component selection by prof. bitar. power supply example input: 120vac / 60hz (nominal) output: 5v...
TRANSCRIPT
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)
D1
D2
C1
+
12
0V
AC
, 6
0H
z
INGND
OUT
U1
LoadC2
Vout
N1N2
N3
TR1
N1 N2
TR1
D1
C1
+
12
0V
AC
, 6
0H
z
INGND
OUT
U1
LoadC2
Vout
D4
D3
D2
Typical Voltage WaveformsT
Secondary Voltage (A)
Secondary Voltage (B)
After Rectifying and Filtering Ripple VoltageAfter Regulator
Time (s)
0.00 10.00m 20.00m 30.00m 40.00m 50.00m
Out
put
-10.00
-5.00
0.00
5.00
10.00
V drop across regulator
Ripple VoltageAfter Regulator After Rectifying and Filtering
Secondary Voltage (B)
Secondary Voltage (A)
Begin Distributor Part Searchfor “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:$0.20(Not as well supported, but CHEAP!)
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. What voltage do we need?
2. What is the maximum current?
3. What configurations do we need?
4. 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