# Why diode series on Input of boost converter?

Simple question:

I'm new to electronics, but have one straight forward question. I know all boost converters are made up of diodes, caps and coils with some sort of feedback system to regulate voltage.

I bought a 150w boost converter: BMT DC/DC BOOSTER 12-35VOUT 150W

SPECS:

Module Properties : Non-isolated Step-up Module (BOOST)
Input Voltage : 10-32V
Output Current : 6A (max)
Input Current : 10A (max) (Please Enhance Heat Dissipation if more than 10A)
Output Power : Enhance Heat Dissipation 150W (MAX)
Conversion Efficiency: 94% (measured at Input 16V, Output 19V 2.5A)
Output Ripple : 2% (max) 20m-Bandwidth
Operating Temperature: Industrial (-40 ~ +85°) (ambient temperature exceeds 40°, lower power use, or to enhance heat dissipation)
Dynamic response speed : 5% 200uS
Short Circuit Protection : None (Please Install fuses and protection circuits at Input port.)
Input Reverse Polarity Protection : None (Please Series diode at the input port.)


In short it recommends to place a diode (out of interest I've bought a schotkky 10SQ050) in series at the input port to protect against reverse polarity, but what I don't understand is; do I simply just place the diode (with Cathode connected directly to the in+) inline of the In+ line? see figure 1. OR must it be placed in parallel with the in+ and in-? If so then in which direction would the diode be placed? see figure 2

I would really like to understand more. It doesn't make sense to me that the diode is to be placed in series with the input, despite it stating it needs to be in series, so I just want to understand. Please help me understand! Thanks a ton for your time!

Figure 1:

Figure 2:

The web page says this: -

Please Series diode at the input port


And that makes sense so use this: -

Other useful information: -

What to check for when buying an electronic component or module

• Thanks Andy. I will place in series as stated. But could you perhaps explain why it is placed in series? Or more so what is the point of the diode? I know for reverse voltage, but is the diode for if there is reverse polarity on the OUTPUT side boost? OR if there is reverse polarity on the INPUT side of the boost? Aug 23 '20 at 12:11
• Also thanks for the link, busy checking it out. Appreciate your time Aug 23 '20 at 12:33
• The diode is for input voltage reversing due to making an error when wiring it up. Aug 23 '20 at 13:34
• Okay great, thanks for that. Makes obvious sense now thinking about it. But thanks for helping me understand! Aug 23 '20 at 15:18
• @Audiosine do you know what to do next regards site etiquette? Aug 23 '20 at 17:10
• Series blocking reverse prevents damage but reduces input by diode drop at high current.
• Some Schottky diodes at high current drop more than Silicon if under-rated. But this is 0.7V @ 10A so ok.

The preferred way now is to use the ideal diode dual FET blocking IC’s, but only necessary for low voltage battery chargers.

• Thanks for this tony. I made sure when researching diodes to look for one with a low forward voltage and found that schotkky's were best suited for this. I should look more into the diode duel FET "system" thanks a ton. Aug 23 '20 at 21:37
• Use the ones i said Aug 23 '20 at 21:38
• Thanks i certainly will. Also l, thanks for the insight into some schotkky diodes inscreasing proportionally to higher current. The max current flowing through the diode shouldn't exceed 6amps. Aug 23 '20 at 21:41
• Schottky diodes lack the high PIV rating Aug 23 '20 at 21:50

"In series" means in series, therefore option 1.

Option 2 and 3 are "in parallel".

• Thanks Marcus. I do understand series and parallel i just wanted to understand why in series? Aug 23 '20 at 12:08
• well, you seem to know what a diode does. So, mentally try out what the other two options do when you connect the supply correctly and reversed. Not quite sure what the remaining question would then be? Aug 23 '20 at 14:41
• Thanks Marcus. I take a quote from a previous comment: "I will place in series as stated. But could you perhaps explain why it is placed in series? Or more so what is the point of the diode? I know for reverse voltage..." I think what I'm getting at is the fact that i don't understand how, by placing the diode on the input of the boost, it works." Aug 23 '20 at 15:24
• Understanding that the diode only allows the current to flow toward the boost. So if i flip the polarity meaning my + voltage is now flowing into the -VIn meaning that the boost is being given voltage in the negative side of the boost, does this mean current tries to flow out of the +Vin? But cannot due to the diode? Not sure. Apologies in my abstract questions. I'm trying to grasp HOW the diode prevents this reverse polarity. Aug 23 '20 at 15:25