Power Supply Introduction


This stage supplies the "regular" 5 volt power rail, for powering the CMOS chips on the main part of the board and providine the 2.5V rails via voltage dividers.

Following the diode at the power input point, there is a 12V dc takeoff for powering the pre-amp in the RF/Control Stage.

Top, Bottom Orientation

Note: throughout these notes, they will refer to the board in terms of:

Unless otherwise noted, all photos/graphics of the board layout are displayed herein with the top edge UP.

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Power Supply Schematic

(Resistor testpoints (hairpin, top, or left-hand lead), as physically installed on the board, are marked in the schematic with red dots)

Power Supplyschematic

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

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Power Supply Bill of Materials

Stage Bill of Materials

(resistor images and color codes courtesy of WIlfried, DL5SWB's R-Color Code program)

mtg_hdw4 X #4-40 hdw (nut, bolt, washer, spacer) HDW (optional) install the mounting hardwarePower Supply
PCBEnsemble RX PCB (board)Main Board  Power Supply
D031N40031N4003 1N4003AxialS-NMount as hairpinPower Supply
R1168 1/6W 5%bl-gry-blk-gld bl-gry-blk-gld1/6WS-N Power Supply
U06LM78L05 voltage regulatorLM78L05 LM78L05TO-92flat side to left Power Supply
C054.7 uF 10% 16V X7R RAD475 475Ceramichoriz Power Supply
C064.7 uF 10% 16V X7R RAD475 475Ceramicvert Power Supply
Cbl2Power-Leads for 12VUser-Supplied  Power Supply
J03DC Power Jack PCB Mount (rt-angle) Jack-RA  Power Supply
P1DC Power Plug 5.5/2.1mm Pos Ctr Plug Solder appropriate 12V power leads onto this plugPower Supply
/QSD ENshunt wire (cut-off lead)Cutoff Install as ground test pointPower Supply

Power Supply Summary Build Notes

Power Supply Detailed Build Notes

Top of the Board

Power Supply Top View

Install Topside Components

Install the resistor and diode first, then the voltage regulator, then the caps, and, finally the Jack and the ground point

Install the diode in a hairpin fashion, such that the catgode (the band) end is the hairpin.

The kit allows you to build it so as to support PTT switching in and out of the Quadrature Sampling Detector by connecting/disconnecting the "/QSD EN" (pins 1 and 2 of U8) to ground. Herein, we will use the simpler scenario of full-time QSD enabling by mounting the shunt wire on the QSD-EN connections on the board (also serves as a convenient ground test point)

Install Topside Components photo
mtg_hdw4 X #4-40 hdw (nut, bolt, washer, spacer) HDW 
(optional) install the mounting hardware
PCBEnsemble RX PCB (board)Main Board 
D031N40031N4003 1N4003AxialS-N
Mount as hairpin
R1168 1/6W 5%bl-gry-blk-gld bl-gry-blk-gld1/6WS-N
U06LM78L05 voltage regulatorLM78L05 LM78L05TO-92flat side to left
C054.7 uF 10% 16V X7R RAD475 475Ceramichoriz
C064.7 uF 10% 16V X7R RAD475 475Ceramicvert
Cbl2Power-Leads for 12VUser-Supplied 
J03DC Power Jack PCB Mount (rt-angle) Jack-RA 
P1DC Power Plug 5.5/2.1mm Pos Ctr Plug 
Solder appropriate 12V power leads onto this plug
/QSD ENshunt wire (cut-off lead)Cutoff 
Install as ground test point

Power Supply Completed Stage

Top of the Board

View of Completed Top

Power Supply Testing

PWR Resistance/Current Draw

Test Setup

Measure the resistance (after the input diode) on the power input to ensure there is no short circuit. Measurement can be taken from the hairpin of D3 and the "/QSD EN" ground wire and should read in the Megohm range.

If the measured input resistance is within reason, measure the current draw with your mA meter inserted in series into the positive power lead.

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
D3 hairpin lead (WRT "/EN QSD" ground point)> 1M7M and rising_______
Current DrawmA< 84.3_______

Voltage Tests

Test Setup

With 12 V dc applied to the board (author's gel cell was at 12.89 Vdc), measure the voltage after D3 and measure the output of U7 (the 5 Vdc rail)

Measurements are with respect to (WRT) the regular ground plane (i.e., the non-USB side) of the board.

Voltage Tests

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
At Cathode of D3 (WRT regular ground)V dc0.6 less than input voltage12.3_______
At hole for R18 hairpin lead (WRT regular ground)V dc54.94_______
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