# Tagged Questions

A type of bipolar transistor comprised of p-type semiconductor in contact with n-type semiconductor which in turn is in contact with a p-type semiconductor -> thus PNP. The transistor has three terminals, the Emitter, Base and the Collector. Current injected into the base controls the flow of ...

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### PNP transistor circuit

When switch S is at position 1: 1) Vb = R2/(R1+R2)Vcc=30/130-20=-4.62V 2) Rth=100*30/100+30=23.1k ohm 3) Vth-Ie*Re-Vbe-Ib*Rth=0 where Ib= Ie/beta and Vbe =0.7V so, Ie= Vth-Vbe/(Re + ...
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### Voltage divider circuit pnp transistor

From the above circuit I wanted to know If the switch is in position 2, will the 100kΩ resistor be parallelt to the resistor R? Is the power dissipated by the transistor equal to Vce*IC
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### Applying hybrid-pi model of an npn-BJT to a pnp BJT in small signal analysis

When doing the small signal analysis of a circuit containing a pnp BJT connected to either the emitter or collector (or base?) of a npn BJT, is it possible to apply the hybrid-pi model for the npn-BJT ...
123 views

### Improving a simple bipolar current limiter

Is there a way to remove the Vbe dependence on bipolar current limiters, or at least, lessen the effects of process variation & mismatch in the topology below? Vin is nominal 22V, but could ...
87 views

### Why do we assume VGS<Vth and Vds>0 for a mosfet in cuttoff and Vce>0 for a BJT in cutoff?

The devices below are both n polarity devices, the BJT is a NPN and the MOSFET is a NMOS. For the BJT in cut-off, why do we have to assume $V_{ce}>0$? For the MOSFET in cut-off, why do we have ...
113 views

### Can I Use TIP42 as Q1?

The Circuit Below is a "Short Circuit Protection", and Circuit Detail is : Voltage Regulator: LM2576 Maxixmum Load Current (i): 3A Output Voltage: 5,12 and 15 Volts The Original Circuit is Low ...
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### How to pull low with a transistor? [duplicate]

I have a 3.3v line, which I will need to pull low intermittently with a microcontroller to send data. I have tried using a BC547B NPN transistor (also tried BC337, BC517 and BD139) with the Collector ...
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### Reverse momentary N.O. Switch behavior using PNP Transistor?

I want to install an led board with a switch in my car. The switch would be pressed down by the lid of the arm rest when closed. I only have N.O. tact switches to use for this, since I need momentary ...
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### Understanding specs of PNP transistor for replacement

I want to replace an ON Semicondutor BC557 PNP transistor with a Multicomp BC557 PNP transistor. It is just for general switching of LEDs. But the specs look different although they are same mode. ...
352 views

### How do I check a BJT transistor if it is still functional?

Is there a simple method to do a sanity check on a bipolar junction transistor whether it is still functional or defective? simulate this circuit – Schematic created using CircuitLab Say ...
166 views

### PNP switching circuit - How it will be correct?

Following circuit is used as a switch in one my circuits. The collector is connected to the Vcc and emitter is supplying current. Theoretically it is wrong, right? The supply should be connected in ...
130 views

### Bipolar transistor static forward current transfer ratio

My book (teach yourself electricity and electronics) talks about the static forward current transfer ratio ... ratio of collector current v.s. emitter current when we place the base at electrical ...
418 views

### Sinking and sourcing current

I have been reading that NPN transistors are sinking and PNP are sourcing devices. I do not really understand this concept. It says current source device connects load to Vcc and current sinking ...
300 views

### Using an NPN vs a PNP transistor

Is the following circuit electrically sound? My recollection is that the right way to do it is to use a PNP transistor on the high side and an NPN transistor on the low side. Will it work if they are ...
131 views

### Will the PNP and the diode circuit behave differently?

Need to repair a legacy system that has been discontinued and am considering replacing the PNP based circuit with the diode based circuit. The input signal (max. freq = 20Khz) is applied at IN and is ...
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I'm using the LTC5598 IC for modulation. I am confused as to how to properly feed my BaseBand analog signal into the chip. According to its datasheet: The circuit is optimized for a common mode ...
3k views

### Can the Common Emmiter Amplifier use a PNP Transistor instead?

This is a simple Class A amplifier using an NPN transistor: Is there a way this can use a PNP transistor, instead (with only 0V and +Vcc, not 0V and -Vcc)? Why or why not?
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### Can I use a PNP Transistor with an Electret Microphone to get an non-inverting output for my Arduino?

I'm looking to simply read the generic sound level from an Electret Microphone. I've seen a number of schematics with NPN transistors, that will provide an inverted output (~5V when quiet, ~0V when ...
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### Connecting a N.O. grounded switch to a scanning switch matrix

I am working on a project that includes a scanning switch matrix. It also includes a joystick with an integrated push button. I am out of IO pins on the micro, but there are gaps in my switch matrix, ...
657 views

### Shortcircuit protection with PNP

R1 became RS R2 bacame R 1)Is this a correct shortcircuit protection? 2)What is the max current that can flow before the transistor enters in saturation?
222 views

### Voltage at common node in transistor

This is a rather elementary question but I think my fundamentals are not clear on this. What is the voltage at the common node? Firstly, I thought voltage was taken across something i.e it's taken ...
337 views

### Why not to use a P-Channel MOSFET in this circuit?

Why not to use a P-Channel MOSFET in this circuit? It makes more sense, to me since the MOSFET act as a resistor when turned on which is better then the constant volage drop of a PNP.
107 views

### Will a MMBT5087 saturate with a 1K resistor in the base?

I am using the configuration in picture and the MMBT5087 PNP transistor. I am not using the top base resistor, just the lower one, so there will be 5V on the base. My question is: Using a 1K ...
247 views

### How to calculate a PNP transistor thermal dissipation?

I am working with a dual power circuit for using USB and a LDO at the same time with a PIC18F2550. The circuit is the same as the one in the PIC's datasheet. My question is: How do I calculate the ...
602 views

### Is it possible to attach PNP counter to an NPN encoder? [closed]

As a follow-up of my previous too generic question I have a signal generator (shaft encoder) that has 2 NPN outputs. I have a high speed counter that needs PNP signals. How can I convert the encoder ...
3k views

### How can I convert a PNP to NPN transistor?

I have a circuit which requires a PNP transistor. I only have an NPN transistor. Is there a way to convert one to the other given that they have the same characteristics (apart from the npn/pnp ...
160 views

### Which part of a pnp-transistor is the buried layer connected to?

I am preparing for exam and one of the questions is this: "Which part of a pnp-transistor is the Buried Layer normally connected to?" According to the lecture notes handed out, the correct answer ...
2k views

### PNP transistor to command LED

Usually I use NPN to drive LEDs but in my project I have to use PNP because the cathode of the LED is tied to GND. Then I have a question, is it possible to have a command of 3.3V and the PNP tied to ...
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### Exam question: measure amplifier $h_{oe}$ using a signal generator and oscilloscope

I'm running through some old exam papers at the moment and one of the questions are: The parameter $h_{oe}$ is needed to calculate the output impedance of an amplifier. Explain in detail how to ...
557 views

### LM3915 to drive more LEDs / basic questions about PNP transistors in saturation

As a few others here, I'm trying to drive a few (10) LEDs from each output of a LM3915 vu-meter chip. I've read different posts, and it seems the universal recommendation is this great answer. I ...
570 views

### Can someone help me understand this H-Bridge?

I have an old RC car but without the transmitter so I built my own Rx/Tx using MCU and 2.4Ghz transceiver, however, I want to use the car's original H-Bridge but not sure if I understood how that ...
283 views

### Pulling a pin to 12 V using 3.3V

I'm building a boost converter and want to implement a shutdown feature. The particular chip I'm using, LM3478, has a shutdown feature which is activated by a high level on the frequency adjust pin. ...
874 views

### Basic PNP transistor on a microprocessor output pin

I have a 5v microprocessor that needs a PNP transistor between it and the common anode of an LED display, as it can't source enough current to drive all of the LED's without burning up. I understand ...
698 views

### PNP transistor switching time - puzzler

Updated based on feedback with better screenshots (I hope) - I am also working on getting the files onto a file sharing site so they can be accessed at full resolution I am really confused about the ...
388 views

### How to design for a component that says “Electrical Design: DC PNP” in the datasheet?

I'm not a guy from electrical engineering and I'm having a little trouble with a small garage project that I'm working on. I want to use a photoelectric sensor to measure distances. I'll probably ...
557 views

### Do PNP transistors have low noise?

I read somewhere that PNP transistors have lower noise than NPN transistors. The majority carriers in NPN are electrons where as in PNP they are holes, so I thought the noise would be much be less in ...
593 views

### How to use PNP transistor as a switch for serial communication

I am trying to interface a 3.3volt TTY bluetooth dongle to my arduino. The dongle requires 3.3volt but the arduino's Tx and Rx signals are 5 volt. Apperently the 3.3volt is enough for the arduino ...
197 views

### Calculating node voltages

This question is somewhat modified from the original which was asked by someone else. Note that there is more to this than meets the eye. The OP07 or OP070xxx is a 30+ year old op amp, the transistor ...
273 views

### Is one circuit better than the other to drive the PNP transistor?

Of the two circuits, would you prefer one over the other?
9k views

### What's the difference between NPN and PNP transistors?

This is not a duplicate of this question. I would like to know what the differences in their characteristics are. I'm thinking for example about their majority carriers (electrons for NPN, holes ...
1k views

### Is this a proper use of a PNP transistor?

I'm attempting to use a transistor to switch on and off an SSR, which in turns switches on and off a solenoid. I originally used an NPN transistor (2N222), but this caused problems when the MCU ...
1k views

### What's the difference between NPN and PNP transistors?

Suppose that I know how an NPN transistor works. How different is a PNP transistor? What are the operational differences between a PNP and a NPN?
945 views

### Using a P-channel mosfet instead of a PNP

With the LPC1343 microcontroller (Cortex M3), there is a USB_CONNECT line which goes low when the micro is ready to connect to the computer via USB. This "soft connect" feature is implemented on the ...
2k views

### Switching relay with a PNP and TTL levels

I can not wrap my head around the fact how I can drive a relay (24V, 160ohm) with an tip32a PNP transistor which has TTL inputs from a controller. I can easily calculate my resistors when I use the ...