Problem with DC/DC Boost converter circuit with MC34063A

[Mithun_K_Das]

I was trying to make a DC/DC boost converter with MC34063A. It is a good IC for the purpose but its not working well.
Having a lots of trouble.

Here is the PCB diagram:


And the circuit diagram is here:



The problems are:

* Its taking high current at startup, frequently MOSFETs blows away.
* If current is reduced from the supply and then controlling the current tuning current controlling VR, it genaretes 30-35V[unstable]. But whenever load is applied, it become short again.
* Genareting lots of heat in Fets and Inductors.

I tried with changing inductors by 47uH,100uH,120uH,220uH. Timing cap: 222,102,104,103. Diodes: UF5408,HER308,SR560. Fets: IRF3205, 75n75, IRFZ44N,

no improvement. All similar problem. :-(

Need help.

 

[DeepOne]

it will be a bit better in such type

 

[Mithun_K_Das]

Thanks man, I'm trying this one now... I'll update what happen....

 

[FvM]

it will be a bit better in such type

Hopefully fixing the most obvious design flaws.

It's not so good to divide Vgate down with 100:150 ohm , I think.

Generally, a 20 A switching boost converter should deserve a little bit of a state-of-the-art switch mode controller. Why one of the cheapest available at the market that just barely performs the job?

 

[Mithun_K_Das]

No upgrade bro... having same problem as before... @ DeepOne


Can you suggest anything good @ FvM ?

 

[DeepOne]

possible to do more perfectly but it seems the deal is not in scheme

 

[Mithun_K_Das]

Thanks DeepOne, I'll try this circuit tomorrow and update the result.

 

[Mithun_K_Das]

I changed the MOSFET, and inserted IRF740B, now its generating HV(up to 623V I got). But Fet is becoming hot without any load. and with load, voltage drops. And Fets get extremely heated.

 

[DeepOne]

"and inserted IRF740B, now its generating HV(up to 623V I got)"

max D_S voltage for this FET is 400V, as we see in datasheet

 

[Mithun_K_Das]

hmm. That is why after few min it blows away....!!!! I've built another one. It is working well but generating too much heat.