Hi,
I'm using a small +5V (TO-92) volatge regulator, namely a LE50CZ by ST electronics. I've calculated that my load devices should consume less than 100mA of current so this device should be OK. However the spec sheet says that it can handle a Vin = 20V (max) or 18V (max) !!! depending on what part of the spec sheet you look at. Now common knowledge suggests that the input to output should not exceed 2 to 3V else the thing will overheat and may shut down but they never seem to tell you this in the spec sheet other than a Test Condition that happens to be 7V.
In any case I need to run my system (for only 2 hours) from a 12V 1.2Ah SLA battery so am proposing to use a basic volatge divider (on the front end before the input of the Vreg) using 47 Ohm (1 Watt) and 68 Ohm (1 Watt) resistor to ground. Tapping off in the middle will result in 7V (and give 104mA of current) arriving at the input of the Vreg.
(If I use resistors of higher values then I will increase my overall battery run time and can use smaller Wattage resistors. But all at the cost of reducing my available output current).
I realise that the voltage divider is necessary to drop the input voltage to a suitable level but wastes energy in the form of heat. Is this good standard practice or is there a method that is more efficient and better suited than this approach?
Hope there's enough info here for a resonse.
Thanks.
I'm using a small +5V (TO-92) volatge regulator, namely a LE50CZ by ST electronics. I've calculated that my load devices should consume less than 100mA of current so this device should be OK. However the spec sheet says that it can handle a Vin = 20V (max) or 18V (max) !!! depending on what part of the spec sheet you look at. Now common knowledge suggests that the input to output should not exceed 2 to 3V else the thing will overheat and may shut down but they never seem to tell you this in the spec sheet other than a Test Condition that happens to be 7V.
In any case I need to run my system (for only 2 hours) from a 12V 1.2Ah SLA battery so am proposing to use a basic volatge divider (on the front end before the input of the Vreg) using 47 Ohm (1 Watt) and 68 Ohm (1 Watt) resistor to ground. Tapping off in the middle will result in 7V (and give 104mA of current) arriving at the input of the Vreg.
(If I use resistors of higher values then I will increase my overall battery run time and can use smaller Wattage resistors. But all at the cost of reducing my available output current).
I realise that the voltage divider is necessary to drop the input voltage to a suitable level but wastes energy in the form of heat. Is this good standard practice or is there a method that is more efficient and better suited than this approach?
Hope there's enough info here for a resonse.
Thanks.