Dimming light circuit using operational amplifier

The dimmer light circuit using an operational amplifier is shown in Figure 49 (a). It is controlled by two buttons. When one
of , the light gradually changes from dark to bright; when the other button is pressed, the light gradually becomes brighter. It gradually turns from bright to dark
until it goes out.
    Operational amplifier F081 is used as a comparison amplifier here, and a large capacitor G is connected to its inverting input terminal as a
reference comparison voltage. It is charged through two key switches SB1 and SH2, thereby changing C. Electricity
/voltage at both ends. The AC voltage introduced from the iov winding on the secondary side of transformer T is rectified by bridge VD5-VD8 and clipped
by vs. Charge the charging circuit composed of R s and f1 . When the pulsating DC voltage is zero, C passes through
VD9 and R. Discharge, in C. A sawtooth transition voltage is formed, and this voltage is added to the non-inverting input terminal of the arithmetic amplifier
. VD9 means only discharging the diode, so that each cycle of the thyristor VTH has an equal conduction
delay angle. "When the l-phase terminal voltage v J of the operational amplifier - the inverting terminal voltage V of the operational amplifier, the operational amplifier The ⑥
pin of the output terminal outputs a high level to turn on VTH; when V+ is less than v-, the output is zero and VTH is turned off.
The input and output waveforms are as shown in (a) in 49(b) (assuming that at this time The reference comparison voltage V--Va, V. is
the output voltage of the operational amplifier (that is, the voltage that triggers VTH). In this case, the conduction delay angle of VTH is ∞. When
the reference comparison voltage of the operational amplifier becomes When it is Vb, its output waveform is shown in (b) of Figure 49(b), and
the delayed firing angle of VTH becomes adjacent. Va and Vb are both the inverting input terminal voltage of the voltage comparator in Figure 19(a)
(that is, c - The voltage at both ends), the voltage can be changed by pressing SBl and SB2. It can be seen that controlling
SR1 and SB2 can make the reference comparison voltage of the operational amplifier change between o≤V-≤Vz (Vz is
the stable voltage value of vs ).The conduction angle of the thyristor VTH can be changed between 0--180', thereby controlling
the brightness of the load bulb E.