Re: Favorite Tektronix Scope

"mc" <look@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in
news:1Xhxf.117904$k76.74558@xxxxxxxxxxxxxxxxxxxxxx:

>>> Tell me more. How do I recognize startup resistors? What is their
>>> position in the circuit?
>>
>> They charge up a PWM IC's housekeeping supply capacitor before the
>> supply actually begins switching.
>> Generally directly from the rectified line V,and there might be a
>> xfmr winding and diode to take over once switching has
>> begun.(usually,in TEK supplies)
>
> What sort of resistances and wattages are we looking for?
>
>
>

It depends.Some TEK supplies used 0.5w carbon film resistors,some used 1W
carbon film,replaced under mods by carbon comp resistors for longer life.I
can't recall specific R values.Some used two R's in series,some 2 in
parallel.
The 2215 pre-reg schematic I have shows a single 150K 1W res.

R Values also depend on the housekeeping cap's value.You want the HK cap to
charge slow enough that the line caps reach full V before the PWM IC
starts.

--
Jim Yanik
jyanik
at
kua.net
.

Relevant Pages

  • Re: Driving LEDs from PIC weak pullup, saving resistors?
    ... Ok, that's to high to be a valid low voltage, is that a valid high ... There is a PWM output, I have implented it in the soft, but it is intended to ... The issue here is not so much variable brightness, but sparing out X resistors. ... So it is a green solution, even with blue or red LEDs. ...
    (sci.electronics.design)
  • Re: led dimmer circuit
    ... But there should also be no problem using resistors. ... about PWM and its advantages. ... it is a very basic question. ... LEDs are current operated ...
    (sci.electronics.design)
  • Re: Op-amp circuit help
    ... Do you think I'd strike any problems if I used 1M resistors instead ... the inputs directly from the PWM filter capacitors? ... requested motor speed, a 20kHz PWM signal, and Vin2 is the motor ... a 1uF cap and Vin2 is smoothed by a 10uF cap) ...
    (sci.electronics.design)
  • Re: LiPos in parallel?
    ... The last time I got into parallel cells-- needed added resistors would work ... Since they all charge to the same 4.20V/cell, ... The fire might damage the other packs though! ... The reason for this is that *as long as the cells are identical chemistry ...
    (rec.models.rc.air)
  • Re: "PPP" transistor
    ... Some of these PWM outputs I want to use to generate audio tones. ... to make the dimmer happy. ... resistors, and then there's the RC network to smooth it. ...
    (sci.electronics.basics)