Periodic Pulse

Hi

I an working on Joule Heating and would like to generate 3 repeated voltage pulse
Conditions:
Pulse Width: 100e-9
Rise and fall: 10e-9
Period: 150e-9


This is what I tried

Rect1>>
Lower Limit: 0
Upper Limit: 100e-9
Size of transition: 10e-9
Amplitude: 3V

An1>>
Parameters >> Expression: rect1(mod(t,150e-9)
Argument:t
Derivatives: Automatic

Units>>Arguments: t

Plot Parameters>> Argument:t, Lower limit: 0, Upper Limit:0.001*

*With these setting, I can see the periodic waveform

Calling An1 in Electric Potential>>
V0: 3*an1(t[1/s])

Study >> Time: range(0,1e-9,4.5e-7)
Time stepping: Intermediate


Trying to see the temperature profile but it seems that the temperature keep rising up till 4.5e-. However, I do expect temperature to drop after each pulse interval before the next pulse starts.

What should I correct?

Please help. Thank you.