150-Volt Series Regulator

A regulator capable of delivering 100 mA (DC) to a 150-volt load is shown above. This regulator was designed for use with choke-input-filter rectifier system which is not shown but which produces about 170 volts to the input of the regulator. The output voltage is sensed by the voltage divider comprised of R₅, R₆, and R₇, and is compared with the voltage reference by Q₄. The voltage reference of about 12.9 volts is developed by two Zener diodes in series, D₂ and D₃, which were chosen to produce a voltage temperature coefficient which would tend to compensate for the change in V_BE in Q₄ with temperature.

The output load for the collector of Q₄ is about 138 volts from the emitter of Q₄ so that voltage breakdown and high dissipation could be a severe problem with Q₄. Both problems are solved by the use of D₄, a 100-volt Zener diode which reduces both the voltage and dissipation in Q₄ to manageable levels.

Transistor Q₁ is used as a constant-current source of about 2.8 mA (DC) in conjunction with R₁, R₂, D₁ and C₁. It provides a high-impedance source of current for both Q₃ and Q₄ and maximizes the gain available from Q₄. Transistor Q₃ acts as an emitter follower in transferring the regulating signal from Q₄ to the series-regulating transistor, Q₂, which also operates as an emitter follower.

The network C₂ and R₄ is used to stabilize the feedback loop.