![]() If it is 0.8V, then, for an LED strip that requires 1A of current, that's a Power Dissipation of: PD = 0.8V * 1A = 0.8W But, on the plus side - by not driving the LEDs as hard as they would be driven at the full 12V, might, actually, extend their lifespan That means only around 12V - 0.8V or 11.2V will reach the LED strip, and that might be significant. But for an LED strip that takes around 1A, the typical V CE(sat) is estimated to be 0.8V to 0.6V. I can't say for sure what the expected V CE(sat) will be, because there is no mention of the amount of current this LED strip requires. Where did I get that voltage of 3.5? The voltage at the Base-Emitter junction is estimated to be 1.5V, so 5V - 1.5V is 3.5Vīe aware, though, because of the voltage drop from the Collector, to the Emitter, the LED strip will not glow as brightly as it would if connected directly to 12V. R1 = (3.5V * 250) / Istrip where: I strip is the current required by the LED strip. You can calculate that value using the following formula: ![]() The R1 resistor value is for around 1A through the LED strip. 1k is a good default value likely to work with most loads.TIP122_transistor_schem.png 1407×1449 109 KB If the load is 2A you want at least 2mA into the base, so a base resistor You want the output transistor of the darlington to carry about 0.1 times the Ic value,Īnd the first transistor has a gain of about 100 probably, so Ib of 1/1000 I is always current (no idea why), Ic = collector current The is Vsat, the saturation voltage when the transistor is hard on at 5A. Ratio of collector current to base current. The maximum current through the collector without risking damage Voltage is developed across a component, it doesn't flow The high current is though the solenoid so it has to flow round theĬollector/emitter circuit since the Arduino isn't allowing large currents (due to theĪll the charge carriers are reverse polarity in a PNP compared to NPN, The fact the emitter is common toīoth circuits cannot affect the current, only bring the voltage to a common valueĪt the emitter. Means a loop, current flows round a loop. at 120mA) will not flow to the GND on Arduino which will then damage Arduino, but will flow to the cathode of the power sourceīecause the collector/emitter and base/emitter circuits are different circuits. Got a simple question here though, why the current from solenoid or from the connected Emitter Pin of transistor (e.g. The current through the collector/emitter circuit depends on the current through theīase/emitter circuit, the ratio being called the "gain". Thank you very much guys for helping a learning noob here So how do I know what is the correct current I should send to its Base Pin from Arduino ? And it seems I need to connect a resistor between the Base Pin and Arduino digital Pin, how do I work out the resistor ? Transistor Polarity:NPN - not sure what NPN differs from PNPĬollector Emitter Voltage V(br)ceo:100V - the maximum voltage that can flow through the transistor ?ĭC Collector Current:5A - the maximum current that can flow through the transistor ?ĭC Current Gain hFE:1000 - really no ideaĪv Current Ic:5A - average current 5A ? no ideaĬollector Emitter Voltage Vces:2V - how does this differ from the 100V ?Ĭontinuous Collector Current Ic Max:5A - what does the term 'Ic' mean.Ĭurrent Ic Continuous a Max:5A - no idea And can you tell me if I understand those information correctly ? ![]() I think it's switched by current, so I have to supply the correct current to its Base Pin, but I can not find what is this correct current from its information below. ![]() I am using the TIP122 transistor and have listed its specifications as below. The digital Pin on Arduino also requires a complete circuit to work right ? For example, it goes like from the digital Pin to a resistor then to the Base Pin of transistor and exits from the Emitter pin and back to the GND on Arduino ? I guess I am really asking how does the negative common ground or buses on the breadboard work. at 120mA) will not flow to the GND on Arduino which will then damage Arduino, but will flow to the cathode of the power source, please refer to my attached picture. I just learned how the transistor works, basically after receiving a HIGH signal, Arduino sends a signal to the Base Pin of the transistor through a resistor, and then the transistor will connect its Collector Pin and Emitter Pin to finish the circuit. Can I just ask you some questions about the TIP122 ST Trans Darlington Transistor please.
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