Philips TDA6107JF manual Cathode output, Dissipation, Flashover protection, Switch-offbehaviour

Philips Semiconductors	Product specification
Triple video output amplifier	TDA6107JF
Cathode output	Dissipation

The cathode output is protected against peak current (caused by positive voltage peaks during high-resistance flash) of 3 A maximum with a charge content of 100 μC (1).

The cathode is also protected against peak currents (caused by positive voltage peaks during low-resistance flash) of 6 A maximum with a charge content of 100 nC (1).

The DC voltage of VDD (pin 6) must be within the operating range of 180 to 210 V during the peak currents.

Flashover protection

The TDA6107JF incorporates protection diodes against CRT flashover discharges that clamp the cathodes output voltage up to a maximum of VDD + Vdiode.

To limit the diode current an external 1.5 kΩ carbon high-voltage resistor in series with the cathode output and a 2 kV spark gap are needed (for this resistor value, the CRT has to be connected to the main PCB (1).

VDD must be decoupled to GND:

1.With a capacitor >20 nF with good HF behaviour (e.g. foil); this capacitor must be placed as close as possible to pins 6 and 4, but definitely within 5 mm.

2.With a capacitor >3.3 μF on the picture tube base print, depending on the CRT size.

Switch-off behaviour

The switch-off behaviour of the TDA6107JF is controllable. This is because the output pins of the TDA6107JF are still under control of the input pins for low power supply voltages (approximately 30 V and higher).

Bandwidth

The addition of the flash resistor produces a decreased bandwidth and increases the rise and fall times; see “Application Note AN96072”.

(1)External protection against higher currents is described in “Application Note AN96072”.

Regarding dissipation, distinction must first be made between static dissipation (independent of frequency) and dynamic dissipation (proportional to frequency).

The static dissipation of the TDA6107JF is due to voltage supply currents and load currents in the feedback network and CRT.

The static dissipation Pstat equals:

Pstat = VDD × IDD + 3 × VOC × IOC

Where:

VDD = supply voltage

IDD = supply current

VOC = DC value of cathode voltage

IOC = DC value of cathode current.

The dynamic dissipation Pdyn equals:

Pdyn = 3 × VDD × (CL + Cint) × fi × Voc(p-p) × δ

Where:

CL = load capacitance

Cint = internal load capacitance (≈4 pF)

fi = input frequency

Voc(p-p)= output voltage (peak-to-peak value)

δ= non-blanking duty cycle.

The IC must be mounted on the picture tube base print to minimize the load capacitance CL.

2002 Oct 18 11