DC power supplies

Introduction

most portable devices run from DC power
the source of the DC power is either from:
- household AC power (240V 50Hz in Australia) and then converted to lower voltage DC via AC-DC transformers / “chargers”, or,
- solar panels via a solar regulator (see solar power for camping), or,
- batteries
  - obviously these come in many sizes and voltages such as:
    - 1.5V alkaline AAA/AA/D batteries
    - various “button” batteries usually around 3.2V
    - 3.2V LiFePO4 rechargeable batteries
    - 3.7V lithium polymer rechargeable batteries
      - eg. in power banks, laptops or other devices - usually have a USB outlet
    - 9V alkaline batteries
    - “12V” lead acid car batteries
    - “12V” 12.8V nominal LiFePO4 rechargeable batteries - see 12V batteries and battery boxes
- other power generators
  - eg. DC-DC charging of auxiliary batteries using your car's alternator
if the voltage you need is not the same then you need a transformer to step up the voltage or step down the voltage - these are discussed below
NB. if you need AC power from a DC power source, you need an AC inverter

these are the “old style” heavy transformers but they have a major advantage in that they give off very little RF noise
these first use an AC-AC transformer to reduce the AC voltage then use diodes and capacitors to convert the sine wave to an almost linear voltage
a diode is a simple electronic 'valve' 'rectifier'- it only lets current flow one way and thus can only output the positive current but this leaves half the cycle with no current at all and the positive current is not linear but a half sine wave. This is improved by using 4 diodes in a special way to give a full wave rectifier that effectively inverts the negative cycle.
adding in a capacitor AFTER the diode will smooth out that half sinewave positive part and the null negative part so that there is always a reasonable level of positive voltage throughout the cycle
basic AC-DC power adapters will have a variable voltage output dependent upon the current draw which may be dangerous for some electronic circuitry. They are often rated at a certain voltage with a given current draw but current draw higher than this will drop the voltage below this value while current draw less than this may even double the rated voltage
see https://learn.adafruit.com/power-supplies/transformer-based-ac-dc-converters

these are much smaller and lighter (eg. USB chargers, etc) but the price you pay is a LOT more RF and EFI noise as they convert the sine wave into a square wave (unlike sine waves these are harmonically richer and generate much more RF noise) which can have its duty cycle modified by a feedback circuit to ensure the voltage remains the same irrespective of the current load
see https://www.youtube.com/watch?v=tS7SvoT8Ivw

these take a USB input and usually have a dial-like adjuster to change the output DC voltage

these usually take a 12V DC input and output DC at various selectable voltages such as 5V/9V/12V/15V

eg. https://maxvoltagestore.com/ - Makita, Milwaukee, DeWalt, Ryobi, Hitachi, Ozito or Bosch - Anderson plug or cig lighter output connection max 10A, 5-13V output, Low Voltage Cutoff Protection set at 15V to protect your tool batteries ~$AU120
these batteries (18V or the 18V/54V Dewalt Flex batteries) typically are 5Ah = 90Wh

these are now ubiquitous especially in remote settings such as vehicles, camping, etc or built into power banks or power “stations”
take a 12V source from either a vehicle cigarette lighter port, or from a 12V battery
often provide a range of USB options including USB-A 1A/2A, 18W 12V USB-A QC and/or USB-C PD of variable capabilities

FNIRSI® DPS-150 Mini DC Adjustable CNC Programmable Regulated Switching Power Supply
- 5-32V input USB-C, DC
- 0-30V, 0-5A, 0-150W DC output via 4mm banana female ports
- also is programmable via PC