The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: email@example.com (Nico Coesel)
Subject: Re: Low power SMPS with good Power factor
Date: Thu, 26 Sep 2002 19:44:50 GMT
NNTP-Posting-Date: Thu, 26 Sep 2002 19:34:53 +0000 (UTC)
X-Newsreader: Forte Free Agent 1.21/32.243
>Which topology should I use when I want to develop a low power OFF line
>SMPS (230Vac to 16Vdc, 25W with galvanic isolation), with low hamonic
>distortion. (EN61000-3-2 C)
>For cost reason, I would not like to build a two-stage power supply like ex
>PFC + Flyback.
>Can I use a sor of PFC - circuit (an extra winding on the choke) to pull
>out the power?
>Is there a passive sollution (no 50Hz chokes, the are too big)?
Yes there is...
>>There is a simple PFC method, but you'll need a transformer with a tap
>>halfway the primary coil. You'll need an extra (fast) diode and 100uH
>>coil. If my memory serves me well it needs to be connected as follows:
>>The + from the AC rectifier goed into the 100uH coil. The other end of
>>the coil is connected to the anode of the extra diode. The cathode is
>>connected to the half-way tap. The buffer capacitor(s) is (are)
>>connected to the upper tap of the transformer, the switching
>>transistor is connected to the lower tap of the transformer. This
>>setup results in a power factor around 0.85
rectifier / |
+----+ 100uH D1 |. |
AC ---| +|-------////---->|------+ | +
| | | === buffer cap.
AC ---| -|----+ / | -
+----+ | / |
| / |
| |. |
| T1 -- |
| ---|| |
| -- |
| | |
This is what the primary side looks like (for a flyback PSU). D1 must
be a fast diode. When the input voltage is at is lowest point, the PSU
is powered by the buffer capacitor. When the line voltage is at
heigher levels, the PSU is powered by the line. Secondly, the buffer
capacitor is charged by the line voltage at this time.
The charm of this circuit is that the current peaks are eliminated.
The current is still not sinusoidal, but it's a whole lot better than
without the PFC.
Reply to nico@nctdevpuntnl (punt=.)
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup