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Kits: Plug-In Bread Board Power Supply Module (Kit) | CuriousInventor.com Store

Kits: Plug-In Bread Board Power Supply (V2)

by David @ uCHobby.com
Short Description:
This power supply module plugs straight into common bread boards, allowing you to cleanly and easily power your board with a wall wart plug or with wires into screw terminals. It features a variable voltage regulator that can be set to output 3.3 or 5V with a jumper, or any voltage if a potentiometer is added. The input has a rectifier that accepts AC or DC (polarity doesn't matter)--just make sure the input is about 2V greater than the output you want. Skill level: beginner
An alternative to wall-wart hacking:

Instructions: online or downloadable pdf
Buy:
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This power module plugs straight into common bread board sizes, giving you 3.3V or 5V (and more) of regulated voltage on your supply lines. It features a barrel jack that lets you plug a wall-wart straight in, or alternatively, screw terminals for neatly attaching stripped wires.
in stock - $13.99
Just the PCB for our plug-in kit, RoHS Compliant (lead-free).
in stock - $6.99
Features / Specs:
  • This is a great learn-to-solder or electronics introduction kit. The instructions cover basic circuit building and soldering techniques, and the end result is useful for all your future bread-board prototypes.
  • The outer power rail headers fit into bread boards that have outer rows spaced 1.85" apart, but it can also be used on other bread boards by running jumpers either underneath or over the board (see pics). For reference, the outer rows on an Elenco 9830 fit this kit. If you really want to be certain, print out this pdf (be sure to print to scale or 100% scale, and not scale-to-fit).
    • The above pic shows the board working on a non-typical bread-board where the outer rails are too far apart. In this case, the outer header pins were left off and jumper wires are run underneath the board.
  • When the jumper is on, it outputs 5V, and when the jumper is off, the output is 3.3V
  • It can be powered with AC or DC power (5-37V), either through the barrel plug jack (2.1mm x 5.5mm) or screw terminals (a built-in rectifier can handle either polarity--ie, hooking wires up backwards still works, along with negative centered barrel plugs). In our testing, if powered by an 9V AC supply (cheaper usually since they're just a transformer), it can supply about 300mA of current at 5V without any ripple. If you use a DC supply, heat is the only limitation. By adding a sufficient heat sink, the regulator is spec'd to supply over 1.5A. Without a heat sink, out testing showed that it could supply around 375mA at 5V with a 9V input at typical room temperature.

    What about different input and output voltages? The regulator works by dumping any excess energy not needed by the circuit straight into heat. Since energy is Voltage * Current, the heat from the regulator = (Vin - Vout) * Current, so in our testing, it could handle (9-5V) * .375A = 1.5 Watts. If you were to power it with 37V of input and had a 3.3V output, 1.5 Watts of heat would come from only 1.5 / (37 - 3.3V) = 45 mA.

  • Additional headers provide bread board access to the input voltage for relays, solenoids, motors, lamps etc.
  • The adjustment point of the voltage supply is also brought into the bread board which allows for infinite adjustment with a potentiometer (after removing R1).
  • An easy to access ground test point is available. If you're short on clips, you can wedge a standard .08" probe into the loop (see instructions).
  • Power switch and indicator LED -- no wondering whether the power is on or frantically grabbing wires to turn off the power.
Parts List and Spec Sheets:
  • Variable Voltage Regulator (LM317T) (spec)
  • Rectifier (spec)
  • Capacitors (3): .1uF ceramic, 1uF electrolytic, 330uF electrolytic
  • 2 position screw terminal
  • Barrel jack power connector (2.1mm x 5.5mm)
  • Red LED
  • SPDT Slide Switch - SPDT = Single Pole Double Throw, which means it connects one input pin to one of two output pins
  • Test point
  • 7 header pins
  • Resistors (4): 240 Ohms, 270, 330, 820
  • Jumper / Shunt (1)
Building Instructions:
How it Works:

A couple things of interest:

  • Rectifier: The four diodes in a rectifier work to flip negative voltages to positive ones, so the supply can accept either AC or DC in either polarity.
  • Voltage Regulator: By changing two resistors, this one part can be setup to output between 1.2 and 37 Volts. It works by maintaining a constant 1.25 voltage between the adjust and output pins. That 1.25 voltage drop across R2+R3 forces a current (I = 1.25V / (R2+R3) ) to go through R1 (it can't go into the regulator), so the output voltage is just I*(R1) + 1.25.
  • Capacitors: What are all those caps for?
    • The 330uF serves two purposes: one to help filter AC signals into DC, and also to supply a reserve of energy for the circuit. When the AC signal is high, it charges the capacitor, and when the AC goes low, the capacitor picks up the slack to keep a relatively steady voltage available. One interesting thing to note is that this capacitor was placed before the regulator, rather than after it. By doing this, the total energy it can store is higher. It will hold the same number of electrons on either side, but those electrons will have a higher voltage upstream.
    • Why are there two capacitors right next to each other? Why not just use one big one?

      The .1uF capacitor is called an "input bypass capacitor," and its job is to keep some of the noise generated by the regulator from spreading to the rest of the circuit. The regulator is basically a high-frequency switch, and every time it flips a large amount of noise can be released. The bypass capacitor gives this noise a quick return path, acting as a shunt. But why doesn't the larger 330uF capacitor do this? All real-world capacitors have something called "Equivalent Series Resistance," or ESR, which can be thought of as a small resistor in series with the capacitor. As it turns out, electrolytics have somewhat high ESR compared to small ceramic capacitors, so you'll almost always see ceramics (or tantalums) near power supplies or the power pins on ICs, rather than electrolytics.

      Here's an article on suppressing EMI from power supplies, for reference.
    • The last 1uF cap on the output is there to improve transient response, which essentially means "be able to supply extra energy quickly when the load changes quickly."

      • This article talks about many of the issues involved with capacitor selection for voltage regulators.