Shadowless lamp circuit principle

Self-excited oscillation circuit coupled with transformer of Mingtai shadowless lamp. After the power is turned on, the initial base current is provided to the transistor through the potentiometer w and the resistor R to turn it on, and the collector current increases. The collector potential of the shadowless lamp develops in a positive direction. Due to the positive feedback winding and the inductive coupling of the surgical lamp, the base current is further increased, and the collector potential tends to be more positive. The strong positive feedback causes the avalanche process of the transistor, causing it to quickly enter the saturation zone.

Due to the action of the pulse transformer, the saturation state of the transistor cannot be maintained for a long time in the surgical lamp. During the saturation period, Vce is close to zero, and the power supply voltage of the surgical lamp is directly added to L. Both ends. Due to the large inductance impedance of the surgical lamp, the excitation current gradually increases, the collector current Ic also gradually increases, and the base current Ib is approximately constant. After a period of time, the saturation condition Ib>{≥(B is the current amplification factor) will be destroyed. And make the transistor automatically out of saturation. At this time, the pole current decreases, causing the collector current to drop, and the collector potential develops in a negative direction.

The operating lamp then produces a positive feedback to cause a chain reaction; the transistor is quickly turned off. The induced potential in the transformer of the surgical lamp is discharged through the parasitic capacitance and the lamp load. The shadowless lamp completes a cycle of the transistor from on to off, and a voltage similar to a rectangular wave is induced on the fluorescent lamp.