HH2 -- first cut

[Aziz]

Hello friends,

here is the lowcost PI MOSFET driver spice model circuit for all, who wish to experiment on this and find the issues rised from Carl. This model does not contain the improvements yet.
I have rebuilt the lost model again and put this here for download (good for backupping). Use the latest Linear Technology LTSpice IV software in "Alternate" mode (Tools/Control Panel/SPICE tab/Engine Solver: Alternate).

Happy finding...

Aziz

[porkluvr]

Hi Carl,

it seems, that nobody besides me is interested on your speed limitations. Aziz

I'm interested, but I'm relatively clueless. In trying to adapt the Aziz drive to a LM555 output, it occurs to me that the Deltapulse and the (original)Hammerhead have opposite drive logic. Why didn't I notice that before... duh.

Well, if this was easy then everybody would be doing it.

Let me spend a few more days bogged down in this small detail. Then maybe I'll get an inkling.
***************************
I've started with the DP transmitter and managed to get a complex waveform (1 long + 3, 4,or 5 short pulses). Now - if I can work this in and maybe come up with a blanking gate, then I'll eventually do some prospecting.

[barry]

Look forward to your findings aziz. Thanks for sharing.

[Aziz]

Hi friends,

the improvements addresses the following features:
- softer (slower) TX switch-on producing lower ripple noises in the electronics during switch-on, while keeping the fast switch-off feature

- faster switch-off achieving quicker the breakdown voltage of the MOSFET (fast dI/dt)
We can saturate (energize) the target with slightly smaller transmit pulse width. This will save battery power a little bit.

- driving higher Cin MOSFETs (input capacitance) or parallel stacked MOSFETs (for higher coil current flow or lowering the total Rds-on).

The common available integrated MOSFET drivers can not achieve the features above as they are optimized for both switch-on and off. The design proposal is a slight modification of the low-cost variant shown already above. The switching latency delay isn't important here. I will post the schematics soon until I am finished with the simulations.

Aziz

[Aziz]

Hi Carl,

it seems, that nobody besides me is interested on your speed limitations. At the moment, I am currently again on this topic and have some more improvements which addresses also the battery power efficiency.

I will post this as soon as I am finished with analysis.

Regards,
Aziz

[Carl-NC]

There is an obvious error in my schematic, R7 should not be there. Also, for fastest speed R8 & R15 should be zero.

But bipolar will still work just fine, as long as you pay attention to details. With R8 & R15 = 0, there are still 2 speed limitations in my driver circuit... what are they? Hint: Aziz's low-cost variant addresses one but not the other.

- Carl

[Aziz]

Forgot to mention: Pay attention to the pulse logic level! It is changed with the low cost variant (inverting totem pole gone). So the micro should give right logic levels.

Aziz

[Aziz]

Here is the low cost variant (initiated from Andy) with same switch-off behaviour expect the switch-off delay is extended about 0.5 µs.

The diode and the BJT is important to discharge the MOSFETs gate charge. This cannot be omitted. Switch-on isn't important and can be delayed and be slow for our purpose.

Aziz

[Andy_F]

I recently analysed the totem pole MOSFET driver of the HH. This can be optimized using small signal FET's (BS170/BS250)...

U14 And U15 in the offered scheme do not do anything (it can be removed). At the same time, in gate X7 it is necessary to put the resistor 10-20 Ohm (protection from latch).

By the way, diode U11 too does not carry out any useful function, only worsens switch (IRF740) characteristics in open state.

[Aziz]

MOSFET fast switch-off circuit proposal with FET's

Hi Carl,

I recently analysed the totem pole MOSFET driver of the HH. This can be optimized using small signal FET's (BS170/BS250). The proposed schematics below is optimized for fast switch-off. It improves the turn-off fall time and turn-off delay time compared to the BJT solution in HH.

The gate charge in the MOSFET IRF740 will be discharged through Q1 (2N2907). R40/R41 resistors can even be omitted.

The performance is almost equal to the standard fast switching MOSFET driver IC's.

Regards,
Aziz

[barry]

keeping a keen eye on this one. looking forward to the source code.

[ivconic]

I like what i see on this schematic, also i like the way pcb is projected.
So... only code we need to start making this. Looking forward.
Regards!

[Carl-NC]

Actually, I threw it in as a placeholder... I haven't researched low-cap diodes. The 4007 is probably fine.

- Carl

[1843]

Hi Carl

Why not to use a 1N4007 instead of 1N4004? The junction capacitance is about half...

[Carl-NC]

To my recollection, the Deltapulse does not use a PIC. In this design, the PIC controls the coil pulse & the sample timing. It is also possible to digitize the analog output and create a VCO audio using the PWM.

The source code will be in C, using the free Microchip C compiler. I did most of the work on this project last year, including the microcode, but never got it finished. When I switched jobs a few months ago I managed to lose the source code, I think it was on my Maxim laptop that I turned in. So I am starting over on that, but it shouldn't take long.

- Carl