Datasheet U2008B (Atmel) - 4

link to page 7 link to page 8
2.2 Voltage Monitoring
When the voltage is built up, uncontrolled output pulses are avoided by internal voltage monitor- ing. Apart from that, all latches of the circuit (phase control, load limit regulation) are reset and the soft start capacitor is short circuited. This guarantees a specified start-up behavior each time the supply voltage is switched on or after short interruptions of the mains supply. Soft start is ini- tiated after the supply voltage has been built up. This behavior guarantees a gentle start-up for the motor and automatically ensures the optimum run-up time.
2.3 Phase Control, Pin 6
The function of the phase control is identical to that of the well-known Atmel® IC U211B. The phase angle of the trigger pulse is derived by comparing the ramp voltage V at pin 2 with the set 2 value on the control input, pin 3. The slope of the ramp is determined by C and its charging cur- 3 rent Iϕ. The charging current can be regulated, changed or altered using R at pin 6. 8 The maximum phase angle, α , (minimum current flow angle ϕ ) can also be adjusted by max min using R (see Figure 5-1 on page 7). 8 When the potential on pin 2 reaches the set point level of pin 3, a trigger pulse is generated whose pulse width, t , is determined from the value of C (t = 9µs/nF, Figure 5-3 on page 8). At p 3 p the same time, a latch is set with the output pulse, as long as the automatic retriggering has not been activated, then no more pulses can be generated in that half cycle. Control input at pin 3 (with respect to pin 4) has an active range from –9V to –2V. When V = –9V the phase angle is 3 at its maximum amax, i.e., the current flow angle is minimum. The minimum phase angle amin is set with V ≥ –1V. 3
2.4 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 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
2.5 Current Synchronization, Pin 8
Current synchronization fulfils two functions: • Monitoring the current flow after triggering. In case the triac extinguishes again or it does not switch on, automatic triggering is activated as long as triggering is successful. • Avoiding triggering due to inductive load. In the case of inductive load operation, the current synchronization ensures that in the new half wave no pulse is 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. A special feature of the IC is the realization of current synchronization. The device evaluates the voltage at the pulse output between the gate and reference electrode of the triac. This results in saving the separate current synchronization input with specified series resistance.
4 Atmel U2008B
4712D–AUTO–03/11 Document Outline Features Applications 1. Description 2. Pin Configuration 2.1 Mains Supply, Pin 5 2.2 Voltage Monitoring 2.3 Phase Control, Pin 6 2.4 Automatic Retriggering 2.5 Current Synchronization, Pin 8 2.6 Voltage Synchronization with Mains Voltage Compensation, Pin 7 2.7 Load Current Detection, Pin 1 3. Absolute Maximum Ratings 4. Thermal Resistance 5. Electrical Characteristics 6. Ordering Information 7. Package Information 8. Revision History