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I'm designing a circuit that has the following protection requirements:

  • Reverse polarity
  • Over voltage (60v max)
  • Over current (approx 1A)

There's quite a large input voltage range, 10v to 60v.

48v is nominal, drawing about 150mA. At 10vin, it draws rougly 750mA.


I made and tested the following circuit to satisfy the conditions: (Values are working but not proved optimal) Protection circuit 00

M1 was my starting point for reverse polarity, then the zener, divider & M2 were added for over voltage.

I found that D1 was needed when I breadboarded it, much to my annoyance as I wanted to avoid much voltage drop. (I smell redundancy...)

The fuse is the most frustrating element. I don't want to have to replace any components if there is a fault (even a fuse in a housing), so I was working with a PTC resettable fuse. Not only does this have an horrific tripping time (~4 seconds!), it also has a large footprint on the PCB; much too large for me I'm afraid :(

I decided it is more beneficial to me to monitor the current and turn off a FET for example, than to crowbar the circuit if such a fault should occur.

My question is...

A) Is there an IC that can take care of these three elements? I've been looking at battery charger protection ICs but I haven't found anything yet.

B) Does anyone have a suggestion about incorporating the over current requirement in my circuit without a fuse? My initial thoughts were to use a sense resistor, comparator and another FET, but I can't help but think the whole circuit could then be simplified a great deal.

Thanks for looking.

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  • \$\begingroup\$ Google for "crowbar circuit". It is usually based around a SCR, which is triggered on a fault condition and in turn blows the fuse. \$\endgroup\$ – jippie Apr 2 '13 at 19:28
  • \$\begingroup\$ related thread: electronics.stackexchange.com/q/39600 \$\endgroup\$ – Nick Alexeev Nov 14 '15 at 20:05
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Try this IC: http://www.linear.com/product/LT4356-1

LT4356-1 and -2 - Surge Stopper Features

Stops High Voltage Surges
Adjustable Output Clamp Voltage
Overcurrent Protection
Wide Operation Range: 4V to 80V
Reverse Input Protection to –60V
Low 7μA Shutdown Current, LT4356-1
Adjustable Fault Timer
Controls N-channel MOSFET
Shutdown Pin Withstands –60V to 100V
Fault Output Indication
Guaranteed Operation to 125°C
Auxiliary Amplifier for Level Detection Comparator or Linear Regulator Controller
Available in (4mm × 3mm) 12-Pin DFN, 10-Pin MSOP or 16-Pin SO Packages

You should note that the previously commended LT4361 IC is similar but does not support your input voltage range requirements; many ICs out there are intended to support protection of low voltage supply buses, less support the higher voltage ranges you seek. LTC4361-1/LTC4361-2 - Overvoltage/Overcurrent Protection Controller Features

2.5V to 5.5V Operation
Overvoltage Protection Up to 80V
No Input Capacitor or TVS Required for Most Applications
2% Accurate 5.8V Overvoltage Threshold
10% Accurate 50mV Overcurrent Circuit Breaker
<1μs Overvoltage Turn-Off, Gentle Shutdown
Controls N-Channel MOSFET
Adjustable Power-Up dV/dt Limits Inrush Current
Reverse Voltage Protection
Power Good Output
Low Current Shutdown
Latchoff (LTC4361-1) or Auto-Retry (LTC4361-2) After Overcurrent
Available in 8-Lead ThinSOT™ and 8-Lead (2mm × 2mm) DFN Packages
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  • \$\begingroup\$ whatever102904, that is exactly what I've been looking for, thanks! \$\endgroup\$ – raaymaan Apr 3 '13 at 6:32
  • \$\begingroup\$ @whatever102904 how do I get the LT4356 to work at 24v 1Amp? \$\endgroup\$ – warath-coder Dec 1 '15 at 22:30
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If you want your circuit to be tolerant of over-voltage, you will have to specify up to which voltage, because your protection circuit must be built to withstand that voltage.

If you can afford the drop a diode bridge is a sure way to be polarity independent. You can eliminate the drop by using a relay.

For over-current you will have to decide what to do when you detect over-current. Limit the current to the maximum value? That implies a linear element, and hence (lots of) power dissipation! Another option is to cut of the power to your gadget until power is removed. This implies some memory element, a thyristor can be convenient for this purpose.

Note that your wish not to have a fuse makes a huge difference in cost: otherwise a fuse + power zener diode would do the reverse and over voltage protection, and a current triggered thyristor crowbar would do over-current.

You seemed to be unhappy with the drop for a series diode. You must realize that almost any form of current monitoring will need some voltage drop, and lower drops require a more complex circuit..

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  • 1
    \$\begingroup\$ To add to your last point instead of using a diode which drops th voltage by minimum of 0.3V (schottky ) one can go for MOSFET which consumes voltages in the range of tens of millivotls. \$\endgroup\$ – Durgaprasad Apr 2 '13 at 17:45
  • \$\begingroup\$ Durgaprasad, can you elaborate on using Mosfet like a diode? thx. \$\endgroup\$ – MikeTeX Oct 7 '16 at 12:28
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There are chips that do provide for functions of over voltage detect or over current detect. It can be quite inexpensive to build your own circuit though. There is a reasonably good article in EDN online which describes a discrete component circuit as shown below:

enter image description here

A neat feature of the above circuit is that it operates like a circuit breaker and removes the load from the faulted input. It stays removed until reset via a tact switch or the input power is removed.

It is my suggestion that the reverse polarity protection can best be provided via a series Schottky diode in the Vin+ supply line. I also suggest that you design your over voltage detector and over current detector in a manner that leaves the GND of the circuit intact. Someday when your project ideas turn into a real product that you must take off to a lab for emissions and immunity testing you will really appreciate using design techniques that keep a single GND, GND planes and chassis/enclosure references.

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Yes. You can find umpteen number of ICs for your requirements. Below is for the Linear Technologies' LTC4361. All the LTC43 series are one or the other protectory ICs. You can go through the datasheet of the below IC and design the peripherals accordingly for your requirements. enter image description here

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protected by W5VO Apr 2 '13 at 18:02

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