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# Islam Amer

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2. ## Help Under standing Schematic PSU

Hello guys ! Can any one help analyse this linear regulated PSU https://www.rapidonline.com/pdf/554305_v1.pdf The schematic diagram at the end of portable document format file PDF where there are transformer of several secondary winding part of transformer used to output regulated+12 volts and reference 2.5V through wl431 and -15v and -6v with exactly the same method used in that PSU to obtain -5.6 voltage rail which will power the op amps and other part of the circuit. The other wingdings are used to power the linear regulator 6 NPN 2n3055 transistors and then to load. The 2 op-amp(HA17741) regulate current and voltage through current source darlington transistor with vcc of 12 volt through bases of 6 NPN 2n3055 transistors which carry shunt resistors in their emitter path where the load after that could attached those 6 transistors are connected to same transformer in their collector where it can output 0-15 or 0-30 or 0-50 volt with maximum current of 3 Amps My inquires about how the current source with +12 volt can force 6 parallel transistors to out put 15 or 20 or 30 or even 50 volt through collector emitter path while 15 volt be at emitter need 15 volt + minimum vbe value 0.6 = 15.6 and 20 need 20.6 and so on ? The other thing how the reference of 2.5 volt could be used to() maintain voltage level(15-20-30-50) prevent 2 op amps from sinking current before access to bases of 6 parallel transistors? Also adding a shunt resistor which located before the load so voltage return to current regulated op amp will be higher than reference voltage at non inverting input of current regulated amplifier make it always sinking base current of 6 parallel transistors? 554305_v1.pdf
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