7805 circuit that gives an output current of more than 1A QUESTION

[lloydi12345]

Hi I've been searching around the web and seen this thread from the site. Since it's already an old thread I'm creating a new one.

https://www.electro-tech-online.com/threads/converting-12vdc-to-5vdc.106816/

**broken link removed** Is this possible? Originally it's from this link: Increasing Regulator Current PSU Circuit - Power Supply Circuit

I'm planning to use 7805 here and hoping to have 2A output to power my 5v 2A Wireless Camera. My input voltage is 10.3v Lithium-Ion Battery the one that can be found on laptops. Thank you in advance for your kind help.

 

[Grossel]

Sure it's possible.

Just make sure that the pinouts on the transistor is right and that you actually pick a PNP to the task.

If you think THIS is great, you can really look forward to get in touch with switch mode circuits.

 

[lloydi12345]

Hi Grossel, I've seen you from this thread Yeah, I'm choosing PNP tip42 which has a reverse current of 6A.

 

[MikeMl]

Read this entire thread

 

[lloydi12345]

Thanks for that MikeMl but it's not available locally

 

[JimB]

I'm choosing PNP tip42 which has a reverse current of 6A.

REVERSE currrent of 6A ?

You may want to re-read the datasheet

JimB

 

[lloydi12345]

REVERSE currrent of 6A ?

You may want to re-read the datasheet

JimB

Sorry, I used the word "reverse" since it is negative. I'm referring to max collector current.

 

[lloydi12345]

I tried the circuit above but the 7805's still get's hot

 

[blueroomelectronics]

Of course it does, so will the transistor. They have to dissipate 14W when you draw 2A.
As mentioned before a switchmode supply is the way to go.

 

[ronv]

Bet you didn't read the whole thread. What value did you use for 1R?

 

[mvs sarma]

Bill's suggestion is best if you want to conserve energy.

by using 1 ohm, you are driving 600mA or so, through the 7805 with input to output differential of 7V.
obviously the device gets HOT.
why not try 2 ohms/ 2 watt so that the current through the device would be around 300 to 350mA, balance taken over by the series pass transistor? it helps to cool down the 7805. however , when you try to mount the TIP2955 on the same heat-sink and close to 7805, it conducts the heat into the regulator.
So, place it either far away or use another heat-sink to suite the needs.
the 10 ohms could be at least 1/2 watt

 

[lloydi12345]

I used 3 ohms (supposedly 1ohm) made using adjusted 10k trimmer potentio since the resistors not yet available and 8 ohms (supposedly 10ohms) using adjusted 10k trimmer pot

Are the capacitors really essential?

 

[lloydi12345]

Bill's suggestion is best if you want to conserve energy.

by using 1 ohm, you are driving 600mA or so, through the 7805 with input to output differential of 7V.
obviously the device gets HOT.
why not try 2 ohms/ 2 watt so that the current through the device would be around 300 to 350mA, balance taken over by the series pass transistor? it helps to cool down the 7805. however , when you try to mount the TIP2955 on the same heat-sink and close to 7805, it conducts the heat into the regulator.
So, place it either far away or use another heat-sink to suite the needs.
the 10 ohms could be at least 1/2 watt

Hi, who's Bill?
I used Tip42 here and they are far from each other. I've also posted what I did. Hope to discover what's wrong with my circuit

 

[blueroomelectronics]

I'm Bill.
The caps are necessary. You might also need a 0.33uF on the output to keep it from oscillating.

 

[lloydi12345]

Of course it does, so will the transistor. They have to dissipate 14W when you draw 2A.
As mentioned before a switchmode supply is the way to go.

Hi Bill, what do you mean with the switchmode supply? Currently the problem is on the 7805's temparature.

BTW, Is it okay If instead on the circuit of 7805? I replaced it with 7808, then the output is fed to the input of 7805. It worked fine giving 5v and enough Amp to power my circuit. Will it help reduce the heat that will occur on 7805? because both of them are now heating up

 

[blueroomelectronics]

A switchmode supply is much more efficient than a linear regulator.

Here's Roman Black's version.
2-transistor Black Regulator

For an IC solution National Semiconductors Simple Switchers are excellent.

 

[ronv]

That one may not give you 2 amps without some changes. Look into something like this.

**broken link removed**

 

[lloydi12345]

A switchmode supply is much more efficient than a linear regulator.

Here's Roman Black's version.
2-transistor Black Regulator

For an IC solution National Semiconductors Simple Switchers are excellent.

What is the value of L1 inductor?

That one may not give you 2 amps without some changes. Look into something like this.

**broken link removed**

Thanks ronv but we only have 3 days 'til deadline and shipping takes time. If it's possible I would like to do a circuit as simple as it can be.

 

[blueroomelectronics]

It was an example, you really need an IC like this.
**broken link removed**

Personally I like the LM2676 3A 5V regulator.

 

[nsklavos]

Why not use a LM323K or better yet a LT1085CT-5 instead of the 7805? Both are capable of 3A output with proper heatsinking.