P1
during scan, using the external diode and the resistor
R2. The cathode of the capacitor C2 is connected to
the positive rail during flyback. Thus, the flyback
voltage is twice the supply voltage.
Vertical output
The vertical output stage is a quasi-complementary
class-B amplifier with a high linearity. The output contains
SOAR (short-circuit protection) and thermal protection.
The output current on pin 5 is reduced for a short time
(to let the temperature decrease to T
j
< 150
°
C), when the
junction temperature (T
j
) exceeds 160
°
C.
Deflection GUARD
Pin 9 will go HIGH if the junction temperature goes too
high (see Fig.3). A pulse signal with 50% duty cycle is
output on pin 9, if the deflection coil is open-circuit.
A flyback pulse signal is output at normal conditions.
Further watching can be achieved by means of an external
GUARD circuit as shown in Fig.4. The 22
µ
F capacitor is
charged during flyback time (V
5
> V
8
) at normal conditions.
In the event of failures, the capacitor is discharged and the
GUARD output goes HIGH.
GUARD output level (see Fig.4):
•
LOW for normal conditions
•
HIGH for deflection coil short-circuit respectively
open-circuit
•
HIGH when there are neither input or output signals.
