Current mode boost converter

7 months ago

Profile:oiiojo

Open source license: Public Domain

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Description

A current mode boost converter is a type of boost converter in which the peak switch current limit during the on-time is controlled in each cycle. This is done by sensing the switch current, adding a ramp to it and comparing it to the error signal generated by an error amplifier. This comparison leads to the generation of reset pulses which help generate the required PWM signal.

This curcuit takesin 10V and outputs 35V at over 1A.

Screenshot 320.png

A close up of the output voltage looks like this:

Screenshot 330.png

The switch current looks like this:

Screenshot 321.png

and the inductor current looks like this:

image.png

The switch current is sensed using a current sensing resistor. The voltage drop across this resistor is sensed.

Screenshot 323.png

In order to prevent subharmonic oscillations, a ramp is added to the voltage generated from the switch current (the parameters of the ramp waveform are not calculated and are selected arbitrarily, but the circuit works fine none-the-less):

Screenshot 324.png

Screenshot 325.png

This ramp waveform is compared with an error signal in order to generate reset pulses, which are fed to an op-amp based SR latch. The clock pulses set the SR latch while the reset pulses from the comparator reset the SR latch, thus creating a PWM signal.

Screenshot 326.png

Screenshot 328.png

Vn009 : PWM signal
Vn012: Set pulses from clock(green)
vn008: Reset pulses from comparator(blue)

image.png

This is how the required PWM signal is generated.

The efficiency of the circuit is 92.46%

Screenshot 329.png

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