Does Psu Protect Agains Burn Out
Over-voltage Protection for Power Supplies
Power supply over-voltage protection is really useful - some PSU failures can put damaging large voltages on the equipment. Over-voltage protection prevents this happening on both linear regulators and switch mode power supplies.
Ability Supply Circuits Primer & Tutorial Includes:
Ability supply electronics overview Linear power supply Switch mode ability supply Over-voltage protection PSU specs Digital Power Ability direction bus: PMbus Uninterruptible power supply
Although modernistic power supplies are at present very reliable, there is always a small-scale simply real chance that they tin fail.
They can neglect in many ways and i particularly worrying possibility is that the serial pass chemical element, i.e. master laissez passer transistor or FET may fail in such a way that it goes brusque excursion. If this happens a very large voltage often referred to as an over-voltage could announced on the circuitry that is being powered causing catastrophic impairment to the whole equipment.
By adding a trivial extra protection circuitry in the course of over-voltage protection, information technology is possible to protect against this unlikely just catastrophic possibility.
Most power supplies designed for very reliable operation of high value equipment will incorporate some grade of over-voltage protection to ensure that whatsoever power supply failure does not result in damage to the equipment being powered. This applies to both linear power supplies and likewise to switch mode power supplies.
Some power supplies may not incorporate over-voltage protection and these should not exist used for powering expensive equipment - information technology is possible to do a niggling electronic circuit design and to develop a small-scale over-voltage protection circuit and add this on as an extra item.
Over-voltage protection basics
There are many ways in which a power supply tin can fail. However to understand a little more at over-voltage protection and the circuit issues it is piece of cake to take a unproblematic instance of a linear voltage regulator using a very simple Zener diode and a series laissez passer transistor.
Although more complicated supplies give better performance, they also rely on a serial transistor to pass the output current. The principal difference is the way in which the regulator voltage is applied to the base of the transistor.
Typically the input voltage is such that several volts are dropped across the serial voltage regulator element. This enables the serial pass transistor to regulate the output voltage fairly. Often the voltage dropped across the series pass transistor is relatively loftier - for a 12 volts supply, the input may be xviii volts of even more to requite the required regulation and ripple rejection, etc.
This means that there can be a significant level of rut dissipated in the voltage regulator element and combined with whatsoever transient spikes that could appear at the input, this means at that place is always a possibility of failure.
The transistor series pass device would more usually fail in an open circuit condition, only nether some circumstances, the transistor may develop a brusk circuit between the collector and emitter. If this occurs, then the full unregulated input voltage would appear in the output of the voltage regulator.
If the full voltage appeared on the output, then it could damage many of the ICs that are in the circuit beingness supplied. In this example the circuit could well be across economic repair.
The way in which switching regulators operate is very dissimilar, but there are circumstances in which the full output could appear on the output of the ability supply.
For both linear regulated power supplies and switch mode power supplies, some class of over-voltage protection is always advisable.
Types of over-voltage protection
As with many electronic techniques there are several means of implementing a particular capability. This is true for over-voltage protection.
There are several different techniques that can be used, each with its ain characteristics. Performance, cost, complexity and mode of functioning all need to exist weighed up when determining which method to use during the electronic circuit design stage.
-
SCR Crowbar: As the proper name implies the crowbar circuit places a short circuit across the output of the power supply if an over-voltage condition is experienced. Typically thyristors, i.e. SCRs are used for this as they tin can switch big currents and remain on until any charge has dispersed. The thyristor can be linked dorsum to a fuse which blows and isolates the regulator from having any farther voltage placed upon it.
Thyristor crowbar overvoltage protection circuit In this circuit, the Zener diode is called so that its voltage is higher up the normal operating voltage of the output, but beneath the voltage where damage would occur. In this conduction, no current flows through the Zener diode considering its breakup voltage has non been reached and no electric current flows into the gate of the thyristor and it remains off. The power supply volition operate normally.
If the series laissez passer transistor in the ability supply fails, the voltage will start to rise - the decoupling in the unit of measurement will ensure it does non rise instantly. As information technology rises, it will ascent in a higher place the point where the Zener diode starts to conduct and current will menstruation into the gate of the thyristor causing it to trigger.
When the thyristor triggers, it will brusk the output of the ability supply to ground, preventing impairment to the circuitry it powers. This short circuit can as well exist used to blow a fuse or other chemical element, taking the power off the voltage regulator and isolating the unit from further damage.
Often some decoupling in the form of a small capacitor is placed from the gate of the thyristor to footing to prevent sharp transients or RF from the unit being ability from getting on to the gate connection and causing a spurious trigger. However this should not be made as well large equally it may slow the circuit firing in a real case of failure and the protection may be in place also slowly.
Note on Thyristor Crowbar Overvoltage Protection:
The Thyristor or SCR, Silicon Controlled Rectifier can be used to provide overvoltage protection in a power supply circuit. By detecting the loftier voltage, the excursion can fire the thyristor to place a short excursion or crowbar across the voltage rail to ensure it does not rise to high in voltage.
Read more most Thyristor Crowbar Overvoltage Protection Circuit.
-
Voltage clamping: Another very unproblematic form of over-voltage protection uses an approach called voltage clamping. In its simplest class it tin be provided past using a Zener diode placed beyond the output of the regulated power supply. With the Zener diode voltage chosen to be slightly above the maximum track voltage, under normal conditions it will not deport. If the voltage rises too loftier, then it will offset to comport, clamping the voltage at a value slightly above the rail voltage.
If a higher current capability is needed for the regulated power supply then a Zener diode with a transistor buffer can be used. This will increase the current capability over the simple Zener diode excursion, past a factor equal to the current gain of the transistor. Equally a power transistor is required for this excursion, the likely current gain levels will be low - possibly twenty - fifty.
Zener diode over-voltage clench
(a) - simple Zener diode, (b) - college current with transistor buffer -
Voltage limiting: When over-voltage protection is required for switch mode power supplies, SMPS the clamp and crowbar techniques are less widely used because of the ability dissipation requirements and the possible size and toll of the components.
Fortunately near switch mode regulators fail in a low voltage condition. However information technology is frequently prudent to put in place voltage limiting capabilities in case of over-voltage conditions.
Oft this can be achieved by sensing the over-voltage condition and shutting down the converter. This is particularly applicable in the case of DC-DC converters. When implementing this, it is necessary to incorporate a sense loop that is outside the principal IC regulator - many switch way regulators and DC-DC converters employ a chip to achieve the majority of the circuit. It is very important to apply an external sense loop considering if the switch way regulator chip is damaged causing the over-voltage status, the sense machinery may besides exist damaged.
Manifestly this form of over-voltage protection requires circuits that are specific to the detail circuit and switch way power supply chips used.
All iii techniques are used and can provide effective power supply over-voltage protection. Each has its ain advantages and disadvantages and the choice of technique needs to be made dependent upon the given situation.
More than Circuits & Circuit Blueprint:
Op Amp basics Op Amp circuits Power supply circuits Transistor design Transistor Darlington Transistor circuits FET circuits Excursion symbols
Return to Circuit Design card . . .
batistafrenjudipt.blogspot.com
Source: https://www.electronics-notes.com/articles/analogue_circuits/power-supply-electronics/over-voltage-protection.php
0 Response to "Does Psu Protect Agains Burn Out"
Post a Comment