Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Current Regulators

Status
Not open for further replies.

Vizier87

Active Member
Hi all,
I'm driving a light bulb as a heater using a TIP41C and I'm just wondering if the transistor (powered using a 9V battery) is good enough to provide current regulation for heating accuracy?
Just thinking, since batteries will run out of juice either way, but at least if it has a manageable regulation for a certain period rather than a continuous current decay, it'll be good enough for me to demonstrate my larger-than-this-question proto.
 
Without knowing the current you plan on using it's not possible to answer your question, especially without a circuit for your heater control, is the transistor simple switched on and off for regulating the heat? This is the simplest and most efficient way to run a heating element like that. Looking at the datasheet for hte TIP41C it looks like it can handle a modest amount of current and power but it depends on how you're going to use it.
 
How about what? You still haven't said what current you're switching =O It's kind of required info to answer the question.
 
Last edited:
I suppose the max current is when the TIP is in forward-active mode with the bulb as a load with a 9V Eveready battery for the supply, 'cause the bulb will be controlled using PWM. I had no way of knowing how much the bulb can stand, it is off the shelf with no specs at all, except I measured it at 1.2 ohms at base temperature.

I'll get back to you, I need to find more specs on the battery.
 
Last edited:
here's a constant current source. since the resistor sees a diode drop across it (assuming 0.75V in this case), the current required to get 0.75V across the resistor is 1A. you will want to check the actual Vf of the diodes you use, but the current is Vf/R.

CCS.JPG
 
Last edited:
Eveready made carbon-zinc 9V batteries about 50 years ago. The red ones. Energizer has the datasheet for the obsolete #216 battery on its website. It has a very low capacity so it won't last motre than a couple of minutes.
 
I had no way of knowing how much the bulb can stand, it is off the shelf with no specs at all
Usually the bulb will have a number inscribed on it's base. It can be a little hard to see sometimes. That number will help you find the rated voltage/current/wattage of the bulb.
 
Eveready made carbon-zinc 9V batteries about 50 years ago. The red ones. Energizer has the datasheet for the obsolete #216 battery on its website. It has a very low capacity so it won't last motre than a couple of minutes.

I'm using black ones, they still sell 'em here, and from the way the battery is going, I'll have to say it has lasted more than two minutes and still runnin' wild.

Anyway, to save energy, I'm using my wall-wart. According to my DMM connected in series (as required by the manual) the current drawn by the bulb is 0.02 mA with a supply of 3V (Energizer batteries), which I think is very low for a 1.2 ohm light bulb. So is the current-regulation part feasible here?

PS Unclejed thank you for the info, I'll look into it for good measure.
 
Usually the bulb will have a number inscribed on it's base. It can be a little hard to see sometimes. That number will help you find the rated voltage/current/wattage of the bulb.

how did I miss that?!!! thanks kchriste! The inscription is very faint (like marker ink) I think it says 2.5V, 0.5A.

I only need it to be heated as much as a 3V (two AA energizer batteries) can provide for a single bulb, and as stated above, my DMM shows only 0.02mA, which is funny 'coz I think its too low.

All advise will be appreciated.
 
The black Eveready batteries were carbon-zinc "heavy-duty". They also had a very low capacity. Maybe yours are a Chinese copy.

You measured 1.2 ohms when the bulb was cold so it will be about 12 ohms when hot. Its current will be 3V/12 ohms= 250mA. But you measured a current of only 20mA so either your meter drops too much voltage or your lousy old battery is dead.

EDIT:
Now your 50 years old Eveready carbon-zinc battery is a modern Energizer Alkaline battery?
 
Last edited:
But you measured a current of only 20mA so either your meter drops too much voltage or your lousy old battery is dead.

It is certainly not the latter, AG. I tested it myself. So let's say it is 250mA as you said, so I suppose I'm back on track here? The datasheet of TIP41C states an output current of 1.0A for Vcc exceeding 2.0V, so I suppose the regulation part is feasible? I mean for a regulation within 5 minutes is not bad. Just for demonstration purposes.
 
Last edited:
so, if you use the current source circuit shown above with a 3 ohm resistor, you will get 250mA
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top