Members help me to explain the role of the various components in detail. The There D5 regulator is 21V why the output is 20V, they said to reduce the UBE0.7V pressure drop. I do not understand, why should subtract UBE ah? The more detailed the higher probability of adoption. The Remember the details. The The Thank you all the teachers. The
? Mainly three-tier tube is how to complete the regulator?
First, you have to know that the VT working state is in a magnified state or a saturated state, so VT's Ube> 0. VT is in magnified state, Ube = 0.7v.
D5 to ground voltage (ie VT base voltage) = VT Ube + circuit output voltage Uout
Uout = Ud5-Ube
= 21v-0.7v
You are right, the current is so gone. Regulator tube can indeed be seen as a voltage source, but the internal impedance is very large.
By reason, with the regulator can also be directly for the power supply, but then, the resistance is the current limiting resistor, the output current will be small, may not meet your requirements.
With the transistor as a regulator tube, a big reason is to reduce the power supply resistance, increase the power output capacity (current).
This is the standard series regulator circuit, but the transistor is not regulated, it is only used as a regulator tube, used to adjust the voltage.
Circuit connected, A point voltage through the resistor R1 into the regulator D5, as long as the working range, the regulator will be stable at 21V;
In fact, each regulator will have errors, the specific choice of the regulator can be found on its DATASHEET this error;
Output to the voltage on the C3, that is, the voltage regulator tube to reduce the VT BE junction voltage (if it is silicon tube, is about 0.7V);
Obviously, the difference between the input voltage at point A and the output voltage on C3 is added between the CE poles of the transistor.
Whether the output current changes or input voltage changes, the regulator will be through the regulation of the transistor BE to complete the transistor CE to withstand the voltage to adjust to achieve the purpose of stabilizing the output voltage.
