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DC-DC Boost Converter Design Help

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baileychic

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I need help in designing 9V to 12V Boost Converter. Currently I am only testing it in Proteus. Later after simulation works fine I will build the circuit. For simulation purpose I am using 2 KHz PWM. For final hardware circuit I will use say 100 KHz or 200 KHz PWM to reduce the Inductor value.

The problem I am having in simulation is that the output voltage keeps increasing and never stops.

My Topology as calculated at daycounter.com

PHP:
Topology: Boost 

Inductance based on the specified minimum load current.
Item	Value	Units
Volts In	9	V
Volts Out	12	V
Load Current	0.5	A
Freq.	2	KHz
Vripple	0.12	V
Duty Cycle	31.746031746032	%
Ipp Inductor	0.15	A
Ipk Inductor	0.575	A
Irms	0.42720018726588	A
L	9100.5291005291	uH
C	661.37566137566	uF

Find the attached Proteus Simulation file. I have not yet added a Microcontroller (PIC) to the circuit because it will slow down the simulation but in the actual hardware circuit there will be PIC18F46K22.
 

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KlausST

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Hi,

Yes, you continously push energy to the output..but there is no load....for sure the voltage is rising.

* either connect a load
* or control the PWM with a feedback of the output voltage

I recommend to read through some basic tutorials about SMPS operation.

Klaus
 

baileychic

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Yes, Thank you Klaus. I connected Load resistor and got stable output voltage but output voltage is varying with load resistance. For 68k load resistance I got 12.5V output voltage if load resistance decreases then I am getting decreased output voltage.

Boost converter was designed for 0.5 A max output current.

Can you recommend me a few good books and articles related to DC-DC Converter and SMPS Circuit designing ?
 

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FvM

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The circuit should use a fast rectifier diode instead of 1N400x, it will generate considerable losses at higher switching frequencies.

The circuit needs a controller varying the duty cycle, particularly at low load when the switcher operates in discontinuous conduction mode (DCM). At higher load currents, it changes to CCM with roughly load independent output voltage, but you may want to compensate a certain voltage drop due to inductor and switch and diode series resistance.
 

baileychic

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Diode and transistor voltage drop is taken care by the calculator.

https://www.daycounter.com/Calculators/Switching-Converter-Calculator.phtml

I am only concerned about getting fixed voltage with feedback to micrcontroller adc input pin. I will quickly add the micrcontroller circuit and try to control the duty and hence the output voltage with feedback. I will also replace the 1N4007 diode with UF4004 diode and try.
 

CataM

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Speaking of control, seems that all application notes (I was not able to find a single one with another method) are still outdated (or do not care too much) of their accuracy prediction in Current Mode Control e.g. AN149 of Linear Technology called "Modeling and Loop Compensation Design of Switching Mode Power Supplies" in post #6. They still use the Ridley method for Current Mode Control while the Dragan Maksimovic's method is more accurate and was presented about more than 15 years ago.
 
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