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problems with a class B amplifier (high voltage)

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OM222O:
Here is what I meant by adding zeners (I won't use that exact part, just something with 110 to 120V breakdown voltage):


again, I'm not sure if I need R12 and R13 and if I should just remove them?
as for the damping, I have asked and have been told that it's not an issue and to be honest I'm not sure how I can get the system to be "critically damped". Adding a capacitor across the actuator seems like the easiest option to add more damping but feel free to let me know how I can calculate the capacitor value to get correct damping.

here is also a DC sweep to analyze maximum powers (colors are the same as before):


op amp has a maximum of 650mW and transistors have a max of about 4.2w which is manageable with some heat sinks.
The actuators are used in "force driven joints" based on data from pressure sensors.

magic:
But why? :scared:

Just make it a diode from output to V+ and from output to V- such that any transient is fed back into supply capacitors. Make sure they are big enough to absorb the energy.

As for ringing, experiment with C1 and R2 and probe opamp output and inverting input to see what's going on.

OM222O:

--- Quote from: magic on July 14, 2019, 12:35:06 pm ---But why? :scared:

Just make it a diode from output to V+ and from output to V- such that any transient is fed back into supply capacitors. Make sure they are big enough to absorb the energy.

As for ringing, experiment with C1 and R2 and probe opamp output and inverting input to see what's going on.

--- End quote ---

The output is the "emitter" net :-DD resistor is to just save the diode from high currents  :-// I'm not sure if this slows down the zener or not, but the connections are correct.

duak:
OM2220-
Because the load is an inductor it will not suddenly increase current unless its core saturates.  What it will do is generate a voltage that will try to maintain the current flowing through it.  If the driver is trying to increase current, the voltage will rise up to whatever is needed to oppose the change but limited to the supply voltage.  If there's already a high current and the driver is then commanded to deliver a lower or negative current, the opamp output and then the emitter voltage will snap down to whatever the inductor can generate to try to maintain the previous current.  In the limit, the emitter voltage will be slightly more negative than the negative supply. The load current will forward bias Q1's base-emitter junction and then Q2's base-collector junction.  Since Q1 has base current it will turn on and take collector current with a very high collector-emitter voltage leading to high dissipation, perhaps close to the SOA limits.  The opamp output will go to its negative limit and not accept too much current because of R1.   Zener D1 will conduct a current limited by R13.  This may be OK but most designs avoid it by putting clamp diodes between the emiiter net and the supply rails.  If you want to use zener diodes for clamps it's probably better to connect them back-to-back across the coil.

When you mention critically damped, do you mean the driver circuit or the whole electromechanical system?  The decaying sine wave tells me the driver is underdamped but not to the point of instability.  This can be dealt with by adjusting C1 and R1.  When you add the interaction of the coil with the actuator and payload the driver's damping won't change but the system damping will be determined by other characteristics. 

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