Also, its best to give each MOSFET its own independent gate resistor, this can eliminate any potential oscillations (at least thats recommended in amplifier circuits with paralleled output transistors)
The circuit presented here is sized to switch 100W at a minimum pulse width matching 250Hz. But actually it's currently only being asked to switch around 10-20W. The load is an array of LEDs. Q1 and Q2 also have small heat sinks on them for extra measure.
The input circuit actually includes one more BC557 (making the input active-low) and is driven by an Atmega328P PWM output @ 3.3V.
There are two of these circuits (two channels) in a single enclosure, driving remote LED lights.
The lights are part of a solar-powered lighting system, and the lights are often turned on during the day to regulate the charging voltage to the battery.
When this circuit works (which is normally the case) it works very well.
The problem is that occasionally the LEDs are jamming on, eventually draining the battery completely flat.
I'm pretty certain the problem is in this circuit (rather than code), because:
the condition appears physically very fragile. Just opening the (normally sealed) enclosure seems to be enough to have the LEDs turn off - as does picking it up and shaking it! Makes it hard to perform any circuit diagnostics!
But I can tell (wirelessly) that the Atmega has not rebooted.
And because both channels have the same fault, it makes me think it's a design flaw and not a component fault or bad connection.
Also, sticking my fingers all over the circuit (my quick test for high impedance circuitry) doesn't cause the LEDs to react.
And Q1 and Q2 don't appear to be very hot when in this condition, at least not after being in this condition for a fair amount of time - I've never caught it in the act...
On reflection, R3 could also be smaller. But I find it hard to believe that's the problem either.
One possible mistake is the lack of a snubbing diode on the load, since the wire lengths are quite long. But if that was the problem, would I expect to see it turning full-on?
Another mistake could be that I've undersized R1R2 for suppressing some kind of oscillation?
Another mistake could be not allowing for some kind of thermal event's effect on Q1 and Q2? Possibly exacerbated by being out in the sun?
I'm sure someone here can tell me what's going on :)
·OTHER ANSWER:
The circuit presented here is sized to switch 100W at a minimum pulse width matching 250Hz. But actually it's currently only being asked to switch around 10-20W. The load is an array of LEDs. Q1 and Q2 also have small heat sinks on them for extra measure.
The input circuit actually includes one more BC557 (making the input active-low) and is driven by an Atmega328P PWM output @ 3.3V.
There are two of these circuits (two channels) in a single enclosure, driving remote LED lights.
The lights are part of a solar-powered lighting system, and the lights are often turned on during the day to regulate the charging voltage to the battery.
When this circuit works (which is normally the case) it works very well.
The problem is that occasionally the LEDs are jamming on, eventually draining the battery completely flat.
I'm pretty certain the problem is in this circuit (rather than code), because:
the condition appears physically very fragile. Just opening the (normally sealed) enclosure seems to be enough to have the LEDs turn off - as does picking it up and shaking it! Makes it hard to perform any circuit diagnostics!
But I can tell (wirelessly) that the Atmega has not rebooted.
And because both channels have the same fault, it makes me think it's a design flaw and not a component fault or bad connection.
Also, sticking my fingers all over the circuit (my quick test for high impedance circuitry) doesn't cause the LEDs to react.
And Q1 and Q2 don't appear to be very hot when in this condition, at least not after being in this condition for a fair amount of time - I've never caught it in the act...
On reflection, R3 could also be smaller. But I find it hard to believe that's the problem either.
One possible mistake is the lack of a snubbing diode on the load, since the wire lengths are quite long. But if that was the problem, would I expect to see it turning full-on?
Another mistake could be that I've undersized R1R2 for suppressing some kind of oscillation?
Another mistake could be not allowing for some kind of thermal event's effect on Q1 and Q2? Possibly exacerbated by being out in the sun?
I'm sure someone here can tell me what's going on :)
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