# 15v 500mA ower supply questions

#### khatus

Joined Jul 2, 2018
70

Hello guys, I want to know what is purpose of the transistor T3(BC547B) in this circuit. I understand it provides base current to the series pass transistor T5(2N3055). Also i want to know

1. what is the function of transistor T4(BC557B) and T2(BC547B) and T1(BC547B)??

2. Here D1 (1w,15V) is a zener diode?

3.What is BZ1(24V) in this schematic?

#### iimagine

Joined Dec 20, 2010
388
T4 senses voltage, sets by P1, source current to T2 to cutoff T3, T3 stops feeding current to T5
Basically, when voltage rises above reference voltage sets by P1, T4 starts to turn on and cuts off T5 by chain reaction

#### iimagine

Joined Dec 20, 2010
388
2. Here D1 (1w,15V) is a zener diode?
Yes, it limits the turn on point of T3 to 15V.

#### AnalogKid

Joined Aug 1, 2013
8,232
Hello guys, I want to know what is purpose of the transistor T3(BC547B) in this circuit. I understand it provides base current to the series pass transistor T5(2N3055).
That is all it is for. T3 and T5 combine to form a Darlington transistor, developed by Sidney Darlington, a researcher at Bell Labs. If the wording in the patent application had been more generic, Bell would have had the first patent for an integrated circuit five years ahead of TI.

https://en.wikipedia.org/wiki/Darlington_transistor

Sidney was a card-carrying rocket scientist. He developed the basic equations for controlling a rocket from the ground by radio, and they still are used today.

https://en.wikipedia.org/wiki/Sidney_Darlington

ak

#### ScottWang

Joined Aug 23, 2012
6,845
3.What is BZ1(24V) in this schematic?
R1, R2, T1, Bz1, R9 is a alarm circuit, used R1 to do the current sense and V_R1 to activated T1 and to drive the Bz1.