Homework Help: Non-Inverting Buck/Boost Converter Question

1. May 6, 2014

Nabeel

Function of the Circuit:
• Provide a constant voltage of 3.7V at the load for battery charging when there is an input ranging from 0V to 5V.
• When SW1 driven by PWM 1 and SW2 is always OFF, the device will work in Buck Mode. That is if input voltage goes above 3.7V.
• When SW1 is always ON and SW2 is driven by PWM 2, the device will work in Boost Mode. That is if input voltage is below 3.7V.

Question:
How to create a feedback system at the output which will cause the output to stay constant at 3.7V?
• The circuit have to boost the voltage to 3.7V if the voltage at the input is below 3.7 V
• The circuit have to buck the voltage to 3.7V if the voltage at the input is above 3.7V

Note: The circuit is attached in the thread.

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2. May 6, 2014

Baluncore

The usual solution to this situation is to first boost to say +12V, then buck that to +3.7V.

The reason for using +12V rather than +5V is that efficiency is better with the higher intermediate voltage and the capacitor between the stages can be smaller.

You have not specified the charge current output required at +3.7V.

3. May 6, 2014

Staff: Mentor

As it is required to supply 3.7V output even when there is no input, you'll be deriving full power from another source under some conditions.

4. May 6, 2014

Staff: Mentor

Since this is your schoolwork problem, you need to show a fair amount of initial effort, before we can be of tutorial help. Can you show us some techniques that can be used for this problem?