Shorting coil gives back more power

[gyulasun]

....
The problem I'm getting is that the output of pin 3 is completely inverted from the output as measured at the MOSFET drain.

For example, if my input is PWM with 1% duty cycle and a specific frequency, on the drain of the MOSFET I see a 99% duty cycle wave at the same frequency.
.....

Hi,

This is normal, a grounded-source stage inverts its input at its output.

Solution is either you input the high duty cycle into the gate of the MOSFET when you wish low duty cycle at the drain as an output and vice versa,  OR you use an inverting type MOSFET driver between pin 3 of 555 and MOSFET gate as you intend.

Gyula

[Feynman]

@gyula

Okay , got it.   Does a P-channel MOSFET have the same inverting effect when driving the low side?   I know these are probably obvious questions , but I normally deal with microcontrollers and sensors.   This is my first time actually doing serious benching with MOSFETs.

I think I'll buy both kinds of drivers... I know I need non-inverting for my Boyce TPU replication.  I think I'm going to snag the UCC drivers he used in his HEXFET controller (UCC27322P's) .

[gyulasun]

@gyula

Okay , got it.   Does a P-channel MOSFET have the same inverting effect when driving the low side?   

I think I'll buy both kinds of drivers... I know I need non-inverting for my Boyce TPU replication.  I think I'm going to snag the UCC drivers he used in his HEXFET controller (UCC27322P's) .

Yes, a P-channel also has the same inverting effect when you control its gate with an input and use its drain as output.

The UCC27322P is a non-inverting driver indeed and the type UCC27321P is an inverting driver.  A similar pair is TC4421/TC4422, there are several others of course.

Gyula

[Feynman]

@yssuraxu

I read your post carefully, and it reminds me very much of what Rosemary Ainsle is discussing on her blog.

http://newlightondarkenergy.blogspot.com/

The circuit is designed to allow a secondary current flow that is induced from the collapsing fields of RL1 during the OFF period of the duty cycle as a result of counter electromotive force (CEMF). This reverse current path is enabled by the body diodes in the transistor MOSFETs (Q1). This allows a current flow that returns to the battery supply source to recharge it

[yssuraxu_697]

I read your post carefully, and it reminds me very much of what Rosemary Ainsle is discussing on her blog.

I am not familiar with Rosemary Ainsle work, will look at it. I guess that there are thousands of people over the world arriving at the very same conclusions, only each one from slightly different angle and background.

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