Simple WorkBench Dual Power Supply - del20033
Basic Electronics Workbench needs the Regulated
Power Supply, DMM and Continuity Tester. They could
be Variable, Dual Tracking or Fixed Supplies like
+5V or +/- 12V Dual Supplies. The most common being
0-30V CV CC Power Supply.
Practice by Trevor Charlton
I will just explain part of this circuit. D9
and D10 provide a low cost -1.4 from -5
V. This is needed to reach near 0.00 for LM317
Min. setting. An LED also can be used
with proper bias. Note that there is a
Temperature Coefficient in ppm, see The
Diode FAQ. but it may not matter upto 8 bits
TIP2955, TIP3055 (NPN), TIP2955 (PNP) Complementary
Silicon Power Transistors. It is a Darlington, that
means good current gain. See Darlington
- Wikipedia. When current in R1 10E goes
more than 50mA a voltage of 50mA X 10E = 500mV is
applied across Emmiter-Base junction. So lower than
500mV no bias the tap is turned off, 500mV-700mV the
tap starts turning on depending on type of
transistor. The transistor is like a water Tap. So
TIP2955 carries the major current burden thru the
load allowing LM317 to do the decision making when
to turn-on or off. It is analog control, it is
not On-Off but linear-proportional. The LM317 is
very cool as the burden is passed off to TIP2955 who
will need a heatsink to keep going and deliver the
power you want.
Dual Power Supply - del20033
Can be Scrolled by Drag-Drop Left-Click-Mouse
Put the filter caps appropriately. The Hum-Noise
will be filtered. The cap after the regulator should
be a small guy. The main filter cap after the Bridge
can be as big as your cabinet or budget.
Regulators LM7812 and LM317
If you build it and wire it without designing a PCB,
then make all wiring and connection very sound. The
test of this ability you can know easily, If your
project stops working after the last screw of the
cabinet is tightened, then we need to improve.
The Source files of this circuit as an Orcad-9
Design is here 20033.zip.
By using additional chokes and filters you could
make it a very low Ripple Power Supply. We have
Excellent Isolation and Safety in this design in
comparison to SMPS, as it is a Low Frequency Supply.
Using a Torroid Transformer will increase safety and
EMI immunity which is needed for medical
Ensure that the Mains Voltage is safely wired and
shrink sleeved. Use a proper earthing connection at
home and office. Build the entire project in a
Powder Coated Steel Enclosure for Good Shielding.
Earth the cabinet too.