Claimed OU circuit of Rosemary Ainslie

[poynt99]

1) All claims the spikes will damage the mosfet and that the ringing should be stopped (FACT - this mosfet IRFPG50 is designed EXACTLY for this kind of application)

2) All claims that the spike would be too small to be significant (FACT - on a decent circuit the voltage is 4 times the input voltage, it charges batteries or caps - it is VERY significant)

3) All claims that when the mosfet is off, the battery cannot conduct and therefore won't receive a charge (FACT - the diode in the mosfet allows just this exact current conduction as it is designed to do this!)

1) You are correct in that a "ruggedized" (i.e. avalanche rated) MOSFET can take the hammering. However, it's not quite correct to state that they were "designed" to be used this way. In fact using a MOSFET as an avalanche device is not very efficient. There are better devices (such as the diode version) that should be used for avalanche applications, such as pulse generators and voltage suppressors.

In general, active devices such as MOSFETs, BJT's etc, aren't "designed" for any specific application (yes there are exceptions). If for example you know that the switch in your application will experience periodic pulses exceeding it's rated VDS, then yes it would be a very wise choice to use an avalanche-rated MOSFET for this application.

2) The energy in the kickback pulse through the flyback diode (causing current to go back into the coil or external battery) is equal to the energy stored in the inductor prior to the switch opening (turning OFF), minus the energy loss in the inductor's resistor (10 Ohms) and the energy loss in the flyback diode itself. The fact that the voltage is higher than V+  is obviously good if we want to charge a battery, but the voltage itself is not an indication of the energy available in that pulse. When you load that pulse down (as you do when charging a battery), the voltage will drop quite a lot.

3) I have already identified the possible current paths through and around the MOSFET when it is OFF. These are via capacitances in and around the MOSFET. In the case where the flyback diode is removed, and there are large kickback spikes hitting the MOSFET, then the voltage would have to be in excess of 1000V (for the IRFPG50) to cause reverse breakdown of the body diode (actually a NPN transistor) and thus allow conduction current for the battery. From what I've seen in all the tests done by Aaron and TK (and my sims) the kickback voltage is well below 1000V.

.99

[WilbyInebriated]

The "wilby" bot is just a troll. The recent posts are exactly representative of his usual posts. You may safely put him on your "ignore" list as he gets stuck  on single topics and will go on wasting pages and pages on them.

like requesting that you use the specified components? how did that turn out for you again? oh yeah you were wrong, and i was right. furthermore it shows that you care little about correct and proper methodology...

[poynt99]

This one came first:

When I brought up one wire charging. You and MH both were quick to jump on the false idea that all one wire charging must be AC.

In either case, after that soap opera on that subject, you and MH were basically pointing out the false claim that "there is no ac on this circuit" so it is irrelevant.

But it turns out with the diode in the mosfet allowing reverse current, there is ABSOLUTELY AC in this circuit plain and simple.

I'm still trying to put together exactly when where and how I said or implied anything regarding AC present or not present in the RA circuit.

The only mechanisms by which current can pass through or around the MOSFET D-S, are by parasitic capacitances, channel capacitance, body diode capacitance, and by avalanche breakdown of the body diode. In order to break down that body diode in the reverse direction, it's going to need to see at least 1000V from D-S. Now this is not even going to happen if the flyback diode is present across the coil. The Drain to Source voltage is always positive in this circuit, which means the body diode is never forward biased. So this only leaves the capacitances in and around the MOSFET, and they do allow spikes to reach ground potential and hence a spiky reverse current, so in that sense there is AC current in this circuit. The vast majority of the current however (about 99%) is pulsed-DC current.

Aaron's (and most everyone else's) circuit probably exhibits much more reverse spiking due to the higher inductance as compared to the resistor used in the RA circuit.

.99

[Hoppy]

Aaron has agreed with Harvey on Energetic forum who has said that a circuit having a COP > 17 is a bit different than saying the circuit produces more energy than it consumes. Who would like to come forward and define exactly what 'a bit different' actually means in this context?

Hoppy

[fuzzytomcat]

1) You are correct in that a "ruggedized" (i.e. avalanche rated) MOSFET can take the hammering. However, it's not quite correct to state that they were "designed" to be used this way. In fact using a MOSFET as an avalanche device is not very efficient. There are better devices (such as the diode version) that should be used for avalanche applications, such as pulse generators and voltage suppressors.

In general, active devices such as MOSFETs, BJT's etc, aren't "designed" for any specific application (yes there are exceptions). If for example you know that the switch in your application will experience periodic pulses exceeding it's rated VDS, then yes it would be a very wise choice to use an avalanche-rated MOSFET for this application.

2) The energy in the kickback pulse through the flyback diode (causing current to go back into the coil or external battery) is equal to the energy stored in the inductor prior to the switch opening (turning OFF), minus the energy loss in the inductor's resistor (10 Ohms) and the energy loss in the flyback diode itself. The fact that the voltage is higher than V+  is obviously good if we want to charge a battery, but the voltage itself is not an indication of the energy available in that pulse. When you load that pulse down (as you do when charging a battery), the voltage will drop quite a lot.

3) I have already identified the possible current paths through and around the MOSFET when it is OFF. These are via capacitances in and around the MOSFET. In the case where the flyback diode is removed, and there are large kickback spikes hitting the MOSFET, then the voltage would have to be in excess of 1000V (for the IRFPG50) to cause reverse breakdown of the body diode (actually a NPN transistor) and thus allow conduction current for the battery. From what I've seen in all the tests done by Aaron and TK (and my sims) the kickback voltage is well below 1000V.

.99

Hi poynt99,

I'm not aware that you may have seen this from "International Rectifier" Application Note AN-1005 - Power MOSFET Avalanche Design Guidelines this has some good information everyone might like.

http://application-notes.digchip.com/014/14-15377.pdf

Also another good one from "Advance Power Technology"  Understanding the Differences Between Standard Mosfet's and Avalanche Energy Rated Mosfet's

http://www.nalanda.nitc.ac.in/industry/appnotes/APT/APT9402.pdf

Regards,
Fuzzy