Mark Burnley
Well-known member
Yes,
Use a resistor and 10 or 12V zener diode to drop the input voltage before the 7805- or even use a 7812 before the 7805! (they're cheap enough) Pre-regulation is useful in an on/off situation because the current draw won't be constant.
If you just use an input resistor to drop the voltage, when the relay is swithed off the input voltage to the regulator will rise to its full value. True, there is no dissipation within the regulator with no load current, but sometimes the actual voltage at the Input pin can be too large, and damage the regulator.
Mark
Use a resistor and 10 or 12V zener diode to drop the input voltage before the 7805- or even use a 7812 before the 7805! (they're cheap enough) Pre-regulation is useful in an on/off situation because the current draw won't be constant.
If you just use an input resistor to drop the voltage, when the relay is swithed off the input voltage to the regulator will rise to its full value. True, there is no dissipation within the regulator with no load current, but sometimes the actual voltage at the Input pin can be too large, and damage the regulator.
Mark