A very simple portable 12 250V converter can be built using electronic diagram below. This 12 250V converter is designed for portable use with a 12 V car battery. The circuit requires only six transistors, a transformer and some capacitors and resistors and allows to power small consumers. A built astabil multivibrator T1 and T2 generates a rectangular wave at a frequency of 50 Hz. As T1 and T2 drive alternative exit stage system also works in "push-pull".
A Symmetrical voltage power supply circuit, can be made using electronic circuit in the figure below. This Symmetrical voltage power supply circuit is designed using a simple operational amplifier and some classic electronic components
Resistances R1 and R2 form a high impedance voltage divider. Operational amplifier makes sure that artificial potential mass is the same as the voltage at the common point between R1 and R2. The ratio of R1 and R2 determine the relationship between the two output voltages, if R1 and R2 are identical, the two output voltages are symmetrical.
A very simple adjustable power supply that can provide an output voltage between 0 and 60 volts can be designed using electronic scheme in the figure below. Source can be designed with LM723 chip for higher output voltages, with L146 .
Output current is also adjustable, but once established, is always effective. Table 1 shows the values to be modified to have three different versions of the maximum output voltage (30, 40 and 60 V).