SPARKOS LABS SS7909 Discrete Voltage Regulator -9V

Regulator replacement

To replace a monolithic regulator with a discrete model, you need to know its polarity, pinout and output voltage. In the case of an adjustable regulator, its output voltage is fixed by the circuit in which it is integrated via a resistor that must be short-circuited and removed.

It is not recommended to attempt to dynamically adjust the output voltage of these discrete regulators using potentiometers or voltage dividers on the ground pin to achieve the specified performance.

If a regulator to be replaced is mounted on a heat sink, the same heat sink must be used with the discrete replacement regulator. It is not necessary to use a larger heat sink. The existing heat sink will suffice. Since the tongue of these discrete regulators is connected to the voltage input, electrical insulation must be used between the tongue and the heat sink.

The input and output bypass capacitors of the existing circuit should also be adapted and do not require any modification for normal operation. If the output capacitor closest to the regulator is ceramic or film type, a better transient response can be obtained by removing it from the circuit, as ceramic and film capacitors degrade the phase margin of the device. In cases where the output capacitor is removed from the circuit, the 10µF internal tantalum polymer capacitor will be sufficient as the output capacitor, and the device will operate with a higher phase margin and a less transient response.

The best transient response can be obtained by using a Panasonic EEU - FR1H101B (100µF 50V 65mΩ ESR) electrolytic capacitor as the output capacitor. This capacitor can be used to replace the existing output capacitor or it can be added in parallel. It should be noted that the correct polarity must be observed when installing these electrolytic capacitors.