BIPOLAR ALTERNATIVE TO H BRIDGE

[moodz]

Clever circuit. I tried sim from reply8. I needed to add a 1.24V battery to get it to work. I get over 1600mA swing, what am I doing different?

I think the total series R in will affect peak currents. I think I had a 0.1 ohm supply impedance and the coil was 0.2 ohm and then the mosfet model RDS ON may vary in your copy of spice.

The peak flyback and rise time are affected by the value of C across the coil ( inclusive of mosfet capacitance ).

[Tinkerer]

Clever circuit. I tried sim from reply8. I needed to add a 1.24V battery to get it to work. I get over 1600mA swing, what am I doing different?

Add your resistance and capacitance to the TX coil.

[green]

Add your resistance and capacitance to the TX coil.

Not sure what you mean. I assumed .2 ohms and 100p was coil resistance and capacitance.

[Carl-NC]

Deemon is the inventor of this method. We should give him credit for it.

Deemon came up with one solution to CCPI. At the same time, White's was working on a different solution. And, obviously, Minelab was, too. Paul's solution is the simplest I've ever seen, others require either complex self-regenerating kickstart circuits or a high-voltage power supply.

I recall that Eric Foster told me the concept of CCPI dates back to the 1960s or thereabout. Someone wrote about it in a journal paper I think, maybe Eric can elaborate.

[Carl-NC]

Clever circuit. I tried sim from reply8. I needed to add a 1.24V battery to get it to work. I get over 1600mA swing, what am I doing different?

This circuit will be sensitive to components and temperature. The FET resistances and body diode characteristics will matter so you may be looking at differences in Spice models. Drop in e.g. IRF740s and see what happens. Ideally you would add a current-monitoring resistor to the low-side switches and throttle the supply voltage to achieve a particular current.

[green]

Been playing with circuit in spice. Spice doesn't avalanche the Mosets so I added back to back diodes across the coil to avalanche at 600V. Peak current not flat if avalanches. Increasing coil resistance causes a problem also. Does anyone know how flat the current needs to be(Amps/second)?

[Qiaozhi]

Been playing with circuit in spice. Spice doesn't avalanche the Mosets so I added back to back diodes across the coil to avalanche at 600V. Peak current not flat if avalanches. Increasing coil resistance causes a problem also. Does anyone know how flat the current needs to be(Amps/second)?

Teleno posted some mosfet models here -> https://www.geotech1.com/forums/show...656#post226656
that handle the avalanche mode correctly.

[Tinkerer]

Not sure what you mean. I assumed .2 ohms and 100p was coil resistance and capacitance.

I meant: use the resistance and capacitance of your own coil, including cable and shield. This circuit is very sensitive to capacitance and resistance.

[green]

I meant: use the resistance and capacitance of your own coil, including cable and shield. This circuit is very sensitive to capacitance and resistance.

Thanks

Does anyone know how flat the current needs to be(Amps/second)? I'm guessing maybe 3A/second.

[Teleno]

This circuit will be sensitive to components and temperature. The FET resistances and body diode characteristics will matter so you may be looking at differences in Spice models. Drop in e.g. IRF740s and see what happens. Ideally you would add a current-monitoring resistor to the low-side switches and throttle the supply voltage to achieve a particular current.

Larger (external) source resistance and voltage can reduce those variations at the cost of a poorer efficiency.

Thanks

Does anyone know how flat the current needs to be(Amps/second)? I'm guessing maybe 3A/second.

A ramp will induce an offset in the receiver. How much your circuit tolerates would depend on the noise level and the sensitivity of the amplifier.

In my simulations 0.2A/s is about right.

[mickstv]

Maybe a constant current source, similar to this circuit

[mickstv]

Whoops wrong circuit last post. I haven't tested this LTspice is all new to me. I normally breadboard circuits but I don't have the workbench setup....

[moodz]

...the coil resistance in the breadboard circuit is just over 1 ohm, with a 1.24 volt power supply and the pulse rate slowed to 1 pulse per second the "ramp" or "tilt" on the waveform was under 1 ma / second.
Once the coil reaches "terminal" current according to ohms law the only thing that can vary current will be power supply fluctuation or resistance change due to thermals in the FETs etc.
Power consumption was 600 milliwatt for a 800 ma current excursion at 500 volt peak flyback.

[green]

...the coil resistance in the breadboard circuit is just over 1 ohm, with a 1.24 volt power supply and the pulse rate slowed to 1 pulse per second the "ramp" or "tilt" on the waveform was under 1 ma / second.
Once the coil reaches "terminal" current according to ohms law the only thing that can vary current will be power supply fluctuation or resistance change due to thermals in the FETs etc.
Power consumption was 600 milliwatt for a 800 ma current excursion at 500 volt peak flyback.

Some thoughts, maybe doesn't make sense or not correct. Current ramp or tilt causes a X signal. Important when sampling signal.
Tried a couple things with spice. 1A change with polar circuit. Square wave amplitude adjusted for 3.3A/second. R signal 10,000 times greater than X signal. Maybe allowable ramp could be greater than 3.3A/second?

[green]

The polar drive circuit is interesting, would like to try it. My Tx coil resistance is closer to 3 ohms. Tried a spice circuit with Tx=3 ohms and all MOSFETS STW11MN80. Get about 18A/sec ramp at switch point. Is 18A/sec acceptable? Is there a way to modify the circuit to make the ramp less steep?