OPTOFAST-2

Features

• Opto-Isolator card
• 4-Channels
• 4N25 Optoisolators
• Input /Output isolation
• Transistor driver for Opto LED reduces required drive from 10 mA to under 500 uA
• Input channels share their own common VCC/Ground
• Output channels share their own common Vcc/Ground
• 8-pin header for input
• 8-pin header for output
• Configuration Options
  • Speed enhanced
  • Bypass Input transistors
  • Remove Output collector resistors
• 49x49mm
• (4) 4-40 mounting holes

Schematic (One channel)

• U1 represents U1-U4 (channels 1-4)
• Q1 represents Q1-Q4 (channels 1-4)
• R1 (VCC) represents R1,R4,R7,R10 (channels 1-4)
• R2 (DIR) represents R2,R5,R8,R11 (channels 1-4)
• R3 (BASE) represents R3,R6,R8,R12 (channels 1-4)
• R13 (FAST) represents R13-R16 (channels 1-4)
• R17 (COLL) represents R17-R20 (channels 1-4)

Input Options

• Refer to schematic for impact of options

Use Input Transistor - Standard Option

• Common VCC in option
• Install transistor Q1
• R1 = 150
  • LED current is 3.5V/150 Ohms = 23 mA
  • CTR = .20, 4.7 mA
• R2 = Do not populate
• R3 = 10K
  • Base drive ~ (Vin - 0.7V)/R3
  • At 5V drive this is 4.3V/R3
    • Using R3=10K at 5V this is 0.43mA Ib
    • HFE (MMBT3904) = 100 min
    • That is potentially 43 mA (in the switching range of the transistor)
      • Collector resistor and LED voltage drop are current limiter
  • At 3.3V drive this is (3.3-0.7)/10K = .26mA Ib
    • HFE = 100 min
    • That is 26 mA (in the switching range of the transistor)
• H1 do not short

Direct Drive - Special Option

• Do not install Q1
• Do not install R1
• R2 = 150
  • Input current = LED current = 3.5V/150 Ohms = 23 mA
• Do not install R3
• Do not install Q1
• Short H1

Output Options

Standard Output

• R17 = 1.2K
  • 5V/1.2K = 4.1mA of output transistor B-E current
  • Leaves 4.7-4.1 mA = 600 uA of output low current

Open Collector Output - Special Option

• Do not install R17

Fast Option - Standard

• R13 = 20K (empirically determined from the scope eye)

Connectors

P1 - Input

8-pin, right angle, 0.1" pitch

1. Vcc (In)
2. Vcc (In)
3. IN 1
4. IN 2
5. IN 3
6. IN 4
7. GND (In)
8. GND (In)

P2 - Output

8-pin, right angle, 0.1" pitch

1. Vcc (Out)
2. Vcc (Out)
3. OUT 1
4. OUT 2
5. OUT 3
6. OUT 4
7. GND (Out)
8. GND (Out)