A simple transistor as an amplifier to boost current drive.
CIRCUIT DETAILS
The maximum output current capability can be worked out as:
Ie = Ib x hfe where Ib = (Vin - 0.7) / R1
In most cases, the circuit shown should supply up to 200mA.
The output voltage will be 0.7v less than Vin
DARLINGTON PAIR
The maximum output current capability can be worked out as:
Ie = Ib x hfe1 x hfe2 where Ib = (Vin - 1.4) / R1
In most cases, the circuit shown should supply up to 3A - but you will need to use a heatsink for Q2 - it will get hot!
The output voltage will be 1.4v less than Vin
COMPONENT TYPES
By changing the transistor types you can increase the current capability of the drivers.
The Darlington Pair can be combined into one device. Some type available are:
TIP122 - 5A
TIP141 - 10A
TIP142 - 8A
Transistor Case Styles
TO92
(BC549B)
TO220
(TIP41A / TIP122)
TO218
(TIP141/2)
If you are driving high current devices you may find the transistor gets very hot. You can attach a heatsink to the tab of the transistor to help cool it.
