The TIP3055 is a fairly robust device and it will probably survive this for a while, but it would be a major pain to have it fail (probably on)- it appears to be rated at 30 seconds maximum 'on' time- and burn out the expensive strike mechanism, whilst leaving the door open for rascals to ransack the place.
The 'going further' page now includes a way to measure these illustrious voltage spikes with a voltmeter.
The feature of ultra low dropout voltage is ideal for applications where output voltage is very close to input voltage.
Rt9095 transistor schematic install#
It's possible there is one already inside, but I see no mention of it on the datasheet or install sheet.Ī 1N4004 or similar will do the trick. The schematic has been updated with a better transistor and includes basic transistor protection in the form of a capacitor and diode. The RT9085A is a high performance positive voltage regulator with separated bias voltage (V BIAS ), designed for applications requiring low input voltage and ultra low dropout voltage, output current up to 1A. To avoid this, a reverse-biased diode should be installed across the solenoid. Diode schematic symbol and actual picture of a common 1N914 diode (the black stripe in the picture is the cathode). Hence comparing the schematic symbol to the pn junction in figure 4, we see the anode is the p-type semiconductor and the cathode is the n-type semiconductor. Also find the value of the Emitter resistor, RE if it has a voltage drop of 1v across it. The circuit schematic symbol of a diode is shown in figure 5. (c) Rectified RF at diode cathode, without C2 filter capacitor. Calculate the maximum Collector current ( Ic) flowing through the load resistor when the transistor is switched fully ON (saturation), assume Vce 0. However there appears to be a flaw in the ointment (sic) here- the solenoid inductance is a powerful storage reservoir of magnetic field energy that will cause the voltage to rise to hundreds of volts and thus break down the TIP3055 when the power is shut off to the strike. A common emitter amplifier circuit has a load resistance, RL of 1.2k and a supply voltage of 12v. To pick a reasonable value say that Xc = (say) 1000 ohms at (say) 100kHz so a few nF would do the trick.
If replaced with a larger value resistor, a capacitor from base to emitter would eliminate the RF concern. The 1K takes 0.7mA of the available base current only when 'on' (a few percent probably, and less than 0.3% of the total current including the solenoid) so it's reasonable enough. It doesn't do much of anything useful if the Arduino is powered and the output is configured to pull down. It also reduces the leakage current if the transistor was hot and the Arduino was not powered. I'm not saying this is what was in the designer's head, but it's possible that with the Arduino microcontroller not powered a powerful RF signal could be rectified by the transistor base and cause the door to unlock or heat up the transistor and solenoid.
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