H-Bridge burns out from one side without load (Randomly)!

PadMasterson

Joined Jan 19, 2021
63
Just wondering why you might not want to use a FET in place of the two power on relays? It would remove the issue of bad contacts and makes control of the incoming voltage better. Might need a few additional parts to control them, but... It's just a thought.
 

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HelpMe2020

Joined Feb 24, 2021
22
Just wondering why you might not want to use a FET in place of the two power on relays? It would remove the issue of bad contacts and makes control of the incoming voltage better. Might need a few additional parts to control them, but... It's just a thought.
First of all this +12V will fetch into 12 more small PCBs which can be turned on and off via relay. The idea was to control them via this board. So, 12V supply has to feed into 12 small boards, which have to be controlled by this PCB.

So, I guess I might use SSR (solid state relay) instead of EMR (electro-mechanical relay). In addition, I can put an inductor in Vsupply to suppress high current initally. That should solve all the problems. Any suggestions?

I am quite flexible. Cost is not a big issue, but I don't want to overkill the design either. I want to get it done with most fundamental reliable components.
 
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HelpMe2020

Joined Feb 24, 2021
22
The problem I see with the circuit is the power-up behaviour. This problem exists in the original circuit and the rework. Switching the power on through relay will give a high rising time of the supply voltage. A Mosfet has capacitance from drain to gate and gate to source. Depending on the speed of the transient the critical situation may be when both M1 and M3 turns on through this capacitive coupling, because there is no passive discharge on the gate on M3. So focus also on that point of the problem and simulate power-up/down transient. Especially a relay may clutter, so try also to simulate that behaviour.
Nevertheless the shoot through is also a problem of the original circuit. But according to the first failure description it was stated that it happens at power up, so this is the main flaw of the circuit. A 10 Kohm from M3 (and M4) to ground may give some improvement, but I recommend to measure the transient voltage rising with a scope and try to simulate that. Then improve the circuit with respect to power up and shoot through.

Yeah, that's also the issue. I guess original design had both shoot through and relay (EMR) based problems. I have added the resistors near M3 and M4. That make sense and it works fine. That should take care of shoot through in my understanding.

The problem does arise during the power up. However, it has also failed when I had bypassed the relay if I remember correctly. I used to get lot of spark/arc when I used to plug the power wires in the board irrespective of via the relay or bypassing the relay. Now, I don't remember exactly how the very first failure had had happened. I might have to restart the old board and see if I can do some R&D around it.

What do you mean by relay may clutter? Can SSR (solid state relay) fix these issues? I can also add one powerful inductor in the Voltage line to suppress the inrush current!
 

Thread Starter

HelpMe2020

Joined Feb 24, 2021
22
Another consideration is that with the possibility of high dv/dt switching transients, your circuit could be going into high frequency oscillation with high current draw destroying the MOSFets. Parasitics on the PCB may be a contributing factor here. Take a look with a scope and see if there is any evidence of HF ringing or sustained oscillation with your case of no load. Bypassing the MOSFETs to subdue the oscillations could solve the problem, if you see any of the above behaviors, but I'm not sure where the placement of bypass caps would be most effective - probably gate to GND?
This might be so true. However, it's beyond my skill sets to perform all these tests. I do have nice instruments (DVM and oscilloscope etc) and additional tools to test these things. But not an expert to perform! Somebody should help me in this. I guess I have to monitor current/voltage spikes waveform(high frequency spectrum) during the power supply from t=0 to t= 2 secs I guess via oscilloscope.

Again, I am thinking of using solid state relay to overcome all these dirty issues due to the traditional relay. Cost is not important but it should make sense to spend more if that really makes a lot of difference. This is not a high volume design. It's an industrial design. So, cost associated with the PCB is not highly critical but somewhat important to justify the expense.
 

iggnator

Joined Jan 30, 2019
15
This is not a high volume design. It's an industrial design.
Then any failure results in down time. You need to do some sort of qualification testing to ensure a robust design.
I designed avionics, there the standard was RTCA DO-160() that had all tests that were either required by the performance standards, or the desire to be installed on end type aircraft (e.g. rotor, turbo prop, fan jet, piston). And when you have either humans that paid for a ticket, or a fat cat CEO, they got pissed when there was a failure that prevented dispatch of the aircraft.
Factory production is no different.
I do not know of any commercial qualification standards. But somewhere this should exist, with suggested diagrams of how to perform the tests. Most of these will be to the power pins for surge and lightning. I can tell you from experience that pulses on the power input pins to a low voltage supply, make it through a transformer, and can blow up the rectifier diodes on the secondary low voltage supply outputs.
The use of arbitrary waveform generators into audio amplifiers was coming into use when I retired.
If your not doing this project for anything outside your own personal use, then all this is moot.
 

Thread Starter

HelpMe2020

Joined Feb 24, 2021
22
Then any failure results in down time. You need to do some sort of qualification testing to ensure a robust design.
I designed avionics, there the standard was RTCA DO-160() that had all tests that were either required by the performance standards, or the desire to be installed on end type aircraft (e.g. rotor, turbo prop, fan jet, piston). And when you have either humans that paid for a ticket, or a fat cat CEO, they got pissed when there was a failure that prevented dispatch of the aircraft.
Factory production is no different.
I do not know of any commercial qualification standards. But somewhere this should exist, with suggested diagrams of how to perform the tests. Most of these will be to the power pins for surge and lightning. I can tell you from experience that pulses on the power input pins to a low voltage supply, make it through a transformer, and can blow up the rectifier diodes on the secondary low voltage supply outputs.
The use of arbitrary waveform generators into audio amplifiers was coming into use when I retired.
If your not doing this project for anything outside your own personal use, then all this is moot.

I am making this project as a prototype for a startup where there is no industry standards to follow for this kind of a industrial product. No safety requirements are needed to be followed other than it should work reasonably good in standard conditions.
 
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