Use a current source so you have a current of 20mA regardless of whether you use a 3V or 6V source.What can I do?
How did you find this resistor values?Same circuit basically but shouldn't need to change any parts.
View attachment 232071
\(I = \frac{V}{R} = \frac{0.7V}{20mA} = 35\Omega\)How did you find this resistor values?
What about the 2.2k resistor? Why this value was chosen? The 0.7V is the voltage-drop across the base-emitter of the transistor?\(I = \frac{V}{R} = \frac{0.7V}{20mA} = 35\Omega\)
The nearest 5% value is 33 ohms which would give about 21mA.
That resistor needs to provide base current to Q2 and collector current to Q1 while not dropping more than than 1.6V. With a supply voltage of 3V, it would have 1.6V across it giving it a current of 0.73mA. If Q2 needed to saturate, it would require a current of 2mA; so it would appear that that resistor is too large for a 3V supply. It would work with 6V.What about the 2.2k resistor? Why this value was chosen? The 0.7V is the voltage-drop across the base-emitter of the transistor?
A white LED?my LED ( 3.0 V - 20mA)
Of Q1.The 0.7V is the voltage-drop across the base-emitter of the transistor?
This Current Regulator is available in 20ma, and 25ma versions,
and has only 1-Volt Forward Voltage .
Good to 90- Volts in the D-Pack Package,
available in TO-92 Transistor Package also.
CL520
CL525