MC34063A 10v to 20v 150ma converter

[RayMonster]

Hi!
i have build a step up converter using the connection in the datasheet.
The test with no load is able to produce a 10v input to 20v output, Which is great! And to check whether it is producing the desired output current of 150mA, abt 3w output, resistive loads were used. 

However after testing under loaded condition by using two 270ohms rated 2w each connected in parallel, the load shorted.

i have also tried with two 100 ohms rated 10w which also shorted the load.

I tried with 4.7k resistance load and it does work but i am unable to tell whether the circuit can produce 150ma from this load.

May i know what other options can i try to test for the current?

The used  componenents are
L: 180uh
Co: 220uF
rsc:0.5ohms
r1:10k r2 150k
Ct: 470pF
Diode: 1N5819

[mariush]

It looks like you calculated everything using a low frequency. you should redo all formulas aiming for a higher frequency.

Download MC34063 universal calculator and play around with the numbers, it will tell you what works : https://sourceforge.net/projects/mc34063uc/

Here's an example, with a proper genuine MC34063 you can aim for up to 100khz frequecy, which means smaller inductors... in the example below you can put 4 x 1ohm in parallel for the Rsc giving you ~ 0.25 ohm (which is close enough to 0.27 ohm), you can choose the next standard inductor in value (for example 68uH in our example, but it's important to be capable of the Ipeak current) and all the other values are standard and common. The output capacitor should be chosen a bit higher than minimum recommended (150uF in example) and should have ESR lower or equal to calculated one.. in your case you should go with a 330-470uF 25v rated electrolytic or higher.