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| TL431 voltage reference on more than 36V (to generate 2.5V reference)? |
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| Lupin III.:
I have a circuit that's powered by approx. 50V DC (step down DC-DC converter module). I this circuit I'd like to add a TL431 voltage reference for some shenanigans with the current feedback to add external current control. Assuming the supply resistor is sized properly to keep the TL431 within its allowed current range even in the worst case of >50V, the 431 should be fine once it is regulating, because the resistor is dropping all the voltage. But is the 431 fine at switch-on in the few µs before it starts properly regulating? There the full voltage could be at the cathode pin (assuming there's almost no current flowing and therfore almost no voltage drop on the supply resistor). The obvious solution would be to put a zener diode in parallel, but I'm just wondering if it is necessary. |
| StillTrying:
Assuming the >50v takes a millisecond or more to ramp up to >50V I don't think it would be problem for the TL431. |
| Zero999:
I agree, the transient shouldn't be a problem. Most semiconductors are designed to withstand these kind of transients without damage. For your information, another transistor can be added to the TL431 so it can be used at higher voltages. https://www.eevblog.com/forum/projects/tl431-common-base-amplifier-stability/msg599580/#msg599580 |
| Doctorandus_P:
Also: When you put a small capacitor parallel to the TL431 you create a RC constant with a ramp up time, which ensures the TL431 has enough time to get into regulation, but it's probably not needed. |
| Whales:
--- Quote from: Doctorandus_P on March 25, 2020, 10:54:04 pm ---Also: When you put a small capacitor parallel to the TL431 you create a RC constant with a ramp up time, which ensures the TL431 has enough time to get into regulation, but it's probably not needed. --- End quote --- This could be an interesting solution. A tiny cap + R across the TL431 might guarantee that it will be at 0V through turn-on. High-freq transients might be another issue, not sure. You have to make sure the capacitance value you use doesn't make the TL431 unstable (check the datasheet - by memory there is some variation between TL431 vendors). I like the option of an approximate voltage regulator: use an NPN in an emitter follower configuration, base controlled by a voltage divider. 4 parts: two resistors, a capacitor and one NPN. |
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