W nocie aplikacyjnej układu IL300 (jest to również transoptor liniowy) znalazłem taki schemat https://obrazki.elektroda.pl/5173082400_1568813049_thumb.jpg Czy takie rozwiązanie będzie dobre?
VISHAY SEMICONDUCTORS
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Optocouplers and Solid-State Relays
Application Note 55
Optoelectronic Feedback Control Techniques for Linear
and Switch Mode Power Supplies
INTRODUCTION
The power supply designer is continually being pressured to
provide units which have higher efficiency, better regulation,
less EMI and RFI, and smaller size and weight, all at a lower
cost. The solution to this problem is a combination of circuit
topology, layout, and supply control. This application note
will address output control techniques for linear and switch
mode power supplies (SMPS). Specifically, it will cover
control techniques using standard phototransistors and a
new family of linear optocouplers.
ISOLATED REGULATION
National and international safety agencies require a supply’s
output to be isolated and insulated from the AC mains. Many
supply manufacturers have elected to offer power supplies
that satisfy all national and international safety insulation
criteria by selecting power transformers and feedback
devices that meet a 3750 VAC withstand test voltage.
Feedback systems that use optocouplers easily comply with
this insulation criteria. Optocouplers also offer a high degree
of noise rejection or isolation combined with their insulation
characteristics.
LINEAR POWER SUPPLY FEEDBACK
Linear power supplies comply with the main insulation and
isolation safety requirements by virtue of the
primary/secondary insulation of the power transformer.
There are numerous circumstances where isolated
feedback in a linear power supply is needed, such as
monitoring
high-voltage
power
supplies,
current
measurement in the high side of the supply, or monitoring
multiple isolated outputs. Figure 1 shows a typical block
diagram.
Rev. 1.5, 18-Oct-11
Regulator
Isolated
DC
Outputs
Isolated
Feedback
Current or
Voltage
Originally presented at the PCIM® /Power Quality®, 1993
Conference, Irvine, CA, U.S.A.
17832
Fig. 1 - Linear Power Supply Phototransistor Model
IF
ICE
Collector
LED
Emitter
A. Simple Phototransistor
Detector
ICB
LED
IF
Collector
ICE
Base
Emitter
17833
B. Expanded Simple Phototransistor
Fig. 2 - Phototransistor Coupler Schematic
Phototransistor optocouplers are current amplifiers. These
couplers include an infrared light emitting diode, LED,
and an NPN silicon phototransistor. Figure 2A shows
the common schematic of a standard phototransistor
optocoupler. Figure 2B is an expanded schematic that
includes a collector-base photodetector. An input LED
current, IF, creates an optical flux, which is detected by
the photodiode. The photodiode develops a photocurrent,
Icb, which is amplified by the phototransistor. The
phototransistor supplies a collector-emitter current, Ice. The
current gain of the device is defined as a current transfer
ratio (CTR) and is expressed as a percentage. The CTR
relationship is given in equation 1:
I CE x 100 %
(1)
CTR = -------------------------------IF
Document Number: 83711
1
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APPLICATION NOTE
The feedback system for a linear power supply should be
DC transparent and continuous. A standard phototransistor
coupler, when properly specified, can perform the feedback
function. To properly specify the phototransistor it is
important to review the elements that contribute to a
coupler’s operation. Figure 2 shows the phototransistor
optocoupler schematic.
AC/DC
Rectifier
Xformer
Mains
Application Note 55
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Vishay Semiconductors
Optoelectronic Feedback Control Techniques for Linear
and Switch Mode Power Supplies
Combining equation 2 with the transistor current gain, hFE,
provides a more complete optocoupler gain equation:
I cb x 100 %
(3)
CTR = ------------------------------I F x h FE
The relationship given in equation 3 can be shown in a block
diagram of the four elements that make up the DC transfer
function of the phototransistor coupler. These elements are
shown in figure 3.
LED
IF
ηe Time
IF
Temp
Package
transmission
separation
alignment
Detector
Rφ
Amplifier
hFE
Ice
Ib
Temp
Vce
17834
Fig. 3 - Phototransistor Block Diagram
APPLICATION NOTE
The LED, package, detector, and transistor components
have independent variables contributing to the optocoupler
transfer function. The performance of the LED is influenced
by four variables. These include the LED’s external quantum
efficiency, ηe, the forward current, IF , junction temperature,
TJ , and the total operation time.
The LED’s external quantum efficiency, ηe, specifies the
electrical-to-optical conversion factor. The optimum
efficiency is determined by LED construction. For example,
a GaAs LED has an ηe of approximately 10 %, while the ηe
for a AlGaAs LED may be as high as 30 %. The operational
LED efficiency is determined by the three remaining
variables. The two most important are junction temperature
and LED current. The LED’s ηe has a negative temperature
coefficient, typically - 1 %/°C. Figure 4 shows the
temperature dependence. This figure shows that when the
LED junction experiences a 50 °C temperature change, for
example, from 25 °C to 75 °C. The output of the LED may
be reduced by as much as 50 %. The temperature
characteristic is more pronounced at a lower LED drive
current. As the LED current is increased this coefficient may
fall to - 0.5 %/°C.
Rev. 1.5, 18-Oct-11
1.2
TA = 25 °C
Normalized LED Efficency
The relationship of the LED forward current flux creation and
the generation of photocurrent is called current transfer ratio
collector-base (CTRcb). See equation 2.
I cb x 100 %
(2)
CTR cb = ------------------------------IF
TA = 50 °C
1.0
TA = 70 °C
0.8
0.6
0.4
0.2
0.1
17835
1
10
100
IF - LED Current (mA)
Fig. 4 - Normalized LED Efficiency
The influence of forward current on LED efficiency is also
shown in figure 4. Note that a standard GaAs LED efficiency
will be reduced by 50 % when the LED current is changed
from 10 mA to 2 mA. One can conclude that in a DC circuit
designs, the LED introduces large variations as a function of
forward current and junction temperature.
Today’s LED processing techniques have all but eliminated
efficiency reduction as a function of time. LED efficiency
reduction is commonly called CTR degradation. Typical
degradation is less than 10 % at 10 k/h and increases at a
logarithmic rate.
The second element is the optical coupling (Kφ) within the
package. Numerous assembly techniques exist for creating
the LED-photodiode coupling path. However manufacturing
variations introduce coupling deviations, such as optical
transmission media, emitter-detector separation distance,
and alignment. Kφ is set at the time of manufacturing and is
constant as a function of time and temperature.
The third element is the phototransistor’s collector-base
photodetector responsivity. This factor is the most
consistent and linear element of the coupler. Process
variations introduce worst case responsivity, Rφ, variations
of less than 25 %. The nonlinearity of the detector, over the
designed photocurrent range, is less than ± 0.1 %.
The fourth element is the phototransistor current gain, hFE.
The typical DC current gain showing the temperature,
collector current, and VCE influence on DC current gain is
illustrated in figure 5. Note that Vishay phototransistors do
not exhibit the typical beta peak found at low ( & lt; 1 mA)
collector currents. It shows a typical hFE temperature
coefficient of + 0.5 %/°C. The most noticeable is the
influence that VCE has on current gain. Figure 5 shows that
the saturated gain (VCE & lt; 0.4 V) is reduced by 30 % for an
LED current of 10 mA.
Document Number: 83711
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THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
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Application Note 55
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Vishay Semiconductors
Optoelectronic Feedback Control Techniques for Linear
and Switch Mode Power Supplies
This circuit responds to positive unipolar voltages, as found
at the voltage output of the power supply. Initially, when the
power supply is energized, Vin = 0 V, IF and IP1 are also zero.
As the input voltage rises, U1 forces a voltage across the
LED causing it to emit light. The LED's optical flux generates
a servo photocurrent (IP1) which is proportional to the input
voltage, IP1 = Vin/R1. The LED's current increases until
sufficient servo photocurrent is generated to keep the
difference between U1's inverting-noninverting inputs equal
to zero volts.
800
HFE - Transistor Current Gain
Vce = 10 V
Ta= 50 °C
Ta = 70 °C
600
400
Ta = 25 °C
200
Vce = 0.4 V
Ta = 25 °C
The servo photocurrent is proportional to the LED's current.
This relationship is defined as servo gain, K1 = IP1/IF.
Combining the two equations describes the LED's current
dependence on input voltage:
V in
(5)
I F = --------------------K1 x R1
0
0
17836
10
20
30
40
50
60
Ice - Collector Emitter Current (mA)
Fig. 5 - Phototransistor H
These four optocoupler elements create a linear DC transfer
function, implying that a change in any one of these
elements creates a factored change at the output.
Functionally, the relationship is shown in equation 4:
I CE = I F x [ η e ( I F , T J , time ) x
K φ ( T, A, S ) x R φ x HFE ( lb, T J , VCE ) ]
(4)
This section has presented the basic DC model and
resulting transfer equation of the standard phototransistor.
The goal was to illustrate factors that effect the DC
current gain. The designer is encouraged to review the
characteristics of the optocoupler being considered and be
aware of the temperature and LED current influences on the
current transfer ratio of a simple phototransistor.
Most designers compensate for these variations by
selecting narrow-binned CTR optocouplers. Designers often
compensate for gain variations by introducing negative
feedback within a control loop. Equation 4 illustrates that
typical voltage or current feedback techniques are not
possible if insulation or noise isolation is to be maintained.
APPLICATION NOTE
OPTICAL FEEDBACK CONTROL TECHNIQUE
The factors that influence the DC current gain of the
optocoupler can be compensated by introducing optical
feedback within the LED or input side of the coupler. This
technique consists of including an optical detector or
photodiode on the input that monitors the LED’s output flux,
which is possible now with the introduction of the Vishay
family of linear optocouplers.
The isolated output circuit consists of a zero-biased
photodiode transresistance amplifier. This output amplifier
is configured to generate an output voltage proportional to
IP2 and the transresistance R2. The output photocurrent, IP2,
is determined by the output transfer gain, K2 = IP2/IF. The
output gain equation is Vo = IP2 x R2. Solving for LED current
by combing the preceding equations results in:
VO
(6)
I F = --------------------K2 x R2
The composite DC transfer function of the input and output
amplifiers can be determined when the equations 5 and 6
are combined resulting in the voltage gain equation:
V O K2 R2
(7)
------- = ------ x ------V in K1 R1
For simplicity, the ratio of K2/K1 is defined as the transfer
gain, K3. The transfer gain can be rewritten as:
VO
R2
------- = K3 x ------(8)
V in
R1
The coupler’s transfer gain (K3) is determined by the
bifurcation of the LED’s optical path within the coupler
package. The time, temperature, and LED current have little
effect on the transfer gain (figure 7).
A DC coupler optical isolation amplifier using the new IL300
linear optocoupler is shown in figure 6.
This optical isolation amplifier uses an operational amplifier
(U1) as an electro-optical servo amplifier that controls the
LED current. The servo photodiode is operated in the
photovoltaic mode and is zero biased from its connection to
U1's inverting and non-inverting inputs.
Rev. 1.5, 18-Oct-11
Document Number: 83711
3
For technical questions, contact: optocoupleranswers@vishay.com
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000
Application Note 55
www.vishay.com
Vishay Semiconductors
Optoelectronic Feedback Control Techniques for Linear
and Switch Mode Power Supplies
VCC
+
R3
100 Ω
I
6 F
3
OP-07
R1
Vin
IL300
1
R2
8
10 kΩ
2
–
10 kΩ
K2
2
100 pF
Vin = 0 to + 1 V
7
K1
3
4
–
6
5
2
Ip1
GND 1
IP1
IP2
OP-07
3
6
Vout
+
GND 2
17837
Fig. 6 - Optical Feedback Amplifier
1.010
Normalized to IF = 10 mA, TA = 25 °C
K3 - Transfer Gain (K2/K1)
0 °C
1.005
Mains
Xformer
AC/DC
rectifier
DC output
25 °C
50 °C
0.995
75 °C
0
Regulator
5
10
15
20
Control
Isolated
feedback
17840
25
IF - LED Current (mA)
17838
Fig. 7 - IL300 Transfer Gain, K3
TA = 25 °C, VR = 10 V, MOD = 40 %
RL = 2.2 k, IQ = 10 mA
5
Fig. 9 - SMPS Block Diagram
45
0
Phase
- 45
0
Amplitude
-5
- 90
- 10
- 135
- 15
101
17839
102
103
104
105
Ø - Phase Response (°)
10
Amplitude Response (dB)
Switch
1.000
0.990
APPLICATION NOTE
AC/DC
rectifier
- 180
106
Frequency (Hz)
Fig. 8 - IL300 Frequency and Phase Response
Rev. 1.5, 18-Oct-11
Document Number: 83711
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THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
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Application Note 55
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Vishay Semiconductors
Optoelectronic Feedback Control Techniques for Linear
and Switch Mode Power Supplies
R1 20 kΩ
7
3
VCC1
+5V
Va
R2
U1
IL300
1
6
LM20
30 kΩ
VCC
8
+
2
1
1
Vb
R4
–
8
2
7
100 Ω
K1
VCC1
K2
VCC2
6
3
100 pF
4
5
4
IP1
IP2
R3
30 kΩ
To regulator input
R5
30 kΩ
17841
Fig. 10 - + 5 V Isolated Feedback Amplifier
MAINS ISOLATED SWITCHING POWER SUPPLY
Figure 9 shows a block diagram of a typical SMPS. The
isolated feedback section can be viewed as an isolated
piece of wire connecting the DC output to the control pin of
the switch mode regulator. A simple design using a LM201
low-cost differential op-amp is shown in figure 10. R1 and
R2 function as a voltage divider, dividing the + 5 V supply
output to 3 V. The servo/feedback photodiode sources a
feedback current (IP1) to R1 (30 kΩ). This resistor will
develop 3 V when 100 μA flows through it. With K3 = 1, a
similar value of 100 μA will flow through R5 (30 kΩ).
Thus IP2 of 100 μA will develop the 3 V DC signal needed by
the control pin of the regulator. Figure 11 shows the DC
response of this amplifier. Figure 12 shows the phase and
frequency response.
Rev. 1.5, 18-Oct-11
3.25
3.00
2.75
2.50
2.25
4.0
17842
4.5
5.0
5.5
6.0
Vin - Input Voltage (V)
Fig. 11 - LM201 DC Transfer Gain
LM201, Ta = 25 °C
dB
0
PHASE
-2
0
- 45
-4
- 90
-6
- 135
-°
45
2
Amplitude Response (dB)
APPLICATION NOTE
Today’s mains connected switch mode power supplies
require an insulated and isolated output voltage control
method. Standard phototransistor optocoupler are one of
the various techniques used to effect this regulation. With
the goal of high switching frequencies, the use of
phototransistors is being pushed to its frequency response
limits. Most power supply designers have found that gain
and phase flatness can only be assured to operating
frequencies of ≤ 10 kHz. Given these limitations, designers
are considering the optical feedback optocoupler.
Vout = 14.4 mV + 0.6036 x Vin
LM201 Ta = 25 °C
Response
The optical feedback technique greatly improves the main
characteristic needed for a feedback amplifier used in a
linear power supply.
3.50
-8
102
17843
103
104
105
Phase
Figure 8 shows the frequency and phase response curve
that shows the - 3 dB point and a phase shift of 45° occur at
a frequency in excess of 100 kHz.
3.75
Vout - Output Voltage (V)
Figure 7 shows that the IL300’s gain typically varies by only
± 0.2 % over an LED current range of 5 mA to 20 mA, and
has a temperature stability of ± 50 ppm/°C.
- 180
106
F - Frequency (Hz)
Fig. 12 - LM201 Phase and Frequency Response
This feedback circuit offers linearity and gain accuracy of
± 0.02 % over a 4.0 V to 6.0 V input (figure 13).
Document Number: 83711
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THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000
Application Note 55
www.vishay.com
Vishay Semiconductors
Optoelectronic Feedback Control Techniques for Linear
and Switch Mode Power Supplies
The previous examples use differential amplifiers as the
summing device. It is possible to configure a single-input
DC amplifier that will perform the sample optical-servo
control. One such design is shown in figure 14.
0.025
LM201
Linearity Error (%)
0.020
0.015
0.010
0.005
0.000
- 0.005
- 0.010
- 0.015
4.0
4.5
5.0
5.5
6.0
Figure 14 shows a DC-coupled current feedback amplifier.
Q1 and Q2 form the gain stages. The feedback
photocurrent, IP, is supplied to the summing network at VA.
By inspection, the nodal equation indicates that the
photocurrent will be that necessary to create a 2 VBE drop
across R1. The input resistor is also sourcing current to this
node. Thus, as the input voltage rises, the photocurrent will
drop. For this reason this amplifier functions as an inverting
amplifier
Vin - Input Voltage (V)
17844
Fig. 1 - LM201 Linearity Error
5V
R2 4.7 kΩ
VCC1
MPSA10
IIN
Rin
v
MPSA12
Q1
b
Q2
8
2
K1
ib
104 kΩ
7
K2
3
4
iR
Vin
IL300
1
iP
R1
25.5 kΩ
17845
6
IP1
IP2
5 V VCC2
Vout
5
R3
100 Ω
R4
10 kΩ
GND2
GND1
Fig. 2 - Discrete Isolation Amplifier
The frequency response and phase response for figure 14 is
shown in figure 15.
0.02
Phase response reference
to amplifier gain of - 1; 0° = 180°
0
0
dB
Phase
-5
- 45
- 10
- 90
- 15
102
Ø - Phase Response (°)
Amplitude Response (dB)
APPLICATION NOTE
45
- 135
17846
103
104
105
106
F - Frequency (Hz)
Fig. 13 - Discrete Isolation Phase and Frequency Response
Given this circuit’s simplicity, gain accuracy and linearity are
not compromised. The linearity error for this amplifier is
± 0.015 %, as shown in figure 16.
Rev. 1.5, 18-Oct-11
Gain Linearity Error (%)
TA = 25 °C
5
0.01
0.00
- 0.01
- 0.02
4.50
17847
4.75
5.00
5.25
5.50
Vin - Input Voltage (V)
Fig. 14 - Discrete Isolation Linearity Error
Most power supply designers are familiar with TL431 and
LM4041 precision adjustable zener diodes. When you look
more closely at the internal operation of this device you will
find that it too can function as a optical feedback amplifier
for the IL300 (figure 17).
Document Number: 83711
6
For technical questions, contact: optocoupleranswers@vishay.com
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000
Application Note 55
www.vishay.com
Vishay Semiconductors
Optoelectronic Feedback Control Techniques for Linear
and Switch Mode Power Supplies
CONCLUSION
V- Supply monitor
100 Ω
1.5 kΩ
R1
This application note was a generic presentation of the DC
model of the standard phototransistor. Most designers have
overcome many of standard phototransistor’s temperature
and initial gain variations by selecting well-specified
couplers such as the CNY17-X family.
2N3906
+
Q2
Q1
Vref
IL300
1
U1
+
8
2
7
K1
TL431
K2
3
VCC2
6
LM4041
4
IP2
IP1
Vout
5
When wider bandwidth and greater gain stability is required,
power supply designers are using the new optical feedback
linear optocouplers. The circuits provided and their
performance characteristic will satisfy even the most
demanding high-frequency SMPS applications.
R2
GND2
17848
Fig. 15 - Shunt Voltage Regulator
The three terminal regulators include U1, Q1, and the
precision reference, Vref. The linear coupler will supply
sufficient photocurrent to develop a difference voltage
across R1. The transfer equation for this amplifier is given in
equation 9:
VO
R2
(9)
----------------------- = ------- x K3
V in - V ref R1
The precision voltage reference (Vref) is 2.5 V for the TL43.
When lower voltage supplies, i.e. 3.3 V, are to be regulated,
the new LM4041 with a reference of 1.225 V can be used.
The designer may be more familiar with the circuit
schematic shown in figure 18.
100 Ω
+
Q1 2N3906
IL300
1
1.5 kΩ
8
7
2
K1
VCC2
K2
6
3
TL431
U1
-
R1
4
IP1
IP 2
5
Vout
APPLICATION NOTE
R2
GND1
17849
GND2
Fig. 16 - Shunt Voltage Regulator Isolation Amplifier
Rev. 1.5, 18-Oct-11
Document Number: 83711
7
For technical questions, contact: optocoupleranswers@vishay.com
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000