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Automotive Protection Circuit

I'm designing a Automotive Regulator Circuit for a system that runs at about 100mA at 7V with a max current draw of around 600mA for 10secs. The problem i'm having is with the protection circuit. I'm using the RBO40-40GT

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literature/ds/5484.pdf). This is the best chip I have found that can easily suppress voltages up to 120V(highest that I've tested it against). The problem is that this chip only clamps the voltage to a max of 40V. I'd like to use a linear regulator if possible, due to various load changes. I've been using an LT1129 from Linear Tech, but the problem is that it has a max input of 30V. Most linear regulators that can handle this current usually have a max input of 30V. I'd also like to keep the circuit small and surface mount if possible.

Any idea what I can do to clamp the voltage to 30V, while still using the RBO40-40GT? If I add another Zener diode between the regulator and the RBO, clamping the voltage to 30V - will this work? Any ideas would be great. Thanks

Reply to
eaglecbr
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How about using a circuit that goes open circuit instead of clamping. You might have to do it with discretes. Actually Jim Thompson posted a link here to just such a circuit on his website a few months ago. Goes something like this: A p-channel mosfet in the top rail with source connected to the positive power supply and base tied to ground provides reverse protection. To get overvoltage protection you use a TL431, a transistor and another mosfet in the rail. With a voltage divider to the reference terminal of the TL431, an overvoltage condition will cause the TL431 "cathode" to sink current, turning on a pnp transistor that connects the source and gate of the mosfet to turn it off. Plus the various resistors you would need in a circuit such as this. Remember the TL431 may sink some bit of current even when the reference pin sees low voltage, so you should put a resistor from the cathode to the top rail.

Reply to
gearhead

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...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
Jim Thompson

For the benefit of the OP.

This circuit is not suitable for your application as drawn. The FETs don't have the drain to source voltage rating and if you put in suitable FETs M1will go phut when you exceed its gate source voltage rating.

Reply to
Raveninghorde

So replace M1 with a diode as its only there for the reverse protection and the OP has plenty of headroom with a 7V regulated output even if one needs to run right down to 10V in. I'm more concerned about M2. Given a suitable FET, I suppose it

*should* survive provided the trigger point for the TL431 is less than its Vgs rating and the TL431 protect itself as it triggers but if you aren't muntzing it, a Zener connected gate-source would prevent transient stress on the gate oxide. If you *are* muntzing it, make M2 the pass transistor in the regulator as well.
Reply to
IanM

The first question is is it acceptable to shut down during a load dump. If it is you can buy LDO regulators with reverse battery and 60v load dump protection built in.

I presume 60v is enough for 12v automotive systems else they wouldn't bother trying to sell them?

Reply to
nospam

The posted circuit was to meet a specific SED functional request. Scale voltage ratings and take appropriate additional protective measures as necessary for your application.

In other words, act like a designer ;-)

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
Jim Thompson

Depends on the circuit configuration. Many of my ignition system designs protected themselves by turning off appropriate devices _during_ the load dump pulse.

I haven't looked "under the hood" with a 'scope in years, so I'm not familiar with what load-dump controls that might have been added.

But I can assure (scare) you that I ran storage 'scope investigations in the '60's that showed load dump pulses as high as 400V :-(

And I have chips turned to beads of silicon to prove it ;-) (Inductance-driven arc discharge across the chip.)

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
Jim Thompson

[snip]

I should have noted here that BVCER (or even better BVCEX) transistor ratings are generally substantially higher than BVCEO or even BVCBO standoffs.

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
Jim Thompson

MIL-STD-1275 for 24V vehicles specifies a single fault spike of 250V for 70us with 100V surges of 50ms. So 251V is allowed to fry the electronics.

Reply to
Raveninghorde

I was thinking of making a load dump simulator/generator "one day".

There is a circuit in the datasheet for the "LDP24M" (p4).

The energy and currents involved are huge!

I have seen voltages specified up to ~150V.

47,000uF charged to 150V dumped through 2 ohms is a pretty serious pulse. I've actually gone as far as snapping up a cheap box of 200V, 1500uF electrolytics to build the capacitor bank required. 
--

John Devereux
Reply to
John Devereux

The 100v load dump requirement is intended to cover cases where the vehicle is operated with no battery connected.

Higher voltages are low energy spikes which can be absorbed, the load dump tests can source about 200J. Your typical 1500W transient suppressor can absorb about 1.5J.

We were talking about cars on 12v not military vehicles on 24v.

If 100v is good enough for 24v military systems with no battery connected a

60v requirement on 12v systems seems quite adequate.
Reply to
nospam

A/C thermostat driving compressor clutch will do it ;-)

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
Jim Thompson

I guess I am a bit too electronics orientated - because I have no idea what those words mean (when put in that order)!

--

John Devereux
Reply to
John Devereux

(Automotive) Air Conditioning thermostat (mechanical/bi-metal plus relay) opening a _very_ inductive magnetic clutch between pulley drive and (Freon) compressor.

I guess I'm too automotive oriented... it's where I spent the years of my youth in electronics... I love cars... just saw a baby-shit-yellow colored Lamborghini in traffic... neck-snapping acceleration... drool.

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
Jim Thompson

Oh I see! Maybe... I was wondering if it was possible to store the energy magnetically somehow but it seemed like there would not be enough in anything reasonable. It's 500-1000J as far as I can make out.

Is the energy just in the inductance, or is it mechanical energy in the movement of the clutch (or compressor rotation)?

--

John Devereux
Reply to
John Devereux

also you need to increase R3 to about 3K to save the TL431 from having to conduct 1A during faults.

to compensate you may need to add some voltage drop (three 1m914's in series) in series with R4 (which should also be increased to about 3K)

Reply to
Jasen Betts

Both as i understand it. Kind of like large solenoids.

Reply to
JosephKK

Cool. The "official" simulator circuit I referenced in the datasheet above contains a 12mH inductor. A simulation indicates it can see currents of >50A.

12mH, 50A inductors are a bit thin on the ground... I found a 5mH one, it's a 10 inch diameter toroid :) 
--

John Devereux
Reply to
John Devereux

Thanks for the help everyone. Sorry I didn't respond earlier. It is not acceptable to power down the system during a large load dump. I need an always on system. I might end up putting like a battery backup system that will switch to backup battery during long load dump pulses. I would prefer a system that I described earlier, but don't know if its possible to clamp the voltage to 30V.

Reply to
eaglecbr

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