Temperature sensing circuit for transmitting data across isolation barrier
An isolated temperature sensing system includes a thermistor that measures a temperature of a compressor system. An isolation circuit charges a capacitor, sets an output signal to a first state during charging of the capacitor, discharges the capacitor to the thermistor, and sets the output signal to a second state during discharging of the capacitor to the thermistor. The first state is different than the second state. A control module receives the output signal via an isolation barrier and determines the temperature of the compressor system based on a ratio of: (i) a first period that the output signal is in the first state to (ii) a second period that the output signal is in the second state.
1. An isolated temperature sensing system, comprising:
a thermistor that measures a temperature of a compressor system;
an isolation circuit that charges a capacitor, that sets an output signal to a first state during charging of the capacitor, that discharges the capacitor to the thermistor, and that sets the output signal to a second state during discharging of the capacitor to the thermistor,
wherein the first state is different than the second state, and
wherein the isolation circuit transitions from charging the capacitor to discharging the capacitor when a voltage of the capacitor is greater than a first voltage threshold; and
a control module that receives the output signal via an isolation barrier and that determines the temperature of the compressor system based on a ratio of: (i) a first period that the output signal is in the first state to (ii) a second period that the output signal is in the second state.
2. The isolated temperature sensing system of claim 1 wherein the temperature of the compressor system includes a discharge line temperature (DLT) of a compressor.
3. The isolated temperature sensing system of claim 1 further comprising the isolation barrier,
wherein the isolation barrier includes an optocoupler.
4. The isolated temperature sensing system of claim 1 wherein the isolation circuit charges the capacitor via a resistor and discharges the capacitor to the thermistor and at least one discharge circuit component.
5. The isolated temperature sensing system of claim 4 wherein the control module determines the temperature of the compressor system further based on a first resistance of the resistor and a second resistance of the at least one discharge circuit component.
6. The isolated temperature sensing system of claim 1 wherein the control module determines the temperature of the compressor system as a function of a duty cycle of the output signal.
7. The isolated temperature sensing system of claim 1 wherein the control module determines the temperature of the compressor system based on a duty cycle of the output signal using a look-up table that relates duty cycles to temperatures.
8. The isolated temperature sensing system of claim 1 wherein the control module determines a resistance of the thermistor based on the ratio and determines the temperature of the compressor system based on the resistance of the thermistor.
9. The isolated temperature sensing system of claim 1 wherein the isolation circuit transitions from discharging the capacitor to charging the capacitor when the voltage of the capacitor is less than a second voltage threshold,
wherein the second voltage threshold is less than the first voltage threshold.
10. The isolated temperature sensing system of claim 1 wherein the control module further controls the compressor system based on the temperature.
11. An isolated temperature sensing method, comprising:
by a thermistor, measuring a temperature of a compressor system;
by an isolation circuit, charging a capacitor, setting an output signal to a first state during charging of the capacitor, transitioning from charging the capacitor to discharging the capacitor when a voltage of the capacitor is greater than a first voltage threshold, discharging the capacitor to the thermistor, and setting the output signal to a second state during discharging of the capacitor to the thermistor,
wherein the first state is different than the second state;
receiving the output signal via an isolation barrier; and
determining the temperature of the compressor system based on a ratio of: (i) a first period that the output signal is in the first state to (ii) a second period that the output signal is in the second state.
12. The isolated temperature sensing method of claim 11 wherein the temperature of the compressor system includes a discharge line temperature (DLT) of a compressor.
13. The isolated temperature sensing method of claim 11 wherein the isolation barrier includes an optocoupler.
14. The isolated temperature sensing method of claim 11 wherein:
charging includes charging the capacitor via a resistor; and
discharging includes discharging the capacitor to the thermistor and at least one discharge circuit component.
15. The isolated temperature sensing method of claim 14 wherein determining the temperature of the compressor system includes determining the temperature of the compressor system further based on a first resistance of the resistor and a second resistance of the at least one discharge circuit component.
16. The isolated temperature sensing method of claim 11 wherein determining the temperature of the compressor system includes determining the temperature of the compressor system as a function of a duty cycle of the output signal.
17. The isolated temperature sensing method of claim 11 wherein determining the temperature of the compressor system includes determining the temperature of the compressor system based on a duty cycle of the output signal using a look-up table that relates duty cycles to temperatures.
18. The isolated temperature sensing method of claim 11 further comprising determining a resistance of the thermistor based on the ratio,
wherein determining the temperature of the compressor system includes determining the temperature of the compressor system based on the resistance of the thermistor.
19. The isolated temperature sensing method of claim 11 further comprising transitioning from discharging the capacitor to charging the capacitor when the voltage of the capacitor is less than a second voltage threshold,
wherein the second voltage threshold is less than the first voltage threshold.
20. The isolated temperature sensing method of claim 11 further comprising controlling the compressor system based on the temperature.