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Under Voltage Protection

Under Voltage Protection. Chapter 12 Switch mode Power Supply Handbook Keith Billings. What is Under Voltage?. Under Voltage condition occurs when a load is suddenly connected to a power supply. The load will start to draw current, this causes the voltage to temporarily drop.

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Under Voltage Protection

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  1. Under Voltage Protection Chapter 12 Switch mode Power Supply Handbook Keith Billings

  2. What is Under Voltage? • Under Voltage condition occurs when a load is suddenly connected to a power supply. • The load will start to draw current, this causes the voltage to temporarily drop.

  3. Graphical Example of Under Voltage • Graph A shows the sudden rise in current going to the load • Graph B shows the sudden voltage drop without an adequate under voltage protection circuit. • Graph C is the same circuit with a under voltage protection circuit.

  4. Dangers of Under Voltage • Premature Shutdown of circuit • Lose of Data • Very important in navigation and automotive application were data is constantly being processed and updated.

  5. Example of Under Voltage Protection Circuit

  6. What makes a good Under Voltage Protection Circuit? • Fast response time • Able to supply a large voltage in order to keep the voltage drop small. • Able to handle voltage drops for extended periods of time.

  7. Example of a Under Voltage Protection Circuit.

  8. What does this circuit do? • This circuit prevents the output from going under 5 mV. • When it goes under 5mV, S1 will turn on providing additional voltage to supplement the load.

  9. How does this circuit work? • E2 and R6 form the Thevenin Equivalent of the DC power source. • R1,C1,R2,C2 form the circuit to lift up the voltage if needed. • R3 and R4 form a voltage division.

  10. How does this circuit work? How does this circuit work? • E1 is the voltage reference, if the voltage across the load drops below E1. The output of the comparator is high. • If the output of the comparator is high. S1 turns on thus provide the output with the voltage of C1 and C2 in series.

  11. Results

  12. Results

  13. Advantages Cheap easy to implement. Circuit protection level can be adjusted by changing the value of R3,R4 and the value of the reference voltage. Disadvantages Can only be used in the mV range. Can only be used in high frequency circuit. (Above 10 kHz) Advantage and Disadvantages

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