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astouffer 12th June 2009 02:25 AM

MC34063 blues
2 Attachment(s)
Can anyone help me figure out why this circuit with an MC34063 is not working correctly? I followed the datasheet and also used the design tool to try and boost 12 volts up to 20.

Without a load the voltage slowly creeps up to about 18 and then drops with even a few milliamps applied. My first inductor was a 100uH toroid which I thought was too low so I changed it for a 250uH ferrite core choke. Then I lowered the timing cap from 220pF to 100pF to increase the switching frequency, that also had little effect.

Any ideas as to whats wrong?

astouffer 12th June 2009 02:28 AM

2 Attachment(s)
Here is the pcb layout in case thats an issue. Red is the top layer and blue is the bottom.

star882 12th June 2009 02:41 AM

The inductor needs to connect before the 180R resistor.

astouffer 12th June 2009 01:23 PM


Many thanks, thats been bothering me for a while. :smash:

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