TFA3352 datasheet, PDF - EEWORLD Datasheet

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TFA3352: DescriptionControl- and Monitoring-IC for Electronic Transformers operating Low-Voltage Halogen Lamps; File Size104KB，15 Pages; ManufacturerGSG; Websitehttp://www.gsg-asia.com/

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Control- and Monitoring-IC for Electronic Transformers operating Low-Voltage Halogen Lamps

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GSG

勁力

TFA3352

EDITION 09/00

半導½

Gunter

Semiconductor

GmbH

Control and Monitoring IC for

electronic transformer operating

low-voltage halogen lamps. It

triggers, monitors and turns-off RF

oscillation dependent on several

control and guarding function

For inquiry please contact :

China

Tel: 0086-755-3200442

Fax: 0086-755-3355520

Hong Kong

Tel : 00852-26190748

Fax: 00852-24948080

e-mail

sales@gsg-asia.com

Functional Description

The integrated circuit TFA3352 implements control and monitoring functions for electronic transformers. It assisted

corresponding with the circuit concerned the action principle of a push-pull flow converter, the oscillation of which

is modulated with the envelope of the mains frequency rectified for ac mode operation.

By means of the switching transistors shown, the transistor connected to reference potential is controlled via its

base, therefore, the integrated circuit does not come into contact with high voltages. The IC picks the oscillation

frequency by a trigger pulse to this base and evaluates the control frequency applied via inductive coupling by

means of an oscillation detector, in order to cut further triggers.

Furthermore, the oscillation can be attenuated via base terminal and with that reliably finished by a turn-off

transistor integrated in the IC.

This principle enables affecting of the oscillation in optional time regimes.

The IC consists of several logic units responding to zero crossings, overvoltage, overload, overtemperature, as

well as to the moment selected for phase cutting-off, and depending on that, it enables to control the oscillatory

circuit.

A temperature stable reference voltage and the low average current consumption enables the temperature circuit

to record the temperature within the chip.

Values recorded as overtemperature or overload are stored and cause the turn-off of the component.

Reset of the corresponding error memory is possible by power on reset.

Current supply takes place via an external dropping resistor, backup capacitor and an external voltage limiter

containing a Zener diode. During start phase, while the supply voltage is built up, the circuit minimizes its current

consumption.

Only when the flow converter successfully starts, the operating current consumption appears.

The constructional arrangement of the IC allows that short duration negative peak currents up to 300 mA can be

applied to the output TR.

The IC enables the scanning of the oscillation of the switch mode power supply during dc voltage operation, thus

there can also be dimmed with dc voltage supply.

Pin Description

Pin 1

Dim Input

An RC network is connected with the dim input D. By variation of RD it can be dimmed. In every zero crossing, the

RC-network is charged to the reference voltage of 4 V with a current of 500 µA. When the subsequent discharge

reaches a threshold of 2 V at input D, the turn-off transistor breaks the oscillation via output TR, and the trigger

pulses are cut till to the end of the following zero crossing.

By that, a phase cutting is carried out.

The minimum resistance of the RC network should be approximately 15 kΩ because otherwise the reference

voltage could be loaded by currents higher than 300 µA.

The IC is also able to dim in dc voltage operation. For this a 12.5 ms clock internally generated is used, which

controls the RC network at the dim input similar to the mains zero crossings in ac voltage operation.

A dim input that is not used can be kept unconnected.

In order to prevent possible coupling-in of distortions into the non used dim input surely, it has to be blocked or to

be connected with V

Pin 2

Clock Generator

The clock generator generates clock pulses of 20 µs width with a repetition rate of 4 kHz by defined reversing the

charge of the ramp capacitor of 390 pF connected to terminal CT.

From the clock rate of 250 µs there are derived all time lapses (except trigger width) generated by the IC. It has to

be considered, that with modification of the clock capacitor, three cycles of the frequency to be monitored by the

oscillation detector can be acquired within one clock cycle.

The capacity range of the clock capacitor has to be choiced between 200 pF and 500 pF, in order to guarantee a

save adjustment of the overload thresholds in ac and dc operation.

09/00

TFA3352

Pin 3

Trigger Output, Oscillation Detector, Turn-off attenuation

• Trigger Output

Trigger pulses are directly branched from the internal clock pulses. Via a delay line result the typical pulse width

of 1.5 µs for pulses, being applied every 250 µs to the trigger output. These trigger pulses are permanently

generated outside the time window of the mains zero crossings, detected by the IC, as well as separately from the

blanking intervals defined by dimming, as long as the circuit starts.

• Oscillation Detector

The oscillation detector realizes the control applied to the base of the switching transistor as a stabilized

oscillation for a period of a clock cycle of 250 µs, when more than three cycles of a sine-shaped less than 300 kHz

having an amplitude wider than 1 Vss are applied.

After an oscillation has been realized, further trigger pulses will be cut for the output TR by means of the logic.

Such an evaluation happens in every clock period. With lost load for instance by this means no oscillations are

recognized and, therefore, triggers generated for periods for which an oscillation shall be applied.

• Turn-off attenuation

By a turn-off transistor with a low saturation voltage the base of the external switching transistor, applied to

reference potential is surely cut, and by that the oscillation is finished during dim operation for the period of

230 µs. That 230 µs result from the clock rate minus an internal clock pulse width.

In the case of overload the turn-off transistor is statically controlled by approximately 10 mA, as long as the supply

voltage at terminal V

which is breaking down by that, again switch-off the turn-off transistor with a threshold

of 6 V.

The specifically designed turn-off transistor, as well as further constructive measures take over the protection of

the integrated circuit against transients which can be applied via inductive control.

An external Schottky diode D of corresponding power prevents the possible increase of the current consumption

of the IC caused by those negative transients.

Diode D1 (see schematic circuit) supplies the efficiency of the turn-off transistor at high power transformers.

Pin 4

GND

Connection to ground

Pin 5

Overtemperature protection input

The internal protection circuit is multiple usable.

If the input TE is connected to ground, the overtemperature protection is deactivated and the range of the

operating temperature runs between -10 °C and 110 °C.

The input TE enables, if it is unconnected, permanently to turn-off the oscillation circuit similar to the overload

recognition via temperatures between 80 °C and 95 °C on chip.

A detected overtemperature is stored by the same enquiry cycle used with overload. The circuit can only

sucessfully start after cooling down and mains interruption once again.

By wiring the temperature input with an external temperature-sensitive resistor into a divider between supply

voltage and ground, a switching voltage can be generated, which deactivates the temperature monitoring for

values < 0.1 V, and the temperature monitoring is directly activated for values > 3 V, therefore, the oscillation will

be turned-off after the delay time.

Therefore, any optional heat source can be monitored by a sensitive resistor.

Hereby has to be taken into consideration, that an already activated temperature monitoring mode is only

resetable by turning-off the mains.

Only one external resistor is required to upshift the internal switch-off temperature. The internal resistor 7.1 kΩ,

shown in the internal wiring diagram, only is effective for a switch-off temperature between 80 °C and 95 °C.

If the pin TE is connected with ground, the internal resistors 7.1 kΩ and 30.4 kΩ are connected in parallel. That

causes a switch-off temperature higher than 110 °C. In this case the overtemperature protection is not active in

the permissible operating temperature range.

A resistor of 50 kΩ, connected between pin TE and ground increases the switch-off temperature of approximately

15 degrees.

09/00

TFA3352

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