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It only takes a minute to sign up. The actual circuit is the one in this question: Review of my first ever PCB design for a watering control robot. I've seen some versions of the regulator data sheets where the application notes recommend a diode from Vout to Vin in order to protect the device from burning out if the output voltage goes higher than the input. Hence I assumed it wasn't necessary with their implementation. The programming failed, and the target device has a "electronic" smell not present before.
When I next plugged in the DC cord I got a spark from the ground terminal and there is a black residue from it on the solder mask of the DC plug and immediately unplugged the DC cord. Further I measure in situ only R or so between the Vout and GND pins on the regulator both ways which is much less than what I would have expected.
Desoldered the regulator, all pin combinations with polarity measure within tolerance of a new one and it doesn't smell. Also the relay smells funny. It seems rather unlikely to me that this is the cause.
The output voltage has to be greater than the reverse breakdown of the B-E junctions in the regulator to cause damage, and 5V is not. There also has to be significant current flowing back both conditions are necessary for damage to occur. I suggest proceeding with caution and looking for something else that may have caused what appears to be significant damage. For example, reversed power connections. Bad news - You probably need the diode.
The has an emitter follower on the output stage, so you have probably let the smoke out. I have blown this specific part with the charge from large output decoupling capacitors when the input was shorted.
I'm not sure how you damaged your target. For ICSP, you can add the diode but realize your programmer will have to power whatever is on the back side, or you can select the target's vdd on some programmers. However, I usually put a blocking Schottky diode in series with the output. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Asked 2 years, 11 months ago. Active 2 years, 11 months ago.
Viewed 2k times. So my questions are: Is my regulator shot? Should I have had the DC power connected to the target? Any other measurements I should make?
Emily L. At this stage I think my move would be to replace the , check any diodes for short circuits, power the board from a current-limited PSU and try again measuring the current draw and all supply voltages first! Active Oldest Votes. For example, the TI datasheet specifically says: I suggest proceeding with caution and looking for something else that may have caused what appears to be significant damage. Spehro Pefhany Spehro Pefhany k 9 9 gold badges silver badges bronze badges.
Also they mention short circuit protection. Jul 9 '17 at They're all pretty similar.. But those protections can't save the chip if it's abused by putting 10V on the output with input grounded or 50V on the input. For example, your ICSP setup has a ground to earth through the computer if it's a desktop or many notebook computers. That can cause issues if your circuit also has a ground to earth somewhere, and very serious issues if the two are not nominally at the same potential.
Jul 10 '17 at John Birckhead John Birckhead 6, 1 1 gold badge 6 6 silver badges 20 20 bronze badges. I'll have to see how if that affects the rest of my circuit. For now I think I'll jurryrig a shunt diode on the pins as the board is already made. Sign up or log in Sign up using Google.
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July General Description. With adequate heatsinking, they can deliver in excess of. Typical applications would include local. Connection Diagrams. Bottom View.
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3-Terminal Positive Voltage Regulators