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2025-04-02 12:18 pm
I need to design power section for my board which will take input of 9v and step it down. The main SoC requires 1.2v(Core) and 3.3v(IO) voltages. The absolute max ratings for the 1.2v rail is 95mA and for 3.3v is 20mA. 1.2v is dedicated for the Soc and 3.3v rail will be used to power other peripherals which will also be in mA and will not make major difference. Then there is requirement of 4v @ 2Amps for Network card section.......So how shall i proceed with the design. For 9v to 4 v I understand I will need switching regulator but for 3.3v and 1.2 v can I use LDO as current rating is in mA. Or switching regulator for 9 to 3.3v and then ldo for 3.3v to 1.2v. Cost is our major concern. We want system to be efficient as well as cost effective.
2025-04-02 6:08 pm
Hi @shar,
This sounds a bit like a request for a commercial design. If this is a commercial design, then I personally do not think this social forum is appropriate, from both moral and commercial standpoints. In particular, this forum usually uses readily available components, typically including prebuilt modules, etc., which are often fine for quick and easy prototyping, hobby and experimental one-off projects, but unsuitable for building in quantity.
So I will not consider cost, which is highly dependent on many factors outside my scope. In addition, there are many technical issues to take into consideration, including electrical noise, etc. So I just offer a short description of how to start:
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This leaves efficiency, and related technical aspects, as a driving force of this question.
LDO linear regulators reduce the voltage by acting as a 'magic' resistor, so that the amount of heat they must dissipate is a product of voltage drop and current flow:
e.g 9V to 3.3V, at 20mA, implies (9 - 3.3) * 20 = 5.7 (V) * 20 (mA) = 114 mW
The linear regulator will also dissipate a little extra power for its control circuit, but, with a suitable regulator choice, may be negligible in your case.
Switch mode regulator efficiencies are dependent on many factors, so each design must be judged on its own merits, taking the actual voltage and current demands of the system into account.
Sometimes, switch mode regulators are custom designed to produce more than 1 voltage, as an alternate approach to consider.
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A common trick is to try to minimise the voltage drop across the linear regulator, using a switch-mode regulator to get 'close' to the required voltage. In this case, the 4V output from the switching regulator, to supply linear regulators for 3.3V and 1.2V could be considered.
However, many linear regulators need the input voltage to be about 1V above the output, so careful reading of data sheets is required, to try to find a suitable device, when considering the 3.3V regulator.
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There are also many other technical issues to consider, but perhaps the above description can be used for a starting point.
Good luck and best wishes with your project, Dave