圖中的電路可以實現輸出電壓0.7～24V連續(xù)可調，并且可以實現50mA～2A可調的最大輸出電流限制。

P1用來設置輸出電流最大限值，調整它可以在相應的輸出電壓時，給出50mA～2A的電流限制。P1設置輸出電流最大限值的原理如下：從圖中可以看出，輸出電流主要來自Q4的發(fā)射極，這樣，當輸出電流增大，電路中a、b點間的電壓也跟著增大，這時，a點(即Q3的e極)和Q3的b極間的電壓也增大，而Q3的e、b極間電壓不可能超過0.7V，當Q3的e、b極間電壓增大時，Q3的e極會分流走流往Q4的b極的電流，這樣，就限制了a、b點間電壓的增大，從而實現最大輸出電流限制的目的。

P2用做輸出電壓調節(jié)。當輸出電壓增大，Q1的e、b極間電壓也增大，這導致Q1分流走流往Q2的b極的電流，Q2導通電流下降后，不難看出Q4的導通電流也下降，從而使輸出電壓下降。當輸出電壓減小時，原理類似。

P2建議用對數型的電位器，這樣輸出電壓的可調性和線性會更好些。

電源變壓器的輸出電壓和容量應根據你所需要的輸出電壓和電流來選區(qū)。最佳的方案是：變壓器次級電壓為36、40、48V或帶中間抽頭的50、75、80V，容量為100VA。

電容C1可以從2200～6800uF／35～50V之間選擇。

電路中，BC182為50V／100mA／NPN三極管，BD139為80V／1.5A／NPN三極管，BC212為50v／100mA／PNP三極管，2N3055為60V／15A／NPN三極管。Q4必須使用散熱器，另外它可以使用TIP3055代替。

google translate:

0.7 ~ 24V continuously adjustable current limiting power supply
The circuit diagram can be achieved output voltage 0.7 ~ 24V continuously adjustable, and can be adjusted to achieve 50mA ~ 2A maximum output current limit.
P1 is used to set the maximum output current limit, you can adjust the output voltage in the corresponding given 50mA ~ 2A current limit. P1 to set the maximum output current limit of the principle is as follows: As can be seen from the diagram, mainly from the Q4 output current emitter, so that when the output current increases, the circuit in a, b points, also followed the voltage between the increase Then, a point (that is Q3 of e pole) and Q3 of the b pole voltage between the increase and Q3 of the e, b can not exceed the voltage between 0.7V, when the Q3 of e, b the voltage between electrodes increased time, Q3 e-flow to the most would be diverted away most of the current Q4 of b, so that the limits a, b point between voltage increases, the maximum output current limit in order to achieve the purpose.
P2 used as the output voltage regulation. When the output voltage increases, Q1 of the e, b the voltage between electrodes is also increased, leading to the Q2 Q1 flow diversion away the b-polar current, Q2 conduction current decreases, not difficult to see Q4 current will also decrease so that the output voltage drops. When output voltage decreases, the principle of similar.
P2 suggested logarithmic potentiometers, so the output voltage is adjustable and linear will be better.
Power transformer output voltage and capacity you need should be based on the output voltage and current to constituency. The best option is: Transformer secondary voltage 36,40,48 V or with intermediate tap 50,75,80 V, capacity of 100VA.
Capacitor C1 can be 2200 ~ 6800uF/35 ~ 50V to choose between.
Circuit, BC182 transistor for the 50V/100mA/NPN, BD139 to 80V/1.5A/NPN transistor, BC212 to 50v/100mA/PNP transistor, 2N3055 transistor to 60V/15A/NPN. Q4 must use the radiator, while it can use TIP3055 replace.