I have a Power Supply of 24 volts and 2.5A.  I need something like that:    I need a power supply of 24V and almost 1500mA and another of around 8 volts and 500mA (to suplpy an Arduino). It is possible with this connection? Or I nees something like   How much the resistors would be?  Thanks!
11268
When would you use a voltage regulator vs a resistor voltage divider?  Are there any uses for which a resistor divider is particularly bad?
79082
I am trying to build a computer, placing an  in a custom .  The case is an extra small form factor which can accommodate the Mini ITX board, but it requires an external power supply, similar to the power-bricks that laptops use.  I am looking at different power supplies and like , but I cannot figure out whether/how to power this system, because they provide a 24-pin connector, but the motherboard has a 4-pin connector as well.  Is the 4-pin connector optional or is it required? If it is required, how can I provide power for this system?
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?
110066
I want to make a adapter from a vehicles 24v to a 5v usb phone charger. Can I simply connect the wires from a cigaret lighter jack to a usb and add a resister in between (using a voltage divider)? If so does it matter how strong the resistors are (assuming the ratio is correct?
110413
I'm currently interested in following  tutorial which explains how to create a  (ESP8266) controlled 12v RGB strip which is exactly what I've been looking for. However, whilst I do believe this project will work perfectly for an RGB strip up to about 5m, I am aware that lengths larger than 5m require additional consideration when it comes to powering them.  For my project, I wish to make a 30m RGB LED strip to be placed around the perimeter of the ceiling in my living room. My question is; what is the best way of powering a 12v RGB LED strip for 30m whilst keeping just 1 controller as linked above (ESP8266)?  Whilst researching this question online, I was unable to find any definitive answers for exactly what I needed. For example, in this image:    Whilst the idea presented in the second figure down makes sense (injecting 12v periodically) makes sense; it raised a few questions for me.   Do I only need to inject just the voltage at these intervals, or do I also need to include the R, G and B lines in the 'blue' wire pictured in the diagram? Do the amps matter in this case? Correct me if I am wrong, but a 5m RGB strip will usually run fine off 2A. So, do I only need a 2A supply if I am 'injecting' at 5m intervals? Or would I need a 12A supply (30/5 *2)? Is this even the correct approach for what I am trying to achieve? I.e. would this process of 'injecting' at 5m intervals work for a full 30m trip? If so, could I stretch the intervals to 10m for example in order to reduce the amount of wiring round my ceiling? If it's not the right solution, would using an  at 5/10m intervals be a better solution? Or, would something like this work:     Would the diagram shown above help in any way, or is it completely the wrong approach for what I'm trying to achieve? If it is kind of the right approach, could I ignore the method of 'injecting' 12v at intervals by supplying a higher voltage 24v at this first 'junction' so that 12v would be supplied to either side, or is that not how it works?  P.S.  are the RGB LED strips I am looking to use (RGB, no waterproof).
25415
I am trying to build a DC-DC Buck-Boost Converter using  basic schematic and an Arduino with the analogWrite() function as my PWM generator. I only want to step up 2.4-3V to ~5V. If it's just the capacitor and no load, the converter works so good that I have to switch it off after a few seconds since the voltage I measure on my capacitor is exceeding the capacitor limit. However, when I connect any load to the capacitor(for example a motor or a resistor) my voltage drops to a really low value(0.1-2v) and stays that way no matter what frequency PWM signal I send to the transistor using Arduino. I really tried but couldn't find the cause of the problem. Is it because I have two grounds, the battery pack one and the Arduino one? Is it because of the inductor(I tried using a smaller, 45uH, torroidal one but couldn't get any better results)? So what am I doing wrong?   I only expect to draw 500mA of current at 5 volts at the output side, and according to  calculator my inductor and transistor should be fine.  Components: 100uF 35V electrolytic capacitor, 200uH inductor, BYW29 rectifier diode, TIP 120 power transistor, 1k resistor    A schematic of the circuit or at least how it is supposed to look. Maybe I miswired something? The resistor is to represent  the load, the value doesn't matter since my problem persists at any value but the multimeters "infinite" resistance.   This is how my circuit looks   I used one coil of an old transformer as my inductor    However I also tried this inductor
103351
I want to know what size transformer for LM317 at full 30 VDC. I know its a 24 VAC center tapped transformer but is 1 A or 5 A transformer best suited for a linear power supply of 1.5-30 VDC?  I will be using a standard LM317 variable power supply circuit with the 2200 uF 50 V smoothing and the 240 ohm drain resistor and potentiometer. I have a homemade oversized aluminum heat-sink that is quite large.
49632
I'm making this right now -   Each 5m roll of LED takes 60W power (). He's using two of these rolls, so a total of 10m LED Strip.  My question is, that he's using a 19v 3.14A adapter which gives out a wattage of 60W. Isn't this lesser than what is required for the overall 10m (60w + 60w = 120w?). What's the effect of using this lower wattage on the LED output?   Instead, I thought of connecting the two rolls in parallel but the 19V adapter and connecting in parallel will probably burn the LEDs due to the fact that the LED strips are rated at 12v. Can I connect the two sets of 5m LEDs in parallel to a 12V 5A (which will result in 60W, the maximum wattage the LEDs can handle) DC Power supply? I'm assuming that then both the 5m strips are running at full brightness then. Or am I wrong and since a total of 120W is required, should I go for a 12v 10A DC SMPS Power supply? I studies Physics a long time ago in school and I'm pretty clueless here. What I'm looking for basically is the best way to extract the maximum light out of the LEDs. Thanks a lot guys!
83287
For the circuit of opamp 741. we have to supply the dual power for it. How can I make a dual power supply from single. For example, make a (+9V)-GND-(-9V) from single 9V battery ?
49071
So I'm trying to power 2 of these  together in series. I know that I have to add the voltage of the two lights together and get a resistor that restricts the power to that level. I have a 9V battery and the lights are 3V each. I brand new to all of this, and understand almost nothing, so any help would be appreciated. Can someone help me choose the correct resistor (And how to identify that resistor with the color branding thing) so two of those lights listed above can be wired in series? Thanks!
26160
I do understand that similar questions and maybe even the same question has been asked before, I've found them but unfortunately as a result of inexperience on my part I have been unable to adapt the posted solutions to my design specifically.  I am currently working to build the power side of my overall circuit that uses an 18650 (3.7v, 2600mAh) battery that is charged through an MCP73833 IC. The source power for charging will be a 5V wall wart power supply. What I am trying to accomplish now is to create a path or switch that disconnects the battery when the 5V power supply is connected, while preferably allowing the the 5V to be used to power the project and charge the battery at the same time.  Based on prior answers here on EE, I've heard that two Schottky diodes can be used with a little forward voltage drop; I've also seen recommendations for FET's. I'm trying not to add any more IC's to the project if I do not need too especially since I'm hand soldering all of this (not meaning FET's, but actual IC's).   Forward voltage drop is not critical since I'll need to step-up the battery voltage anyway after this circuit (to 5V for MAX7219). So it wouldn't be a big deal to run both power sources through the same booster.  My problem is that I have zero experience with Schottky diodes and even less with Mosfets. I've been reading and trying to understand but just when I think I do, I look at my circuit and my brain turns to mush.     Obviously if you see any errors within the circuit and wouldn't mind pointing them out, I'd appreciate that as well.
86962
I have 16 meters of  LED Strips . The strips have 60 LED/s per meter and run on 5 volts. They come in 4 meter reels.  I know how i want to control them but i am unsure about how to hook them up safely and so that they draw enough power. I know that i cannot just hook up a power supply to one end and expect the entire 16 meters to be powered. I read online that for the non-addressable ones that run on 12volts you need to hook up the power supply in multiple places, is this the same case with the 5Volts?   Also how do i know what kind of power supply i need and how do i hook it up so that all the LEDs are fully powered? Will i need more than one power supply or should one be enough?
81403
I'm new to EE so my theory isn't that strong. I want to trigger a  5v relay with my Arduino using a PN2222 transistor and a flyback diode. I plan on using the schematic below:         &ndash; Schematic created using   Now my question is: If I'm powering the Arduino via USB, will the current draw be too much for the Arduino's Vcc pin, thus requiring external power? I believe I'm reading that the relay will draw ~90mA and the Vcc pin from the Arduino can handle up to 200mA total. However, the transistor drives how much current is actually drawn, correct? Which is a function of the digtal pin voltage, R1 and the Hfe rating of the transistor? So if you were to mess that up, the current flowing to the relay would be incorrect and would not trigger it?   Thanks!
102279
[![enter image description here][1]][1]I am trying to build a simple circuit to power a load with two different power supplies (5 V and 0.7 V).    When one is active the other one is not and it's disconnected from the load. I know that this would be straightforward with a manual switch but I need this application to be automatic, maybe using a MOSFET as a switch controlled by a uC but it's not clear to me how I can achieve that. I wouldn't use a relay since I have constraints on cost and size of the footprint.  Thanks. Claudio
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?
77814
I'm attempting to build an LED bed lamp that will be powered by 240V mains. The LEDs are  which if I use with a 12V supply and have calculated correctly will draw 0.24W each. I plan to use 5 or 6 of them in the lamp so will consume a maximum of 1.5W.  Initially I thought I'd use a transformer and bridge rectifier to get the required 12V DC but the transformer weighs a ton and is too bulky. The next option was to use a  but I'm wondering is there is a better way?  I think it would be possible to power the LEDs directly from mains using only a rectifier without mains and stepping down the voltage but then it's not safe. Are there any smallish components that can both isolate the mains and supply a DC voltage?
122783
I'm making a voltmeter for the college senior project, and the problem is that voltage divider should equally split 17V into two 9V(nominal value of the batteries. As of now, an actual voltage is 8.5V and eventually will go down as the batteries die, so don't freak out too much by my round errors.) sources, but as soon as I connect Arduino board to the circuit, voltage( across the resistor it's connected to) drops to 2-3 Volts. Which is apparently enough to power the micro controller, but not enough to light the display up. (it's also enough to use the other resistor as a space heater with 14 Volts across it).    Please feel free to look at the schematic of the device provided above. (either models, or specs of the components are written on the schematic)  Now I'll explain the design thoroughly: The idea is to use piezoelectric element (thin laminated  flexible piezoelectric beam), place it into a fluid flow (air) and rectify the outgoing AC signal with a full wave bridge. The next step is to amplify the signal, because it has very low magnitude and arduino analog pin can't register it without amplification.   Amplifier needs at least +-7V supply, so it's provided to it from the two 9V batteries, that are connected to a voltage divider. Therefore, the virtual ground of the circuit is in between the two batteries.   At the same time I want the arduino board (Actually it's not arduino, it's arduino compatible board dubbed Pro Micro 5V) to be powered from the same two batteries.  The whole thing works fine from USB, but from the batteries it works as it pleases!  Here are the design constraints of the device:   The entire device shall hang somewhere in a remote location, so it has to be powered from an autonomous power supply (two 9V batteries in my solution). The device should be as light, and as small, as possible. (solutions like adding another battery are not desirable). Arduino board have to have 5V on it to light the display.   Additionally I'd like to learn why micro controller has variable input resistance and what it depends on.  I've tried to figure out what is the resistance across the arduino's ground and RAW by assuming that the resistor of the voltage divider and the arduino are connected in parralel. In three different setups I've got the arduino's resistance to be equal to 221.93, 527.73 and 743.4 Ohm.  As I understand, the board has some kind of reducer at the voltage input that prevents the board from burning at supplied voltages above 5V and below 12V, but why it drops the supplied voltage from 8V to 2-3V?