# DC/DC converter in LTspice

Discussion in 'General Electronics Chat' started by strantor, Apr 30, 2012.

1. ### strantor Thread Starter AAC Fanatic!

Oct 3, 2010
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I want to simulate my DC/DC converter in LTspice. it is 12Vin, 1000V out, 1.5W. The way it behaves is that it will output 1000V into a high resistance load, but when the resistance gets below a certain number, the output voltage starts to drop, as the wattage is exceeded. I calculate that the converter should put out 1000V into a 666,666Ω load; anything below that, and the voltage should trail off linearly to zero as resistance goes down to zero (I think).

I have not been able to figure out how to do this. I input a series resistance of 666,666Ω but that results in serious loading which is not right.

BTW this is the part.

2. ### crutschow Expert

Mar 14, 2008
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Post your LTspice simulation and .asc file.

3. ### strantor Thread Starter AAC Fanatic!

Oct 3, 2010
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I put in 666,666Ω series resistance into the voltage source and it causes the output voltage to drop to 600V when I introduce a 1MΩ resistor to the circuit. This is the correct thing to happen if the voltage supply really had 600Kohm series resistance but I need it to output 1000V is there is a 1MΩ resistor in the circuit.

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4. ### Ron H AAC Fanatic!

Apr 14, 2005
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Your description of your DC-DC converter is that of a voltage regulator with current (or power) limiting. You simulation is simply a battery with a series resistor. That is not a voltage regulator.
Here is a simulation of an ideal 1000V source with 1.5mA current limiting.

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• ###### 1kV source with current limiting.asc
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5. ### crutschow Expert

Mar 14, 2008
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As Ron stated, a fixed resistor in series with a power supply is not the type of current limiter they use in a power supply. It is an active circuit that performs the function of Ron's ideal circuit.

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6. ### strantor Thread Starter AAC Fanatic!

Oct 3, 2010
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That's great, works just like I want. Thank you.