ruffrecords
Well-known member
I have been playing around with this HT SMPS PCB and got it basically going (outputting 250V square wave at 50KHz). It converts 12V dc to tube HT type voltage.
The I added a diode (UF4007 I thought) and a 100uF/400V cap. No problems. Well nearly 400V dc on the cap. So I tried adding about 35mA of load resistance. Seemed OK initially but the second time I turned it on my bench supply went into current limit and the and its output volts dropped to 7.5V. At first I thought I had blown the cap but it still would not work with just s 22uF/400V cap. So I replaced the diode and it worked. SO I decided to add just a few mA of laod and the same thing happened. Checked the diode and it was shorted.
Now I thought these were UF4007 types which should have been perfectly OK. Turns out I had some old 1N4007 left in the same drawer and that is what I had been using. Proof positive of the need for fast diodes in a SMPS.
Cheers
Ian
The I added a diode (UF4007 I thought) and a 100uF/400V cap. No problems. Well nearly 400V dc on the cap. So I tried adding about 35mA of load resistance. Seemed OK initially but the second time I turned it on my bench supply went into current limit and the and its output volts dropped to 7.5V. At first I thought I had blown the cap but it still would not work with just s 22uF/400V cap. So I replaced the diode and it worked. SO I decided to add just a few mA of laod and the same thing happened. Checked the diode and it was shorted.
Now I thought these were UF4007 types which should have been perfectly OK. Turns out I had some old 1N4007 left in the same drawer and that is what I had been using. Proof positive of the need for fast diodes in a SMPS.
Cheers
Ian
