Can LDO Voltage Regulators be driven at max current output?

[aiq25]

Hi. I was wondering if there is anything wrong with running LDO Voltage Regulators at max current output for extended periods of time (>12 hrs). The reason I ask is because I have a application where I have to drive a load that is less than 5Ω with a constant current of 500mA at 5V. I could use a resistor to limit the current but I was thinking if I could use a LDO Voltage Regulator and not use a current limiting resistor. With a 5Ω load at 5V I get a current of 1A but I need 500mA, so couldn't I use a LDO Volt Reg with a internal current limit of 500mA? I don't know much about voltage regulators, that's why I'm asking. The input voltage to my system is 6V, so I don't think the power dissipated in the voltage regulator would be that big of an issue. I'm willing to use a heatsink for the voltage regulator for better heat dissipation.

I could use a current source but I'm curious if this method will work or is there a problem with it.

 

[berkeman]

Hi. I was wondering if there is anything wrong with running LDO Voltage Regulators at max current output for extended periods of time (>12 hrs). The reason I ask is because I have a application where I have to drive a load that is less than 5Ω with a constant current of 500mA at 5V. I could use a resistor to limit the current but I was thinking if I could use a LDO Voltage Regulator and not use a current limiting resistor. With a 5Ω load at 5V I get a current of 1A but I need 500mA, so couldn't I use a LDO Volt Reg with a internal current limit of 500mA? I don't know much about voltage regulators, that's why I'm asking. The input voltage to my system is 6V, so I don't think the power dissipated in the voltage regulator would be that big of an issue. I'm willing to use a heatsink for the voltage regulator for better heat dissipation.

I could use a current source but I'm curious if this method will work or is there a problem with it.

Per Ohm's Law, you can set 2 out of the 3: V=IR. You cannot put 5V across a load of "less than 5 Ohms" and get a current of 500mA.

"So which is it you want, young feller?" (Quiz Question -- what movie is that line from?)

 

[Baluncore]

500 mA through 5 ohm will drop only 2.5V across the load.

There may be no need for a regulator if your 6V is sufficiently stable.
You could drop the 3.5V with a (3.5V/0.5A) = 7 ohm series resistor. A difficult value to find.
It will need to be rated at 0.5A*3.5V = 1.75W.
You might just use 7 series 1 ohm ¼ watt resistors. Each will drop half a volt and dissipate 0.25W.

LDO linear regulators are only as efficient as a series resistor.
You could use a +5V LDO with a 5 ohm series resistor to your 5 ohm load.
From 6V only one volt will drop across the LDOR so it will dissipate 0.5A*1V=1W.

You could use a variable regulator such as a LM317. Two small resistors will set the Vout to 2.5V.
An LM317 will drop (6V – 2.5V) = 3.5V, it is linear so it will dissipate 0.5A*3.5V = 1.75W

Alternatively, use an adjustable switching regulator. It will be more efficient.
It will only draw about 250mA from the 6V rail to give 500mA out at 2.5V.
http://www.dx.com/ have a product SKU 280240 which will do the job efficiently without a heatsink.
http://www.dx.com/p/hzdz-adjustable-step-down-buck-module-blue-3a-280240# US$2.52 postage is free.
Alternatively; SKU 255394 for US$1.99

 

[analogdesign]

To directly answer you question running an LDO at maximum rated current indefinitely should be possible (unless it is explicitly forbidden in the datasheet)

 

[alphy]

I can provide a response to this question. LDO (Low Drop-Out) voltage regulators have a maximum current output that they can handle. Using them at max current output for extended periods of time can lead to overheating and potential damage to the regulator. It is important to consult the datasheet of the specific LDO voltage regulator being used to determine its maximum current output and operating conditions.

In this case, it is not recommended to use an LDO voltage regulator at its maximum current output for extended periods of time. It is best to use a resistor to limit the current or to find a different solution, such as a current source, to meet the required specifications for the load.

Additionally, it is important to consider the input voltage and power dissipation when using an LDO voltage regulator. If the input voltage is significantly higher than the output voltage, the regulator will have to dissipate a lot of power, which can lead to overheating. In this case, using a heatsink may help with heat dissipation, but it is not a guarantee.

In summary, while it may seem like using an LDO voltage regulator with an internal current limit of 500mA is a solution to driving a load of less than 5Ω with a constant current of 500mA at 5V, it is not recommended to operate the regulator at its maximum current output for extended periods of time. It is best to consult the datasheet and consider other solutions to meet the required specifications for the load.