Phase Controlled AC Switch

The circuit

Pairs of complementary bipolar transistors can be used to form versatile circuits capable of simulating many negative resistance devices. In the following example, a thyristor model will be described.

With increasing voltage v(3,4) both transistors are nonconducting. The critical level, determined by the r3 / r4 ratio, causes regeneration to occur producing an avalanche breakdown analogous to discharge in gaseous tubes. The initial condition is restored by the zero crossing of a sine wave voltage. This will be demonstrated with following phase control circuit.

The input file

phase controlled ac switch

.control
tran 250us 50ms
plot v(1) v(1,2) xlabel t[s] ylabel 'input output[V]' title 'TRAN analysis'
.endc

v1 1 0 dc 0 sin 0 20V 50Hz

r1 1 2 100
r2 6 3 1k
r3 5 3 3.3meg
* r4 4 5 optional

d1 3 2 noname1
d2 2 4 noname1
d3 3 0 noname1
d4 0 4 noname1

q2 5 6 3 noname3
q3 6 5 4 noname2

.model noname1 d
.model noname2 pnp rb=10 cjc=100pF
.model noname3 npn rb=10 cjc=100pF

.end

The results