SPVA023 July   2025 LM25184 , LM2611 , LM27761 , LM5158 , LMR33640 , TLV171 , TPS63700

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Methods to Design a Negative Power Supply from Positive Voltage 
    1. 2.1 Generate Negative Power Supply by Using a Charger Pump
    2. 2.2 Generate Negative Power Supply Using An Inverter Regulator
    3. 2.3 Generate Negative Power Supply Using A Buck Regulator
    4. 2.4 Generate Negative Power Supply Using A Cuk Regulator
    5. 2.5 Generate Negative Power Supply With A Fly-Back Converter
  6. 3Summary
  7. 4References

2.3 Generate Negative Power Supply Using A Buck Regulator

There are fewer inverter converters compared to buck regulators in the market. This potentially means that the designer cannot find a good inverter converter to meet miscellaneous specific requirements for example, large input voltage or more output current. In this condition, a designer can build an inverter regulator by reconfiguring an ordinary buck regulator. Figure 2-6 shows a buck topology and inverter topology. A designer can see the topology between buck regulator and inverter is exactly the same except one terminal of inductor was grounded and low side MOSFET is the output. This means that a buck regulator potential can be configured to an inverter converter by reconfiguration. Figure 2-7 shows how to build an inverter converter with a traditional LMR33640 buck regulator.

Buck Converter Topology and Inverter Buck-Boost Topology Figure 2-6 Buck Converter Topology and Inverter Buck-Boost Topology

The connection changes are shown in the following list:

  1. Reassign buck positive output as system ground.
  2. Reassign buck regulator ground nodes as the negative output voltage node.
  3. Positive input stays the same.
  4. Feedback input always referred to GND of regulator chips.

Designers can use any buck regulator to build an inverter converter to meet the specific application by following the four rules that were mentioned previously.

Inverter Buck Boost Converter Based LMR33640 Figure 2-7 Inverter Buck Boost Converter Based LMR33640

Designers must also check the following list during actual design course.

  1. The maximum endure voltage of MOSFET in buck regulator now is need big than Vin-Voutput.
  2. The saturation current of inductor needs big than 1.2Io(1+Vo/(Vin × ƞ))
  3. The setup output voltage as a buck regulator but note that the reference voltage always refers to the GND of chips. The output voltage is shown in Equation 7
Equation 7. V o u t p u t = - 1 + R F B T R F B B × V R E F