Lilly Wave vs. single ended

I’m busy building a simple PIC based estim boxie. My solution uses a single MOSFET and an audio transformer I found in my junk box. It gives excellent results and I will make a separate topic for that. But looking at the MK312 I notice its push-pull design that needs no less than three MOSFETs. Looking at the scope pictures here on this board it is very clear how that works and that it emulates the Lilly Wave. Since my estim boxie is purely intended as punitive device I don’t think that it’s a real issue. Lacking any experience with estim devices I’m wondering how bad that is.

It not so bad because many electrosex units have unipolar wave (btw. i dont see any of medical ems unit without bipolar wave shape…)


unipolar wave not so safe… because of some sort of galvanization (there are medical devices for this purpose but ems is not). so) in short term with low voltages it may be ok. but long sessions + high intensity may be dangerous… (each person have his own resistance, capacitance and many other parameters. so here all things is vary but…)

p.s. about punishment:
©. many shock collars have bipolar wave

Bipolar pulses are my religion :wink: The Estim 2B (unipolar) is so harsh and the 312 so smooth. They also don’t cause any lingering sensations.

My shock collar is still in transit from China. It may take a while for it to appear on my doorstep… The shock collar seems to be unipolar but specially tuned (with a capacitor) so that the OFF pulse is almost identical to the ON pulse. But with a varying duty cycle (which my boxie has) that is impossible to achieve. But since the pulse is output from a transformer the net DC level will be zero. A transformer cannot transfer DC. Clearly more experimenting is called for!

you can’t create DC from transformer, but you can create any voltage because load have resistance and capacitance. just create equivalent schematics in LTspice and look

@mer: No, you can’t. LTSpice is a great tool, especially for this but I just realize that I’m barking up the wrong tree. The physical phenomenon that I use is the flyback pulse that gets more powerful the longer my MOSFET stays on. That means that I cannot create a Lilly Wave even if I wanted to because the amplitude stays constant. To illustrate: this is a short pulse:

On the left you see the forward pulse as the MOSFET conducts. When it switches off, there is a flyback pulse with about the same amplitude as the forward pulse, in this case 70 V. Horizontal is 50 µs/div.

But when I set my boxie to max you get this:

My forward pulse is now much longer but still 70 volts (the vertical gain has been reduced to 50 V/div). The flyback pulse is now off screen, maybe 300 V. The first pulse is almost unnoticable, the second one is a sharp jab. Still, there is no DC because the area under both pulses is about the same. Oh, and note the droop in the forward pulse. This is the core of my small transformer saturating…

Boxies like the MK312 use only the forward pulse and you can only change the amplitude by modulating the supply voltage into the transformer. I’m not familiar with the hardware of this box but it looks like that is done by the P-MOSFETs driven from the opamps. Took me a while to figure that out because there is no feedback from the P-FETs to the opamps.

schematics here
page 5

several thoughts:

  • there may be no DC, but we need to look at average voltage. and it not zero… (in almost all cases) you can balance your schematics to create “bipolar” wave. but it possible only in a narrow corridor of resistance and voltage on transformer values
  • there is no current or voltage feedback. so you cant stabilize the system. Resistance of the skin is very vary from like 100k to 1-2m and it for dry skin. (much less for mucous membranes or piercing)
  • second part of impulse - because of Self-inductance (I hope I spelled the term correctly). mosfet injects energy to transformer. transformer “send” energy to 2nd coil. we see 1st signal. then mosfet off and coil started to send self-inductance impulse (sorry for simplifying things). this impulse usually have less time than primary impulse and more (or much more) voltage. for safety reason you need to shortcut transformer and self-inductance current go thru mosfet. and you will not have this part of signal.
  • safety (from
  • with a load resistance of 500 Ω, the output current shall not exceed
    • 80 mA at DC
    • 50 mA below 400 Hz pulse frequency
    • 80 mA at 400–1500 Hz
    • 100 mA above 1500 Hz
  • for pulse durations less than 0.1 s, the pulse energy into a 500 Ω load shall not exceed 300 mJ per pulse, for longer pulses the above DC limit applies
  • the output shall not exceed a peak voltage of 500 V when measured under open-circuit condition

BTW. as i mentioned any person’s body have his own parameters so maybe for many people this type of signal is ok. we dont trying to create a medical EMS device. medical device can have only 1 way of impulse generation: bipolar.

about et312
some internal signals here

it have calibration sequence with feedback by current

My goal is not to create a Lilly wave. This device is intended as punitive device and as such it works fine. The output has no DC because it’s a transformer. A transformer is physically unable to transfer DC. If you take the area above the zero line it would be equal to the area below it. Only because it takes some time for the energy to dissipate it looks like there is a DC component. If the pulse was generated by just a coil there would have been DC on the terminals.

As for safety, the little transformer can generate nowhere near the levels quoted. 50 mA into 500 ohms is more than 1 W! I will perform that test at the highest level it can produce. The level of 500 V may be a challenge though. Having said that, I now have a load resistor across the output (68k) that should take care of that.

I agree with your BTW. I am not trying to create a medical device. I also studied the MK312 schematics and now I understand the concept. Not sure whether the current feedback works as advertized but I guess it does. This depends on the firmware as well and I don’t have that woohoo…

i saw resistor like 33K in the medical devices (and dont in the esims…) looks like its good for safety.

MK312 schematics is a bit old. it was created many years ago. and i personally dont like the way it works. now we have several estims that much better than mk312.

now im trying to create something like medical ems with small set of not outdated components. and because of that im collecting things about that.

I’m trying to simulate an output stage to generate a Lilly wave:
floating_h-bridge.txt (2.6 KB)

Change extension to asc then open in LTSpice. The resistor is the load. Single primary (not center tapped) transformer. Have some gate drive issues…