Philips Colour Television Specifications download pdf (Page 44)

Circuit Descriptions and Abbreviation List

GB 96 EM3E9.

Main Supply is switched ‘off’ (via TS7529). A relay (1550) is

used to switch the Degaussing circuit. It is switched ‘on’ after

set start-up and switched ‘off’ by the

mP after 12 s.

The Main Supply, an SMPS that is based on the 'down-

converter' principle, generates the 141 V (V

BAT

) and the +/-

16 V for the audio part. Difference with former MG-sets is that

BAT

is not mains isolated ('hot') and is alignment free.

9.3 Power Supply (diagram A1 & A2)

The power supply has a number of main functions:

• Mains harmonic filter.

• Degaussing picture tube.

• Standby power supply.

• Main supply.

9.3.1 Mains Harmonic Filter (diagram A1)

Figure 9-2

The mains harmonic filter has 2 functions: to prevent that

high frequency signals (harmonics) are transferred into the

mains and to protect the set from lightning damage.

C2507 prevents that the high frequency signals, generated

by the set, are conveyed into the mains (it forms a short-

circuit).

In case of a lightning surge between the 2 phases (differential

mode) the energy is immediately bled away through the VDR

(R3509) to the other phase.

In case of a lightning surge on both phases of the mains in

relation to the aerial earth, the filter acts as a high resistance

EMK

=L * dI/dt), as a result of which the voltage across coil

L5503/04 increases. A spark gap (1590) prevents that the

voltage increases too much, which would lead to a damaged

coil. When ignited, the current will be discharged via this

spark gap.

Resistor R3500 is used for limiting the inrush-current.

9.3.2 Degaussing (diagram A1)

The 5V2 is present, as soon the set is switched 'on' via the

mainsswitch.Asthe‘DEGAUSSING’ signal from the

processor (OTC) is ‘low’, transistor 7528 will conduct and

relay 1550 is activated. Initially a considerable current will

flow, via PTC 3516, through the degaussing coil. The PTC

will heat up, resistance will rise and the current will decay

rapidly. The OTC makes the ‘DEGAUSSING’ signal ‘high’

after 12 s, which will switch the relay ‘off’.

9.3.3 Standby power supply (diagram A2)

Principle

This power supply is of a SOPS type (Self-Oscillating Power

Supply) and is regulated by the controlled switching of an

oscillator. It uses the so-called 'Flyback' principle:

Figure 9-3

• After closing switch 'S', the current ID will increase linear

in time. The magnetic energy in the primary coil is directly

proportional with the self-inductance of the coil and

current ID (thus with the time the switch is closed). The

voltage polarity at the secondary winding is negative

(due to different winding direction), meaning that diode D

will block. Capacitor C will discharge via RL, U

OUT

will

decrease.

• Opening switch 'S' will generate a counter-e.m.f. in the

primary winding, trying to maintain current ID. Through

this the polarity of the secondary voltage will inverse. The

magnetic energy, stored in the coil, will now be

transformed to the secondary side. Diode D will now

conduct, capacitor C will be charged and

OUT

will

increase.

Implementation

Figure 9-4

To apply this on the EM3E (diagram A2): replace switch 'S'

by FET TS7102, coil L by L5101/L5100, diode D by D6111

and C by C2104.

– Time interval t0 - t1: After switching ‘on’ the TV-set, the

gate of MOSFET TS7102 will be high (max. 15 V due to

zener diode D6105). This will drive the FET into

saturation (U

= 0 V). The DC-voltage U

MAINS

will be

transposed across the primary winding of L5101 (3, 5),

resulting in a linear increasing current through this coil.

The voltage across the co-coupled coil (1, 2) is also

positive and will keep the FET into conductivity via

C2101, R3103/3105/3102 and R3117 for some time.

The self-induction of the coil and the magnitude of the

supply voltage (+375 V) determine the slope of the

primary current. The maximum current is determined by

the time the FET stays into conductance (t0 - t1). This

time is directly determined by the voltage across R3108/

CL 16532044_020.eps

140501

2507

mains

3521

4M7

1501

1590

3501

9503

Mains harmonic

diversity

3551

9504

+375V

2516

2537

3500

5502

5511 or 5516

5503 or

5504

96532156_020.eps

210100

out

375V

out

375V

Isec

CL 16532044_019.eps

160501

3103

3105

3113

22R

3124 6122

68R 3V9

7101

6105

15V

3102

3117

47R

3126

10K

3125

15R

7100

3104

47R

3101

STARTUP

V-START

10M

3127

5K6

3120

10R

31063107

1K 1K

2101

2n2

5102

-13V

6111

6103

MAINS

OUT

2104

2m2

6106

15V

3114

220R

2109 +

2149

6108

3108

//3118

+5V2

HOT COLD

GND-STB

2114

7102

6105

15V

10n

2102

10µ

MAIN

SEC

PRIM

SEC

7104

Usec

ON OFF

t0 t1 t2

5101

3110

2R2

+375V

2111

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Philips Colour Television Specifications Page 44

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