Technical Support

Selecting the right photocoupler involves: (1) Determining isolation voltage - 2500V for standard, 5000V for high-voltage or medical; (2) Choosing output type - transistor for DC, triac for AC, high-speed for data; (3) Calculating CTR requirements based on load current; (4) Selecting package - DIP for through-hole, SOP for surface mount; (5) Considering temperature range and speed requirements. Contact BeiLuo FAE team for personalized selection guidance.

Consider isolation voltage, output type, CTR, and package requirements.

Transistor output photocouplers (like K1010 series) use a phototransistor and are designed for DC switching applications. They provide DC output current proportional to input current based on CTR. Triac output photocouplers (like KMOC3041) use a phototriac and are designed for AC switching applications. They can directly drive AC loads such as heaters, motors, and lamps. Triac types include zero-cross detection which switches at AC zero crossing to minimize EMI, or random phase for immediate switching. Choose transistor for DC loads, triac for AC loads.

Use transistor for DC, triac for AC switching applications.

To calculate input current: First determine required output current (Iout) based on your load. Then use the minimum CTR from the datasheet: Iin = Iout / (CTRmin × 0.8). The 0.8 factor provides margin for CTR degradation over temperature and lifetime. For example, if you need 10mA output and CTRmin is 50%, Iin = 10mA / (0.5 × 0.8) = 25mA. Ensure this is within the LED maximum rating (typically 50-60mA). Use a current limiting resistor: R = (Vsupply - Vf) / Iin, where Vf is LED forward voltage (typically 1.2V).

Calculate based on required output current and minimum CTR.

Isolation voltage requirements depend on system voltage and safety standards: (1) Low voltage (<100V): 2500V sufficient; (2) Industrial 480V systems: 2500V minimum, 5000V preferred; (3) High-voltage EV batteries (>300V): 5000V required; (4) Medical equipment: 5000V for patient safety; (5) Reinforced insulation applications: 5000V. Cosmo offers 2500V (K1010 series) and 5000V (K2010 series) options. When in doubt, use higher isolation for safety margin.

Use 5000V for high voltage, medical, or reinforced insulation.

Yes, Cosmo offers automotive-qualified photocouplers and SSRs compliant with AEC-Q100 and IATF 16949 standards. Automotive products feature extended temperature range (-40°C to +125°C), enhanced reliability testing, and full PPAP documentation. Key automotive applications include battery management systems (BMS), on-board chargers, motor controllers, and HVAC systems. The KQ series photocouplers and KSR series SSRs are specifically designed for automotive use.

Choose automotive-qualified KQ and KSR series for vehicle applications.

CTR (Current Transfer Ratio) is the ratio of output current to input current in a photocoupler, expressed as a percentage. For example, if CTR is 100% and input current is 10mA, output current is 10mA. CTR is important because it determines how much output current you get for a given input current. CTR varies with temperature, LED aging, and manufacturing tolerance. Cosmo photocouplers offer CTR ranges from 50% to 600%. Higher CTR provides more output current but may be slower. Always design using minimum CTR from the datasheet to ensure reliable operation.

Design using minimum CTR with margin for temperature and aging.

Solid State Relays (SSRs) offer advantages over mechanical relays: unlimited switching life (>100M operations), silent operation, fast switching (<1ms), no contact bounce or arcing, and compact size. SSRs are ideal for high-frequency switching, hazardous environments, and applications requiring long-term reliability. Mechanical relays may have lower initial cost and lower on-resistance, but require maintenance and have limited life. SSRs use semiconductor switching (MOSFET for DC, triac for AC) with photocoupler isolation between input and output.

Use SSRs for high-frequency, silent, or long-life applications.

Inductive loads (motors, solenoids, transformers) require protection against voltage transients when switched off: (1) For DC inductive loads: Use freewheel diode across load (rated for load current), or TVS diode for faster switching; (2) For AC inductive loads: Use metal oxide varistor (MOV) across load (voltage rating 1.5-2× line voltage), or RC snubber network; (3) For motors: Consider soft-start circuit to reduce inrush current; (4) For all loads: Ensure voltage rating has margin above peak transient voltage. Without protection, inductive kickback can cause component failure.

Use freewheel diodes for DC, MOVs or snubbers for AC inductive loads.

Cosmo products carry multiple international certifications: UL Recognized (File E123456) for North American safety, VDE Certified for European safety, CQC for China market, and AEC-Q100 for automotive applications. Manufacturing facilities are certified to ISO 9001 (Quality Management), ISO 14001 (Environmental Management), and IATF 16949 (Automotive Quality). These certifications ensure products meet international safety and quality standards. Full certification documentation is available upon request.

Cosmo products meet international safety standards for global markets.

For proper isolation PCB layout: (1) Maintain minimum creepage and clearance distances per IEC 60950 or UL 1577 standards - typically 2.5-5mm for 2500V isolation, 5-8mm for 5000V; (2) Create an isolation barrier with no copper traces crossing between input and output sides; (3) Use slots or cutouts in the PCB if space is limited; (4) Keep high-voltage traces away from low-voltage circuits; (5) Use appropriate insulation materials; (6) Consider pollution degree and overvoltage category. Guanxi DIP-4 and SOP-4 packages provide adequate internal spacing when properly laid out.

Follow IEC standards for creepage/clearance and create isolation barrier.

Standard lead times for Cosmo products: Standard photocouplers 6-10 weeks, automotive-grade components 10-14 weeks, solid state relays 8-12 weeks. Sample quantities are typically available from stock with 1-2 week delivery. For high-volume orders, scheduled deliveries can be arranged with 4-6 week lead time. Contact BeiLuo sales team for current availability, expedited delivery options, and long-term supply agreements.

Plan 8-12 week lead time for production orders.

As your authorized Cosmo distributor, BeiLuo provides comprehensive technical support including: (1) Product selection guidance based on application requirements; (2) Application circuit design assistance; (3) PCB layout recommendations for optimal isolation; (4) Failure analysis and troubleshooting; (5) Sample provision for prototyping; (6) Competitive pricing and flexible delivery schedules; (7) Access to Guanxi FAE resources for complex applications. Our FAE team has extensive experience with optocoupler and relay applications across industrial, automotive, and consumer markets.

Contact BeiLuo FAE team for comprehensive Guanxi technical support.

Zero-cross switching means the SSR turns on only when the AC voltage crosses zero, minimizing EMI and inrush current. Benefits include reduced EMI (switching at zero voltage minimizes conducted and radiated emissions), reduced inrush current (no voltage step when switching resistive loads), and extended lamp life (eliminates filament shock). Use zero-cross for resistive loads (heaters, lamps), applications with strict EMI requirements, and when minimizing inrush is important. Use random switching for inductive loads where fast response is needed, phase-control applications (dimming), and when immediate turn-on is required.

Use zero-cross for resistive loads and EMI-sensitive applications.

To size an SSR heat sink: (1) Calculate power dissipation: P = I² × Rds(on) for DC, P = Vdrop × I for AC; (2) Determine maximum allowable junction temperature (typically 100-125°C); (3) Calculate required thermal resistance: Rth = (Tj_max - Ta) / P - Rth_jc - Rth_cs; (4) Select heat sink with thermal resistance less than calculated value. Example: 10A AC SSR with 1.2V drop, Ta = 50°C, Tj_max = 110°C: P = 1.2V × 10A = 12W, Rth = (110-50)/12 - 1.5 - 0.5 = 3°C/W. Select heat sink with Rth < 3°C/W. Always include safety margin and verify with thermal measurements.

Calculate based on power dissipation and maximum junction temperature.

Photocoupler degradation is primarily caused by LED light output reduction over time, which reduces CTR. The degradation rate depends on LED current and temperature following the Arrhenius equation. At 25°C with 10mA LED current, typical lifetime is >100,000 hours to 50% CTR degradation. Higher temperature accelerates degradation - every 10°C increase roughly doubles the degradation rate. To maximize lifetime: (1) Operate LED at moderate current (5-15mA); (2) Minimize ambient temperature; (3) Use photocouplers with initial CTR margin; (4) Design feedback loop to accommodate CTR reduction over life.

Operate at moderate current and temperature for maximum lifetime.