| Electronics > Projects, Designs, and Technical Stuff |
| SMD alternative to TIP31 and TIP32 |
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| v8dave:
With the massive number of transistors on the market, I am looking for anyone who has done this and what options they chose. I have a design that drives servo valves at 5V and max 500mA current. The current design us all through-hole but I need to rework this to SMD to get it smaller. This uses the standard TO220 TIP31 and TIP32 and I'd like to use an SMD transistor instead. As these devices don't have any direct replacement for SMD use, has anyone got any experience of swapping these out for SMD parts? I have a working simulation in Tina and this works with real hardware too so I can easily plug in the values from the SMD parts and make sure that it works, simulation wise at least. |
| graybeard:
I have not looked but I would be shocked if there were not SMD equivalents. Have you tried looking? |
| jhpadjustable:
5V at 500mA is an easy spec to meet, and a BJT switch doesn't need very tight matching when substituting. Parametric selection guides on the manufacturer or distributor websites are essential resources for finding what's out there. On the other hand, maunfacturer-specific simulation/design tools tend to be stifling unless verifying one of their odd parts for which no generic model is available. It's easy to find SOT-89 packaged BJTs from Nexperia, Infineon and other major manufacturers, also second-sourced by various Chinese semiconductor startups. For example, one recent addition to my home lab stock, BCX56: * 1 A average collector current, 1.5A peak * 80V Vceo * 0.5W dissipation on a conservative footprint or 1.3W with more copper on the collector pad * hFE minimum 25 at your chosen 500mABCX53 is its PNP complement with very similar specs. In any case, you should consult the full datasheets and specifically the safe-operating-area graph to make sure the collector currents and on-times in your application remain within limits. You can get further size reduction if you can redesign for MOSFETs. There are hundreds if not thousands of part numbers in SOT-23 packages with multi-ampere drain-source ratings, 3.3V-friendly threshold voltages, and low on-resistance. AO3400 and AO3401 are my go-to components for switching an ampere or two at low voltages. |
| george.b:
MJD31 and 32 are probably what you're looking for. |
| mikerj:
The original transistors seem a little over-specified for the application, unless the valves are being switched rapidly and continuously. There are plenty of high current bipolar switching transistors available in SOT-23 packages with gains much higher than the ancient TIP31/32 and lower saturation voltages. e.g. On Semiconductor have a decent range, as do Diodes Inc. |
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