Question related to circuit for actuating Fuel Injector

[core7916]

In my project, I have two PCBs, each containing a fuel injector actuation circuit powered by a HRL3024S200P converter. Both PCBs include four injector circuits, which operate continuously. However, the injectors (4) are connected to only one of the boards at any given time, based on a selection for redundancy. The issue I'm encountering is that the board actively controlling the injectors maintains the set voltage, while the other PCB experiences a voltage drop. The voltage on the inactive PCB only returns to the set value when the circuit is turned off and on again. How can I resolve this issue?
I have included the circuit diagram for reference.

[Screenshot of circuits inserted by a Mentor]

 

[berkeman]

So each circuit board contains one INJ_VBOOST circuit and 4 of the Injector Circuits with INJx_SIG outputs (x=1:4)? And only one of the two PCBs has those INJx_SIG outputs connected the actual injectors? So you must use a 4PDT type relay circuit to do the switching the drive lines to the injectors?

And the problem you are seeing is that for the PCB that is not currently connected to the injectors, the INJ_VBOOST voltage is drooping? What kind of load do the injectors present to the drive circuit? Probably something like an inductor in series with a resistor (or maybe in parallel?)? I haven't looked up the specs for the boost converter IC yet, but does it have a minimum output current to stay in regulation?

 

[berkeman]

Hmm, I'm not seeing a minimum output current on the datasheet:

https://www.xppower.com/portals/0/pdfs/SF_HRL30.pdf

 

[core7916]

So each circuit board contains one INJ_VBOOST circuit and 4 of the Injector Circuits with INJx_SIG outputs (x=1:4)? And only one of the two PCBs has those INJx_SIG outputs connected the actual injectors?

Yes

So you must use a 4PDT type relay circuit to do the switching the drive lines to the injectors?

I have another main PCB that consists of relays to select which one of these PCBs must be active.

And the problem you are seeing is that for the PCB that is not currently connected to the injectors, the INJ_VBOOST voltage is drooping? What kind of load do the injectors present to the drive circuit?

Injectors are capacitive load.

 

[DaveE]

Sorry, I'm confused. Why do you care about the voltage measurement of an inactive injector driver? Is the inactive board connected to a load? If the load is switched on to a previously inactive driver, wouldn't the voltage change significantly in response?

 

[core7916]

Why do you care about the voltage measurement of an inactive injector driver?

If the active board fails, then it automatically switches to another board and I need it to work identically.

Is the inactive board connected to a load?

No only the active board will be connected to load, but if the active board fails then it switches to another board.

If the load is switched on to a previously inactive driver, wouldn't the voltage change significantly in response?

Until I restart the unit, it doesnt come back to the expected voltage.

 

[Rive]

the board actively controlling the injectors maintains the set voltage, while the other PCB experiences a voltage drop. The voltage on the inactive PCB only returns to the set value when the circuit is turned off and on again.

- is this a newly developed problem, or was it always present, or maybe related to a specific series of converters/boards? Do you have access to more than one set of boards, or you just stuck with a defective system which you are trying to diagnose?
- Are there changes on the control/measure pins of the converters? (measured to common ground and to device ground)
- are there voltage differences between the grounds of the different boards during operation?
- how big are those voltage changes actually?

 

[DaveE]

Until I restart the unit, it doesnt come back to the expected voltage.

OK, got it. It's not a power supply problem it's a control problem. It's not that you can't measure the voltage of a disconnected driver, it's that it doesn't recover as you like or expect. Sorry, I can't help. Except to suggest that you read every bit of the data sheets for those ICS.

 

[Baluncore]

Look at the diode D13, and capacitor C399, that provide and maintain the IR2110 high-side driver gate supply. The low-side MOSFET must be turned on occasionally, to top up the high-side driver's gate supply capacitor. Loss of the high-side gate drive supply, will prevent the top MOSFET from turning fully on, so the output signal voltage will appear to collapse.
When inactive, park the half-bridge signal output low, not high.

 

[core7916]

is this a newly developed problem, or was it always present, or maybe related to a specific series of converters/boards? Do you have access to more than one set of boards, or you just stuck with a defective system which you are trying to diagnose?

This is a new board in which I am trying to solve the above mentioned problem.
I am having one set of unit only.

Are there changes on the control/measure pins of the converters? (measured to common ground and to device ground)
- are there voltage differences between the grounds of the different boards during operation?
- how big are those voltage changes actually?

Will check this.

 

[Ivan Nikiforov]

I suggest you consider the following option. Apply the nozzle simulator on an inactive board. If the nozzles are a capacitive load, you can load the inactive board using capacitors. To do this, you will need to determine their capacity and finalize the nozzle switching scheme.