Datasheet U2010B (Atmel) - 5

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Atmel U2010B 3.4 Automatic Retriggering
The current-detector circuit monitors the state of the triac after triggering by measuring the voltage drop at the triac gate. A current flow through the triac is recognized when the voltage drop exceeds a threshold level of typically 40mV. If the triac is quenched within the relevant half-wave after triggering (for example owing to low load currents before or after the zero crossing of the current wave, or for commutator motors, owing to brush lifters), the automatic retriggering circuit ensures immediate retriggering, if necessary with a high repetition rate, t /t , until the triac remains reliably triggered. pp p
3.5 Current Synchronization
Current synchronization fulfils two functions: – Monitoring the current flow after triggering. In case the triac extinguishes again or does not switch on, automatic triggering is activated until the triggering is successful. – Avoiding triggering due to an inductive load. In the case of inductive load operation, the current synchronization ensures that in the new half wave, no pulse will be enabled as long as there is a current available from the previous half wave, which flows from the opposite polarity to the actual supply voltage. The current synchronization as described above is a special feature of the Atmel® U2010B. The device evaluates the voltage at the pulse output between gate and reference electrode of the triac. As a result, no separate current synchronization input with specified series resistance is necessary.
3.6 Voltage Synchronization with Mains Voltage Compensation
The voltage detector synchronizes the reference ramp with the mains supply voltage. At the same time, the mains-dependent input current at pin 15 is shaped and rectified internally. This current activates the automatic retriggering and at the same time is available at pin 5. By suitable dimensioning, it is possible to obtain the specified compensation effect. Automatic retriggering and mains voltage compensation are not activated until ⏐ V ⏐ increases to 8V. 15 - 10 The resistance R defines the width of the zero voltage cross over pulse, synchronization sync. current, and hence the mains supply voltage compensation current.
Figure 3-1.
Suppression of Mains Voltage Compensation and Automatic Retrigger Mains R2 15 2 x
Atmel
C6V2
U2010B
10 If the mains voltage compensation and the automatic retriggering are not required, both func- tions can be suppressed by limiting ⏐ V ⏐ ≤ 7V, see Figure 3-1. 15 - 10
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4766D–INDCO–03/11 Document Outline Features Applications 1. Description 2. Pin Configuration 3. General Description 3.1 Mains Supply 3.2 Voltage Monitoring 3.3 Phase Control 3.4 Automatic Retriggering 3.5 Current Synchronization 3.6 Voltage Synchronization with Mains Voltage Compensation 3.7 Load-current Compensation 3.8 Load-current Limitation 3.8.1 Mode Selection 4. Absolute Maximum Ratings 5. Thermal Resistance 6. Electrical Characteristics 7. Diagrams 8. Ordering Information 9. Package Information 10. Revision History