- #1
amenhotep
- 29
- 1
Hi,
I started using Proteus Isis and was playing around just to get used to it. I designed a simple transistor circuit that should work in the saturated region. The LED needs 2.3V. For saturation, the collector and emitter terminals should be shorted or have a tiny voltage drop across it. So, since the LED requires 20mA, I calculated that the series resistance should be around 139. The BC547 transistor has a dc gain around 110 at that current. This means that a base current of 0.2mA or more should should be enough to saturate the transistor. The circuit is shown below. Whatever base current I used, ##V_{CE}## didn't get below 0.2V which indicates a transistor is near saturation. I've cross-checked values from the datasheet. Surely, something is terribly wrong !
I started using Proteus Isis and was playing around just to get used to it. I designed a simple transistor circuit that should work in the saturated region. The LED needs 2.3V. For saturation, the collector and emitter terminals should be shorted or have a tiny voltage drop across it. So, since the LED requires 20mA, I calculated that the series resistance should be around 139. The BC547 transistor has a dc gain around 110 at that current. This means that a base current of 0.2mA or more should should be enough to saturate the transistor. The circuit is shown below. Whatever base current I used, ##V_{CE}## didn't get below 0.2V which indicates a transistor is near saturation. I've cross-checked values from the datasheet. Surely, something is terribly wrong !