The schematic I am studying comes from page 116 of Mims' Timer, Op Amp & Optoelectronic Circuits & Projects book. The circuit is a relaxation oscillator which pulses an LED 240 times per second.
A +6V source is attached to the positive end of the LED and the emitter of a
2N2907 PNP. The collector of the 2N2907 leads to the base of a 2N2222 NPN. The 2N2222's emitter is grounded and its collector goes to the negative side of the LED. The junction between the LED and the 2N2222 leads through a 0.02uF capacitor and a 22k resistor to the base of the 2N2907, which then is grounded through a 2.2M resistor.This is the netlist I created in PSPICE:
D_D1 N00292 N00346 D1N4148 R_R2 N00573 N00543 22k R_R3 0 N00573 2.2m C_C1 N00543 N00346 0.02u Q_Q1 N00261 N00573 N00292 Q2N2907A Q_Q2 N00346 N00261 0 Q2N2222 V_V1 N00292 0
+PULSE 0 6 0.01 0 0I used a VPULSE because I don't know how to set the initial charge on the C to 0V through Capture. I also used a D1N4148 because there were no models for an LED.
Questions:
A. Is the configuration of the PNP and NPN transistors a programmable unijunction transistor?
B. When I ran this circuit in PSPICE there was no oscillation. How is this circuit supposed to work, and what changes should I make to the netlist to cause the correct results?