Circuit Principle Analysis of Transistor Regulated Power Supply
One is a transistor shunt regulated power supply. Where T1 is the regulator, D1 is the reference regulator, R1 is the current limiting resistor of D1, R2 is the current limiting resistor, R3 is the load. The output voltage of this voltage regulator circuit is approximately equal to the regulated value of the regulator D1 (actually add the T1 emission junction voltage, generally germanium tube take 0.3V, silicon tube take 0.7V). This is due to the power supply in operation, T1 emitter junction conduction, the emitter voltage and base voltage to maintain the same, while the base voltage is stabilized by D1 at a fixed value. This circuit can be regarded as T1 will be D1 voltage regulator amplified β times, equivalent to the access to a regulated value for the D1 regulated value, the voltage regulator effect is β times the effect of D1 voltage regulator.
The circuit works as follows:
UI↑→UD1↑→(UT1)EC↑→(IT1)EC↑→IR2↑→UR2↑→(UT1)EC↓
UI↓→UD1↓→(UT1)EC↓→(IT1)EC↓→IR2↓→UR2↓→(UT1)EC↑
Component selection for transistorized voltage regulator
The steps for selecting components for this circuit are similar to those for the parallel voltage regulator circuit with silicon regulator, mainly from the following aspects.
(1) Initial selection of regulator T1 and voltage regulator D1
When selecting the regulator T1, the main consideration is that its rated current ICM should be greater than the output current IO, in order to ensure that the regulator will not be damaged by excessive current when the load is open. In addition, in order to ensure that the adjustment tube has a good adjustment effect, but also requires a large β value, small leakage current. Selection of regulator D1, the main consideration of its stabilization voltage and the sum of the T1 emitter junction voltage should be equal to the output voltage.
(2) Selected input voltage
In order to ensure the efficiency of the regulated power supply, the input voltage is generally not too high, not more than 2 UI is appropriate.
(3) Select current limiting resistor R2
For the parallel voltage regulator circuit, the current limiting resistor R2 is the key to the whole circuit work well or not. R2 choose a large, the voltage regulator effect is better, but the power consumption is large (because the resistor power consumption P = I2R), while requiring the input voltage increases, the power supply's efficiency is relatively low. Specific calculations can be referred to the third step of the silicon voltage regulator parallel voltage regulator circuit components selection.
(4) Check circuit stability
The stability of the entire circuit needs to be determined according to the requirements of the actual circuit, if the stability is not enough, you can increase R1 and UI appropriately, you can also choose a larger β value, smaller leakage current regulator tube.
