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G8MNY > TECH 10.03.26 16:57l 137 Lines 7367 Bytes #6 (0) @ WW
BID : 54015_GB7CIP
Read: GUEST
Subj: 0-35V 0-5A Lab PSU CS FL-305
Path: JH4XSY<N3HYM<N2NOV<VE2PKT<PY2BIL<HB9ON<VK7AX<GB7CIP
Sent: 260310/0751Z @:GB7CIP.#32.GBR.EURO #:54015 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Corrections Nov 19)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Here is a very unusual circuit principles, of this Italian 0-35V 0-5A PSU. It
uses a transformer variac secondary to make an efficient linear regulated PSU,
together with variable current limiting & dissipation power fold back.
ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
ｳﾚﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄﾄｿ ( ) FL-305 ｳ
ｳｳ \ V ｳ \ A ｳ Fine V ___ ｳ It was all blown up &
ｳｳ \ ｳ ｳ \ ｳ .- -. ｳ modified into a simple
ｳﾃﾄﾄﾄﾄﾄﾄﾄｴ ﾃﾄﾄﾄﾄﾄﾄﾄｴ / Course\ ｳ raw PSU. So I did a lot
ｳﾀﾄﾄﾄﾄﾄﾄﾄﾙﾄﾄﾄﾄﾄﾄﾄﾙ \ V / ｳ of reverse engineering,
ｳ overload ( ) '-___-' ｳ to find out it how it
ｳ on trip sw A ｳ originally worked, before
ｳ ! ﾚﾄﾄﾄﾄｿ + - e + - ｳ attempting the restoration.
ｳ � � ﾀﾄﾄﾄﾄﾙon� (o)(o)(o)(o)(o) ｳ
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
SCHEME 15A Power NPN 15A
Lﾄﾄo-oﾄｿ 6-42V AC Darlington__ Amp Trip
2A )||(<ﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾂﾄﾄﾄﾄﾄﾄｴ~~~\_/e ﾃﾄRshuntﾄMeterﾄﾂﾄﾄﾄﾄﾂﾄﾄﾄﾄﾂﾄﾄ\ﾄﾄ +ve
Mains _)||( \ ~ｳ15Aｳ+ ｳ8-60V ｳ ｳ ｳ ｳ Control ｳ
)||( Var Bridge ｳ ｳ Drive ﾃﾄﾄﾄﾄImonﾄﾄﾄﾄﾄﾄｴ PSU 0V! ｳ 0-35V
ON )||( R ~ｳ ｳ- ｳ ｳ ｳOut ｳ Volt
N___ \_)||(________ｳ ｳ ===16mF ｳ+In Outｳ Vmon Meter 0-5A
|| ___ ｳ ｳ 65V ﾀDrop Monﾙ ｳ ｳ
300W ||(30V Control ﾀﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄ\ﾄﾄ -ve
Eﾄﾂﾄﾄe ﾀﾄﾄﾄ +/-12V PSU
///
The coarse Voltage Variac control has stops on it to give between 6V - 42V AC,
& a 50K Var R to control the course regulated Volts. Unusually a separate 30V
winding is used to make a floating +/-12V @ 40mA zener PSU on the +ve O/P rail,
for 5 Op amps, 6 transistors & 3 LEDs of the complex control circuit.
The 1st Op amp with input protection diodes & 1K Rs, monitors the output Volts,
compares PSU -ve through VarR & Fine VarR to +ve from 5K preset & 5K6 using +6V
zener reference. And with 2 transistors it shunts away the 3mA drive to the
darlington, & lights up the green OK LED.
+12Vﾄﾄﾄﾂﾄﾄﾄ2K7ﾄﾄﾂﾄ470Rﾄ>Darlington Base 0-3mA
Voltage Comparitor ﾚﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄｴ (Or a Mosfet)
ｳ\ ｳ ｳ ｳ /ｳ
+6V 0Vﾄ1Kﾄﾂﾄﾄﾂﾄｴ+\ ｳ/e 1K2 e\ｳ /+ﾃ
ｳ preset /_\\~/ｳ1 >ﾄｴ<ﾃﾄｴPNP ﾚﾄﾄﾁﾄﾄｿ PNPﾃﾄﾂﾄｴ>ﾃﾄ< 2ｳ Current Limit
ﾀ5K6ﾄﾄ5Kﾄﾄﾂﾄ1Kﾄﾁﾄﾄﾁﾄｴ-/ ｳ\ OK OVERLOAD /ｳ ｳ \-ﾃ Comparitor
2K ｳ/ ｳ LED LED ｳ ｳ \ｳ
Fine VarR 10K ｳ ｳ 10K ｳ
ｳ ｳ ｳ/ \ｳ ｳ ｳ /ｳ
50K ﾃﾄﾄﾄｴNPN NPNﾃﾄﾄﾄｴ ｳ /+ﾃ
Course VarR ｳ ｳ\e e/ｳ ｳ ﾀﾄｴ>ﾃﾄ< 5ｳ Power Foldback
ｳ 10K ｳ ｳ 10K \-ﾃ Comparitor
-Ve -12Vﾄﾄﾁﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾙ \ｳ
A 2nd Op amp monitors the output current & compares it to the current set pot &
-6V ref zener. Overloads, limit the drive current & with 2 more transistors, by
again shunting away the 3mA darlington drive, & lighting the red OVERLOAD LED,
instead of the green OK LED.
A 3rd Op amp monitors the voltage drop across the darlington pass transistor.
And converts this into current to feed the emitters of a "dual transistor long
tailed pair" mixer, with a sample of PSU O/P current into one of the bases.
Darlington ﾚﾄﾄﾄﾂﾄﾄﾄ+12V Power Dissapated ｳ\
Volts Monitor 10K 10K ｳ\ 0Vﾄ1Kﾄｴ+\
ﾚﾄﾄﾄ68Kﾄﾄｿ ﾃﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄｴ+\ ｳ5 >ﾄ Power
ｳｳ\ ｳ ｳ ｳ ｳ ｳ4 >ﾄﾂﾄ680Rﾄﾂﾄﾄｴ-/ Foldback
+Outﾄ680Kﾁｴ+\ ｳ ｳ ﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾂﾄｴ-/ ｳ 3K3 ｳ/ Comparitor
ｳ3 >ﾂ6K8ｴ ｳ/ V&I \ｳ ﾚﾄ1K5ﾄ+Out ｳ ｳ ｳ/ ｳ ｳ
+Inﾄﾄ680Kﾂｴ-/ ｳ ｳ ﾚﾄｴ Mixer ﾃﾄ>Ipot ｳ ﾀﾄﾄﾄ10Kﾙ 5K
ｳｳ/ ｳ ｳ ｳ ｳ\e e/ｳ 100R 10K preset Set Max Power
ﾀﾄ68Kﾙ ﾀﾄ)ﾄﾄﾄﾁﾄﾄﾄﾙ ｳ ｳ ｳ Dissipated
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁ<+ve & 0V -6V
The resultant balanced mix product, feeds the 4th Op amp, to give an accurate
signal proportional to the power being dissipated. And that then feeds the 5th
Op amp & also uses the -6V to set the Max Power Dissipated, & also light the
OVERLOAD LED.
CALIBRATION
A high power DC load is needed, I used a large tapped WW resistor 2+2+4R 1kW.
Set the start position of the Variac VarR, & then the 4 presets are used to
determine, 1 Max overhead voltage, 2 Max Current range, 3 Current foldback
sample Ipot, & 4 Max foldback power. When correctly set the head voltage is
always just enough for a cool regulator at all output voltages & currents!
DOUBLE CURRENT MODIFICATION
As the PSU has a huge mains transformer & a roomy chassis, I decided to see if
it could be made to do 10A! (350W Regulated DC O/P!)
1/ Transfer the 2 heatsink reverse voltage protection tab diodes to the PCB,
as they don't need heatsinking.
ﾚﾁﾁﾁﾁﾁﾁﾁﾁﾁﾁﾁﾁﾁﾁﾂﾄﾄﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂｿ
ｳｳ pcb ｳｳ C ｳpotﾃﾄBrｴｳ 2/ Re-use the 2 spare heatsink holes for 2
ｳ~~~~~~~~~~~~~~ﾀﾂﾄﾄﾄﾂﾙ~T~ ｳ more NPN insulated Darlington 15A
ｳ _ _ _ _ Rs ﾚﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄｿｳ transistors, pointing away from each other,
ｳ(_)(_)(_)(_) ﾝ ｳ VARIAC ｳｳ to spread the heat.
ｳ Cs ﾝ ｳTRANSFORMERｳｳ File rear case hole to give clearance, &
ｳ ﾚﾁﾄﾁｿ ﾚﾁﾄﾁｿﾝ ｳ___________ｳｳ wire them up in parallel to PCB, with a 3A
ﾀﾂﾁﾄﾄﾄﾁﾂﾄﾂﾁﾄﾄﾄﾁﾂﾂﾂﾄﾄﾄﾂﾄﾁﾄﾂﾄﾄﾄﾄﾙ fuse in each emitter, as current share Rs.
~~~~~ ~~~~~ ﾀﾙ ﾀﾄﾄﾄﾙ
3/ Remount 16mF C & bridge, from PCB metal panel, on to the rear case either
side of the VarR, making sure the pillar mounted PCB will fit back OK.
4/ Remove the PCB metal panel, & add more main 65V smoothing (I used 4x 5mF) in
the new space, to maintain low DC ripple @ 10A before regulation.
5/ Shunt 5A meter with resistance wire to now read 10A FSD, & re-label 2x/10A.
6/ Shunt the large current sampling 0.1R with resistance wire to bring it down
to < 0.06R, & mount it with the left over pillars behind Amp meter mounting
screw.
Then do the calibrations again with current limit set to @ 10A max, & the fold
back current to 1.5A when set @ 35V. It is all just doo able, right on the
limit of the PSU & still not running too hot.
CONCLUSION
This is now quite useful bench test PSU, able to test low current circuits
with the new current limit from "10mA to 10A" @ voltages from "75mV to 35V".
Used for testing prototypes, zapping & charging batteries, run modest power
rigs (30W) etc.
Be aware not to over voltage kit, as it is a Lab PSU not just a Rig one!
If it is often to be used at this "higher power limit", a 60 thermal trip
glued on the transformer might be a good safety feature to add!
See also tech buls "Lab PSU", "Simple 20A PS", "High AMP Crowbar Protected PSU"
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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