| Electronics > Beginners |
| Data sheet question. |
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| sureshot:
So for a first attempt at pnp to npn output from a lnear regulator, i can do the configeration below with say a 50 ohm resistor on the input to the regulator ? Then add the emitter and base and collector of the image below, keeping the resistors as per that schematic ? Think ive got it right. Thanks again for the help. |
| David Hess:
Figure 7.4 shows how to replace the input PNP power transistor shown in figure 7.3 with an NPN power transistor and PNP driver transistor. I am not sure if they meant the 50 ohm resistor in Figure 7.4 to replace R3 or be placed in parallel but the value is not critical; anything between 10 and 50 ohms will work fine. |
| sureshot:
Yes that's what i was wandering, do i need a base collector resistor. As there is already the 50 ohm base emitter resistor. I think i do, but only want the regulator doing a small amount of the current supply. If the additional base collector resistor isn't needed i would probably soon know as it will be not running properly. I have a hard time with the maths, i find it easier to open the circuit and take some current measurements. Also measure across resistors to see what voltage is dropped across them. From them numbers i can do the maths. Is just theory straight off the bat i struggle with, like equation maths, transistor or multiple transistor circuit equations. Thanks again for your help. |
| sureshot:
The reason i think i need that additional input resistor is the 22 ohm resistor showing in the schematic below. Going by that its got the R3 resistor, although its 5K, but that diagram leads me believe i need that input resistor. But then the figure 1 schematic just has the R3 resistor. Bit conflicting. I think I'm going for the figure 1 schematic with 50 ohm and 75 ohm resistors first. If it's a total flop I will move on to the schematic in the first image of this post. I know I don't need such a punchy transistor for the driver, but I've a few TIP2955, and TIP3055's also a fare few TIP36C's and TIP35's. |
| sureshot:
Just wanted to say thanks again for all the help from everyone. :) |
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