Why We Need a Negative Voltage Supply Rail
Let’s say you are designing analog measurement front end circuitry for an analog to digital converter (ADC) with a measurement input range for -10V to 10V. You want to use the full range of the ADC to obtain maximum resolution, so you need to provide a negative -10V voltage rail to your front end signal conditioning circuitry (Op Amps) so the output signal can swing between -10V and 10V.
Charge Pump DC to DC Converter
Charge pumps provide a simple solution. They can produce a few 10s of mAs — enough to power your front end op amps.
- For example, our charge pump (U1, TC766) can produce 20mA.
In most cases, they provide an exact mirror of the voltage provided at input.
- For example, we provide +10V to our charge pump, and it creates -10V.
- Similarly, if you supplied +3.3V, you would get -3.3V.
Read the data sheet for your charge pump chip carefully, some charge pumps produce 1/2 of the supplied input voltage.
Voltage Stability
A charge pump is a type of switched regulator — as such, the voltage produced has a little ripple.
In almost all cases, this is not a problem as the noise rejection on modern ops amps is quite good.
In the highly unlikely case you need a super stable negative voltage rail, you can place a linear regulator after the charge pump to produce a supper clean negative voltage supply.
DNP Note
DNP = Do Not Populate. In the above schematic, DNP populate components are not fitted on the PCB. These positions are left open for future flexibility in the design.
Need Some Help?
We’re always happy to share our knowledge — feel free to email us at:
- support@magicdaq.com
Working Model
Want to play with a working model? You can find this circuit on the M&A Board at MagicDAQ.com
