Re: message repost

At 01:53 PM 9/4/97 -0700, you wrote:
>
>messages on the list are limited to 40k, so this message just bounced.
>i'll put the schematic up on the spies web page --al
>
>From: Anders Knudsen <Anders_Knudsen@btc.adaptec.com>
>Subject: Re: WG failures
>In-Reply-To: <2.2.16.19970903151924.29c74da0@pop3.concentric.net>
>Mime-Version: 1.0
>Content-Type: multipart/mixed; boundary="=====================_873426376==_"
>
>--=====================_873426376==_
>Content-Type: text/plain; charset="us-ascii"
>
>At 03:23 PM 9/3/97 PDT, Zonn wrote:
>>
>>3) The best so far. Run the deflection and HV off a beefed up regulator. I
>>removed all the low voltage components (Those uprotected zener diodes and
>>Q100/Q101 stuff). I then used a LM317/LM337 regulator pair using the WG's
>>low voltage power transistors as current boosts.
>>
>>This gives very stable noise free vectors. But there is a trade off between
>>supply voltage and HV disappation though. Higher voltages going to the
>>deflection allows for a faster slew rate, higher voltages going to the HV
>>supply allows for shorter HV life.
>>
>
>This is exactly what I did a while ago. I removed all the parts to the LV
>supply, *except* the large 4700uF filter caps, the diode bridge, and the
>power output transistors. i.e., removed: Q100, Q101, R100, R101, R102,
>R103, D104, D105, ZD100, ZD101, C102, C103. Note that ZD100 and ZD101 are
>mislabled on the P314 as R104 and R105.
>I then designed a regulated supply using LM317 and LM337 plus support
>components, using small pots to allow for some adjustability. I think I can
>range from around +/- 22 to +/- 30. A gif of the schematic is enclosed.

The difference between this design and the one I was using is that this
design places the full current load on the regulators.

The HV alone can draw more than 1 amp of current. The 7824 and 7924
regulators used to regulate the HV supply in the Amplifone monitors were
bypassed with a 50ohm resistor to allow higher current draw during the white
screen explosions of Star Wars. I believe the 7824/7924 have similar
current specs as the LM317T / LM337T parts.

The low voltage supply must supply the constant one amp of current to the
HV, and on top of that, the current needed by the deflection circuitry. The
deflection circuit is fused at 5 or 6.25 amps (depending on revision). I'm
guessing an amp or two average, though instantaneous peaks could be quite high.

The low voltage supply should be rated to supply, at least, 7 amp peaks. I
believe the ratings of the LM317T and LM337T are around 1.5 amps, with
proper heatsinks. They are very bullet proof and will going into both
thermal shutdown and current limit mode if overdriven. Unless I'm wrong
about the current spec's of the LM317T/LM337T series, you can't get the 3 to
4 amp peaks that are going to be typical here, and no where near the 7 amp
worst case peaks.

With a very slight modification to this design you can use the original WG
PNP pass transistor to boost the current on the positive rail, and the NPN
transistor for the negative rail (the opposite of the way WG currently uses
them). Assuming only a current gain of 10, for the power transistors, this
allows the regulators to only dissapate 500ma for 5 amps of current.

I don't have the schematic here, (it's hand drawn) but I can scan it in this
weekend and send to to Al to post.

-Zonn
Received on Thu Sep 4 15:49:03 1997