LAoE Figure 6L.19
The opamp does not directly sources current, rather trough a PNP BJT. The voltage after the 470Ohm resistor is 12.2V (2.8V drop) which results in 5.86mA current. The 12.2V reference voltage is set by the voltage divider. To keep the inverting input to the reference level (12.2V), the opamp set its output voltage that the transistor sink 5.86mA of current .
The delayed start with relay is to avoid "Cannot find solution" error.
