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Bargain Optocouplers

C

Chris

Jan 1, 1970
0
I picked up some optocouplers cheap from the bargain bin. I was
expecting to find 4 useful pins (2 in, 2 out, 2NC), but these turned
out to be 4N32 units with a mysterious pin 6 connected to the base of
the output phototransistor. Can I ground this pin to get the device
to work as a 4 pin coupler? Connect it to supply voltage?

I just want to switch the output side on/off without an electrical
connection to the circuit on the input side, no amplification,
inversion, etc required.

Thanks,
Chris
 
R

Rheilly Phoull

Jan 1, 1970
0
Chris said:
I picked up some optocouplers cheap from the bargain bin. I was
expecting to find 4 useful pins (2 in, 2 out, 2NC), but these turned
out to be 4N32 units with a mysterious pin 6 connected to the base of
the output phototransistor. Can I ground this pin to get the device
to work as a 4 pin coupler? Connect it to supply voltage?

I just want to switch the output side on/off without an electrical
connection to the circuit on the input side, no amplification,
inversion, etc required.

Thanks,
Chris

I cant speak with experience but would imagine you could use them '4 pin'
and should the need arise the base would give you an alternate switching
method ??
(when in doubt experiment :)
 
C

CBarn24050

Jan 1, 1970
0
Subject: Bargain Optocouplers
From: [email protected] (Chris)
Date: 18/12/2004 02:38 GMT Standard Time
Message-id: <[email protected]>
I picked up some optocouplers cheap from the bargain bin. I was
expecting to find 4 useful pins (2 in, 2 out, 2NC), but these turned
out to be 4N32 units with a mysterious pin 6 connected to the base of
the output phototransistor
Can I ground this pin to get the device
to work as a 4 pin coupler? Connect it to supply voltage?

You can sometimes just leave it unconnected but it is better to connect it to
the emitter via a 47k resistor.
 
J

James T. White

Jan 1, 1970
0
Chris said:
I picked up some optocouplers cheap from the bargain bin. I was
expecting to find 4 useful pins (2 in, 2 out, 2NC), but these turned
out to be 4N32 units with a mysterious pin 6 connected to the base of
the output phototransistor. Can I ground this pin to get the device
to work as a 4 pin coupler? Connect it to supply voltage?

I just want to switch the output side on/off without an electrical
connection to the circuit on the input side, no amplification,
inversion, etc required.

Thanks,
Chris

Chris,

You can use the 6-pin optocouplers just like the 4-pin ones if you leave the
transistor base unconnected. In 4-pin optocouplers, the phototransistor
turn-off time is usually quite a bit longer than the turn-on time. This limits
the maximum repetition rate and distorts the waveform. For higher speed
operation, the base connection of the 6-pin optocoupler is tied to the emitter
via a resistor. This reduces the transistor turn-off time (drains charge from
the base quicker). There are some good application notes on the
Vishay-Telefunken web site that explain this and can help you figure out how to
size the resistor if you are trying to speed up your optocoupler or reduce the
distortion.
 
R

Rich Grise

Jan 1, 1970
0
Chris,

You can use the 6-pin optocouplers just like the 4-pin ones if you leave the
transistor base unconnected. In 4-pin optocouplers, the phototransistor
turn-off time is usually quite a bit longer than the turn-on time. This limits
the maximum repetition rate and distorts the waveform. For higher speed
operation, the base connection of the 6-pin optocoupler is tied to the emitter
via a resistor. This reduces the transistor turn-off time (drains charge from
the base quicker). There are some good application notes on the
Vishay-Telefunken web site that explain this and can help you figure out how to
size the resistor if you are trying to speed up your optocoupler or reduce the
distortion.

Excellent answer. I've wondered this myself on occasion.

Thanks!
Rich
 
R

Robert Monsen

Jan 1, 1970
0
Rich said:
Excellent answer. I've wondered this myself on occasion.

Thanks!
Rich

Ah. This was probably Jagman's problem when he was using the same part...

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.
 
J

John Larkin

Jan 1, 1970
0
Chris,

You can use the 6-pin optocouplers just like the 4-pin ones if you leave the
transistor base unconnected. In 4-pin optocouplers, the phototransistor
turn-off time is usually quite a bit longer than the turn-on time. This limits
the maximum repetition rate and distorts the waveform. For higher speed
operation, the base connection of the 6-pin optocoupler is tied to the emitter
via a resistor. This reduces the transistor turn-off time (drains charge from
the base quicker). There are some good application notes on the
Vishay-Telefunken web site that explain this and can help you figure out how to
size the resistor if you are trying to speed up your optocoupler or reduce the
distortion.


The b-e resistor trades CTR for speed. It also increases the breakdown
voltage of the transistor, which is sometimes useful.

John
 

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