Low DC Voltage Stabilization

The circuit

Realising stabilised dc voltages below a zener boundary of about 2V is difficult. Higher voltages may be reduced by ohmic voltage dividers, but too much of the power must be dissipated if the resistors need to be at low values. A 1.5V zener diode can be simulated by a complementary pair of bipolar transistors having zero dynamic impedance.

In the case of r2 = 0, both transistors are like two diodes connected in series. If r2 is omitted a regenerative process starts which leads to a negative resistance characteristic similar to tunnel diodes. Between these two extremes, an adjustment may be found for which the resulting impedance is zero over an extended current range. The coefficient of the temperature is approximately -5mV/°C.

The input file

low dc voltage stabilizator

.control
dc v1 0 10V 0.1V
alter i0 dc = 25mA
dc v1 0 10V 0.1V
alter i0 dc = 50mA
dc v1 0 10V 0.1V
plot dc1.v(2) dc2.v(2) dc3.v(2) xlabel v1[V] ylabel v(2)[V] title 'DC analyses'
.endc

v1 1 0 dc 0

i0 2 0 dc 0

r1 1 2 100
r2 3 4 3.3

q1 3 4 2 noname1
q2 4 3 0 noname2

.model noname1 pnp
.model noname2 npn

.end

The results