Suitable for fluorescent lamp ignition circuits in low voltage areas

In the figure, kl is the switching contact of relay K, where position "l" is the normally closed end and position "2" is the normally open end. S is
the general power switch. When turning on the light, just close the switch S. At this time, the 220V AC power ( the actual voltage in low-voltage areas is only
more than a hundred volts) is superimposed by the secondary autocoupling of the transformer to 34V (actually only about 20 volts). Volts, because the primary is less than 22 (JV), it is sent to
the fluorescent lamp circuit, so that the fluorescent lamp can be ignited and illuminated normally. The AC output from the other half of the secondary winding of the transformer T
is bridge rectified by the diodes VDI~VD4 and filtered by the capacitor C to output a voltage that changes with the grid voltage. DC voltage, because the grid voltage is low, the
DC voltage is also low, which is not enough to breakdown the Zener diode VD7, so the transistor VT is in the cut-off state, the relay K does not
act, and kl is still in the normally closed end. At this time, the entire controller is The fluorescent lamp circuit boosts the voltage.
    When the mains voltage rises and returns to normal, the DC voltage output at both ends of the capacitor C also rises. VD7 is broken down and turned on
, VT is also turned on, and the relay K is powered on. kl reverses to the normally open state "2". At this time, the fluorescent lamp circuit is directly powered by
the mains power grid, and no voltage boosting process is performed. From the above analysis, it can be seen that as the grid voltage fluctuates, the switching contact of the relay
will automatically switch between normally open and normally open. Switching between closed ends ensures the normal power supply of the fluorescent lamp circuit
.     The function of VD5, VD6 and LED is to step down, because when the mains power is normal, both ends of the capacitor C can output
a DC voltage of up to 20V, which is much higher than that of the relay. Working voltage. LED also serves as a normal power supply indicator for the mains.