Direct shipment from Picotest, USA

The circuit is a discrete BJT (bipolar junction transistor) voltage regulator with a 7‐10 V input and a 3.3 V output. The BJT is controlled by a TL431 shunt regulator. C1 and R5 provide frequency compensation, R2 is the injection transformer terminating resistor and R3 and R4 are the output voltage sense divider.
Two different output capacitors can be selected using S1‐1 and S1‐2. One capacitor, an aluminum electrolytic capacitor provides excellent phase margin while the other results in approximately 40 degrees phase margin. A blue LED is powered by the output, providing a visual indication of power on and also a load of approximately 20 mA. An additional 25 mA of load current can be switched on or off using S1‐3.