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Discover how to drive the load transistor

In Electronic Infomation Category: D | on April 20,2011

In electronic production, we often involves the need to control the buzzer, relay, motor and MC68HC705P6ACP datasheet and other components found in the load transistor connected in different, varied widely, and MC68HC705P6ACP price and some even lead to the circuit connection is not working reliably, the following will be introduced to my experience for discussion.

Transistor (also known as the transistor) can be divided into the NPN type and MC68HC705P6ACP suppliers and PNP-type, currently used NPN-type transistor has 8050,9013,2 N5551, etc., PNP-type transistor has 8550,9012,2 N5401 and so on.

1, common load drive circuit

Figure 1 is a NPN type, PNP transistor drive various loads typical circuit. Required to get the maximum load power, minimum power consumption of transistors.

Figure 1 NPN type, PNP transistor drive various loads typical circuit

2, drive circuit and component selection

Transistor to drive the load with the main use of transistor switching characteristics, that is, by controlling the transistor in the saturation region and the cutoff switch to control the load between the on and off. Then some electronics enthusiasts will ask: When

choose NPN transistor drive circuit? When selected PNP transistors to drive the load? For the same type of transistor, how to choose the specific type transistor? Base resistance should be how to choose? Below is a brief description about these issues.

2.1. Load drive circuit selection

Use NPN type, or a PNP transistor to drive the load, depending on the designers requirements. Figure 1 (a), (c), (e) is the use of NPN transistor to drive the load circuit, high level "1" can control transistor (load power), low level "0" so that transistor is off ( load power). While Figure 1 (b), (d), (f) is to use the PNP transistor to drive the load of the circuit, turn the opposite conditions.

2.2. Transistor models of choice

NPN transistor 8050,9013,2 N5551 maximum collector currents were 1500mA, 500mA, 600mA, PNP transistor 8550,9012,2 N5401 maximum collector currents were 1500mA, 500mA, 500mA. Drive buzzer, relay, motor load, mainly to see whether it can meet the transistor collector current load requirements.

2.3. Base resistance selection

Shown in Figure 2 is a 2N5551 NPN transistor characteristic curve of the bottom curve corresponds to the selected Ib = 1mA, the top curve corresponds to Ib = 5mA.

Figure 2 NPN transistor 2N5551 characteristic curve

Can be seen from Figure 2, the greater the base current Ib, the greater the corresponding collector current Ic. If we want to get a big load current, then the base current you need as large as possible. Figure 1 shows a variety of drive circuits, we often take the base resistance of about 1k, the corresponding base current is about 4 ~ 5mA, the collector current to meet the load requirements.

3, Multisim simulation

Beginners transistor driven load, the load is sometimes mistakenly connected to the transistor emitter side, as shown in Figure 3 (b) below, this power load will be relatively small. We can analyze by simulation.

Figure 3

To illustrate the load transistor connected in different effects on the drive circuit, we use simulation software Multisim 10 of the load resistance is 100,1 k, 10k cases, Figure 3 (a), (b) the parameters of the circuit to get The simulation results are shown in Table 1 and Table 2.

Table 1 NPN transistor connected collector load

Table 2 load connected NPN transistor emitter

From Table 1 and Table 2 can be seen in Figure 3 (a) shows the load connected transistor collector drive circuit, the load voltage Ur get close to the supply voltage, received power Pr larger. Figure 3 (b) shows the load connected emitter transistor drive circuit, the transistor turns need to meet the Ube> 0.7V, therefore, the load on the bias voltage are lower than the voltage 0.7V, the maximum of about 4.3V, result, the power load are small.

Similarly, for the PNP transistor, the collector end of the load when the load connected transistors get the power as well.

4, hardware experiment

We make the transistor test circuit board, respectively NPN transistor 2N5551, PNP transistor 2N5401 the same as the load drive circuit connected in different physical tests done. Figure 4 (a) is a transistor schematic test circuit board, the Figure 4 (a) on the left of 1,2 J1 pin shorted, you can test drive NPN transistor load circuit; to J1 pin shorted 2,3 , PNP transistors can test the load drive circuit.

Figure 4 (a) is a transistor schematic of the test circuit board

Figure 4 (b) the kind of transistor test circuit connection diagram

Figure 4 (b) the kind of transistor test circuit connection diagram, the left side of the current meter display circuit the base current Ib, the middle of the ammeter shows the collector current Ic or the emitter current Ie, set the right voltage table shows the transistor between the electrode and the emitter voltage Uce. The measured data shown in Table 3.

Table 3 (Test Conditions Vcc = 5.04V)

Can be seen from Table 3, in the same case load, irrespective of the selected NPN transistor or PNP transistor, the load connected to the transistor collector terminal voltage when the load get bigger, get more power but also the transistor pressure drop.

5, Conclusion

By Multsim software simulation and hardware-kind test, we draw the following conclusions: The use of transistors as switches to drive the load, in order to get higher power load, the load should be connected to the transistors collector used by the base most of the current to 0.1 times the load current or greater.

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