0
\$\begingroup\$

I'm trying to make a 300V H Bridge for an electrostimulator. The circuitry is as posted here, using MOSFET P20NM60GP:

Schematics

When I tested it with low voltage supply (just for the sake of safe testing), and a 15 Watts 1kOhm resistor I get the output waveform I desire, that is:

Output in low voltage

However, when I try to change the supply voltage to 300V (galvanically isolated, safety first!), with the same 15Watts, 1kOhm resistor I get this output:

I don't know what this means

I didn't take a picture of what that output looks like in 250us but the spikes shown in the image before were not square waves as the ones that showed up in low voltage. The ground for the Source of the low side MOSFETs is isolated from the one used in the IR2110 and the rest of the electronical devices (microcontroller, ICs, etc)

Any ideas as to why is this H Bridge misbehaving on High voltage? Thanks in advance!

\$\endgroup\$
7
  • \$\begingroup\$ "The ground for the Drain of the low side MOSFETs is isolated from the one used in the IR2110 and the rest of the electronical devices (microcontroller, ICs, etc)" What do you mean? How do you isolate the drain (which is not even connected to ground to begin with) from the ground that everything else? \$\endgroup\$
    – DKNguyen
    May 29 '20 at 19:33
  • \$\begingroup\$ Oops, sorry-- I meant Source, I corrected it on the question as well. What I meant is that I get the 300V from connecting a 1:1 transformer into the main power grid and rectifying it afterwards. Thus, the ground draining the current that goes through the load in the H-Bridge is isolated from the one I use for everything else (sorry if I can't explain myself correctly, English is not my primary language) \$\endgroup\$ May 29 '20 at 19:41
  • \$\begingroup\$ I still don't quite understand but I will say that the the MCU, the IR2110, and the GND on the H-bridge all need to be shared. If any one of those is disconnected from any other, then things won't work. So if you disconnected you H-bridge GND (shown in your schematic which would be the negative terminal of your smoothing capacitor after the rectifier) from the GND on your MCU and gate-driver, don't. \$\endgroup\$
    – DKNguyen
    May 29 '20 at 19:42
  • \$\begingroup\$ The gate-driver and MCU need to share GNDs so they have a common reference with which to communicate with each other, and your gate driver needs to share the GND with your H-bridge since it is assuming the source is at GND when it tries to drive the low-side MOSFETs (since it is trying to use a GND referenced voltage to produce a gate-source voltage difference). \$\endgroup\$
    – DKNguyen
    May 29 '20 at 19:45
  • \$\begingroup\$ How are you probing the signal, and where? \$\endgroup\$ May 29 '20 at 19:46
0
\$\begingroup\$

The GND on the MCU, IR2110, and H-bridge all need to be shared. If any one of those is disconnected from any other, then things won't work. So if you disconnected you H-bridge GND (shown in your schematic which would be the negative terminal of your smoothing capacitor after the rectifier) from the GND on your MCU and gate-driver, reconnect them

The gate-driver and MCU need to share GNDs so they have a common reference with which to communicate with each other, and your gate driver needs to share the GND with your H-bridge since it is assuming the source is at GND when it tries to drive the low-side MOSFETs (since it is trying to use a GND referenced voltage to produce a gate-source voltage difference).

\$\endgroup\$
1
  • \$\begingroup\$ Thank you for answering; I was going to try connecting GND and accidentally connected the leads backwards, burning part of the circuit; couldn't find replacement parts as of today because of the quarantine, so i'll try this now! \$\endgroup\$ Jun 11 '20 at 14:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.