光耦使用参考资料

[8]Explanations2.How to Use Photocouplers2.1LED Control Circuits2.1.1DC DriveFigure 8.2.1 shows an example of controlling LED drive current by switching the power supply on and off. In this case, the resistor R is R= VIN − VF IFIF R IF VIN VFVIN R IF VFVFVINFigure 8.2.1 Simple Drive Circuit for an LEDFor example, when IF = 10 mA, VF (max) = 1.35 V, and VIN = 5 V, R = (5 − 1.35) V 10 mA = Ω 365Therefore, the resistor should be selected as R = 360 Ω. Assuming that VF = 0.9 V due to its fluctuation or temperature dependence, the value of IF is 11.4 mA.2.1.2Reverse Voltage ProtectionWhen a reverse surge voltage may be applied to a light emitting diode, a Si diode (for example, 1SS348) should be connected in reverse parallel with the light emitting diode, so that the reverse surge voltage bypasses the LED.R Si DiodeFigure 8.2.2 Protection from Reverse Voltage by Silicon Diode144[8]2.1.3 Threshold VoltageExplanationsWhen the input voltage is not absolutely zero or some unnecessary steady current flow is in a data transmission line, the threshold voltage of the LED should be raised up to a certain level by connecting a resistor in parallel with the light-emitting diode. (Figure 8.2.3)R VIN RSFigure 8.2.3 Threshold VoltageIf the forward voltage of the LED in the zero-light-emission state VT, the OFF-level input voltage VIN (OFF), and the OFF-level input current IIN (OFF) are given by VIN (OFF) = VT + R = (1 + IIN (OFF) = VT RS R RS VT RS ) VTThen in the case of the Toshiba IRED, the value of VT is 0.5 V.2.1.4Driving by Transistor or ICIn Figure 8.2.4 are shown examples of using an LED for driving circuits by utilizing a transistor or IC.VCC IF R IF VCCRR=VCC − VF − VCE (sat) IFR=VCC − VF − VOL IFFigure 8.2.4 Driving by Transistor or IC145[8]Explanations2.4Interface Circuit between TTLs Using a Phototransistor CouplerA circuit using a DIP 4 pin photocoupler as an interface between TTLs is shown in Figure 8.2.22. In order to assure positive ON/OFF operation of the TTL, the LED current IF should be set to satisfy IOL which is determined by RC and IIL. Example of Design Specifications Operating temperature: 0 to 70°C Data transmission rate: 5 kbit/s Supply voltage: VCC = 5 V ± 5% Operating life: 20 years (170,000 hours) System working ratio: 50% Specifications of products required for designing interface circuits are shown in Table 8.2.1.R IF VCC TLP521-1 VCC II IC RC IIL IC > II + IILFigure 8.2.22Interface Circuit between TTLs Using a 4 pin PhotocouplerTable 8.2.1 Principal Characteristics of the TLP521-1Item Forward voltage Collector to emitter Breakdown voltage Emitter to collector Breakdown voltage Collector dark current V (BR) ECO V (BR) CEO Symbol VF Test Condition (Ta = 25°C) IF = 10 mA IC = 0.5 mA IE = 0.1 mA IF = 0, VCE = 24 V IF = 0, VCE = 24 V, Ta = 85°C A rank Current transfer ratio CTR (IC/IF) IF = 5 mA VCE = 5 V GB rank GR rank BL rank Collector to emitter Saturation voltage VCE (sat) IF = 5 mA, IC = 1 mA min 1.0 55 typ. 1.15 ⎯ max 1.3 ⎯ Unit V V7 ⎯ ⎯ 50 100 100 200 ⎯⎯ 10 2 ⎯ ⎯ ⎯ ⎯ 0.1⎯ 100 50 600 600V nA µAICEO% 300 600 0.4 V146 155[8]2.4.1 Setting of RC (max)ExplanationsRC (max) should be set according to the switching time and dark current ICEO (max) at the maximum operating temperature of the photocoupler. The relations of switching time to RL (load resistance) and RC are shown as follows: As the data transmission rate is 5 kbit/s, the total switching time is T = tr + td + tf + ts < 200 µs = The load resistance RL is obtained from the switching time characteristic (for saturated operation) in Figure 8.2.23 so that T becomes 100 µs, taking account of variability in the device’s switching characteristic in order to secure T < 200 µs. RL < 4.7 kΩ is obtained from this graph. Here, RL can be = = expressed in terms of RC and the parallel resistance of the standard TTL input resistance RIN. (Figure 8.2.24) RL = RC ∥ RIN As RL = 4.7 kΩ > RIN = 4 kΩ, RC may be indefinite (RC = ∞) but RC (max) against the dark current ICEO (max) is limited. The relation between ICEO (max) and RC (max) is shown below. RC (max) = VCC (min) − VIH ICEO (max) + IIHThen, ICEO (max) must be estimated at Ta = 70°C. Temperature dependencies of ICEO (typ.) at alternative parameter values of VCE = 5 V, 10 V, and 24 V are shown in Figure 8.2.25.1000 800 600 400 200tf IF = 5 mA RL VOUTSwitching time (µs)100 80 60 40 20 10 8 6 4tsVOUT 5V 0V td tr tr90% 10% ts tf2 td 1 0 1 2 4 6 8 10 20 40 60 80 100Load resistance (kΩ)Figure 8.2.23 Load Resistance vs. Switching Time+5 V 4 kΩ TTL Coupler RINVCC RCFigure 8.2.24 RL can be Expressed by RIN and RC147 156[8]ExplanationsIn the case of the TLP521-1 phototransistor coupler, ICEO (max) = 50 µA at Ta = 85°C and VCE = 24 V. Therefore, taking VCE dependency and Ta dependency into consideration from Figure 8.2.25, ICEO(max) is estimated at Ta = 70°C and VE = 5 V.VCE dependency: ICEO (typ.) is reduced by 1/4 when VCE is varied form 24 to 5 V Ta dependency: ICEO (typ.) is reduced by 1/4 when Ta is varied form 85 to 70°C Therefore, ICEO (max) at Ta = 70°C and VCE = 5 V is estimated to be, ICEO (max) = 50 µA × 1 4 × 1 4 = 3.1 µAAccordingly, IIH is 40 µA for general TTLs and RC (max) will be obtained as follows: RC (max) = 4.75 V − 2 V 3.1 µA + 40 µA = 64 kΩ10 VCE = 24 V 110 5(µA) ICEO10−110−210−310−4 0 20 40 60 80 100 120Temperature (°C)Figure 8.2.25 ICEO vs. Temperature148 157[8]2.4.2 Setting of Forward Current IFExplanationsThe maximum forward current IF is obtained as IF = 16 mA subject to the constraint IF < IOL, and = the maximum allowable value of IF found from Figure 8.2.26 is 50 mA. However, IF should be kept as small as possible because CTR degradation increases with the increase of forward current. Figure 8.2.27 shows degradation of CTR. In order to realize the designed continuous operating life of approx imately. 100,000 hours, the forward current should be set at IF = 10 mA ± 50%.100 Test conditions IF = 70 mA, PC = 150 mW, Ta = 25°C80IC (t)/IC (t = 0) (VCE = 5 V, IF = 5 mA, Ta = 25°C)Allowable forward current(mA)1.0600.8400.6200.40 −200204060801000102103104Ambient temperature (°C)Test time (h)Figure 8.2.26 Ambient Temperature vs. Allowable Forward Current (TLP521-1)Figure 8.2.27Lifetime Test Data (CTR degradation)Setting of the IF limiting resistance RD Forward current (typ.) is expressed by the following formula: IF (typ.) = VCC − VF (typ) − VOL RD (typ)40 Ta = 25°C VCE = 5 Vwhere VF (typ.) is obtained from technical data. then, VF (typ.) = 1.15 V (at IF = 10 mA)(mA)20 10 6 4 2 IC/IF = 600% 370% 280% 185% 125% 80%Therefore, RD is determined as follows: RD = 5 V − 1.15 V − 0.4 V 10 mACollector current IC1 0.6 0.4 0.2= 345 Ω Therefore, RD = 330 Ω ± 5% will be optimum.0.1 0.06 0.04 0.4 6 8 1 2 4 6 10 20 40Forward current IF(mA)Figure 8.2.28IC vs. IF Curves Varying According to Different IC/IF Rations149 158[8]ExplanationsThen IF (min) and IF (max) should be checked to make sure that realized values of IF will remain within allowable tolerances: IF (min) = = VCC (min) − VF (max) − VOL RD (max) 4.75 V − 1.3 V − 0.4 V 314 Ω= 9.7 mA IF (max) = = VCC (max) − VF (min) − VOL RD (min) 5.25 V − 1.0 V − 0.4 V 347= 11.1 mA1.4 1.2 IF = 5 mARelative collector current1.02 mA1.2 5V 1.0 2V VCE = 0.4 V0.8IF = 10 mAIC/IF0.6 5 mA 0.40.80.20 0.10.6 0.2 0.4 0.6 0.8 1 2 4 6 8 10−20020406080100VCE(V)Ta(°C)Figure 8.2.29 IC/IF vs. VCESetting of pull-up resistance RCFigure 8.2.30 Collector Current vs. TaWhen the realized value of the collector current IC is assumed in the worst case to be min IC, RC can be expressed by the following relation: RC < = VCC (max) − VOLmin IC − IILmin IC = IC (min) × DIF × Dt × DVCE × DTa where, Dt: IC degradation rate after a certain time has passed. DIF: IC change rate at an IF setting for your designing. DVCE: IC drop rate under VCE (sat) condition. DTa: IC fluctuation rate with changes in the operating temperature Topr. These values are obtained from technical data. In the case of the TLP521-1:150 159[8]From Figure 8.2.27, Dt = 0.5 (t = 17 × 104 h, 50% operating ratio) From Figure 8.2.28, DIF = 2.5 (at IF = 10 mA) From Figure 8.2.29, DVCE = 0.8 (at VCE = 0.4 V) From Figure 8.2.30, DTa = 0.75 (at Ta = 70°C)ExplanationsOn the other hand, as IC (min) = 2.5 mA (at IF = 5 mA × IC/IF (min) = 50%), and min IC = 2.5 mA × 2.5 × 0.5 × 0.8 × 0.75 = 1.8 mA However, if based on these data, the following inequality cannot be met: min IC − IIL > VCC (max) − VOL RC (min)Therefore, a photocoupler with a higher CTR should be selected. In the case of the TLP521-1 (GB), because IC (min) is guaranteed to be 5 mA, the min IC will become 3.6 mA. Accordingly, IIL is 1.6 mA for general TTLs and RC (min) can be obtained as follows: RC (min) = 5.24 − 0.4 3.6 − 1.6 ∼ 2.4 kΩ −In other words, RC can be set from 2.4 kΩ to 64 kΩ, but it is also necessary to consider the switching speed required by a system and the requirement for certainty of logical ON or OFF conditions. If the switching speed is considered to be relatively more important, RC should be set to be near to RC (min). On the other hand, if the certainty of ON and OFF operation is considered to be the most important criterion, a value close to RC (max) should be selected (the operating life of the device may be defined as the period during which there is certainty of the ON and OFF conditions being properly set.). In this case, since Dt is assumed to be 0.5 with a relatively high margin the switching speed should be considered to be more important. So, RC is obtained as 4.7 kΩ.151 160[8]Explanations2.7Photocoupler Circuit Design2.7.1Transistor Output PhotocouplersFigure 8.2.33 shows a basic transistor photocoupler interface circuit, where collector current IC flows on the output side as IRED current IF is applied on the input side. The following points are important to determine each value in circuit design work: (1) IF = 0 (OFF state) Only a leakage current ID flows at the output transistor in this state. In order to maintain the OFF state, the output voltage VOUT (OFF) should be higher than VH (the required high level voltage) as follows: VCC − ID × RL = VOUT (OFF) > VH here, VCC: Applied voltage (supply voltage)RL VOUT IF ICVCCFigure 8.2.33 Transistor photocoupler152 163[8]ExplanationsThe leakage current ID increases as the ambient temperature rises (see Figure 8.2.34 Id vs. Ta), so the ID value will have to be considered at the worst case, which is at the maximum of operating temperature. Accordingly, the value of RL should meet the following formula: RL < VCC − VH IDlogIDTaFigure 8.2.34 Id vs. Ta(2) IF = Iin (ON state) When the collector current IC (ON) flows on the output side of the photocoupler, output VOUT (ON) has to be less than VL (the required low level voltage) as follows: VCC − IC (ON) × RL = VOUT (ON) < VL Accordingly, RL > VCC − VL IC (ON)Generally when the RL value is large, the switching response time increases, so the RL value should be kept as small as possible. (3) Considerations concerning the input current Iin in the “ON” status Normally technical data sheets of photocouplers show the characteristic curves IC vs. IF, CTR vs. Ta, and CTR vs. t as shown in Figure 8.2.35, Figure 8.2.36, Figure 8.2.37. The photocoupler CTR test is performed at the specific point be done by the following procedure; i) Draw the extrapolated CTR min curve (Note2) in parallel with the typical curve. Note2: This curve is the expected CTR min line. The cross point specification value. Here CTR = IC/IF, IC min = CTR min × IF1 ii) Find IF2 from the cross points of IC = IC (ON) with the B characteristic curve. This IF2 point indicates the minimum input current at Ta = 25°C and operating time t = 0 hour. When considering the relationship between CTR and Ta (Figure 8.2.36), as well as CTR degradation (Figure 8.2.37), the minimum input current Iin has to conform to the following formula.; Iin > IF2 × 1 DTa × 1 Dt ×α shows the “CTR min” in Figure 8.2.35. This point is not always the same as the actual operating point, so some compensation work is required toHere, DTa: Rate of CTR fluctuation within the operating temperature range Dt: CTR degradation rate after “t” hours of operation α: System design margin153 164Figure 8.2.39 I FT vs. TaFigure 8.2.40 I FT vs. tNote3: R S and C S are snubber circuits and recommended to be 47 Ω and 0.033 µF, respectively.I2.7.3 Photovoltaic CouplersRecently, in PBX systems, power MOSFETs* are beginning to replace mechanical relays. Thesepower MOSFETs require a voltage output type photocoupler (photovoltaic coupler).As devices become smaller, photorelays which combining a photovoltaic coupler and a MOSFET in a single package are starting to be used. As far as design is concerned, photovoltaic couplers andphotorelays are handled the same. In obtaining the photovoltaic output voltage to drive the MOSFET, how to determine input current I F is an important consideration.Figure 8.2.41 Photovoltaic CouplerIn photovoltaic couplers, both output voltage V OC , and short current I SC (output current) increase as input current increases. (see, Figure 8.2.42, Figure 8.2.45).Input current I in (Note4) has to be determined so that the output voltage V OC becomes high enough to drive the power MOSFET gate.These V OC and I SC values will change as a function of the ambient temperature Ta and operating time “t” as shown in Figure 8.2.43, Figure 8.2.46, and Figure 8.2.44.Considering these factors, the input current I in has to conform to the following formula:Figure 8.2.44 V OC vs. tvs. I Fvs. TaFigure 8.2.47 I SC vs. t1 1I in >I F ×D Ta × D t× αHere, D Ta : The fluctuation rate of V OC and I SC within the operating temperature range D t : The degradation rate of V OC and I SC after “t” hours of operationα: System design marginNote4: Turn-on time of the power MOSFET depends on the charging time of the gate capacitance. Thelarger the short current I SC (output current) becomes, the shorter the turn-on time is. So a power MOSFET transistor should be used whose input capacitance is as small as possible.Note5: There are many patents relating to MOSFET drivers.**: Normally this external resistor (high value) has to be connected. (1 M Ω)IVV2.7.4 I C Output Photocouplers(1) High-speed transistor output:6N135, 6N136, 6N138, 6N139TLP112, TLP112A, TLP114A, TLP550, TLP559, TLP759, TLP2530, TLP2531Output current I O depends upon input LED current I F and changes according to the formulaI O= CTR × I F (see Figure 8.2.48). This point should be considered in design work.As a representative example, the fundamental design rules in a TTL/TTL interface, which usesthe TLP550, are shown in Figure 8.2.49.Figure 8.2.48 I O vs. I F Figure 8.2.49 TTL/TTL Interface (TLP550)V CC1− V F− V OL1I O (min) = I F× CTR (min) R IN=I FV CC2− V OLR L(min)=I O(min) ×α+ I ILα: System design margin(2) High speed I C output:6N137TLP115A, TLP250, TLP251, TLP557, TLP558, TLP2200, TLP2601, TLP2630, TLP2631In these types, output status is inverted at a certain threshold I FH (or I FL) of input LEDcurrent I F (Figure 8.2.50). Therefore the input LED current I F should be designed to exceed themaximum specified value of I FH (or I FL) as shown in Figure 8.2.51.Figure 8.2.50 V O vs. I F Figure 8.2.51 TTL/TTL Interface (TLP2601)V CC1− V F− V OL1R IN (max)=I FH (max) ×α(α: system design margin)I FVFlogITable 8.2.2 I FH , I FL max SpecificationsProduct Number I FH (or I FL ) maxGuaranteed temperature range6N137, TLP115ATLP2601, TLP2630 TLP2631 5 mA0 to 70°C TLP557−30 to 70°C TLP250, TLP251 5 mA −20 to 70°C TLP2200, TLP5581.6 mA−25 to 85°C(3) Other precautions(a) Bypass capacitorHigh-gain amplifiers are built into the output detector I C in the photo I C couplers. Due to noise voltage on the V CC power line or on the GND line, or because of the V CC transient voltage caused by load switching, internal oscillation may occur and lead to abnormal operation. To prevent this, a bypass capacitor (0.1 µF) with good high-frequencycharacteristics should be connected between V CC and GND within 1 cm from each pin. (see Figure 8.2.52)The 0.1 µF bypass capacitor should be connected for the following I C output couplers; 6N137, TLP113, TLP115, TLP115A, TLP558, TLP2601, TLP2630, TLP2631 Toshiba recommends 0.1 µF bypass capacitor to use externally to all IC output type photocouplers for designing safety.Figure 8.2.52 Bypass Capacitor (ceramic)(b) Enable terminalsThe 6N137, TLP2200, TLP2601 and TLP558 all have enable terminals. When not utilizing this enable function, the terminals are to be treated as follows;Figure 8.2.53 Enable Terminal Treatment(c) Photocoupler insulation performanceOur photocoupler insulation performance designations are based on maintaining that performance for a period of one minute. This equipment is not generally recommended for applications using high voltage for long continuous periods. If the usage may involve a long continuous period of exposure to high voltage, contact a Toshiba sales office.6N137 TLP2601CCV E (pin 7): Open (or V CC directly connected) 1324V E (pin 6): GND Directly Connected V E (pin 7): V CC Directly ConnectedCC。