Itsu and all,
Here is another optional test that we will re-visit which uses two paralleled mosfets and in this case it is the 14N05L's. See the attached schematic below. If you were to substitute the mosfets with say Schottky diodes, the maximum voltage across C1 with a load would be slightly less than 1/2 the supply voltage at a 50% duty cycle. Here however, we see a voltage across C1 with the load that is greater than 1/2 the supply due to the parametric pumping of the mosfet's non-linear capacitance. This is the simplest configuration that demonstrates the principle I can think of at the moment. This should be easy to replicate by anyone who desires and the results will vary with the devices and the component values used.
The tuning is easy. Apply a frequency that is high enough to generate a voltage that is less than 1/2 the supply across C1 with the load. Then, carefully lower the frequency until the point is reached where the C1 voltage increases to be >1/2 the supply and then suddenly jumps to a higher stable value. Now raise the frequency until the voltage across C1 again drops to <1/2 the supply and lower the frequency again until you have the maximum output across C1 without the sudden jump. IOW, we will now be operating in Mode1 not Mode2. This may require several tries to find the "sweet" spot.
The load resistance can be found by experimentation if one does not the ability to do a 100ms or equivalent sweep as it is not that critical.
In the scope shot we see a C1 voltage of 22.28v with the 7.451 ohm load for a Pout = 22.28^2/7451 = 66.62mw. Pin is seen to be 46.67mw for a COP = 66.62/46.67 = 1.43. I used my current probe for this test but the results should be the same if a CSR is used. Note the mean current value as it alone does not account for the load's output voltage. The balance of output energy is supplied by the AC parametric pumping.
What I like about this circuit is the possibility of looping by using a low power highly efficient boost converter to build the supply voltage from the voltage across C1 with the load although it would help if the power levels were higher IMO.
Pm
Hmmm, PM, i tried the above circuit, using 40V on the ixdd614pi, L1 is the 322uH one, 2x 14N05L with schottky diodes (bat42) C1 = 3.3uF Rload is 8.14K R1 = 10 Ohm optional csr. Screenshot shows input calculated in red (from yellow x green) = 17.17mW output across 8140 Ohm resistor is 23.55V meaning output power (23.55² / 8140) = 68mW. Purple is voltage across 10 Ohm csr, so 1.25mA so confirms the green current probe value of 1.128mA. Went from 650Khz slowly down to 638Khz after which the voltage across the load resistor switch to 33V or so. So 638Khz gave the 23.55V across the Rload. Tried severall times, and got similar results allthough the current (green) is not stable over long periods. 17.17mW input, 68mW output, COP = 3.96. I did not calculate the power loss across the 10 Ohm csr. Itsu
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Topic: Parametric Charging (Read 61278 times)
