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The OB2263 plus totem drive

Author:Roadsunny Date:2012-12-19 19:41:15
Because the OB2263 direct drive, only fit to do so 36W To reduce your cost, many engineers in practical applications, plus the totem pole driver, then, what is the totem pole driver? In practical applications, there will be the problem?
Drawn schematic of this structure is a bit like Indian totem pole (shown in the lower left corner of the photo), so they are called a totem pole output (also called totem-output). The output stage, respectively, an NPN transistor and a PNP-type transistor. NPN tube collector connected to the positive power supply (or ground), the transmitter pole following the PNP emitter, while output; PNP tube collector ground (or negative supply). The two base access the preamp control terminal. Two output tubes, from a DC point of view are in series, from the exchange to see parallel, two emitter connected at the output terminal, the actual is a pair of emitter follower. Follow the input level, turned on the tube, down tube cut-off output high turn-down tube, top tube cutoff output low, the output is high impedance state if the up and down two cutoff. In the switching power supply, a similar circuit is often referred to as a "half-bridge". 1 OUT high, the transistor is turned off down transistor, Rgate connected Vdrv opened MOS

OUT low, in turn, Rgate ground, MOS off.

2.Output pole with an upper resistor connected to a collector of the NPN transistor, a collector electrode connected to the tube below the emission of this tube simultaneously output; down tube emitter is grounded. Two base respectively connected to the front stage control is up and down two output tubes, from DC series, the two join at the output end of the tube conduction tube cut output high, lower tube is turned on the tube cutoff, output low, if the circuit logic upper and lower pipe cut-off the output is high impedance.

Actually NPN and PNP tube with use open NPN work when the rising edge of the time, when the falling edge PNP job was closed cycles.

3.This circuit seems simple, in fact, use them to consider more talk briefly about the personal opinion, the first statement, but readily summarize, there is something wrong or inadequacies

1) The first thing to determine is how much you need to drive capacity? How much of the load to be driven (generally considered to be the power tube)? The MOSFET, for example, the drive is actually MOS gate level capacitance charging and discharging, it is necessary to consider that you have several MOS parallel capacitance of gate-level? The MOS of Rg how, plus the driver circuit parasitic inductance, in fact, a LRC series circuit.

2) drive capability with a simplified formula to count I = C * Du / Dt MOS gate level capacitance make sure to consider you come ready to V gate-level voltage, then, is the voltage and eliminate time also involved in the opening of the MOS turn-off speed, which will directly affect the power tube loss and other problems, such as stress. These, it came out to be the drive current.

3) to give the desired drive current, and then consider the bunch of parasitic parameters of the driving circuit etc., and also can be introduced totem pole circuit is required to provide the number of drive current (note that this is a pulse current).

4) this time to reconsider your PCB board layout space position, ready to spend much money for this circuit selected devices using MOS or the BJT, considering, and then wanted to selected devices, of course, but also consider the IC output between the signal and you choose the totem pole device (MOS or BJT) is a loop, this will not have a problem?

5) Another thing to consider is, can completely turn off the totem pole, which will have to consider the N in on P, is open or negative open, such as the choice of PMOS off off totem pole output equal to Vgs voltage, there is still a voltage is applied to the load MOS, if the voltage is higher than the load MOS threshold, ---- which means you do not turn off the front of you off. More painful, in front of and behind the MOS threshold voltage tolerance will be very large, taking into account the temperature coefficient, ... to sit down and calculate the

6) is also important to consider is the totem pole, the device is also a power loss, so you want to consider the temperature and power consumption will not be a problem.

In short, the specific issues to consider when really a lot, singled out are very simple, but add a really want to take the time to research some calculations. Do product specifications, parasitic parameters, tolerance, temperature, cost, PCB space and so on and so on, back and forth a bunch of questions had to face, is not as easy as writing a paper or simulation, and hold on to some other could be considered the ideal state, so that, of course soon Release desired results. 

I encountered in the practical application of the problem: the interference of the output waveform miscellaneous Xun great. Solution Layout lines to go well, and driven away from the MOS G pole distance is as short as possible.