OPTOFAST-2

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OptoFast-2-P447-720px.jpg

Optocoupler Performance Video Series

Related Product

Tindie-larges-v2.png This is the OptoSmall card.

This is the OptoSmall card

Tindie-larges-v2.png This is the previous revision OptoFast card.

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)

OPTOFAST-2-Schematic-TransIn.PNG

  • 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

OPTOFAST-2-Schematic-Direct.PNG

  • 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)


Test Card Measurements

OptoFast-TestSetup-720px.jpg

Setup

  • Goal was to determine the performance of the OPTOFAST card
  • 5V operation
  • Same 5V input/output power supply
  • Each of the channels were configured uniquely/individually
  • MHS-5200A - Digital DDS Dual-channel Signal Generator
    • 1 KHz square wave
    • 5V signal level
  • Single channel checked at a time
  • Oscilloscope
    • Rigol DS1054Z
    • 50 MHz
    • Ultra Sigma software used for screen captures

Notes

  • Note that the input buffer transistor inverts the signal
  • Built a card that has four different configurations
  • Options
    • Fast/Slow
    • Direct drive input LED/Transistor Buffered input

Test Results

Channel Fast/Slow TransBuff/Direct Input Rise/Fall Time(uS)
1 Slow Transistor Buffer Fall 28.6
1 Slow Transistor Buffer Rise 1.8
2 Fast Transistor Buffer Fall 6.68
2 Fast Transistor Buffer Rise 3.6
3 Slow Direct Input Fall 1.84
3 Slow Direct Input Rise 27.4
4 Fast Direct Input Fall 4.24
4 Fast Direct Input Rise 5.28

Observations

  • Input Transistor effect
    • Value of the input transistor is that does not require a high drive level input
    • The input transistor has very little effect on speed - a couple hundred nS slower than direct drive
    • The inversion effect of the input transistor moves the "slow" time around
    • Downside of the input transistor is that it has less noise immunity since the transistor turns on at 0.6V vs the internal LED in the optocoupler at 1.5V?
  • Output "fast" circuit
    • Output pullup of 4.7K affects the rise time of the output
    • The fast is faster, but not in some conditions
      • Average of rise/fall is better
      • Transistor buffer instance rise input is slower with the fast output
      • Fast output helps the output rise time

Ch1-Slow-NPNBuffer-InFall

Ch1-Slow-NPNBuffer-InFall.png

Ch1-Slow-NPNBuffer-InRise

Ch1-Slow-NPNBuffer-InRise.png

Ch2-Fast-NPNBuffer-InFall

Ch2-Fast-NPNBuffer-InFall.png

Ch2-Fast-NPNBuffer-InRise

Ch2-Fast-NPNBuffer-InRise.png

Ch3-Slow-Direct-InFall

Ch3-Slow-Direct-InFall.png

Ch3-Slow-Direct-InRise

Ch3-Slow-Direct-InRise.png

Ch4-Fast-Direct-InFall

Ch4-Fast-Direct-InFall.png

Ch4-Fast-Direct-InRise

Ch4-Fast-Direct-InRise.png

Layout

OPTOFAST-2 PWB.PNG

Assembly Sheet

OptoFast Assembly Sheet