# Universal Driver 2.1b

Some of this content is originally created by Steve Ward (stevehv.4hv.org) and is re-posted with his permission.

Steve Wards work with phase lead compensated drivers is most likely based off the work that Finn Hammer did on his driver modifications called the “Prediktor” that was a DRSSTC driver with phase lead.

The content of the folder stevehv.4hv.org/stevehv/lead_comp/ did not contain much written information, except the quotes below here with some details on the circuit. The pictures are from Steve, but the descriptions of them is the interpretation of Mads Barnkob.

It is recommended to read the article on the Universal Driver 1.3b to understand how the driver works and the changes from 1.3b to 2.1b will not seem to radical afterwards.

26th October 2009

Steve Ward built and tested the universal driver 2 with phase lead on his “DRSSTC Magnifier – Mark I” Created 4/15/05: http://www.stevehv.4hv.org/DRSSTCmag1.htm

The first tests was done on an unknown IGBT, and not the magnifier system above. Green is primary circuit current and light blue is inverter output voltage. Yellow is presumably gate drive signal.

For the tests that are known to be done on a CM300 IGBT brick, on the magnifier system, the following collection of oscilloscope screenshots was available. Green is primary circuit current and yellow is inverter output voltage.

26th March 2011

R26 added in series with C33 because when it was only C33 the peak voltage of the positive feedback (hysteresis)
was outside the save range for the comparator inputs. R26 and C33 provide short positive feedback pulses which helps keep the comparator from self-oscillating.

R27 added across C5: There seemed to be some instability in start up, sometimes the TL3116 would start off with
output HI, sometimes output LOW. R27 restores proper bias to the comparator input by discharging the DC offset that may be left across C5. I picked 100k for R27, but perhaps values as low as 10K may be required, i would not suggest going lower than 10k.

Steve Ward, 26th March 2011

The files for the quoted text above is the old files called UD2_1 and is listed at the bottom of this article.

2nd September 2012

You need EAGLE by Cadsoft (google it) to look at the board and schematic. You can get a free version on the web.

This project was created before i knew the importance of linking a schematic and board file. These files are not linked, consequently errors do happen!

I changed some biasing resistors for the phase lead comparator, if you have referenced the older versions you might notice this.

Im not sure the parts list is 100% up to date, i had to make some mods to the design after i ordered everything.

C33 controls a “no switch” time after each output transition on the comparator. Originally i found C33 could be just 220pF, but recently using CM600DU-24NF modules with a loooong 1uS or so delay in switching, i found i had to boost C33 up to 2.2nF.
This provided a longer period where the comparator has high immunity to noise, and without this there was severe “glitching” where the IGBT switch noise caused the comparator to switch several times instead of once per half-cycle.

R11 R12 and C9 with IC4E form a pulse-width limiter that is frequency dependent. You can disable it by shorting out C9.

Steve Ward, 2nd September 2012

The files for the quoted text above is UD2_1revb files, which are the latest and those that you should use!

1st May 2013

This is pictures of a finished universal driver 2.1b as I made it for my own large Tesla coil called Kaizer DRSSTC 3.

Freewheeling driver

The /leadcomp/ folder also contained a folder called /UD freewheeling driver/ which contained schematic, PCB layout, Atmel microcontroller code and gerber files for a freewheeling driver add-on

Old files that should not be used, only listed for historical reference

# IGBT gate drive calculator

Published on: Feb 17, 2016. Updated: Dec 06, 2017.

To insure that we switch our IGBT fast enough to lessen losses, slow enough to avoid ringing and the drive circuitry is stable we have to calculate the power, current and peak currents in our drive circuit. Detailed explanation further down.

A much more detailed description will be available in the GDT / driver chapter of the DRSSTC design guide, here is only presented limited information needed to use the calculator.

The results are only valid and absolute minimum for a single gate, so if you have 4 IGBTs in a fullbridge, you need atleast 4 times the driving power available.

Adjust the gate resistor so that the gate drive peak current is lower or equal to the capabilities of your IGBT driver IC or circuit.

Switch between the input fields to automatically calculate the values.

 Gate charge of IGBT(IXGN60N60 example) nCoulomb Switching frequency Hz Vgate (on) Volt Vgate (off) Volt Gate resistor (ext) Ohm Gate resistor (int) Ohm Gate drive power needed Watt Gate drive current needed mA Gate drive peak current(*) mA DRSSTC specific See description below Optional: BPS Hz Optional: on-time in uS uS Gate drive power needed Watt Gate drive current needed mA

DRSSTC specific: optional BPS and on-time are DRSSTC specific for calculating a reduced power need at lower duty cycles. BPS is how many times a second the IGBT is turned on for the duration of the on-time, these two figures gives a average duty cycle.

### Mathematic used

When developing the power supply for the driver section it is important to know how much it has to deliver. The power needed to drive a IGBT gate is given by the energy needed to drive the gate and the frequency at which it should be driven. The energy needed is the gate charge(QC) times the difference between turn-on and turn-off voltages from the driver or GDT.

$P_{\mbox{gate drive}}=Q_{\mbox{Gate}}\cdot\left ( V_{\mbox{Gate(on)}}-V_{\mbox{Gate(off)}}\right )\cdot\mbox{f}_{switching}$

Enough current also has to be supplied to charge and discharge the input capacitances of the IGBT in order to switch the IGBT on and off. This calculated current is the minimum average output current of the driver output stage per channel:

$I_{gate}=I_{GE}+I_{GC}=Q_{Gate}\cdot\mbox{f}_{switching}$

If the gate peak current is increased, the turn-on and turn-off time will be shorter and the switching losses lessened. Switching faster has disadvantages too like ringing voltage on the gate that could result in overvoltage spikes from switching too fast across the internal stray inductance of the IGBT module. (*) A theoretical peak current can be easily calculated, the IGBTs internal gate resistor must be taken into account and the result is in practice lower as the internal stray inductance limits this theoretical value.

$I_{\mbox{gate peak}}=\dfrac{\left (V_{\mbox{Gate(on)}}-V_{\mbox{Gate(off)}}\right )}{\left (R_{\mbox{gate resistor external}}+R_{\mbox{gate resistor internal}}\right )}$

In the data sheet of an IGBT driver, a maximum peak current is given, as are the minimum values for the gate resistors. If both these maximum and minimum ratings are exceeded, the driver output may not be able to properly drive the IGBT.

# DRSSTC design guide

### Introduction to the guide

This is a guide that aims to explain a few in depth details and best practices that one should have in mind when designing and building a Dual Resonant Solid State Tesla Coil (DRSSTC).

It is not a complete instruction in how to make a entire DRSSTC system work, but food for thought and explanations on why some parts are chosen over others. The lessons learned over the years by other people who built Tesla coils have resulted in some parts being the only one used, just due to the fact that they were used by the original designer and proven to work good.

This guide should hopefully give you an insight to chose among a wider selection of parts for your DRSSTC and that could help on lowering the construction price and time spent looking for parts. The math and calculations used are simplified for practical use.

### Topics of the DRSSTC design guide

1. Rectifiers
2. Busbar and primary circuit
3. IGBTs
4. DC bus capacitor
5. PFC (20% done)
6. Snubber capacitor
7. MMC / tank capacitors
8. GDT / driver (20% done)
9. Secondary coil