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 voltage across the heater, indicative of a temperature of the heater, with a target value;

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

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

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, if the measured voltage across the heater does not exceed the target value, supplying power to the heater.

5. The method according to claim 1 , further comprising supplying power to the heater as pulses of electrical current, wherein, if the measured voltage across the heater 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 voltage across the heater is measured when power is supplied to 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 voltage across the heater, indicative of a temperature of the heater, with a target value,

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

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

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

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

13. The system according to claim 9 ,

wherein the controller is further configured to supply power to the heater as pulses of electrical current, and

wherein, if the measured voltage across the heater 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 claim 9 , wherein the controller is further configured to measure voltage across the heater during periods in which power is supplied to the heater.

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