An ideal operational amplifier (op-amp) will be used within a comparator circuit. A section of the comparator is illustrated in Fig. 7.1. To finish the circuit, there are three resistors, each with resistance $1000\,\Omega$, together with a negative temperature coefficient thermistor. The arrangement must be set up so that the output $V_{\text{OUT}}$ is $-5.0\,\text{V}$ at low temperatures and $+5.0\,\text{V}$ at higher temperatures.
(a)[4]
On Fig. 7.1, draw the input circuit feeding the inverting and non-inverting inputs of the op-amp.
(b(i))[1]
State a suitable resistance value for the thermistor when it is at low temperature and $V_{\text{OUT}}$ is $-5.0\,\text{V}$.
(b(ii))[1]
State a suitable resistance value for the thermistor when it is at a higher temperature and $V_{\text{OUT}}$ is $+5.0\,\text{V}$.
Worked solution & mark scheme
This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “divider of two resistors in series” …