A p p l i c at i o n N o t e
AN3017
PSPICE Model for a Phototransistor
CEL Staff Application Engineer, CEL Opto Semiconductors
CEL Product Marketing Manager, CEL Opto Semiconductors
Graduate Intern (MSEE), SJSU
Introduction
PSPICE is a circuit simulation program, used to provide a
reasonably detailed analysis of circuits containing active
components such as bipolar transistors, field effect transistors, diodes, opamps, and lumped components such as
resistors, capacitors and inductors. Its measurement parameters include voltage and current. However, when it comes
to model opto electronics components, the SPICE program
does not possess the capability to evaluate or simulate opto
electronics components with outputs measured in radiometric or photometric units like watt (w) or lumen (lm), or
other variables like optical intensity, radiant power, irradiance with unit measurements in mW/sr, mW/m2, lumens.
In many instances, the desired output will still end up with
measurement units in voltage or current and this application note provides an example of a model of an optocoupler
using the SPICE model.
CTR Characteristics
CURRENT TRANSFER RATIO vs.
FORWARD CURRENT
600
Current Transfer Ratio CTR (%)
Current Transfer Ratio CTR (%)
Authors: Van N. Tran
Larry Sisken
Wei Z. Jiang
VCE=5V
n=2P
500
400
300
200
100
600
CURRENT TRANSFER RATIO vs.
FORWARD CURRENT
VCE=5V
n=2P
0
500
0.1
1
10
400
Forward Current IF (mA)
300
Pulse Input
200
100
Note: TA=25°C, unless otherwise specified
This data is reference only, not guaranteed.
VCC
PW = 100
100 μ s
Duty Cycle = 1/10
0
An Optocoupler Device
Typically, an optocoupler is an optically coupler isolator
using a GaAs LED as a light source and a bipolar NPN phototransistor as a receiver. The forward current, If, through
the LED emitter produces the photons that impinge on the
active area of a phototransistor and its output, collector
current, will be a product of If and Current Transfer Ratio
(CTR). The PS2561F-1 will be used as an example for this
application note.
IF 1time
Test circuit0.1
for switching
10
Forward Current IF (mA)
50 Ω
Pulse Input
100
VOUT
RL = 100 Ω
VCC
PW = 100 μ s
Duty Cycle = 1/10
IF
50 Ω
VOUT
RL = 100 Ω
From the PS2561F-1 data sheet, the CTR can vary from
300% to 600% at If = 5 mA and VCE = 5.0 V from device
to device. Below is a summary of the PS2561F-1 electrical
characteristics that can be found in the PS2561F-1 data
sheet at www.cel.com for reference.
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AN3017
Electrical Characteristics (TA = 25˚C)
Diode
Transistor
Parameter
Forward Voltage
Reverse Current
Terminal Capacitance
Collector to Emitter Dark Current
Symbol
VF
IR
Ct
ICEO
CTR
Current Transfer Ratio (IC/IF)*1
Coupled
Conditions
IF = 10 mA
VR = 5 V
V = 0 V, f = 1.0 MHz
IF = 0 mA, VCE = 80 V
IF = 5 mA, VCE = 5 V
IF = 1 mA, VCE = 5 V
IF = 10 mA, IC = 2 mA
VI-O = 1.0 kVDC
V = 0 V, f = 1.0 MHz
VCC = 10 V, IC = 2 mA
RL = 100 W
Collector Saturation Voltage
Isolation Resistance
Isolation Capacitance
Rise Time*2
Fall Time*2
VCE (sat)
RI-O
CI-O
tr
tf
An Optocoupler Circuit Model
Below is the schematic of the optocoupler with phototransistor output used in this application note for PSPICE
modeling.
Rd
R
A
T
C
If
+
_
VSENSE
V=If
+
_
Cd
IB
IC
B
Q1
O
K
E
Below is the written text file of the PSPICE model for
operation at TA = 250°C
Model: PS2561F-1
* A = PIN 1: diode anode
* K = PIN 2: diode cathode
* E = PIN 3: BJT emitter
* C = PIN 4: BJT collector
.SUBCKT PS2561F A K E C
D1 A D LED
*OptoLED
Vsense D K 0
*Forward If current sense
*using Vsense
Hd
R 0 Vsense 1
*I-V (current dependent voltage source)
MIN.
TYP.
1.2
10
300
60
450
MAX. Unit
1.4
V
5
μA
pF
100
nA
600
%
0.3
1011
0.5
5
7
V
Ω
pF
μs
Rd
R T 100K
Cd
T 0 20p
Gctr C B TABLE
* Photodetector {(IC vs IF) / * Q1 BF}
* where the data of the collector current
* versus forward current
* are derived from the CTR
* graph using polynomial fit
+ {If(V(T)<=3m,
+ ((-80000000000*PWR(V(T),5)+800000000*
+ PWR(V(T),4)-3000000*PWR(V(T),3)
++5177.2*PWR(V(T),2)+0.2453*V
+ (T)-0.00005)*1.04/700),
+ ((9000000*PWR(V(T),5)+998113*PWR(V(T),4)+42174*PWR
+ (V(T),3)+ 861.32*PWR(V(T),2)+
+ 9.0836*V(T)-0.0078)*0.945/700))}
+ (0,0) (0.1m, 0.1m)
Q1 C B E detector
.model LED D IS=1p N=1.999644
+ RS=0 BV=6 IBV=10u
+ CJO=10p EG=1.424 TT=500n
.model detector NPN IS=2.857P BF=700
+ NF=1.1786653 BR=20 TF=80.64p
+ TR=4.56886n
+ CJE=16.315P CJC=21.1189P VAF=250 ISS=0
+ CJS=44.5657p ISC=120p
.ends
*$
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AN3017
The Results of the PSPICE Model
Comments:
This SPICE model is intended to simulate the device
behavior at Ta=25°C. Please note that the model
cannot duplicate exact device performance in the real
world under all conditions and they can't replace the
breadboarding for final design verification.
A. CTR
The PSPICE model for the CTR curve comes quite close to
the data in the data sheet as shown below.
CTR vs. IF
6.00
Conclusion
5.00
CTR
4.00
3.00
Data Sheet
SPICE Model
2.00
1.00
0.00
0.1
1.0
10.0
PSPICE model can be a helpful tool for simulation of an
optocoupler in a circuitry that incorporates optocouplers
in its design. However, care has to be taken and need to
test and verify with the real devices in the test circuit to
ensure that the result. Please visit our website for more
PSPICE models of Renesas/CEL optocouplers at
http://www.cel.com/spice.
do?command=showByType&group=2
100.0
IF (mA)
B. Switching Time
When it comes to match the same performance of the
rise and fall time of the device, it becomes difficult
to select the parameters of the NPN transistor model
that will duplicate the same performance, as a result,
a compromise is made, such that, the model could be
considered as the typical or worst case performance as
shown below.
Switching Time (us)
1000
100
tr
10
tf
tr_Spice
tf_Spice
1
0.1
0.1
1
Load Resistancer RL (kΩ)
10
Information and data presented here is subject to change without notice. California
Eastern Laboratories assumes no responsibility for the use of any circuits described
herein and makes no representations or warranties, expressed or implied, that such
circuits are free from patent infringement.
© California Eastern Laboratories 11/11
4590 Patrick Henry Drive, Santa Clara, CA 95054-1817
Tel. 408-919-2500
FAX 408-988-0279 www.cel.com
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