MC34063 blues

astouffer · 12th June 2009, 02:25 AM

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

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

Doh!

Many thanks, thats been bothering me for a while.

12th June 2009, 02:41 AM	#3
star882 diyAudio Member Join Date: Mar 2007	The inductor needs to connect before the 180R resistor. __________________ "Fully on MOSFET = closed switch, Fully off MOSFET = open switch, Half on MOSFET = poor imitation of Tiffany Yep." - also applies to IGBTs!

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12th June 2009, 01:23 PM	#4
astouffer diyAudio Member Join Date: Jun 2004 Location: Pittsburgh, crumbling wasteland	Doh! Many thanks, thats been bothering me for a while.