Automotive Protection Circuit
in [Design]
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From: Telkom on 18 Dec 2008 19:12 I would use a switching regulator to feed the linear circuit
From: gearhead on 18 Dec 2008 11:13 On Dec 18, 5:58 am, eaglecbr <Christopher.B.Robe...(a)gmail.com> wrote: > 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(http://www.stmicroelectronics.com/stonline/products/ > 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 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.
From: Jim Thompson on 18 Dec 2008 11:22 On Thu, 18 Dec 2008 08:13:19 -0800 (PST), gearhead <nospam(a)billburg.com> wrote: >On Dec 18, 5:58 am, eaglecbr <Christopher.B.Robe...(a)gmail.com> wrote: >> 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(http://www.stmicroelectronics.com/stonline/products/ >> 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 > >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. http://analog-innovations.com/SED/OverAndReverseVoltageProtection.pdf >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. ...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
From: Raveninghorde on 19 Dec 2008 06:03 On Thu, 18 Dec 2008 09:22:00 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Thu, 18 Dec 2008 08:13:19 -0800 (PST), gearhead ><nospam(a)billburg.com> wrote: > >>On Dec 18, 5:58�am, eaglecbr <Christopher.B.Robe...(a)gmail.com> wrote: >>> 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(http://www.stmicroelectronics.com/stonline/products/ >>> 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 >> >>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. > >http://analog-innovations.com/SED/OverAndReverseVoltageProtection.pdf > >>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. > > ...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.
From: IanM on 19 Dec 2008 08:07
Raveninghorde wrote: > On Thu, 18 Dec 2008 09:22:00 -0700, Jim Thompson > <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: > >> On Thu, 18 Dec 2008 08:13:19 -0800 (PST), gearhead >> <nospam(a)billburg.com> wrote: >> >>> On Dec 18, 5:58 am, eaglecbr <Christopher.B.Robe...(a)gmail.com> wrote: >>>> 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(http://www.stmicroelectronics.com/stonline/products/ >>>> 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 >>> 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. >> http://analog-innovations.com/SED/OverAndReverseVoltageProtection.pdf >> >>> 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. >> ...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. 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. |