MC34063 step_up regulator loading problem

[nikhilele]

have designed the following step up conveter

the only things which are differing are
1>
For Rsc I have used a short wire
2>
I have used 50uH of inductor even I am not sure of its value.
I have inductors but I cannot read their values.
I got 50 by using parallel combination of 100uH but I am not sure they are 100uH or what.

3>Instead of MBR1645
I am uisng 1N5822

Input voltage is 6.4V from a SLA battery. 4.2AH marking

NOW the problem is
1>
when I am connecting a load which just takes 300mA to 400mA the voltages fall from 12V to 6.8V or so
2>
without ouput capacitor and load the voltage at ouput is constant 12V
but when i connect a 2200uF/35V capacitor the voltage fluctuates a little and voltage drop to 11.6 to 11.7Vs
I think this is what they called they need less ESR of capacitor

 

[vicbin]

One of key factor for successful switching power circuits is the inductor.

Looks like the sympton you got is the inductor has reached it's saturation level. It could be various reason such as too small in term of size (not the uH value), not a ferrite core, etc.

If you have difficulty of finding a decent inductor core, look for old PC power supply and get the toroid core in there and most of the time it is yellow colored, it would be enough for you circuits for it's peak inductor current at 5.2 Amps.

Also another culprit is your mosfet switch, it will be slowly recover from on to off since the gate charges is slowly drained from the resistor, not good for switching circuit.

 

[nikhilele]

when I increased the load current one of my inductor burnd out. I think I have to get a good inductor

What u were telling about SMPS inductor

Added after 3 minutes:

do u their approximate value

Added after 6 seconds:

do u know their approximate value