Pnp transistor as a high side switch driver

Its more common to use a pnp transistor or a pchannel mosfet as a high side driver. You could select another resistive load if you wish. Given the gain of 350 in your comment 2 ma would be about right so if we set r2 to 1k well get 9 ma and that will be sure to work. This section covers the use of pnp transistors to perform high side switching with a microcontroller. Working of transistor as a switch npn and pnp transistors. When there is no flow of current at the base of the transistor, the transistor switches on. Analog devices growing portfolio of highside switches and mosfet fet drivers provides a simple and effective solution to drive single, dual, triple, or quad nchannel or pchannel fets. This requires both a robust, low onresistance power switch and accurate analog circuitry for diagnostic, protection and control functions.

With and npn transistor a high voltage on the base turns it on and a low voltage turns. Referring to plate 1 whenever the voltage difference between the gate g and source s exceeds around 5volts this opens a conductive channel between source s and drain d allowing current flow from the source back to the power supply. To explain with a pspice model, pn2907a transistor has been selected. The higher resistivity of ptype silicon, resulting from its lower carrier mobility, put it at a disadvantage compared to ntype silicon. Generally, the pnp transistor can replace npn transistors in most electronic circuits, the only difference is the polarities of the voltages, and the directions of the current flow. Understanding a highside switch supposes knowledge of pnp transistor operation. A transistor works best as a switch when it is connected with a common emitter configuration, meaning the emitter of the bjt must be always connected directly with ground line. Pchannel mosfets, the best choice for highside switching historically, pchannel fets were not considered as useful as their nchannel counterparts. Mosfet is an acronym for metal oxide semiconductor field effect transistor and it is the key component in high frequency, high efficiency switching applications across the electronics industry. Basic transistor relay driver, actuated on high input npn. Similar to the npn circuit, the base is our input, and the emitter is tied to a constant voltage. Theres now essentially a lowside switch in front of the pnp. The device is housed in the to92 package, which is designed f. Need advices on driving a pnp transistor to switch higher voltage.

We can also use the pnp transistors as a switch, the difference this time is that the load is connected to ground 0v and the pnp transistor switches the power to it. Based on the voltage applied at the base terminal of a transistor switching operation is. This is often known as a series pass configuration. If you understand the analog emitter follower, youll see that it is the same as using an npn transistor as a highside switch. Some of the applications use a power transistor as switching device, at that time it may necessary to use another signal level transistor to drive the high power transistor. Transistor work as a switch when it is in cutoff and saturation regions. Apr 20, 2018 driver applications where one side of the load is grounded.

So now that weve gone over the basics of pnp transistors, we can now go over how to connect a pnp transistor in a circuit to provide switching andor amplification. Comparatively, the pnp is a little understood device. Pnp switching method electronics forum circuits, projects. To turn it off, you need to add a switch to the circuit. What is the difference between a high side and low side. Why do npn transistors not work for high side switching of higher.

I would suggest starting with an npn transistor as a low side switch first before stepping up to pnp. Basic transistor relay driver, actuated on low input pnp. Alternatively, we can use a pnp transistor to create a highside switch. Pnp transistor no switch with raspberry pi need help with the circuit. One other option is to use high side driver ic such as the udn2981a octal high side driver, which can be driven direct from an arduino pin just like the uln2803. This time however, the emitter is tied high, and the load is connected to the transistor on the ground side. Stn9360 high voltage fastswitching pnp power transistor. If thats important use the common emitter pnp with its emitter connected to 3. Something i couldnt find was an example of using an npn for the high side switching of a lower voltage source. Which means that pnp transistor shown in the first image will always be on, regardless of the io pin state. How to use a pnp transistor with a microcontroller to switch a high side load. The easiest way to switch a higher power load than a microcontroller can handle is to use an npn transistor as explained in part 7. The pnp transistor, like almost all transistors, is a 3lead device.

The first transistor can be a low power type, but normally the second transistor will need to be high power. Something i couldnt find was an example of using an npn for. The high voltage pnp bipolar transistor is designed for general purpose switching applications. Controlling an led using a transistor tl188 ask question. Pnp transistor no switch with raspberry pi need help with. It uses a cellular emitter structure with planar edge termination to enhance switching speeds while maintaining a wide rbsoa. Zetex zxtp25012efh 12v, sot23, pnp medium power transistor high power dissipation sot23 package high peak current very high gain 500 min low saturation voltage mosfet and igbt gate driving dc dc converters motor drive high side driver line disconnect switch created date. As source follower circuit voltage gain is near 1, this circuit is stable. Figure 6 shows an isolated gate driver circuit driving both nchannel and pchannel mosfet with a single pulse transformer. Im really not sure how correct these are and if they work just in a simulator and just by a chance, but here are the circuits i came up with variable voltage is the gpio pin use slider on the right to see the switch in action.

High side switches can safely drive high currents into complex resistive, inductive and capacitive grounded loads in compliance with the harsh automotive environment. This switch will operate on the positive side of a power supply with a negative common. Figure 11 a, nchannel mosfet is high side hs and pchannel mosfet is low side ls. To switch on a pnp transistor, you need the base voltage to be less than the emitter voltage. Its one of the transistors that james lewis recommends in his article on the best 4 transistors to keep in your parts kit the photoresistor i used has about 10 k. Its a simple hookup and sketch and it illustrates how simple it is to control a load with a transistor and an arduino. R3 just has to pull the q2 base high when q1 is off to prevent it turning on with any leakage through q1. It seems logical to assume that a pnp transistor could provide a mirrored circuit to make a simple highside switch. What is the most common solution for a high side switch. This type of switching is used for negative ground configurations. The peak current that could flow through the collector pin is 200ma, this combined with the high gain value makes it an ideal choice for audio amplification applications. Highside switches can safely drive high currents into complex resistive, inductive and capacitive grounded loads in compliance with the harsh automotive environment. Using pnp transistors to switch higher voltage loads.

Jul 15, 2008 to turn it off, you need to add a switch to the circuit. Pnp highside transistor switching with microcontroller. Well need a more complex circuit to implement a practical highside poweron switch. The emitter of the pnp is connected to the drive voltage, and the other side of the load is connected to the collector. I dont understand why it matters whether the load is on the collector vs the emitter. This is where a pnp transistor differs from a npn transistor. We can fix this at the expense of adding an npn lowside switch. But these are not easily driven by a microcontroller and consume more space on pcb for biasing and stuff. Pnp transistor works same as npn for a switching operation, but the current flows from the base. Pnp transistor no switch with raspberry pi need help. There will be a no logic inversion if you use an npn common emitter as the driver. And when we say low side, we generally mean the neutral or groundcommonreturn side. Hi, i would like to use an npn transistor as a high side switch, but i have seen multiple websites stating that a pnp transistor should be used for a high side switch.

Transistor switches can be used to switch a low voltage dc device e. Here we are using electron flow from negative to positive. On this page we will look at transistor driver circuits using both bipolar transistors and power mosfets and will use them as electrical switches. Driving it in either cutoff or saturation mode, the transistor can create the binary onoff. Usually, a pchannel will be configured as a high side switch as i show here. The low side switch is very simple as shown in figure 1a. The nchannel mosfet is used as a high side switch, while the pchannel mosfet is the low side switch. The lowvoltage logic just has to feed sufficient current into the npn transistor to turn it fully on. What is the difference between a high side and low side driver. They are connected in a source to source configuration. The audio amplifier output stage is a sort of source follower circuit.

Low cost mosfet high side driver or load switch embedded world. Pnp or p channel mos transistors are used for high side switches. Using pnp bipolar transistors with arduino, pic youtube. The transistor i used in this video is a bc557 pnp transistor. For example lets assume my io pins are 5v and the motor i am driving is 9v. I know this can sound a bit confusing, so read on to see how you can design a circuit with the pnp transistor. Fundamentals of mosfet and igbt gate driver circuits.

Nov 09, 2014 this feature is not available right now. Remember that emitter followers have a voltage gain of nominally 1. When io is 0, no current flows into the base of the npn transistor, which means. In a pchannel device the conventional flow of drain current is in the negative direction so a negative gatesource voltage is applied to switch the transistor on. Npn transistor to switch on and off a mosfet page 1. Pchannel mosfets, the best choice for highside switching. My logic is that since it is a series circuit the mosfet should handle the current whether the load was in. Automotive applications for example usually require driving a grounded load with 12v. However, it just comes down to the voltage difference between gate and source. In figure 3 the micro drives q2 as in a normal npn lowside switch. High speed switching with a gate driver ic is preferred as it would reduce power losses. We will use the most widely used pnp transistor for our circuit, the 2n3906.

The best transistors to keep in your stock of parts blogs virtual. This tutorial will explore the use of a pchannel and nchannel mosfets as a power switch and general transistor theory. For my highcurrent load, im using a 6volt incandescent light bulb. How to use a transistor as a switch in different applications. Hi, i was trying to use an npn transistor as a high side driver the collector connected to 5v and the emitter connected to my load and the other side of the load to ground. It seems logical to assume that a pnp transistor could provide a mirrored circuit to make a simple high side.

The current is sinked into the pnp transistor and current flows from emitter to collector and this is the main difference between the npn and pnp transistor. I saw a suggestion on using a pnp for switching a load on the low side with the collector grounded, emitter following the input first diagram as opposed to the high side. Key features include wide input range of operation, extended temperature range of operation, a powerful gate. Low cost mosfet high side driver or load switch embedded. Getting ntype performance out of ptype fets has meant. Npn transistor to switch on and off a mosfet page 1 eevblog electronics community forum. For the pnp transistor, the base terminal is always negatively biased with respect to the emitter. The pnp is presented with an electrode connected to a negative voltage gasp. I normally would switch the high side second diagram, but i guess the first method should also work, although it would dissipate more power in the transistor and not have. This device is a high voltage fastswitching pnp power transistor. Datasheet zxtp25012efh 12v, sot23, pnp medium power transistor keywords. It is manufactured using high voltage multi epitaxial planar technology for high switching speeds and medium voltage capability. The operation you see seems to be completely correct when you understand how a pnp works.

The uln serves as a high side driver for the pnp pullups. It is very common to use an npn driver with a pnp bjt or pchannel mosfet, when the load voltage is higher than the signal voltage. Hi, i would like to use an npn transistor as a high side switch, but i have seen multiple websites stating that a pnp transistor should be used for a. A transistor switch, which is used for opening or closing of a circuit, that means the transistor is commonly used as a switch in the electronic devices only for the low voltage applications because of its low power consumption. Dec 19, 2016 by setting the base voltage of a pnp transistor to 0. Pnp transistor tutorial the bipolar pnp transistor. The npn common emitter configuration makes it easy to make a low side to switch loads connecte to positive supply. In this instance the mosfet switch is connected between the load and the positive supply rail high side switching as we do with pnp transistors. Because of how transistors work, these can be a little more difficult to use in an arduino or raspberry pi circuit. Well need a more complex circuit to implement a practical high side poweron switch.

May 19, 20 i could find lots of examples on the net of why npn transistors cant be used for high side switching which illustrate the point using a schematic with a 5v signal controlling a 9v or 12v load. Darlington pairs are available as complete packages but you can make up your own from two transistors. Sep 16, 2015 building a high side switch with 2 components. For highside switch circuits, you need a pnp type transistor. So, when the driver is off, the lamp is at ground potential, with little or no current flow. Why do npn transistors not work for high side switching of. Part 8 showed how to use a pnp transistor allowing the load to be at ground potential, as is sometimes necessary. My logic is that since it is a series circuit the mosfet should handle the current whether the load was in the source or in the drain. The application of an pnp transistor is to work as a high side switch.

Arduino forum using arduino general electronics need advices on driving a pnp. On the other hand, the npn lowside switch is similar to the commonemitter amplifier, which can have voltage gain. What i found was that when the base was high, a much smaller than expected current would flow. Driver applications where one side of the load is grounded. It uses a cellular emitter structure with planar edge termination to. Why do npn transistors not work for high side switching of higher voltages. Q1 will turn on and led will light and will not switch off. Usually, a pchannel will be configured as a h ighside switch as i show here. The potentiometer r s will control the sensitivity of the automation. Also note the concept of sinksource as we go along. On the face of it, this looks like a reasonable means of achieving a high side switch. There is a temptation to think that we could do the same trick with an pnp transistor as shown in figure 1b.

Ltspice simulation of an example circuit is shown below. I could find lots of examples on the net of why npn transistors cant be used for high side switching which illustrate the point using a schematic with a 5v signal controlling a 9v or 12v load. When a switch supplies a voltage on the hot side such as a household light switch, we say the switch sources the voltage. It might be surprising, but fet technology was invented in 1930, some 20 years before the bipolar transistor. Typically thats done with an npn driver transistor. The opposite of the low side switch is the high side switch.

Apr 03, 2008 i saw a suggestion on using a pnp for switching a load on the low side with the collector grounded, emitter following the input first diagram as opposed to the high side. The first important thing to bear in mind to use a current limiting resistor at base. Pnp transistors can also be used as switching devices and an example of a pnp transistor switch is shown below. Need advices on driving a pnp transistor to switch higher. These are not suitable for driving loads higher than the microcontrollers operating voltage. Zxtp25012efh 12v, sot23, pnp medium power transistor.

To drive a highside transistor from a gpio pin we need a level translator. Both npn and pnp transistors can be used as switches. Pchannel mosfet tutorial with only positive voltages. To turn the pnp transistor operating as a switch on, the base terminal is connected to ground or zero volts low as shown. Key features include wide input range of operation, extended temperature range of operation, a powerful gate drive, and shortcircuit protection. Pnp highside transistor switching with microcontroller electrical. Here the ground refers to the negative line for an npn and the positive line for a pnp bjt. Alternatively, we can use a pnp transistor to create a high side switch. Questions about using npn transistor as a high side switch. From what i have read the problem is something like this.