In this Power Supply transformer is not been used for step down the voltage. Thus it saves a lot of space and weight of the Power Supply Unit.
To construct this Power Supply following steps have been taken into account. Firstly a rough 40 volts power supply has been made using some passive and active components. And subsequently use this rough 40 volts supply to the Step down Converter IC (LM 2595 -*). This converter IC will be able to operate maximum at 40V. On proper using this converter IC a stable low voltage @1 Amp can be achieve.
CIRCUIT DESCRIPTION: The 230V AC mains supply voltage is fed to the Fuse (F) and then converted to DC voltage using a bridge rectifier stage. One MOSFET (TR2) has been used as a switch and that can be turned off when the supply voltage may be greater than 40 volts. Thus the Gate of TR2 is driven via R4 & R5. Suppose when the voltage exceeds 40V transistor TR1 conduct and resulting the Gate-Drain voltage of TR2 arrest the supply voltage at TR2 limits to 40V This 40V supply has been fed to the IC LM2595-* and related components to achieve the desired * voltage. [NOTE: The * voltage is either 3.3 or 5 or 12; i.e. the nomenclature of the IC is LM2595 – 3.3 or LM 2595 – 5 or LM 2595 – 12]
CAUTION: As the above mentioned Power supply Unit is working directly on 230V AC Power Supply, it is highly essential to be very much causes not to touch any part or component/s when the circuit is in operating condition.