The following article presents a very simple low current mains operated transformerless power circuit using an inexpensive MJE13005 transistor and few other passive electronic components.
As can be witnessed in the given circuit diagram, the design is extremely straightforward.
How the Circuit Works
Transistor T1, which is a high voltage NPN transistor MJE13005 forms the main active component in the circuit.
Rest of the components are positioned just for supporting the conduction of T1 and for the required stabilization.
The circuit can be understood with the following points:
Mains input is fed across D2 and the negative line of the circuit.
D2 rectifies the mains AC, while C1 filters to some reasonable levels.
R1 drops the current to tolerable limits in order to provide the required base bias for T1.
C2 provides further filtration to the voltage generated after R1.
D1 clamps the base voltage at the base of T1 to 24V, such that the maximum output voltage can never exceed this limit.
A mirror voltage which is always equal to the zener value is generated at the output, however the presence of R2 enables the response to become variable.
The adjustments made through R2 effectively varies the zener voltage right from zero to the maximum value, that is up to 24V.
Thus the obtained output becomes variable from zero to 24V.
However since the voltage is acquired across the emitter/ ground of the transistor, the current gets restricted to very modest levels, at 25mA to be precise.
The zener voltage though may be increased to any desired limits.
WARNING: THE WHOLE CIRCUIT IS NOT ISOLATED FROM MAINS AC, THEREFORE IS EXTREMELY DANGEROUS TO TOUCH WHILE IT'S UNCOVERED, AND POWERED CONDITION
R1 = 100k
R2 = 10K POT
C1 = 4.7uF/300V
C2 = 10uF/100v
C3,C4 = 100uF/30V
D1 = 24V, 1WATT, ZENER DIODE
D2 = 1N4007
T1 = MJE13005