1

MP573 Microphone preamplifier / DI fet sk170 question

« on: October 04, 2022, 10:13:07 PM »

I have measured every component before I soldered it in the PCB and the SK170 fet was not recognized as a fet but as two diodes. I use Peak CDA75 component tester for transistors.
Should i require a new one even though they seems very rare or get a replacement if thats possible.

2

501 Single Host / Re: Switcher is not working as expected

« on: August 30, 2022, 10:16:09 AM »

It seems that i was making a measuring mistake, because i just measured each rail separately and the switcher is only using feedback from the positive rail. When I take both rails and put some load on it just works fine. I have not worked with switch mode power supplies before and was a little puzzled about what to expect.
Thanks for help.

3

501 Single Host / Switcher is not working as expected

« on: August 28, 2022, 07:41:56 PM »

Hi
I have just soldered the Switcher and tested it and made a little error shorcircuiting +19v to ground very briefly with my DVM probe and was afraid that i have ruined the circuit.
I have made following tests with a ordinary laboratory linear PSU and a Electronic load to test the performance

Input voltage 12V
Current
10mA    +19,1V   -19,01V
50mA    +18,9V   -18,5V
100mA  +18,8V   -16,6V

I wonder why the negative voltage is not able to deliver more than a few mA.
Normally a SMPSU is much more robust, so maybe I have burned a component even though I just think I emptied the capacitors, but everything looks good.

Any suggestions would be appreciated