Devices for power supply of electronic systems must provide the necessary operational voltage to all premissible variations of input voltage. In a cases of protection against voltage transients, additional protection of power supply devices is required. Damage to electronic installations and devices caused by overvoltage are larger and larger because of the wider use of electronic devices and systems (comp-uters with a modem connection to the Internet, ADSL devices, ...). Decrease of of the device operational signals level increases device susceptibility to overvoltages. The paper analyzes the damage caused by atmospheric discharge and overvoltage protection.