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Need transistor circuit for PIC16F873 programmer

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dasa

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Hi there

I am making a PIC programmer for the PIC16F873 device. I need to use transistors in order to be able to switch the voltage on the MCLR pin to 13V. could someone give me a schematic or diagram of a transistor circuit that can do that? i have the npn 100 and pnp 200 transistors.

all help will be appreciated.

thanks
 

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Re: transistor circuit

VVV said:
See the schematic for thisprogrammer from microchip. It shows exactly how to do it. D3 high turns on the transistors and applies +13V to /MCLR

www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en011060

hi there
thanks for your reply.

the problem is that i am trying to program one PIC with another PIC and when the first PIC gives out 5V, the transistor should be able to switch it to 13V to the target PIC's MCLR pinand when the PIC gives out 0V, the transistor should give out 0V.

what i had tried was that i connected the base(B) using a 1K resistor to 5V and the collector(C) to 13 V and ried to measure what i was gwtting out at the emitter(E) but i get out a 5.30 V and it doesnt matter what resistor value that i use. i still get out the same value.

then i tried to use the same circuit above but connect the base using another resistor to 13V supply as well and now it gives me 12.9 V but when i remove the 5V supply to make it zero, it still gives me 12.9 V therefore it seems as if the voltage is only between base and emitter and whatever i give out at the base comes into the emitter.

how do i solve this problem?

thanks
am in need of urgent help
 

VVV

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Re: transistor circuit

The circuit in the appnote will work just fine. Driving D3 high will drive /MCLR to 13V, then driving D3 back low and driving D4 high will turn on the transistor that connects /MCLR to GND. With both D3 and D4 driven low /MCLR will be pulled up to +5V.
Both D3 and D4 are driven by a TTL compatible signal, so you will be able to drive it with another PIC.
 

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