TIP30 substitute for regulated -12V

[Levente]

Hello Guys, i as hoping to swap the TIP30 transistor in a simple -12V regulated circuit. I thought the bd242 would be a very close match. However, at the output I am getting -16V.

The whole circuit is a full wave rectifier and an extra 47uF capacitor/diode, going into the BD242 through a 470uF filter cap to the output.

This circuit is fed from a 15VAC approx. 200Ma transformer winding.

the BD242:

Type - PNP
Collector-Emitter Voltage: -45 V
Collector-Base Voltage: -55 V
Emitter-Base Voltage: -5 V
Collector Current: -3 A
Collector Dissipation - 40 W
DC Current Gain (hfe) - 25

the TIP30:

Type - PNP
Collector-Emitter Voltage: -40 V
Collector-Base Voltage: -40 V
Emitter-Base Voltage: -5 V
Collector Current: -1 A
Collector Dissipation - 30 W
DC Current Gain (hfe) - 15 to 75

The original circuit had the TIP30 and this suppose to provide a regulated output of 12V (?) according to the note in the user manual.

Am I missing something why the DC is up by 4-5 V's here?

[ionburn]

It would be useful if you posted the circuit diagram. What it seems to me is that there is a problem with regulation. Do you have a zener or similar reference to set the voltage?

[Diabolical Artificer]

Pinout's the same so it's not that, check the base voltage and Vbe, which should be a few volts.As mentioned you should have reference voltage somewhere.

Andy.

[Cobaltblue]

Originally Posted by Levente

The whole circuit is a full wave rectifier and an extra 47uF capacitor/diode, going into the BD242 through a 470uF filter cap to the output.

So whats connected to the base what's doing the actual regulation?

May be completely wrong but are you sure it wasn't a 3 terminal voltage regulator chip in there before?

something like a 7912?

Cheers

Mike T

[Levente]

Thanks Guys... there is no available schematic for this unit sadly. (its a double sided pcb will try and draw a schematic as soon as i can)

I only have a manual and with regards the 12V supply stating the following:

" The power supply provides -12 volts at bout 200mA from an IC 12 volt regulator, full wave bridge rectifier, and separate transformer winding. This supply is current limited and is used only on the Delay Modules" .

I think someone on the past 40 years did change some caps in in as it was full with radioshack cap's and doubt that this is original. This is a Lexicon delay unit, and got this with totally off DC's everywhere. Now I did manage to nearly set everything but the -12 V. This seems to be separate from any other voltage regulator within the unit.

i am unsure if this TIP30 was at some point indeed a voltage regulator?

Will try and put some drawings together later on...

Thanks guys

[dave cox]

"IC 12 volt regulator" would seem to describe a 7912 as MIke T suggests!
The power levels will mean it could be in a TO220 package.

dc

[mickm3for]

Hi if this is a corect desc. ( The power supply provides -12 volts at bout 200mA from an IC 12 volt regulator ) it would have been a 12 regulator ic as stated 7912

[Levente]

Thanks guys again,

I did take two quick pics of this circuit. Top and Bottom. I've marked with a red line where the border of this -12V circuit is, meaning that the other components behind these lines are responsible for other part of the circuits....at least to my understanding.

The blue cap you see on the pic is a 1000uF cap, and the negative goes right to the output where the -12V suppose to be, the positive side of this cap goes to pin1 Base of the transistor.

I am a bit confused on the rest... its such a shame that no one really has this schematic on line..many forums, several sites asking for this.. its so bad as I have the original blue prints of the whole unit, but the PSU section..

Without the schematic i am not sure if this needs to be rewired for the LM7912 or is it ready just to solder in and thats it...

pretty please ....help

[Chris55000]

Hi!

What actually is the unit – make and model no?

Chris Williams

[Refugee]

Positive to the base of the transistor....
That tells me that someone has fitted the transistor in a 7912 position.
Just fit the correct 7912 rgulater and forget...

[arjoll]

Component designation is U3 - that'll originally have been an IC so 7912 makes sense to me too.

[Diabolical Artificer]

That looks like a zener there after the bridge rectifier just to confuse things, can you check it to see whats written on it and or test it? It could be a protection diode though.

Also it's designated U3 what are other standard transistors o the boards designated as? If they're different EG T5 or Q5 it could mean U3 is a reg IC and not a tranny.

Andy.

[Refugee]

That big diode looks like an added bodge.

[Levente]

Thanks guys...

U1, U2 and U4's are all voltage regulators. LM104H, 723 and SG3501.

That big fat diode connected to the 47uF wet tantalum is a 1N5408, the rest of the bridge rectifiers are 1N4004s.

I did order a 7912 and will swap that with the BD242

I hope this will fix the voltage issue

Thanks guys again for your input

[Levente]

Guys, if you are still seeing this thread, please help...

I did soldered in the LM7912 negative voltage regulator. Something is not right.

Pin1 I am getting +12V
Pin2 I am getting -7.2V
Pin3 is going to digital ground

Looking at the LM7912 data sheet

Pin 1 Ground
Pin 2 Input
Pin 3 Output

This is not right... ? I did solder in this how the previous TIP30 was in place, did change nothing...

I am lost in this big time.. please help ...

[Levente]

Originally Posted by Levente

Guys, if you are still seeing this thread, please help...

I did soldered in the LM7912 negative voltage regulator. Something is not right.

Pin1 I am getting +12V
Pin2 I am getting -7.2V
Pin3 is going to digital ground

Looking at the LM7912 data sheet

Pin 1 Ground
Pin 2 Input
Pin 3 Output

This is not right... ? I did solder in this how the previous TIP30 was in place, did change nothing...

I am lost in this big time.. please help ...

please ignoer the post#15...the attachment is showing the circuit..still, not sure why i am only gettint -7V.. is that big diode doing something odd?

[Pamphonica]

According to that last diagram, the regulator is in the positive side, not the negative side of the circuit, as convention would normally have it. Negative from the bridge goes straight out, and positive from bridge goes via a regulator. So it actually needs to be a positive regulator - 7812, surely? and the reference leg of the regulator has to be returned to the -12V line, surely, not the "digital ground".

I suggest you start again, using a conventional positive regulator circuit and a 7812, but with "+12v out" taken to signal earth and the "0V" rail taken to feed the -12V supply. Or even use that 7912, as a conventional negative regulator. This circuit is definitely very odd.

[Levente]

Originally Posted by Pamphonica

According to that last diagram, the regulator is in the positive side, not the negative side of the circuit, as convention would normally have it. Negative from the bridge goes straight out, and positive from bridge goes via a regulator. So it actually needs to be a positive regulator - 7812, surely? and the reference leg of the regulator has to be returned to the -12V line, surely, not the "digital ground".

I suggest you start again, using a conventional positive regulator circuit and a 7812, but with "+12v out" taken to signal earth and the "0V" rail taken to feed the -12V supply. Or even use that 7912, as a conventional negative regulator. This circuit is definitely very odd.

Thanks Jeremy, I understand your point. But I am really confused...the pcb is original Lexicon, it was not altered so the connections are factory made...this means that the -12V voltage regulator is not his type? The user manual calls for a -12 voltage regulator here.. maybe there is another type with different pin out?

When I got this I had a TIP30 there where now the LM7912 is.. really confused. Not sure what to do now..

[snowman_al]

I agree a 7812 regulator makes much more sense.
Two reasons, as stated it is on the positive side of the circuit and the Pin Out is different. The tab and Pin 2 of the 78xx regs are ground. If you look at the pictures the regulator tab (and hence pin 2) is mounted on the aluminium chassis, which I guess is ground?

[Pamphonica]

Try a 7812, they are cheap enough! But maybe detach the output lead to the rest of the amp until the voltage is testing correct.
I still have no idea what that TIP30 was doing!