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I’m trying to recreate an over voltage protection circuit using LT1394 form the LtSpice library. Unfortunately, the circuit does not work as expected – or I do something wrong. I assume when voltage exceeds 36V the Q output should go high (36V) and switch the mosfet gate and disconnects the load. First, the voltage is around 19V, not close to VCC and the mosfet still conducts. Thanks, Jurek
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I’m sorry, i meant LT1011 – not LT1394. J ? From: <[email protected]> on behalf of "jerzy przezdziecki via groups.io" <jprzezdziecki@...>
Reply to: <[email protected]>
Date: Sunday, 2 February 2025 at 14:35
To: <[email protected]>
Subject: [LTspice] Over-voltage protection circuit does not work as expected
Resent from: <jprzezdziecki@...>
Resent date: Sun, 02 Feb 2025 05:35:37 -0800 I’m trying to recreate an over voltage protection circuit using LT1394 form the LtSpice library. Unfortunately, the circuit does not work as expected – or I do something wrong. I assume when voltage exceeds 36V the Q output should go high (36V) and switch the mosfet gate and disconnects the load. First, the voltage is around 19V, not close to VCC and the mosfet still conducts. Thanks, Jurek
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On 2/2/25 7:35 AM, jerzy przezdziecki via groups.io wrote: I’m trying to recreate an over voltage protection circuit using LT1394 form the LtSpice library. Unfortunately, the circuit does not work as expected – or I do something wrong.
From the data sheet: "If offset balancing or hysteresis is not used, the BALANCE pins should be connected together with a 0.1?F capacitor." -- David Schultz
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Isn't that what it is supposed to do?? 19V is not overvoltage so you would expect the mosfet to conduct.
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Works a heck of a lot better, with the S pin NOT grpinded…
As David Schultz suggested, maybe add the bypass cap between B and S,. but don’t ground it – that forces the out out to an open/pulled-up state.
?
Dave
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From: [email protected] <[email protected]>
On Behalf Of Roy McCammon via groups.io
Sent: Sunday, February 02, 2025 8:58 AM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Over-voltage protection circuit does not work as expected
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Isn't that what it is supposed to do?? 19V is not overvoltage so you would expect the mosfet to conduct.
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Two other suggestions:
Keep Vcc at 36V, but add a separate PWL(0 0 1 36) source to the comparator signal input, rather than the R2/R3 divider.
THEN(!) swap the + & - inputs. As is, it turns the output FET ON when the test voltage exceeds the Zener.
?
Dave
?
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From: [email protected] <[email protected]>
On Behalf Of Bell, Dave via groups.io
Sent: Sunday, February 02, 2025 10:01 AM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Over-voltage protection circuit does not work as expected
?
Works a heck of a lot better, with the S pin NOT grpinded…
As David Schultz suggested, maybe add the bypass cap between B and S,. but don’t ground it – that forces the out out to an open/pulled-up state.
?
Dave
?
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Isn't that what it is supposed to do?? 19V is not overvoltage so you would expect the mosfet to conduct.
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Roy, The overvoltage – as I understand it - is when the supply voltage exceeds eg. 36V – than output should go HIGH and disconnect the load. HIGH means full VCC, right? Where the voltage drops? Also, it looks like neither HIGH or LOW does not affects the P-MOS. Conducting all the time. ? Jurek ? From: <[email protected]> on behalf of "Roy McCammon via groups.io" <roymccammon@...>
Reply to: <[email protected]>
Date: Sunday, 2 February 2025 at 17:58
To: <[email protected]>
Subject: Re: [LTspice] Over-voltage protection circuit does not work as expected Isn't that what it is supposed to do?? 19V is not overvoltage so you would expect the mosfet to conduct.
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Ok, I have overlooked the 16V Zener, so all is fine. ? From: <[email protected]> on behalf of "Roy McCammon via groups.io" <roymccammon@...>
Reply to: <[email protected]>
Date: Sunday, 2 February 2025 at 17:58
To: <[email protected]>
Subject: Re: [LTspice] Over-voltage protection circuit does not work as expected Isn't that what it is supposed to do?? 19V is not overvoltage so you would expect the mosfet to conduct.
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Hello, ? I have uploaded circuit that finally works as executed with a good TLV1805 model found online. The problem was the ic. I have used a voltage comparator from the LTSpice library list with an open collector – instead of an original TLV1805 push-pull one. This made a simulation not working properly. So everything was fine with the PMOS. ? Anyway thanks to all for advices. ? Jurek ? From: <[email protected]> on behalf of "Bell, Dave via groups.io" <Dave.Bell@...>
Reply to: <[email protected]>
Date: Sunday, 2 February 2025 at 19:08
To: "[email protected]" <[email protected]>
Subject: Re: [LTspice] Over-voltage protection circuit does not work as expected
Resent from: <Dave.Bell@...>
Resent date: Sun, 02 Feb 2025 10:08:17 -0800 Two other suggestions: Keep Vcc at 36V, but add a separate PWL(0 0 1 36) source to the comparator signal input, rather than the R2/R3 divider. THEN(!) swap the + & - inputs. As is, it turns the output FET ON when the test voltage exceeds the Zener. ? Dave ?
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From: [email protected] <[email protected]> On Behalf Of Bell, Dave via groups.io
Sent: Sunday, February 02, 2025 10:01 AM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Over-voltage protection circuit does not work as expected? Works a heck of a lot better, with the S pin NOT grpinded… As David Schultz suggested, maybe add the bypass cap between B and S,. but don’t ground it – that forces the out out to an open/pulled-up state. ? Dave ? ? Isn't that what it is supposed to do?? 19V is not overvoltage so you would expect the mosfet to conduct.
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I would not designate the proposed circuit as an overvoltage protection circuit. At most it's something like a "voltage clipper" or "voltage limiter" for excessive input voltage excursions. Let's assume there are any failures within the control circuit, or a defective Power-MOSFet, or even overvoltages, coming from external sources directly to the Load, then you will get in trouble with that circuit.
A true overvoltage protection circuit requires a crowbar arrangement, as well known in the power electronics industry.
Best regards Udo?? Am Mi., 5. Feb. 2025 um 15:40?Uhr schrieb jerzy przezdziecki via <jprzezdziecki= [email protected]>:
Hello, ? I have uploaded circuit that finally works as executed with a good TLV1805 model found online. The problem was the ic. I have used a voltage comparator from the LTSpice library list with an open collector – instead of an original TLV1805 push-pull one. This made a simulation not working properly. So everything was fine with the PMOS. ? Anyway thanks to all for advices. ? Jurek ? Two other suggestions: Keep Vcc at 36V, but add a separate PWL(0 0 1 36) source to the comparator signal input, rather than the R2/R3 divider. THEN(!) swap the + & - inputs. As is, it turns the output FET ON when the test voltage exceeds the Zener. ? Dave ? ? Works a heck of a lot better, with the S pin NOT grpinded… As David Schultz suggested, maybe add the bypass cap between B and S,. but don’t ground it – that forces the out out to an open/pulled-up state. ? Dave ? ? Isn't that what it is supposed to do?? 19V is not overvoltage so you would expect the mosfet to conduct.
-- Dipl.Ing.Udo Huhn-Rohrbacher Albert-Kratz-Str.1 D-75180 Pforzheim phone: +497231-352339 fax: +497231-140338 mobile: +491523-3612096 E-mail: u.huhn.rohrbacher@...
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As much as a defective Power MOSFET can prevent a
series-protected voltage limiter, a problem with the crowbar
thyristor or its control circuit can defeat its purpose.
Nothing is ever perfect.
Le 05/02/2025 à 16:41, Udo
Huhn-Rohrbacher via groups.io a écrit?:
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I would not designate the proposed circuit as an
overvoltage protection circuit. At most it's something like a
"voltage clipper" or "voltage limiter" for excessive input
voltage excursions.
Let's assume there are any failures within the control
circuit, or a defective Power-MOSFet, or even overvoltages,
coming from external sources directly to the Load, then you
will get in trouble with that circuit.
A true overvoltage protection circuit requires a crowbar
arrangement, as well known in the power electronics industry.
Best regards
Udo??
Am Mi., 5. Feb. 2025 um
15:40?Uhr schrieb jerzy przezdziecki via
<jprzezdziecki= [email protected]>:
Hello,
?
I have uploaded circuit that
finally works as executed with a good TLV1805 model
found online.
The problem was the ic. I
have used a voltage comparator from the LTSpice
library list with an open collector – instead of an
original TLV1805 push-pull one.
This made a simulation not
working properly. So everything was fine with the
PMOS.
?
Anyway thanks to all for
advices.
?
Jurek
?
Two other suggestions:
Keep Vcc at 36V, but add a
separate PWL(0 0 1 36) source to the comparator
signal input, rather than the R2/R3 divider.
THEN(!) swap the + & -
inputs. As is, it turns the output FET ON when the
test voltage exceeds the Zener.
?
Dave
?
?
Works a heck of a lot better,
with the S pin NOT grpinded…
As David Schultz suggested,
maybe add the bypass cap between B and S,. but don’t
ground it – that forces the out out to an
open/pulled-up state.
?
Dave
?
?
Isn't that
what it is supposed to do?? 19V is not overvoltage
so you would expect the mosfet to conduct.
--
Dipl.Ing.Udo
Huhn-Rohrbacher
Albert-Kratz-Str.1
D-75180 Pforzheim
phone: +497231-352339
fax: +497231-140338
mobile: +491523-3612096
E-mail: u.huhn.rohrbacher@...
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I understand that overvoltage protection (OVP) must be a very simple and reliable circuit.
I've had a lot of problems with this circuit because sudden load variations can cause transients in the output voltage and reach high values triggering the triac! That's terrible.
Extreme situations can generate noise and lead to malfunctioning protection circuits.
My overvoltage detection, for this reason, is done by simple zener diodes and only components like the TLV1805 are suitable, as they have been designed for this purpose.
Because of these problems, in one specific case I used a microcontroller to trigger the crowbar. The microcontroller was able to distinguish between an overvoltage and a transient.
?
?
?
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I can imagine that crowbar is much better, but I would not be afraid about transients. This chip is extremally fast, a few ns. So – as you said – the TLV1805 is made for this purpose. Jurek ? I understand that overvoltage protection (OVP) must be a very simple and reliable circuit.
I've had a lot of problems with this circuit because sudden load variations can cause transients in the output voltage and reach high values triggering the triac! That's terrible.
Extreme situations can generate noise and lead to malfunctioning protection circuits.
My overvoltage detection, for this reason, is done by simple zener diodes and only components like the TLV1805 are suitable, as they have been designed for this purpose.
Because of these problems, in one specific case I used a microcontroller to trigger the crowbar. The microcontroller was able to distinguish between an overvoltage and a transient.
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Is there a circuit for this thread? Ild like to look at it myself when i get home.
On Wed, Feb 5, 2025 at 3:41 PM, jerzy przezdziecki via groups.io <jprzezdziecki@...> wrote: I can imagine that crowbar is much better, but I would not be afraid about transients. This chip is extremally fast, a few ns. So – as you said – the TLV1805 is made for this purpose. Jurek ? I understand that overvoltage protection (OVP) must be a very simple and reliable circuit.
I've had a lot of problems with this circuit because sudden load variations can cause transients in the output voltage and reach high values triggering the triac! That's terrible.
Extreme situations can generate noise and lead to malfunctioning protection circuits.
My overvoltage detection, for this reason, is done by simple zener diodes and only components like the TLV1805 are suitable, as they have been designed for this purpose.
Because of these problems, in one specific case I used a microcontroller to trigger the crowbar. The microcontroller was able to distinguish between an overvoltage and a transient.
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Yes, it’s uploaded in TEMP as “TLV1805_overvoltage_protection_circuit_works” ? Jurek ? From: <[email protected]> on behalf of "Richard Andrews via groups.io" <richardandrews.ma@...>
Reply to: <[email protected]>
Date: Wednesday, 5 February 2025 at 21:49
To: <[email protected]>
Subject: Re: [LTspice] Over-voltage protection circuit does not work as expected
Resent from: <richardandrews.ma@...>
Resent date: Wed, 05 Feb 2025 12:49:16 -0800 Is there a circuit for this thread? Ild like to look at it myself when i get home. ?
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On Wed, Feb 5, 2025 at 3:41 PM, jerzy przezdziecki via groups.io <jprzezdziecki@...> wrote: I can imagine that crowbar is much better, but I would not be afraid about transients. This chip is extremally fast, a few ns. So – as you said – the TLV1805 is made for this purpose. Jurek ? I understand that overvoltage protection (OVP) must be a very simple and reliable circuit.
I've had a lot of problems with this circuit because sudden load variations can cause transients in the output voltage and reach high values triggering the triac! That's terrible.
Extreme situations can generate noise and lead to malfunctioning protection circuits.
My overvoltage detection, for this reason, is done by simple zener diodes and only components like the TLV1805 are suitable, as they have been designed for this purpose.
Because of these problems, in one specific case I used a microcontroller to trigger the crowbar. The microcontroller was able to distinguish between an overvoltage and a transient.
|
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Show quoted text
On Wed, Feb 5, 2025 at 3:51 PM, jerzy przezdziecki via groups.io <jprzezdziecki@...> wrote: Yes, it’s uploaded in TEMP as “TLV1805_overvoltage_protection_circuit_works” ? Jurek ? From: <[email protected]> on behalf of "Richard Andrews via groups.io" <richardandrews.ma@...>
Reply to: <[email protected]>
Date: Wednesday, 5 February 2025 at 21:49
To: <[email protected]>
Subject: Re: [LTspice] Over-voltage protection circuit does not work as expected
Resent from: <richardandrews.ma@...>
Resent date: Wed, 05 Feb 2025 12:49:16 -0800 Is there a circuit for this thread? Ild like to look at it myself when i get home. ? On Wed, Feb 5, 2025 at 3:41 PM, jerzy przezdziecki via groups.io <jprzezdziecki@...> wrote: I can imagine that crowbar is much better, but I would not be afraid about transients. This chip is extremally fast, a few ns. So – as you said – the TLV1805 is made for this purpose. Jurek ? I understand that overvoltage protection (OVP) must be a very simple and reliable circuit.
I've had a lot of problems with this circuit because sudden load variations can cause transients in the output voltage and reach high values triggering the triac! That's terrible.
Extreme situations can generate noise and lead to malfunctioning protection circuits.
My overvoltage detection, for this reason, is done by simple zener diodes and only components like the TLV1805 are suitable, as they have been designed for this purpose.
Because of these problems, in one specific case I used a microcontroller to trigger the crowbar. The microcontroller was able to distinguish between an overvoltage and a transient.
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You’re right - it does work!
I found the output voltage curve a little confusing by itself, with the ramp Up and ramp Down.
But reducing the output cap to 10u or increasing the load to 100 ohms, it became clear; it was just the slooow decay that looked weird.
?
Dave
?
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From: [email protected] <[email protected]>
On Behalf Of jerzy przezdziecki via groups.io
Sent: Wednesday, February 05, 2025 12:51 PM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Over-voltage protection circuit does not work as expected
?
Yes, it’s uploaded in TEMP as “TLV1805_overvoltage_protection_circuit_works”
?
Jurek
?
Is there a circuit for this thread? Ild like to look at it myself when i get home.
?
On Wed, Feb 5, 2025 at 3:41 PM, jerzy przezdziecki via groups.io
I can imagine that crowbar is much better, but I would not be afraid about transients. This chip is extremally fast, a few ns. So – as you said – the TLV1805 is made for this purpose.
Jurek
?
I understand that overvoltage protection (OVP) must be a very simple and reliable circuit.
I've had a lot of problems with this circuit because sudden load variations can cause transients in the output voltage and reach high values triggering the triac! That's terrible.
Extreme situations can generate noise and lead to malfunctioning protection circuits.
My overvoltage detection, for this reason, is done by simple zener diodes and only components like the TLV1805 are suitable, as they have been designed for this purpose.
Because of these problems, in one specific case I used a microcontroller to trigger the crowbar. The microcontroller was able to distinguish between an overvoltage and a transient.
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Dave, thanks for the advice. The ramp down is not needed indeed. Anyway, the original model of TLV1805 is a nice find. ? Jurek ? From: <[email protected]> on behalf of "Bell, Dave via groups.io" <Dave.Bell@...>
Reply to: <[email protected]>
Date: Wednesday, 5 February 2025 at 22:09
To: "[email protected]" <[email protected]>
Subject: Re: [LTspice] Over-voltage protection circuit does not work as expected
Resent from: <Dave.Bell@...>
Resent date: Wed, 05 Feb 2025 13:09:29 -0800 You’re right - it does work! I found the output voltage curve a little confusing by itself, with the ramp Up and ramp Down. But reducing the output cap to 10u or increasing the load to 100 ohms, it became clear; it was just the slooow decay that looked weird. ? Dave ?
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Show quoted text
From: [email protected] <[email protected]> On Behalf Of jerzy przezdziecki via groups.io
Sent: Wednesday, February 05, 2025 12:51 PM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Over-voltage protection circuit does not work as expected? Yes, it’s uploaded in TEMP as “TLV1805_overvoltage_protection_circuit_works” ? Jurek ? Is there a circuit for this thread? Ild like to look at it myself when i get home. ? On Wed, Feb 5, 2025 at 3:41 PM, jerzy przezdziecki via groups.io I can imagine that crowbar is much better, but I would not be afraid about transients. This chip is extremally fast, a few ns. So – as you said – the TLV1805 is made for this purpose. Jurek ? I understand that overvoltage protection (OVP) must be a very simple and reliable circuit.
I've had a lot of problems with this circuit because sudden load variations can cause transients in the output voltage and reach high values triggering the triac! That's terrible.
Extreme situations can generate noise and lead to malfunctioning protection circuits.
My overvoltage detection, for this reason, is done by simple zener diodes and only components like the TLV1805 are suitable, as they have been designed for this purpose.
Because of these problems, in one specific case I used a microcontroller to trigger the crowbar. The microcontroller was able to distinguish between an overvoltage and a transient.
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I get an aborting notice. Sim quits before it starts with "unknown schematic syntax: V".
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I am running version 4.23.
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I can't run it on my 64-bit system because it is bricked. I have a new system coming later today.
?
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Jerzy, the problem is not the speed at which the overvoltage is detected, but whether it is a transient or not. You have to wait and see if the voltage returns to low values (a ringing) or if it remains high. Only in the second case do you have to trigger the triac and open the circuit. Otherwise, you will open the circuit incorrectly ??
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Roy McCammon
Bell, Dave
Marcelo_Pessoa