DC Coupled Transistor Amplifier
This is a The Directly (DC) Coupled Amplifier circuit. This circuit is built from NPN transistor and PNP transistor. This circuit is used to amplify a DC signal. Since there is no coupling capacitor to block DC, this circuit can perform as DC amplifier as well as AC amplifier. Beside that, this circuit can amplify a very low AC frequencies since no capacitive reactance. Here is the circuit:
This circuit has a correct operating voltage because the PNP transistor is upside down with respect the NPN transistor. This circuit is not require a bias resistor for NPN transistor if the PNP collector voltage is fit value for NPN transistor base. However this circuit is influenced by temperature. First transistor will drift DC and then amplified by second transistor. That action cause the normal operating voltages is changed. A DC stabilization can be used to solve this problem.