Transcript SMARC Power Supply

Computer Power Supply
Amateur Radio Conversion
For
Cheap +12 vdc Power
March 17, 2003
1
Advantages
Supplies are Readily Available
They are Inexpensive ($1)
50 watt Radios Only Need 10-15 Amps
New Supplies Have Higher Wattage
100 Watt HF Rig Potential
Or Parallel Supplies
2
Requires
Some Electronic Knowledge
I = E/R
P = E*I
Series/Parallel Resistance
Resistor Color Code
Volt Ohm Meter
Good vision!!!
Persistence
No Standard Design
3
Resistor Color Bands
4
5
However!
With a Little Patience it’s a Lot of Fun
No Rocket Science Required
You Can Do as Much or as Little as You
Feel Comfortable With
Quick and Dirty… (Just 12 vdc)
Moderate… (Try for 13.8 vdc)
Overhaul… (13.8 vdc only)
6
Scope of Presentation
Describe Quick and Dirty
Demonstrate 13.8 vdc Modification
Brief Description of In-depth Changes
Build Comfort Level
7
Assumptions
Power Supply Uses TL494 to Control
Output
TL494
Pin 2 is Reference Voltage
Pin 1 is Sample of Output
Seems to be the “Norm”
8
9
Sample Regulation Circuit
Referenc
e Voltage
From
Supply
Output
10
KØGL Supply
+ 12 vdc
39 K
WØKRB Supply
+ 5 vdc
+ 5 vdc
5600
4300
+ 1.254 vdc
0
a1
Vcc1
1
2
3
4
+ 2.58 vdc
1
1 K POT
2
3
4
a1
b2
a3
b3
a4
b4
5
6
7
8
TL 494
0
Vcc1
b1
a2
b1
a2
b2
a3
b3
a4
b4
5
6
7
8
100 K
TL 494
30 K
1450
(1364.28 Ω)
3300
Voltage Regulation
11
KØGL Supply
WØKRB Supply
12
TL 494
Blk
= GND
Red = +5 vdc
Yellow = +12 vdc
Blue = - 12 vdc
White = - 5 vdc
Voltage
Adjust
Pot
KØGL
Supply
13
Adjust Voltage
TL494
WØKRB Supply
14
How To Start
Take Supply Apart
Blow Out Dirt
Verify Lead Colors (Red +5 vdc etc.)
Connect two 10 ohm 10 Watt Resistors
in Parallel Across the +5 vdc Leads
Separate Wires and Power Up Supply
Measure Voltage and Check Fan
15
Measure Voltage & Check Fan
I = 5v/5Ω = 1A
P = 5v x 1A = 5 watts
Caution: Heat Sinks May be Electrically Hot!
16
Once You Know It Works
BE
Find TL 494
CAREFUL!
Trace Foil From TL494 Pin 1
Measure Voltage on Pin 1 & 2
Draw Schematic of Resistors
Compute Parallel/Series Resistance
Does Voltage on TL494 Pin 1 Make Sense
If so Decide How to Raise Voltage…
If Necessary…
17
KØGL Supply
+ 12 vdc
WØKRB Supply
+ 5 vdc
+ 5 vdc
Increase
This
Resistance
39 K
Adjust
Pot
If
Available
Decrease
Voltage
On Pin 1
NOTE
Only +5
used for
regulation
5600
4300
+ 1.254 vdc
0
a1
Vcc1
1
2
3
4
+ 2.58 vdc
1
1 K POT
2
3
4
a1
b2
a3
b3
a4
b4
5
6
7
8
TL 494
0
Vcc1
b1
a2
b1
a2
b2
a3
b3
a4
b4
5
6
7
8
100 K
TL 494
3300
Voltage Regulation
30 K
1450
Or
Decrease
This
One
18
Resistance Changes
It’s Easier to Lower Resistance Than to
Increase It…
Just Put Another Resistance in Parallel
Lowering Resistance Between Pin 1 and
Ground Will Decrease Voltage (Pin 1).
Regulation Will Immediately Adjust Voltage
Back to Reference by Raising Output
Voltage.
19
A Simple Spreadsheet Helps Determine Resistance Values for 13.5 volts
R2
R1
3350
1330
2200
3300
4700
5100
5600
6800
8200
10000
12000
R1
5100
C
13.5
0.000374328
0.000942857
0.00057
0.00038
0.000266809
0.000245882
0.000223929
0.000184412
0.000152927
0.0001254
0.0001045
32714.59
12988.18
21484.21
32226.32
45898.09
49804.31
54687.08
66405.74
80077.51
97655.5
117186.6
R2 WHAT IF?
33000 13.60684
13000 13.51114
20000
12.654
33000
13.794
33000 10.05868
1.254
56000
13.794
1.254
1.254
91000 12.6654
1.254
R1a
Parallel
C
R2 13.5
82000 4801.378 0.000261 46888.1
Pin 2 REF Voltage:
1.254
Note: After the presentation an
additional slide was added to
further explain this spreadsheet
(Next page). Also if you
double click the picture of the
spreadsheet it will open Excel
so you can look at the formulas.
Finally the spreadsheet was
changed so you can enter a
different Reference voltage and
all values will change
accordingly.
47000 13.52923
R2 WHAT IF?
Yellow Indicates numbers that can be changed
20
Additional Notes on the Resistance Spreadsheet
• This spreadsheet was developed for a single
power supply that had a reference voltage on
Pin 2 on the TL494 of 1.254 volts.
• With the spreadsheet changes you can now
change the reference voltage in the cell in the
bottom left.
• The drawing at the left was the one that was
used in the previous slide.
• The first section only used R1 the second
section used R1 and R1a in parallel.
• The first part in each sections computes the
current for R1 and gives the exact R2 that
would be needed for 13.5 volts.
• The WHAT IF part just gives you the
chance to put a standard value in for R2 to
see what the voltage output would be.
• This was intended to just be a quick
example of how a spreadsheet might help
you compute resistance for one supply.
The TL 494 will try and
maintain the reference voltage
by raising the output voltage.
This “constant” is used to find
the current that must flow
through R! at this voltage.
C = 1.254/R1
+ 13.5 vdc
R2
+ 1.254 vdc
0
a1
Vcc1
1
2
3
4
b1
a2
b2
a3
b3
a4
b4
5
6
7
8
TL 494
R1
R1a
Only in the
parallel
example.
21
Adjust Resistance for 13+ volts
Temporary
Wires
Test Resistance
Solder in
Place
22
What to Expect?
Voltage on Pin 1 Will Stay the Same,
Output Voltage Will Change.
You May Not Get to Exactly 13.8 Volts.
13.5 Volts is Close Enough.
Check Voltage/Regulation Under Load.
Output Voltage Varies by Several Tenths
23
Note…
You Don’t Have to Solder Resistor to the
Bottom of the Board
There Are Usually Two or Three Resistors
in Parallel to Adjust Voltage.
• Just Replace One or Two of Them
This is How I
Modified Ken’s
Supply for 12 volt
Regulation
12 v
24
What Next?
Mount 5 Ω Resistance Between Red and
Black Lead (In Front of Fan if Possible)
Install Binding Posts
Use Several Yellow and Black Leads
AC Switch Installation
Note: Ken’s Supply was Modified for 12
volt Regulation Only and the Supply
Wouldn’t Output Until the 5 Ω Resistance
was Added to the 5 volt Output
25
26
Lessons Learned
Watch What You Touch
Just Because You can
Increase the Voltage
Doesn’t Mean You Have
Regulation
Make Sure You Know
How to Power Up the
Supply
Getting the Cover Off of
the Supply Can be a
Challenge
¼ Watt Resistors are
Hard to Read…
If You Can Find the
Resistors From Pin 1 to
Ground You Can Just
Put a Resistor in Parallel
With Them Most of the
Time
Some Supplies Are
Almost Too Full to
Modify
27
Overhaul Ideas…
Convert for +13.8 vdc Only
Change Regulation to Monitor +13.8
Volts
Move High Power Diodes from +5 volt
Side to 12 volt Side of Supply
Add a Volt Meter
Move Fuse to Front Panel
28
Parallel Operation
I Put Two of the Supplies in Parallel and
Tried My Old HT and the 60 Watt Amp
The Voltage Only Dropped .1 Volt Under
Full Load
It Dropped Almost One Volt With Just One
Supply Turned On
You Should Monitor Voltage During Use
Note: With Only One Supply Turned On (In Parallel), Both Fans Run
29
Created by KØGL
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