Design Notes

The power dissipation and junction temperature in pass transistor Q1 must not exceed the maximum values allowed by the device and by your application. In space applications, the maximum allowed power dissipation in a transistor may be significantly less than the rating of the device. For example, the European Space Agency (ESA) recommends a derating factor of 65%. Similarly, although Q1 is specified with a maximum junction temperature of 200°C, ESA recommends a junction temperature not greater than 110°C. In applications with a large voltage drop across the negative regulator, the power dissipation in Q1 might exceed the maximum allowed. However, in such applications there no need for an LDO regulator and a standard type with larger dropout such as the LM137QML-SP can be used.

The op-amp used in this circuit must have an output stage capable of operating close to the negative supply rail of the op amp. The LM158QML-SP was chosen for this circuit because it meets this criterion, has a long space heritage, and withstands a total ionizing dose up to 100 krad (Si). Other op amps can be used, but the feedback stabilization may need to be adjusted to suit the frequency response of the op amp.