Since Martin from ctc-labs.de decided to close down his website, which was all written in German, I asked him for permission to translate and publish some of his content to keep it online and public for others to use.
So here is the translated article about his small and simple analog circuit that can be use to make a Tesla coil play music. Using just a op-amp and a 555 timer it is possible to recreate the effect from expensive MIDI modulators by instead just using a analog signal. This method is ofcause not as precise as with digitally microcontroller based MIDI interrupters.
The real-time current control (RTC) that can found in some IGBT modules is a protection against short circuits in f.ex. motor drives where they could have been used.
The conditions on which the RTC acts is however sharing area with using IGBT bricks in Tesla coils, as the RTC will never interact while operating the IGBT within its Safe Operating Area (SOA) there is still a risk that it will be activated when driving a IGBT hard in a DRSSTC where it could be used to switch currents many times its rating.
Below is a quote from a Powerex paper on how the RTC works and behaves. I added a few outlines and extrapolated the graph to show the typical 24 VDC gate drive in a DRSSTC.
 4.0 RTC Description and Behavior
F-Series IGBTs include an integrated real-time current control (RTC) circuit for protection against short circuits, which was originally developed for intelligent power modules (IPMs). The RTC is a separate chip wire-bonded directly to the IGBT die and mounted adjacent to it. During normal operation of the device, the RTC is effectively “transparent” to the gate driver. Its power supply is drawn from the main collector-emitter path of the IGBT, so it imposes no additional drain on the gate driver. The RTC is connected to a current mirror emitter on the trench IGBT chip. A simplified diagram of this is shown in Figure 3.
When the IGBT operates in a short circuit, the RTC detects the excessive current in the IGBT and reduces the gate-emitter voltage to limit the short-circuit current. The gate-emitter voltage is reduced to less than 12V, compared with the normal recommended value of 15V. The effect of gate-emitter voltage on short-circuit current is shown by Figure 4. It is important to note that the RTC acts only to limit short-circuit current; it does not switch off the IGBT. Therefore the gate driver circuit should be designed to ensure that the IGBT is turned off within 10µs of a short circuit occurring. The RTC limits the short circuit collector current to 2-4 times rated current, depending on the junction temperature of the IGBT and the short circuit di/dt.
The minimum trip threshold for the RTC is 2 times the rated current of the device and occurs at high Tj and high di/dt. Therefore operation of the IGBT within its normal switching SOA is unaffected by the presence of the RTC
In the following video I show and explain where to locate the RTC circuit and how to disable it with a simple tool like tweezers. Side cutters can also be used but it will make a bigger mess and ruin more of the protective goop that surrounds the die and bonding wires.
After cutting out the bonding wires to the RTC circuit of the CM600DU-24FA IGBT bricks, which we thought could be one of the reasons that we were not able to trip the 1500 A OCD setting, we had a short test run to witness performance. I will do a video with more details of the real-time current control removal later.
While it might have limited the operation a little bit, it was nowhere near hindering performance, this coil is just so high impedance that it runs long on-times instead of high peak currents.
Fed with 3×400 VAC through a variac resulted in a 0.6 power factor. After roughly 8-10 test runs at up to 2 minutes, with peak power consumption hitting 14 kW at 500 BPS, 200uS, the total power consumption over all the tests was 0.281 kW/h, 0.331 kVAr/h and 0.438 kVA/h.
First video shows the coil running 120-500 BPS at somewhere around 200 uS on-time. Peak power consumption from the 3×400 VAC supply was around 14 kW. Sparks are 3 meters to ground and somewhat shorter to the ladder.
Second and third video show tests with a static load, peaking at about 10-14 kW depending on MIDI or interrupter is used.
These are highly modular cable TV amplifiers, they are set up by using a wide range of different insert cards with different frequency ranges or options. These are 38 dB amplifiers in the range from 47 to 862 MHz.
This particular amplifier is set up for 862 MHz, 42 channels and has a return path amplifier for keeping signal strength on the line good. The line equalizer is used to adjust for how close to the community amplifier the house is located, the further away, the less attenuation is needed.
These small amplifiers are used in houses where it is not practical to use a receiving antenna to get the signal from the broadcast headend transmitter. They are called a “service drop”
Instead CATV is used, short for community antenna TV, a large receiving antenna is used, a cable connection runs out to every house in the neighborhood and each house has one of these amplifiers. The return path amplifier can also send some of the signal back into the line to keep the signal good enough for the next house.
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This is an obsolete Kathrein XPol 2-port single band panel antenna. The 2 ports means that it actually has 2 antennas in the one unit. There is a main and a diversity antenna (90° polarized to each other) for 1710 – 2200 MHz (1800-2100 MHz mobile bands).
Newer antennas now have to allow for 700 LTE, 850 UMTS, 900 GSM and UMTS, 1800 LTE/GSM, 2100 UMTS and 2300 LTE so they have considerably more different antennas inside of them.
Each of the two antennas consists of a co-phased stacked array of dipoles. There is a total of 8 dipole pairs per antenna.
The antenna housing also includes a RET (Remote Electrical Tilt) which allows adjusting the direction of the electromagnetic lobe without climbing the tower or even moving the panel. By using a phase shifter located on the backside, the lower elements are phase delayed to electrically drop the front lobe down, without physically tilting the panel.
The phase shifters are actuated via the white glass fiber rod running up the side of the front of the antenna. The position of the arm inside the phase shifter is adjusted by turning the screw mechanism next to the connectors to move the rod.
Frequency bands: 700, 800, 850, 900, 1800, 1900, 1700/2100, 2100, 2300 and 2600 MHz.
Maximum capacity: Up to 6+6+6 GSM or 4+4+4 WCDMA or 1+1+1 LTE at 20 MHz or flexible combination of the above technologies in concurrent mode.
Multi-radio configuration: 1 Flexi 3-sector RF module + 1 system module for GSM/EDGE + 1 system module for WCDMA/HSPA and LTE. Remote Radio Head (RRH) solution also supported.
RF power amplifier technology: Multicarrier power amplifier (multi-standard)
Height x width x depth: 133 x 447 x 560 mm per module, indoors and outdoors. Fits in any 19” rack.
Weight: 25 kg per module
Operating temperature range: -35 °C to +55 °C
Power supply: 40.5 – 57 VDC, 184 – 276 VAC with power module
Typical power consumption: 790W for combined GSM and WCDMA site
Output power: 240 W per RF module or 40 W + 40W per Remote Radio Head (RRH)