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  #1  
Old 01-03-2013, 09:20 AM
morphy_richards morphy_richards is offline
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Default Saturated NPN base to emitter voltage drop?

Hi,
I'm checking for possible problem with a simple H bridge motor control circuit I'm designing using only NPN transistors. The motor supply is 4.5 V and the base will be 'switched' using a 5 V supply.

I understand that as long as the transistor is in saturation there is no appreciable voltage drop from the collector to the emitter but what about from the base to the emitter?

Something I have read elsewhere suggests there is a 0.7 v drop here which would put the base voltage at 4.3 V and below the value of the (4.5 v) emitter voltage which means the transistor wont work as expected? Thanks for any help and advice.
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Old 01-03-2013, 09:46 AM
MKCheruvu MKCheruvu is offline
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Please provide Schematic diagram to understand H Bridge and its Drive configuration.
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Old 01-03-2013, 11:44 AM
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GopherT GopherT is offline
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In general, you are right. Emitter will be 0.5 to 0.7 volts below base voltage (it can be more). If you have a darlington NPN, it will be double. Check your DATASHEET.
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Old 01-04-2013, 02:10 AM
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StayatHomeElectronics StayatHomeElectronics is offline
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A schematic would definitely be helpful.

If you tie the emitter of your drive transistor, npn, to 4.5 volts, the base of the transistor would have to reach approximately 5.2 volts in order to turn the transistor ON. The 5.2 volts is above both your drive and logic supplies. It requires additional "high side drive" circuitry to use only npn transistors.
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Old 01-04-2013, 02:50 AM
tinamishra tinamishra is offline
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A bipolar junction transistor could be a design of transistor that relies on the get in touch with of 2 types of semiconductor for its function. BJTs are often used as built-in amps already built in, changes, or in oscillators. BJTs are often discovered either as personal individual areas, or in large figures as components of incorporated tour.

Bipolar transistors place system thus known as due to their function includes each electrons and gaps. These 2 types of cost providers place system attribute of the 2 types of doped semiconductor content. In difference, unipolar transistors like the field-effect transistors have just one quite cost service provider.
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Old 01-05-2013, 02:26 PM
Audioguru Audioguru is offline
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Please "get in touch" with translation software that works properly.
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