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标题: PNP与NPN管组成的限流电路对比？ [打印本页]

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作者: lukeluck    时间: 2018-4-23 18:04
标题: PNP与NPN管组成的限流电路对比？

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' N9 L! O3 l0 n" t& P欢迎大家帮忙分析对比一下这两种限流电路的优缺点：
* q& \  ?; Q! ^7 c方案A：由PNP三极管组成的约20mA限流电路
方案B：由NPN三极管组成的约20mA限流电路
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" d( o/ I' @; m7 j/ p4 J请忽略这两种三极管的个体差异，这两种电路在实际工作中均有使用，通过我自己的一个仿真发现两个电路确实还是存在差异的，图2是仿真负载电流限流的波形。
8 e" ], d7 O7 j5 d$ y目前已知的情况：
仿真中NPN组成的电路应使基极电阻R3电阻较小<4.7k 如果过大则影响三极管的开通。
个人感觉方案A好一些，原因是基极电阻可以较大，从而降低功耗。
但是方案B的好处是可以通过在三极管T3基极增加不同稳压管来调整电路的输出。

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仿真波形

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作者: lukeluck    时间: 2018-4-23 18:08
附上仿真电路
使用Tina V9搭建。

恒流源3.zip

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恒流源仿真电路

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作者: 超級狗    时间: 2018-4-24 08:50
洋人的分析！

3 @) @8 _1 ?+ ~2 Y, G& WThe Basic Current Mirror with PNP Transistors
A basic current mirror using PNP transistors. All of the current mirror circuits presented in previous pages in this group have used NPN transistors. This is by no means necessary; as shown to the left, we can easily use PNP transistors to build current mirrors. Every mirror configuration that can be built with NPN transistors can also be built with PNP transistors, and the general behavior, advantages, and disadvantages of each configuration will be the same.
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There are only two differences in using PNP rather than NPN transistors in current mirrors. The first is the obvious fact that the applied voltage polarity must be reversed. The emitters are connected to +V, while the collectors are referenced to a more negative voltage. This can be ground as shown here, or any voltage more negative than +V. In many practical circuits, both positive and negative power supplies are used to maintain balanced voltages, and in such circuits the PNP collector circuits are commonly referenced to -V rather than to ground.

The second factor to be considered is that in an IC, while it is always possible to manufacture both NPN and PNP transistors on the same die, it is not possible to make them the same way or to match their parameters. NPN transistors are made vertically, so the width of the base region can be closely controlled to enable high values of current gain. PNP transistors must be constructed horizontally (known as "lateral PNP transistors"), which means the base region must be wider, so the current gain is necessarily more limited. This does not preclude their use, but it does mean that their lower current gain must be accounted for, and in many cases compensated in some way.
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作者: lukeluck    时间: 2018-4-24 09:02

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超級狗 发表于 2018-4-24 08:50
$ i- d& |  U0 G8 [洋人的分析！
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The Basic Current Mirror with PNP Transistors

老外的分析是从哪儿能找到呢？求教！
4 C1 n6 s, q; G7 E5 M1 _/ [! W另外 从谷歌找到的网站来看，似乎我帖子里的电路和老外的current mirror还不一样呀。
current mirror：http://www.play-hookey.com/analog/current_mirrors/current_mirror_pnp.html

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作者: czxjuren    时间: 2018-4-24 09:13
老外分析的很好

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作者: lukeluck    时间: 2018-4-24 09:19

czxjuren 发表于 2018-4-24 09:13
老外分析的很好

0 N& `/ Z; w& ]4 X! B8 K我感觉不是同一个电路，老外分析的是current mirror。我这个是限流电路

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作者: AD9_PCB    时间: 2018-4-24 14:08
感觉没啥区别

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作者: zltwin    时间: 2018-4-24 14:11
学习了

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作者: lukeluck    时间: 2018-4-24 14:24

AD9_PCB 发表于 2018-4-24 14:08
感觉没啥区别

从仿真角度看区别还挺大
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作者: WuJin_eOakJ    时间: 2018-4-25 17:56
学习了

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作者: lukeluck    时间: 2018-4-25 18:13

WuJin_eOakJ 发表于 2018-4-25 17:56
3 p# @5 J* U1 M- f学习了

3 y+ z4 E$ ?3 F! N1 a9 `5 @  ~。。。。。。。学习了哥
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作者: renxiangbing1    时间: 2018-4-26 23:05
学习了

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