Virtual 240Vac Bipolar Active Zener to Extend the SMPS High Voltage Limit

[KerimF]

An SMPS supply (24V/2A for example), working from 100Vac up to about 240Vac, may not be important to most engineers. On my side, I use it to supply most of the controller boards in my products.

I mean it is not really relevant to the issue of limiting maximum voltage.

If you are trying to supply power to a device that will take between 100 and 240 V and you want to prevent the mains 230V going over voltage then you can put a transformer (or autotransformer) that will reduce the voltage from 230V nominal to, say, 160V. That way you are sure to never go over voltage.

In this case, let us calculate the acceptable minimum mains voltage:
Vmin = 100V [minimum for SMPS] * 230 / 160 = 143.75 V

And let us calculate the acceptable maximum mains voltage:
Vmax = 250 [typical maximum for SMPS] * 230 / 160 =359.375V

In general, these two limits look reasonable.

The problem is that local consumers used to buy mains stabilizers working from 110V up to 290V (16-step model by using 4 relays). And above 290V, the saturation high current of their transformer opens their main breaker. These stabilizers don't use an external DC supply. Their controller is supplied by a low AC voltage taken from their main power transformer. Therefore, their protecting power relay has to be at the output, not input (hot line).

To compete in the local market, I let my controllers and their display work normally from 100V to 400V. The input of the stabilizer, excluding its SMPS, is isolated completely from mains by a protecting power relay if the Vac > 290V or below 110V). Things will return back to normal when the mains voltage returns back within limits (no need to switch/close an open mechanical breaker after a mains overvoltage).
 
For instance, ordering or making a special small transformer is not economical on my side.

[KerimF]

Is there a valid reason for you to not just develop your own SMPS capable of doing exactly what you need? Switcher with integrated 700V rated MOSFET's are available for peanuts.

Of course, there is a valid reason on my side
A practical SMPS needs a ferrite transformer. In these days, I have no more the privilege to order such components from abroad (this was possible before year 2011). Now, the local retailers provide them with unknown characteristics and in small quantities for each type.

[soldar]

An SMPS supply (24V/2A for example), working from 100Vac up to about 240Vac, may not be important to most engineers. On my side, I use it to supply most of the controller boards in my products.

I mean it is not really relevant to the issue of limiting maximum voltage.

If you are trying to supply power to a device that will take between 100 and 240 V and you want to prevent the mains 230V going over voltage then you can put a transformer (or autotransformer) that will reduce the voltage from 230V nominal to, say, 160V. That way you are sure to never go over voltage.

In this case, let us calculate the acceptable minimum mains voltage:
Vmin = 100V [minimum for SMPS] * 230 / 160 = 143.75 V

And let us calculate the acceptable maximum mains voltage:
Vmax = 250 [typical maximum for SMPS] * 230 / 160 =359.375V

In general, these two limits look reasonable.

The problem is that local consumers used to buy mains stabilizers working from 110V up to 290V (16-step model by using 4 relays). And above 290V, the saturation high current of their transformer opens their main breaker. These stabilizers don't use an external DC supply. Their controller is supplied by a low AC voltage taken from their main power transformer. Therefore, their protecting power relay has to be at the output, not input (hot line).

To compete in the local market, I let my controllers and their display work normally from 100V to 400V. The input of the stabilizer, excluding its SMPS, is isolated completely from mains by a protecting power relay if the Vac > 290V or below 110V). Things will return back to normal when the mains voltage returns back within limits (no need to switch/close an open mechanical breaker after a mains overvoltage).
 
For instance, ordering or making a special small transformer is not economical on my side.

I realize there is a bit of a language problem but I think I am only now beginning to understand what you want to do.  You are not explaining it very clearly.

You want a device that is connected to the mains and disconnects the load when voltage is under a voltage V1 or over another voltage V2 and connects the load when the voltage is between these values.

Is this what you want to do?

I cannot imagine living somewhere where the mains voltage is so unstable. That has to damage all sorts of appliances and electronics.

[coromonadalix]

exactly my toughts     i what i wrote earlier  is not country specific,  its just a matter of doing things properly with official and reliable tools, they exists and doesn't cost a fortune

you did receive very good answers, and telling  you are in say dire position monetary / political / other ... and not telling the full story is not helping you ...   i can understand you 

but here right now,  you ask for advise / help and you are still mysterious or vague in some instance(s)

you play with voltages and or currents, this is or may be a safety concern     

to have huge voltages swings in ac network / main voltages is not good BUT you need voltage conditioning / limitters, once again you did receive some answers and it seems  you don't want to acknowledge them




https://www.amazon.ca/Automatic-Protector-Reconnect-Reliable-Adjustable/dp/B08RJ6JSZD
https://www.amazon.com/Protection-Adjustable-Automatic-Reconnect-Protector/dp/B07TQH19KQ?th=1
https://www.walmart.ca/en/ip/adjustable-delay-protector-automatic-relay-protector-automatic-reconnect-for-voltage-protector-home/PRD15VKYMJO27WZ
https://www.walmart.ca/en/ip/Protection-Relay-Automatic-Protector-Over-Under-Voltage-Recovery-2P-40A/PRD4CHY6XXFF2Z6

and this one
https://www.automationdirect.com/adc/overview/catalog/relays_-z-_timers/voltage_monitoring_relays

Voltage monitoring relays sense and evaluate AC single-phase (50 to 60 Hz) or DC voltages to protect equipment from fault conditions.

    Over/under voltage relays with fixed or adjustable time-delay drop-out will protect equipment from over- or under-voltage conditions.
    Voltage band relays protect equipment that is required to operate within an upper and lower voltage limit. The relay is energized and will remain that way as long as the monitored voltage remains within the adjustable range.

Features

    Monitors AC single-phase (from 90 to 600 VAC) and DC voltages (from 9 to 138 VDC)
    True RMS voltage measurement supports non-sinusoidal waveforms and ensures more accurate sensing
    All relays offer 10A contact rating
    Wide range of user adjustable pick-up voltages
    8-pin socket mount (sold separately)
    LED indicates output relay status
    Select models support an adjustable drop-out delay (0.1 to 10 seconds)


(VMR-2C-F-120A)



another
https://www.littelfuse.com/products/protection-relays-and-controls/protection-relays/voltage-monitoring-relays.aspx

you have single phase and 3 phases models


No offense

With all the time and money you may lost trying to build something similar,  try some already made solutions,  to buy one, or try to get them shipped to you    unless your country is totally isolated from the planet

[KerimF]

I realize there is a bit of a language problem but I think I am only now beginning to understand what you want to do.  You are not explaining it very clearly.
You want a device that is connected to the mains and disconnects the load when voltage is under a voltage V1 or over another voltage V2 and connects the load when the voltage is between these values.
Is this what you want to do?

No 
What you understood from my previous post is related to the stabilizer and its load (the electrical network of a house or office).
The circuit, I presented, has to keep the SMPS that supplies 24Vdc voltage to the stabilizer's controller active from 100Vac (the SMPS typical minimum) up to 400Vac (the excess power is dissipated by the power hi-voltage MOSFET). It is the job of the controller to monitor the input and output voltages (also the mains current in some models) and activate the relays as it is programmed.

I reI cannot imagine living somewhere where the mains voltage is so unstable. That has to damage all sorts of appliances and electronics.

Me too, I am surprised that many consumers in my city need to install stabilizers. My mains voltage is, typically, in the range from 190V to 235V, not bad.

[Kim Christensen]

Could you not power the SMPS from the output of the stabilizer? Kind of like a reverse "bootstrap" configuration.
ie: The stabilizer's default mode is passthrough and it powers both the SMPS and the load.

[KerimF]

...its just a matter of doing things properly with official and reliable tools, they exists and doesn't cost a fortune

I believe this very true on your side.

you did receive very good answers, and telling  you are in say dire position monetary / political / other ... and not telling the full story is not helping you ...   i can understand you 

but here right now,  you ask for advise / help and you are still mysterious or vague in some instance(s)

It seems my English is really bad. I thought on my OP it was clear that I 'did' an active circuit to limit the voltage at the input of an SMPS specifically, not any other load. And it works fine. My question was:
"I shared this topology here with the hope that someone may know a simpler way to achieve this function."

So far, it seems there are ready-made products which do the same job, if not much better. These products are likely available to most engineers around the world, but not to me.

you play with voltages and or currents, this is or may be a safety concern     

It is about limiting a high voltage while the load current (of a 24V/2A SMPS) is relatively very small (at its input).

to have huge voltages swings in ac network / main voltages is not good BUT you need voltage conditioning / limitters, once again you did receive some answers and it seems  you don't want to acknowledge them

https://www.amazon.ca/Automatic-Protector-Reconnect-Reliable-Adjustable/dp/B08RJ6JSZD
https://www.amazon.com/Protection-Adjustable-Automatic-Reconnect-Protector/dp/B07TQH19KQ?th=1
https://www.walmart.ca/en/ip/adjustable-delay-protector-automatic-relay-protector-automatic-reconnect-for-voltage-protector-home/PRD15VKYMJO27WZ
https://www.walmart.ca/en/ip/Protection-Relay-Automatic-Protector-Over-Under-Voltage-Recovery-2P-40A/PRD4CHY6XXFF2Z6

and this one
https://www.automationdirect.com/adc/overview/catalog/relays_-z-_timers/voltage_monitoring_relays

Could you imagine that, due to world's regulations, all these sites (besides many others) have no right to open their door if knocked by someone living where I am? Otherwise, they broke the rules of their authorities. So, I have no reason to blame them.
   

With all the time and money you may lost trying to build something similar,  try some already made solutions,  to buy one, or try to get them shipped to you    unless your country is totally isolated from the planet

At last, you got my real situation well as you defined it by your last sentence
For instance, this forum is the last technical one that allowed me to join it and be its guest till now.

[KerimF]

Could you not power the SMPS from the output of the stabilizer? Kind of like a reverse "bootstrap" configuration.
ie: The stabilizer's default mode is passthrough and it powers both the SMPS and the load.

In this case there will be no need to use an external SMPS. I mentioned on reply #25:
"These stabilizers (not designed by me) don't use an external DC supply. Their controller is supplied by a low AC voltage taken from their main power transformer. Therefore, their protecting power relay has to be at the output, not input (hot line)."

Converting AC to DC is done on their controller. So, in case of a fault on the mains line, the high voltage saturates the power transformer, and the resulting high current opens their main breaker. I simply liked to avoid this to let my stabilizer full automatic after any situation,

[temperance]

The easiest solution to your problem is a source follower. Just a bridge rectifier, a zener, a couple resistors and a MOSFET and some inrush current limiter.

I can't seem to come up with a better schematic than this one:
https://electronics.stackexchange.com/questions/553703/source-follower-large-signal-analysis-as-level-shifter

Vin is derived from the mains supply with a zener diodes and a resistor. The voltage across Rs (your SMPS) will be at 2...5 V below the zener voltage.

[DavidAlfa]

Still no way you're clamping the mains, forget that idea right now.
What's the power of the smps?
You could make some sort of high voltage linear regulator, so that the transistor acts as a series resistor.
This will create a lot of heat, so meant for short durations events only (spikes, sudden changes).

A proper solution? A PFC circuit that produces stable DC output over a wide range of input voltages, then feed this DC to your smps.

[Kim Christensen]

"These stabilizers (not designed by me) don't use an external DC supply.

No.. Using your "stabilizer" to power your SMPS which powers your "stabilizer"...
ie: On startup, and if input line voltage is lower than 250VAC, the SMPS is connected to the line input via a DPDT relay. The SMPS powers your stabilizer and after a delay, the DPDT relay switches over so the SMPS is now powered by the output of your stabilizer. Now, your line voltage can vary up and down while your stabilizer keeps the voltage on the load and SMPS steady.
If the input voltage goes too high, your system shuts off, but the SMPS does not get reconnected to the line until the input voltage drops below 250VAC. So the input voltage has to drop below 250VAC before the system will auto restart.

[BrokenYugo]

If I'm understanding right what OP is after is a sort of preregulator for the control circuit PSU of a whole house mains tap changer voltage stabilizer. So they can use an available supply that can't handle more than 240V. They cannot use the output of the stabilizer because they want the power supply live full time, so the tap changer can connect and disconnect from the grid as the voltage goes in and out of the limits of the tap changer's transformer, rather than put the transformer into saturation and trip the breaker feeding it as their competitor's designs do.

I think the easiest solution is probably to rectify and buck down the mains to a reasonable value, then feed that DC to the SMPS, not sure that quite qualifies as PFC as DavidAlfa suggested, but it should work and the inductor is much simpler.

[temperance]

@DavidAlfa

You could make some sort of high voltage linear regulator, so that the transistor acts as a series resistor.

You seem rather beta when it comes to reading because that's exactly what I suggested above what you posted

[DavidAlfa]

Well, my apologies, sometimes it's just too long, please send patent documentation to proceed with IP infringement claim 

[KerimF]

The easiest solution to your problem is a source follower. Just a bridge rectifier, a zener, a couple resistors and a MOSFET and some inrush current limiter.

I can't seem to come up with a better schematic than this one:
https://electronics.stackexchange.com/questions/553703/source-follower-large-signal-analysis-as-level-shifter

Vin is derived from the mains supply with a zener diodes and a resistor. The voltage across Rs (your SMPS) will be at 2...5 V below the zener voltage.

Thank you for your suggestion. Right now, this webpage doesn't open properly on my side. I will try it later.

By the way, the proposed topology seems somehow similar to the one I attached on my first post; same components (excluding the inrush current limiter).

[KerimF]

Still no way you're clamping the mains, forget that idea right now.
What's the power of the smps?
You could make some sort of high voltage linear regulator, so that the transistor acts as a series resistor.
This will create a lot of heat, so meant for short durations events only (spikes, sudden changes).

A proper solution? A PFC circuit that produces stable DC output over a wide range of input voltages, then feed this DC to your smps.

In my solution (attached at OP), the MOSFET acts as a dynamic series resistor. You are right, this creates heat up to 10W (@400Vac). But this is not too bad knowing that the mains voltage is below 250Vac most of the time. And a high voltage on the mains line doesn't last for long. The SMPS power is usually 50W (24V/2A DC output) or less. So, its maximum input current is below 1/4 A (mains, 220V 50Hz).

Yes, using a PFC circuit is a very good solution. But it uses a ferrite transformer which I can't get easily in these days for many reasons.

[KerimF]

"These stabilizers (not designed by me) don't use an external DC supply.

No.. Using your "stabilizer" to power your SMPS which powers your "stabilizer"...
ie: On startup, and if input line voltage is lower than 250VAC, the SMPS is connected to the line input via a DPDT relay. The SMPS powers your stabilizer and after a delay, the DPDT relay switches over so the SMPS is now powered by the output of your stabilizer. Now, your line voltage can vary up and down while your stabilizer keeps the voltage on the load and SMPS steady.
If the input voltage goes too high, your system shuts off, but the SMPS does not get reconnected to the line until the input voltage drops below 250VAC. So the input voltage has to drop below 250VAC before the system will auto restart.

It seems a good solution. So, let us go on to some details.
On startup, there is a circuit that monitors the input line voltage.
This startup circuit should be designed for the worst case (Vin=400Vac).
Case 1:
It turns on the DPDT relay if Vin > 250Vac, in order to disconnect the SMPS from mains. In this case, I am not sure if the very short delay (in ms) before disconnecting the SMPS could damage it or not (mainly if Vin is >300Vrms).
Case 2: (opposite)
It turns on the relay if Vin < 250Vac, in order to connect the SMPS to mains line. But the relay should be on even if Vin drops to about 100V. I think this could be done, speaking practically, since the relay DC holding current is usually much lower than its startup current.
But, after a good startup (Vin < 250V), the high limit (250V) needs to be increased, otherwise the stabilizer won't reach its usable upper limit (about 290V).

I will work on it. Thank you.

Kerim

[KerimF]

If I'm understanding right what OP is after is a sort of preregulator for the control circuit PSU of a whole house mains tap changer voltage stabilizer. So they can use an available supply that can't handle more than 240V. They cannot use the output of the stabilizer because they want the power supply live full time, so the tap changer can connect and disconnect from the grid as the voltage goes in and out of the limits of the tap changer's transformer, rather than put the transformer into saturation and trip the breaker feeding it as their competitor's designs do.

I think the easiest solution is probably to rectify and buck down the mains to a reasonable value, then feed that DC to the SMPS, not sure that quite qualifies as PFC as DavidAlfa suggested, but it should work and the inductor is much simpler.

Unfortunately, I have to avoid, in these days, using ferrite transformers in my designs. For this reason, I had to use the E-I iron cores, instead of the ferrite ones, to produce various DC to AC power inverters (500W to 2KW).

[KerimF]

Based on the idea of a simpler solution suggested by Kim Christensen (Reply #35), I designed a circuit that monitors the mains voltage from 100V to 400V though it supplies the SMPS from 100V to 250V only.  Its main components are the two opamps of LM358, a small 24Vdc relay and two high voltage capacitors (1uF/275Vac in series, equivalent to 500nF)

I drew its schematic on Kicad (attached as PDF), then on LTspice to simulate it and test if it functions as expected. I used the available model LT1006 to replace LM358.

[KerimF]

Hi again,

I returned to this thread because there is a new solution which lets all previous ones in it obsolete in case the SMPS unit supplies the controller of a mains stabilizer.
 
Lately, a consumer ordered a mains voltage stabilizer (4KW, 50Hz). Its characteristics are supposed to be as the following:
[1] Its input voltage range is supposed to be 80 to 350 Vrms.
[2] Its output voltage range shouldn’t exceed 220V +/- 15V.
[3] Its controller (with 3+3 LED 7-segment digits) should work properly between 75 and 400 Vrms (consumer's mains voltage).

The first [1] and [2] could be achieved by using 4 power 1P2T relays which give 16 steps (11 for up, 1 for normal and 4 for down).

The challenge was to satisfy [3] with a simple low-cost reliable (non-mechanical) circuit to let a typical 24V/1A SMPS (rated input from 100 to 240 Vac) supply properly the stabilizer board even if the mains input voltage drops to 75V or increases up to 400V (this may happen in network faulty conditions).

I ended up designing for [3] a circuit to be added in front of the SMPS. Its components are:

16 x 1N4007
1 x IRFP460 (high voltage N_MOSFET)
2 x 160V zener (which was available)
1 x 10V zener (between the MOSFET gate and its source)

In case there are some members who may be interested in such a circuit, I will draw its Kicad schematic. Then, I will upload it as PDF.

Kerim

[NiHaoMike]

What about just a solid state switch that is on when the instantaneous voltage is less than 360V or so and off when above? I have seen a similar design to make a small 120V only switching supply able to run on both 120V and 240V. Very little dissipation and almost zero switching losses.

[KerimF]

What about just a solid state switch that is on when the instantaneous voltage is less than 360V or so and off when above? I have seen a similar design to make a small 120V only switching supply able to run on both 120V and 240V. Very little dissipation and almost zero switching losses.

Sorry, you give me the impression that you are not replying to my very last post.

A 24V/1A SMPS (rated from 100 to 240 Vac for its input) supplies the controller board of a 220V-50Hz mains stabilizer (its mains input could be from 80V to 350V while its ouput is 220V +/- 15V).

So, the added circuit (under the discussion here) should help this SMPS to work properly for a wider range of mains voltage (from 75 to 400 Vac, much wider than its rated range).