What's best way to reduce a voltage... (picture) - Page 1
Forum section: electronics / beginners

author: billbyrd1945
author_rank: Regular Contributor
timestamp: March 13, 2019, 06:29:05 pm
content: I just bought a generic looking power supply. It has three 12v terminals. I would like to use one of them to power my Arduino which can use up to 9v. What's the best way to reduce one of the outputs to 9v. Thanks for any help.See photo.

author: RES
author_rank: Regular Contributor
timestamp: March 13, 2019, 06:51:05 pm
content: Found this (just too small) diagram of a S-400-12:http://www.imajeenyus.com/electronics/20151028_smps_variable_voltage/s-400-12_schematic_thumb.gifOn the left you see a pot.(Voltage ....., can't read it)

author: Gyro
author_rank: Super Contributor
timestamp: March 13, 2019, 06:52:03 pm
content: That's a hell of a lot of current capability to power an Arduino safety!... at least without additional short circuit protection.There's an article herehttp://imajeenyus.com/electronics/20151028_smps_variable_voltage/index.shtmlthat might help you with the output voltage adjustment though.

author: Refrigerator
author_rank: Super Contributor
timestamp: March 13, 2019, 06:59:56 pm
content: for an arduino you could get away with a LM7809

author: Gyro
author_rank: Super Contributor
timestamp: March 13, 2019, 07:06:47 pm
content: You can get 7808s too - and a fuse / PTC mounted at the PSU.Just one point from the OP...Quote from: billbyrd1945 on March 13, 2019, 06:29:05 pmThere is only one output - multiple terminals are provided to cater for the high output current capability, but they are paralleled on the PCB.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: March 14, 2019, 01:54:50 am
content: "There is only one output - multiple terminals"Thanks. I didn't realize that. Thought I had three sources of 12V. Oh well...

author: Nerull
author_rank: Frequent Contributor
timestamp: March 14, 2019, 03:24:20 am
content: Arduinos can run off 12V....Quote

author: Zero999
author_rank: Super Contributor
timestamp: March 14, 2019, 01:22:24 pm
content: Reducing the voltage to 9V is not a bad idea, even if the Arduino can handle 12V.There must be adequate overcurrent protection.30A is enough to cause severe burns and a big fire. Use a fuse, circuit breaker or PTC resistor, rated to double the maximum current drawn by the Arduino, with a breaking capacity of more than 30ADC at 12V.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: March 14, 2019, 02:08:28 pm
content: I'll just use a wall wort. I thought it would be simpler than that. I thought that's what a buck converter was for. There's a good reason why I'm in the beginner's section.

author: Gyro
author_rank: Super Contributor
timestamp: March 14, 2019, 02:34:55 pm
content: A wall wart would certainly be safer, but it doesn't need to betoocomplicated.A series chain of 5 diodes would drop about 3 - 3.5V. You just need to ensure that your protective device (low rated fuse or PTC thermistor) is the FIRST thing at the positive terminal of the PSU. Insulate the diodes in a length of heat shrink.You just need the fuse / PTC to trip before your wiring (or Arduino) smokes in case of a short circuit.

author: rsjsouza
author_rank: Super Contributor
timestamp: March 14, 2019, 03:14:35 pm
content: Quote from: Gyro on March 14, 2019, 02:34:55 pmJust be sure you are using Silicon Diodes, which drop about 0.6V per diode, and not Schottky, which drop about 0.2V per diode. Visually they are very similar, thus it is important to pay close attention to its part number.The most common Silicon Diodes that are suitable for this task are from the 1N400x family (1N4001, 1N4002, etc.)

author: mariush
author_rank: Super Contributor
timestamp: March 14, 2019, 03:43:15 pm
content: Your Arduino most likely has a linear regulator on the circuit board that converts the input voltage (on the DC jack) from 9v to 5v.That linear regulator most likely supports voltages up to 15v or 20v or some higher voltage than 9v, they simply say 9v because it's a very popular/common voltage for DC adapters, so such adapters can be easily bought.For example, a very common linear regulator is *1117 (* because it's made by lots of companies so first 1-3 letters represent the company who makes it) ... here's LM1117 :http://www.ti.com/lit/ds/symlink/lm1117.pdfIf you can scroll in the datasheet, you will see the maximum input voltage recommended is 15v, so if your Arduino board has one of these, you can safely power it with 12v.Now, it's important to keep in mind that the more difference is between the input voltage and the output voltage of a regulator, the more that linear regulator will heat. So for example, if your Arduino board consumes 100mA of energy, then at 9v input, your regulator will produce (9v-5v) x 0.1A = 0.4 watts of heat, but with 12v input, that value changes to 0.7w which is a bit higher but still reasonable.For a few leds on your Arduino board, a lcd display, basically if your power consumption is quite small (you can measure by placing a multimeter on current range in series with the input) and the linear regulator on the board supports more than 12v, then you could power with 12v.If you can't tell what regulator you have on your Arduino board, take some clear pictures of your Arduino and post them here and we may be able to help you out.