The advantage of the kit Positive to Negative Voltage Converter is that, the negative voltage together with the original positive supply can be used to simulate a dual supply. In this kit Positive to Negative Voltage Converter the first block is power supply in which the input is 230V AC which is step down using the transformer (12-0-12) .The 12V ac input is fed to the bridge diode to gives 12V pulsating DC. This DC voltage is filtered through the capacitor to remove the ripples. The filtered DC is fed to 7805 regulator to fetch +5v regulated output.
The kit Positive to Negative Voltage Converter based on timer IC NE555. The NE555 is wired as an astable multivibrator operating at around 1 KHz. The square wave output if available at pin no 3 of the IC. During the positive half of the square wave, capacitor C4 (22Uf) charges through diode (E1) 1N4001 .When the output of IC is at zero the C4 (22Uf) discharges through diode (E1) 1N4001 and the capacitor (C5) 100uF gets charged. As a result of this the voltage at the junction of the anode of (E2) 1N4001 and cathode of (C5) 100uF will be always negative with respect to the ground.