Power Supply Introduction


The RLC Meter is powered via a USB connection to an active USB port on a computer or powered hub. The USB (J3) connection provides 5 V dc, which is regulated by U3 to a fairly precise 3.3V dc. The 5V input to U3 is provided via 5 of the six available positions in the "B" gang of S1. The regulated 3.3V output from U3 is provided on the 3.3V rail (and causes the LED (D1) to light up when power is applied and all is working OK in the power supply.

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Power Supply Schematic

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Power Supplyschematic

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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)

cbl1USB-A to USB-B CableUser-Supplied Not furnished with kit.Power Supply
D1red LED LED  Power Supply
S12 pole six pos rotary switch 2P6T  Power Supply
U3LE33CZ 3.3V voltage regulator TO-92  Power Supply
C5100 nF(0,1 uF)104 104Ceramic Leave enough space between the bottom of the cap and the top of the board to allow your DMM probe to get in and touch the lower lead.Power Supply
C410 uF106 106tantalum  Power Supply
J3USB-B pcb jack (rt-angle) Jack-RA  Power Supply
R6330 1/4W 5%ora-ora-brn-gld ora-ora-brn-gld1/4W  Power Supply

Power Supply Summary Build Notes

Power Supply Detailed Build Notes

Top of the Board

Power Supply Top View

Install Voltage Regulator

Mount the USB jack to the board

Mount the voltage regulator, U3, upright in the holes provided

Note the orientation of the U3 IC: align the flat side with the corresponding flat side on the board's silkscreen. The graphic show the alignment of the flat side with the silkscreen marking. Note the transistor must be mounted so that it stands up vertically (not laying down as the graphic might suggest.

Install Voltage Regulator photo
cbl1USB-A to USB-B CableUser-Supplied 
Not furnished with kit.
U3LE33CZ 3.3V voltage regulator TO-92 
J3USB-B pcb jack (rt-angle) Jack-RA 

Install Capacitors

Tantalum capacitors are polarized. Take care to align the tantalum capacitor for correct polarity (see graphic) The positive lead should go to the hole marked "+".

C5100 nF(0,1 uF)104 104Ceramic 
Leave enough space between the bottom of the cap and the top of the board to allow your DMM probe to get in and touch the lower lead.
C410 uF106 106tantalum 

Install Diode and limiting Resistor

Note the orientation of the LED. The cathode lead is the shorter of the 2 leads.

Some LEDs will also have a flat edge/bevel in the ring around the bottem of the LED to signify the cathode lead.

Install Diode and limiting Resistor photo
D1red LED LED 
R6330 1/4W 5%ora-ora-brn-gld ora-ora-brn-gld1/4W 

Install Rotary Switch

Take care to orient the rotary switch so the round "nub" is at the 6 o'clock position.

Hint: to facilitate soldering, you should place the switch pins into their respective holes, then, holding the switch firmly to the board, turn the board over and "tack solder" two opposite pins using a blob of solder on the iron. Once the switch has been "tacked", just to be sure, turn the board over and check for correct orientation, before returning to the bottom side and soldering the remaining pins (and resoldering the "tack solder" joints). Install Rotary Switch photo

S12 pole six pos rotary switch 2P6T 

Power Supply Completed Stage

Top of the Board

View of Completed Top

Power Supply Testing

Power On/Off Switching

Test Setup

Connect the USB Jack (J3) to a powered USB port on your computer (or a powered hub).

Rotate the switch (S1) clockwise through its positions and verify that the LED lights up in five of the 6 possible S1 positions

(This verifies that the voltage regulator has received the 5V from the USB port, regulated it down to 3.3V and passed it on to the LED. If you do not get the LED to light up on any of the positions, then check back through the circuit to the voltage regulator and measure its input voltage - see next test..

Power On/Off Switching

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
left-most position (most counterclockwise) of S1LEDOFFOFF_______
All other positions of S1LEDONON_______

Voltage Regulator Output and Input

Test Setup

With board connected to powered USB port:

Rotate S1 to a position where the red LED lights up.

All voltage measurements in this stage are with respect to ground ("WRT Ground").

Measure the voltage at the 3.3V testpoint. If the voltage regulator is working correctly, you should see a voltage at or very close to 3.3V dc.

When using the 5V testpoint (lower lead of C5), take great care not to short the leads of C5 together. Doing this would short the +5V directly to ground, with unpleasant consequences not limited just to SSZ (smoking, sparking, and zapping).

Voltage Regulator Output and Input

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
3.3V testpoint (see graphic)V dc3.33.31_______
5V testpoint (Careful! Do not short C5's leads)V dc55.01_______
Go to OpAmps/I_O Stage Go to Negative Power Supply Stage Read Datasheet