Application Examples - Vishay Intertechnology

1 Vishay SEMICONDUCTORS. Optocouplers and Solid-State Relays Application Note 02. Application Examples INTRODUCTION For a defined low state at the output of the optocoupler the Optocouplers are used to isolate signals for protection and voltage VL at RL must be VIL V and current safety between a safe and a potentially hazardous or IIL (IILmax. = mA) must be capable of flowing through RL. electrically noisy environment. The interfacing of the from the TTL input. optocoupler between digital or analogue signals needs to be Owing to the phototransistor in this case being blocked at designed correctly for proper protection. The following the output of the optocoupler and ICEO maximum 200 nA. Examples help in this area by using DC- and AC-input (at approximately 60 C), the IL - IIL setting can proceed phototransistor optocouplers. practically without any error. This results in the following maximum value of RL: OPTOCOUPLERS IN IC LOGIC DESIGN. To interface with TTL logic circuits, Vishay offers a wide V IL V.

2 - = ------------------- = 500 . R L < ------- range of 4 pin and 6 pin optocoupler series such as the I IL mA. CNY17x, SFH61xA, TCET110x, or K817P family. a) Supply voltage: VCC = 5 V 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 b) Operation temperature range: - 20 C to + 60 C generated by the collector current IC of the phototransistor. c) Service life of Application : 10 years 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 Example 1: optocoupler of 8 mA. Phototransistor wired to an emitter resistor. With IL = IC + IIH and IIH for standard TTL being maximum, VCC VCC 40 A, IL = IC can be assumed without any essential error. IF IC This allows the minimum value to be determined for RL: RV. V IH 2V. - = -------------- = 250 . R L > -------- IL 8 mA. IIL IIH. If, for example, RL = 390 is selected and 20 % safety is TTL IL TTL computed to the minimum VIH in respect of the high state RL VL (VIH + VIH x 20 % = V), this will then permit IC, IF, and the dropping resistor RV at the input of the optocoupler to be 15096 determined, For simplicity, a typical CTR value of 100 % at IF = 10 mA is V.

3 Application NOTE. selected. Within the temperature range of - 20 C to + 60 C I C = I L > ---------------- = mA. 390 . the CTR undergoes a change between + 12 % and - 17 %. The - 17 % reduction is critical to the functioning of the mA. circuit. - > I F > ----------------------- = mA. CTR. Assuming a 10-year service life period of the interface circuit, allowance needs to be made for additional CTR With VF = V, (the forward voltage of the IR diode) and VOL. reduction of approximately 20 % on account of degradation. V for the TTL output follows: Making an additional tolerance allowance of approximately V CC V F V OL. - 25 % for the CTR will result in a safe minimum value of R V > ---------------------------------------- - = 276 , R V = 270 . approximately 50 %. mA. CTRmin. = 100 % x ( ) x ( ) x ( ) = %. Rev. , 07-Nov-11 1 Document Number: 83741. For technical questions, contact: THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT.

4 ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT Application Note 02. Vishay Semiconductors Application Examples The TTL interface with the optocoupler is able to transmit This results in the following: signals having a frequency of > 50 kHz or a transmission rate of 100 kbit/s. V CC V IL 5 V V. R L > --------------------------- = ----------------------------- = 656 . In the same way, the optocoupler can interface with other I Cmax I IL mA. logic circuits, such as LSTTL, HCMOS, or HCTMOS. components. All that needs to be done is to work the To select the value for RL, the following should be observed. corresponding limit values VIH, VOH, IIL, IOL, etc, into the Proceeding from the voltage VIL = V, the phototransistor computation for the relevant family. is on the limits of saturation. If use is made of LSTTL or HCTMOS components this will Owing to the voltage VCE being relatively unstable in this also bring about an essential reduction in current state, VCE should be selected in such a way that the consumption.

5 Phototransistor is in full saturation. From the diagram VCEsat vs. IC in any given 4 pin or 6 pin Example 2: phototransistor data sheet, CTR reduced by 50 % and for Phototransistor wired to a collector resistor. IC < 5 mA follows VCEsat < V. ICmax. is now reduced to approximately 4 mA and for the VCC VCC minimum RL follows, IF IL. V CC V CEsat 5 V ( ) V. RV RL - = ---------------------------------- = 1875 . R L > -------------------------------------- 4 mA mA mA. IC IIL IIH If a suitable value is selected for the resistor RL, it is possible to determine RV at the input. TTL. Example for RL = k follows: TTL. VIL, VIH V CC V CEsat mA V. I L = ----------------------------------- - = ------------------------- = mA. 15097 RL k . The CTR is determined by applying the same calculation IC = IIL + IL = mA. - 50 % - as that given in example 1. In this example, and with CTR = 25 %, IF = IC/CTR = mA: dimensioning of the interface is launched from the high state at the output of the optocoupler.

6 V CC V F V OL. - = 317 , R V = 330 . R V = ---------------------------------------- In the high state a non-operate current of the IIH - of mA. maximum 40 A - may flow in the TTL input. If RL selection is too high, the entire non-operate current = ICEO + IIH may This interface circuit can be used for transmission rates of produce such a voltage drop through the RL that the critical up to about 28 kbit/s The fact that considerably lower VIH voltage (minimum = 2 V) is not attained. transmission rates are possible here compared with the circuit given in example 1 is partly due to the saturation state V CC V IH 5 V 2 V of the phototransistor, and to a large extent, to the higher R L < -------------------------- = ------------------------ = k . I CEO + I IH A value required for RL. Or if another + 20 % safety is added to the VIH voltage, Application NOTE. Example 3: Here are other circuit configurations to interface with TTL. V CC ( V IH + V IH 20 100 ) 5 V V. R L < ---------------------------------------- -------------------------------------- - = ------------------------------------- = k circuit, specifically the 7400 family.

7 I CEO + I IH A. 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. , 07-Nov-11 2 Document Number: 83741. For technical questions, contact: THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT. ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT Application Note 02. Vishay Semiconductors Application Examples TTL ACTIVE LEVEL LOW (7400). VCC. Vcc 10 k . 12 k 10 k . Note: Use smaller pull-up resistor 17454. for higher speed 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 Obviously, several optocoupler output transistors can be follows: connected to perform logical functions.

8 VCC VCC. 12 k . A. A+B. _ 2 mA 7400. V. B. Note: Best method if negative supply is available VCC. Note: Logical OR connection VCC. 12 k . 240 . A. Note: Requires 10 mA from . A B. transistor and sacrifices 7400. noise margin B. VCC. 10 k . 17457 Note: Logical AND connection Application NOTE. 2 k . Note: High sensitivity but sacrifices 17455. noise margin. Needs extra parts Rev. , 07-Nov-11 3 Document Number: 83741. For technical questions, contact: THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT. ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT Application Note 02. Vishay Semiconductors Application Examples INPUT DRIVING CIRCUITS TTL ACTIVE LEVEL LOW (7400 SERIES). The input side of the optocoupler has an emitter characteristic as shown. VCC. 100 510 . 270 . IR (tnA). 80. 60. Note: More parts required than above 40. Vcc 20. 0. IR ( A). 2 k 330 . 1. 2. 3 Note: Not as good as above circuit. 17460. 8 4 0 Not recommended 17458 VR (V) VF (V).

9 There are obviously many other ways to drive the device with logic signals, but a majority can be met with the above The forward current must be controlled to provide the circuits. All provide 10 mA into the LED, giving 2 mA. desired operating condition. minimum out of the phototransistor. The 1 V diode knee and The input can be conveniently driven by integrated circuit its high capacitance (typically 100 pF) provides good noise logic elements in a number of different ways. 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. TTL ACTIVE LEVEL HIGH (7400 SERIES). VCC AC INPUT COMPATIBLE OPTOCOUPLER. 68 INTRODUCTION. With the rapid penetration and diversification of electronic systems, demand for optocouplers is strengthening. Most popular are products featuring compact design, low cost, Note: Can omit resistor for about and high added value. To meet the market needs, Vishay is 17459 15 mA into diode expanding the optocoupler.

10 This Application note focuses on optocouplers compatible with AC input, and covers configuration, principles of operation, and Application Examples . Application NOTE. Rev. , 07-Nov-11 4 Document Number: 83741. For technical questions, contact: THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT. ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT Application Note 02. Vishay Semiconductors Application Examples CONFIGURATION Example 1: AC/DC converter (INTERNAL PIN CONNECTION DIAGRAM) VCC. C E. 4 3. Line Voltage +. 0. 15099 . 1 2. Fig. 3 - AC-Input-Compatible Optocoupler (Bi-Directional Input). 12710 A,K A,K. VCC. Fig. 1 - 4 Pin AC-Input Optocoupler 4 3 Line Voltage + +. 0 0.. 15100. Fig. 4 - Conventional Optocoupler (One-Direction Input). (Full-Wave Rectification by Means of Diode Bridge). 12590. 1 2. Example 2: detection of a telephone bell signal Fig. 2 - 4 Pin DC-Input Optocoupler Ring Line Figure 1 shows the internal pin connection of a 4 pin AC-input SFH620A-x optocoupler TCET1600, K814P series.