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I have been working on a half bridge Tesla coil circuit. In process of building the Tesla coil, I have come across some problems.

First of all, I’m using the IR2110 gate driver IC to drive the MOSFETs. The logic supply voltage is around 5 V, the gate drive supply voltage is 12 V. The frequency is 450 kHz. The high input duty cycle is 60% and the low input duty cycle is 30%. The problem is while checking the gate to source voltage of the high side MOSFET I have found out that the voltage is only 4.5 V.

The low side MOSFET only receives 3.5 V considering the supply is constant 12 VDC.

enter image description here

There are some changes in components:

  1. The bootstraping capacitor is a 3.3 uF electrolytic capacitor paralleled with a 100 nF ceramic cap.
  2. The diodes D1, D2 and D3 are FR207.
  3. Q1 and Q2 are IRF540N N-channel 100 V MOSFETs.

For the inverting and non-inverting signals I used the 74HC14 hex inverter to the signal high and low for the IR2110 hin and lin. I don’t know what is causing the problem.

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    \$\begingroup\$ What DC voltage do you measure across bootstrap capacitor C1? I would remove the large (IRF540) MOSFETs and then connect OUT directly to Ground. Apply the input signal. Then at HO and LO there should be a 12 V signals (HO about 11 V), are there? If not, your IR2110 might be broken. \$\endgroup\$
    – Bimpelrekkie
    May 31, 2021 at 15:06
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    \$\begingroup\$ At 450kHz is miracle that you even get out something. \$\endgroup\$
    – Marko Buršič
    May 31, 2021 at 15:50
  • \$\begingroup\$ Most likely you have shootthru from the Schmitt drivers and slew rate affecting delays going into the IR2110. Measure the crossover delays at each stage and record in your question. The 1N4xxx is about 2 Ohms and with Rg=10 and Ciss being 2nF results in an approximate skew to avoid output stage shootthru of about 80ns. Use coil spring only on a 10:1 probe with no tip nor gnd clip to paired test points next to target. You may need to change some RC parts or the Schmitt driver to get the proper timing and thus obtain the correct boost voltage. \$\endgroup\$
    – Tony Stewart EE75
    May 31, 2021 at 17:10
  • \$\begingroup\$ How are you measuring Vgs? \$\endgroup\$
    – user16324
    May 31, 2021 at 18:53
  • \$\begingroup\$ Okey i will try to remove the mosfet and measure the voltage .and i will change the 74hc14 hex inverter as andy suggested \$\endgroup\$
    – Mr. Infinite
    May 31, 2021 at 23:36

1 Answer 1

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the diode D1,D2 and D3 is FR207

That is a significant problem. They need to be fast recovery diodes and not sloppy standard recovery diodes: -

enter image description here

If your switching frequency is 450 kHz (a period of 2.222 us) then those diodes are conducting in reverse for a significant time and eating the energy of your circuit. The UF4007 on the other hand has a reverse recovery time maximum of 75 ns i.e. about 7 times better than an FR207. There are reasons why fast diodes are used.

There may be other problems such as not having an accurately drawn schematic and relying on text to modify the components shown - which of course makes me suspicious that you are out of your depth. Or this: -

for the inverting and non-inverting signals I used the 74HC14 hex inverter to the signal high and low for the IR2110 hin and lin

Depending on what you have done here you may get significant shoot-through. You don't want any possibility of overlap between high states for HIN and LIN. Consider using something like this to reduce that unwanted situation: -

enter image description here

Picture taken from here and here.

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  • \$\begingroup\$ Okey i will change the diodes to uf4007 use the nor/and gates with schimmit trigger function \$\endgroup\$
    – Mr. Infinite
    Jun 1, 2021 at 5:43
  • \$\begingroup\$ @Mr.Infinite maybe you should take the tour to understand the motivation behind folk giving time to help. \$\endgroup\$
    – Andy aka
    Jun 1, 2021 at 9:05
  • \$\begingroup\$ Andy aka-ive changed the diodes to uf4007 and the high output works perfect and upon testing i found out that my 74hc14 hex inverter is the culprit the transistors are on for some time,thus momentarily shorting the supply im going to change the circuit as you sugested and any sugestion for the capacitor and resistor value \$\endgroup\$
    – Mr. Infinite
    Jun 1, 2021 at 12:04
  • \$\begingroup\$ Yes sir i did took the tour as you mentioned \$\endgroup\$
    – Mr. Infinite
    Jun 2, 2021 at 1:57
  • \$\begingroup\$ R*C should produce a time constant that covers the potential overlap period. Maybe go for 25 ns - 100 ohms and 220 pF produces an RC time constant of 22 ns. \$\endgroup\$
    – Andy aka
    Jun 3, 2021 at 12:13

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