I have designed this voltage regulator circuit although I am not sure if I have connected the bridge rectifier for reverse polarity protection correctly.

I am confused about whether this is the right way to connect it and the datasheet doesn't much about it.

I am open to any suggestions, and any help will be greatly appreciated!

Datasheets:

5A Fuse
Rectifier
LDO

Circuit:

 

Hi flox.
The Bridge is the wrong way around.
E

 

Hi flox.
The Bridge is the wrong way around.
E

Thanks Eric for pointing this out, I had a feeling I had messed it up!

How does this look now? Is this the correct way to connect it? Is the fuse in the right spot now?

Thank you!

 

hi flox,
You have the 12V input marked as a +/- DC source, is that correct?
E

 

Yes, the bridge is only used as a reverse polarity protection (not as an AC rectifier) so regardless of which way you plug the DC supply, it will always be correct. I have seen it implemented in a few circuits although I am not sure which way is the correct one, I have tried to reverse-engineer it from a circuit I have but it's hard to tell which pin is which.

 

Hi,
OK,
This is the PDF datasheet for the DF02M, it shows the pin details'
E

 

You don’t need bridge D5 if your input is already rectified DC.
However, including it provides protection from reverse polarity with some voltage loss.

 

Yes, the bridge is only used as a reverse polarity protection (not as an AC rectifier) so regardless of which way you plug the DC supply, it will always be correct. I have seen it implemented in a few circuits although I am not sure which way is the correct one, I have tried to reverse-engineer it from a circuit I have but it's hard to tell which pin is which.

It is now connected the right way for your purpose

 

Hi,
OK,
This is the PDF datasheet for the DF02M, it shows the pin details'
E

Thanks for doing some research, I did have a look at Vishay's datasheet although I was not sure, that the configuration would have been the same!

You don’t bridge D5 if your input is already rectified DC.
However, including it provides protection from reverse polarity with some voltage loss.

Yes, you are correct, I will only be using it as reverse polarity protection.

It is now connected the right way for your purpose

Perfect, thanks for clarifying this.


Thank you all for taking the time to answer, I have a curiosity now for future designs, when using a rectifier for reverse polarity protection the AC input will be connected to the DC source and the + would be positive voltage and the - the ground, is this correct? Because looking at the datasheet posted by Eric, that's what I understand.

 

Thank you all for taking the time to answer, I have a curiosity now for future designs, when using a rectifier for reverse polarity protection the AC input will be connected to the DC source and the + would be positive voltage and the - the ground, is this correct? Because looking at the datasheet posted by Eric, that's what I understand.

Yes.

 

Just one more thing. The DC source ground and the ground after the rectifier are not the same. This could lead to some problems if your design is connected to other devices with the same DC source ground.

 

If you wanted to avoid the bridge diode voltage drop, and just block reverse voltages, you could use a power MOSFET.
The MOSFET drop when conducting is just its on-resistance times the current.

 

I am confused about whether this is the right way to connect it and the datasheet doesn't much about it.

I am open to any suggestions, and any help will be greatly appreciated!

Datasheets:
5A Fuse
Rectifier
LDO

Why are you using a 100uF filter cap if the input is DC? Why are you using a 5A fuse on a 500mA regulator that has built-in protection? The fuse symbol doesn't make it obvious that it's a PTC fuse.

Technically 78M05 isn't a low dropout regulator. LDO's have dropout voltages in the several hundred millivolt range, not 2V.

 

Why are you using a 100uF filter cap if the input is DC? Why are you using a 5A fuse on a 500mA regulator that has built-in protection? The fuse symbol doesn't make it obvious that it's a PTC fuse.

Technically 78M05 isn't a low dropout regulator. LDO's have dropout voltages in the several hundred millivolt range, not 2V.

After reviewing the circuit, I have decided to replace the 7805 with an SPX3819 which is a better LDO and will help to keep the noise low while being cheap, this is the circuit now:

(VCC is actually meant to be VDD, and on VIN 1 is GND and 2 is +12)



The enable pin is tied to Vin as per datasheet schematic:



The datasheet mentions where to put decoupling capacitors, but not the recommended capacitance, after looking around, I have found a few circuits using 10uF capacitors, will 10uF be too large for the purpose?

 

If you had drawn the internal circuit of the bridge rectifier it would have been easily understood which direction was correct.

 

I have decided to replace the 7805 with an SPX3819 which is a better LDO

Why do you insist on calling 7805 an LDO regulator? It never has been and never will...

EDIT: corrected punctuation

 

Why do you insist on calling 7805 an LDO regulator? It never has been and never will...

EDIT: corrected punctuation

It is not obvious to many folks that there is a difference among regulators, or even what LowDropOut implies. So some assume that it means something about reliability rather than capability. And some folks have never suffered from regulator dropout.

 

Hi,
to clear up the LDO thing,
Both the 7805 and the SPX3819 are linear voltage regulators, but only the SPX3819 is a low dropout linear voltage regulator. The dropout voltage of the 7805 is around 2V and therefore not considered a LDO (compared to the SPX3819 dropout voltage of only 340mV).

Regarding your question about the ouput capacitor:
On page 7 of the datasheet a 2.2µF capacitor is suggested for most applications, but the 10µF capacitor will work just fine.