VISHAY SEMICONDUCTORS www.vishay.com Optocouplers and Solid-State Relays Application Note 02 Application Examples INTRODUCTION Optocouplers are used to isolate signals for protection and safety between a safe and a potentially hazardous or electrically noisy environment. The interfacing of the optocoupler between digital or analogue signals needs to be designed correctly for proper protection. The following examples help in this area by using DC- and AC-input phototransistor optocouplers. OPTOCOUPLERS IN IC LOGIC DESIGN To interface with TTL logic circuits, Vishay offers a wide range of 4 pin and 6 pin optocoupler series such as the CNY17x, SFH61xA, TCET110x, or K817P family. a) Supply voltage: VCC = 5 V b) Operation temperature range: - 20 °C to + 60 °C c) Service life of application: 10 years Example 1: Phototransistor wired to an emitter resistor. VCC IF Owing to the phototransistor in this case being blocked at the output of the optocoupler and ICEO maximum 200 nA (at approximately 60 °C), the IL - IIL setting can proceed practically without any error. This results in the following maximum value of RL: V IL 0.8 V R L < ------- = ------------------- = 500 Ω 1.6 mA I IL A voltage VL at RL resistor of VIH ≥ 2 V is necessary in order to attain a safe high state at the output. This needs to be generated by the collector current IC of the phototransistor. In the case of the TTL output at the input of the optocoupler, the current should remain IOL ≤ 16 mA. The CTR value of 50 % results in the maximum output current IC for the optocoupler of 8 mA. VCC With IL = IC + IIH and IIH for standard TTL being maximum, 40 μA, IL = IC can be assumed without any essential error. IC This allows the minimum value to be determined for RL: RV IIL TTL For a defined low state at the output of the optocoupler the voltage VL at RL must be VIL ≤ 0.8 V and current IIL (IILmax. = 1.6 mA) must be capable of flowing through RL from the TTL input. IIH IL RL V IH 2V R L > -------- = -------------- = 250 Ω 8 mA IL TTL VL 15096 Assuming a 10-year service life period of the interface circuit, allowance needs to be made for additional CTR reduction of approximately 20 % on account of degradation. Making an additional tolerance allowance of approximately - 25 % for the CTR will result in a safe minimum value of approximately 50 %. 2.4 V I C = I L > ---------------- = 6.15 mA 390 Ω 6.15 mA - > I F > ----------------------- = 12.3 mA CTR With VF = 1.2 V, (the forward voltage of the IR diode) and VOL ≤ 0.4 V for the TTL output follows: V CC – V F – V OL R V > ----------------------------------------- = 276 Ω, R V = 270 Ω 12.3 mA CTRmin. = 100 % x (0.83) x (0.80) x (0.75) = 49.8 % Rev. 1.4, 07-Nov-11 Document Number: 83741 1 For technical questions, contact: [email protected] 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 For simplicity, a typical CTR value of 100 % at IF = 10 mA is selected. Within the temperature range of - 20 °C to + 60 °C the CTR undergoes a change between + 12 % and - 17 %. The - 17 % reduction is critical to the functioning of the circuit. If, for example, RL = 390 Ω is selected and 20 % safety is computed to the minimum VIH in respect of the high state (VIH + VIH x 20 % = 2.4 V), this will then permit IC, IF, and the dropping resistor RV at the input of the optocoupler to be determined, Application Note 02 www.vishay.com Vishay Semiconductors Application Examples The TTL interface with the optocoupler is able to transmit signals having a frequency of > 50 kHz or a transmission rate of ≥ 100 kbit/s. V CC – V IL 5 V – 0.8 V R L > --------------------------= ----------------------------- = 656 Ω 6.4 mA I Cmax – I IL In the same way, the optocoupler can interface with other logic circuits, such as LSTTL, HCMOS, or HCTMOS components. All that needs to be done is to work the corresponding limit values VIH, VOH, IIL, IOL, etc, into the computation for the relevant family. To select the value for RL, the following should be observed. Proceeding from the voltage VIL = 0.8 V, the phototransistor is on the limits of saturation. If use is made of LSTTL or HCTMOS components this will also bring about an essential reduction in current consumption. Owing to the voltage VCE being relatively unstable in this state, VCE should be selected in such a way that the phototransistor is in full saturation. Example 2: Phototransistor wired to a collector resistor. From the diagram VCEsat vs. IC in any given 4 pin or 6 pin phototransistor data sheet, CTR reduced by 50 % and for IC < 5 mA follows VCEsat < 0.5 V. VCC ICmax. is now reduced to approximately 4 mA and for the minimum RL follows, VCC IF IL RV V CC – V CEsat 5 V – ( 0.5 ) V R L > -------------------------------------- = ---------------------------------- = 1875 Ω 2.4 mA 4 mA – 1.6 mA RL IC IIL IIH TTL TTL VIL, VIH 15097 The CTR is determined by applying the same calculation - 50 % - as that given in example 1. In this example, dimensioning of the interface is launched from the high state at the output of the optocoupler. In the high state a non-operate current of the IIH - of maximum 40 μA - may flow in the TTL input. If RL selection is too high, the entire non-operate current = ICEO + IIH may produce such a voltage drop through the RL that the critical VIH voltage (minimum = 2 V) is not attained. V CC – V IH 5 V–2 V R L < -------------------------= ------------------------ = 74.6 kΩ I CEO + I IH 40.2 µA APPLICATION NOTE This results in the following: Or if another + 20 % safety is added to the VIH voltage, V CC – ( V IH + V IH × 20 ⁄ 100 ) 5 V – 2.4 V - = ------------------------------------- = 64.7 kΩ R L < -----------------------------------------------------------------------------I CEO + I IH 40.2 µA If a suitable value is selected for the resistor RL, it is possible to determine RV at the input. Example for RL = 5.1 kΩ follows: V CC – V CEsat 5.5 mA V I L = ----------------------------------- = ------------------------- = 1.08 mA 5.1 kΩ RL IC = IIL + IL = 2.68 mA and with CTR = 25 %, IF = IC/CTR = 10.72 mA: V CC – V F – V OL - = 317Ω, R V = 330 Ω R V = ---------------------------------------10.72 mA This interface circuit can be used for transmission rates of up to about 28 kbit/s The fact that considerably lower transmission rates are possible here compared with the circuit given in example 1 is partly due to the saturation state of the phototransistor, and to a large extent, to the higher value required for RL. Example 3: Here are other circuit configurations to interface with TTL circuit, specifically the 7400 family. For calculating the smallest usable RL value, ICmax = 8 mA is assumed as in example 1 and use is made of the low state of the optocoupler output. In this circuit the current IIL of the TTL input flows through the phototransistor in such a way that the following applies: IC = IL + IIL. Rev. 1.4, 07-Nov-11 Document Number: 83741 2 For technical questions, contact: [email protected] 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 02 www.vishay.com Vishay Semiconductors Application Examples TTL ACTIVE LEVEL LOW (7400) VCC 10 kΩ Vcc 10 kΩ 12 kΩ Note: Use smaller pull-up resistor for higher speed 17454 Note: Extra parts cost but, high sensitivity 17456 It is more difficult to operate into TTL gates in the active level- high configuration. Some possible methods are as follows: Obviously, several optocoupler output transistors can be connected to perform logical functions. VCC VCC 12 kΩ A A+B _ V 2 mA 7400 B Note: Best method if negative supply is available VCC Note: Logical OR connection VCC 12 kΩ 240 Ω A · A B Note: Requires 10 mA from transistor and sacrifices noise margin 7400 B VCC APPLICATION NOTE 10 kΩ 17457 Note: Logical AND connection 2 kΩ 17455 Note: High sensitivity but sacrifices noise margin. Needs extra parts Rev. 1.4, 07-Nov-11 Document Number: 83741 3 For technical questions, contact: [email protected] 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 02 www.vishay.com Vishay Semiconductors Application Examples TTL ACTIVE LEVEL LOW (7400 SERIES) INPUT DRIVING CIRCUITS The input side of the optocoupler has an emitter characteristic as shown. VCC IR (tnA) 100 270 Ω 80 60 Note: More parts required than above 40 Vcc IR (µA) 20 0 2 kΩ 1 330 Ω 2 3 8 17458 4 VR (V) 0 0.8 VF (V) 1.6 The forward current must be controlled to provide the desired operating condition. The input can be conveniently driven by integrated circuit logic elements in a number of different ways. TTL ACTIVE LEVEL HIGH (7400 SERIES) 68 Ω 17459 Rev. 1.4, 07-Nov-11 17460 Note: Not as good as above circuit. Not recommended There are obviously many other ways to drive the device with logic signals, but a majority can be met with the above circuits. All provide 10 mA into the LED, giving 2 mA minimum out of the phototransistor. The 1 V diode knee and its high capacitance (typically 100 pF) provides good noise immunity. The rise time and propagation delay can be reduced by biasing the diode onto perhaps 1 mA forward current, but the noise performance will be increased. AC INPUT COMPATIBLE OPTOCOUPLER VCC APPLICATION NOTE 510 Ω Note: Can omit resistor for about 15 mA into diode INTRODUCTION With the rapid penetration and diversification of electronic systems, demand for optocouplers is strengthening. Most popular are products featuring compact design, low cost, and high added value. To meet the market needs, Vishay is expanding the optocoupler. This application note focuses on optocouplers compatible with AC input, and covers configuration, principles of operation, and application examples. Document Number: 83741 4 For technical questions, contact: [email protected] 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 02 www.vishay.com Vishay Semiconductors Application Examples CONFIGURATION (INTERNAL PIN CONNECTION DIAGRAM) C E 4 3 Example 1: AC/DC converter VCC Line Voltage + 0 – 15099 12710 1 2 A,K A,K Fig. 3 - AC-Input-Compatible Optocoupler (Bi-Directional Input) VCC Fig. 1 - 4 Pin AC-Input Optocoupler 4 Line Voltage 3 + 0 – + 0 15100 Fig. 4 - Conventional Optocoupler (One-Direction Input) (Full-Wave Rectification by Means of Diode Bridge) 12590 1 2 Fig. 2 - 4 Pin DC-Input Optocoupler APPLICATION NOTE Figure 1 shows the internal pin connection of a 4 pin AC-input SFH620A-x optocoupler TCET1600, K814P series; and figure 2, of a 4 pin DC-input optocoupler TCET1100, SFH61xA-x, and K817P series. The main difference is that the AC-input optocouplers incorporate an input circuit with two emitters connected in reverse parallel. In the DC-input optocoupler one emitter is connected in the input circuit so that the emitter emits light to provide a signal when a current flows in one direction(1- > 2 in figure 1) (one-direction input type). However, in the configuration shown in figure 2, when a current flows in direction 1 to 2, emitter 1 emits light to send a signal, and when it flows from 2 to 1, emitter 2 emits light to send a signal (bi-directional input type). Namely, even if the voltage level between 1 and 2 varies, and the positive and negative polarities are changed, either of two emitters emits light to send a signal. This means that the one-direction input optocoupler permits DC input only, while the bi-directional input type permits AC input as well. The next section describes the status of output signals when Vac power is directly input to an AC input compatible optocoupler via a current limit resistor. Rev. 1.4, 07-Nov-11 Example 2: detection of a telephone bell signal Ring Line 15101 + 0 – Fig. 5 - AC-Input-Compatible Optocoupler (Bi-Directional Input) Ring Line + 0 – + 0 15102 Fig. 6 - Conventional Optocoupler (One-Direction Input) (Rectified by CR Circuit) Document Number: 83741 5 For technical questions, contact: [email protected] 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 02 www.vishay.com Vishay Semiconductors Application Examples Example 3: sequencer circuit input section Common AC Line AC Line Common 15104 15103 Fig. 7 - AC-Input-Compatible Optocoupler (Bi-Directioal Input) Fig. 8 - Conventional Optocoupler (One-Direction Input) (Full-Wave Rectified by Diode Bridge) PROGRAMMABLE LOGIC CONTROLLER EXAMPLE APPLICATION NOTE PURPOSE: IN-OUT INTERFACE 17912 Rev. 1.4, 07-Nov-11 Document Number: 83741 6 For technical questions, contact: [email protected] 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