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DC overvoltage protection circuit

RonR399

New Member
I am using a buck converter that is being powered from a pair of 12 vdc batteries in series(24 vdc system)

I need a protection circuit design that will disconnect the output of the buck converter if the voltage goes too high. I have the buck converter adjusted to 12 VDC
and it is very stable but a protection circuit is still needed. rather than use a Crowbar circuit I would rather have an active circuit that disconnects when the power goes near 12.5 vdc. Does anyone have a circuit design I can borrow?
 

gophert

Well-Known Member
Most Helpful Member
Here is an option...

Let me know if you think it might work. Note that it needs the unregulated 24v supply. The 12VDC into the control circuit has been modulated to exceed 12.5v and cause cutoff.

 

AnalogKid

Well-Known Member
Most Helpful Member
The circuit in #4 gets you half-way there. It has a reference voltage, a comparator, and drives a p-channel MOSFET. All good so far. It is missing a latching function, a way to reset the latch, and possibly a power-on delay that allows the output to come up and stabilize before testing it. Since a dual-comparator is a fairly common part, the 2nd comparator in the package can be used for these functions. Is this the kind of thing you are looking for?

ak
 

gophert

Well-Known Member
Most Helpful Member
The circuit in #4 gets you half-way there. It has a reference voltage, a comparator, and drives a p-channel MOSFET. All good so far. It is missing a latching function, a way to reset the latch, and possibly a power-on delay that allows the output to come up and stabilize before testing it. Since a dual-comparator is a fairly common part, the 2nd comparator in the package can be used for these functions. Is this the kind of thing you are looking for?

ak
I assumed he wanted the circuit to cutout when over 12.5v and automatically resume when voltage is back under 12.5v. But the parts listed are certainly required if a manual reset is desired. A better project definition is required.
 

RonR399

New Member
The circuit in #4 gets you half-way there. It has a reference voltage, a comparator, and drives a p-channel MOSFET. All good so far. It is missing a latching function, a way to reset the latch, and possibly a power-on delay that allows the output to come up and stabilize before testing it. Since a dual-comparator is a fairly common part, the 2nd comparator in the package can be used for these functions. Is this the kind of thing you are looking for?

ak
Not really what I am looking for.
 

crutschow

Well-Known Member
Most Helpful Member
Not really what I am looking for.
Gophert's circuit appears to do what you stated in post #1, so what is wrong with that circuit, and what exactly do you want?
 

AnalogKid

Well-Known Member
Most Helpful Member
Not really what I am looking for.
Thanks for all of that useful information. One more guess, then I'm out.
I would rather have an active circuit that disconnects when the power goes near 12.5 vdc.
Disconnects what?

a) Disconnects the load from the output of the regulator when the input to the regulator "goes near" 12.5 Vdc.

b) Disconnects the input to the regulator from the external voltage source when that source sags down from 24 V to 12.5 V.

c) Other.

ak
 

RonR399

New Member
Here is an option...

Let me know if you think it might work. Note that it needs the unregulated 24v supply. The 12VDC into the control circuit has been modulated to exceed 12.5v and cause cutoff.

it appears that external parts are added to an IC that is available, am I correct?
 

RonR399

New Member
You need protection at the Output / Input?
Input is 24V
Output = ?
Load = ?
ok, I will try again and I will simplify.

12.2 vdc source feeding 2 amps. I want to prevent over voltage from getting to the equipment. I prefer something other than
a crowbar circuit.

I want to disconnect the 12.2 vdc from the Equipment if it gets to 12.5 volts or more. a manual reset is fine.
forget about the 24 vdc i mentioned earlier.
 

gophert

Well-Known Member
Most Helpful Member
it appears that external parts are added to an IC that is available, am I correct?
Yes, those shown are generic parts. P-channel Mosfet (transistor) and operational amplifier. You'll need to describe the amperage the load is drawing, an automatic reset takes fewer parts (video above) than adding a manual reset from my first look.

Once you nail down the details and accept a design, we can recommend specific parts.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
ok, I will try again and I will simplify.

12.2 vdc source feeding 2 amps. I want to prevent over voltage from getting to the equipment. I prefer something other than
a crowbar circuit.

I want to disconnect the 12.2 vdc from the Equipment if it gets to 12.5 volts or more. a manual reset is fine.
forget about the 24 vdc i mentioned earlier.
You've already had a suitable and simple circuit from gophert - what you're asking isn't particularly simple.

It's also NOT a very safe solution, which is why crowbar circuits are normally used.
 

AnalogKid

Well-Known Member
Most Helpful Member
that circuit has too many parts.
Not too many for the job. At a minimum you need four circuit functions:

1. A reference voltage to compare against. This does not have to be the same voltage as the trip point (the output voltage level that trips the circuit into its disconnect action), because the output can be scaled down for comparison.

2. A comparator, something that decides if the output voltage is over its limit.

3. A switch device to disconnect the load. This can be a power MOSFET, a bipolar transistor, or a relay.

4. Some kind of feedback to latch the power switch off once it has been tripped. Depending on how the other functions are implemented, this might be anything from a single diode to a separate logic circuit.

Some companies make overvoltage protection (OVP) and electronic circuit breaker chips that combine two or more of these functions, but all four functions are needed for the task you describe.

ak
 

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