Negative Power Supply Introduction


Once the powersupply is working, we need to provide a negative reference voltage that the OpAmps in the final stage can use. This is accomplished with U2 which takes the 3.3V dc from the power supply and outputs a negative 3.3V dc voltage.

(go directly to build notes)

Negative Power Supply Schematic

(Click for Full Schematic)
Negative Power Supplyschematic

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

(go directly to build notes)

Negative Power Supply Bill of Materials

Stage Bill of Materials

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

U2TC7660 charge Pump DC-DC Conv DIP-8  Negative Power Supply
C210 uF106 106tantalum  Negative Power Supply
C310 uF106 106tantalum  Negative Power Supply

Negative Power Supply Summary Build Notes

Negative Power Supply Detailed Build Notes

Top of the Board

Negative Power Supply Top View

Install U2

Take care installing U2. In addition to its sensitivity to electrostatic discharge (ESD), we want to be very careful to orient the chip correctly. The chip will have a dimple on it denoting the location of pin 1.

Insert the chip into the holes using the dimple and the graphic herein to ensure that pin 1 is correctly aligned.

"Tack Solder" two opposite pins to hold the chip in. Then turn the board over from the bottomside to the topside and DOUBLE CHECK YOUR WORK before soldering, then, CHECK AGAIN. You do not want to have to remove the chip because it was improperly oriented!

Be sure to verify that all 8 pins went through their respective holes. If one of the pins gets folded under during insertion, it is nearly impossible to detect and can lead to a frustrating trouble-shooting experience.

Once you are certain of the correct orientation and all pins are through the holes, turn the board over to the bottomside and solder all of the pins.

Install U2 photo
U2TC7660 charge Pump DC-DC Conv DIP-8 

Install the two Tantalum (polarized) Capacitors

Be sure to install these with the correct orientation and polarity. The positive lead of the cap must align with the "+" sign on the silkscreen.

Install the two Tantalum (polarized) Capacitors photo
C210 uF106 106tantalum 
C310 uF106 106tantalum 

Negative Power Supply Completed Stage

Top of the Board

View of Completed Top

Negative Power Supply Testing

Voltage Test

Test Setup

Power up the board via the USB cable

Measure the voltage at the "-3,3V" testpoint, with respect to ground

Measure the voltage at the "+"3.3V" testpoint, with respect to ground.

You can use any of the holes on P2 as a ground reference.

Voltage Test

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
"- 3.3V" (WRT ground)V dc- 3.33.315_______
"+ 3.3V" (WRT ground)V dc+3.33.314_______
Go to (positive) Power Supply Stage Go to OpAmp Stage Read DataSheet