Adjustable from 3 to 9V 100mA power supply circuit

  
3-9V adjustable lOOmA power supply as shown in Figure 12-30 power supply, there is a series regulator circuit using the amplifier tubes, the output voltage from the 3 ~ 9V cont
Adjustable from 3 to 9V 100mA power supply circuit - schematic

inuously adjustable output current can reach lOOmA, suitable for power supply voltage transistor radios use a different variety. Circuit principle: low-voltage AC transformer secondary side, through rectifier diode VD1-VD4 rectifier, filter capacitor c1, that DC power supplied to the regulator section. Regulated in part by the regulator VT1 ,. VTZ amplification and play the role of regulator of silicon dioxide hibiscus tube VD5, VD6 other components. Acronym startling drop tube voltage drop transistor collector and emitter of the plate. Monument tube voltage modulation on takeover VT1 is variable, when the output voltage decreases tendency t voltage drop will automatically become smaller, maintaining constant output voltage when the output voltage tends to increase, and pressure drop automatically become larger, still maintain the output voltage constant. Visible, VT1 is equivalent to a variable resistor, due to its regulatory effect, so that the output voltage is substantially unchanged. The role of the regulator is adjusted by the amplification VT2 control potentiometer output voltage through the voltage divider, the output voltage is applied to the base part VT2 between the electrode and the ground. Since launching Xi VT2 ground voltage through - diode VD5, VD6 stable, can be considered VT2 emitter-to-ground voltage is constant, this voltage is called the reference voltage. such. r: r2 base voltage the change is reflected in the output voltage variation rhyme. If the output voltage is reduced (refer to absolute value, the same below) trend, VT2 base emitter voltage should also be reduced, which makes the collector current of VT2 is reduced, the collector voltage increases. Since VT2 and VT1 is directly coupled Yun, VT2 collector Xi voltage increases, VT1 is the base-emitter voltage is increased, which makes VT1 strengthen conduction voltage drop is reduced to maintain the output voltage constant. Similarly, if the output voltage increasing trend, by the action of the tube drop VT1 VT2 increases, maintain the output voltage constant. VD5, VD6 is to use them in the forward conduction when the forward voltage drop substantially no current change in the characteristics of the regulator. Silicon tube forward voltage drop of about 0. 7V, two silicon diodes in series can get a stable voltage of approximately 1.4V. Regulators did not take advantage of the positive characteristics of the use of anti- breakdown characteristics to good effect, its advantage is the ability to provide a lower regulated voltage. The horse is to provide VD5, limiting resistor VD6 forward current. Load resistance Rz is VT2, VT1 is a bias resistor. Ri to the output current is high time to reduce the pressure drop and set VT1 opposed. C2 is taken into account when the mains voltage is reduced in order to reduce the output voltage of the AC component and set up. G is to reduce the role of stable power supply voltage AC resistance and ripple.




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