So you’re knee-deep in designing an infrared optical switch, and now you’re staring at datasheets trying to figure out which 940nm phototransistor won’t let you down. I’ve been there more times than I can count – tweaking circuits late at night because the wrong part caused false triggers or slow responses. Picking the right 940nm infrared phototransistor can make or break your project, especially when you’re dealing with reliable detection in all sorts of lighting conditions.
Infrared optical switches are everywhere – from industrial sensors that detect objects on conveyor belts to simple interrupter setups in consumer gadgets. The heart of it is pairing an IR LED (usually peaking at 940nm) with a matching IR receiver transistor. Get that match wrong, and your switch might ignore the signal or flip out from sunlight streaming through a window.
Let’s walk through this step by step, like we’re chatting over coffee. I’ll share what I’ve learned from real projects, pull in some solid facts from industry standards, and help you avoid the headaches I’ve seen (and caused) along the way.
Why 940nm Is the Go-To Wavelength for Most IR Optical Switches
Okay, first things first – why bother with 940nm at all? Turns out, it’s not random. Almost every IR remote control out there uses 940nm because it’s a sweet spot. The LED efficiency is decent, the phototransistor sensitivity peaks nicely there, and – big bonus – it cuts down on interference from ambient light.
Sunlight and indoor lights pump out a ton of infrared energy, but it drops off around 940nm compared to shorter wavelengths like 850nm. Real data shows that 940nm setups face less outdoor ambient interference because solar radiation has a dip in that range. That’s why night vision gear or security cameras often lean toward 940nm when they need stealth and reliability without that faint red glow you get from 850nm.
In optical switch design, this means your 940nm infrared phototransistor won’t freak out as much from background IR noise. I’ve worked on a factory sensor project where switching to a properly matched 940nm part slashed false detections by over 70% when the machine was near fluorescent lights.
The peak sensitivity wavelength is key here. Most quality phototransistors are tuned to hit max response right around 940nm. If your LED is 940nm but the detector peaks at 880nm, you’re losing a chunk of signal strength – sometimes 30-50% less current output.
Si-Phototransistor PTCP Serie PTCP001-102
High-sensitivity Silicon Phototransistor designed for precision detection in the 800-1100nm spectral range. This black plastic IR sensor ensures minimal noise and high reliability. Ideal for industrial applications requiring a robust silicon phototransistor with excellent response speed.
Breaking Down the Must-Check Specs for Your 940nm Phototransistor
Alright, you’ve decided on 940nm – now what else matters? Not all 940nm phototransistors are built the same. Here’s the stuff I always scan first on a datasheet.
- Collector Light Current (Sensitivity): This tells you how much output current you get under a standard IR blast (usually 1mW/cm² at 940nm). Higher is better for weak signals, but too high can amplify noise.
- Dark Current: The leakage when no light hits it. You want this super low – like under 100nA – to avoid false triggers in bright rooms.
- Rise/Fall Time (Response Speed): For fast-moving objects in your optical switch, aim for under 10-15µs. Slower ones (over 50µs) work fine for static detection but drag in dynamic setups.
- Angular Response: How wide the detection angle is. Half-angle around 20-30° is common for focused switches.
Real examples from big players like Everlight and Vishay: Their 940nm parts often show peak sensitivity at exactly 940nm, dark currents around 10-100nA, and response times in the 5-15µs ballpark. Everlight’s PT91-21C series, for instance, hits solid sensitivity with a black lens to filter visible light.
Here’s a quick table comparing some typical specs I’ve pulled from common parts (based on real datasheets from Everlight and similar):
| Parameter | Typical Through-Hole (e.g., PT204-6C style) | Typical SMD (e.g., PT91-21C style) | Why It Matters in Optical Switches |
|---|---|---|---|
| Spitzenempfindlichkeit Wellenlänge | 940nm | 940nm | Must match your IR LED for max signal |
| Collector Current (at 1mW/cm²) | 1-5mA | 0.5-3mA | Higher for longer range detection |
| Dark Current | <100nA | <50nA | Lower reduces ambient false triggers |
| Aufgangs-/Fallzeit | 15µs | 10µs | Faster for quick object passing |
| Viewing Angle (half) | ±30° | ±20° | Wider for broader beam interrupts |
These numbers aren’t pulled out of thin air – they’re straight from manufacturer specs you can verify.
Through-Hole vs SMD Phototransistor: Picking Sides for Your Build
This one’s a classic debate. Through-hole phototransistors are the old-school reliable ones with legs that poke through the board. SMD versions sit flat on the surface.
Through-hole wins for prototypes and tough environments. The solder joints are beefier, handling vibration or heat cycles better. I’ve used them in automotive sensor mocks where boards get banged around – no failures.
SMD phototransistors shine in production. They’re tiny, let you pack more on a board, and automated assembly loves ’em. Shorter leads mean less parasitic inductance, which helps at higher switching speeds. Downside? Hand-soldering them sucks if you’re tweaking a lot.
In one client project (keeping it anonymous), we started with through-hole for quick testing an optical interrupter in a printer mechanism. Once dialed in, we swapped to SMD for the final compact design – saved space and cut costs in volume.
If you’re just breadboarding, grab through-hole. For sleek, modern optical switch design, SMD all the way.
Si-Phototransistor PTCP Serie PTCP001-202
Verbessern Sie Ihre Schaltlösungen mit diesem 800-1100nm NPN-Phototransistor. Er eignet sich perfekt für fotoelektrische Schalter und bietet eine hohe Verlustleistung von bis zu 90 mW. Dieser Silizium-Phototransistor bietet eine konstante Leistung in rauen Umgebungen von -40°C bis +85°C.
Real-Life Tips from Years of Messing with Optical Switches
Over the years, I’ve seen designs flop because folks ignored little things. Like adding a daylight filter (those black epoxy lenses) – it blocks visible light while letting 940nm through, dropping ambient interference big time.
Another trick: Pulse your IR LED at 38kHz (standard remote freq) and filter the receiver side. Your 940nm infrared phototransistor ignores steady ambient IR but locks onto the pulsed signal.
One success story – a team building safety gates for machinery. Early versions triggered randomly from shop lights. We matched a high-sensitivity 940nm part with tight angular response, added modulation, and boom – rock steady even outdoors.
Solid Options We Use at Bee Photon
At Bee Photon, we’ve got some favorites that fit perfectly for these apps. Our PTCP001-102 is a through-hole champ – peaks sharp at 940nm, low dark current, great for rugged prototypes. The PTCP001-202 is its SMD sibling, super compact with fast response.
Check out our full lineup of silicon phototransistors – they’re built with these exact needs in mind.
We’ve helped tons of engineers nail their optical switch designs with these. If you’re hitting snags, they’re worth a look.
Frequently Asked Questions About 940nm Phototransistors
Why does peak sensitivity wavelength have to match 940nm exactly?
If it’s off by even 50nm, you lose signal strength – sometimes half the current. Real remote controls stick to 940nm for this reason; mismatch means shorter range or unreliable switching.
Should I go through-hole vs SMD phototransistor for a small consumer device?
SMD for sure if you’re going to production – saves space, cheaper to assemble. But start with through-hole if you’re prototyping; easier to swap and solder by hand.
How do I cut down ambient light messing with my IR receiver transistor?
Use a part with a daylight filter lens, keep dark current low, and modulate your LED. 940nm already helps vs shorter wavelengths, as sunlight interference drops there.
What’s a good response time for fast optical switches?
Under 15µs rise/fall for objects moving quicker than a few cm/s. Slower is okay for static presence detection.
Wrapping It Up – Let’s Get Your Design Sorted
Choosing the right 940nm phototransistor boils down to matching wavelength, nailing the specs, and picking the package that fits your build stage. Do it right, and your infrared optical switch just works – no babysitting needed.
If any of this rings true for your project, swing by Bienen-Photon for more details. We’ve got samples ready, and the team loves chatting specifics.
Need a quote or custom advice? Hit us up at info@photo-detector.com oder über unser Kontaktseite. We’d love to help make your next design a win.
