# Boost Converter why is the calculation result not the same as simulation

guys just asking why is my simulation result not the same as my calculation I am not sure why.

My design has the specification of Vin (power supply) = 1.5V , Vout = 5Volt with a Pout(power output of) = 1 watt , running on 10kHz frequency with 0.1V voltage ripple.

My calculation ^

My Schematic ^

The output voltage ^

Using the MOSFET Si7866DP

I am pretty sure that my calculation is correct but I am not sure why is my output not as my calculation. I did a few tests and I am pretty sure it has nothing to do with the mosfet(not sure if I am right). But can anyone tell me what's wrong and how do I fix it so that the output will be 5V instead of what I got?

• "pulse 0 1.5V" won't turn the MOSFET on very hard. Try 4.5V pulses at which Rds is specified 2.6 mOhm. – Brian Drummond Jun 18 at 19:31
• Your formulas are wrong - it operates in DCM with an on time of 45 us, a discharge time of about 16 us and a dwell time of about 38 us. That's with my diode; yours isn't specified. – Andy aka Jun 18 at 21:03
• "But due to forward voltage drop of the diode we have to see Vs as Vin - 0.7V" - this is wrong. Diode voltage drop subtracts from the output, not the input. Where did you get this information from? – Bruce Abbott Jun 18 at 23:17
• @BruceAbbott Oh I just that that is how I am supposed to calculate it, due to the fact that Vin to the load will ultimately be the Vsupply - 0.7V, So just to clarify I should subtract 0.7V or add 0.7V from the Vout in my calculation? – tw.C4444 Jun 19 at 0:29
• The text says Vs is 1.5V - 0.7V = 0.8V. This is wrong. 0.7V should be added to the output voltage, ie. D = 1 - 1.5V/5.7V = 74%. In simulation (with corrected Gate drive) this ratio gives 5V output to the load when frequency is increased to 50kHz get continuous conduction. – Bruce Abbott Jun 19 at 5:28

• Also add that using zero valued trise/tfall doesn't mean that there is no rise and fall time, they just default to 0.1*min(T, T-Ton). So in this case it's 0.1*(100u-84u)=0.1*16u=1.6u, which not only it might not be what OP wants (large rise/fall transitions), but also increases Ton by 1.6u, or (trise+tfall)/2. – a concerned citizen Jun 18 at 20:22