Keyboard Shortcuts
Likes
Search
Over-voltage protection circuit does not work as expected
开云体育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 |
开云体育I’m sorry, i meant LT1011 – not LT1394. J ? From: <[email protected]> on behalf of "jerzy przezdziecki via groups.io" <jprzezdziecki@...> ? 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 |
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 |
开云体育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 ? 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 ? Isn't that what it is supposed to do?? 19V is not overvoltage so you would expect the mosfet to conduct. |
开云体育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 ? 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 ? From:
[email protected] <[email protected]>
On Behalf Of Roy McCammon via groups.io ? Isn't that what it is supposed to do?? 19V is not overvoltage so you would expect the mosfet to conduct. |
开云体育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@...> ? Isn't that what it is supposed to do?? 19V is not overvoltage so you would expect the mosfet to conduct. |
开云体育Ok, I have overlooked the 16V Zener, so all is fine. ? From: <[email protected]> on behalf of "Roy McCammon via groups.io" <roymccammon@...> ? Isn't that what it is supposed to do?? 19V is not overvoltage so you would expect the mosfet to conduct. |
开云体育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@...> ? 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 ? 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 ? From: [email protected] <[email protected]> On Behalf Of Roy McCammon via groups.io ? Isn't that what it is supposed to do?? 19V is not overvoltage so you would expect the mosfet to conduct. |
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]>:
--
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@... |
开云体育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. Le 05/02/2025 à 16:41, Udo
Huhn-Rohrbacher via groups.io a écrit?:
|
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. ?
?
? |
开云体育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 ? From: <[email protected]> on behalf of "mpessoa via groups.io" <mpessoa@...> ? I understand that overvoltage protection (OVP) must be a very simple and reliable circuit. ? ? ? |
Is there a circuit for this thread? Ild like to look at it myself when i get home.
toggle quoted message
Show quoted text
|
开云体育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@...> ? Is there a circuit for this thread? Ild like to look at it myself when i get home. ?
|
Cool thanks.
toggle quoted message
Show quoted text
|
开云体育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 ? 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 ? From:
<[email protected]> on behalf of "Richard Andrews via groups.io" <richardandrews.ma@...> ? Is there a circuit for this thread? Ild like to look at it myself when i get home. ?
|
开云体育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@...> ? 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 ? 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 ? From: <[email protected]> on behalf of "Richard Andrews via groups.io" <richardandrews.ma@...> ? Is there a circuit for this thread? Ild like to look at it myself when i get home. ?
|
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 ?? |