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Voltage feedback control using NE555 timer with variable load resistance

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Beans

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Hello,

I am busy with a project that boosts 12 V DC to 24 V DC through the use of a boost converter. I am only using 1 power supply - the 12 V DC. For the inductor to charge up and boost the voltage, a PWM is needed to switch a MOSFET so that is can do the boosting. So I have used a NE555 timer to do this successfully.

But at the moment my load to the converter is a constant 48 Ohm resistor, which gives 24 V output. My challenge is that I want to make the load vary. How can I use the timer to manipulate the duty cycle of the circuit to keep boosting at a constant 24 V, doesn't matter what the output resistance of the booster is?
 
Is this a normal voltage doubler circuit?
How much does the voltage chang with differant loads?
Can you post your circuit?

And Welcome, I hope we can help.
 
Hi,

To do this you could use the modulation pin of the 555, but you also need to add an error amplifier/integrator which would be at least one op amp and a few other parts. The op amp detects the error in the output and provides a signal to the modulation control pin of the 555, and the 555 then varies the duty cycle.
Because boost circuits have a couple inherent problems you'd have to do some testing to make sure the pulse width stays within certain limits and the circuit is stable. Testing would mean running the input over the expected range of operation and also adjusting the load over the expected range of load values and load types if not purely resistive.
 
These quick responses are amazing...and thanks for the welcoming ;)

The first circuit is just a normal boost converter with a signal generator for the MOSFET to switch. The voltage ripple at the load must be below 1 V, but the capacitor is there to take care of that. I am only able to use the one 12 V DC power supply, which leads to the second circuit that has the timer integrated.

Mr Al is correct, but I do not know what exactly to use in that voltage feedback circuit...could someone please expand on what to use between the load resistance of the circuit (the 48 Ohm in the picture) and the CV pin of the timer
 

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Why don't you use a simple voltage doubler?
You don't need a full fledged boost converter.
What is your current draw at 24 volts?
A simple 555 voltage doubler with out extra drive;
voltage-doubler-circuit.jpg

This is good for about 22 volts at 50 ma.
 
NorthGuy - an MCU sounds delicious. No idea how to use one though so will have to figure that out.

4pyros - The power of the output needs to be 12W. The 50 mA will not be enough. But that voltage double looks awesome - will definitely use that in the future. The current at the load (24 V) is 500 mA
 
4pyros - You know when I browse the net for days and can't find anything and then you get heaps of info in 10 minutes. Thanks so much man
 
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