# How and when does a regulator draw energy?

I’m working on a wearable battery project and I think I need to use a regulator on the battery output.

Let’s say I were to connect the battery to an LM317 (detailed here) or an LM7812 (see figure 1) circuit with nothing else connected to the output. Would there be current flow through the circuit? Would the battery discharge more quickly than it would in storage?

Figure 1: LM7812 Circuit

Furthermore, does the current draw (in amperes to clarify) from a voltage regulator depend on the requirements of the components connected? If I connected two LEDs in parallel to the output of a voltage regulator, would the current be greater than if only 1 LED was connected? Does the power draw (in watts to clarify) from a voltage regulator differ from the current, or does the current change in direct proportion to the power?

• Yes and yes. Furthermore, yes, yes and yes if the input voltage is unchanged. Main question : see Table 7.5 on the datasheet you linked. Adjust pin current is 50 to 100 uA. Worse, you need a minimum load, 3.5mA to allow it to regulate properly. (This is usually done by careful choice of adjustment resistors). 7812 is different, but no better. Dec 1 '20 at 19:43
• If I connected two LEDs in parallel to the output of a voltage regulator Never directly connect LEDs to the output of a voltage regulator, always use a resistor in series with the LED to limit the current. You ask a lot of basic questions and that's OK, we've all had to begin somewhere. What I advise you to do is search the internet for similar projects and see what those people do, try to understand why they do things like that. Instructables.com is a good site to start. Dec 1 '20 at 19:51
• ...linear regulators are wasteful, switches achieve much greater efficiency and modern ones are cheap... Dec 1 '20 at 21:16
• Re, "...power draw..." Be sure you understand the difference between the power that the regulator delivers to the load, and the power that is dissipated (turned to heat) in the regulator. Suppose input voltage $V_\text{in}$, output voltage, $V_\text{out}$ and load current $I$. The Power used by the load is, of course $IV_\text{out}$. The power consumed by a linear regulator will be at least $I(V_\text{in}-V_\text{out}).$ It could be more than what the load consumes, depending on the voltages. switching regulators (see Chris Stratton's comment) don't have the same problem. Dec 1 '20 at 21:18
• Btw I thought I knew the answers to all these questions, I’ve been working with electronics for years. I wanted to check because the project uses 4 LC18650s. Lithium battery chemistries are explosive and I want to be extremely careful doing any power electronics design with them. Dec 2 '20 at 4:44