These two types of circuits have very different applications.
A resistor divider is generally used to measure voltage so that it can be more easily sensed/detected/analyzed.
For example, let’s say you want to monitor battery voltage. The voltage may reach 15 volts. You are using the analog-to-digital converter for a microcontroller (“ADC”), which uses 3.3 volts as its reference. In this case, you can choose to divide the voltage by 5, which gives you up to 3.0V at the ADC input.
There are two defects. The first is that there is always current flowing through the resistors. This is important in power-constrained (battery-powered) circuits. The second problem is that the septum cannot be the source of any significant current. If you start to draw current, it changes the bulkhead ratio, and things don’t go as planned 🙂 Therefore, they are only used to route high-impedance contacts.
On the other hand, a voltage regulator is designed to provide a constant voltage regardless of its input. This is what you want to use to provide power to other circuits.
Regarding creating multiple voltage rails: In this example, let’s say you’re using switching regulators with 80% efficiency. Let’s say you have 9 volts, and you want to produce 5 volts and 3.3 volts. If you use the regulators in parallel, and connect each one up to 9 volts, then both rails will be 80% effective. However, if you create 5V and then use it to create 3.3V, your 3.3V efficiency is (0.8 * 0.8) = only 64% efficiency. Topology is important!
On the other hand, linear regulators are evaluated differently. They simply lower the output voltage for any given current. The energy difference is lost as heat. If you have 10 volts inside and 5 volts outside, they are 50% efficient.
They do have their benefits, though! They are smaller, less expensive, and less complicated. It is electrically quiet, and produces a smooth output voltage. And if there is not much difference between the input and output voltage, the efficiency can outperform the shunt source.
There are ICs that provide multiple organizations. Linear Tech, Maxim Integrated and Texas Instruments all have a good selection. The LTC3553, for example, offers a combination of a lithium battery charger, a switchable buck regulator, and a linear regulator. They have flavors with or without the charger, some with two no-line adapters, some with several…
One of my current products uses a 3.7V battery and needs 3.3V and 2.5V. The two most effective for me were my 3.3v line, and a 2.5v transformer (battery fed, not the 3.3v rail). I used LTC3553.
You’ll want to take the time to use the product selectors on their website.
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