How to use TIP127

[koolguy]

Hello Here,
I was using TIP 122 for Led sign, it was working as usual i.e. fine.
The emitter to gnd and base to pic micro controller via 4.7K TIP was npn no problem.

but now Tip 127 is pnp so, Emitter to +24V and collector to output so, base via 4.7K to pic out put for switching on/off as a switch.
when emitter is connected to +5V then the output is fine problem come when emitter is at 24V to collector remain at 24V not goes turn off why??
so, what to do?

 

[Mosaic]

A high signal from the micro will forward bias the NPN base P junction and switch the device on.
For a PNP device you will need to drive the base LOW (about 0.7V lower than the emitter supply).
Ok...so your micro is running with about a 4.5V as a high signal....thats 0.5V below the PNP emitter (5V supply)...so it won't switch the PNP. A low from the micro is < 1V which is a lot more than 0.7V under the emitter V and thus the PNP is driven 'on'.

With a 24V supply on the PNP emitter...whether the micro outputs 4.5 or .5V it's still way more than 0.7V under the emitter voltage...thus the PNP is always ON.

To solve your issue...use a pull up resistor on the PNP base to the 24V supply (4.7k or so should be ok) and rather than outputting a HIGH from the micro to switch the PNP OFF....output a Hi Z (tristate). The additional draw on the micro output is about 5mA when driving low to switch the PNP 'ON'.

 

[audioguru]

You need top add a "level shifting" transistor between the 0V and +5V output of the microcontroller and the +24V and +22.5V base of the TIP127 PNP darlington. The level shifting transistor will invert the logic. The darlington already has base-to emitter resistors in it to turn it off when the level shifting transistor turns off.

 

[Colin]

"To solve your issue...use a pull up resistor on the PNP base to the 24V supply (4.7k or so should be ok) and rather than outputting a HIGH from the micro to switch the PNP OFF....output a Hi Z (tristate). The additional draw on the micro output is about 5mA when driving low to switch the PNP 'ON'."

You should NOT do this as you are putting more than 5v on the output and the protection diode is being activated.

 

[koolguy]

hello,
I have connected the PNP With pull up but it was not turning off why?

 

[Colin]

You need 47k on the base to micro and 2k2 between base and emitter. This whole arrangement will hardy work and as I said, it should not be done.

 

[Ian Rogers]

You need 47k on the base to micro and 2k2 between base and emitter. This whole arrangement will hardy work and as I said, it should not be done.

You should not have even suggested it then!!

See AudioGuru's resolve.... You need a NPN level shifter...

 

[Colin]

"but now Tip 127 is pnp so, Emitter to +24V and collector to output so, base via 4.7K to pic out put for switching on/off as a switch."

I NEVER suggested it.

The op used a PNP I said is was not a suitable thing to do.

The only way to make it work suitably is to put a 15v zener in place of the 47k and add a 10k in series with it. Use a 2k2 between base and emitter.

See AudioGuru's resolve.... You need a NPN level shifter...

AudioGuru gave no answer. What is the value on the base???????????????????????

 

[koolguy]

Hello,
By Mistake i have bought TIP127 i was using TIP122 which was simple to use!!
So, You suggested to use 15V zener to base in reversed biased to have 9V and then 2k2 with emitter to base pls clear where is 47K or 4.7K??

 

[Colin]

dont use 47k or 4k7 They are not used in this design

 

[Misterbenn]

The easiest solution is to go and buy the correct device TIP122...

But a level shifter could get the TIP127 working if you want to put in the effort

 

[koolguy]

dont use 47k or 4k7 They are not used in this design

Hello,
Please tell circuit...

 

[audioguru]

AudioGuru gave no answer. What is the value on the base???????????????????????

I said, "The darlington already has base-to emitter resistors in it to turn it off when the level shifting transistor turns off."

 

[MikeMl]

As usual, a picture is worth 10000 words, and a simulation even more. A PNP darlington makes a crappy high-side driver. Here is how to hook it up, but look at the power dissipation in the Darlington (blue trace) with a 4Ω (6A) load. It will have to be on a huge heat sink. A PFET works much better.

 

[koolguy]

Hello,
So, you want to say that to use low side driver . can't we do directly with micro, why??
bc547 npn is also fine?

 

[MikeMl]

Hello,
So, you want to say that to use low side driver .

A low-side NPN Darlington is just as bad as a High-side PNP Darlington for power waste. Both will need a big heatsink.

can't we do directly with micro, why??

To turn on the high-side darlington, the base must be at least -3V with respect to the emitter which is at 24V, so ~21V.
To turn off the high-side darlington, the base must be at 24. The micro pin swings from 0V to 5V. See the mismatch? You need the extra NPN to invert and level-shift.

bc547 npn is also fine?

Should work for the level-shifter, which is non critical.

 

[koolguy]

Hello,
For soldering led how to choose the Iron wattage and other such thing to have long life..!

 

[MikeMl]

The easiest high-current, high-voltage driver which can be directly controlled by micro is a logic-gate NFET low-side driver, which requires the load to be connected between the high positive supply and the Drain of the NFET. More NFETs available than PFETs, NFETs have lower on-resistance than a PFET, NFET's gate can be driven directly from the micro.

 

[MikeMl]

Hello,
For soldering led how to choose the Iron wattage and other such thing to have long life..!

It is important that the Iron be "thermostatically controlled" or "temperature controlled".

 

[audioguru]

Most cheap soldering irons do not control the heat so when sitting doing nothing they get hotter and hotter which makes the tip too hot, burns out the tip, incinerates the rosin in the solder, damages what you are soldering and makes poor soldering. Also when it is used to solder things it gets cooler and cooler until it can't solder anymore without resting until it heats up again.

Some odd soldering irons have adjustable heat from its "light dimmer" circuit that is stupid because it does not control the temperature, it simply adjusts the average temperature that still gets too hot and too cool.

My soldering iron controls the tip temperature all the time so it is always at the correct temperature. When sitting and doing nothing it reduces the power so the tip does not get too hot and when it is soldering all the time it increases the power so it does not get too cool. Therefore each solder joint is fast and perfect. Its tip lasts a very long time.

EDIT: Oh yeah, long life? My soldering iron has been used nearly every day for 50 years. On days it is used it is powered all day long. I replaced its tip a few times in 50 years and the soldering iron and its tip are still being manufactured today.