Re: message repost

If you look at the P314 schematic and "remove" the pre-drive transistors,
zeners, and resistors, you can see that this effectively "disconnects" the
unregulated power from the base of the power transistors. So all I did was
put my LV PCB in the "gap". Now for a visual...
Being inspired by your fine ascii art, Zonn...here
is my attempt at it. My LV PCB is wired up basically as follows:

(+33V unregulated) ---------*----------------------+
                            | /
                            | | / Q102
                            | |/ 2N3716
                            +--[LM317]---------| (NPN)
                                  | |\
                                  | | \
                                  | V---- to + HV and
                                  | + deflection BJTs
                           [adjust parts] adjust to +25V

(-33V unregulated) ---------*----------------------+
                            | /
                            | | / Q103
                            | |/ 2N3792
                            +--[LM337]---------| (PNP)
                                  | |^
                                  | | \
                                  | \---- to - HV and
                                  | - deflection BJTs
                           [adjust parts] adjust to -25V

So as you can see, the regulators keep the base voltage constant, thus
causing the power transistors to "follow" the output of the regulators.
The output voltage of the power transistors goes to the HV and to the
deflection BJTs, and is only one diode drop less than the output voltage
of the regulators.
I designed the adjust circuitry for maximum ripple rejection (80db if you
read the data sheet). So the DC power generated at the emmiters of the
power transistors is *very* clean/flat, and constant. And, since the base
current is approximately two orders of magnitude less than the output
current, the three-terminal regulators "don't get overworked".

An area of improvement that has cropped up in this discussion is to add
some form of current limiting to the unregulated power -- i.e., limiting
the current into the collector of the power transistors.

+------------------------------------------+
| Anders Knudsen
| ASIC Design Engineer
| Adaptec, Inc., Boulder Technology Center
+------------------------------------------+

On Thu, 4 Sep 1997, Zonn wrote:

> At 05:13 PM 9/4/97 -0600, you wrote:
> >At 03:55 PM 9/4/97 PDT, Zonn wrote:
> ><snip>
> >>The difference between this design and the one I was using is that this
> >>design places the full current load on the regulators.
> >
> >No it does not. In my case, if you look at the schematic, and see how the
> >regulated supply is "wired" in, you will see that the *only* thing the
> >regulators do is drive the base of the power transistors -- i.e., in a bjt
> >follower configuration, where the collector of the power transistor is
> >connected directly to the unregulated supply voltage. Thus the only devices
> >to see the high currents are the power transistors, and none of the parts
> >on my LV PCB.
> >
> >So the regulators on my LV PCB only drive the base current to the power
> >transistors, and drop about 8V...i.e., low power through the regulators.
>
> Have you placed you regulators in the same position as the Zener diode and
> pre-drivers were? Are the outputs of the pass transistor part of the
> regulation circuit or is only the base regulated?
>
> -Zonn
>
>
Received on Thu Sep 4 21:44:59 1997