The discussion revolves around reducing a DC voltage from 12V to 5V, specifically exploring methods to achieve this using resistors, voltage regulators, and DC-DC converters. Participants share insights on the implications of each method, including considerations for current requirements and thermal management.
Participants generally agree that using a voltage regulator is preferable to using a resistor for reducing voltage, but there are differing opinions on the specifics of implementation and the best choice of components.
There are considerations regarding the thermal management of voltage regulators and the impact of load current on performance, which remain unresolved in the discussion.
Loading effect
The output voltage of a voltage divider will vary according to the electric current it is supplying to its external electrical load. To obtain a sufficiently stable output voltage, the output current must either be stable or limited to an appropriately small percentage of the divider's input current. Load sensitivity can be decreased by reducing the impedance of the divider, though this increases the divider's quiescent input current and results in higher power consumption (and wasted heat) in the divider. Voltage regulators are often used in lieu of passive voltage dividers when it is necessary to accommodate high or fluctuating load currents.
Applications
Voltage dividers are used for adjusting the level of a signal, for bias of active devices in amplifiers, and for measurement of voltages. A Wheatstone bridge and a multimeter both include voltage dividers. A potentiometer is used as a variable voltage divider in the volume control of many radios.
MattG2826811 said:so i need to reduce a dc 12v to dc 5v. do you know what type of resistor i should use? also could you please suggest an online calculator or an equation so that i can find the resistance i need in the future.
davenn said:using a resistor is far from a good way to do it. This is because a resistor or resistive voltage divider as billy_joule suggested will also limit the current and that may be a bad thing for what you are trying to achieve
billy_joule's second suggestion is the best ... use a voltage regulator and ensure it can handle the current your project needs
And yes there are ways to boost current requirements via a regulator
for current requirements up to ~ 0.75A ( 750mA) a 7805 reg is ideal
for higher currents and much more efficient operation use a switching DC-DC buck converter
eg ...
http://www.ebay.com.au/itm/DC-DC-Buck-Converter-4-5-35V-to-1-25-30V-3A-Power-Module-24V-to-9V-12V-to-5V-etc-/171640130013?pt=LH_DefaultDomain_15&hash=item27f68c89dd
it can take a wide input voltage range and has an adjustable output and is capable of 3 Amps
cheers
Dave
thanks for the tip i think i will use the lm7805billy_joule said:https://en.wikipedia.org/wiki/Voltage_divider
Note that:
A voltage regulator like the LM7805 might be a better solution depending on your application.