However, a small signal across the base is enough to make it work. The transistor will not work if a signal (voltage/current) is applied across the collector and emitter but not across the base. The transistor is now in Reverse Bias mode, which means that no current flows through the collector or emitter. The voltage does not apply to the base terminal when the switch is in the open condition. The following formulae can be used to calculate the value of this resistor (Rb). Any current more than 5mA will damage the transistor, hence a resistor is always connected in series with the base pin. The biasing current should be not more than 5 mA. This biasing can be done by providing the required amount of current to the base pin. When we supply current to the transistor's base, it makes a path for the collector current to flow from the base to the emitter.ĭuring Forward Bias, the transistor will act as an Open switch, and during Reverse Bias, it will act as a Closed switch. When a transistor is used as a switch it is operated in the Saturation and Cut-Off Region. Driver modules for LED, electronic relay.General switching and amplification purposes.We must supply current to the base pin of a transistor to operate it, and this current (IB) should be limited to 5mA. The maximum current that can flow through the Collector pin is 100mA, we can't use this transistor to connect loads that use more than 100mA. The gain value of the BC547 transistor ranges from 110 to 800, and this value determines the transistor's amplification capacity. It also has a negative tail on the collector current, though much smaller than on the 2N2222.This transistor is commonly used for amplification of current as well as switching purposes. The tail in the simulator is also straight rather than curved.Īt any rate, the "tail" isn't a figment of the Nano's imagination. It does in fact have a negative tail, though not as extreme as in my circuit. This is the plot of the collector current against the collector voltage: ICollector is calculated as \$\frac \$ĭoes that explanation seem right, or have I missed something?īetween those two charts, I changed R4 from 1k to 10k and made some software changes to get a little more resolution.Īt a suggestion from Hearth, I simulated the circuit in LTspice. That raises the collector voltage (A3-VCollector) against the bias voltage (A2-VCollectorBias) resulting in a current flowing back through R4. The best explanation I've been able to come up with is that at low collector voltages, some of the base current "goes the wrong way" out through the collector instead of the emitter. It uses oversampling to get better than the 10 bits of resolution of the Arduino ADC. There's an Arduino Nano off to the left connected to the analog and PWM signals. This is the circuit I used to make the plots: I've been trying to figure out what is going on here. You can see the "curlicue" down there at the lower left corner. This is the plot of the collector current and collector voltage for a 2N2222 transistor made with my setup: I noticed a slight curlicue in the low voltage and low current end of the plot for a transistor, and wondered what was going on. I have been working on a home made IV tracer for diodes and transistors.
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