BIPOLAR ALTERNATIVE TO H BRIDGE

[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.

[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.

[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.

[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.

[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 ).

[moodz]

Very witty circuit. ML can only wish they had come up with this, instead their bipolar patent is overly complicated.

Could you shortly comment on how this circuit achieves power efficiency?

In the simulation it seems that the maximum coil current is drawn continuously from the power supply.

I guess the power savings happen because the coil is never discharged, so the energy in the coil remains constant at all times rather than being damped and recharged as in a regular PI. Is this correct?

Anyway it seems the bipolar variant is still a power hog relative to normal PI because there's no pause between the pulses but a continuous high power pulse train.

Yes you are correct the max current is always drawn however the circuit appears to work from very low voltages so the power draw can be under 1 watt with say a 1 or 2 volt supply with reasonable current transitions in the coil.

So when i said it is power efficient I meant it has good power performance compared to more conventional PI circuits.

My actual physical test circuit drew 250 ma from the 1.24 volt supply with 500 volt flybacks .... I only used junkbox fets from my workbench.

[moodz]

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

https://www.geotech1.com/forums/sho

wthread.php?22845-Great-ideas-for-PI-design&p=211691#post211691

https://www.geotech1.com/forums/attachment.php?attachmentid=23210&d=1360192454

there is a post on deemons control method there ... its good work but quite complex.

The first "constant current" square wave I ever saw was patented by berringer back in the 80's i think. It used a h bridge made from scrs.

Deemon has a feedback control circuit to adjust the "tilt" of the current waveforms

I was interested in a circuit that required no feedback control was simple and consumed minimum power eg potentially runs of a single 1.5 volt cell.

moodz.

[green]

For any square wave current driver that's the best you can possibly do. So Paul's approach is close to ideal. I previously said "consider past threads on energy recovery" because those threads focused on kickstart circuits (I couldn't think of the term "kickstart" yesterday) and that is the key element in this circuit.

Edit:



Not so fast... in Paul's sim he shows 800mA p-p current swing, with only a 1.24V power supply! That's a 1W transmitter... AND... it's independent of pulse frequency. Most PI transmitters run at several watts.

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?

[Tinkerer]

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

https://www.geotech1.com/forums/sho

wthread.php?22845-Great-ideas-for-PI-design&p=211691#post211691

[Carl-NC]

In the simulation it seems that the maximum coil current is drawn continuously from the power supply.

For any square wave current driver that's the best you can possibly do. So Paul's approach is close to ideal. I previously said "consider past threads on energy recovery" because those threads focused on kickstart circuits (I couldn't think of the term "kickstart" yesterday) and that is the key element in this circuit.

Edit:

Anyway it seems the bipolar variant is still a power hog relative to normal PI

Not so fast... in Paul's sim he shows 800mA p-p current swing, with only a 1.24V power supply! That's a 1W transmitter... AND... it's independent of pulse frequency. Most PI transmitters run at several watts.