Under Voltage Protection

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# Under Voltage Protection - PowerPoint PPT Presentation

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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Presentation Transcript

### 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.
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.
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.
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.
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.
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.
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.