■ FIGURE 3
Ton + Toff = .05 mS = 50uS max = Ton +
Ton(1.083)=50uS, Ton = 46 uS
Ct = 4* 10-5* 46 uS = 18. 5 nF ( 18 or 20 nF
is close enough)
Io = 10V/9.5 ohms = 1A = Ipk with no filter
cap (we don’t need to filter the output)
Ipk = 2*Io max is arbitrary.
Lmin = ((Vi-Vsat-Vo)/Ipk)*Ton = 32uH
I would like the current to be continuous, so
won’t use the minimum inductance.
Simulation indicates that 200 uH will give
continuous current at low power ( 10 uS Ton).
Rsc = 0.33 ohms, 1/2 watt
You will be checking the
temperature with your RTD but for
temperature feedback, I will use
LM35 — a Celsius temperature
sensor. The output is 10 mV per deg
C, so the output will be 1.5V at 150
deg C. I want to be able to read the
set temperature with a digital
voltmeter, so I can’t use the internal
reference of 1.25V. The LM4040-2
( 2.048 volt reference) will be able to
provide 1.5 volts to set the 150 deg
C temperature (see Figure 3).