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sd_pwr Assembly Guide
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sd pwr Power Supply Assembly and User Guide

The sd pwr board is a power supply specially developed to fit the low voltage needs of ECE 44x students. With basic functionality and versatile use-cases, the sd pwr board is ready to be integrated into your project for reliable voltage and current supply.

Included in kit:

The sd pwr board may be assembled with the parts included with the kit, however use-case-specific modifications and integration are encouraged.

Board Power Specifications

Voltage IN

4.5 vdc min. 24vdc max.

Voltage OUT

0.8 vdc min. 12vdc max. (with vin >= 14v)

Current OUT

1.5 Amps max.

Input

The board has two power input connectors; a 2.1mm female barrel jack and a screw terminal. These components are included with the kit to be soldered by the user. Either of these inputs can be used to power the board. Additionally, these inputs are protected from reverse polarity by Schottky diodes. Take care when soldering to attach the screw terminals facing outwards. Alternatively, power input wires can be soldered directly to the board.

Output

Power output is provided by a screw terminal and a set of binding posts. These components are included with the kit to be attached by the user. Either of these outputs can be used to take power from the board. The power outputs are not protected from reverse polarity. Take care when soldering to attach the screw terminals facing outwards. Alternatively, power output wires can be soldered directly to the board.

Voltage Trim

To adjust the output voltage of the board, there is a place labeled “Voltage Adjust” to mount the included 100k ohm potentiometer. Turning it clockwise will increase the voltage output and turning it counter-clockwise will decrease it.

Output Voltage Monitoring

Included in the board kit is a small independent voltmeter board. The power supply is designed to allow for the mounting of this voltmeter to show voltage output. To mount the voltmeter, first solder the black wire to gnd, the red wire to vin, and the yellow wire to vout; as shown in figure 1.1. Next, use the included nuts and bolts to attach the meter to the board. Take care to only finger tighten the nuts as overtightening could lead to an unintentional short circuit. Alternatively, hot glue could be used to attach the meter.

Figure 1.1 - soldering the multimeter to the board

Modifications

The sd pwr board is intended to fit a range of use cases, if you find that it does not work for your project in the configuration outlined in this guide, please modify it as you see fit. Below are a few suggestions on how to make changes to the board. Linked at the end of the document are the Schematics and KiCad files for the board.

Modification: voltage range

The voltage range on the sd pwr board is a 0.6vdc to 12vdc swing with the included 100k potentiometer. This range can be adjusted by swapping the included potentiometer with a one of a different value; or it can be locked to a single, tuned, voltage by soldering a resistor (or a string of resistors) onto the board in place of the potentiometer. The latter would be optimal for a use-case where the power supply is being built into a project and only needs to supply one voltage. The equation to find the correct size of capacitor is shown in figure 2.1

Figure 2.1 - equation to find resistor value R to set for desired voltage Vout

For example: if I want an output voltage of 15 volts, you can solder two 10k resistors in series with a 100k resistor. This will lock the output voltage to 15v. Figure 2.2 shows this in action.

Figure 2.2 - 120k ohm equivalent resistance soldered in place of a potentiometer

Modification: low profile capacitors

The board comes with two 63v 10uF capacitors soldered to it. These capacitors have been picked to play nicely with the rest of the circuit, however they are the largest (and most obtrusive) component on the board. If the board is going to be integrated into a small form factor system, it could be advantageous to replace these with lower profile capacitors of the same capacitance. Figure 2.3 shows an example of this mod.

Figure 2.3 - lower profile 10uF capacitors make the sd power board fit in tighter spaces