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Old 26th February 2005, 09:10 AM   #1
senee is offline senee  Thailand
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Thumbs up How to matching PNP with NPN Transistor

Hi,
Anyone to know, How to matching PNP with NPN Transistor?
I buy 2N5551= 20 ea. and 2N5401 = 20 ea. then hFE measure is more difference

hFE of 2N5551 = 110 to 130
hFE of 2N5401 = 210 to 230

I am making the power amplifier, when I put them in the circuit, It may be not good sound.

Have anyone suggestion?

sorry!!! My english is not good.

Senee
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Old 26th February 2005, 10:40 PM   #2
anatech is offline anatech  Canada
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Hi Senee,
The best you can do, short of buying more transistors, is put the closest ones together. If these are for n and p diff pairs, match your pairs then use the closest n and p pairs. This will be better than most production amps so don't worry too much about it.
-Chris
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Old 27th February 2005, 05:52 AM   #3
senee is offline senee  Thailand
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Thanks, Chris
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Old 27th February 2005, 07:58 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
are you matching Hfe at 1 bias current?
Once you have sets that closely match try measuring the Vbe at a very low current(100uA to 1ma). Select for both Vbe and Hfe matching.
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Old 28th February 2005, 12:53 AM   #5
thanh is offline thanh  Viet Nam
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i think if you build a fully symmetry amp, you only need match npn ann npn, pnp and pnp .This topo has a very high capacity of cancel offset .I'm sorry! my english is not goog.Can you correct my sentence?
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Old 28th February 2005, 01:12 AM   #6
anatech is offline anatech  Canada
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Hi thanh,
My experience shows that, in order of importance, the pairs must be matched (NPN to NPN, PNP to PNP). Then, each pair should be matched to the other. There is a difference if you include the last step.

If you match these at one current, say 1 mA (common test current), you are already ahead of the game. To complete a great job, thermally tie the pairs together. Now they track.

-Chris
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Old 28th February 2005, 01:18 AM   #7
DonoMan is offline DonoMan  United States
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You can choose different resistor values for each transistor to try to account for different gains. Though matching transistors is better.
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Old 28th February 2005, 07:08 PM   #8
K-amps is offline K-amps  United States
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Quote:
Originally posted by DonoMan
You can choose different resistor values for each transistor to try to account for different gains. Though matching transistors is better.

Base resistors or emitters or both?
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Old 28th February 2005, 08:22 PM   #9
DonoMan is offline DonoMan  United States
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Just a base resistor should do it, but don't change the DC offset.

I THINK (and someone please correct me if I'm wrong) that if Q1 HFE = 100 and Q2 HFE = 200, then R2 = (200 / 100) * R1
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Old 28th February 2005, 11:19 PM   #10
anatech is offline anatech  Canada
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I don't know about that. Why not just match them since you have measured them???

-Chris
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