Short circuit in H Bridge

Thread Starter

vbezerra

Joined Sep 29, 2022
5
Hi everyone,

I already assembled this design of an H Bridge. I can see all the 4 switching signals from Vgs1 to Vgs4. However, when I turn the 15V external together with my Power (+VDC, -VDC) I get a short circuit on the Power part. What am I missing here?

1713365005626.png


1713365023274.png
 

Thread Starter

vbezerra

Joined Sep 29, 2022
5
why shouldn't you get the short circuit? what is it that you see that you are not sharing? what prevents PWMs on same side of the bridge to overlap?
The pwm on the same side of the bridge are not overlapping. I have a dead time between them. I get the short circuit even with all pwm shutted down.

I’m wondering if the problem is related to the isolated dcdc P3 and P4 because they are connected with the -VDC (?)
 

Irving

Joined Jan 30, 2016
3,974
Do your PWM1 thru 4 leave sufficient dead-time between 'on' phases to avoid shoot-through at the gates, not just at the driver input?

1713368707505.png
Assuming this strange construct means C19 pin 1 is connected to +15V_OUT2 only and not to R14/R15 and is wired as such, there's nothing in the schematic that looks wrong, so its either a wiring error or timing error...

Incidentally, you don't need an isolated supply for the lower MOSFET drivers as VS2 = VS4
 

Thread Starter

vbezerra

Joined Sep 29, 2022
5
Do your PWM1 thru 4 leave sufficient dead-time between 'on' phases to avoid shoot-through at the gates, not just at the driver input?

View attachment 320145
Assuming this strange construct means C19 pin 1 is connected to +15V_OUT2 only and not to R14/R15 and is wired as such, there's nothing in the schematic that looks wrong, so its either a wiring error or timing error...
yes, I’m making sure there is enough dead time.
Only valuable thing to point out is that I get a short circuit even with my pwm off. When I have stable 15V in the external part and start to increase voltage in the power part, there is then a short circuit on the power part
 

Irving

Joined Jan 30, 2016
3,974
Must be a wiring error then or a faulty MOSFET. Disconnect lower gates and connect to ground. Do you still get short? What are voltages at VS1 and VS3?
 

panic mode

Joined Oct 10, 2011
2,793
and conform how capacitors like C19 are connected. is the right side connected to resistors and transistor gate?
i see no connecting dots so this may be just sloppy dwg.
also you have several net names shown on same equipotential.
for example -VDC, Vs2 and Vs4 are tied together
there are other things like resistors that have no value, one of the DC/DC converter is a different from the other three...

1713370027231.png
 

Thread Starter

vbezerra

Joined Sep 29, 2022
5
and conform how capacitors like C19 are connected. is the right side connected to resistors and transistor gate?
i see no connecting dots so this may be just sloppy dwg.
also you have several net names shown on same equipotential.
for example -VDC, Vs2 and Vs4 are tied together
there are other things like resistors that have no value, one of the DC/DC converter is a different from the other three...

View attachment 320146
C19 is connected between pin 8 and 5.
All dc dc converters are ROE-0515S
 

MisterBill2

Joined Jan 23, 2018
18,934
What I see in that circuit drawing is that the VddOUT is directly tied to the gates. ANd now a question which is are the Vdd in and out adequately isolated?? Driving the top gates in a"H" bridge demands isolated power.
AND, presenting a circuit as a collection of separate snippets would not be accepted by any of my clients.It is OK for PCB layout and routing, totally unaccepted for circuit analysis. I am aware that some programs produce such, that fails to make it OK.
 
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