Dual supply H-Bridge driver using transistors wouldn't work

Thread Starter

sherelle

Joined Dec 1, 2021
6
I'm trying to make a biphasic functional electrical stimulator using the circuits in this paper. But I modified it by using MPSA BJT transistors instead of MOSFET. I'm in the middle of developing a Multisim simulation for it. The boost converter worked fine and could climb up/down to around +-40 Volts. But when I connect it to the driver, the positive voltage would climb up tp two volts, then comes back down to around 1 Volts.

Transistors used are MPSA42 and MPSA92. Can anyone help me figure out what is wrong with this?

PDF of the Multisim circuit is attached. I'm trying to figure out how to attach the ms14 file.
 

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AlbertHall

Joined Jun 4, 2014
11,695
It sounds like both transistors on one side of the H are turned on at the same time causing a short across the supply.
Both sides of the H are fed the same signal (which would be bad) except for the little box A1 (4ms). What is that box and what frequency is CLKin?
 

Thread Starter

sherelle

Joined Dec 1, 2021
6
It sounds like both transistors on one side of the H are turned on at the same time causing a short across the supply.
Both sides of the H are fed the same signal (which would be bad) except for the little box A1 (4ms). What is that box and what frequency is CLKin?
CLKin frequency is 1kHz with duty cycle of 30% (0.3ms on out of 1ms period). The little box is an analog delay of 0.4ms to create the effect of delay and deadtime (0.1ms) while maintaining the same duty cycle. These signals are planned to be generated by STM32 PWM.

This is what I think is missing, how can both transistors on the same side be activated at the same time if the clock signal even has a deadtime?

Thank you for answering
 

AlbertHall

Joined Jun 4, 2014
11,695
phi1 and phi2 have the same phase, they will both be high at the same time except for the small 'deadtime'.
One of the H input signals should be inverted so that when one is high the other is low.
 

Yaakov

Joined Jan 27, 2019
3,986
Yes! Hopefully this can be my bachelor's thesis
Respectfully, you are planning to build a device intended to provide high voltage shocks to a human. While I understand you are doing this with all the right intentions, helping someone to build a device that is potentially hazardous remotely is not something that seems prudent.

Don’t you have university resources to assist you? Qualified and local electrical engineers who can check the safety of the device?

This seems to come very close to the prohibition in Section 6 of the TOS here against devices intended to “electrocute or shock a person”. While I know you don’t intend the shock to cause harm, a mistake in your construction could do that.

I sincerely wish you the best with your thesis but were I you, I wouldn’t rely on random Internet advice to build what amounts to a potentially dangerous medical device.
 

Thread Starter

sherelle

Joined Dec 1, 2021
6
phi1 and phi2 have the same phase, they will both be high at the same time except for the small 'deadtime'.
One of the H input signals should be inverted so that when one is high the other is low.
Thank you, I will try to find a way to solve this.
 

Thread Starter

sherelle

Joined Dec 1, 2021
6
Respectfully, you are planning to build a device intended to provide high voltage shocks to a human. While I understand you are doing this with all the right intentions, helping someone to build a device that is potentially hazardous remotely is not something that seems prudent.

Don’t you have university resources to assist you? Qualified and local electrical engineers who can check the safety of the device?

This seems to come very close to the prohibition in Section 6 of the TOS here against devices intended to “electrocute or shock a person”. While I know you don’t intend the shock to cause harm, a mistake in your construction could do that.

I sincerely wish you the best with your thesis but were I you, I wouldn’t rely on random Internet advice to build what amounts to a potentially dangerous medical device.
Yes I do have university support. This device will not be tested on human until there is a green light from my professors (who are well experienced in developing monophasic FES). I feel like this problem that I ran into is a simple electronics problem that is not worth asking them (I tell myself I'm supposed to be able figure them out my self. Ha!)

Thank you for your concern. This device will go through safety inspection before subject testing. But to be able to do said inspection, I need a working device
 

Yaakov

Joined Jan 27, 2019
3,986
Yes I do have university support. This device will not be tested on human until there is a green light from my professors (who are well experienced in developing monophasic FES). I feel like this problem that I ran into is a simple electronics problem that is not worth asking them (I tell myself I'm supposed to be able figure them out my self. Ha!)

Thank you for your concern. This device will go through safety inspection before subject testing. But to be able to do said inspection, I need a working device
You can understand why I might be concerned, I'm glad you have good support locally. I hope you are successful.
 
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