Boost Converter, please help

Hello everyone, please help...



When i connect the circuit as the schematic above: the output is not changeable which means when I alter my Pot, the output remains the same. ( the frequency is about 2.3Khz)

One thing that I have observed is, the output is now depending on my Inductor value.

1mH = 100V++;10mH= 51V.

I burned my 3mH inductor while I was using C1=47uF (last time, the inductor wasn't burned !!! I wonder why)

The duty cycle is about 60%.

Things that I've summarized are :
1. When switching frequency is up to 23kHz, the inductor is alright but the output is not alterable; When switching frequency is low as 1.4kHz, the output can be altered but inductor will be burst ( it's like overheat and cause the outside(cover) of the coil inductor melts.)

2. The feedback system seems like failure when frequency is as high as 20kHz. But, why?

3. For 1 &2 are the conditions under resistor as load. And, I just connected it to the real load that I wanted to connect. Things happen:
The output voltage was less than just now: for 10mH, it became 30V;for 1mH, it became 80V [the output voltage is less 20V compare the just now]
(ii) When I connected to 1mH inductor, both of the inductor and Mosfet is quite hot ( i just connect it about 10++min)

4. Previously, with low frequency, it had "hiss" sound. Now, "Hiss" sound is gone when the switching frequency is 20kHz with 60%duty cycle; "hiss" sound appears when switching frequency is 1.4kHZ...

Does anyone have any ideas regarding my problem? What should I do? Thanks a lot in advanced.

You need at least 0.6V at the potentiometer wiper in order to start the transistor conducting but you are dividing the output by almost 50 times before it reaches the potentiometer. I suggest you look at the divider resistor values to ensure you have enough feedback voltage. Inductor value should be chosen according to the frequency of the oscillator, if you change the inductance it should be expected that the efficiency and voltage changes. Are you using a fast diode for D1, I do not know what an RU2 is.

Brian.

Have you considered using a UC3843 current mode control IC? It is designed to do this sort of thing.

https://www.ti.com/lit/gpn/uc3842

Here is a simplified LTSpice model of a possible solution,




You should be able to recognise some of the components from the data sheet block diagram. The design is to give 50V out with 12V in with a switching frequency of 100KHz. The load will draw 1A. The input inductor is scaled for continuous current with about 1A of ripple current. There is 'slope compensation' applied from VTRI via R7 to prevent subharmonic oscillation. Most of the components, in particular those to do with compensation, were 'guessed' at and could probably be better optimised.

Start Up,



Regulation



Shout if you need more help..

Genome

Magnelab is the home of the Split Core Current Transformers. These split core current sensors measure AC current from 1 Amp to 10,000 Amps.

Rey25 said:

Magnelab is the home of the Split Core Current Transformers. These split core current sensors measure AC current from 1 Amp to 10,000 Amps.

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Good to know that one Rey25.... and this will help in which way?



Oooooo...

Magnelab : Home

Magnelab is a world leader in the design and manufacture of AC current transformers and home of the Split-Core current transducers. For over 40 years Magnelab has served many industries with a commitment to quality and service.

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I do hope you are not associated with Magnelab but if you are then given your selection of this particular thread for your spam I might have to assume Magnelab really does not have a clue and will be relieving you of your spamming duties sometime soon.

Genome.