For a particular design, I need to take an unregulated voltage from a battery and regulate 5 different DC voltages from it. What's worse is that I need step-up and step-down converters. What's even worse is that some voltages need more current than others.  Note: To clarify the question, I've given the specific voltages that I need. However, keep in mind that I'm wondering what to do in general, not just this specific case.  The battery voltage is 11.1 V, which drops as it discharges. I need to create:   15 V 12 V 5.5 V 5.0 V 3.3 V   The 12 V level needs to run at least 1 A, and the three lowest need to run about 200 mA each. The 15 V level doesn't use more than 50 mA.  So this is my question: would it be better to go from the battery to 15 V to 12 V to 5.5 V to 5.0 V to 3.3 V, or would it be better to just connect all 5 regulators directly to the battery?
12988
Sorry if this is a stupid question, but I am mainly working with 5V PIC circuits and now want to integrate a component (nRF24l01+) that needs a 3.3V supply.  As I have a box full of ~7V wall-warts, I normally use a 7805 or similar LDO regulator to power the circuit. Now I want to also get 3.3V without using a separate external supply.  I'm looking for guidance on the "right" way to do this. I think the options are:   Use a voltage divider on the output of my 5V regulator to get 3.3V Use a 3.3V LDO regulator fed directly from the 7V wall-wart   Use the output of the 5V regulator as input to a 3.3V regulator   I can see that all of these would work (would they?) and that option 3 seems to waste least power, but I don't know what gotchas might arise by chaining two regulators like this.  What things do I need to consider when making this choice?
121000
I have a project running with MCU supplied with a 24V power supply regulated via an SMPS to 9V also, I have Li-ion battery pack 9V  how to connector these two sources to run the MCU with battery pack when the power failure occurs?  or   what is the best way to switch from battery to power supply and power supply to battery?
65384
I want to make a power DC supply with voltage rating 0-200V. I want it to be a variable power supply with voltage from 1V to 200v. What should be my approach?
36128
Following on an earlier  I am looking for a circuit where it powers from USB when it is available and uses the battery when USB is not plugged in.  I want voltage drop to be minimal, zero if possible. So using oring diodes is not possible. The mosfet power oring ICs mentioned in the answer are extremely expensive (4$ for 1K) although they have low voltage drop.   I am looking for a discrete solution where I can build with simple switches or even a cheap LDO. I didn't try to build it but I thought I could use the existence of the Vbus to do a simple switch to control LDO's one from VBus, the other from VBat.   UPDATE   Ideally zero drop is wanted however up to 100mV can be tolerated.  My system has 4 AA batteries, so there could be cases where the battery voltage is larger than 5V, that is why I focus on the existence of VBus. The small drop comes from the Operation voltage of one of the ICs, it needs to be 3.5V (min) and the larger voltage drop eats into the battery life. (i.e. 4 battery, 0.9 each, 3.6V, 100mV drop, I can squeeze the batteries). If there is a 0.7V drop, I can not use the full battery power. (I have to shut down the system at some point of time to ensure proper operation but batteries has still a lot of juice left)
91388
Can you help me with a way to step up a voltage of about 3.29 to 4.5/5V? I need a simple and efficient circuit to implement this.
107643
I asked a similar question  about this, but I still don't  quite understand.  Say I grab onto two wires from a standard 120V 20A wall socket. I would fry. I would have 20A at 120 forced on my body.  But, when speaking in terms of circuits, as in my linked question, if I have a power supply outputting 100mA maximum at 5v, for some reason my device only gets exactly what it needs? Why is this?  Most things flow from an area of high concentration to low concentration, taking the path of least resistence. If you connect two wires to a power supply, why don't the maximum number of electrons want to go through your circuit?  If current behaves this way...why do you have to regulate voltage?
102245
I would like to transform 5V 500mA (from USB power) into 12V with a few cheap components.  Is this possible with the help of some generic parts (and not with the help of some expensive transformer, etc.)?  Also, how many milliamps would this provide?
10727
What would be the least expensive way to boost a DC voltage?   The aim is to convert 1.2&nbsp;V/1.5&nbsp;V (from an AA/AAA cell) to 3.3&nbsp;V to power a small 8-bit microprocessor, like Atmel ATtiny45 or ATtiny2313, and also (if possible) 6&nbsp;V to power a buzzer.  Also, what would be the maximum current one could draw safely from an alkaline battery, after boosting it to 3.3&nbsp;V/6&nbsp;V?  Finally, how I could compute the duration for which the alkaline battery would last, given a certain consumption?
112179
I am designing a flyback converter, input 170V output 1200V at 2mA.  I am having trouble finding an appropriate transformer, most do not have a high enough N. Current transformers seem to have ranges in 1:500, so I could work with that.  Is it proper to use a current transformer as a conventional step up voltage transformer?
73760
My requirements are: I need a UPS system which supplies power to a 9 volt modem. UPS should Charge 12v battery (SLA , charging curent 800ma), and it should have overcharge/discharge protection system [optional: it should show the battery capacity with four leds(25% interval)]. I want to achieve this without using ADC. I can make 230V AC to 12v DC converter with step down transformer. Switching from mains to battery can also be achieved with two diodes. But i want to make overcharge/discharge with led indicator which i cant figure out without ADC. Is there any way to achieve this without microcontroller and ADC. Any suggestion would be appreciated. Thanks in advance.  I am thinking about something like this. I have designed this circuit on my own. But i have no idea how to link these two switches to charge level indicator.
26415
I have a  that converts 4.2V  (two 4.2V cells in parallel) to 5V. Another option is to use a  from 8.4V (two 4.2V cells in series) to 5V. Considering both cited circuits are well implemented, which choice would be more efficient in terms of power dissipation?  I am looking for some general rule as "step-down is always preferable than step-up" or "the absolute voltage difference matters" etc.
86803
I want to run a micro-controller from a 1S lipo through a 3V linear regulator. I need to measure the battery voltage however. The problem with using a voltage divider is that it would drain the battery over time which may or may not have protection circuitry built in. Since the AVR I'm using has a recommended input impedance of no higher than 10K I can't make the divider too large either.  Can anyone suggest a solution that would allow me to monitor this voltage without killing an unprotected battery over a couple of months? The circuit might enter deep sleep mode for an extended period meaning a voltage divider solution would consume the most power.    I ended up using both Hanno and Andy's solution. Thanks for all the input. Can only choose one answer unfortunately.
21141
I am curious if there are practical differences between a DC power supply based on a half wave rectifier or a full wave rectifier.  I mean I have a few small DC power supply units which should give 12V 0.1A each. They all have a transformer 240V->18V, then 1 diode or 4 diodes, then 78L12 (0.1A regulator) and one or two capacitors (typically 220uF or 470uF).  My question is if the power supply can give a good quality DC voltage with just a half wave rectifier (a single diode) when a 470uF capacitor and 78L12 is added, or if bridge rectifier (4 diodes) is better.  I also have one old 12V 0.2A power supply based on a Zener diode instead of 7812 regulator. It also has 18V going to just a single diode, then 33R resistor which limits current to 0.2 Amp, then Zener diode parallel with a 1000uF capacitor. Again: Would it be better to have 4 diodes there, or is the half wave rectification good enough here thanks to the 1000uF capacitor?  (All my power supplies work well, I am just curious "why" and "how" these things work.)  Update:  I found two more interesting information:   Capacitor should be approximately 500 uF for each .1 Amper of output (or more). This applies to full wave rectifier. Since I saw the same values in half wave rectifiers, it isn't enough and they are bad design. 4-diode rectification cannot be used when we want to have a combined 5V/12V output (or any other two voltages) with a simple transformer, because it can't provide a common ground for two different circuits. (A more complicated real example: I have got a power supply with four output wires from transformer -7/0/+7/+18 Volt. Then it uses 2-diode rectification to get full wave 7V output, and 1-diode rectification to get half wave 18V output. The 18V line can't be "upgraded" to 4-diode rectification here.)
12855
I have a Canon SX210 IS, which doesn't have the possibility to plug-in a external power source.  Because of that, I want to make a connection to the pins where the battery usually is. I'm a little confused about the voltage requirement because the battery says 3.7V and the base of the camera says 4.2V.  Since I have a car battery and a 7805 voltage regulator I thought I could power the camera directly with the 5V the regulator would give me. But I don't know if it's safe to do that.  You may ask why would I want to power the camera with 5V instead of using 4.3 from a DC regulator. Well, I'm outside the city right now so there is no way to get a DC power supply like that.  (don't ask where I took the 7805 from).  I've found out that my helicopter charger has a voltage of 4.2V and a maximum  current of 850 mA, but it's a typical switched power supply (like the cell phone ones). Is it dangerous to feed my camera with that? What about a little paralell capacitor to filter noises?
64304
How do most voltage regulator ICs work? Are they the same as hooking up a variable resistor and a voltmeter and turning the knob until you get the desired voltage?
16937
As I'm relatively new to the electronics world, I was wondering if you can connect multiple  ground terminals (corresponding to several different voltage outputs) to the same ground. Or do they each need their own?  In my case I have 5 lines, one 12V, one 3.3V, two 5V and one variable from a 12V in using a  voltage regulator that already has its own ground. So I'm guessing that each would need its own ground, but it is never bad to ask.
84214
The circuit is an altered Joule Thief of my design that is driven by an AA or AAA battery. I’m observing the current at the battery anode with my DMM in series. (Extech EX330) This circuit is extremely efficient (In relation to other Joule Thief I've build.) and does some weird stuff - like, it needs a pushbutton sometimes.    Measurements: It is drawing 9.21 mA DC and 6.48 mA AC in series with the battery. It shows 1.364 VDC and 0.010 VAC in parallel with the battery. Output on the LED is 2.572 VDC and 0.011 VAC with no measurable frequency. (with my DMM at least) All measurements are taken with the same configuration and voltage.    But how is it drawing AC and DC and how do I calculate power consumption? --> Could it be because the emitter pin of the NPN is directly connected to ground? --> Or is the circuit just "switching on and off"?     Download schematic:  (I tried to simulate the circuit in LTspice. Thanks for making me aware of this amazing program, Sredni Vashtar!)     What the pushbutton is used for: The pushbutton is used to "kickstart" the oscillation when it wont start by itself. For example: I have to manually "oscillate" using this button to start the circuit if the capacitor is too big and battery voltage is low. Pushing the button releases the energy in the transformer into the capacitor. If it reaches LED forward voltage the circuit keeps oscillating on it's own. It does work without manual intervention when then capacitor in parallel with the LED is not too big, like &lt;5000 µF, and it's a fresh battery.    . Thank you for your answers! I'm learning so much! :D