Uc3842 current mode pwm controller - how to test?

[Teufelwolf]

I picked up a lot of the above chips, and was trying to find a simple test circuit...
Found this circuit on a Chinese site... Built it, and nothing.
DATASHEET
**broken link removed**
Also found this test circuit, but I do not have a 110VAC to 12vac PS. I was wondering if 12VDC would work? Since the two diodes would filter the AC to DC, right? Or am I missing something.

 

[ronv]

It needs external components. Look at some of the circuits here:

https://www.ti.com/lit/an/slua143/slua143.pdf

 

[Teufelwolf]

Thanx. Seems like that will take some reading, and the acquiring of a few more parts. The Low Power Buck Regulator in fig 30 looks like it something in my skill level. Am I reading correctly that the Under voltage lockout UVLO requires a voltage over 16v to start the IC?

 

[ChrisP58]

Yes, 16Volts is needed to start it running. The 3842 is optimized for off line power supplies that will have a high value resistor charging a cap up to the start voltage. Then the supply runs for a few milliseconds on energy in that cap until an additional winding on the transformer starts supplying the operating power.

The 3843 is an identical device but with a startup voltage of only 8.5V.