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Topic: Silicon diode as voltage step down  (Read 759 times) previous topic - next topic

Tom-4

May 31, 2020, 09:19 am Last Edit: May 31, 2020, 04:59 pm by Tom-4
Hello everyone,
It sounds not smart, but, is it a good idea to use a large silicon diode to step down battery voltage from 14.5 v to something like 13 v if the load is big and drags about 8 amps?

6v6gt

That is 12 watts, spread across 2 silicon diodes.

Tom-4

#2
May 31, 2020, 10:08 am Last Edit: May 31, 2020, 10:08 am by Tom-4
That is 12 watts, spread across 2 silicon diodes.
So may I use two large silicon diodes in series?
I thought of LDO or linear regulators since the voltage which I want to sink is almost the same voltage drop in LDO or linear regulators so it wont be so power loss and heat, but, I can't find one which can handle 8 amps and I'm not sure if I can use two LDO in parallel!  

Paul__B

#3
May 31, 2020, 12:17 pm Last Edit: May 31, 2020, 12:19 pm by Paul__B
So yes, if you use two diodes rated at 10 Amps, it will drop approximately 1.5 V, from 14.5 to (less than) 13.  At low current draw, it will rise a little.

If the diodes are indeed rated at 10 Amps and used with whatever heatsinking is recommended, they must necessarily safely dissipate the 12 Watts.

Note that a single 10 Amp rectifier bridge will perform the same job.  :smiley-lol:

Wawa

So may I use two large silicon diodes in series?

I thought of LDO or linear regulators since the voltage which I want to sink is almost the same voltage drop in LDO or linear regulators so it wont be so power loss and heat
Power (heat) = voltdrop x current, so both produce the same heat.

A bridge rectifier has two diodes in series, and a second pair in parallel, so is a good solution.
10-25Amp ones (low voltage) are common, and have a hole in the middle to screw them to a heatsink.
Only use the + and - terminals, not the AC terminals.
Leo..

Tom-4

#5
May 31, 2020, 12:37 pm Last Edit: May 31, 2020, 12:37 pm by Tom-4
So yes, if you use two diodes rated at 10 Amps, it will drop approximately 1.5 V, from 14.5 to (less than) 13.  At low current draw, it will rise a little.
Do you think two of this cutie diode in series will do the job?  ;)
https://www.elfa.se/Web/Downloads/0_/en/qqSTM_GRDn-STTH20_EN.pdf?pid=${product.code}

Tom-4

A bridge rectifier has two diodes in series, and a second pair in parallel, so is a good solution.
10-25Amp ones (low voltage) are common, and have a hole in the middle to screw them to a heatsink.
Only use the + and - terminals, not the AC terminals.
Leo..
Good idea, but, the bridge rectifier isn't PCB-mounting friendly!
I'm thinking of using two STTH2002C in series with one big heat sink (which I didn't calculate yet).
Tommy

PerryBebbington

An alternative suggestion is to use a buck-boost converter. A possible problem with what you are suggesting is that if your supply is a battery then while the voltage might be 14V5 when the battery is fully charged it will be somewhat less as the battery discharges. A buck-boost converter will take care of this.

Tom-4

#8
May 31, 2020, 01:49 pm Last Edit: May 31, 2020, 01:50 pm by Tom-4
An alternative suggestion is to use a buck-boost converter.
Nice suggestion, but, it's not easy to find 8 to 10 Amps buck-boost converter which reliable and safe!

A possible problem with what you are suggesting is that if your supply is a battery then while the voltage might be 14V5 when the battery is fully charged it will be somewhat less as the battery discharges. A buck-boost converter will take care of this.
Good point, but, as long as I'm going to get at least 10 v so it's ok for the load.
Do you see another possible problem which I can face in future?
Thank you in advance.
Tommy

TheMemberFormerlyKnownAsAWOL

#9
May 31, 2020, 01:51 pm Last Edit: May 31, 2020, 01:59 pm by TheMemberFormerlyKnownAsAWOL
Please, it is "silicon" not "silicone"
Please don't PM technical questions - post them on the forum, then everyone benefits/suffers equally

Tom-4

Please, it is "silicon" not "silicone"
I changed it... thank you :)
Any more ideas?

PerryBebbington

Quote
Nice suggestion, but, it's not easy to find 8 to 10 Amps buck-boost converter which reliable and safe!
Well, they are certainly available, I have just found several on Amazon for under £10. As for reliable and safe....  :smiley-confuse:
Quote
Do you see another possible problem which I can face in future?
Any battery capable of supplying 10A is also capable of supplying enough current into a short circuit to start a fire. Include a HRC (high rupture capacity) fuse in your circuit as close to the battery as physically possible, between 2 cells if possible.

Tom-4

#12
May 31, 2020, 02:13 pm Last Edit: May 31, 2020, 02:14 pm by Tom-4
Any battery capable of supplying 10A is also capable of supplying enough current into a short circuit to start a fire. Include a HRC (high rupture capacity) fuse in your circuit as close to the battery as physically possible, between 2 cells if possible.
Well, I'm planning to use Mini Automotive Blade Fuse. Is it ok or HRC fuses must be used?

MarkT

Yup, automotive fuses prevent wiring fires just as well as other types!
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Paul__B

#14
May 31, 2020, 02:30 pm Last Edit: May 31, 2020, 02:41 pm by Paul__B
Yup, automotive fuses prevent wiring fires just as well as other types!
One would most certainly hope so!  :smiley-eek:

Good idea, but, the bridge rectifier isn't PCB-mounting friendly!
I'm thinking of using two STTH2002C in series with one big heat sink (which I didn't calculate yet).
The datasheet suggests they would be suitable but having to use a heatsink (as you would for any solution including the power converters) is simply not "PCB-mounting friendly" anyway, so no real difference there.  :smiley-lol:

I changed it... thank you :)
Any more ideas?
No, you clearly didn't:smiley-roll:

You need to modify your first post here to correct the subject line.

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