U 210 B / U 210 B–FP
The U 210 B is fitted with voltage limiting and can therefore be supplied directly from the mains. The supply voltage
between Pin 2 (+pol/ă) and Pin 3 builds up across D1 and R1 and is smoothed by C1. The vaIue of the series resistance
can be approximated using:
Further information regarding the design of the mains supply can be found in the data sheets in the appendix. The reference
voltage source on Pin 13 of typ. –8.9 V is derived from the supply voltage. It represents the reference level of the control
unit. Operating using an externally stabiIised DC voltage is not recommended.
If the supply cannot be taken directly from the mains because the power dissipation in R1 would be too large, then the
circuit shown in the following Figure 3 should be employed.
Figure 3 Supply voltage for high current requirements
The function of the phase control is largely identical to that of the well known components U 111 B and TEA 1007. The
phase angle of the trigger pulse is derived by comparing the ramp voltage, which is mains synchronised by the voltage
detector, with the set value on the control input Pin 9. The slope of the ramp is determined by C2 and its charging current.
The charging current can be varied using R2 on Pin 5. The maximum phase angle amax can also be adjusted using R2.
When the potential on Pin 6 reaches the nominal value predetermined at Pin 9, then a trigger pulse is generated whose
width tp is determined by the value of C2 (the value of C2 and hence the pulse width can be evaluated by assuming 8 ms/nF).
At the same time, a latch is set, so that as long as the automatic retriggering has not been activated, then no more pulses
can be generated in that half cycle.
The current sensor on Pin 1 ensures that, for operation with inductive loads, no pulse will be generated in a new half cycle
as long as current from the previous half cycle is still flowing in the opposite direction to the supply voltage at that instant.
This makes sure that ”Gaps” in the load current are prevented.
The control signal on Pin 9 can be in the range 0 V to –7 V (reference point Pin 2).
If Vpin9 = –7 V then the phase angle is at maximum = amax i .e. the current flow angle is a minimum. The minimum phase
angle amin is when Vpin9 = Vpin2.
As the voltage is built up, uncontrolled output pulses are avoided by internal voltage surveillance. At the same time, all
of the latches in the circuit (phase control, soft start) are reset and the soft–start capacitor is short circuited. Used with
a switching hysteresis of 300 mV, this system guarantees defined start–up behaviour each time the supply voltage is
switched on or after short interruptions of the mains supply.