Device and method for controlling an electrical heater to limit temperature according to desired temperature profile over time

1. A method of controlling heating in an aerosol-generating system comprising a heater, the method comprising:

comparing a measured parameter, indicative of a temperature of the heater, with a target value for the measured parameter;

preventing a supply of power to the heater for a first time period if the measured parameter exceeds the target value by greater than or equal to a first amount; and

preventing the supply of power to the heater for a second time period, shorter than the first time period, if the measured parameter exceeds the target value by less than the first amount.

2. The method according to claim 1 , further comprising varying the target value with time.

3. The method according to claim 1 , further comprising discontinuously varying the target value with time.

4. The method according to claim 1 , further comprising supplying power to the heater if the measured parameter does not exceed the target value.

5. The method according to claim 1 , further comprising supplying power to the heater as pulses of electrical current, wherein, if the measured parameter does not exceed the target value, determining if the supply of power would result in a duty cycle of the pulses of electrical current exceeding a maximum duty cycle over a first time period, and supplying power to the heater only if the supply of power would not result in the duty cycle of the pulses of electrical current exceeding the maximum duty cycle.

6. The method according to claim 1 , wherein the measured parameter is an electrical resistance of the heater.

7. The method according to claim 1 , wherein the aerosol-generating system is an electrically heated smoking system.

8. The method according to claim 7 , wherein the electrically heated smoking system is configured to heat a tobacco substrate.

9. An electrically heated aerosol-generating system, comprising:

a heater;

an electrical power supply; and

a controller configured to

compare a measured parameter, indicative of a temperature of the heater, with a target value for the measured parameter,

prevent a supply of power to the heater for a first time period if the measured parameter exceeds the target value by greater than or equal to a first amount, and

prevent the supply of power to the heater for a second time period, shorter than the first time period, if the measured parameter exceeds the target value by less than the first amount.

10. The system according to according to claim 9 , wherein the controller is further configured to vary the target value with time according to a desired target profile stored in a memory.

11. The system according to according to claim 9 , wherein the controller is further configured to discontinuously vary the target value with time.

12. The system according to according to claim 9 , wherein the controller is further configured to supply power to the heater from the power supply if the measured parameter does not exceed the target value.

13. The system according to according to claim 9 , wherein the controller is further configured to supply power to the heater as pulses of electrical current, wherein, if the measured parameter does not exceed the target value, determine if the supply of power would result in a duty cycle of the pulses of electrical current exceeding a maximum duty cycle over a first time period, and supply power to the heater only if the supply of power would not result in the duty cycle of the pulses of electrical current exceeding the maximum duty cycle.

14. The system according to according to claim 9 ,

wherein the measured parameter is the electrical resistance of the heater, and

wherein the controller is further configured to measure an electrical resistance of the heater during periods in which power is supplied to the heater.

15. The system according to according to claim 9 , wherein the system is an electrically heated smoking system.