32
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What are the disadvantages of using a Zener diode over a linear voltage regulator?
1) When using a Zener diode as the regulation element like in this circuit:
the disadvantage is that the circuit needs to be configured such that there's always some current flowing through the ...
- 81k
19
votes
Why 7805 regulator gives output 6 volt?
Your circuit is fine. The battery in your meter needs to be replaced.
The voltmeter is reading high by more than 20% because the internal voltage reference has gone out of regulation (low) and the ...
- 407k
16
votes
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Connecting Voltage Regulators 7812 in Parallel for High Current
No, that is a bad idea. The two regulators won't have exactly the same output voltage. The one with the higher output voltage will take more current. You can't guarantee that both regulators will ...
- 314k
10
votes
What are the disadvantages of using a Zener diode over a linear voltage regulator?
If I understand correctly, this phenomenon will happen only when the Zener diode is connected with the load in parallel. What if I connected my Zener diode with my load in parallel?
Then you have the ...
- 177k
9
votes
Accepted
Why 7805 regulator gives output 6 volt?
You need a minimum load for them to regulate. Add a resistor to give 100 uA of load and the situation should improve.
- 15.7k
9
votes
Accepted
Which capacitors to use with voltage regulator IC such as 7805?
Many of the tutorials suggest to use a large smoothing capacitor (tens and even hundreds of uF) with a full wave rectifier
An interesting property of AC voltage is that it goes down to zero twice per ...
- 79.5k
8
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How much power does LM7805 dissipate?
Take a look at package thermal data section in your datasheet page two.
Depending on the package of the regulator you are using, lets say the thermal junction-ambient coefficient \$\theta_{JA}\$ is ...
- 834
8
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What are the disadvantages of using a Zener diode over a linear voltage regulator?
This is more like an extended comment on @Bimpelrekkie's answer than really an answer in and of itself. I'm just going to outline a couple more cases where a linear regulator can make more sense than ...
- 3,514
7
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LM7805 Voltage Drop too big
You have miswired the ATmega328P MCU on the breadboard.
This is a crop from your photo, showing the problems:
You have connected the Gnd rail to pin 20, which is the AVcc pin and should be connected ...
- 17.9k
7
votes
Zener Diode vs LM78XX
Zener
You need to supply a standing current to the Zener that is greater than the largest load current. This current is always being consumed in the power supply. Moreover, a Zener diode doesn't ...
- 46.6k
6
votes
Zener Diode vs LM78XX
7805 is a complex IC that can regulate the output fairly well with about 4% tolerance and is in series with the load. Just like other ICs, it needs the capacitors to keep voltages on input and output ...
- 159k
6
votes
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Series pass transistor, LM7812
Here is the diagram from page 20 of the datasheet you linked:
Image source: Fairchild LM78xx datasheet, Figure 13
Notice that the pass transistor is PNP. The mistake in your design, is that you are ...
- 17.9k
6
votes
Why 7805 regulator gives output 6 volt?
I know this is dead but I had the exact same issue.
Turns out I had the chip backwards.
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6
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Connecting Voltage Regulators 7812 in Parallel for High Current
7812 datasheet page 25, figures 12 and 13. You can use an additional pass transistor to increase the regulator's current capability. You cannot parallel them without risking unequal current sharing ...
- 20k
6
votes
Running Regulator Under Voltage
You might see 11V, but you have no guarantee that it is a regulated 11V
- 30.1k
6
votes
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Do 74HCxx chips require a linear voltage generator?
There is no requirement that would require a linear regulator for 74HCx. You should read the family spec to assure yourself.
Read section 5 on the voltage ratings.
In particular look at Figure 16 ...
- 21.8k
6
votes
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78L24 outputs high voltage >24v - Harman Kardon AVR 151
The zener voltage ends up being added to the voltage stamped on the part, so 12V+24V = 36V.
Pin 2 of the 78L24 acts as an almost constant current source of about 4.5mA, which flows through Zener diode ...
- 407k
5
votes
LM7812 and decoupling capacitor value
From Texas Instruments datasheet:
9 Power Supply Recommendations
If the device is more than six inches from the input filter capacitors, an input bypass capacitor, 0.1 μF or greater, of any type is ...
- 8,083
5
votes
How to fix dc 12 led lights that burn out due to excess voltage or current
Unfortunately you do not tell us how much current is needed by your LEDs and fans.
Assuming that this current is less than 2 A you could consider using a buck-boost converter like this:
In the ...
- 81k
5
votes
Accepted
Transistor for increasing current output of linear voltage regulator
First, to answer your question, you want a PNP power transistor rated for at least twice the peak input voltage and twice the max output current. The transistor will see less than either of these max ...
- 21.4k
4
votes
LM7812 and decoupling capacitor value
Ci can be as large as you want. A 0 impedance input voltage isn't going to hurt the regulator. In fact, the lower the better. I'd probably use a 10 µF ceramic, more if the input voltage is of ...
- 314k
4
votes
Do 74HCxx chips require a linear voltage generator?
A regulator of some kind is advisable. It doesn't have to be the ancient 7805. Anything that provides a clean 5V should be OK. Provide good decoupling and make sure the regulator can provide enough ...
- 72.5k
4
votes
Accepted
Jumper out an LM7805
Well, I decided to simply breadboard it. See below for the Summary.
I fully recognise @glen_geek's comment regarding overlooking the jumper - but I figure that's my lookout!
Yes, I realise that ...
- 1,493
4
votes
Accepted
Does the output bypass capacitor of an LM7805 double as a decoupling capacitor?
The most important thing about about decoupling capacitors is that they are placed physically close to the device they are decoupling, to minimize the trace inductance. The actual capacitance is often ...
- 19.6k
4
votes
Which capacitors to use with voltage regulator IC such as 7805?
The definition in the datasheet is mostly to prevent the regulator to get into a state where it starts to oscillate. If your power source has "large" output capacitors and is reasonably ...
- 3,539
4
votes
Accepted
Why does the LM7805 heat up?
You are feeding the 7805 from a 9 volt battery, so there will be a 4 volt voltage drop over it. If your motor draws 500 mA, it results in power dissipation of:
4 V * 0.5 A = 2 W
In the 7805. Depending ...
- 3,604
4
votes
Can LM7805 take 30 V max as input if the load current doesn't exceed 50 mA?
A TO-220 7805 will survive fine, especially given a small heat sink.
Without a heatsink, the thermal resistance junction to ambient is given as 23.9°C/W so you'll have 30V*5mA + 25V*50mA = 1.4W ...
- 407k
4
votes
Accepted
A question about 78XX power supply design
The power dissipated in a linear regulator is the difference between the input and output voltage times the current. So just to use 1 A as an example, the top 7805 would dissipate \$(24 V - 5 V) \...
- 25.1k
4
votes
Accepted
What could have caused my power supply to fail?
Moritz Klein does a great job with his tutorials. I've built this same circuit for my modular synth explorations.
The LM7812/7912 regulator is rated at 1 to 1.5 A. They usually have over-temperature ...
- 34.3k
4
votes
Accepted
Why is the LM7812 getting hot in this circuit?
The LM7812 is rated for 40V on the input. At some point above that, it will start drawing excessive current.
I can't say for sure, but I assume that what's happening with your circuit is that the ...
- 46.6k
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