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Topic: Amplifying current with high power transistor (Read 1 time) previous topic - next topic

Rapid80

Hi everyone, I just needed to clarify something. In general, if you are using transistors with low current outputs in a circuit, and it can't provide enough current at the output, you just have to use one higher power transistor that can deliver more current at the output to amplify the current, and then use it as a new output that can deliver more current, or do all transistors have to be able to output a lot of current? I don't think it's the latter, but I need verification. Thanks!

PaulRB

#1
Mar 24, 2020, 07:32 am Last Edit: Mar 24, 2020, 08:01 am by PaulRB
Different transistors have different current capabilities. But they all have many different characteristics making them more or less suitable for a particular circuit. Swapping a transistor with low current capability for one with a higher capability might cause other problems because the transistor you choose might be unsuitable for some other reason.

So ask a more specific question. Post your circuit schematic and tell us what transistor you have now, what it is controlling, what voltage & current is needed and maybe we can suggest a suitable replacement.

Rapid80

#2
Mar 24, 2020, 07:49 am Last Edit: Mar 24, 2020, 07:52 am by Rapid80
Hi! I am going to bed now, but I will post a full schematic in the morning. Basically I'm just wondering if in order to get a high current output, would I need all high power transistors, or just one to amplify the smaller current into a larger one? I am currently using all 2n5551's and will be using at least one 2sd965's. Can I just use that at the output and get a higher current?Its probably hard to say without the schematic, so sorry about that. I will try to get it to you as soon as possible. Thanks for the reply.

Rapid80

Here is the schematic:

All transistors are NPN 2N5551's, and I want to replace "Q4" with a 2SD965 high power NPN transistor. Is that the only transistor I will have to replace to get a high current output?

PaulRB

#4
Mar 24, 2020, 08:47 pm Last Edit: Mar 24, 2020, 08:55 pm by PaulRB

Sorry, I don't understand your schematic, it looks crazy to me, and you have given no indication of the currents or voltages involved. I can't give you an answer.

6v6gt

It looks like an implementation of specimen logic circuits.
Q4 will have a hard time if (S11 && S12) or  (S13 && S14) is closed and both Q2 and Q3 are conducting.

Rapid80

#6
Mar 24, 2020, 09:12 pm Last Edit: Mar 24, 2020, 09:13 pm by Rapid80
For my needs, it is only physically possible to have (S12 and S13) or (S11 and S14) on at the same time, thus you cannot get a short circuit. VCC is 5 volts. I need to run 1.5 amps max on the output. I might be able to figure it out, but thanks anyways.

PaulRB

Good luck with that. If/when you smell burning, switch it off.

6v6gt

You might just get away with a 2SD965 depending on what package it is, whether there is a heat sink, and the duty cycle. If it gets unbearably hot, find an alternative.
Better would be an n-channel logic level mosfet with a low RDS(on).

MarkT

#9
Mar 24, 2020, 10:13 pm Last Edit: Mar 24, 2020, 10:13 pm by MarkT
My observations:

1) high current doesn't necessarily mean high power, nor vice versa.

2) words like "high" are not very useful, one person might thing 2A is high current, another might thing 1000A
is high current.  Use numbers and units, not adjectives, if you want an answer that's actually relevant to your problem.

3) You need your transistor to handle the voltage, the current and the power - 3 things you have to check
on the datasheet.  For MOSFETs the on-resistance and power are the things to check rather than current as such.

4) High power devices may need heatsinks to reach their power ratings.  A 100W transistor without a heatsink might only handle 1.5W before burning out.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Rapid80


6v6gt

#11
Mar 26, 2020, 04:15 am Last Edit: Mar 26, 2020, 04:19 am by 6v6gt
What would be a low RDS(on)?
The ones suggested here would be OK assuming your Vcc is 5 volts or greater. https://www.sparkfun.com/products/10213
The RDS(on) is around 50 milli ohms if you can drive the gate at 5 volts.

The parameter RDS(on) is the effective resistance of the device in series with your load. The lower this resistance, the lower the heating effect, allowing higher currents to be used.

Rapid80

Would the RFP30N06LE be an alright option?


Rapid80

#14
Mar 26, 2020, 06:06 am Last Edit: Mar 26, 2020, 06:07 am by Rapid80
Kind of, but I am just discussing transistors and mosfets here. And not sure who, but I got a karma from someone! Thanks!

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