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Now since the opto-isolator we are using inverts the logic, it makes sense to use a NAND gate instead. This way, output from the opto-isolator will be the same as Fig. 3. above, and can then be latched with the SR Latch.
Changes for Rev2
- Fix diode silkscreen on the bottom of the board
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- Remove R1, replace R2 with a smaller value for more current into comparator
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- Q1 should have 1/2/4/6 and 4 swapped
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- Ultra-fit and Dura-Clik connectors instead of Clik-Mates
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- Add passthrough for relay sense line (shorted when relay is closed, open circuit when relay is open)
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- Fix voltage drop with MOSFET stages
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- Add hysteresis to avoid bouncing
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- Add an NAND gate between negative input and comparator output
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- Try to increase voltage going into opto-isolator. Around 2V right now due to voltage division
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- Consider using non-tented vias or through hole test points. Some TPs were ripped off
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- Also don't put TPs directly on a trace as if it falls off it takes the entire trace with it
Rev 2 Retrospective
Overall, it worked well. Taiping Lireflowed one side using the reflow oven and did the other by hand. This seemed to be a good strategy, with only a reversed LED and non-functional relay requiring rework.
- Required rework to test with 12V - needed to modify resistor dividers
- Connectors are great and really useful when testing a board
- 0 ohm resistors are great for disconnecting things and changing resistor values
- Resistor dividers need to be biased towards IN- (increase R13)
- Need to tune values - greatly influences time precharge takes
- Need to add a decoupling/bulk cap between HV relay 12V and GND to reduce ripple - 10uF seems to work fine
Rev 2 Testing
To ensure proper functionality and that nothing in the car is negatively affected by the board, these tests should be completed prior to the final revision
- Noise in the 12V line when the relay is on
- Voltage droops when the relay switches
- Test for noise in the isolated DCDC
- Pre-Charge sometimes doesn't happen when the circuit is turned off then turned on again before the capacitor is fully discharged, this should be further looked into