Constant-on-time buck-boost regulator converts a positive input to a negative output

Constant-on-time buck-boost regulator converts a positive input to a negative output

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Based on National Semiconductor’s LM5010, this buck-boost regulator operates over a wide input-voltage range.

This is a LM5010 buck-boost regulator able to convert a positive input ranging from 10-50Vdc to -12V output. by Robert Bell @ www.edn.com

Buck regulators find wide application as step-down regulators for converting large positive input voltages into a smaller positive output voltages. Figure 1 shows a simplified buck regulator that operates in continuous-conduction mode—that is, the inductor current always remains positive. The output voltage, VOUT, is equal to D×VIN, where D is the duty-cycle ratio of the buck switch, Q1, and VIN is the input voltage. The duty cycle, D, is equal to TON/TS, where TON is the on-time of Q1 and TS is the switching-frequency period.

Figure 3 shows a low-cost buck-boost converter based on the LM5010 buck-regulator IC that converts a 10 to 50V positive supply voltage into –12V. Although many applications use a fixed switching frequency and modulate the output pulse width, this design features a constant-on-time approach in which the IC’s internal output transistor turns on for an interval that’s inversely proportional to the difference between the circuit’s input and output voltage.

Mike is the founder and editor of Electronics-Lab.com, an electronics engineering community/news and project sharing platform. He studied Electronics and Physics and enjoys everything that has moving electrons and fun. His interests lying on solar cells, microcontrollers and switchmode power supplies. Feel free to reach him for feedback, random tips or just to say hello :-)

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