[SOLVED] Diode to reduce voltage?

[Cambo]

Hi,

I'm currently working on a project that requires both 5V and 3V7 with a max current demand of about 2A - I'm wondering if it's acceptable to simply reduce the 5V by placing a diode inline to the 3V7 input? Perhaps there is a better way of doing this? I have tried an adjustable buck boost regultor but the noise seems to be causing me problems.

Thanks for any advice.

 

[brushhead]

You might as well use a linear regulator which has some kind of control rather than a diode which does not. They would both be dissipating the same power.

Rob.

 

[Cambo]

Thanks Brushhead - are you able to suggest a suitable voltage regulator to try?

 

[brushhead]

No but there are loads out there...3V7 is an odd requirement though?

 

[Cambo]

Thanks - for all those with a similar question to this a couple of regulators to look at are: MIC29302 & LM317

 

[schmitt trigger]

The LM317 has two pitfalls:
It has only a guaranteed 1 amp current output.
It won't regulate to 3.7v with only a 5v overhead.

The LT1529 may be a better option

 

[BradtheRad]

Simple transistor and zener regulator. (The zener can also be a combination of diodes/ led's/ resistors.)

Bias current goes through the load, so it may not be satisfactory with every load.

 

[Cambo]

Thanks folks, that's really helpful.

Good call on the LM317, two oversights on my part!
Thanks for the transistor method too, do you have any values for the resistors? I will try both methods and learn something

 

[BradtheRad]

Thanks for the transistor method too, do you have any values for the resistors?

The transistor must dissipate 2.6 W. The resistor value depends on your transistor gain. It must be low enough to supply sufficient bias to turn on the transistor.

My simulator has transistor gain of 100. If your gain is greater, then the resistor value can be greater.