Constant current with 2 type

Easy and low cost constant current. U can see the led current will keep current when change from 12v to any larger voltage. 1. using zener to handle BJT. BJT Beta=100 Rb=(12-5)/(20mA/100)=3.1Kom Re=(5-0.7)/20mA=220om 2. using BJT handle MOSFET.