Power Supply Introduction

Theory of Operation

This stage provides the +5 volt power rail for the radio. The incoming voltage (from 9 - 12 Vdc) is regulated by U1 to a nominal 5 Vdc (4.5 - 5.1 Vdc range). D1 serves to protect the circuit from accidentally reversed polarity.

Power Supply Schematic

(Resistor testpoints (hairpin, top, or left-hand lead) are marked with red dots)

(Click for Full Schematic) Power Supplyschematic

(above schematic has clickable areas that can be used for navigation)

Power Supply Bill of Materials

Detailed Bill of Materials

CheckDesignationComponentMarkingCategoryOrientationNotesCircuit
[____ ]C014.7 uF 10%475Ceramic  Power Supply
[____ ]C024.7 uF 10%475Ceramic  Power Supply
[____ ]C130.1 uFblack stripe black stripeSMT 1206SMT Power Supply
[____ ]D11N40031N4003AxialE-W Power Supply
[____ ]gndshunt wire (cut-off lead)misc  Power Supply
[____ ]U1LM78L05 voltage regulatorLM78L05 LM78L05TO-92  Power Supply

Power Supply Summary Build Notes

Power Supply Detailed Build Notes

Bottom of the Board

Power Supply Bottom View

Install SMT cap

Install C13 SMT 0.1 uF cap

Take care to avoid solder "splashover" that could clog up the thru-holes above and to the right of C13 (see red dots in above graphic)

CheckDesignationComponentMarkingCategoryOrientationNotes
[____ ]C130.1 uFblack stripe black stripeSMT 1206SMT

Top of the Board

Power Supply Top View

Install topside components

Install the two blue capacitors, U1, and D1. Install D1 such that the cathode end (the end with the band) is facing up and forms a hairpin. The hairpin lead will go into the square thru-hole (refer to the Completed Stage, Topside picture below).

CheckDesignationComponentMarkingCategoryOrientationNotes
[____ ]U1LM78L05 voltage regulatorLM78L05 LM78L05TO-92 
Take ESD precautions
[____ ]D11N40031N4003AxialE-W
[____ ]C014.7 uF 10%475Ceramic 
[____ ]C024.7 uF 10%475Ceramic 

Install ground test loop

Using a short length of cut-off resistor or capacitor lead, fashion a short wire loop and solder it to the "ground" hole, such that the loop is available on the topside to provide a ground point for tests.

Install ground test loop photo
CheckDesignationComponentMarkingCategoryOrientationNotes
[____ ]gndshunt wire (cut-off lead)misc 

Power Supply Completed Stage

Top of the Board

View of Completed Top

Bottom of the Board

View of Completed Bottom

Power Supply Testing

Visual Inspection

Test Setup

Using very good lighting and magnification, carefully inspect the solder joints to identify bridges, cold joints, or poor contacts.

Current Test

Test Setup

Test for current draw in 2 ways:

Current Test

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
With limiting resistormA< 121.8_______
Without limiting resistormA1 - 41.8_______

Voltage Test

Test Setup

Once the current draw test is successfully passed:

Go to External Connections