12v to 18v DC Converter by LT1170
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The supply works by shorting the inductor across the 12 volts through the regulator. This stores energy in the inductor. When the internal switch in the LT1170 goes off, the inductor is placed in series with the 12 volts, adding to it. This voltage pulse is stored in the output capacitor and smooths the output. The diode is used to keep the output capacitor from discharging during switching.
It contains a 100 khz current based oscilator whose output is controled by feedback provided by R1 and R2. These make a voltage divider such that at the wanted output voltage there is 1.24V at the junction of these two resistors. They carry only 1 ma of current and are there to provide a reference voltage to an op amp in the IC. As you draw more current from the output the total voltage would drop as would the 1.24v reference signal. The op amp feeds this to the oscillator telling it to provide more current to fill the demand. This brings the voltage up to 1.24v reference or 18 output. Reduce the load and the opposite happens.
Part list:
L1 inductor 100 µH Hurricane HL-AK210Q
Coiltronics PL52E-100-5000 must handle at least 3 amps
C1 capacitor 56 µf
33 µf Nichicon x1 UPL1E330MAH 25V ESR=.800 Irms=.155A
C2 capacitor 330 µf
390 µf Nichicon x2 UPL1V391MPH 35V ESR=.028 Irms=2.440A
Cc capacitor 1 µf
LT IC switching regulator Linear Technologies LT1170CT data sheet
D1 Schottky 5A Motorola 1N5824
1N5821 Any high speed diode that can handle the power would do. Schottky type is best but not absolutely required.
R1 resistor 16.7k; 1% R1 and R2 set the output voltage; The ratio of R1 to R2 should be 13.5 to 1.
R2 resistor 1.24k; 1%
Rc resistor 1k
Read More Source:
http://obs.nineplanets.org/meade/1812/1812.html
Thank you.
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