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G8MNY  > TECH     15.02.19 10:30l 125 Lines 6282 Bytes #2 (0) @ WW
BID : 59197_GB7CIP
Subj: A Common High Current PSU
Sent: 190215/0924Z @:GB7CIP.#32.GBR.EURO #:59197 [Caterham Surrey GBR]

By G8MNY                                        (Updated Dec 12)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

This is a simple & therefore reliable common design used on commercial PSU.
e.g. TRIO PS30 & ICOM PS55. Component values differ slightly between models.

The rectifiers charge up C1 to 25V. R3 puts some voltage on the output (>1.5V),
a fraction of this turns (pot arm) on Q2 (0.5V on Q2 base). This turns on Q1
that drives the 2 large high current power pass Transistors T1 & 2. When the
output voltage is >10V the zener conducts turning off Q2 as it pulls up the
emitter voltage compared to Q2's base on the VR1 pot output fraction setting.

    +19-25V    4m7+ R1 +C3  4k7       /e TIP
  __       __    ===    ===    Ĵ   Driver
  /_\       /_\   C44m7        Q1\ 2SD596
   D1       D2     +15-25V              
       ))))ͻ  2x TO-3
      / \                        \      /   Fan Cooled
AC__/' B1`\_AC     R3            T2ĴT1  & Insulated
 ~  \     /  ~      56           e/  2x   \e  on Heatsink
     `\ /'35A                       2SD797  
        Bridge                 R8          R7
L __                          0.05      0.05      20A
E \_/                )o--o>+13.8V
D  D2     68mF +  R6 1k8     Ŀ                            @ 20A
  __       C1 ===        Q2/  C7  __D3      R9   
D4\_/       25V     500<Ĵ  ===  '/_\10V     220 +
                  POT VR1  \e 10n  Zener       ===C5
 390                                     4m7
                  R5 820      R4 120             

Some of the reference numbers are repeated as components are on different PCBs.

The mains transformer is a conventional (not toroidal) type 17V @ 26A (2x 13A)
for the 20A rated PSU. The high pulse current AC wiring to the bridge & to the
reservoir C, are in thick & twisted wire to keep the losses & magnetic pulse
radiation down. A slow blow mains fuse of 6A is used.

It has 2 power rails, this is because the bridge rectifier & capacitor losses
under heavy load can give the driver's supply up to 1V more. This allows for
better peak drive current when it is needed.

The 2R2 limits the drive current when C5 is exhausted allowing for higher peak
currents than the steady rating, but this current limiting is very dependent on
the mains voltage! Current "Foldback" is provided with reference zener D3 fed
from the output. The start up current comes from the R3 56, & R9 220 is the
minimum discharge load.

A quiet thermally switched DC cylinder fan comes in when the heatsink is at a
scalding 60C.

On the ICOM unit, the mains is remotely switched on the rig with the same lead
as the high current DC output. Polarity of the plug is "VERY CRITICAL", as if
it is forced to accidentally connect upside down, (not easy to do) live mains
will flow to the +ve DC side of your Rig! (it may be safer to remotely switch
neutral as that current would be lighter!)

There is no rig protection from a shorts of T1/2 pass transistors & 25V output
will damage your rig!

Ŀ  Leads
   Ŀ       Fuse
|P    Cap     F  
|C   /   \    A    Bridge
|B          N    2x T03
     \   /       

MODIFICATIONS. I have done to my ICOM one..
1/ Heatsink added to Q1 & bolted flat to PCB location provided.
2/ Blackened main T1 & T2 heatsink, so the thermal controlled fan runs less.
3/ Fused added on T1 & T2 emitters on PCB tags (13A ones soldered in).
4/ Squeezed in more main smoothing 2x 33mF @25V for /P work with poor AC power.
5/ Proper current limiting (@ 15A/transistor) with 2 extra PNPs Q5 & Q6.
   These will also shut the PSU down if a 13A fuses blows.
6/ Removed the 2R2 the old current limiting method, to gain more output current
   drive when the AC supply is poor.
7/ Changed D1 & 2 for lower voltage drop BYW29, for when the AC supply is poor.
8/ Added an output overvoltage protection zener (like an SCR Crowbar).
9/ Larger output Cap (10mF 16V) wired across PCB output tags.
10/ Mains Transformer tuned (PF=1) for /P work with 1uF 250VAC.
11/ Added a trip switch fuse low current output, for accessories.
12/ Added Battery "crock leads" & 30A trip.

   +18-25V    4m7+ +4m7 4k7           /e TIP Driver
 __       __    === ===    Ĵ   on Heatsink
 /_\ BYW29 /_\   C4C5             Q1\
  D1       D2    +15-25V                          2x TO-3
      ))))ͻ Mounted on
     / \                     \            T2/  Blackened Fan
AC_/' B1`\_AC     R3         T1Ĵ   Cooled Heatsink
 ~ \     /  ~     56         e/               \e
    `\ /'35A                 Ŀ 1nĶ
       Bridge                 e  === ===  e  
           +              Fuse   \ 1n  /   Fuse                Rig
      ͵͹                 Q3Ĵ   ĴQ4              >+13.8V
L__     33mF              0.05  /1k5 1k5\   0.05              @20A
E\_/       +      )))͹ 2A
D     ͵͹   1k8     Ŀ                     10mF+ o-o>+13.8V
 __     33mF        Q2/     __)    __   ===     > 2A
 \_/           +  500<Ĵ  === '/_\           +  '/_\ 16V   30A
D4        C1 ===  POT   \e 10n  10v     R9  ===   17V    o-o<>Batt+
 390     68mF            220  C5  75A    <>Batt-
                 820       120               4mF        >Earth

With these modifictions the PS will do 22A @ 13.8V output with 200-240V input.

Why Don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP

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