Download Component Selection

Component Selection
By
Prof. Bitar
Power Supply Example
• Input:
• 120VAC / 60Hz (nominal)
• Output:
• 5V +/- 5% (4.5 to 5.5 V)
• 100mA (max)
Possible Full-Wave Topologies
(Assuming Linear Voltage Regulators)
U1
D1
TR1
Vout
OUT
GND
C1
+
120VAC, 60Hz
IN
C2
N2
N1
N3
D2
U1
D1
IN
TR1
D2
Vout
OUT
GND
+
120VAC, 60Hz
Load
N1
N2
D3
D4
C1
C2
Load
Typical Voltage Waveforms
T
10.00
Secondary Voltage (A)
After Rectifying and Filtering
After Regulator
Ripple Voltage
5.00
Output
V drop across regulator
0.00
-5.00
Secondary Voltage (B)
-10.00
0.00
10.00m
20.00m
30.00m
Time (s)
40.00m
50.00m
Begin Distributor Part Search
for “Voltage Regulators”
Yikes! Only 41,864 Possibilities…
41,864
Possibilities!
Narrow the Search!
In Stock !!!
6,241 Linear
Further Search Criteria
•
•
•
•
•
Current (100mA)
Package / Case (TO-92 Thru-Hole!)
Packaging (for shipping)
Topology (Positive Fixed)
Voltage (5V)
Down to Mfg & Pricing
(Note Sorting Criteria)
• Fairchild Semiconductor
$0.32
(More $, but better spec sheets & support.)
• Micro Commercial Co:
(Not as well supported, but CHEAP!)
$0.20
Selecting Part-Number Link Yields More
Information Including Price Breaks!
Finally a Data
Sheet!
Component Data Sheet
•
Absolute Maximum Ratings
(Not to be exceeded !!)
• Input Voltage Max (30V)
• Operating Temp (-20 to 120 C)
• Storage Temp (-55 to 150 C)
•
Electrical Characteristics
(Under very specific test conditions!)
• Output Voltage
(4.8 to 5.2 V @ T = 25 C)
•
Load Regulation (ΔVOUT / Δ ILOAD)
(60mV MAX from 1 to 100mA)
•
Line Regulation (ΔVOUT / Δ VIN)
(150mV MAX, Vin from 7 to 20V)
•
•
•
•
Quiescent Current (5.5mA MAX)
Output Noise Voltage (40uV TYPICAL)
Ripple Rejection (41dB MIN)
Dropout Voltage (1.7V TYPICAL)
Q: Does this Voltage Regulator
Meet our Specifications? YES!
• OK, Repeat this Process for Every
Component…
• Power Transformer
• Diodes
• Filter Capacitors
Selecting a Power Transformer
• Questions:
1.
2.
3.
4.
What voltage do we need?
What is the maximum current?
What configurations do we need?
What configurations are available?
Single or Dual Primary
Single or Dual Secondary
1. What Voltage Do We Need?
•
•
•
•
•
Desired DC Output = 5V
Minimum Drop Across Regulator = 1.7V (spec)
Maximum Ripple Voltage = 1V (guess)
Drop Across Rectifier Diodes = 0.7 or 1.4V
Therefore, for C.T. Transformer:
• Vpk = 5+1.7+1+0.7 = 8.4V = 5.9VRMS
• Or for Full-Wave Bridge:
• Vpk = 5+1.7+1+1.4 = 9.1V = 6.4VRMS
• OK, Looking for 6.4VRMS @ 100mA (min)
Parts Distributor Search
Possible Choices
Tamura 3FS212 : 6.3VAC, 180mA Transformer $3.75
Transformer Spec Sheet
Electrical Specifications
Mechanical Specifications
Hole Pattern Spacing
Configuration Options
Available Voltages / Currents