Circuit Review

Gene you have time to check out a 12V DC power supply with reverse polarity/surge  protection?

I need a second pair of eyes.....

Tom,

Sure, post it and I'll review it.

Gene

U2 & U3 are  the protection circuit.

U7 is a simple 12vdc regulator for 12VDC connections

U1 is my 12VDC dual output source

Tom,

I am having trouble reading your schematic (even if I click on it and enlarge it).  Some of the font is too tiny to make out (like I can not read the part number on U2).  Is there any way to get a larger view?  Or maybe message me with a PDF?

Thanks,

Gene

Tom,

Ok, I have managed to determine most of the ICs in the design, and it looks like a close match to the appnote for the LTC4365.  I still can not make  out most of the resistors, so I can not comment on the limits logic.  The design seems like a bit of an over design, but without an understanding of the input voltage range and the desired current ranges for the supplies, it is hard to tell.  I did find one wiring issue (red line - see attached).

Good luck,

Gene

I tried to send you a message but the system says I can not send messages to people you are not connected too.

Tom,

Yeah, sending direct messages is a little difficult.  I sent a request to follow you, once you accept it, you will be able to direct message me.

Thanks,

Gene

Tom,

I am not sure how this happened, but some of the components have their values scrambled (RM281 should be 1820K , or 1.82M), it did make it a little difficult to determine what was going on.  Here are some of the things that I am thinking in regards to your design.

1) The LTC4365 is not really going to be much help.  I understand the desire to create some protection, but this does not buy you much protection given the 12V battery input and the 12 volt regulator stage.  As configured, the LTC4365 allows 3.5 - 18Volts pass through to the regulator (sure you could tighten this range by changing the voltage divider circuit on the LTC4365).  First 3.5 is way to low, as the bottom end of the range for the 12Volt regulator is ~12.5V. The high limit of 18V is not really providing the protection you would want, as the LM2937-12 can tolerate up to 26 Volts.  All this, given a 12Volt battery being the supply, none of these extremes should happen.  Depending on your battery chemistry, you should get no where near 18V.  I would provide negative protection by using a Schottky diode inline with the power input.

2) The 12 volt battery might be too low (again depending on chemistry), if you want to regulate to 12Volts (you really need at least 12.5-13Volts at the input of the regulator, maybe even 12.8-13.3Volts with the Schottky diode in place).  Running the sensors at 10V would allow you to regulate an a lower voltage, giving you a great margin on the input voltage (if the sensor would work at 10V).

3) The LT3256 regulator should work fine.  I have never used that part, but it seems pretty nice, in that you have a wide input voltage range, and due to the switching front end, there is not a huge power waste associated with the higher input voltage. Just keep in mind that the total output current (on the sum of the two outputs) is limited to 350mA .  Also, keep in mind that switching regulators (like the LT3256) can generate a fair amount of electrical noise due to the switching.

4) Your LEDs ('fault' and 'power on') are currently setup to draw ~20mA of current (510 ohm current limit at 12V).  This might be a little too high (i.e. bright), most LEDs produce enough light with 1-2mA.

In general, I tend to keep my power supplies clean and simple.  For any application that is going to involve sensors, ADCs, or and noise sensitive analog circuits, I prefer to use linear regulators, if possible.  I would lean towards a cascading of regulators, where you step the voltage down to values that you need.  Here is a simple example of what I mean.

To get the necessary power, the 10V regulator might need to be an adjustable (LM1117-ADJ), the rest could be fixed.  You need the current levels of the regulators to include any downstream regulators (i.e. the 5V part need to supply current to both the 5V devices and the 3.3V devices).

Just a thought.

Good luck!

Gene

Ok. How is everyone today? Emmm Coffee!

Ok for the power supply. I`ve removed somethings and added others.

Basics (not much into typing). This is a triple output power supply. Regulated 12VDC, 5VDC and 3.3VDC. On the front end you will see I added a P-FET to protect against reverse polarity issues.

If you add a P-FET to any circuit you need to pay close attention to the Vdss, Vgss and RDS on and make sure they match the circuit.

Ok. How is everyone today? Emmm Coffee!

Ok for the power supply. I`ve removed somethings and added others.

Basics (not much into typing). This is a triple output power supply. Regulated 12VDC, 5VDC and 3.3VDC. On the front end you will see I added a P-FET to protect against reverse polarity issues.

If you add a P-FET to any circuit you need to pay close attention to the Vdss, Vgss and RDS on and make sure they match the circuit.

Tom,

That looks good.  I see that you were able to correct some of the text fields (component values) so they are no longer character reversed.

Good job!

Gene