Voltage Regulator: Need 2 Amps? What Can I Do?

In summary, the 7805 can supply up to 1 amp at 5 volts, but you will need at least 2 amps to run a load at 1.5 amps. A heatsink may help dissipate the extra heat.
  • #1
jh24628
23
0
I was going to use a +5V Fixed-Voltage Regulator 7805, for a project until I noticed that I need 2 amps and the 7805 can supply at max 1 amp. what can I do?
 
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  • #2
There are a number of different things you could do.

A quick google search on '3 amp 5v regulator' shows
http://www.national.com/mpf/LM/LM323.html [Broken]
 
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  • #4
go to digikey and seach linear regulator. put in a filter for 5v and 3amp
 
  • #5
after doing some more research I found out I need about 900mA to 1 amp. will the 7805 guarantee putting out that much? and should I put a heatsink on it to help (and how)?
 
  • #7
I agree, datasheets are our friends. Also, google can be useful if you know a couple keywords... I just googled heatsink tutorial, and got lots of good hits. This is one of the first ones on the hit list:

http://sound.westhost.com/heatsinks.htm

It describes the concepts of thermal resistance and heatsink sizing, plus gives some useful tips for how to use heatsinks.
 
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  • #8
ranger said:
The datasheet for the respective regulators will tell you all that info.
http://www.google.com/search?hl=en&q=7805+datasheet&btnG=Google+Search

Learning how to read datasheets is a good thing.

yes I know, but you did not read my question. my question was how does heat impact its performance, I know the hotter the chip is the lower the current output will be. do I need to worry about a heatsink on it at all? according to this at 25 degrees Celsius, it will output 1 amp ( http://www.national.com/mpf/LM/LM78M05.html [Broken] )
 
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  • #9
berkeman said:
I agree, datasheets are our friends. Also, google can be useful if you know a couple keywords... I just googled heatsink tutorial, and got lots of good hits. This is one of the first ones on the hit list:

http://sound.westhost.com/heatsinks.htm

It describes the concepts of thermal resistance and heatsink sizing, plus gives some useful tips for how to use heatsinks.

thanks
 
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  • #10
jh24628 said:
yes I know, but you did not read my question. my question was how does heat impact its performance, I know the hotter the chip is the lower the current output will be. do I need to worry about a heatsink on it at all? according to this at 25 degrees Celsius, it will output 1 amp ( http://www.national.com/mpf/LM/LM78M05.html [Broken] )

The current of a voltage regulator does not go down with higher chip temperature, at least not until any internal thermal current limiting circuit kicks in.

Check out the heatsink link I provided -- that should help you figure out your answer.


EDIT -- we're posting simultaneously! LOL.
 
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  • #11
berkeman said:
I agree, datasheets are our friends.

I hate datasheets...:grumpy:
 
  • #12
I have a couple more questions. is it absolutely necessary to have the two capacitors in the circuit

"*Required if regulator input is more than 4 inches from input filter capacitor
(or if no input filter capacitor is used). <- ON INPUT
**Optional for improved transient response." <-ON OUTPUT

and is there a recommended input current? I know the higher the current the more heat made.
 
  • #13
input current depends on how much you draw.

heat depends on Vin and current draw. if your 5V regulator can take Vin up to 24V, applying Vin of 24V would generate more heat dissipation than applying Vin of 12V keeping all else constant. Remaining unused voltage gets dissipated as heat i believe.
 
  • #14
I guess for the current question i should have rephrased it. I need the regulator to output one amp, would I be safe putting more than one amp to the input of the regulator?
 
  • #15
if your regulator can output more than 1 amp, then yes. it will draw what it needs
.
lets say your regulator can output upto 2A, and you require 1.5A,then yes it will draw only that much
if it can output upto 500mA, and you require 1.5A, your regulator will still output 500mA and cap at that much. You cannot put in 1.5A into the regulator because it can only take in 500mA.
 
  • #16
jh24628 said:
I guess for the current question i should have rephrased it. I need the regulator to output one amp, would I be safe putting more than one amp to the input of the regulator?

A linear regulator like you are asking about has current going through it from input to output, and it drops a controlled voltage to maintain the output voltage in regulation, even if the input voltage varies. You do not put current into a linear regulator. You supply it with an input voltge, the regulator drops whatever voltage is necessary to make the regulated output voltage, and the output current is determined by that output voltage and the load impedance. The input and output currents for the voltage regulator are equal. (Well, except for the small bias current Iq which flows down through the regulator circuit to ground, which means that Iin = Iout + Iq.)
 
  • #17
(maybe this is why I'm not an EE major) but if you are supplying the 7805 with power from a DC power supply, how can the 7805 only have voltage as an input when the dc power supply has both a voltage and current output?
 
  • #18
jh24628 said:
(maybe this is why I'm not an EE major) but if you are supplying the 7805 with power from a DC power supply, how can the 7805 only have voltage as an input when the dc power supply has both a voltage and current output?

Yes, you are getting a bit confused about the details and the semantics. I'll try again, the output voltage across the load impedance determines the output current of the regulator. This output current is basically identical to the input current, since a linear regulator is basically a pass element. So the input current that the regulator draws from the source power supply is determined by the load impedance, not by any characteristic of the voltage regulator. The input current equals the output current (the current all just flows through the linear regulator), and the input voltage is determined by the voltage setting on the source power supply.
 
  • #19
berkeman said:
... The input current equals the output current (the current all just flows through the linear regulator), and the input voltage is determined by the voltage setting on the source power supply.

that clears everything up. thanks
 
  • #20
jh24628 said:
I have a couple more questions. is it absolutely necessary to have the two capacitors in the circuit

"*Required if regulator input is more than 4 inches from input filter capacitor
(or if no input filter capacitor is used). <- ON INPUT
**Optional for improved transient response." <-ON OUTPUT

and is there a recommended input current? I know the higher the current the more heat made.

Yes.

They keep the regulator stable.

If you leave them out, it may well oscillate.

Series regulators are very good at oscillating.

Usually at about 40 to 50MHz.

Which tends to make whatever circuitry you are supplying do very interesting and unusual things.
 
  • #21
It may help you to understand that your load draws the current and that determines how much current your regulator "passes" and not the regulator or power supply themselves necessarily; their current spec is a max rating rather than a given constant so it means they can go up to 1A for example, but they will only ever supply as much current as the load is drawing which could be anything less than 1A. The regulator just varies how much current it takes from the input voltage, your power supply for example, and passes to the output voltage so that no matter the variation of current your load takes, the voltage will remain at a constant regulated level (just remember ohm's law and power equation to see the relationships your regulator is trying to control). Your heat will be generated by how much internal resistance is present in the switching or passive components of your regulator. The bigger drop in voltage across the regulator (a bigger difference between input voltage and output voltage), the more power you will dissipate with the regulator for a given current (because current is determined by the load) by the equation of Power = I*V.
 
  • #22
If you regulator MAX output current is 1A, your load should be equal or less than 1A. Otherwise, the regulator will be burnt.
Base on you choice of using 7805, there are several ways to design a regulator higher than the max current using "your" 7805 IC.
1. Pick uA7805 type that provides 3A (there have 1A and 3A), or
2. Since your design is not too high power (5V * 3A = 15W), you can find other regulator from linear technology or analog devices
3. Use a shunt circuit with the 7805 to increase the output current.
 
  • #23
And above all, don't forget the heatsink!

And the capacitors.
 
  • #24
TheAnalogKid83 said:
It may help you to understand that your load draws the current and that determines how much current your regulator "passes" and not the regulator or power supply themselves necessarily; their current spec is a max rating rather than a given constant so it means they can go up to 1A for example, but they will only ever supply as much current as the load is drawing which could be anything less than 1A. The regulator just varies how much current it takes from the input voltage, your power supply for example, and passes to the output voltage so that no matter the variation of current your load takes, the voltage will remain at a constant regulated level (just remember ohm's law and power equation to see the relationships your regulator is trying to control). Your heat will be generated by how much internal resistance is present in the switching or passive components of your regulator. The bigger drop in voltage across the regulator (a bigger difference between input voltage and output voltage), the more power you will dissipate with the regulator for a given current (because current is determined by the load) by the equation of Power = I*V.

P = (Vin - Vout)*Iout (15W is the max these regulators can handle with a heatsink)

Mike Phan said:
If you regulator MAX output current is 1A, your load should be equal or less than 1A. Otherwise, the regulator will be burnt.
Base on you choice of using 7805, there are several ways to design a regulator higher than the max current using "your" 7805 IC.
1. Pick uA7805 type that provides 3A (there have 1A and 3A), or
2. Since your design is not too high power (5V * 3A = 15W), you can find other regulator from linear technology or analog devices
3. Use a shunt circuit with the 7805 to increase the output current.

where are you getting 3 amps from? I never mention that.
 

1. How does a voltage regulator work?

A voltage regulator is an electronic component that controls the voltage output of a power supply. It takes in a varying voltage input and maintains a steady output voltage by adjusting the resistance or using a feedback mechanism.

2. What is the purpose of a voltage regulator?

The main purpose of a voltage regulator is to provide a stable and consistent voltage output to power electronic devices. This ensures that the devices receive the correct amount of power and prevents damage from voltage fluctuations.

3. Why do I need 2 amps for my voltage regulator?

The amperage rating of a voltage regulator refers to the maximum current it can handle without overheating or malfunctioning. If your electronic device requires 2 amps of current, you will need a voltage regulator that can safely provide this amount of current to power the device.

4. What can I do if my voltage regulator is not providing enough amps?

If your voltage regulator is not providing enough amps for your device, you can either replace it with a higher amperage regulator or use a separate power supply to supplement the current. It is important to always use a voltage regulator that can handle the required amperage to avoid damaging your device.

5. Can I use a voltage regulator for both AC and DC circuits?

Yes, there are voltage regulators that can work for both AC and DC circuits. However, it is important to make sure that the voltage regulator is compatible with the type of circuit you are using it for. Some regulators may only work for either AC or DC, so it is important to check the specifications before use.

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