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G8MNY > TECH 13.10.17 11:35l 130 Lines 7013 Bytes #999 (0) @ WW
BID : 60578_GB7CIP
Read: GUEST
Subj: 0-35V 0-5A Lab PSU CS FL-305
Path: IZ3LSV<I0OJJ<GB7CIP
Sent: 171013/0752Z @:GB7CIP.#32.GBR.EURO #:60578 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Oct 17)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Here is a very unusual circuit principles of this 0-35V 0-5A PSU. It uses a
transformer variac secondary to make an efficient linear regulator, together
with variable current limiting & dissipation power fold back.
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ÚÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄ¿ ( ) FL-305 ³
³³ \ V ³ø³ \ A ³ Fine V ___ ³ It was all blown up &
³³ \ ³ ³ \ ³ .- -. ³ modified into a simple
³ÃÄÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄ´ / \ ³ raw PSU. So I did a lot
³ÀÄÄÄÄÄÄÄÙøÀÄÄÄÄÄÄÄÙ \ / ³ of reverse engineering,
³ overload ( ) '-___-' ³ to find out it how it
³ on trip sw A Course V ³ originally worked, before
³ ! ÚÄÄÄÄ¿ + - e + - ³ attempting the restoration.
³ ø ø ÀÄÄÄÄÙonø (o)(o)(o)(o)(o) ³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
SCHEME 15A Power NPN 15A
LÄÄo-oÄ¿ 6-42V AC Darlington__ Amp Trip
2A )||(<ÄÄÄÄÄÄÄ¿ ÚÄÄÂÄÄÄÄÄÄ´~~~\_/e ÃÄRshuntÄMeterÄÂÄÄÄÄÂÄÄÄÄÂÄÄ\ÄÄ +ve
Mains _)||( \ ~³15A³+ ³8-60V ³ ³ ³ ³ Control ³
)||( Var Bridge ³ ³ Drive ÃÄÄÄÄImonÄÄÄÄÄÄ´ PSU 0V! ³ 0-35V
ON )||( R ~³ ³- ³ ³ ³Out ³ Volt
N___ \_)||(________³ ³ ===16mF ³+In Out³ Vmon Meter 0-5A
|| ___ ³ ³ 65V ÀDrop MonÙ ³ ³
300W ||(30V Control ÀÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÁÄÄ\ÄÄ -ve
EÄÂÄÄe ÀÄÄÄ +/-12V PSU
///
The coarse Voltage Variac control has stops on it to give between 6V - 42V AC,
& a 50K Var R to control the 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.
+12VÄÄÄÂÄÄÄ2k7ÄÄÂÄ470Ä>Darlington Base 0-3mA
Voltage Comparitor ÚÄÄÄÄÄÄÄÄ)ÄÄÄÄÄÄÄÄ´ (Or a Mosfet)
³\ ³ ³ ³ /³
+6V 0VÄ1KÄÂÄÄÂÄ´+\ ³/e 1K2 e\³ /+Ã
³ preset /_\\~/³1 >Ä´<ÃÄ´PNP ÚÄÄÁÄÄ¿ PNPÃÄÂÄ´>ÃÄ< 2³ Current Limit
À5k6ÄÄ5KÄÄÂÄ1KÄÁÄÄÁÄ´-/ ³\ OK OVERLOAD /³ ³ \-Ã Comparitor
2K ³/ ³ LED LED ³ ³ \³
Fine VarR 10K ³ ³ 10K ³
³ ³ ³/ \³ ³ ³ /³
50K ÃÄÄÄ´NPN NPNÃÄÄÄ´ ³ /+Ã Power
Course VarR ³ ³\e e/³ ³ ÀÄ´>ÃÄ< 5³ Comparitor
³ 10K ³ ³ 10K \-Ã Foldback
-Ve -12VÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÙ \³
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 emmitters of a "dual transistor long
tailed pair" mixer, with a sample of PSU O/P current into one of the bases.
Darlington ÚÄÄÄÂÄÄÄ+12V Power Dissapated ³\
Volts Monitor 10K 10K ³\ 0VÄ1KÄ´+\
ÚÄÄÄ68KÄÄ¿ ÃÄÄÄ)ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄ´+\ ³5 >Ä
³³\ ³ ³ ³ ³ ³4 >ÄÂÄ680ÄÄÂÄÄ´-/ Power
+OutÄ680KÁ´+\ ³ ³ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ)ÄÂÄ´-/ ³ 3K3 ³/ Comparitor
³3 >Â6K8´ ³/ V&I \³ ÚÄ1K5Ä+Out³ ³ ³/ ³ ³
+InÄÄ680K´-/ ³ ³ ÚÄ´ Mixer ÃÄ>Ipot ³ ÀÄÄÄ10KÙ 5K
³³/ ³ ³ ³ ³\e e/³ 100 10K preset Foldback
ÀÄ68KÙ ÀÄ)ÄÄÄÁÄÄÄÙ ³ ³ ³ Power
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÁ<+ve & 0V -6V
The resulant balanced mix product, feeds the 4th Op amp, to give an accurate
signal proportional to the power being dissapated. And that then feeds the 5th
Op amp & also uses the -6V to set the drive fold back level, & also light the
OVERLOAD LED.
CALIBRATION.
A high power DC load is needed, I used a large tapped WW resistor 2+2+4ê 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 hugh mains transformer & a roomy chassis, I decided to see if
it could be made to do 10A! (350W Regulated DC O/P!)
1/ Transfure the 2 heatsink reverse voltage protection tab diodes to the PCB,
as they don't need heatsinking.
2/ Re-use the 2 spare heatsink holes for 2 more NPN insulated Darlington 15A
transistors, pointing away from each other, to spread the heat. File chassis
hole to give clearence, & wire them up in parrallel to PCB, with a 3A fuse
in each emmitter.
3/ Remount 15mF C & bridge, from PCB blanking panel, on to the rear case either
side of the VarR, making sure the piller mounted PCB will fit back OK.
4/ Remove the PCB metal panel, & add more main 65V smoothing (I used 4x 5000uF)
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 pillers 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 usefull 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 60øC 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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